📄 Cheat Sheets — Biology

Key facts, formulas and common mistakes for 19 of 19 chapters

132 key facts·17 formulas·97 common mistakes·555 definitions·103 exam tips

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Definitions

555

cell: The basic unit of all living organisms; it is surrounded by a cell surface membrane and contains genetic material (DNA) and cytoplasm containing organelles.
organelle: A functionally and structurally distinct part of a cell, e.g. a ribosome or mitochondrion.
nucleus: A relatively large organelle found in eukaryotic cells, but absent from prokaryotic cells; the nucleus contains the cell’s DNA and therefore controls the activities of the cell; it is surrounded by two membranes which together form the nuclear envelope.
eukaryote: An organism whose cells contain a nucleus and other membrane-bound organelles.
prokaryote: An organism whose cells do not contain a nucleus or any other membrane-bound organelles.
cell surface membrane: A very thin membrane (about 7 nm diameter) surrounding all cells; it is partially permeable and controls the exchange of materials between the cell and its environment.
chromatin: The material of which chromosomes are made, consisting of DNA, proteins and small amounts of RNA; visible as patches or fibres within the nucleus when stained.
chromosome: In the nucleus of the cells of eukaryotes, a structure made of tightly coiled chromatin (DNA, proteins and RNA) visible during cell division; the term ‘circular DNA’ is now also commonly used for the circular strand of DNA present in a prokaryotic cell.
nucleolus: A small structure, one or more of which is found inside the nucleus; the nucleolus is usually visible as a densely stained body; its function is to manufacture ribosomes using the information in its own DNA.
protoplasm: All the living material inside a cell (cytoplasm plus nucleus).
cytoplasm: The contents of a cell, excluding the nucleus.
mitochondrion: The organelle in eukaryotes in which aerobic respiration takes place.
cell wall: A wall surrounding prokaryote, plant and fungal cells; the wall contains a strengthening material which protects the cell from mechanical damage, supports it and prevents it from bursting by osmosis if the cell is surrounded by a solution with a higher water potential.
plasmodesma: A pore-like structure found in plant cell walls; plasmodesmata of neighbouring plant cells line up to form tube-like pores through the cell walls, allowing the controlled passage of materials from one cell to the other; the pores contain ER and are lined with the cell surface membrane.
vacuole: An organelle found in eukaryotic cells; a large, permanent central vacuole is a typical feature of plant cells, where it has a variety of functions, including storage of biochemicals such as salts, sugars and waste products; temporary vacuoles, such as phagocytic vacuoles (also known as phagocytic vesicles), may form in animal cells.
tonoplast: The partially permeable membrane that surrounds plant vacuoles.
chloroplast: An organelle, bounded by an envelope (i.e. two membranes), in which photosynthesis takes place in eukaryotes.
photosynthesis: The production of organic substances from inorganic ones, using energy from light.
grana: Stacks of membranes inside a chloroplast.
magnification: The number of times larger an image of an object is than the real size of the object; magnification = image size ÷ actual (real) size of the object.
eyepiece graticule: Small scale that is placed in a microscope eyepiece.
resolution: The ability to distinguish between two objects very close together; the higher the resolution of an image, the greater the detail that can be seen.
stage micrometer: Very small, accurately drawn scale of known dimensions, engraved on a microscope slide.
micrograph: A picture taken with the aid of a microscope; a photomicrograph (or light micrograph) is taken using a light microscope; an electron micrograph is taken using an electron microscope.
nuclear envelope: The two membranes, situated close together, that surround the nucleus; the envelope is perforated with nuclear pores.
nuclear pores: Pores found in the nuclear envelope which control the exchange of materials, e.g. mRNA, between the nucleus and the cytoplasm.
endoplasmic reticulum (ER): A network of flattened sacs running through the cytoplasm of eukaryotic cells; molecules, particularly proteins, can be transported through the cell inside the sacs separate from the rest of the cytoplasm; ER is continuous with the outer membrane of the nuclear envelope.
ribosome: A tiny organelle found in large numbers in all cells; prokaryotic ribosomes are about 20 nm in diameter while eukaryotic ribosomes are about 25 nm in diameter.
Golgi apparatus (Golgi body, Golgi complex): An organelle found in eukaryotic cells; the Golgi apparatus consists of a stack of flattened sacs, constantly forming at one end and breaking up into Golgi vesicles at the other end.
Golgi vesicles: Carry their contents to other parts of the cell, often to the cell surface membrane for secretion; the Golgi apparatus chemically modifies the molecules it transports, e.g. sugars may be added to proteins to make glycoproteins.
lysosome: A spherical organelle found in eukaryotic cells; it contains digestive (hydrolytic) enzymes and has a variety of destructive functions, such as removal of old cell organelles.
cristae: Folds of the inner membrane of the mitochondrial envelope on which are found stalked particles of ATP synthase and electron transport chains associated with aerobic respiration.
ATP (adenosine triphosphate): The molecule that is the universal energy currency in all living cells; the purpose of respiration is to make ATP.
ADP (adenosine diphosphate): The molecule that is converted to ATP by addition of phosphate (a reaction known as phosphorylation) during cell respiration; the enzyme responsible is ATP synthase; the reaction requires energy.
microtubules: Tiny tubes made of a protein called tubulin and found in most eukaryotic cells; microtubules have a large variety of functions, including cell support and determining cell shape; the ‘spindle’ on which chromatids and chromosomes separate during nuclear division is made of microtubules.
centriole: One of two small, cylindrical structures, made from microtubules, found just outside the nucleus in animal cells, in a region known as the centrosome; they are also found at the bases of cilia and flagella.
centrosome: The main microtubule organising centre (MTOC) in animal cells.
cilia: Whip-like structures projecting from the surface of many animal cells and the cells of many unicellular organisms; they beat, causing locomotion or the movement of fluid across the cell surface.
flagella: Whip-like structures projecting from the surface of some animal cells and the cells of many unicellular organisms; they beat, causing locomotion or the movement of fluid across the cell surface; they are identical in structure to cilia, but longer.
thylakoid: A flattened, membrane-bound, fluid-filled sac which is the site of the light-dependent reactions of photosynthesis in a chloroplast.
bacteria: A group of single-celled prokaryotic microorganisms; they have a number of characteristics, such as the ability to form spores, which distinguish them from the other group of prokaryotes known as Archaea.
peptidoglycan: A polysaccharide combined with amino acids; it is also known as murein; it makes the bacterial cell wall more rigid.
plasmid: A small circular piece of DNA in a bacterium (not its main chromosome); plasmids often contain genes that provide resistance to antibiotics.
virus: A very small (20–300 nm) infectious particle which can replicate only inside living cells; it consists of a molecule of DNA or RNA (the genome) surrounded by a protein coat; an outer lipid envelope may also be present.
phospholipid: A lipid to which phosphate is added; the molecule is made up of a glycerol molecule, two fatty acids and a phosphate group; a double layer (a bilayer) of phospholipids forms the basic structure of all cell membranes.
macromolecule: A large molecule such as a polysaccharide, protein or nucleic acid.
polymer: A giant molecule made from many similar repeating subunits joined together in a chain; the subunits are much smaller and simpler molecules known as monomers; examples of biological polymers are polysaccharides, proteins and nucleic acids.
monomer: A relatively simple molecule which is used as a basic building block for the synthesis of a polymer; many monomers are joined together by covalent bonds to make the polymer, usually by condensation reactions; common examples of monomers are monosaccharides, amino acids and nucleotides.
condensation reaction: A chemical reaction involving the joining together of two molecules by removal of a water molecule.
hydrolysis: A chemical reaction in which a chemical bond is broken by the addition of a water molecule; commonly used to break down complex molecules into simpler molecules.
monosaccharide: A molecule consisting of a single sugar unit and with the general formula (CH2O)n.
disaccharide: A sugar molecule consisting of two monosaccharides joined together by a glycosidic bond.
glycosidic bond: A C–O–C link between two sugar molecules, formed by a condensation reaction; it is a covalent bond.
Benedict’s test: A test for the presence of reducing sugars; the unknown substance is heated with Benedict’s reagent, and a change from a clear blue solution to the production of a yellow, red or brown precipitate indicates the presence of reducing sugars such as glucose.
polysaccharide: A polymer whose subunits are monosaccharides joined together by glycosidic bonds.
glycogen: A polysaccharide made of many glucose molecules linked together, that acts as a glucose store in liver and muscle cells.
cellulose: A polysaccharide made from beta-glucose subunits; used as a strengthening material in plant cell walls.
hydrogen bond: A relatively weak bond formed by the attraction between a group with a small positive charge on a hydrogen atom (Hδ+) and another group carrying a small negative charge (δ−), e.g. between two –Oδ– Hδ+ groups.
ester bond / ester linkage: A chemical bond, represented as –COO– , formed when an acid reacts with an alcohol.
triglyceride: A type of lipid formed when three fatty acid molecules combine with glycerol, an alcohol with three hydroxyl (−OH) groups.
peptide bond: The covalent bond joining neighbouring amino acids together in proteins; it is a C–N link between two amino acid molecules, formed by a condensation reaction.
polypeptide: A long chain of amino acids formed by condensation reactions between the individual amino acids; proteins are made of one or more polypeptide chains; see peptide bond.
primary structure: The sequence of amino acids in a polypeptide or protein.
secondary structure: The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an α-helix or β-pleated sheet).
α-helix: A helical structure formed by a polypeptide chain, held in place by hydrogen bonds; an α-helix is an example of secondary structure in a protein.
β-pleated sheet: A loose, sheet-like structure formed by hydrogen bonding between parallel polypeptide chains; a β-pleated sheet is an example of secondary structure in a protein.
tertiary structure: The compact structure of a protein molecule resulting from the three-dimensional coiling of the chain of amino acids.
quaternary structure: The three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule.
haemoglobin: The red pigment found in red blood cells, whose molecules contain four iron atoms within a globular protein made up of four polypeptides; it combines reversibly with oxygen.
globular protein: A protein whose molecules are folded into a relatively spherical shape, often has physiological roles and is often water-soluble and metabolically active, e.g. insulin, haemoglobin and enzymes.
sickle cell anaemia: A genetic disease caused by a faulty gene coding for haemoglobin, in which haemoglobin tends to precipitate when oxygen concentrations are low.
collagen: The main structural protein of animals; known as ‘white fibres’, the fundamental unit of the fibre consists of three helical polypeptide chains wound around each other, forming a ‘triple helix’ with high tensile strength.
fibrous protein: A protein whose molecules have a relatively long, thin structure that is generally insoluble and metabolically inactive, and whose function is usually structural, e.g. keratin and collagen.
biuret test: A test for the presence of amine groups and thus for the presence of protein; biuret reagent is added to the unknown substance, and a change from pale blue to purple indicates the presence of protein.
enzyme: a protein produced by a living organism that acts as a biological catalyst in a chemical reaction by reducing activation energy
active site: an area on an enzyme molecule where the substrate can bind
lock-and-key hypothesis: a hypothesis for enzyme action; the substrate is a complementary shape to the active site of the enzyme, and fits exactly into the site; the enzyme shows specificity for the substrate
induced-fit hypothesis: a hypothesis for enzyme action; the substrate is a complementary shape to the active site of the enzyme, but not an exact fit – the enzyme, or sometimes the substrate, can change shape slightly to ensure a perfect fit, but it is still described as showing specificity
activation energy: the energy that must be provided to make a reaction take place; enzymes reduce the activation energy required for a substrate to change into a product
colorimeter: an instrument that measures the colour of a solution by measuring the absorption of different wavelengths of light
Vmax: the theoretical maximum rate of an enzyme-controlled reaction, obtained when all the active sites of the enzyme are occupied
Michaelis–Menten constant (Km): the substrate concentration at which an enzyme works at half its maximum rate (½Vmax), used as a measure of the efficiency of an enzyme; the lower the value of Km, the more efficient the enzyme
competitive inhibition: when a substance reduces the rate of activity of an enzyme by competing with the substrate molecules for the enzyme’s active site; increasing substrate concentration reduces the degree of inhibition; increasing inhibitor concentration increases the degree of inhibition
non-competitive inhibition: when a substance reduces the rate of activity of an enzyme, but increasing the concentration of the substrate does not reduce the degree of inhibition; many non-competitive inhibitors bind to areas of the enzyme molecule other than the active site itself
immobilised enzymes: enzymes that have been fixed to a surface or trapped inside beads of agar gel
fluid mosaic model: The currently accepted model of membrane structure, proposed by Singer and Nicolson in 1972, in which protein molecules are free to move about in a fluid bilayer of phospholipid molecules.
cholesterol: A small, lipid-related molecule with a hydrophilic head and a hydrophobic tail which is an essential constituent of membranes; it is particularly common in animal cells and gives flexibility and stability to the membrane as well as reducing fluidity.
cell signalling: The molecular mechanisms by which cells detect and respond to external stimuli, including communication between cells.
ligand: A biological molecule which binds specifically to another molecule, such as a cell surface membrane receptor, during cell signalling.
transduction: Occurs during cell signalling and is the process of converting a signal from one method of transmission to another.
diffusion: The net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of the random movements of particles.
facilitated diffusion: The diffusion of a substance through a transport protein (channel protein or carrier protein) in a cell membrane; the protein provides hydrophilic areas that allow the molecule or ion to pass through the membrane, which would otherwise be less permeable to it.
channel protein: A membrane protein of fixed shape which has a water-filled pore through which selected hydrophilic ions or molecules can pass by facilitating diffusion or active transport.
carrier protein: A membrane protein which changes shape to allow the passage into or out of the cell of specific ions or molecules by facilitated diffusion or active transport.
osmosis: The net diffusion of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
water potential: A measure of the tendency of water to move from one place to another; water moves from a solution with higher water potential to one with lower water potential; water potential is decreased by the addition of solute, and increased by the application of pressure; the symbol for water potential is ψ or ψw.
protoplast: The living contents of a plant cell, including the cell surface membrane but excluding the cell wall.
plasmolysis: The loss of water from a plant or prokaryote cell to the point where the protoplast shrinks away from the cell wall.
incipient plasmolysis: The point at which plasmolysis is about to occur when a plant cell or a prokaryote cell is losing water; at this point the protoplast is exerting no pressure on the cell wall.
active transport: The movement of molecules or ions through transport proteins across a cell membrane, against their concentration gradient, using energy from ATP.
sodium–potassium pump (Na+–K+ pump): A membrane protein (or proteins) that moves sodium ions out of a cell and potassium ions into it, using ATP.
endocytosis: The bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell, by the infolding of the cell surface membrane to form vesicles containing the substance; endocytosis is an active process requiring ATP.
exocytosis: The bulk movement of liquids or solids out of a cell, by the fusion of vesicles containing the substance with the cell surface membrane; exocytosis is an active process requiring ATP.
phagocyte: A type of cell that ingests (eats) and destroys pathogens or damaged body cells by the process of phagocytosis; some phagocytes are white blood cells.
chromatid: One of two identical parts of a chromosome, held together by a centromere, formed during interphase by the replication of the DNA strand.
mitosis: The division of a nucleus into two so that the two daughter cells have exactly the same number and type of chromosomes as the parent cell.
cell cycle: The sequence of events that takes place from one cell division until the next; it is made up of interphase, mitosis and cytokinesis.
kinetochore: A protein structure found at the centromere of a chromatid to which microtubules attach during nuclear division.
asexual reproduction: The production of new individuals of a species by a single parent organism.
telomere: Repetitive sequence of DNA at the end of a chromosome that protects genes from the chromosome shortening that happens at each cell division.
stem cell: A relatively unspecialised cell that retains the ability to divide an unlimited number of times, and which has the potential to become a specialised cell (such as a blood cell or muscle cell).
