Secondary 4 Combined Science Biology Practice Paper 5

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Secondary 4 Combined Science Biology Quiz - Cells Biomolecules

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 50

Duration: 60 Minutes
Total Marks: 50

Instructions:

• Answer all questions in the spaces provided.
• Use scientific terminology where appropriate.
• For structured questions, ensure your explanations link structure to function.

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Section A: Basic Concepts and Identification (Questions 1–5)

1. State the process by which oxygen from the surroundings reaches a cell in the liver. [1]

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2. Identify the organelle that is present in a plant cell but absent in an animal cell, which is responsible for providing structural support. [1]

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3. Name the biomolecule that serves as the primary building block for proteins. [1]

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4. State the function of the ribosome within a cell. [1]

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5. Identify the part of the cell membrane that is selectively permeable. [1]

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Section B: Organelles and Cell Specialisation (Questions 6–12)

6. A table shows the number of mitochondria in three different cell types:

   • Skin cell: 200
   • Heart muscle cell: 2,500
   • Red blood cell: 0 Explain the difference in mitochondria count between the skin cell and the heart muscle cell. [2]

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7. Why do mature red blood cells lack a nucleus? [2]

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8. Describe the relationship between the structure of a root hair cell and its function in water absorption. [3]

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9. Compare the distribution of chloroplasts in the palisade mesophyll and the spongy mesophyll of a leaf. [2]

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10. Suggest why a cell secreting large amounts of digestive enzymes would have a highly developed Golgi apparatus. [2]

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11. State two differences between a prokaryotic cell and a eukaryotic cell. [2]

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12. Explain why the cell membrane is described as a "fluid mosaic model". [2]

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Section C: Movement of Substances (Questions 13–20)

13. Define the term diffusion. [2]

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14. A potato cylinder is placed in a solution of 20% sucrose. (a) Predict whether the mass of the potato cylinder will increase or decrease. [1]

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    (b) Explain your answer in (a) in terms of water potential. [3]

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15. Describe the process of osmosis. [2]

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16. Explain why active transport requires energy in the form of ATP. [2]

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17. A student observes a cell under a microscope. The cell is shrinking (plasmolyzed). (a) Was the cell placed in a hypotonic or hypertonic solution? [1]

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    (b) Explain the movement of water molecules in this scenario. [2]

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18. State one example of a substance that is moved into a cell via active transport. [1]

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19. Describe how the surface area to volume ratio affects the rate of diffusion in a cell. [3]

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20. Explain the role of carrier proteins in the movement of glucose across a cell membrane. [3]

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Answer Key - Secondary 4 Combined Science Biology Quiz (Cells Biomolecules)

1. Diffusion (1m)

• Award 1 mark for "Diffusion".

2. Cell wall (1m)

• Award 1 mark for "Cell wall".

3. Amino acids (1m)

• Award 1 mark for "Amino acids".

4. Protein synthesis (1m)

• Award 1 mark for "Protein synthesis" or "Producing proteins".

5. Phospholipid bilayer / Cell membrane (1m)

• Award 1 mark for "Phospholipid bilayer".

6. Heart muscle cells require more energy (ATP) for contraction (2m)

• 1m: Heart muscle cells have a higher metabolic rate/require more energy.
• 1m: Mitochondria are the site of aerobic respiration/ATP production.

7. To maximize space for haemoglobin (2m)

• 1m: To provide more space for haemoglobin/oxygen transport.
• 1m: Allows the cell to take a biconcave shape for increased surface area.

8. Long extension / Large surface area (3m)

• 1m: Root hair cells have a long projection/extension.
• 1m: This increases the surface area to volume ratio.
• 1m: Increases the rate of water absorption via osmosis.

9. Palisade has more chloroplasts than spongy (2m)

• 1m: Palisade cells are tightly packed with more chloroplasts.
• 1m: They are located at the top of the leaf to maximize light absorption.

10. Modification and packaging of proteins (2m)

• 1m: Golgi apparatus modifies, sorts, and packages proteins into vesicles.
• 1m: High secretion of enzymes requires more packaging for transport out of the cell.

11. Nucleus / Membrane-bound organelles (2m)

• 1m: Prokaryotes lack a defined nucleus (nuclear membrane); Eukaryotes have one.
• 1m: Prokaryotes lack membrane-bound organelles (e.g., mitochondria); Eukaryotes have them.

12. Fluidity and protein arrangement (2m)

• 1m: "Fluid" refers to the phospholipid bilayer where molecules can move laterally.
• 1m: "Mosaic" refers to the pattern of proteins embedded in the bilayer.

13. Net movement of particles (2m)

• 1m: Net movement of particles from a region of higher concentration.
• 1m: To a region of lower concentration, down a concentration gradient.

14. Potato Experiment (4m)

• (a) Decrease (1m).
• (b) 1m: The 20% sucrose solution has a lower water potential than the cell sap.
• 1m: Water moves out of the vacuole/cell by osmosis.
• 1m: From a region of higher water potential to lower water potential.

15. Diffusion of water (2m)

• 1m: Net movement of water molecules from a region of higher water potential.
• 1m: To a region of lower water potential across a partially permeable membrane.

16. Against concentration gradient (2m)

• 1m: Active transport moves substances against the concentration gradient (low to high).
• 1m: This is an endergonic process requiring ATP to power carrier proteins.

17. Plasmolysis (3m)

• (a) Hypertonic (1m).
• (b) 1m: Water potential outside the cell is lower than inside.
• 1m: Water leaves the cell by osmosis, causing the cytoplasm to shrink away from the cell wall.

18. Mineral ions / Glucose (1m)

• Award 1 mark for "Mineral ions" (e.g., nitrates) or "Glucose" (in specific contexts).

19. SA:V Ratio and Rate (3m)

• 1m: As a cell grows larger, the surface area to volume ratio decreases.
• 1m: A smaller ratio means the surface area is insufficient to meet the metabolic needs of the volume.
• 1m: This slows down the rate of diffusion relative to the cell's needs.

20. Carrier Protein Function (3m)

• 1m: Carrier proteins bind to specific glucose molecules.
• 1m: They change shape to transport the molecule across the membrane.
• 1m: This allows glucose to move even if the membrane is otherwise impermeable to it.