📝 Exam Questions — Biology

Plant and animal cells are both eukaryotic cells but exhibit significant structural differences. (a) Compare the structure of a mature plant cell with that of an animal cell as observed using an electron microscope, highlighting three key differences. [6] (b) Discuss how the presence of a cell wall and a large central vacuole in plant cells are advantageous for their functions. [4]

Plant and animal cells exhibit key structural and functional differences that reflect their distinct roles and environments. (a) Compare the structure and function of the cell wall in a plant cell with the cell surface membrane in an animal cell. [5] (b) Explain why a mature plant cell typically contains a large, permanent central vacuole, while animal cells usually have small, temporary vacuoles, if any. [3]

The rough endoplasmic reticulum (RER) is a prominent organelle in cells that are highly active in protein synthesis and secretion. (a) Discuss the structural features of rough endoplasmic reticulum and explain how these features facilitate its function in protein synthesis and modification. [6] (b) Draw a labelled diagram of a section of rough endoplasmic reticulum, showing its association with ribosomes and the nuclear envelope. [4]

Fig 1.1 shows an electron micrograph of a bacterial cell. (a) Calculate the actual length of the bacterial cell in micrometers (µm). [3] (b) Explain why it is important to calibrate an eyepiece graticule for each objective lens used with a light microscope. [4]

The cell surface membrane and the nuclear envelope are both crucial membrane structures within eukaryotic cells, each with distinct roles. (a) Compare the structure and function of the cell surface membrane with the nuclear envelope. [6] (b) Explain how the fluid mosaic model describes the dynamic nature of the cell surface membrane, referring to Fig 1.2. [4]

Light microscopes are essential tools for observing cells and their structures. Accurate measurement of cell size often requires the use of an eyepiece graticule calibrated against a stage micrometer. (a) Draw a simple diagram of a light microscope and label four key components involved in focusing and magnifying the image. [4] (b) An eyepiece graticule has 100 divisions. When calibrated with a stage micrometer, 20 divisions of the eyepiece graticule correspond to 0.1 mm. Calculate the actual size of a cell that measures 60 divisions using this eyepiece graticule. [4]

Accurate biological drawings are essential for recording observations from microscopy. (a) Draw a plan diagram of a transverse section of a plant stem as it would appear under a low power light microscope. Label the epidermis, cortex, vascular bundles, and pith. [7] (b) A student measures the diameter of a cell in their biological drawing to be 50 mm. If the actual diameter of the cell is 25 µm, calculate the magnification of the drawing. Show your working and state the units. [5]

Electron microscopes are powerful tools used to visualise the intricate structures within cells. (a) Explain why electron microscopes have a higher resolution than light microscopes. [3] (b) An organelle appears 50 mm long in an electron micrograph taken at a magnification of ×250 000. Calculate the actual size of this organelle. Give your answer in micrometers (µm). [4]

The cell surface membrane is a vital component of all living cells, controlling the passage of substances into and out of the cell. (a) Describe the general structure of the cell surface membrane. [3] (b) Explain how the partially permeable nature of the cell surface membrane is crucial for cell function. [5]

Ribosomes are essential organelles found in all living cells, playing a crucial role in protein synthesis. (a) Name the two types of molecules that make up a ribosome. [2] (b) State the primary function of ribosomes in a cell. [2] (c) Identify the difference in size between prokaryotic and eukaryotic ribosomes. [2]

Cells are the basic units of life and can be observed using a light microscope. (a) Identify two organelles that are clearly visible in both plant and animal cells when viewed with a light microscope. [2] (b) State the approximate size range of a typical plant cell when viewed with a light microscope. [2] (c) Describe one difference in appearance between the nucleus of a plant cell and an animal cell under a light microscope. [2]

The genetic material within a eukaryotic cell exists in different forms depending on the cell cycle stage. Fig 1.2 shows a condensed chromosome during metaphase. (a) Compare the structure and composition of chromatin and a condensed chromosome. [4] (b) Explain why chromosomes are typically visible only during cell division. [3] (c) Calculate the actual length of a chromosome if its observed length in an electron micrograph is 25 mm and the magnification is ×5000. [3]

Microvilli are small, finger-like extensions found on the surface of some cells. (a) State the primary function of microvilli in a cell. [2] (b) Explain how the structure of microvilli contributes to their primary function, referring to specific examples of cells where they are found. [4]