cancers: A group of diseases that result from a breakdown in the usual control mechanisms that regulate cell division; certain cells divide uncontrollably and form tumours, from which cells may break away and form secondary tumours in other areas of the body (metastasis).
mutation: A random change in the base sequence (structure) of DNA (a gene mutation), or in the structure and/or number of chromosomes (a chromosome mutation).
carcinogen: A substance or environmental factor that can cause cancer.
oncogene: The term for a mutated gene that causes cancer.
metastasis: The spread of cancers in this way is called metastasis.
nucleotide: a molecule consisting of a nitrogen-containing base, a pentose sugar and a phosphate group
polynucleotide: a chain of nucleotides joined together by phosphodiester bonds
dinucleotide: two nucleotides joined together by a phosphodiester bond
phosphodiester bond: a bond joining two nucleotides together; there are two ester bonds, one from the shared phosphate group to each of the sugars either side of it
complementary base pairing: the hydrogen bonding of A with T or U and of C with G in nucleic acids
DNA polymerase: an enzyme that copies DNA; it runs along the separated DNA strands lining up one complementary nucleotide at a time ready for joining by DNA ligase
leading strand: during DNA replication, the parent strand that runs in the 3′ to 5′ direction is copied to produce the leading strand
lagging strand: during DNA replication, the parent strand that runs in the 5′ to 3′ direction is copied to produce the lagging strand
DNA ligase: an enzyme that catalyses the joining together of two nucleotides with covalent phosphodiester bonds during DNA replication
semi-conservative replication: the method by which a DNA molecule is copied to form two identical molecules, each containing one strand from the original molecule and one newly synthesised strand
gene: a length of DNA that codes for a particular polypeptide or protein
transcription: copying the genetic information in a molecule of DNA into a complementary strand of mRNA; a single strand of the DNA is used as a template (this is called the template or transcribed strand) – the enzyme responsible is RNA polymerase
translation: a stage in protein synthesis during which a sequence of nucleotides in a molecule of messenger RNA (mRNA) is converted (translated) into a corresponding sequence of amino acids in a polypeptide chain; it takes place at ribosomes
codon: sequence of three bases on an mRNA molecule that codes for a specific amino acid or for a stop signal
anticodon: sequence of three unpaired bases on a tRNA molecule that binds with a codon on mRNA
gene mutation: a change in the base sequence in part of a DNA molecule
chromosome mutation: a random and unpredictable change in the structure or number of chromosomes in a cell
frame-shift mutation: a type of gene mutation caused by insertion or deletion of one or more nucleotides, resulting in incorrect reading of the sequence of triplets in the genetic code due to a shift in the reading frame
vascular system: a system of fluid-filled tubes, vessels or spaces, most commonly used for long-distance transport in living organisms; examples are the blood vascular system in animals and the vascular system of xylem and phloem in plants
vascular: a term referring to tubes or vessels (from the Latin ‘vascul’, meaning vessel)
xylem: a tissue containing tubes called vessels and other types of cell, responsible for the transport of water and mineral salts through a plant and for support
phloem: a tissue containing tubes called sieve tubes and other types of cell, responsible for the transport through the plant of organic solutes (assimilates) such as sucrose
vascular tissue: a tissue in plants consisting mainly of xylem and phloem but also containing sclerenchyma and parenchyma cells
dicotyledon: flowering plants can be classified as monocotyledons or dicotyledons; the seeds of dicotyledonous plants contain an embryo with two cotyledons (seed leaves) in their seeds and the adult plant typically has leaves with a blade (lamina) and a stalk (petiole)
eyepiece graticule: small scale that is placed in a microscope eyepiece
stage micrometer: very small, accurately drawn scale of known dimensions, engraved on a microscope slide
vascular bundle: a strand of vascular tissue running longitudinally in a plant; within the bundle, the arrangement of tissues like xylem, phloem and sclerenchyma varies in different plants and organs
parenchyma: a basic plant tissue typically used as packing tissue between more specialised structures; it is metabolically active and may have a variety of functions such as food storage and support; parenchyma cells also play an important role in the movement of water and food products in the xylem and phloem
collenchyma: a modified form of parenchyma in which the corners of the cells have extra cellulose thickening, providing extra support, as in the midrib of leaves and at the corners of square stems; in three dimensions the tissue occurs in strands (as in celery petioles)
epidermis: the outer layer of cells covering the body of a plant or animal; in plants it is usually one cell thick and may be covered with a cuticle which provides additional protection against loss of water and disease
endodermis: the layer of cells surrounding the vascular tissue of plants; it is most clearly visible in roots
sclerenchyma: a plant tissue consisting of thick-walled cells with a purely mechanical function (strength and support); the cell walls have usually become impregnated with lignin and the mature cells are dead with no visible contents; many sclerenchyma cells take the form of fibres
lignin: a hard material made by plants and used to strengthen the cell walls of certain types of cell, particularly xylem vessel elements and sclerenchyma cells; it is the main material in wood
transpiration: the loss of water vapour from a plant to its environment; it mostly takes place through the stomata in the leaves
mesophyll: the region of a leaf between the upper and lower epidermis; in dicotyledonous plants the mesophyll has an upper palisade layer and a lower mesophyll layer; the palisade mesophyll cells are column-shaped and form the main photosynthetic layer, whereas the spongy mesophyll has large air spaces between the cells for gas exchange
stoma: a pore in the epidermis of a leaf, bounded by two guard cells and needed for efficient gas exchange
xerophyte: a plant adapted to survive in conditions where water is in short supply
cuticle: a layer covering, and secreted by, the epidermis; in plants it is made of a fatty substance called cutin, which helps to provide protection against water loss and infection
symplast pathway: the living system of interconnected protoplasts extending through a plant, used as a transport pathway for the movement of water and solutes; individual protoplasts are connected via plasmodesmata
apoplast pathway: the non-living system of interconnected cell walls extending throughout a plant, used as a transport pathway for the movement of water and mineral ions
xylem vessel element: a dead, lignified cell found in xylem specialised for transporting water and for support; the ends of the cells break down and join with neighbouring elements to form long tubes called xylem vessels
xylem vessel: a dead, empty tube with lignified walls, through which water is transported in plants; it is formed by xylem vessel elements lined up end to end
source: a site in a plant which provides food for another part of the plant, the sink
sink: a site in a plant which receives food from another part of the plant, the source
sieve tube element: a cell found in phloem tissue, with non-thickened cellulose walls, very little cytoplasm, no nucleus and end walls perforated to form sieve plates, through which sap containing sucrose is transported
companion cell: a cell with an unthickened cellulose wall and dense cytoplasm that is found in close association with a phloem sieve tube element to which it is directly linked via many plasmodesmata; the companion cell and the sieve tube element form a functional unit
sieve tube: tube formed from sieve tube elements lined up end to end
circulatory system: A system that carries fluids around an organism’s body.
closed blood system: A circulatory system made up of vessels containing blood.
double circulation: A circulatory system in which the blood passes through the heart twice on one complete circuit of the body.
systemic circulation: The part of the circulatory system that carries blood from the heart to all of the body except the gas exchange surface, and then back to the heart.
pulmonary circulation: The part of the circulatory system that carries blood from the heart to the gas exchange surface and then back to the heart.
artery: Vessel with thick, strong walls that carries high-pressure blood away from the heart.
vein: Vessel with relatively thin walls that carries low-pressure blood back to the heart.
arteriole: Small artery.
venule: Small vein.
capillary: The smallest blood vessel, whose role is to deliver oxygen and nutrients to body tissues, and to remove their waste products.
endothelium: A tissue that lines the inner surface of a structure such as a blood vessel.
squamous epithelium: One or more layers of thin, flat cells forming the lining of some hollow structures, e.g. blood vessels and alveoli.
smooth muscle: A type of muscle that can contract steadily over long periods of time.
elastic arteries: Relatively large arteries, which have a lot of elastic tissue and little muscle tissue in their walls.
muscular arteries: Arteries that are closer to the final destination of the blood inside them than elastic arteries, with more smooth muscle in their walls which allows them to constrict and dilate.
vasoconstriction: The narrowing of a muscular artery or arteriole, caused by the contraction of the smooth muscle in its walls.
vasodilation: The widening of a muscular artery or arteriole, caused by the relaxation of the smooth muscle in its walls.
semilunar valve: A half-moon shaped valve, such as the ones in the veins and between the ventricles and arteries.
plasma: The liquid component of blood, in which the blood cells float; it carries a very large range of different substances in solution.
plasma proteins: A range of several different proteins dissolved in the blood plasma, each with their own function; many of them are made in the liver.
tissue fluid: The almost colourless fluid that fills the spaces between body cells; it forms from the fluid that leaks from blood capillaries.
neutrophil: One type of phagocytic white blood cell; it has a lobed nucleus and granular cytoplasm.
monocyte: The largest type of white blood cell; it has a bean-shaped nucleus; monocytes can leave the blood and develop into a type of phagocytic cell called a macrophage.
macrophage: Phagocytic cell found in tissues throughout the body; they act as antigen-presenting cells (APCs).
lymphocyte: A white blood cell with a nucleus that almost fills the cell, which responds to antigens and helps to destroy the antigens or the structure that is carrying them.
partial pressure: A measure of the concentration of a gas.
percentage saturation: The degree to which the haemoglobin in the blood is combined with oxygen, calculated as a percentage of the maximum amount with which it can combine.
dissociation curve: A graph showing the percentage saturation of a pigment (such as haemoglobin) with oxygen, plotted against the partial pressure of oxygen.
carbonic anhydrase: An enzyme found in the cytoplasm of red blood cells that catalyses the reaction between carbon dioxide and water to form carbonic acid.
Bohr shift: The decrease in affinity of haemoglobin for oxygen that occurs when carbon dioxide is present.
chloride shift: The movement of chloride ions into red blood cells from blood plasma, to balance the movement of hydrogencarbonate ions into the plasma from the red blood cells.
carbaminohaemoglobin: A compound formed when carbon dioxide binds with haemoglobin.
cardiac muscle: The type of muscle that makes up the walls of the heart.
coronary arteries: Arteries that branch from the aorta and spread over the walls of the heart, supplying the cardiac muscle with nutrients and oxygen.
septum: The layer of tissue that separates the left and right sides of the heart.
atrium: One of the chambers of the heart that receives low-pressure blood from the veins.
ventricle: One of the chambers of the heart that receives blood from the atria and then pushes it into the arteries.
atrioventricular valve: A valve between the atria and ventricles that closes when the ventricles contract and stops backflow of blood into the atria.
bicuspid valve: The atrioventricular valve on the left side of the heart.
tricuspid valve: The atrioventricular valve on the right side of the heart.
cardiac cycle: The sequence of events that takes place during one heartbeat.
atrial systole: The stage of the cardiac cycle when the muscle in the walls of the atria contracts.
ventricular systole: The stage of the cardiac cycle when the muscle in the walls of the ventricles contracts.
diastole: The stage of the cardiac cycle when the muscle in the walls of the heart relaxes.
myogenic: A word used to describe muscle tissue that contracts and relaxes even when there is no stimulation from a nerve.
sinoatrial node (SAN): A patch of cardiac muscle in the right atrium of the heart which contracts and relaxes in a rhythm that sets the pattern for the rest of the heart muscle.
atrioventricular node (AVN): A patch of tissue in the septum of the heart which transmits the wave of excitation from the walls of the atria and transmits it to the Purkyne tissue.
Purkyne tissue: A bundle of fibres that conduct the wave of excitation down through the septum of the heart to the base (apex) of the ventricles.
gas exchange surface: Any part of an organism that allows the movement of gases between the surroundings and the body.
alveolus: A small air sac in the lungs composed of a single layer of squamous epithelium and some elastic fibres.
trachea: The tube-like structure that extends from the larynx to the bronchi.
bronchus: A major branch of the trachea that extends into the lungs.
bronchiole: A microscopic branch of a bronchus that leads to the alveoli.
cartilage: A type of skeletal tissue that is strong and flexible and supports the larynx, trachea and bronchi in the gas exchange system.
goblet cell: A cell shaped like a drinking goblet that secretes mucus.
ciliated epithelium: An epithelium that consists mainly of ciliated cells.
mucin: Any glycoprotein that forms part of the mucus secreted by goblet cells and mucous cells.
elastic fibres: Bundles of the fibrous protein elastin which can stretch and recoil like elastic bands.
infectious disease: A disease caused by an organism such as a protoctist, bacterium or virus.
pathogen: An organism that causes disease.
disease transmission: The transfer of a pathogen from a person infected with that pathogen to an uninfected person; transmission may occur by direct contact, through the air or water or by animal vectors, such as insects.
disease carrier: Person infected with a pathogen who shows no symptoms, but can be the source of infection in other people (not carrier of an inherited disease).
transmission cycle: The passage of a pathogen from one host to another is continually repeated as the pathogen infects new hosts.
disease eradication: The complete breakage of the transmission cycle of a pathogen so that there are no more cases of the disease caused by the pathogen anywhere in the world.
endemic disease: A disease that is always in a population.
disease vector: An organism which carries a pathogen from one person to another or from an animal to a human.
HIV: Human immunodeficiency virus.
AIDS: Acquired immunodeficiency syndrome.
opportunistic infection: An infection caused by pathogens that take advantage of a host with a weakened immune system, as may happen in someone with an HIV infection.
antibiotic: A substance derived from a living organism that is capable of killing or inhibiting the growth of a microorganism.
antibiotic resistance: The ability of bacteria or fungi to grow in the presence of an antibiotic that would normally slow their growth or kill them; antibiotic resistance arises by mutation and becomes widespread when antibiotics are overused.
immune system: The body’s internal defence system.
antigen: A substance that is foreign to the body and stimulates an immune response (e.g. any large molecule such as a protein).
self: Refers to substances produced by the body that the immune system does not recognise as foreign, so they do not stimulate an immune response.
non-self: Refers to any substance or cell that is recognised by the immune system as being foreign and will stimulate an immune response.
antibody: A glycoprotein (immunoglobulin) made by specialised lymphocytes in response to the presence of a specific antigen; each type of antibody molecule has a shape that is complementary to its specific antigen.
immune response: The complex series of responses of the body to the entry of a foreign antigen; it involves the activity of lymphocytes and phagocytes.
clonal selection: Individual lymphocytes have cell surface receptors specific to one antigen; this specificity is determined as lymphocytes mature and before any antigens enter the body (during an immune response the only lymphocytes to respond are those with receptors specific to antigens on the surface of the invading pathogen).
clonal expansion: The increase in number of specific clones of lymphocytes by mitosis during an immune response.
plasma cell: Short-lived, activated B-lymphocyte produced during clonal expansion; plasma cells produce and release antibody molecules.
memory B cell: Long-lived, activated B-lymphocyte that is specific to one antigen; memory cells are activated to differentiate (develop) into plasma cells during secondary immune responses to the specific antigen.
primary immune response: The first immune response to a specific antigen.
secondary immune response: The second and any subsequent immune responses to a specific antigen.
immunological memory: The ability of the immune system to mount a larger and more rapid response to an antigen that has already been encountered before.
variable region: Region of an antibody molecule composed of parts of the light and heavy polypeptide chains that form the antigen-binding site; the amino acid sequences of the variable site form a specific shape that is complementary to a particular antigen.
antigen presentation: The process of preparing antigens and exposing them on the surface of host cells (e.g. macrophages) for recognition by T-lymphocytes.
T-helper cell: Type of T-lymphocyte that secretes cytokines to coordinate activity during immune responses.
T-killer cell: Type of T-lymphocyte that attaches to cells, releasing toxic substances to kill infected cells and cancer cells.
cytokine: Any signalling molecule released by cells to influence the growth and/or differentiation of the same or another cell.
active immunity: Immunity gained when an antigen enters the body, an immune response occurs and antibodies are produced by plasma cells.
