Exam questions · Biology
Cell Structures
- 22 exam questions
- 63 marks
- 24 quick checks
Eukaryotic and Prokaryotic Cells
Just this lesson-
1 Name [1 mark]
Name the type of cell that has no nucleus.
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Model answer
A prokaryotic cell, for example a bacterial cell.
Mark scheme
- Prokaryotic (cell) — 1 mark
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2 Describe [2 marks]
Describe two differences between a bacterial cell and an animal cell.
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Model answer
Any two from: a bacterial cell has a cell wall but an animal cell does not; the DNA of a bacterial cell is a single loop in the cytoplasm but in an animal cell it is enclosed in a nucleus; a bacterial cell may have plasmids but an animal cell does not; a bacterial cell is much smaller than an animal cell.
Mark scheme
- Cell wall present in bacteria but not in animal cells — 1 mark
- DNA is a single loop (no nucleus) in bacteria, but enclosed in a nucleus in animal cells — 1 mark
- Plasmids in bacteria only — 1 mark
- Bacterial cell is smaller — 1 mark
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3 Name [3 marks]
Figure 1 shows a bacterial cell. Name the structures labelled A, B and C.
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Model answer
A is the cell wall. B is the (single loop of) DNA. C is a plasmid.
Mark scheme
- A: cell wall — 1 mark
- B: DNA / single loop of DNA / genetic material — 1 mark
- C: plasmid — 1 mark
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4 Calculate [2 marks]
A bacterial cell is 2 µm long. Calculate how many of these cells, laid end to end, would stretch 1 mm.
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Model answer
1 mm = 1000 µm. 1000 ÷ 2 = 500 cells.
Mark scheme
- Converts 1 mm to 1000 µm — 1 mark
- 1000 ÷ 2 = 500 — 1 mark
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5 Calculate [2 marks]
The width of an animal cell is \(2 \times 10^{-5}\text{ m}\). The width of a bacterial cell is \(2 \times 10^{-6}\text{ m}\). Calculate how many times wider the animal cell is, and give the difference as an order of magnitude.
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Model answer
\(\dfrac{2 \times 10^{-5}}{2 \times 10^{-6}} = 10\). The animal cell is 10 times wider, which is one order of magnitude bigger.
Mark scheme
- Divides the two widths to give 10 — 1 mark
- One order of magnitude — 1 mark
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6 Describe [4 marks]
Describe the structure of a bacterial cell.
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Model answer
A bacterial cell is a prokaryotic cell with no nucleus. Its genetic material is a single loop of DNA lying free in the cytoplasm, and it may also contain small rings of DNA called plasmids. The cytoplasm is surrounded by a cell membrane, and outside the membrane there is a cell wall.
Mark scheme
- Cytoplasm and cell membrane — 1 mark
- Cell wall (outside the membrane) — 1 mark
- Single loop of DNA, not in a nucleus — 1 mark
- Plasmids — 1 mark
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7 Compare [6 marks]
Compare the structure of a bacterial cell with the structure of a plant cell.
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Model answer
Both cells have a cell membrane, cytoplasm, ribosomes and a cell wall. In a plant cell the wall is made of cellulose, but a bacterial wall is not. A plant cell has its DNA enclosed in a nucleus, whereas a bacterial cell has no nucleus and its DNA is a single loop in the cytoplasm. A plant cell has chloroplasts and a permanent vacuole, which a bacterial cell does not. A bacterial cell may have plasmids and a flagellum, which a plant cell does not. A bacterial cell is much smaller.
Mark scheme
- Both have a cell membrane, cytoplasm and a cell wall — 1 mark
- Plant cell DNA is in a nucleus; bacterial DNA is a loop in the cytoplasm — 1 mark
- Plant cells have chloroplasts — 1 mark
- Plant cells have a permanent vacuole — 1 mark
- Bacterial cells may have plasmids (and a flagellum) — 1 mark
- Bacterial cell is smaller / plant cell wall is cellulose — 1 mark
Quick check
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1
Which type of cell has no nucleus?
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C: Bacterial cell
A prokaryotic cell, such as a bacterium, has no nucleus. Its DNA lies free in the cytoplasm.
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2
What is a plasmid?
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B: A small ring of DNA in a bacterial cell
A plasmid is a small extra ring of DNA found in bacteria, separate from the main loop of DNA.
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3
Which structure is found in both bacterial cells and plant cells?
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C: Cell wall
Both have a cell wall, although a plant cell wall is made of cellulose and a bacterial one is not. Neither the nucleus nor chloroplasts nor mitochondria are found in bacteria.
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4
How is the genetic material arranged in a bacterial cell?
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A: As a single loop in the cytoplasm
Bacteria have a single loop of DNA in the cytoplasm, and sometimes plasmids too.
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5
What is the value of 1 µm in metres?
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D: \(1 \times 10^{-6}\text{ m}\)
Micro means one millionth, so 1 µm is one millionth of a metre.
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6
One cell is 1000 times wider than another. How many orders of magnitude bigger is it?