Eukaryotic cells, whether plant or animal, share several common fundamental structures. (a) Draw a diagram of a generalised eukaryotic cell as seen with a light microscope, showing structures common to both plant and animal cells. Label five of these structures. [5] (b) Explain the function of two of the labelled structures identified in (a). [4]

Microscopy is a fundamental technique in biology, often requiring careful preparation of specimens. A student is preparing a temporary slide of an onion epidermal cell. (a) Describe the steps involved in preparing a temporary slide of an onion epidermal cell for observation under a light microscope. [4] (b) Explain the purpose of adding a drop of water or a staining solution (e.g., iodine) to the specimen on the slide. [3] (c) A student observes an onion epidermal cell under a light microscope. The eyepiece graticule has 100 units, and when calibrated with a stage micrometer, 100 eyepiece units correspond to 0.2 mm. If the observed length of the onion cell is 40 eyepiece units, calculate the actual length of the cell in micrometres (µm). [3]

Lysosomes play a crucial role in maintaining cellular health and responding to cellular stress. (a) Define the term 'self-digestion' in the context of a cell. [2] (b) State two situations where self-digestion might occur in a eukaryotic cell and identify the organelle primarily responsible. [4]

The study of cell structure often involves using different types of radiation from the electromagnetic spectrum. (a) State two types of radiation from the electromagnetic spectrum that are commonly used in microscopy. [2] (b) Name the relationship between the wavelength of radiation and the maximum resolution achievable when viewing a specimen. [3]

The endoplasmic reticulum (ER) is a vital network of membranes within eukaryotic cells, playing a crucial role in cellular processes. (a) Identify two distinct types of endoplasmic reticulum found in eukaryotic cells. [2] (b) Outline the general role of the endoplasmic reticulum in the transport of molecules within a cell. [4]

The endoplasmic reticulum is a complex network of membranes found in eukaryotic cells, existing in both rough and smooth forms. (a) Explain how the structure of the smooth endoplasmic reticulum (SER) is adapted to its functions. [5] (b) Suggest which cells in the human body would have a highly developed smooth endoplasmic reticulum and justify your answer. [5]

Mitochondria are essential organelles found in eukaryotic cells, playing a critical role in energy production. (a) Describe the main function of mitochondria within a eukaryotic cell. [3] (b) Explain how ATP is synthesised in the mitochondria. [3] (c) If a mitochondrion has an observed length of 2.5 cm in an electron micrograph with a magnification of ×12500, calculate its actual length in µm. [2]

Fig. 1.1 shows a diagram of a mitochondrion, an organelle vital for cellular respiration. (a) Identify the labelled structures X and Y in Fig. 1.1. [2] (b) Explain the significance of the folds of the inner membrane (Y) shown in Fig. 1.1. [3] (c) Draw a simple diagram to show how a molecule of ATP is formed from ADP and phosphate, indicating where the energy is stored. [3]

Electron microscopy requires specific specimen preparation techniques to ensure high-quality images. (a) State two reasons why specimens must be prepared in a vacuum for electron microscopy. [2] (b) Outline the main steps involved in preparing a biological specimen for viewing with a Transmission Electron Microscope (TEM). [4]

Electron microscopy offers detailed insights into cellular structures, but different types of electron microscopes serve distinct purposes. Fig. 1.1 shows a simplified representation of the beam paths in a Transmission Electron Microscope (TEM) and a Scanning Electron Microscope (SEM). (a) Compare the principles of image formation and the types of images produced by a Transmission Electron Microscope (TEM) and a Scanning Electron Microscope (SEM). [6] (b) Discuss one advantage and one disadvantage of using an SEM compared to a TEM for studying cell surfaces. [4]

The endosymbiont theory proposes that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by a host cell. (a) Discuss the evidence that supports the endosymbiont theory for the origin of mitochondria. [6] (b) Suggest why the evolution of mitochondria was a significant step in the evolution of eukaryotic life. [4]

The Golgi apparatus is a vital organelle in eukaryotic cells, involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. (a) Describe the process of protein modification and packaging within the Golgi apparatus. [5] (b) Draw a simple diagram of the Golgi apparatus, labelling the cis face, trans face, and Golgi vesicles. [3]

Lysosomes are important organelles involved in the breakdown of various cellular components. (a) Describe the structure of a lysosome. [3] (b) Explain how lysosomes are involved in the digestion of worn-out organelles. [4]