natural active immunity: Immunity gained by being infected by a pathogen.
vaccine: A preparation containing antigens to stimulate active immunity against one or several diseases.
artificial active immunity: Immunity gained by putting antigens into the body, either by injection or by mouth.
vaccination: Giving a vaccine containing antigens for a disease, either by injection or by mouth; vaccination confers artificial active immunity without the development of symptoms of the disease.
passive immunity: The temporary immunity gained without there being an immune response.
artificial passive immunity: The immunity gained by injecting antibodies.
natural passive immunity: The immunity gained by a fetus when maternal antibodies cross the placenta or the immunity gained by an infant from breast milk.
herd immunity: Vaccinating a large proportion of the population; provides protection for those not immunised as transmission of a pathogen is reduced.
ring immunity: Vaccinating all those people in contact with a person infected with a specific disease to prevent transmission in the immediate area.
monoclonal antibody (Mab): An antibody made by a single clone of hybridoma cells; all the antibody molecules made by the clone have identical variable regions so are specific to one antigen.
hybridoma: A cell formed by the fusion of a plasma cell and a cancer cell; it can both secrete antibodies and divide to form other cells like itself.
anabolic: A chemical reaction in which small molecules are built up into larger ones.
respiration: The enzymatic release of energy from organic compounds in living cells.
substrate-linked reaction: In the context of ATP formation, the transfer of phosphate from a substrate molecule directly to ADP to produce ATP, using energy provided directly by another chemical reaction.
chemiosmosis: The synthesis of ATP using energy released by the movement of hydrogen ions down their concentration gradient, across a membrane in a mitochondrion or chloroplast.
glycolysis: The splitting (lysis) of glucose; the first stage in aerobic respiration.
phosphorylation: The addition of a phosphate group to a molecule.
NAD (nicotinamide adenine dinucleotide): A hydrogen carrier used in respiration.
oxidation: The addition of oxygen, or the removal of hydrogen or electrons from a substance.
reduction: The removal of oxygen, or the addition of hydrogen or electrons to a substance.
decarboxylation: The removal of carbon dioxide from a substance.
dehydrogenation: The removal of hydrogen from a substance.
coenzyme A (CoA): A molecule that supplies acetyl groups required for the link reaction.
acetyl coenzyme A: A molecule made up of CoA and a 2C acetyl group, important in the link reaction.
link reaction: Decarboxylation and dehydrogenation of pyruvate, resulting in the formation of acetyl coenzyme A, linking glycolysis with the Krebs cycle.
Krebs cycle: A cycle of reactions in aerobic respiration in the matrix of a mitochondrion in which hydrogens pass to hydrogen carriers for subsequent ATP synthesis and some ATP is synthesised directly; also known as the citric acid cycle.
oxidative phosphorylation: The synthesis of ATP from ADP and Pi using energy from oxidation reactions in aerobic respiration.
electron transport chain: A chain of adjacently arranged carrier molecules in the inner mitochondrial membrane, along which electrons pass in redox reactions.
redox reaction: A chemical reaction in which one substance is reduced and another is oxidised.
ATP synthase: The enzyme that catalyses the phosphorylation of ADP to produce ATP.
anaerobic: Without oxygen.
ethanol fermentation: Anaerobic respiration in which pyruvate is converted to ethanol.
lactate fermentation: Anaerobic respiration in which pyruvate is converted to lactate.
aerenchyma: Plant tissue containing air spaces.
respiratory quotient (RQ): The ratio of the volume of carbon dioxide produced to the volume of oxygen used.
respirometer: A piece of apparatus that can be used to measure the rate of oxygen uptake by respiring organisms.
redox indicator: A substance that changes colour when it is oxidised or reduced.
chlorophyll: A green pigment that absorbs energy from light, used in photosynthesis.
light-dependent stage: The first series of reactions that take place in photosynthesis; it requires energy absorbed from light.
light-independent stage: The final series of reactions that take place in photosynthesis; it does not require light but does need substances that are produced in the light-dependent stage.
photolysis: Splitting a water molecule, using energy from light.
photophosphorylation: Producing ATP using energy that originated as light.
NADP: A coenzyme that transfers hydrogen from one substance to another, in the reactions of photosynthesis.
Calvin cycle: A cycle of reactions in the light-independent stage of photosynthesis in which carbon dioxide is reduced to form carbohydrate.
stroma: The background material in a chloroplast in which the light-independent stage of photosynthesis takes place.
lamellae: Membranes found within a chloroplast.
thylakoid membranes: The membranes inside a chloroplast that enclose fluid-filled sacs; the light-dependent stage of photosynthesis takes place in these membranes.
thylakoid spaces: Fluid-filled sacs enclosed by the thylakoid membranes.
photosynthetic pigments: Coloured substances that absorb light of particular wavelengths, supplying energy to drive the reactions in the light-dependent stage of photosynthesis.
absorption spectrum: A graph showing the absorbance of different wavelengths of light by a photosynthetic pigment.
photosystem: A cluster of light-harvesting pigments surrounding a reaction centre.
reaction centre: The part of a photosystem towards which energy from light is funnelled; it contains a pair of chlorophyll a molecules, which absorb the energy and emit electrons.
chromatography: A technique that can separate substances in a mixture according to their solubility in a solvent.
Rf value: A number that indicates how far a substance travels during chromatography, calculated by dividing the distance travelled by the substance by the distance travelled by the solvent; Rf values can be used to identify the substance.
action spectrum: A graph showing the effect of different wavelengths of light on a process, for example the rate of photosynthesis.
cyclic photophosphorylation: The production of ATP using energy from light, involving only photosystem I.
photoactivation: The emission of an electron from a molecule as a result of the absorption of energy from light.
non-cyclic photophosphorylation: The production of ATP using energy from light, involving both photosystem I and photosystem II; this process also produces reduced NADP.
oxygen-evolving complex: An enzyme found in photosystem II that catalyses the breakdown of water, using energy from light.
ribulose bisphosphate (RuBP): A five-carbon phosphorylated sugar which is the first compound to combine with carbon dioxide during the light-independent stage of photosynthesis.
rubisco: The enzyme that catalyses the combination of RuBP with carbon dioxide.
glycerate-3-phosphate (GP): A three-carbon compound which is formed when RuBP combines with carbon dioxide.
triose phosphate (TP): A three-carbon phosphorylated sugar, the first carbohydrate to be formed during the light-independent stage of photosynthesis.
limiting factor: The requirement for a process to take place that is in the shortest supply; an increase in this factor will allow the process to take place more rapidly.
homeostasis: The maintenance of a relatively constant internal environment for the cells within the body.
negative feedback: A process in which a change in some parameter (e.g. blood glucose concentration) brings about processes which return it towards normal.
receptor: A cell or tissue that is sensitive to a specific stimulus and communicates with a control centre by generating nerve impulses or sending a chemical messenger.
effector: A tissue or organ that carries out an action in response to a stimulus; muscles and glands are effectors.
stimulus: A change in the external or internal environment that is detected by a receptor and which may cause a response.
corrective action: A response or series of responses that return a physiological factor to the set point so maintaining a constant environment for the cells within the body.
set point: The ideal value of a physiological factor that the body controls in homeostasis.
hormone: A substance secreted by an endocrine gland that is carried in blood plasma to another part of the body where it has an effect.
positive feedback: A process in which a change in some parameter such as a physiological factor brings about processes that move its level further in the direction of the initial change.
excretion: The removal of toxic or waste products of metabolism from the body.
urea: A nitrogenous excretory product produced in the liver from the deamination of amino acids.
deamination: The breakdown of excess amino acids in the liver, by the removal of the amine group; ammonia and, eventually, urea are formed from the amine group.
nephron: The structural and functional unit of the kidney composed of Bowman’s capsule and a tubule divided into three regions: proximal convoluted tubule, loop of Henle and distal convoluted tubule.
Bowman’s capsule: The cup-shaped part of a nephron that surrounds a glomerulus and collects filtrate from the blood.
glomerulus: A group of capillaries within the ‘cup’ of a Bowman’s capsule in the cortex of the kidney.
proximal convoluted tubule: Part of the nephron that leads from Bowman’s capsule to the loop of Henle.
loop of Henle: The part of the nephron between the proximal and distal convoluted tubules.
distal convoluted tubule: Part of the nephron that leads from the loop of Henle to the collecting duct.
collecting duct: Tube in the medulla of the kidney that carries urine from the distal convoluted tubules of many nephrons to the renal pelvis.
afferent arteriole: Arteriole leading to glomerular capillaries.
efferent arteriole: Arteriole leading away from glomerular capillaries.
ultrafiltration: Filtration on a molecular scale separating small molecules from larger molecules, such as proteins (e.g. the filtration that occurs as blood flows through capillaries, especially those in glomeruli in the kidney).
selective reabsorption: Movement of certain substances from the filtrate in nephrons back into the blood.
podocyte: One of the cells that makes up the lining of Bowman’s capsule surrounding the glomerular capillaries.
osmoregulation: The control of the water potential of blood and tissue fluid by controlling the water content and/or the concentration of ions, particularly sodium ions.
osmoreceptor: Type of receptor that detects changes in the water potential of blood.
antidiuretic hormone (ADH): Hormone secreted from the posterior pituitary gland that increases water reabsorption in the kidneys and therefore reduces water loss in urine.
islet of Langerhans: A group of cells in the pancreas which secrete glucagon and insulin.
glucagon: A small peptide hormone secreted by the α cells in the islets of Langerhans in the pancreas to bring about an increase in the concentration of glucose in the blood.
insulin: A small peptide hormone secreted by the β cells in the islets of Langerhans in the pancreas to bring about a decrease in the concentration of glucose in the blood.
glycogenesis: Synthesis of glycogen by addition of glucose monomers.
adenylyl cyclase: Enzyme that catalyses formation of the second messenger cyclic AMP.
cyclic AMP (c-AMP): A second messenger in cell-signalling pathways.
protein kinase A: Enzyme that is activated by c-AMP and once activated adds phosphate groups to other proteins, including phosphorylase kinase, to activate them.
phosphorylase kinase: An enzyme that is part of the enzyme cascade that acts in response to glucagon; the enzyme activates glycogen phosphorylase by adding a phosphate group.
glycogenolysis: The breakdown of glycogen by removal of glucose monomers.
gluconeogenesis: The formation of glucose in the liver from non-carbohydrate sources such as amino acids, pyruvate, lactate, fatty acids and glycerol.
biosensor: A device that uses a biological material such as an enzyme to measure the concentration of a chemical compound.
guard cell: A kidney-shaped epidermal cell found with another, in a pair surrounding a stoma and controlling its opening or closure.
electrochemical gradient: A gradient across a cell surface membrane that involves both a difference in concentrations of ions and a potential difference.
abscisic acid (ABA): An inhibitory plant growth regulator that causes closure of stomata in dry conditions.
endocrine gland: An organ that secretes hormones directly into the blood; endocrine glands are also known as ductless glands.
endocrine system: Consists of all the endocrine glands in the body together with the hormones that they secrete.
nerve impulse: (usually shortened to impulse) a wave of electrical depolarisation that is transmitted along neurones.
neurone: A nerve cell; a cell which is specialised for the conduction of nerve impulses.
sensory neurone: A neurone that transmits nerve impulses from a receptor to the central nervous system (CNS).
motor neurone: A neurone whose cell body is in the brain, spinal cord or a ganglion (a swelling on a nerve), and that transmits nerve impulses to an effector such as a muscle or gland.
myelin: Insulating material that surrounds the axons of many neurones; myelin is made of layers of cell surface membranes formed by Schwann cells so that they are very rich in phospholipids and therefore impermeable to water and ions in tissue fluid.
node of Ranvier: A very short gap between Schwann cells where myelinated axons are not covered in myelin so are exposed to tissue fluid.
action potential: A brief change in the potential difference from –70 mV to +30 mV across the cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions.
potential difference: The difference in electrical potential between two points; in the nervous system, between the inside and the outside of a cell surface membrane such as the membrane that encloses an axon.
resting potential: The difference in electrical potential that is maintained across the cell surface membrane of a neurone when it is not transmitting an action potential; it is normally about –70 mV inside and is partly maintained by sodium–potassium pumps.
voltage-gated channel protein: A channel protein through a cell membrane that opens or closes in response to changes in electrical potential across the membrane.
depolarisation: The reversal of the resting potential across the cell surface membrane of a neurone or muscle cell, so that the inside becomes positively charged compared with the outside.
threshold potential: The critical potential difference across the cell surface membrane of a sensory receptor or neurone which must be reached before an action potential is initiated.
repolarisation: Returning the potential difference across the cell surface membrane of a neurone or muscle cell to normal following the depolarisation of an action potential.
refractory period: A period of time during which a neurone is recovering from an action potential, and during which another action potential cannot be generated.
saltatory conduction: Movement of an action potential along a myelinated axon, in which the action potential ‘jumps’ from one node of Ranvier to the next.
chemoreceptor: A receptor cell that responds to chemical stimuli; chemoreceptors are found in taste buds on the tongue, in the nose and in blood vessels where they detect changes in oxygen and carbon dioxide concentrations.
receptor potential: A change in the normal resting potential across the membrane of a receptor cell, caused by a stimulus.
all-or-none law: Neurones and muscle cells only transmit impulses if the initial stimulus is sufficient to increase the membrane potential above a threshold potential.
synaptic cleft: A very small gap between two neurones at a synapse; nerve impulses are transmitted across synaptic clefts by neurotransmitters.
synapse: A point at which two neurones meet but do not touch; the synapse is made up of the end of the presynaptic neurone, the synaptic cleft and the end of the postsynaptic neurone.
neurotransmitter: A chemical released at synapses to transmit impulses between neurones or between a motor neurone and a muscle fibre.
presynaptic neurone: A neurone ending at a synapse from which neurotransmitter is released when an action potential arrives.
postsynaptic neurone: The neurone on the opposite side of a synapse to the neurone in which the action potential arrives.
noradrenaline: A type of neurotransmitter, which is also released by cells in the adrenal glands as a hormone.
acetylcholine (ACh): A type of neurotransmitter released by cholinergic synapses.
cholinergic synapse: A synapse at which the transmitter substance is ACh.
voltage-gated calcium ion channel protein: A channel protein in presynaptic membranes that responds to depolarisation by opening to allow diffusion of calcium ions down their electrochemical gradient.
receptor protein: A protein on a postsynaptic membrane that is a ligand-gated channel protein opening in response to binding of a neurotransmitter.
acetylcholinesterase: An enzyme in the synaptic cleft and on the postsynaptic membrane that hydrolyses ACh to acetate and choline.
neuromuscular junction: A synapse between a motor neurone and a muscle.
striated muscle: Type of muscle tissue in skeletal muscles; the muscle fibres have regular striations that can be seen under the light microscope.
sarcolemma: The cell surface membrane of a muscle fibre.
sarcoplasm: The cytoplasm of muscle cells.
sarcoplasmic reticulum (SR): The endoplasmic reticulum of a muscle fibre.
transverse system tubule (or T-system tubule or T-tubule): Infolding of the sarcolemma that go deep into a muscle fibre and conducts impulses to the SR.
myofibril: One of many cylindrical bundles of thick (myosin) and thin (actin) filaments inside a muscle fibre.
myosin: The protein that makes up the thick filaments in striated muscle; the globular heads of each molecule break down ATP (they act as an ATP-ase).
actin: The protein that makes up the thin filaments in striated muscle.
sarcomere: The part of a myofibril between two Z discs.
tropomyosin: A fibrous protein that is part of the thin filaments in myofibrils in striated muscle; tropomyosin blocks the attachment site on the thin filament for myosin heads so preventing the formation of cross-bridges.
troponin: A calcium-binding protein that is part of the thin filaments in myofibrils in striated muscle.
sliding filament model: The mechanism of muscle contraction; within each sarcomere the movement of thin filaments closer together by the action of myosin heads in the thick filaments shortens the overall length of each muscle fibre.
plant growth regulator: (plant hormone) any chemical produced in plants that influences their growth and development (e.g. auxins, gibberellins, cytokinins and ABA).
auxin: A plant growth regulator (plant hormone) that stimulates cell elongation.