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C: 3
Each order of magnitude is a factor of 10, and \(1000 = 10^{3}\), so the difference is 3 orders of magnitude.
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7
Which of these is the smallest?
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B: A virus
A virus is about 100 nm across, much smaller than a bacterium (about 2 µm), an animal cell or a plant cell.
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8
Which organisms are made of prokaryotic cells?
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A: Bacteria
Bacteria are prokaryotes. Fungi, plants and animals are all made of eukaryotic cells.
Animal and Plant Cells
Just this lesson-
1 State [1 mark]
State the function of the nucleus.
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Model answer
It contains the genetic material (DNA) and controls the activities of the cell.
Mark scheme
- Contains DNA / controls the cell's activities — 1 mark
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2 State [2 marks]
State two structures that are found in plant cells but not in animal cells.
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Model answer
Any two from: cell wall, chloroplasts, permanent vacuole.
Mark scheme
- Cell wall — 1 mark
- Chloroplasts — 1 mark
- Permanent vacuole — 1 mark (maximum 2 marks)
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3 Name [4 marks]
Figure 1 shows a plant cell. Name the structures labelled A, B, C and D.
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Model answer
A is the nucleus. B is a chloroplast. C is the (permanent) vacuole. D is the cell wall.
Mark scheme
- A: nucleus — 1 mark
- B: chloroplast — 1 mark
- C: (permanent) vacuole — 1 mark
- D: cell wall — 1 mark
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4 Explain [2 marks]
Muscle cells contain many mitochondria. Explain why.
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Model answer
Mitochondria are where aerobic respiration takes place, which releases energy. Muscle cells contract, and contraction needs a lot of energy.
Mark scheme
- Mitochondria release energy in (aerobic) respiration — 1 mark
- Muscle cells need a lot of energy to contract — 1 mark
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5 Explain [3 marks]
Palisade cells in a leaf contain many chloroplasts. Explain why.
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Model answer
Chloroplasts contain chlorophyll, which absorbs light. Light is needed for photosynthesis. Palisade cells carry out most of the leaf's photosynthesis, so more chloroplasts means more light absorbed and more glucose made.
Mark scheme
- Chloroplasts contain chlorophyll that absorbs light — 1 mark
- Light is needed for photosynthesis — 1 mark
- More chloroplasts means more photosynthesis / more glucose made — 1 mark
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6 Describe [4 marks]
Describe the functions of the cell membrane, the cytoplasm, the cell wall and the ribosomes.
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Model answer
The cell membrane controls what passes into and out of the cell. Most chemical reactions take place in the cytoplasm. The cell wall (in plants) strengthens the cell and supports the plant. Ribosomes are where proteins are made.
Mark scheme
- Cell membrane controls what enters and leaves — 1 mark
- Cytoplasm is where chemical reactions happen — 1 mark
- Cell wall strengthens / supports — 1 mark
- Ribosomes make proteins — 1 mark
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7 Compare [6 marks]
Compare the structure of an animal cell with the structure of a plant cell.
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Model answer
Both cells have a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes. A plant cell also has a cellulose cell wall, which gives it a fixed shape, but an animal cell has no cell wall. A plant cell often has chloroplasts, which absorb light for photosynthesis, but an animal cell has none. A plant cell has a large permanent vacuole filled with cell sap, whereas an animal cell does not.
Mark scheme
- Both have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes — 1 mark
- Plant cells have a cell wall; animal cells do not — 1 mark
- The plant cell wall is made of cellulose — 1 mark
- Plant cells have chloroplasts; animal cells do not — 1 mark
- Plant cells have a permanent vacuole; animal cells do not — 1 mark
- Links a structure to its function (for example chloroplasts absorb light for photosynthesis) — 1 mark
Quick check
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1
Which structure is the site of aerobic respiration?
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B: Mitochondrion
Aerobic respiration takes place in the mitochondria, where energy is released from glucose.
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2
Which structure makes proteins?
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C: Ribosome
Ribosomes join amino acids together to make proteins.
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3
Which of these is found in a plant cell but not in an animal cell?
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D: Chloroplast
Chloroplasts are found only in plant cells (and some other organisms). Animal cells have a nucleus, mitochondria and a cell membrane.
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4
What is the cell wall of a plant cell made from?
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A: Cellulose
Plant cell walls are made of cellulose, which is strong and rigid.
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5
Why do root cells not have chloroplasts?
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C: There is no light underground for photosynthesis
Chloroplasts absorb light for photosynthesis, and there is no light underground.
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6
What is the permanent vacuole filled with?
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B: Cell sap
The permanent vacuole contains cell sap, a solution of sugars and salts.
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7
A cell needs to release a great deal of energy. Which structure would you expect it to contain a lot of?
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A: Mitochondria
Mitochondria release energy in aerobic respiration, so cells with a high energy demand have many of them.
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8
Which statement about mitochondria is correct?
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D: They release energy by aerobic respiration
Mitochondria release energy from glucose in respiration. Energy cannot be made or destroyed, only transferred.
Microscopy and Magnification
Just this lesson-
1 State [1 mark]
State the formula used to calculate magnification.