Cells constantly maintain their internal environment by removing unwanted or damaged components. (a) Name two types of unwanted cell components that might be removed by a lysosome. [2] (b) Outline the general role of hydrolytic enzymes in the breakdown of these components. [3]

Fig 1.2 shows an electron micrograph of a plant cell. (a) The observed diameter of a chloroplast within the cell is 45 mm. The scale bar provided on the micrograph is 10 mm long and represents an actual length of 1 µm. Calculate the actual diameter of the chloroplast in micrometres (µm). [3] (b) Determine the magnification of the image if the actual diameter of the nucleus is 15 µm and its observed diameter in the micrograph is 30 mm. [3] (c) Discuss the challenges of accurately measuring the size of organelles from micrographs, considering potential sources of error. [4]

The nucleolus is a distinct structure found within the nucleus of eukaryotic cells. (a) Describe the primary function of the nucleolus within a eukaryotic cell. [3] (b) An electron micrograph shows a nucleolus with an observed diameter of 35 mm. If the actual diameter of the nucleolus is 7 µm, calculate the magnification of the micrograph. Show your working. [4]

Microtubules are dynamic protein polymers that play crucial roles in maintaining cell shape, cell division, and intracellular transport. Centrioles, shown in cross-section in Fig 1.1, are structures made of microtubules. (a) Identify the protein that makes up microtubules. [2] (b) Describe the arrangement of microtubules in a centriole, as seen in Fig 1.1. [4] (c) Explain the role of centrosomes as microtubule organising centres (MTOCs). [3]

Fig 1.1 shows a bacterial cell viewed under an electron microscope. (a) The observed length of the bacterial cell is 50 mm on the micrograph. The magnification of the micrograph is ×10 000. Calculate the actual length of the bacterial cell in micrometres (µm). [3] (b) Convert the length calculated in (a) into millimetres (mm). [2] (c) Explain why it is important to use appropriate units of measurement when describing cell sizes. [3]

The concept that cells are the fundamental building blocks of all living organisms is a cornerstone of modern biology. This idea, known as the cell theory, has profoundly influenced our understanding of life. (a) State two characteristics that define a 'cell' as the basic unit of life. [2] (b) Outline how the discovery of cells led to the development of the cell theory. [4]

Microscopy is a fundamental tool in biology, allowing scientists to observe the intricate structures of cells and tissues. Two key characteristics of a microscope's performance are magnification and resolution. (a) Define the term 'resolution' in microscopy. [2] (b) A student views a plant cell under a light microscope. The observed length of the cell is 48 mm, and its actual size is 120 µm. Calculate the magnification used to view this cell. Show your working. [4] (c) Explain why increasing the magnification beyond a certain point does not necessarily lead to more detail being observed. [2]

The nucleus is a prominent organelle found in eukaryotic cells, essential for controlling cellular activities. (a) State the primary function of the nucleus in a eukaryotic cell. [2] (b) Identify three key components found within the nucleus. [3]

Fig 1.1 shows an electron micrograph of a mitochondrion (labelled X) within a eukaryotic cell. (a) Identify the organelle labelled X. [1] (b) The scale bar in Fig 1.1 represents 1 µm and measures 1.5 cm on the micrograph. The measured diameter of organelle X on the micrograph is 4.5 cm. Calculate the actual diameter of the organelle labelled X, showing your working. [3] (c) Describe how the internal structure of organelle X is adapted for its function in cellular respiration, as seen with an electron microscope. [5]

The packaging of DNA within the nucleus is a dynamic process, with chromatin undergoing significant changes throughout the cell cycle. (a) Outline the process by which chromatin condenses to form visible chromosomes. [4] (b) Deduce the effect on gene expression if chromatin remains highly condensed throughout the cell cycle. [4]

Fig. 1.1 shows a diagram illustrating a cell undergoing phagocytosis. (a) Describe the process of phagocytosis shown in Fig. 1.1. [3] (b) Explain how the cell surface membrane is involved in forming a phagocytic vesicle. [4] (c) Calculate the magnification of the image if a phagocytic vesicle with an actual diameter of 0.5 µm is observed as 15 mm in a micrograph. [2]

Fig 1.2 shows a diagram illustrating the fluid mosaic model of a cell surface membrane. (a) Describe the fluid mosaic model of the cell surface membrane as shown in Fig 1.2. [4] (b) Explain the roles of any three components of the cell surface membrane, other than phospholipids, in controlling the exchange of materials. [6]