gibberellin: A plant growth regulator (plant hormone) that stimulates seed germination and regulates plant height (stem growth); a lack of gibberellin causes dwarfness.
expansins: Proteins in the cell walls of plants that loosen the attachment of microfibrils of cellulose during elongation growth.
endosperm: A tissue in some seeds, such as barley, that is a store of starch and other nutrients.
aleurone layer: A layer of tissue around the endosperm that synthesises amylase during germination.
sexual reproduction: Reproduction involving the fusion of gametes (fertilisation) to produce a zygote.
gamete: A sex cell; during sexual reproduction, two gametes fuse together to form a zygote; gametes are usually haploid.
fertilisation: The fusing of the nuclei of two gametes, to form a zygote.
zygote: A cell formed by the fusion of the nuclei of two gametes; most zygotes are diploid.
diploid: Containing two complete sets of chromosomes; can be signified by the symbol 2n.
homologous chromosomes: Two chromosomes that carry the same genes in the same positions.
haploid: Containing one complete set of chromosomes; can be signified by the symbol n.
meiosis: Nuclear division that results in the production of four daughter cells with half the chromosome number of the parent cell and with reshuffled alleles; in animals and plants it results in the formation of gametes.
bivalent: Two homologous chromosomes lying alongside each other during meiosis I.
chiasma (plural: chiasmata): A position at which non-sister chromatids of homologous chromosomes cross over each other.
crossing over: The exchange of alleles between non-sister chromatids of homologous chromosomes during meiosis I.
reduction division: Nuclear division that results in a reduction in chromosome number; the first division of meiosis is a reduction division.
locus (plural: loci): The position of a gene on a chromosome.
allele: A variety of a gene.
independent assortment: The production of different combinations of alleles in daughter cells, as a result of the random alignment of bivalents on the equator of the spindle during metaphase I of meiosis.
genotype: The alleles possessed by an organism.
homozygous: Having two identical alleles of a gene.
heterozygous: Having two different alleles of a gene.
phenotype: The observable features of an organism; it is affected by genes and also by environment.
dominant: A dominant allele has the same effect on phenotype, whether or not another allele is present.
recessive: A recessive allele only affects phenotype if no dominant allele is present.
multiple alleles: The existence of three or more alleles of a gene, as, for example, in the determination of A,B,O blood groups.
codominant: Codominant alleles each affect phenotype when both of them are present.
monohybrid inheritance: Inheritance of one gene.
genetic diagram: A standard format in which the results of a genetic cross are predicted and explained.
Punnett square: Part of a genetic diagram in which the genotypes of the offspring are worked out from the genotypes of the gametes.
F1 generation: The offspring resulting from the cross between individuals with a homozygous recessive and a homozygous dominant genotype.
F2 generation: The offspring resulting from a cross between two F1 individuals.
test cross: A genetic cross in which an organism showing the dominant characteristic is crossed with a homozygous recessive organism; the phenotypes of the offspring can indicate whether the original organism is homozygous or heterozygous.
sex chromosomes: The chromosomes that determine sex; in humans, these are the X and Y chromosomes.
sex-linked gene: A gene found on a region of a sex chromosome that is not present on the other sex chromosome; in humans, most sex-linked genes are found on the X chromosome.
carrier: An individual that possesses a particular allele as a single copy whose effect is masked by a dominant allele, so that the associated characteristic (such as a hereditary disease) is not displayed but may be passed to offspring.
dihybrid inheritance: The inheritance of two genes.
epistasis: The interaction of two genes at different loci; one gene may affect the expression of the other.
autosomal linkage: The presence of two genes on the same autosome, (any chromosome other than a sex chromosome) so that they tend to be inherited together and do not assort independently.
parental type: Offspring that show the same combinations of characteristics as their parents.
recombinant: Offspring that show different combinations of characteristics from their parents.
chi-squared (χ2) test: A statistical test that is used to determine whether differences between observed and expected results are significant.
β-galactosidase: An enzyme that catalyses the hydrolysis of lactose to glucose and galactose.
structural gene: A gene that codes for a protein that has a function within a cell.
regulatory gene: A gene that codes for a protein that helps to control the expression of other genes.
operon: A functional unit of transcription; a cluster of genes that are controlled by the same promoter.
lac operon: An operon (see above) found in some bacteria that controls the production of β-galactosidase and two other structural proteins.
inducible enzyme: An enzyme that is synthesised only when its substrate is present.
repressible enzyme: An enzyme that is normally produced, and whose synthesis is prevented by the presence of an effector.
transcription factor: A molecule that affects whether or not a gene is transcribed.
genetic variation: Differences between the DNA base sequences of individuals within a species.
phenotypic variation: Differences between the observable characteristics of individuals within a species.
discontinuous variation: Differences between individuals of a species in which each one belongs to one of a small number of distinct categories, with no intermediates.
continuous variation: Differences between individuals of a species in which each one can lie at any point in the range between the highest and lowest values.
polygenes: A number of different genes at different loci that all contribute to a particular aspect of phenotype.
environmental factor: A feature of the environment of an organism that affects its survival.
biotic factor: An environmental factor that is caused by living organisms (e.g. predation, competition).
competition: The need for a resource by two organisms, when that resource is in short supply.
abiotic factor: An environmental factor that is caused by non-living components (e.g. soil pH, light intensity).
fitness: The ability of an organism to survive and reproduce.
selection pressure: An environmental factor that affects the chance of survival of an organism; organisms with one phenotype are more likely to survive and reproduce than those with a different phenotype.
natural selection: The process by which individuals with a particular set of alleles are more likely to survive and reproduce than those with other alleles; over time and many generations, the advantageous alleles become more frequent in the population.
stabilising selection: Natural selection that tends to keep allele frequencies relatively constant over many generations.
directional selection: Natural selection that causes a gradual change in allele frequency over many generations.
disruptive selection: Natural selection that maintains relatively high frequencies of two different sets of alleles; individuals with intermediate features and allele sets are not selected for.
polymorphism: The continued existence of two or more different phenotypes in a species.
genetic drift: The gradual change in allele frequencies in a small population, where some alleles are lost or favoured just by chance and not by natural selection.
gene pool: The complete range of DNA base sequences in all the organisms in a species or population.
founder effect: The reduction in a gene pool compared with the main populations of a species, resulting from only two or three individuals (with only a selection of the alleles in the gene pool) starting off a new population.
evolutionary bottleneck: A period when the numbers of a species fall to a very low level, resulting in the loss of a large number of alleles and therefore a reduction in the gene pool of the species.
artificial selection: The selection by humans of organisms with desired traits to survive and reproduce; also known as selective breeding.
inbreeding depression: A loss of the ability to survive and grow well, due to breeding between close relatives; this increases the chance of harmful recessive alleles coming together in an individual and being expressed.
inbreeding: Breeding between organisms with similar genotypes, or that are closely related.
outbreeding: Breeding between individuals that are not closely related.
hybrid vigour: An increased ability to survive and grow well, as a result of outbreeding and therefore increased heterozygosity.
evolution: A process leading to the formation of new species from pre-existing species over time.
morphological: Relating to structural features.
physiological: Relating to metabolic and other processes in a living organism.
reproductive isolation: The inability of two groups of organisms to breed with one another; two populations of the same species may be geographically separated, or two different species are unable to breed to produce fertile offspring.
genetically isolated: No longer able to breed together; there is no exchange of genes.
speciation: The production of new species.
geographical isolation: Separation by a geographical barrier, such as a stretch of water or a mountain range.
allopatric speciation: The development of new species following geographical isolation.
sympatric speciation: The development of new species without any geographical separation.
ecological separation: The separation of two populations because they live in different environments in the same area and so cannot breed together.
behavioural separation: The separation of two populations because they have different behaviours which prevent them breeding together.
biological species: A group of organisms with similar morphology and physiology, which can breed together to produce fertile offspring and are reproductively isolated from other species.
morphological species: A group of organisms that share many physical features that distinguish them from other species.
ecological species: A population of individuals of the same species living in the same area at the same time.
population: All of the organisms of the same species present in the same place and at the same time that can interbreed with one another.
biological classification: The organisation of living and extinct organisms into systematic groups based on similarities and differences between species.
taxonomy: The study and practice of naming and classifying species and groups of species within the hierarchical classification scheme.
hierarchical classification: The arrangement of organisms into groups of different rank, from species (lowest) to domain (highest), where similar groups are nested within larger, more inclusive groups.
taxonomic rank: One of the groups used in the hierarchical classification system for organisms, such as species, genus, family, order, class, phylum, kingdom and domain.
taxon (plural: taxa): A taxonomic group of any rank, such as a particular species (e.g. Giraffa camelopardalis), a family (e.g. Elephantidae), a class (e.g. Mammalia) or a kingdom (e.g. Plantae).
domain: The highest taxonomic rank.
kingdom: The taxonomic rank below domain.
Bacteria: The domain that contains all prokaryotic organisms except those classified as Archaea.
Archaea: The domain of prokaryotic organisms that resemble bacteria but share some features with eukaryotes.
Eukarya: The domain that contains all eukaryotic organisms: protoctists, fungi, plants and animals.
Protoctista: Kingdom of eukaryotic organisms which are single-celled or made up of groups of similar cells.
protoctist: A member of the Protoctista kingdom.
Fungi: Kingdom of eukaryotic organisms which do not photosynthesise and have cell walls but without cellulose.
Plantae: Kingdom of eukaryotic organisms which are multicellular, have cell walls that contain cellulose and can photosynthesise.
Animalia: Kingdom of eukaryotic organisms which are multicellular and heterotrophic and have a nervous system.
biodiversity: The variety of ecosystems and species in an area and the genetic diversity within each species.
endemic: Of species, a species that is only found in a certain area and nowhere else.
ecosystem: A relatively self-contained, interacting community of organisms, and the environment in which they live and with which they interact.
community: All of the living organisms, of all species, that are found in a particular ecosystem at a particular time.
habitat: The place where an organism, a population or a community lives.
niche: The role of an organism in an ecosystem; it is how the organism ‘fits into’ the ecosystem.
species diversity: All the species in an ecosystem.
genetic diversity: All the alleles of all the genes in the genome of a species.
random sampling: Method of investigating the abundance and/or distribution of populations which is determined by chance and shows no bias on the part of the person carrying out the sampling.
systematic sampling: A non-random method of investigating the abundance and/or distribution of populations in which the position of sampling points are determined by the person carrying out the sampling (e.g. at every 2 m along a transect).
quadrat: A square frame which is used to mark out an area for sampling populations of organisms.
mark–release–recapture: A method of estimating the numbers of individuals in a population of mobile animals.
Simpson’s index of diversity (D): Used to calculate the biodiversity of a habitat; the range of values is 0 (low biodiversity) to 1 (high biodiversity).
transect: A line marked by a tape measure along which samples are taken, either by noting the species at equal distances (line transect) or placing quadrats at regular intervals (belt transect).
Pearson’s linear correlation: A statistical test used to determine if there is a linear correlation between two variables that are normally distributed.
Spearman’s rank correlation: A statistical test to determine if there is a correlation between two variables when one or both of them are not normally distributed.
assisted reproduction: Any technique that is involved in treating infertility or protecting a female mammal of an endangered species from the health risks of pregnancy.
artificial insemination (AI): Injection of semen collected from a male into the uterus.
embryo transfer: Embryos are removed from the uterus of a female mammal of an endangered species shortly after fertilisation and transferred to surrogate females to bring to full term.
surrogacy: A female becomes pregnant with an embryo from another female and carries it to full term; embryos can be conceived naturally, by AI or by IVF.
in vitro fertilisation (IVF): The fertilisation of an egg that occurs outside the body of a female (e.g. in a Petri dish).
frozen zoo: A facility where genetic materials taken from animals are stored at very low temperatures (–196 °C); sperm, eggs, embryos and tissue samples are examples of these genetic materials.
seed bank: Facility where seeds are dried and kept in cold storage to conserve plant biodiversity.
alien species: A species that has moved into a new ecosystem where it was previously unknown; also known as invasive species.
genetic engineering: Any procedure in which the genetic information in an organism is changed by altering the base sequence of a gene or by introducing a gene from another organism; the organism is then said to be a genetically modified organism (GMO).
recombinant DNA (rDNA): DNA made by artificially joining together pieces of DNA from two or more different species.
transgenic organism: Any organism that contains DNA from another source, such as from another individual of the same species or from a different species.
genetically modified organism (GMO): Any organism that has had its DNA changed in a way that does not occur naturally or by selective breeding.
vector: A means of delivering genes into a cell used in gene technology; e.g. plasmids and viruses.
restriction endonuclease (restriction enzyme): An enzyme, originally derived from bacteria, that cuts DNA molecules; each type of restriction enzyme cuts only at a particular sequence of bases.
bacteriophage (phage): A type of virus that infects bacteria; phages have double-stranded DNA as their genetic material.
gene probe: A length of DNA that has a complementary base sequence to another piece of DNA that you are trying to detect.
genome: The complete set of genes or genetic material present in a cell or an organism; the genome of a eukaryote includes the DNA in the nucleus and in the mitochondria; the genomes of plants include chloroplast DNA.
sticky ends: Short lengths of unpaired bases that form hydrogen bonds with complementary sequences of bases on other pieces of DNA cut with the same restriction enzyme.
cDNA: Double-stranded complementary DNA formed from an mRNA template using reverse transcriptase and DNA polymerase.
promoter: A length of DNA that includes the binding site for RNA polymerase where transcription of a gene or genes begins; in eukaryotes, promoters also have sites for binding of transcription factors.
gene editing: A form of genetic engineering in which the genome of an organism can be changed by deleting, inserting or replacing a length of DNA using a method such as the Crispr/Cas9 system.
polymerase chain reaction (PCR): An automated process that amplifies selected regions of DNA using alternate stages of polynucleotide separation (denaturation of DNA) and DNA synthesis catalysed by DNA polymerase.
gel electrophoresis: The separation of charged molecules (e.g. DNA) by differential movement through a gel in an electric field; the degree of movement is dependent on the mass of the fragments of DNA.
microarray (also known as gene or DNA chips): Slides that are printed with thousands of tiny spots in defined positions, with each spot containing a known DNA sequence; the DNA molecules attached to each slide act as probes to detect lengths of DNA or RNA with complementary sequences.
DNA hybridisation: Binding together of two molecules of single-stranded DNA by complementary base pairing.
bioinformatics: The collection, processing and analysis of biological information and data using computer software.
genetic screening: Testing an embryo, fetus or adult to find out whether a particular allele is present.
cystic fibrosis (CF): A genetic disease caused by recessive alleles of the CFTR (cystic fibrosis transmembrane regulator) gene.
gene therapy: Treatment of a genetic disorder by inserting genetically corrected cells into the body or introducing functioning genes directly into affected cells.
Bt toxin: Insecticidal toxin produced by the bacterium Bacillus thuringiensis; the gene for Bt toxin is transferred to crop plants to make them resistant to insect pests.

