Cell Structure: Biology 9700 (Cambridge International AS & A Level)
Syllabus 1.1, 1.2 · Strand 1 Cells and biological molecules
- Questions
- 10
- Total marks
- 41
- Tier mix
- 10 Core
0 of 10 questions completed
Syllabus coverage
- 1.1 3 questions completed
- 1.2 8 questions completed
Every organism is built from cells, so this topic (syllabus 1.1 and 1.2) is the foundation for almost everything that follows. It begins with the tools biologists use to look at cells. A light microscope passes light through a specimen and is limited by the wavelength of that light, while an electron microscope uses beams of electrons to reveal far finer detail. This is why the two terms you must separate carefully are magnification, meaning how many times larger an image is than the real object, and resolution, meaning the smallest distance between two points that can still be seen as separate. You are also expected to calculate magnification and actual sizes, working confidently in millimetres, micrometres and nanometres.
The core of the topic is the eukaryotic cell. You should recognise organelles such as the nucleus, rough and smooth endoplasmic reticulum, Golgi body, mitochondria, ribosomes, lysosomes, chloroplasts and the cell wall, and outline how each contributes to the life of the cell. Comparing typical plant and animal cells, then contrasting both with the smaller, simpler prokaryotic cell of a bacterium, draws these ideas together. Finally, viruses are introduced as non-cellular particles of nucleic acid and protein, prompting the question of whether cells really are the basic unit of life.
The exam-style questions below are original, written to match these objectives, each with a full worked solution so you can check your reasoning step by step.
Question 1
A biology class compares a light microscope and an electron microscope, both used to study the same prepared slide of onion epidermis cells. The teacher increases the magnification on the light microscope to its maximum setting, but no extra internal detail becomes visible inside the cells. The image simply becomes larger and more blurred. Later, a similar numerical magnification is reached on an electron microscope, and fine internal detail, such as the double membrane surrounding a mitochondrion, becomes clearly visible.
Which property of the electron microscope explains why it reveals this extra detail, even at a magnification the light microscope could also reach?
Question 2
A biologist examines an electron micrograph of a palisade mesophyll cell taken from a leaf near the top of a sunflower plant. The cell contains a large nucleus with a clearly visible nucleolus, many chloroplasts packed close to the cell surface membrane, and a number of mitochondria scattered through the cytoplasm.
(a) State the function of the nucleolus. [1]
(b) Describe how the internal structure of a chloroplast is adapted to carry out photosynthesis efficiently. [3]
(c) Explain why a palisade mesophyll cell, despite carrying out photosynthesis, still contains a substantial number of mitochondria. [2]
Question 3
A textbook shows two images produced from electron micrographs taken by a research group studying liver cells.
Image 1 shows a single mitochondrion. In the printed image, the mitochondrion measures 24 mm in length. The image is labelled with a magnification of ×15 000.
Image 2 shows a chloroplast granum from a different, plant cell, included for comparison. In this image, the granum has a width of 3.6 mm, and its actual width is known from other data to be 0.4 μm.
(a) Calculate the actual length of the mitochondrion in Image 1, giving your answer in micrometres (μm). Show your working. [3]
(b) A student claims that this mitochondrion could never be seen using a light microscope. Using the resolution of a light microscope, evaluate whether the student is correct. [2]
(c) Calculate the magnification of the chloroplast granum in Image 2. [2]
Question 4
A microbiologist compares electron micrographs of two very different single-celled organisms: Chlorella, a eukaryotic green alga, and Bacillus subtilis, a species of bacterium.
(a) State two structural features, other than overall cell size, that would allow the micrographs to be identified correctly as the eukaryotic cell and the prokaryotic cell. [2]
(b) The ribosomes in the Chlorella cell are 80S, while the ribosomes in the Bacillus subtilis cell are 70S. Explain why a light microscope could never be used to see this size difference directly, however much the image is enlarged. [2]
(c) State two ways in which the cell wall of Bacillus subtilis differs from the cell wall of a typical plant cell. [2]
Question 5
A gland cell lining the small intestine synthesises a digestive enzyme, which is a protein, and then secretes it out of the cell.
Which sequence correctly shows the structures this enzyme passes through, in order, from its synthesis to its release from the cell?
Question 6
A white blood cell (phagocyte) engulfs a bacterium, enclosing it within a vacuole in its cytoplasm. Powerful digestive (hydrolytic) enzymes are then released into this vacuole, breaking the bacterium down.
Which organelle releases these digestive enzymes into the vacuole?
Question 7
Electron micrographs of a liver cell and a pancreatic acinar cell are compared. The liver cell contains extensive regions of tubular membrane that are not studded with ribosomes, together with many mitochondria. The pancreatic acinar cell, which secretes digestive enzymes, contains extensive stacks of flattened membrane that are studded with ribosomes, feeding into a prominent Golgi body. The Golgi body in the pancreatic cell also buds off small enzyme-filled vesicles that do not leave the cell.
(a) Name the type of endoplasmic reticulum found extensively in the liver cell, and describe one function of this type of ER that fits the liver's known role in detoxifying substances such as alcohol. [2]
(b) Name the type of endoplasmic reticulum found extensively in the pancreatic acinar cell, and describe how its appearance in an electron micrograph differs from that of the type of ER named in (a). [2]
(c) State how the small enzyme-filled vesicles described above are formed, and name the type of organelle they become. [2]
Question 8
An electron micrograph of a pancreatic acinar cell includes a printed scale bar. The scale bar represents an actual distance of 1 μm and measures 4 mm in length when measured with a ruler on the printed image.
In the same image, a single mitochondrion measures 8 mm in length, and the width of a stack of Golgi membranes measures 0.6 mm.
(a) Use the scale bar to calculate the magnification of the micrograph. Show your working. [2]
(b) Calculate the actual length of the mitochondrion, giving your answer in micrometres (μm). [2]
(c) Calculate the actual width of the stack of Golgi membranes, giving your answer in nanometres (nm). [3]
Question 9
Which statement correctly describes the structure of the nucleus in a eukaryotic cell?
Question 10
A researcher places a sample of identical human red blood cells and a sample of identical onion epidermal cells into separate beakers of pure water. After several hours, the red blood cells have burst, but the onion cells remain intact and firm.
(a) Name the structure present in the onion cell but absent from the red blood cell that prevents the onion cell from bursting. [1]
(b) Describe two properties of this structure that allow it to prevent the onion cell from bursting while still permitting water to enter the cell. [2]
(c) State two functions of this structure other than preventing the cell from bursting. [2]