Ribosomes are essential organelles found in all living cells, playing a crucial role in protein synthesis. (a) Describe the structure and function of ribosomes in a eukaryotic cell. [4] (b) Calculate the magnification of the image if the observed diameter of a eukaryotic ribosome in a micrograph is 75 nm and its actual diameter is 25 nm. [3]

Secretory cells are specialised to produce and release substances such as hormones or enzymes. (a) Describe the process of exocytosis in a secretory cell. [5] (b) Explain why exocytosis is considered an active process. [3]

Living organisms are broadly classified into two major groups based on their cellular organisation: prokaryotes and eukaryotes. Fig 1.1 shows a diagram of a generalized prokaryotic cell and a generalized eukaryotic animal cell. (a) Compare the structure of a prokaryotic cell with that of a eukaryotic cell, highlighting three key differences. [6] (b) Explain the functional significance of the absence of membrane-bound organelles in prokaryotic cells. [4]

Fig 1.2 shows an electron micrograph of a cell containing a mitochondrion. (a) Determine the actual diameter of the mitochondrion in micrometers (µm). [4] (b) Discuss the advantages and disadvantages of using a scale bar compared to stating the magnification when presenting micrographs. [6]

Microscopes are essential tools for observing the intricate structures within cells. (a) Define the term 'resolution' in the context of microscopy. [2] (b) Explain why electron microscopes have a higher resolution than light microscopes. [3] (c) Calculate the observed size of the image of a chloroplast, in millimetres (mm), if its actual size is 5 µm and it is viewed at a magnification of ×4000. [3]

The nucleus, shown in Fig 1.1, is a defining feature of eukaryotic cells, enclosed by a specialized membrane system. (a) Describe the structure of the nuclear envelope. [4] (b) Explain the importance of nuclear pores in the function of the nucleus. [3]

Bacteria are prokaryotic organisms with a relatively simple cell structure. (a) Describe the main structural features of a typical bacterium. [3] (b) Explain how the presence of a cell wall protects a bacterium from osmotic lysis in a hypotonic environment. [5]

Fig 1.2 shows a diagram of a prokaryotic cell with a large circular chromosome (labelled C) and several smaller circular plasmids (labelled P) within the cytoplasm. (a) Compare the structure and function of the main circular DNA in a bacterium (labelled C) with a plasmid (labelled P). [6] (b) Discuss the significance of plasmids in the context of antibiotic resistance in bacteria. [4]

Centrioles are small, cylindrical organelles found in the cytoplasm of animal cells, playing various organisational roles. (a) Draw a labelled diagram of a centriole as it would appear in a transverse section. [4] (b) Explain how the arrangement of microtubules in a centriole differs from that in a cilium or flagellum. [3] (c) State one other function of centrioles besides their role in cell division. [2]

Fig 1.1 shows a simplified diagram of a bacterial cell, highlighting its protective layers. (a) Compare the composition and location of a bacterial capsule with its cell wall. [4] (b) Discuss the advantages a capsule provides to pathogenic bacteria in terms of survival and infection. [6]

Vacuoles are important organelles in eukaryotic cells, though their characteristics can vary significantly between different cell types. (a) Compare the structure and permanence of vacuoles in mature plant cells and animal cells. [4] (b) Explain the role of the tonoplast in maintaining the turgor of a plant cell. [3] (c) Sketch a simple diagram of a plant cell, labelling the central vacuole and cell wall. [3]

Lysosomes are crucial organelles within eukaryotic cells, playing a vital role in cellular waste management and recycling. (a) Define the term lysosome. [2] (b) State three functions of lysosomes within an animal cell. [3]

Cilia and flagella are whip-like structures found on the surface of some eukaryotic cells. They are involved in cell locomotion or the movement of fluids. Fig. 1.1 shows a cross-section of a cilium. (a) Describe the structure of a cilium as seen in an electron micrograph. [4] (b) Explain how the structure of cilia and flagella contributes to their beating mechanism. [4]

Fig 1.1 shows an electron micrograph of a bacterium with a single flagellum. (a) Describe the structure of a bacterial flagellum. [4] (b) Explain how the flagellum contributes to the survival of motile bacteria. [4]