∑

Formulas

Ch 01

Magnification

magnification = \frac{observed size of the image}{actual size}

This formula is used to calculate the magnification of an image or to determine the actual size of a specimen if the magnification and image size are known.

Ch 08

Haemoglobin-oxygen binding

H b + 8 O ⇌ H b O_{8}

Represents the reversible binding of four oxygen molecules (eight oxygen atoms) to one haemoglobin molecule.

Ch 08

Carbon dioxide to carbonic acid

C O_{2} + H_{2} O carbonic anhydrase H_{2} C O_{3}

Catalysed by carbonic anhydrase in red blood cells, this reaction is the first step in CO2 transport as hydrogencarbonate ions.

Ch 08

Carbonic acid dissociation

H_{2} C O_{3} ⇌ H^{+} + H C O_{3}^{-}

Carbonic acid dissociates into hydrogen ions and hydrogencarbonate ions, contributing to the Bohr shift and CO2 transport.

Ch 12

Respiratory Quotient (RQ)

\frac{volume of carbon dioxide given out in unit time}{volume of oxygen taken in unit time}

Used to determine the type of respiratory substrate or if anaerobic respiration is occurring.

Ch 12

Respiratory Quotient (RQ) from moles/molecules

\frac{moles or molecules of carbon dioxide given out}{moles or molecules of oxygen taken in}

Used when a balanced chemical equation for respiration is available.

Ch 13

Overall equation for photosynthesis

6 C O_{2} + 6 H_{2} O light energy in the presence of chlorophyll C_{6} H_{12} O_{6} + 6 O_{2}

Represents the overall input and output of photosynthesis, not the detailed steps.

Ch 13

Photolysis of water

H_{2} O \to 2 H^{+} + 2 e^{-} + \frac{1}{2} O_{2}

Occurs in photosystem II during the light-dependent stage.

Ch 13

Reduction of NADP

2 H^{+} + 2 e^{-} + NADP \to reduced NADP

Occurs at the end of the electron transport chain in non-cyclic photophosphorylation.

Ch 13

Rf value calculation

R_{f} = \frac{distance travelled by pigment spot}{distance travelled by solvent}

Used in chromatography to identify substances; values are always between 0 and 1.

Ch 16

Chi-squared test

\sum \frac{( O - E ) ^{2}}{E}

Used to determine if differences between observed and expected results are statistically significant. Compare calculated χ² value to critical value from a table based on degrees of freedom (number of classes - 1) and a chosen probability (e.g., 0.05).

Ch 17

Hardy–Weinberg Equation 1

p + q = 1

Used to calculate allele frequencies in a population where only two alleles for a gene exist.

Ch 17

Hardy–Weinberg Equation 2

p^{2} + 2 pq + q^{2} = 1

Used to calculate genotype frequencies in a large, randomly mating population with no significant selective pressure, migration, or non-random mating.

Ch 18

Lincoln Index (Population Size Estimate)

N = \frac{n _{1} \times n _{2}}{m _{2}}

Used for estimating population size of mobile animals using the mark–release–recapture technique. Assumes no immigration, emigration, births, or deaths between samples, and that marking does not affect survival or recapture probability.

Ch 18

Simpson’s index of diversity (D)

D = 1 - \sum (\frac{n}{N})^{2}

Used to calculate the biodiversity of a habitat. Values range from 0 (low diversity) to 1 (high diversity). A higher value indicates greater species diversity, considering both richness and evenness.

Ch 18

Spearman’s rank correlation coefficient (rs)

r_{s} = 1 - \frac{6 \times \sum D ^{2}}{n ( n ^{2} - 1 )}

Used to determine if there is a correlation between two variables when one or both are not normally distributed, or when using ordinal data. Values range from -1 (perfect negative correlation) to +1 (perfect positive correlation).

Ch 18

Pearson’s linear correlation coefficient (r)

r = \frac{\sum x y - n x ˉ y ˉ}{( n - 1 ) s _{x} s _{y}}

Used to determine if there is a linear correlation between two continuous variables that are normally distributed. Values range from -1 (perfect negative linear correlation) to +1 (perfect positive linear correlation). Correlation does not imply causation.

