Secondary 4 Combined Science Biology Cells Biomolecules Quiz

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

Section A: Short Answer Questions [15 marks]

1. State the process by which oxygen from the surroundings reaches muscle cells during exercise. [1] Answer: Diffusion Marking: Accept "diffusion" or "diffusion down concentration gradient"

2. Name the organelle responsible for ATP production in cells. [1] Answer: Mitochondrion / Mitochondria Marking: Accept either singular or plural form

3. Write the word equation for photosynthesis. [2] Answer: Carbon dioxide + Water → Glucose + Oxygen (in the presence of light and chlorophyll) Marking: 1 mark for correct reactants, 1 mark for correct products. Accept if conditions mentioned separately.

4. Identify the type of transport that moves glucose from the small intestine into blood against a concentration gradient. [1] Answer: Active transport Marking: Must specify "active transport" - do not accept "diffusion" or "osmosis"

5. State TWO factors that affect the rate of diffusion across cell membranes. [2] Answer: Any two from:

• Concentration gradient
• Temperature
• Surface area
• Membrane thickness
• Molecular size Marking: 1 mark each for any two correct factors

6. Name the hormone responsible for increasing blood glucose levels. [1] Answer: Glucagon Marking: Do not accept "insulin" (this decreases blood glucose)

7. Complete the following sentence about enzyme activity: [2] Answer: As temperature increases from 20°C to 40°C, enzyme activity increases because molecules have more kinetic energy / more enzyme-substrate collisions occur Marking: 1 mark for "increases", 1 mark for correct explanation

8. State the function of chloroplasts in plant cells. [1] Answer: Photosynthesis / To carry out photosynthesis Marking: Accept "make glucose" or "convert light energy to chemical energy"

9. Name the process by which water moves across a partially permeable membrane. [1] Answer: Osmosis Marking: Must be "osmosis" - do not accept "diffusion"

10. Identify the main storage carbohydrate in: [3] Answer: (a) Plants: Starch (b) Animals: Glycogen (c) Location in animal cells: Liver / Muscle Marking: 1 mark each for correct answers

Section B: Structured Response Questions [20 marks]

11. (a) Explain why heart muscle cells have more mitochondria than skin cells. [3] Answer:

• Heart muscle cells require more energy/ATP (1)
• For continuous muscle contraction/pumping blood (1)
• Mitochondria carry out cellular respiration to produce ATP (1) Marking: Award marks for linking high energy demand to mitochondrial function

(b) Suggest why red blood cells contain no mitochondria. [2] Answer:

• Red blood cells have no nucleus (1)
• They obtain energy through anaerobic respiration/glycolysis only (1) Alternative: More space for hemoglobin to carry oxygen (1) Marking: Accept either explanation linking to cell specialization

12. (a) State TWO variables that should be kept constant in this investigation. [2] Answer: Any two from:

• Temperature
• Carbon dioxide concentration
• pH of water
• Type/species of plant
• Volume of water Marking: 1 mark each for any two appropriate variables

(b) Explain why the rate of photosynthesis eventually stops increasing even when light intensity continues to increase. [3] Answer:

• Light is no longer the limiting factor (1)
• Another factor becomes limiting, such as CO₂ concentration or temperature (1)
• Maximum rate of enzyme activity is reached (1) Marking: Must mention limiting factors and identify what becomes limiting

13. Describe the role of the following components in maintaining blood glucose homeostasis: [5]

(a) Insulin: [2] Answer:

• Released when blood glucose is high (1)
• Increases glucose uptake by cells/converts glucose to glycogen (1)

(b) Glucagon: [2] Answer:

• Released when blood glucose is low (1)
• Stimulates conversion of glycogen to glucose in liver (1)

(c) Liver: [1] Answer:

• Stores glucose as glycogen/releases glucose when needed Marking: Accept either storage or release function

Section C: Extended Response Question [10 marks]

14. Describe the complete pathway from glucose entry into the cell to ATP production in the mitochondrion. [10]

Answer:

• Glucose enters muscle cell by facilitated diffusion through glucose transporters (1)
• Glucose undergoes glycolysis in the cytoplasm (1)
• Glycolysis breaks glucose into pyruvate and produces small amount of ATP (1)
• Pyruvate enters mitochondrion (1)
• Pyruvate is converted to acetyl-CoA in mitochondrial matrix (1)
• Acetyl-CoA enters Krebs cycle/citric acid cycle (1)
• Krebs cycle produces CO₂, NADH, and FADH₂ (1)
• NADH and FADH₂ donate electrons to electron transport chain (1)
• Oxygen acts as final electron acceptor, forming water (1)
• ATP is produced by oxidative phosphorylation/chemiosmosis (1)

Marking Scheme:

• Award marks for correct sequence and scientific terminology
• Accept alternative correct descriptions of the same processes
• Look for understanding of aerobic respiration pathway
• Maximum 10 marks even if more than 10 correct points given

Common Errors to Watch:

• Confusing location of glycolysis (cytoplasm) vs Krebs cycle (mitochondria)
• Forgetting role of oxygen as final electron acceptor
• Not mentioning transport mechanism for glucose entry
• Mixing up anaerobic and aerobic respiration

Total: 45 marks