Prokaryotic cells, such as bacteria, lack membrane-bound organelles but possess specialised structures to carry out essential metabolic functions. (a) Describe the structure of the infolding of the cell surface membrane in a prokaryotic cell. [3] (b) Explain the functions of this infolding in a bacterial cell. [4]

Chloroplasts are organelles found in plant cells and algal cells, where photosynthesis takes place. Fig. 1.2 shows an electron micrograph of a chloroplast. (a) Identify the structures labelled P and Q in Fig. 1.2. [2] (b) The observed diameter of the chloroplast in Fig. 1.2 is 75 mm. If the actual diameter of the chloroplast is 5 µm, calculate the magnification of the image. Show your working. [4] (c) Explain how the internal structure of a chloroplast is adapted for its function. [4]

Viruses are unique biological entities that blur the line between living and non-living. Their existence highlights fundamental differences in biological organisation. (a) Describe the basic structure of a virus, including the components that may be present. [4] (b) Discuss why viruses are considered non-living and how their mode of replication differs from that of prokaryotic or eukaryotic cells. [6]

Plant cells possess a cell wall, a rigid outer layer that provides structural support. (a) State two functions of the cell wall in plant cells. [2] (b) Describe the structure of a plant cell wall. [4]

Plants produce a diverse array of chemical compounds, many of which are not directly involved in primary metabolic processes like growth and reproduction. These are known as secondary metabolites and play crucial roles in their interaction with the environment. (a) Discuss the roles of secondary metabolites in plant defence against herbivores and pathogens. [6] (b) Draw a simple diagram of a plant cell and label the organelle primarily responsible for storing secondary metabolites. [4]

Cilia and flagella are motile appendages found on the surface of some eukaryotic cells, sharing a common internal structure. Fig 1.1 shows an electron micrograph of a cilium and a flagellum. (a) Identify two structural similarities between cilia and flagella as seen under an electron microscope. [2] (b) Calculate the actual length of the cilium labelled X, given its observed length is 10 mm and the magnification is x5000. [2] (c) Suggest why cells lining the trachea have numerous cilia, while sperm cells have a single flagellum. [4]

A bacterial population was grown in a controlled environment and its size was monitored over 12 hours. The graph in Fig 1.1 shows the bacterial population size (in arbitrary units) over time. (a) Interpret the growth pattern of the bacterial population shown in Fig 1.1. [3] (b) Calculate the percentage increase in bacterial population size between 2 hours and 6 hours. [4] (c) Explain one factor that might limit the growth of the bacterial population after 8 hours. [3]

Fig 1.2 shows a bacterial cell, illustrating its genetic material. (a) State one common function of plasmids in bacteria. [2] (b) Outline how plasmids can be used in genetic engineering. [4]

Lysosomal enzymes play a critical role in cellular processes. The graph in Fig 1.1 shows the concentration of lysosomal enzymes within a cell over a period of 10 hours, in response to a specific stimulus. (a) Interpret the graph to describe how the concentration of lysosomal enzymes changes over time in the presence of a specific stimulus. [3] (b) Explain how the observed changes in lysosomal enzyme concentration might contribute to the cell's response to the stimulus. [4]

Plant cells possess structural features that provide support to the organism. (a) Explain how the cell wall contributes to the support of a plant cell. [4] (b) Describe how turgor pressure provides support in plant tissues. [4]

All living cells produce metabolic waste products that must be managed to maintain cellular function. (a) Compare the mechanisms by which animal cells and plant cells deal with their metabolic waste products. [6] (b) Discuss the potential benefits and drawbacks for a plant cell of storing waste products in its central vacuole. [6]

Cells are the fundamental units of life, yet they exhibit significant structural diversity. The study of cell structure often involves the use of electron microscopes due to their high resolution. (a) Compare the structure of a prokaryotic cell with that of a eukaryotic cell, as observed with an electron microscope. [5] (b) State two functions of the cell wall in a prokaryotic cell. [2] (c) A prokaryotic cell has a diameter of 1.5 µm. If an electron micrograph shows this cell with an observed diameter of 75 mm, calculate the magnification of the micrograph. Show your working. [2]

Organisms store energy in various forms to meet their metabolic demands. Plants primarily use starch, while animals use glycogen, as their main carbohydrate food reserves. (a) Describe the main difference in the chemical composition of starch and glycogen as food reserves. [4] (b) A plant cell stores starch granules that have an observed diameter of 2.5 cm in an electron micrograph taken at a magnification of ×25000. Calculate the actual diameter of the starch granule in micrometres (µm). [4]