📌

Key Facts

132

Cells are the basic units of life, categorised into prokaryotic (no nucleus/membrane-bound organelles) and eukaryotic (nucleus/membrane-bound organelles) types.Ch 01
Light microscopes use light and lenses, while electron microscopes use electron beams, offering significantly higher resolution to reveal ultrastructure.Ch 01
Magnification is the image size divided by the actual size; resolution is the ability to distinguish between two separate points.Ch 01
Key eukaryotic organelles include the nucleus (controls cell, contains DNA), mitochondria (aerobic respiration, ATP production), ribosomes (protein synthesis), ER (synthesis/transport), Golgi (modifies/packages proteins), lysosomes (digestion), and in plants, chloroplasts (photosynthesis), cell walls (support), and large central vacuoles (storage/turgor).Ch 01
Prokaryotic cells (e.g., bacteria) have a cell wall, cell surface membrane, cytoplasm, circular DNA, ribosomes, and may have a flagellum, capsule, or plasmids.Ch 01
Viruses are acellular, obligate intracellular parasites, consisting of genetic material (DNA/RNA) enclosed in a protein coat, and lack organelles.Ch 01
Polymers (macromolecules) are built from monomers via condensation reactions (water removed) and broken down by hydrolysis (water added).Ch 02
Carbohydrates: Monosaccharides are joined by glycosidic bonds. Starch/Glycogen (α-glucose) are for energy storage; Cellulose (β-glucose) is for structure.Ch 02
Lipids: Triglycerides (1 glycerol + 3 fatty acids joined by ester bonds) are for energy storage. Phospholipids (hydrophilic head, hydrophobic tails) form cell membranes.Ch 02
Proteins: Polymers of amino acids joined by peptide bonds. A protein's function is determined by its specific 3D tertiary structure.Ch 02
Protein Structure Bonds: Primary (peptide), Secondary (hydrogen), Tertiary/Quaternary (hydrogen, ionic, disulfide, hydrophobic interactions).Ch 02
Water is a polar solvent due to hydrogen bonding, giving it high specific heat capacity and high latent heat of vaporisation.Ch 02
Enzymes are globular proteins that act as biological catalysts, lowering a reaction's activation energy.Ch 03
The induced-fit hypothesis states the active site changes shape upon substrate binding to form an enzyme-substrate complex.Ch 03
Enzyme activity is affected by: temperature (optimum/denaturation), pH (optimum/denaturation), enzyme concentration (linear relationship), and substrate concentration (plateaus at Vmax).Ch 03
Vmax is the maximum reaction rate when all active sites are saturated. Km (Michaelis-Menten constant) is the substrate concentration at ½Vmax.Ch 03
Competitive inhibitors are structurally similar to the substrate and bind to the active site. Non-competitive inhibitors bind to an allosteric site, changing the active site's shape.Ch 03
Enzymes can be intracellular (catalysing reactions within the cell) or extracellular (secreted to work outside the cell).Ch 03
Immobilised enzymes are fixed to a surface or trapped in beads, allowing for reuse and greater stability.Ch 03
The cell membrane is a fluid mosaic model: a phospholipid bilayer with proteins embedded, which is dynamic and not static.Ch 04
Cholesterol regulates membrane fluidity: it reduces fluidity at high temperatures but increases it at low temperatures by preventing phospholipids from packing too closely.Ch 04
Passive transport (simple/facilitated diffusion, osmosis) moves substances down a concentration gradient and does not require ATP.Ch 04
Active transport moves substances against a concentration gradient, requires a carrier protein, and uses energy from ATP.Ch 04
Osmosis is the net movement of WATER molecules from a region of higher water potential (less negative) to a region of lower water potential (more negative) across a partially permeable membrane.Ch 04
Carrier proteins change shape to transport molecules, whereas channel proteins form fixed water-filled pores.Ch 04
Bulk transport moves large quantities of material: endocytosis brings material into the cell and exocytosis expels material from the cell, both requiring ATP.Ch 04
The cell cycle has two main phases: Interphase (G1, S, G2 for growth and DNA replication) and the Mitotic phase (mitosis and cytokinesis).Ch 05
Mitosis is nuclear division that produces two genetically identical daughter nuclei.Ch 05
The four stages of mitosis are Prophase, Metaphase, Anaphase, and Telophase (PMAT).Ch 05
Mitosis is essential for growth of multicellular organisms, repair of damaged tissues, and asexual reproduction.Ch 05
Telomeres are repetitive DNA sequences at the ends of chromosomes that protect genes from being lost during replication.Ch 05
Stem cells are unspecialised cells that can divide an unlimited number of times and differentiate into specialised cells.Ch 05
Cancers are diseases caused by uncontrolled cell division due to mutations in genes that regulate the cell cycle (oncogenes).Ch 05
A nucleotide is a phosphate group, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a nitrogen-containing base (A, T, C, G in DNA; A, U, C, G in RNA).Ch 06
DNA is a double helix of two anti-parallel polynucleotide strands joined by hydrogen bonds between complementary bases: Adenine (A) with Thymine (T), and Cytosine (C) with Guanine (G).Ch 06
DNA replication is semi-conservative: each new DNA molecule contains one original strand and one newly synthesised strand.Ch 06
Key enzymes in replication are DNA polymerase (lines up and joins nucleotides) and DNA ligase (joins fragments on the lagging strand).Ch 06
The genetic code is a triplet code (3 bases code for one amino acid), is degenerate (most amino acids have more than one code), and non-overlapping.Ch 06
Protein synthesis has two stages: Transcription (copying a gene from DNA to mRNA in the nucleus) and Translation (using mRNA to assemble a polypeptide at a ribosome in the cytoplasm).Ch 06
Xylem transports water and minerals passively via the transpiration stream, driven by cohesion-tension.Ch 07
Phloem transports organic assimilates (e.g., sucrose) actively from source to sink via mass flow, driven by a hydrostatic pressure gradient.Ch 07
The Casparian strip in the root endodermis is impermeable, blocking the apoplast pathway and forcing water and selected minerals into the symplast pathway before entering the xylem.Ch 07
Xylem vessels are dead, hollow tubes with lignified walls that provide both a conduit for water and structural support.Ch 07
Phloem consists of living sieve tube elements (lacking most organelles for efficient flow) and companion cells (which provide metabolic support and actively load sucrose).Ch 07
Transpiration is the evaporation of water from leaf surfaces (mainly via stomata), which creates the tension that pulls the water column up the plant.Ch 07
Mammals have a closed double circulation: the pulmonary circuit (heart to lungs & back) and the systemic circuit (heart to body & back).Ch 08
Vessel structure fits function: Arteries have thick elastic walls for high pressure; capillaries are one-cell thick for exchange; veins have thin walls and valves for low-pressure return.Ch 08
Tissue fluid is formed when high hydrostatic pressure at the arteriole end of capillaries forces plasma (minus large proteins & RBCs) out. Most returns at the venule end due to a lower water potential in the blood.Ch 08
Haemoglobin's cooperative binding of oxygen results in a sigmoidal (S-shaped) dissociation curve, ensuring efficient oxygen loading in the lungs and unloading in tissues.Ch 08
The Bohr shift: Increased CO₂ in respiring tissues lowers blood pH (↑H⁺), reducing haemoglobin's affinity for O₂, causing more oxygen to be released.Ch 08
Most CO₂ is transported as hydrogencarbonate ions (HCO₃⁻) in the plasma, a process involving the enzyme carbonic anhydrase in RBCs and the chloride shift.Ch 08
The cardiac cycle involves atrial systole, ventricular systole, and diastole. Atrioventricular and semilunar valves ensure one-way blood flow.Ch 08
The heartbeat is initiated by the sinoatrial node (SAN), with the atrioventricular node (AVN) delaying the impulse before it passes to the ventricles, ensuring atria contract first.Ch 08
The human airway pathway is: Trachea → Bronchi → Bronchioles → Alveoli.Ch 09
C-shaped cartilage rings support the trachea and bronchi, preventing collapse.Ch 09
Goblet cells secrete mucus, which is moved by ciliated epithelium to trap and remove debris from the air.Ch 09
Alveoli are adapted for gas exchange with a large surface area, thin (one-cell thick squamous epithelium) walls, and a rich capillary network to maintain a steep concentration gradient.Ch 09
Bronchioles lack cartilage but contain smooth muscle to regulate airflow to the alveoli.Ch 09
Elastic fibres in the alveoli walls allow them to stretch during inspiration and passively recoil during expiration.Ch 09
Gas exchange is the movement of gases (O₂ in, CO₂ out) between an organism and its surroundings.Ch 09
Infectious diseases are caused by pathogens (e.g., bacteria, viruses, protoctists) and can be transmitted between hosts.Ch 10
Cholera (bacterium: *Vibrio cholerae*) is transmitted by contaminated water; Malaria (protoctist: *Plasmodium*) is transmitted by a vector (female *Anopheles* mosquito).Ch 10
Tuberculosis (bacterium: *Mycobacterium tuberculosis*) is transmitted via airborne droplets; HIV (virus) is transmitted through exchange of body fluids.Ch 10
HIV is the virus that attacks the immune system; AIDS is the syndrome of opportunistic infections that occurs when the immune system is severely weakened.Ch 10
Antibiotics kill bacteria or inhibit their growth by targeting structures like cell walls.Ch 10
Antibiotics are ineffective against viruses because viruses lack the metabolic pathways and structures (e.g., cell walls) that antibiotics target.Ch 10
Antibiotic resistance arises from natural selection: antibiotics kill susceptible bacteria, leaving resistant ones to survive, reproduce, and pass on resistance genes.Ch 10
Phagocytes (neutrophils & macrophages) engulf and destroy pathogens in a non-specific process called phagocytosis.Ch 11
B-lymphocytes, upon activation by a specific antigen, undergo clonal expansion to produce plasma cells and memory cells.Ch 11
Plasma cells are short-lived factories that secrete large quantities of specific antibodies to combat a current infection.Ch 11
Memory cells are long-lived and provide long-term immunity by enabling a faster and stronger secondary immune response upon re-exposure to the same antigen.Ch 11
Antibodies are glycoproteins that do not kill pathogens directly; they cause agglutination, neutralise toxins, or act as markers for phagocytosis.Ch 11
Active immunity involves the body producing its own antibodies and memory cells (long-term), whereas passive immunity is the temporary acquisition of ready-made antibodies.Ch 11
Vaccination induces artificial active immunity, stimulating a primary response to create memory cells without causing disease.Ch 11
Monoclonal antibodies are produced from a single clone of hybridoma cells and are specific to a single antigen epitope, used in diagnosis and treatment.Ch 11
ATP is the universal energy currency, released by respiration for anabolic reactions.Ch 12
Aerobic respiration has 4 stages: Glycolysis (cytoplasm), Link Reaction (matrix), Krebs Cycle (matrix), Oxidative Phosphorylation (inner mitochondrial membrane).Ch 12
Glycolysis is the anaerobic splitting of glucose into two pyruvate, with a net gain of 2 ATP and 2 reduced NAD.Ch 12
The Krebs cycle's main purpose is producing reduced coenzymes (NAD & FAD) via dehydrogenation and decarboxylation.Ch 12
Oxidative phosphorylation involves chemiosmosis, where a proton gradient across the inner mitochondrial membrane drives ATP synthesis.Ch 12
In the absence of oxygen, anaerobic respiration regenerates NAD so glycolysis can continue, producing lactate or ethanol.Ch 12
The Respiratory Quotient (RQ = CO2 produced / O2 consumed) indicates the type of respiratory substrate being metabolised.Ch 12
Overall Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This is an energy transfer process converting light energy into chemical potential energy.Ch 13
Location: The light-dependent stage occurs in the thylakoid membranes. The light-independent stage (Calvin cycle) occurs in the stroma of the chloroplast.Ch 13
Light-Dependent Products: ATP and reduced NADP are produced. Oxygen is a by-product from the photolysis of water (H₂O → 2H⁺ + 2e⁻ + ½O₂).Ch 13
Photophosphorylation: In non-cyclic photophosphorylation, ATP and reduced NADP are made. In cyclic photophosphorylation, only ATP is made.Ch 13
Light-Independent Stage (Calvin Cycle): Uses ATP (as an energy source) and reduced NADP (as a source of hydrogen/reducing power) to fix CO₂ and produce carbohydrates.Ch 13
Photosynthetic Pigments: Chlorophylls and carotenoids, located in the thylakoid membranes, absorb light energy of specific wavelengths.Ch 13
Limiting Factors: The rate of photosynthesis is determined by the factor in shortest supply: light intensity, carbon dioxide concentration, or temperature.Ch 13
Homeostasis is the maintenance of a relatively constant internal environment, fluctuating around a set point.Ch 14
Negative feedback is the primary control mechanism: a change is detected, and a corrective action is triggered to reverse the change.Ch 14
The kidney produces urine via ultrafiltration at the glomerulus and selective reabsorption in the tubules.Ch 14
Osmoregulation is controlled by ADH, which increases the water permeability of the distal convoluted tubule and collecting duct.Ch 14
High blood glucose triggers insulin release, causing liver and muscle cells to take up glucose and store it as glycogen.Ch 14
Low blood glucose triggers glucagon release, causing the liver to break down glycogen into glucose (glycogenolysis).Ch 14
Excretion is the removal of metabolic waste; excess amino acids are deaminated in the liver to form urea for excretion.Ch 14
The resting potential of a neurone is ~-70mV, established by Na+/K+ pumps and K+ leak channels, making the membrane polarised.Ch 15
An action potential is an 'all-or-none' depolarisation to ~+30mV, triggered at a threshold potential by the opening of voltage-gated Na+ channels.Ch 15
Nerve impulses are transmitted across a synapse via neurotransmitters, which diffuse across the synaptic cleft from the presynaptic to the postsynaptic membrane.Ch 15
Myelination allows for saltatory conduction, where the action potential 'jumps' between nodes of Ranvier, dramatically increasing the speed of transmission.Ch 15
In the sliding filament model of muscle contraction, myosin heads bind to actin filaments and pull them inwards, shortening the sarcomere; the filaments themselves do not change length.Ch 15
Nervous communication is rapid, targeted, and short-lived, whereas hormonal (endocrine) communication is slower, widespread, and long-lasting.Ch 15
Plant growth regulators like auxins and gibberellins are chemical messengers produced in various plant tissues (not glands) that control responses like cell elongation.Ch 15
Meiosis is a reduction division producing four genetically unique haploid (n) gametes from a single diploid (2n) parent cell.Ch 16
Genetic variation arises from: 1) Crossing over (exchange of alleles between non-sister chromatids at chiasmata), 2) Independent assortment (of homologous chromosomes), and 3) Random fertilisation.Ch 16
Genotype is the combination of alleles an organism has (e.g., Tt), while phenotype is the observable characteristic (e.g., tall).Ch 16
A dominant allele is always expressed in the phenotype. A recessive allele is only expressed when homozygous. Codominant alleles are both fully and separately expressed in the phenotype.Ch 16
Autosomal linkage occurs when genes are on the same autosome and are inherited together, unless separated by crossing over.Ch 16
Epistasis is when one gene masks or modifies the expression of another gene at a different locus, leading to non-standard dihybrid ratios.Ch 16
Sex-linked genes are located on a sex chromosome (usually the X), resulting in different inheritance patterns between males and females.Ch 16
The chi-squared (χ²) test determines if the difference between observed and expected results is statistically significant or due to chance. Formula: Σ((O-E)²/E).Ch 16
Variation is the foundation of evolution. Discontinuous variation is controlled by a single gene (e.g., blood groups), while continuous variation is controlled by multiple genes (polygenes) and influenced by the environment (e.g., height).Ch 17
Natural selection is the process where selection pressures (biotic/abiotic factors) lead to differential survival and reproduction, causing changes in allele frequencies over generations.Ch 17
There are three types of selection: Stabilising (favours the mean), Directional (favours one extreme, e.g., antibiotic resistance), and Disruptive (favours both extremes).Ch 17
Genetic drift is a random change in allele frequencies due to chance, most significant in small populations. The founder effect and bottleneck effect are key examples.Ch 17
The Hardy–Weinberg principle describes a non-evolving population. Use p + q = 1 for allele frequencies and p² + 2pq + q² = 1 for genotype frequencies.Ch 17
Speciation is the formation of new species, occurring when populations become reproductively isolated. Allopatric speciation involves a geographical barrier; sympatric speciation occurs in the same area.Ch 17
Artificial selection is when humans act as the selection pressure, choosing individuals with desirable traits to breed, as seen in improving milk yield in cattle or disease resistance in wheat.Ch 17
The taxonomic hierarchy is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.Ch 18
Life is classified into three domains: Bacteria (prokaryotic), Archaea (prokaryotic), and Eukarya (eukaryotic).Ch 18
The four eukaryotic kingdoms are Protoctista, Fungi, Plantae, and Animalia.Ch 18
Biodiversity exists at three levels: Ecosystem (range of habitats), Species (richness and evenness), and Genetic (variation of alleles within a species).Ch 18
Simpson's Index of Diversity (D) measures species richness and evenness. A value closer to 1 indicates higher biodiversity.Ch 18
Conservation methods are either *in situ* (in the natural habitat, e.g., National Parks) or *ex situ* (outside the natural habitat, e.g., Zoos, Seed Banks).Ch 18
Key international conservation bodies include CITES (regulates trade in endangered species) and IUCN (assesses conservation status).Ch 18
Genetic engineering involves isolating a gene, inserting it into a vector (e.g., a plasmid) using restriction enzymes and DNA ligase, and introducing the recombinant DNA into a host organism.Ch 19
Key enzymes: Restriction endonucleases cut DNA at specific recognition sites creating 'sticky ends'; Reverse transcriptase synthesises complementary DNA (cDNA) from an mRNA template.Ch 19
Vectors, like plasmids, are used to transfer genes into cells. They must contain essential elements like a promoter for transcription to occur and often genetic markers for identification.Ch 19
PCR (Polymerase Chain Reaction) rapidly amplifies specific DNA sequences using primers, heat-stable Taq polymerase, and repeated cycles of heating and cooling to denature, anneal, and extend.Ch 19
Gel electrophoresis separates DNA fragments by size. Since DNA is negatively charged, it moves towards the positive electrode, with smaller fragments travelling further through the gel.Ch 19
Crispr/Cas9 is a precise gene editing tool that can be used to alter specific sequences within an organism's genome.Ch 19
Applications include producing recombinant human insulin in bacteria, creating herbicide/insect-resistant crops (GMOs), and gene therapy for genetic disorders like SCID.Ch 19