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Model answer
Magnification = size of image ÷ size of real object.
Mark scheme
- Magnification = image size ÷ real size — 1 mark
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2 Give [2 marks]
Give two advantages of using an electron microscope instead of a light microscope.
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Model answer
It has a higher magnification, and it has a higher resolution so more detail can be seen.
Mark scheme
- Higher magnification — 1 mark
- Higher resolution / shows more detail — 1 mark
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3 Calculate [3 marks]
Figure 1 shows a drawing of a cell. The magnification is ×1500. Calculate the real width of the cell. Give your answer in micrometres.
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Model answer
real size = 54 ÷ 1500 = 0.036 mm. 0.036 mm × 1000 = 36 µm.
Mark scheme
- Uses real size = image size ÷ magnification — 1 mark
- 54 ÷ 1500 = 0.036 mm — 1 mark
- Converts to 36 µm — 1 mark
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4 Calculate [2 marks]
A student looks at a slide using a ×10 eyepiece lens and a ×40 objective lens. Calculate the total magnification, and name the wheel the student should use to make the image sharp.
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Model answer
Total magnification = 10 × 40 = ×400. The student should use the fine focus wheel.
Mark scheme
- 10 × 40 = ×400 — 1 mark
- Fine focus wheel — 1 mark
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5 Describe [4 marks]
Describe how to use a light microscope to look at a slide of onion cells.
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Model answer
Place the slide on the stage and secure it with the clips. Select the lowest power objective lens. Use the coarse focus wheel to bring the image roughly into focus, looking from the side first so the lens does not hit the slide. Then use the fine focus wheel to make the image sharp. Change to a higher power lens and refocus with the fine wheel if more detail is needed.
Mark scheme
- Slide on the stage, held by clips — 1 mark
- Start with the lowest power objective lens — 1 mark
- Coarse focus to find the image — 1 mark
- Fine focus to sharpen it — 1 mark
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6 Explain [4 marks]
Explain how electron microscopy has increased our understanding of sub-cellular structures.
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Model answer
An electron microscope has a much higher magnification and resolving power than a light microscope. This means it can show structures that are too small to be seen with a light microscope, such as ribosomes, plasmids and the internal structure of mitochondria and chloroplasts. Scientists have used this detail to work out how the structures carry out their functions.
Mark scheme
- Electron microscopes have higher magnification — 1 mark
- Electron microscopes have higher resolution / resolving power — 1 mark
- Shows structures not visible with a light microscope, for example ribosomes or the inside of mitochondria — 1 mark
- Understanding of how structures work (their functions) has improved — 1 mark
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7 Calculate [2 marks]
An electron micrograph shows a chloroplast that is 25 mm long. The real chloroplast is 5 µm long. Calculate the magnification. Give your answer in standard form.
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Model answer
25 mm = 25 000 µm. Magnification = 25 000 ÷ 5 = 5000, which is \(5 \times 10^{3}\).
Mark scheme
- Converts 25 mm to 25 000 µm and divides by 5 — 1 mark
- \(5 \times 10^{3}\) — 1 mark
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8 Calculate [3 marks]
A ribosome is 25 nm across. In an electron micrograph the image of the ribosome is 5 mm across. Calculate the magnification. Give your answer in standard form.
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Model answer
5 mm = 5 000 000 nm. Magnification = 5 000 000 ÷ 25 = 200 000, which is \(2 \times 10^{5}\).
Mark scheme
- Converts 5 mm to 5 000 000 nm — 1 mark
- 5 000 000 ÷ 25 = 200 000 — 1 mark
- \(2 \times 10^{5}\) — 1 mark
Quick check
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1
What does magnification tell you?
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B: How many times bigger the image is than the real object
Magnification is how many times bigger the image is than the real object.
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2
Which microscope has the higher resolution?
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C: An electron microscope
An electron microscope has much higher resolving power than a light microscope, so it shows more detail.
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3
A cell is 2 mm wide in a drawing. The real cell is 0.02 mm wide. What is the magnification?
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D: ×100
Magnification = image size ÷ real size = 2 ÷ 0.02 = 100, so ×100.
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4
Which of these can a light microscope show?
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A: A chloroplast
A light microscope shows nuclei, cell walls and chloroplasts. Ribosomes and plasmids are too small and need an electron microscope.
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5
Which lens should you use first when focusing a specimen?
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B: The lowest power objective lens
Start with the lowest power lens so that you can find the specimen in a wide field of view.
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6
How many micrometres are there in 1 mm?
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C: 1000
Milli and micro differ by a factor of 1000, so 1 mm is 1000 µm.
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7
A drawing shows a cell as 45 mm wide. The cell is really 15 µm wide. What is the magnification?
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D: ×3000
Convert 45 mm to 45 000 µm, then divide by 15 µm to get 3000.
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8
An image is 6 mm wide and the magnification is ×200. What is the real width?
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B: 30 µm
Real size = image size ÷ magnification = 6 ÷ 200 = 0.03 mm, which is 30 µm.