Cell walls are found in various organisms, including plants and bacteria, but their composition and precise functions can differ. (a) Compare the structure and composition of the cell wall in a plant cell with that of a bacterial cell. [6] (b) Explain the importance of plasmodesmata in plant cells. [4]

Cellular organisation is a key aspect of biology, distinguishing between different forms of life. Electron microscopes provide detailed views of these structures. (a) Draw a large, labelled diagram of a generalized prokaryotic cell, as seen with an electron microscope. Include the cell wall, cell surface membrane, cytoplasm, circular DNA, ribosomes, and a pilus. [5] (b) A eukaryotic cell has an actual diameter of 40 µm. If it is observed in an image with a magnification of ×2500, calculate the observed diameter of the cell in mm. Show your working. [3] (c) Explain why light microscopes cannot resolve the internal structures of ribosomes, unlike electron microscopes. [2]

Bacteria possess several distinct genetic elements crucial for their survival and adaptation. (a) Describe the key structural features of a plasmid in a bacterial cell. [4] (b) A plasmid has an actual length of 2.5 µm. If it is observed in an electron micrograph with a measured length of 50 mm, calculate the magnification of the image. [4]

Cilia and flagella exhibit a characteristic beating motion essential for various cellular functions, from locomotion to fluid movement. (a) Describe the 'sliding microtubule' mechanism responsible for the beating movement of cilia and flagella, including the role of ATP. [5] (b) Evaluate the likely consequences for a cell if the protein dynein, essential for ciliary movement, was non-functional. [5]

Bacteria are single-celled prokaryotic organisms that exhibit a unique cellular organisation. (a) Draw a large, labelled diagram of a bacterium, showing its major organelles and structures. [6] (b) Calculate the actual diameter of a bacterium that appears 50 mm long in a micrograph taken at a magnification of ×25 000. Give your answer in micrometres (µm). [4]

Centrioles are key organelles in animal cells, playing a crucial role in cell organisation and division. (a) Describe the structure of a centriole, including its protein components. [3] (b) Explain the role of centrosomes in animal cells during cell division. [4]

Prokaryotic cells, such as bacteria, possess genetic material in a different arrangement compared to eukaryotic cells. (a) Describe the structure and location of circular DNA in a typical prokaryotic cell. [5] (b) A plasmid has an observed diameter of 0.5 cm in an electron micrograph with a magnification of ×20000. Calculate the actual diameter of the plasmid in micrometres. [3]

Plant cells and bacterial cells both possess a cell wall, but their structures and compositions differ. (a) State two main functions of the cell wall in plant cells. [2] (b) Identify the primary component of the plant cell wall. [2] (c) Give one difference in composition between a bacterial cell wall and a plant cell wall. [2]

Fig. 3.1 is an electron micrograph showing a bacterium. Bacteria are prokaryotic organisms with distinct cellular features. (a) Identify the structures labelled P and Q in Fig. 3.1. [2] (b) Describe the function of structure P in bacterial cells. [3] (c) Explain why the presence of a capsule (structure Q) can increase the pathogenicity of certain bacteria. [3]

Plants exhibit a variety of structural adaptations to provide support against gravity and mechanical stresses. (a) Discuss the structural adaptations of different plant cell types (e.g., parenchyma, collenchyma, sclerenchyma) that contribute to their specific support functions. [6] (b) A plant cell has an actual diameter of 40 μm. If a micrograph shows the cell with an observed diameter of 2.0 cm, calculate the magnification of the micrograph. Show your working. [5]

Fig 1.1 shows a generalised plant cell as seen with a light microscope. (a) Measure the observed length of the plant cell from Fig 1.1 and use the scale bar to determine its actual length. [3] (b) State two features visible in Fig 1.1 that are absent in a typical animal cell. [3]

Fig 1.3 shows a drawing of a generalised plant cell as seen with a light microscope. (a) Measure the observed length of the large central vacuole in the plant cell drawing and use the scale bar to determine its actual length. (b) Calculate the approximate volume of the vacuole, assuming it is cylindrical with the measured length and an actual diameter of 15 µm. Give your answer in µm³. (c) Explain how the large central vacuole contributes to the support of the plant cell.