⚠️

Common Mistakes

✗Don't confuse magnification (making larger) with resolution (seeing more detail).Ch 01
✗Remember that not all organelles are membrane-bound (e.g., ribosomes, centrioles).Ch 01
✗Don't confuse the cell wall (external, rigid, freely permeable in plants/bacteria) with the cell surface membrane (internal, thin, partially permeable, in all cells).Ch 01
✗Don't assume vacuoles are exclusive to plant cells; animal cells can have small, temporary ones.Ch 01
✗Don't confuse the simple rotating bacterial flagellum with the complex '9+2' microtubule structure of eukaryotic flagella.Ch 01
✗Don't describe viruses as living cells; they are acellular and require a host to replicate.Ch 01
✗Not all disaccharides are reducing sugars. Sucrose is a key example of a non-reducing sugar and requires acid hydrolysis before testing with Benedict's reagent.Ch 02
✗Hydrogen bonds are weak intermolecular forces, NOT strong covalent bonds. They form between molecules (like water) or parts of a large molecule (like a protein).Ch 02
✗R groups determine a protein's tertiary structure. Secondary structure (α-helices/β-sheets) is formed by H-bonds between the C=O and N-H groups of the polypeptide backbone.Ch 02
✗Polysaccharides like starch and cellulose are not sweet and are generally insoluble, unlike the monosaccharides they are made from.Ch 02
✗The term 'macromolecule' specifically refers to a polymer built from repeating monomer subunits, not just any large molecule.Ch 02
✗Confusing Km and affinity: A LOW Km indicates a HIGH affinity of the enzyme for its substrate, not the other way around.Ch 03
✗Stating enzymes are 'used up': Enzymes are regenerated at the end of a reaction and can be reused.Ch 03
✗Describing the active site as a rigid 'lock': The induced-fit model shows the active site is flexible and changes shape to accommodate the substrate.Ch 03
✗Thinking enzymes 'provide energy': They do not add energy; they provide an alternative reaction pathway with a lower activation energy barrier.Ch 03
✗Reading Vmax directly from a graph's plateau: Vmax is a theoretical maximum and is often estimated by first finding the rate at ½Vmax and then doubling it.Ch 03
✗Confusing facilitated diffusion with active transport. Facilitated diffusion is passive (no ATP) and moves substances down a gradient.Ch 04
✗Mistaking osmosis for the movement of solutes. Osmosis is exclusively the net movement of WATER.Ch 04
✗Thinking a 'higher' water potential is a more negative number. A higher water potential is less negative (e.g., -10 kPa is higher than -50 kPa). Pure water is 0 kPa.Ch 04
✗Believing cholesterol only makes membranes more rigid. It also prevents them from becoming too rigid at low temperatures, thus maintaining fluidity.Ch 04
✗Describing the cell membrane as a rigid, static barrier. It is fluid, and its components can move relative to one another.Ch 04
✗Interphase is not a 'resting phase'. It is a period of intense metabolic activity, growth, and DNA synthesis.Ch 05
✗A replicated chromosome consists of two identical sister chromatids joined by a centromere. Don't confuse a chromatid with a whole chromosome before anaphase.Ch 05
✗Mitosis is nuclear division only. The entire process, including cytoplasmic division, is called cell division.Ch 05
✗Do not confuse the terms: Centromere (joins chromatids), Centrosome (microtubule organising centre), and Centrioles (within the centrosome of animal cells).Ch 05
✗All stem cells are not equally potent. Their ability to differentiate varies (e.g., pluripotent vs. multipotent).Ch 05
✗DNA is the genetic molecule, not protein.Ch 06
✗Only one DNA strand (the template strand) is copied during transcription, not both.Ch 06
✗Translation occurs at ribosomes in the cytoplasm, not inside the nucleus.Ch 06
✗Not all gene mutations are harmful. Due to the degenerate code, some are neutral ('silent'), and some can be beneficial.Ch 06
✗Avoid confusing base names: it's Adenine, not adenosine; Thymine, not thiamine.Ch 06
✗Forgetting xylem's dual role: its lignified walls provide significant structural support, not just transport.Ch 07
✗Assuming phloem sap only moves downwards. It moves from a 'source' to a 'sink', which can be in any direction depending on the plant's needs.Ch 07
✗Stating that xylem vessel elements are living cells. They are dead at maturity, forming an empty, continuous tube (lumen).Ch 07
✗Ignoring the Casparian strip. Water cannot freely enter the xylem; the endodermis regulates its passage.Ch 07
✗Thinking stomata are always open. They close at night or during water stress to conserve water.Ch 07
✗Arteries do NOT always carry oxygenated blood. The pulmonary artery carries deoxygenated blood from the heart to the lungs.Ch 08
✗Veins do NOT always carry deoxygenated blood. The pulmonary vein carries oxygenated blood from the lungs to the heart.Ch 08
✗Tissue fluid is NOT the same as blood plasma. It lacks large plasma proteins and red blood cells.Ch 08
✗The heart muscle is NOT supplied with oxygen from the blood passing through its chambers. It receives oxygenated blood via the coronary arteries.Ch 08
✗CO₂ does NOT bind to the same site as O₂ on haemoglobin. O₂ binds to the haem group; CO₂ binds to different amine groups.Ch 08
✗The AVN does not initiate the heartbeat. The SAN is the pacemaker; the AVN's key role is to introduce a delay before ventricular contraction.Ch 08
✗Forgetting gas exchange is bidirectional: it's for CO₂ removal as well as O₂ intake.Ch 09
✗Confusing bronchi and bronchioles: Bronchi are larger and have cartilage; bronchioles are smaller, lack cartilage, and have more smooth muscle.Ch 09
✗Thinking elastic fibres actively 'contract'. They do not; they passively 'recoil' after being stretched.Ch 09
✗Describing alveoli as rigid bags. They are highly elastic, allowing them to expand and shrink with each breath.Ch 09
✗Confusing HIV and AIDS. Remember: HIV is the virus, AIDS is the late-stage syndrome.Ch 10
✗Assuming antibiotics work on all microbes. They are ineffective against viruses and fungi.Ch 10
✗Thinking all transmission requires direct contact. Vectors (malaria) and contaminated environments (cholera) are key indirect routes.Ch 10
✗Believing all microorganisms are pathogens. Most are harmless or beneficial.Ch 10
✗Using 'vector' and 'carrier' incorrectly. A vector is an organism that transmits a pathogen (e.g., mosquito); a carrier is an infected person who shows no symptoms but can transmit the disease.Ch 10
✗Confusing antibodies (proteins made by your immune system) with antibiotics (drugs that kill bacteria).Ch 11
✗Thinking antigens are always whole pathogens; they are specific molecules (often on a pathogen's surface) that trigger the immune response.Ch 11
✗Stating that antibodies directly kill pathogens. They primarily neutralise or mark them for destruction by other cells like phagocytes.Ch 11
✗Mixing up clonal selection (the initial binding of an antigen to a specific lymphocyte) with clonal expansion (the subsequent mitotic division of that lymphocyte).Ch 11
✗Believing passive immunity (e.g., from mother to baby) is long-lasting. It is temporary because the recipient does not produce their own memory cells.Ch 11
✗Confusing cellular respiration (energy release in cells) with breathing (gas exchange).Ch 12
✗Thinking glycolysis requires oxygen; it is an anaerobic process.Ch 12
✗Believing the Krebs cycle directly produces large amounts of ATP; its main output is reduced NAD and FAD.Ch 12
✗Forgetting that ATP is made by both substrate-linked phosphorylation (in glycolysis/Krebs) and chemiosmosis.Ch 12
✗Defining oxidation as only the addition of oxygen; it's the loss of electrons or hydrogen.Ch 12
✗Source of Oxygen: Forgetting that the oxygen produced comes from the photolysis (splitting) of water, NOT from carbon dioxide.Ch 13
✗Light-Independent Stage Timing: Thinking the Calvin cycle can run indefinitely in the dark. It requires the products of the light-dependent stage (ATP, reduced NADP), so it stops when they run out.Ch 13
✗Coenzyme Confusion: Mixing up NADP (used in photosynthesis) with NAD (used in respiration). Remember 'P' for Photosynthesis.Ch 13
✗Limiting Factors Logic: Assuming that increasing any factor will increase the rate. Only increasing the specific *limiting* factor will boost the rate.Ch 13
✗Spectra Confusion: Confusing an absorption spectrum (which wavelengths a pigment absorbs) with an action spectrum (which wavelengths are most effective for photosynthesis).Ch 13
✗Final Product: Stating that glucose is the direct product of the Calvin cycle. The cycle produces triose phosphate, which is then used to synthesise glucose and other organic molecules.Ch 13
✗Confusing homeostasis with a static, unchanging state. It's a dynamic equilibrium with slight fluctuations.Ch 14
✗Mistaking excretion (removal of metabolic waste like urea) for egestion (removal of undigested food).Ch 14
✗Thinking ADH actively transports water. It only increases the permeability of tubules, allowing water to move by osmosis down a water potential gradient.Ch 14
✗Assuming glucagon acts on muscle cells. Its primary target is the liver; muscle cells lack glucagon receptors.Ch 14
✗Describing negative feedback as a 'bad' thing. It is the essential mechanism for maintaining stability by reversing a change.Ch 14
✗A nerve impulse is a wave of ion movement (depolarisation), not a flow of electrons like an electric current.Ch 15
✗Action potentials have a constant amplitude. A stronger stimulus increases the *frequency* of action potentials, not their size.Ch 15
✗Actin and myosin filaments slide past one another during muscle contraction; they do not shorten.Ch 15
✗There is a physical gap (the synaptic cleft) at a synapse; the pre- and postsynaptic neurones do not touch.Ch 15
✗Plant hormones are produced in various tissues throughout the plant, not in specialised endocrine glands like in animals.Ch 15
✗Confusing homologous chromosomes (a pair, one from each parent) with sister chromatids (identical copies of one chromosome).Ch 16
✗Assuming a dominant allele is always more common in a population. Dominance relates to expression, not frequency.Ch 16
✗Mistaking codominance (both alleles expressed distinctly) for incomplete dominance (a blended, intermediate phenotype).Ch 16
✗Assuming independent assortment for all dihybrid crosses. Genes on the same chromosome are linked and do not assort independently.Ch 16
✗Forgetting that a Punnett square is only one component of a full genetic diagram, which must also show parental genotypes, gametes, and offspring phenotypes/ratios.Ch 16
✗Only genetic variation is heritable and can be acted upon by natural selection. Environmentally-induced variation is not passed on to offspring.Ch 17
✗Evolution is not a conscious process. Organisms do not 'try' to adapt; natural selection acts on pre-existing random variation within a population.Ch 17
✗Don't confuse genetic drift with natural selection. Genetic drift is a random process due to chance, whereas natural selection is non-random, driven by environmental pressures.Ch 17
✗Biological 'fitness' is not about physical strength. It refers specifically to an organism's reproductive success and its ability to pass alleles to the next generation.Ch 17
✗Inbreeding is not always bad. It increases homozygosity, which can fix desirable traits in artificial selection, but it also raises the risk of expressing harmful recessive alleles.Ch 17
✗Thinking organisms that look similar must be the same species. The biological species concept is based on reproductive isolation (ability to produce fertile offspring).Ch 18
✗Believing Kingdom is the highest taxonomic rank. It is Domain.Ch 18
✗Confusing Fungi with Plants. Fungi are heterotrophic and have cell walls made of chitin, not cellulose.Ch 18
✗Equating species diversity with only the number of different species (richness). It also includes the relative abundance of each species (evenness).Ch 18
✗Using random sampling with quadrats in an area with a clear environmental gradient. Systematic sampling along a transect is required here.Ch 18
✗Confusing genetic engineering with selective breeding. Genetic engineering is the direct manipulation of DNA, often between species, while selective breeding is not.Ch 19
✗Thinking restriction enzymes cut DNA randomly. They are highly specific and only cut at particular base sequences called recognition sites.Ch 19
✗Assuming PCR copies the entire DNA sample. It only amplifies the specific target region located between the two primers.Ch 19
✗Mistaking a gene probe for a primer. A probe is a labelled DNA strand used to detect and identify a specific sequence, while a primer is a short strand that provides a starting point for DNA synthesis.Ch 19
✗Defining recombinant DNA as any altered DNA. It specifically refers to DNA made by joining fragments from two or more different sources.Ch 19