Fig 1.4 shows a transmission electron micrograph (TEM) of a nucleus from a bat pancreas cell, clearly depicting the nuclear envelope and several nuclear pores. (a) Measure the observed diameter of a nuclear pore from Fig 1.4. [2] (b) Using the scale bar provided in Fig 1.4, calculate the actual diameter of the nuclear pore in nanometers (nm). [3]

Fig. 1.4 shows a simplified diagram of a Transmission Electron Microscope (TEM). (a) Compare the maximum resolution of a TEM (0.1 nm) with that of a light microscope (200 nm), expressing the difference as a ratio. (b) State one advantage of using a TEM over a light microscope, based on the resolution values.

Fig 1.3 shows a simplified diagram of a Transmission Electron Microscope (TEM). (a) Calculate the de Broglie wavelength (λ) of an electron accelerated by 100 kV. Use the formula λ = h / √(2meV), where: h = Planck's constant (6.63 × 10⁻³⁴ J s) m = mass of an electron (9.11 × 10⁻³¹ kg) e = elementary charge (1.60 × 10⁻¹⁹ C) V = accelerating voltage (100 kV) [3] (b) Compare the calculated electron wavelength with the wavelength of visible light (e.g., 550 nm). [3] (c) Evaluate the theoretical resolution limit of an electron microscope compared to a light microscope based on the wavelengths calculated and provided. [3] (d) Discuss one practical limitation that prevents electron microscopes from always achieving their theoretical maximum resolution. [3]

Fig 1.2 shows a transmission electron micrograph (TEM) of a cell surface membrane at very high magnification, revealing its characteristic three-layered appearance. A scale bar is included. (a) Measure the observed thickness of the cell surface membrane from Fig 1.2 and the observed length of the scale bar. [2] (b) Calculate the actual thickness of the cell surface membrane in nanometers. [2]

Fig 1.2 shows a transmission electron micrograph (TEM) of a mitochondrion, clearly illustrating its double membrane and the folded inner membrane forming cristae. (a) Measure the observed length of the mitochondrion from Fig 1.2 and use the scale bar to determine its actual length in micrometers (µm). [3] (b) Calculate the approximate surface area of the inner mitochondrial membrane if it were unfolded, assuming the mitochondrion is cylindrical. Use the actual length you calculated in (a) and an estimated actual diameter of 0.5 µm. Assume the cristae increase the surface area by a factor of 5 compared to a smooth inner membrane of the same dimensions. [4] (c) Explain the significance of the large surface area of the inner mitochondrial membrane for its function. [3]

Fig 1.4 shows a diagram of a typical bacterium, including its ribosomes. (a) Calculate the actual diameter of a prokaryotic ribosome from the diagram. Show your working and give your answer in nm. [2] (b) Eukaryotic ribosomes have an actual diameter of 25 nm. Compare the actual diameter of the prokaryotic ribosome calculated in (a) to that of a eukaryotic ribosome, expressing the difference as a percentage of the eukaryotic ribosome's diameter. [3]

Fig. 1.1 shows an eyepiece graticule scale and a stage micrometer scale used for microscopical measurement. (a) Calculate the calibration of one eyepiece graticule unit in micrometers (µm). (b) A particular cell is measured to be 40 eyepiece graticule units long. Determine the actual length of this cell in micrometers (µm).

Fig 1.4 shows a diagram of a cilium in transverse section (TS), illustrating its characteristic '9 + 2' arrangement of microtubules and a basal body. A scale bar representing 0.2 µm is provided. (a) Measure the observed diameter of the cilium in transverse section from Fig 1.4 and use the scale bar to determine its actual diameter. (b) Calculate the total number of tubulin dimers present in one cross-section of a cilium, given that each microtubule is made of 13 protofilaments and each protofilament consists of tubulin dimers. Assume one tubulin dimer per protofilament in a cross-section. (c) Explain how the '9+2' arrangement of microtubules contributes to the beating mechanism of cilia.

Fig 1.1 shows a transmission electron micrograph (TEM) of rough endoplasmic reticulum (RER) covered with ribosomes. (a) The observed distance between two adjacent ribosomes on the RER is 0.5 cm. The magnification of the image is ×50,000. Calculate the actual distance, in nanometres (nm), between these two adjacent ribosomes. (b) Using your answer from (a), calculate the number of ribosomes that would fit along a 1 µm stretch of rough ER.