💡

Exam Tips

103

→When asked to 'outline' structure and function, provide concise descriptions for each organelle, linking structure to its role.Ch 01
→Practice calculating magnification and actual size using the formula: Magnification = Image size / Actual size. Ensure consistent units.Ch 01
→Be precise when comparing prokaryotic and eukaryotic cells; focus on the presence/absence of a nucleus, membrane-bound organelles, and DNA form.Ch 01
→For microscopy questions, clearly state the advantages of electron microscopes (higher resolution, greater magnification) over light microscopes.Ch 01
→When drawing cells, include clear labels for all visible structures and indicate magnification if provided.Ch 01
→Remember the role of ATP as the universal energy currency, produced primarily by mitochondria in eukaryotes.Ch 01
→When comparing molecules (e.g., starch vs. cellulose), always link their structural differences (e.g., α/β-glucose, branching) directly to their functional differences (e.g., energy storage vs. structural support).Ch 02
→For food test questions, state the reagent, conditions (e.g., heat), and the specific positive colour change. For the non-reducing sugar test, state the initial negative result, the hydrolysis step, and the final positive result.Ch 02
→Practice drawing and labelling: α-glucose, a triglyceride (showing ester bonds), and the general structure of an amino acid. Be able to show how a peptide or glycosidic bond is formed.Ch 02
→Be precise with bond names: use 'glycosidic' for carbohydrates, 'ester' for lipids, and 'peptide' for linking amino acids. Specify where hydrogen bonds are found (water, protein secondary/tertiary structure).Ch 02
→For proteins like haemoglobin and collagen, explicitly relate their structure (globular vs. fibrous, quaternary structure, prosthetic groups) to their specific biological role.Ch 02
→When explaining temperature effects, always mention both the increase in kinetic energy (more frequent collisions) up to the optimum, and the breaking of bonds causing denaturation beyond the optimum.Ch 03
→When explaining pH effects, refer specifically to the alteration of charges on amino acid R-groups in the active site, which disrupts bonds and changes the tertiary structure.Ch 03
→In practical investigation questions, always state that the 'initial rate' of reaction should be measured, as substrate concentration is not yet a limiting factor.Ch 03
→For graphs of substrate concentration vs. rate, be prepared to label the axes correctly, and identify or calculate Vmax and Km.Ch 03
→To distinguish inhibitors, remember: competitive inhibition can be overcome by increasing substrate concentration (Vmax is unchanged, Km increases), while non-competitive cannot (Vmax is lowered, Km is unchanged).Ch 03
→When describing how to measure reaction progress, suggest a specific method like using a colorimeter to measure the absorbance of a coloured product over time.Ch 03
→When defining osmosis, you must include three points for full marks: 1) net movement of water, 2) from a higher to a lower water potential, 3) across a partially permeable membrane.Ch 04
→For questions on practicals involving plant tissue (e.g., potato cylinders), always explain changes in mass/length by referring to the water potential of the tissue versus the surrounding solution.Ch 04
→Be ready to compare transport mechanisms. Use a table to revise the differences between simple diffusion, facilitated diffusion, and active transport (Gradient? Protein needed? ATP needed? Specificity?).Ch 04
→When explaining rates of transport, remember that facilitated diffusion and active transport can be limited by the number of available protein channels or carriers.Ch 04
→In diagrams of the fluid mosaic model, be precise with labels. Distinguish between glycoproteins, glycolipids, channel proteins, carrier proteins, and cholesterol.Ch 04
→Always link a larger surface area to volume ratio with a faster rate of diffusion in application questions.Ch 04
→When asked to describe the stages of mitosis, focus on the behaviour and arrangement of the chromosomes at each stage.Ch 05
→For practical questions on the root tip squash, be able to explain why the root tip is used (meristematic cells are actively dividing) and the purpose of staining.Ch 05
→In cancer-related questions, always link the disease to a loss of control of the cell cycle, leading to the formation of a tumour.Ch 05
→Use precise terminology. For example, state that 'sister chromatids' are separated during anaphase, not 'chromosomes'.Ch 05
→When explaining the importance of mitosis, always link it to the production of genetically identical cells and give a specific example like growth or repair.Ch 05
→Be prepared to draw a nucleotide and show the formation of a phosphodiester bond between two of them.Ch 06
→When comparing DNA and RNA, use a table and state clear differences: pentose sugar (deoxyribose vs. ribose), bases (T vs. U), and structure (double vs. single strand).Ch 06
→Always use the term 'semi-conservative' when describing DNA replication. Clearly state the specific roles of DNA polymerase and DNA ligase.Ch 06
→For descriptions of transcription or translation, always state the precise location (nucleus/cytoplasm), the key molecules involved (e.g., mRNA, tRNA, ribosome), and the final product.Ch 06
→Use sickle cell anaemia as a specific example of a substitution mutation, explaining how a single base change alters the polypeptide and protein function.Ch 06
→For low-power plan diagrams, draw the distribution of tissues with clear, un-shaded outlines. Do NOT draw individual cells.Ch 07
→When explaining water movement up the xylem, you must use and explain the terms cohesion (water-water attraction), adhesion (water-xylem wall attraction), and tension (the pull from transpiration).Ch 07
→Structure your mass flow explanation logically: 1. Active loading of sucrose at source lowers water potential. 2. Water enters by osmosis, creating high hydrostatic pressure. 3. Unloading at sink raises water potential. 4. Water leaves by osmosis, creating low hydrostatic pressure. 5. Sap flows down the pressure gradient.Ch 07
→For xerophyte adaptations, always link the feature to its function. E.g., 'Sunken stomata trap a layer of humid air, which reduces the water potential gradient between the leaf and the atmosphere, slowing transpiration.'Ch 07
→In high-power drawings, draw only a few representative cells accurately. Use a sharp pencil for single lines and include clear labels pointing to the specific structure.Ch 07
→When describing blood vessels, always link structure to function. E.g., 'The thick elastic wall of the artery allows it to stretch and recoil to maintain high pressure'.Ch 08
→For full marks on the Bohr shift, state the full sequence: ↑CO₂ → ↑H⁺ (lower pH) → change in haemoglobin's tertiary structure → reduced affinity for O₂ → more O₂ released to respiring tissues.Ch 08
→Use precise terminology for tissue fluid formation. Refer to 'hydrostatic pressure' forcing fluid out and a 'water potential gradient' (due to plasma proteins) drawing fluid back in.Ch 08
→When describing the cardiac cycle, be systematic. For each stage, state which chambers are contracting (systole) or relaxing (diastole) and the status (open/closed) of both the atrioventricular and semilunar valves.Ch 08
→In explanations of CO₂ transport, explicitly name the enzyme 'carbonic anhydrase' and the process of the 'chloride shift' to score maximum marks.Ch 08
→Always link structure to function. For example, 'The single layer of squamous epithelium in the alveoli provides a short diffusion path for gases'.Ch 09
→When asked to describe gas exchange, always mention the maintenance of a steep concentration gradient by breathing and blood flow.Ch 09
→For microscope drawing questions (Practical 9.1), be sure to accurately place tissues. Show cartilage in the trachea/bronchus but NOT in a bronchiole.Ch 09
→Use precise terminology: 'squamous epithelium', 'ciliated epithelium', 'goblet cells', 'elastic recoil' will score more marks than vague descriptions.Ch 09
→Be ready for 'compare and contrast' questions. Know the key structural differences between the trachea, bronchi, and bronchioles regarding cartilage, smooth muscle, and epithelial cells.Ch 09
→For any named disease, structure your answer using: Pathogen, Mode of Transmission, Treatment, and Prevention methods.Ch 10
→When discussing prevention, always link the method directly to breaking the pathogen's transmission cycle. E.g., 'Clean water supplies prevent ingestion of *Vibrio cholerae', breaking the transmission cycle.'Ch 10
→Explain antibiotic resistance using the principles of natural selection: variation (random mutation), selection pressure (the antibiotic), and inheritance (resistant bacteria survive and reproduce).Ch 10
→Use precise terminology. Name the specific pathogen (e.g., *Plasmodium*) and vector (e.g., *Anopheles* mosquito) where relevant.Ch 10
→Be prepared to discuss the biological, social, and economic factors involved in disease control. For example, the cost of drugs (economic), public health education (social), and drug resistance (biological).Ch 10
→When describing the immune response, always distinguish between the primary and secondary response. Link the secondary response's speed and magnitude to the presence of memory cells.Ch 11
→For questions on vaccination, explain its role in creating herd immunity, which protects vulnerable individuals in a population by reducing pathogen transmission.Ch 11
→Be precise when describing phagocytosis: use key terms like phagosome, lysosome, phagolysosome, and hydrolytic enzymes in a clear sequence.Ch 11
→When explaining antibody function, use specific terms like 'agglutination' or 'neutralisation' and state that the variable region determines antigen specificity.Ch 11
→In comparisons, clearly differentiate between active and passive immunity by mentioning the source of antibodies, presence/absence of memory cells, and duration of protection.Ch 11
→For monoclonal antibody production, remember the key fusion step: a specific B-lymphocyte (plasma cell) is fused with a myeloma cell to create an immortal, antibody-producing hybridoma cell.Ch 11
→Always state the precise location for each stage of respiration (e.g., 'mitochondrial matrix for the Krebs cycle').Ch 12
→Use specific terminology: 'dehydrogenation' for hydrogen removal, 'decarboxylation' for CO2 removal, and 'phosphorylation' for adding phosphate.Ch 12
→For RQ calculations, always write the formula (RQ = CO2/O2), show your substitution, and then state the final calculated value.Ch 12
→Explicitly link mitochondrial structure to function: cristae provide a large surface area for the electron transport chain and ATP synthase.Ch 12
→When describing oxidative phosphorylation, clearly state that oxygen is the 'final electron acceptor'.Ch 12
→Label Chloroplasts Accurately: Be able to draw and label a chloroplast, clearly identifying the stroma, grana, and thylakoids, and state which reaction stage occurs in each location.Ch 13
→Use Precise Terminology: Use specific terms like 'photophosphorylation' for ATP production, 'photolysis' for splitting water, and 'reduced NADP' as the hydrogen carrier.Ch 13
→Master the Calvin Cycle: Don't just memorise the cycle. Be able to explain the roles of ATP (energy) and reduced NADP (reducing power) in the conversion of GP to TP.Ch 13
→Analyse Limiting Factor Graphs: When interpreting a graph, state which factor is limiting on each part of the curve. For example, on the plateau of a light intensity graph, state that CO₂ concentration or temperature is now the limiting factor.Ch 13
→Calculate Rf Values: For chromatography questions, remember the formula R_f = (distance travelled by pigment spot) / (distance travelled by solvent).Ch 13
→Describe Experiments Clearly: When asked to investigate photosynthesis (e.g., using an aquatic plant), state the independent and dependent variables and describe how you would control all other variables to ensure a valid result.Ch 13
→When describing negative feedback, always state the stimulus, receptor, coordinator, effector, and the corrective action that reverses the initial change.Ch 14
→For ultrafiltration, always mention the high hydrostatic pressure in the glomerulus forcing small molecules from the blood into the Bowman's capsule.Ch 14
→Link the structure of the proximal convoluted tubule (PCT) to its function: microvilli for large surface area and many mitochondria for active transport in selective reabsorption.Ch 14
→Be precise about ADH's mechanism: it binds to receptors, causing aquaporins to be inserted into the cell surface membranes of the collecting duct and DCT.Ch 14
→Clearly distinguish between insulin and glucagon effects. Use key terms: insulin promotes glycogenesis (glucose to glycogen), while glucagon promotes glycogenolysis (glycogen to glucose).Ch 14
→Use specific terminology accurately, such as 'water potential gradient', 'selective reabsorption', and 'deamination' to maximise marks.Ch 14
→When describing an action potential, state the sequence of events: resting potential, stimulus, threshold, depolarisation (Na+ influx), repolarisation (K+ efflux), and hyperpolarisation. Quote potential difference values (e.g., -70mV, +30mV).Ch 15
→For muscle contraction, be able to label a sarcomere diagram (Z-line, I-band, A-band, H-zone) and clearly state which bands shorten (I-band, H-zone) and which stay the same length (A-band).Ch 15
→Always link structure to function. For example, the myelin sheath acts as an electrical insulator, and the many mitochondria in a presynaptic knob provide ATP for neurotransmitter synthesis.Ch 15
→Use precise terminology. Distinguish between 'neurone' (a cell) and 'nerve' (a bundle of axons). Use terms like 'presynaptic terminal', 'synaptic cleft', and 'postsynaptic membrane' correctly.Ch 15
→Be prepared for comparison questions. Create a table comparing nervous vs. endocrine control based on speed, duration, transmission method (neurones vs. blood), and nature of the message (electrical vs. chemical).Ch 15
→Structure genetic diagrams precisely: 1. Parental Phenotype, 2. Parental Genotype, 3. Gametes, 4. Punnett Square, 5. Offspring Genotype(s), 6. Offspring Phenotype(s) & Ratio.Ch 16
→For sex-linked traits, always use X and Y notation with the allele as a superscript (e.g., X^H, X^h). Remember males only have one X chromosome.Ch 16
→Recognise key phenotypic ratios: 3:1 (monohybrid), 9:3:3:1 (unlinked dihybrid), 1:2:1 (codominance). Deviations from 9:3:3:1 often indicate linkage or epistasis.Ch 16
→When using the chi-squared test, always state your null hypothesis, show your calculation of the χ² value, determine degrees of freedom (n-1), and compare your value to the critical value to make a conclusion.Ch 16
→In questions about linkage, look for offspring phenotypes that are disproportionately like the parents. These are the non-recombinant offspring.Ch 16
→When explaining genetic variation, always refer to the three key sources: crossing over, independent assortment, and random fertilisation.Ch 16
→For Hardy-Weinberg calculations, always start by identifying the frequency of the homozygous recessive phenotype, which is q². From q², you can calculate q, then p, and then all other frequencies.Ch 17
→When explaining examples of selection (e.g., antibiotic resistance, industrial melanism), structure your answer clearly: 1. Variation exists in the population. 2. A selection pressure is applied. 3. Individuals with advantageous alleles have greater survival and reproductive success (fitness). 4. The frequency of the advantageous allele increases in the next generation.Ch 17
→In speciation questions, always state that 'reproductive isolation' is the key step that prevents gene flow between populations, leading to the evolution of separate species.Ch 17
→Be prepared to draw and label graphs showing the effects of stabilising, directional, and disruptive selection on the distribution of phenotypes in a population.Ch 17
→When comparing natural and artificial selection, clearly state the difference in the selection pressure (environment vs. humans) and the goal (survival vs. human benefit).Ch 17
→For all calculations (Simpson's, Lincoln, Spearman's), write out the formula, show your full working, and give your answer to an appropriate number of significant figures.Ch 18
→When interpreting a calculated correlation coefficient, always state the strength (strong/weak), direction (positive/negative), and conclude by stating that correlation does not prove causation.Ch 18
→When asked for reasons to maintain biodiversity, structure your answer with ecological, economic, and ethical points.Ch 18
→Be prepared to draw and interpret kite diagrams. Remember the width of the kite at any point along the transect line represents the abundance of the species.Ch 18
→When describing sampling techniques, be specific. For random sampling, state you would use a grid and random number generator to place quadrats. For systematic, mention laying a transect line and sampling at regular intervals.Ch 18
→When describing how to create a recombinant plasmid, always state that the *same* restriction enzyme must be used on both the gene and the plasmid to create complementary sticky ends.Ch 19
→For PCR questions, clearly state the purpose of each temperature stage: ~95°C to denature DNA (separate strands), ~55-65°C to anneal primers, and ~72°C for extension by heat-stable Taq polymerase.Ch 19
→In gel electrophoresis diagrams, remember that the wells are at the negative electrode end. The smallest/shortest DNA fragments will be found furthest from the wells.Ch 19
→For questions on the social or ethical implications of genetic technology (e.g., GMOs, gene therapy), provide a balanced argument, discussing both potential benefits and potential risks or concerns.Ch 19
→Use precise terminology. Refer to 'restriction endonucleases', 'vectors', 'recombinant DNA', and 'transgenic organisms' rather than vague terms like 'genetic scissors' or 'changed organism'.Ch 19
→Remember to mention the role of a promoter. A gene inserted into a vector will not be expressed unless it is placed after a suitable promoter sequence that allows RNA polymerase to bind and begin transcription.Ch 19

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