Secondary 3 Biology Cells Biomolecules Quiz

Secondary 3 Biology Quiz - Cells Biomolecules (Answer Key)

Total Marks: 50

Section A: Multiple Choice Questions [10 marks]

1. B - Rough endoplasmic reticulum
Explanation: Radioactive amino acids are first incorporated into proteins at ribosomes on the rough ER, before being processed by the Golgi apparatus.

2. B - Cells → Tissues → Organs → Organ systems
Explanation: This represents the correct hierarchical organization of biological structures from smallest to largest.

3. C - Golgi apparatus
Explanation: The Golgi apparatus modifies and packages proteins received from the rough ER before transport to their final destinations.

4. A - Amylase
Explanation: Amylase works optimally at pH 7 (neutral). A change to pH 2 (acidic) would denature this enzyme, while pepsin naturally works at pH 2.

5. C - Reducing sugar
Explanation: Benedict's solution turns brick-red/orange when heated with reducing sugars like glucose, fructose, or maltose.

Section B: Structured Questions [25 marks]

6. (a) Cell C (Nerve cell) [1 mark]

6. (b) [4 marks total - 2 marks per adaptation]

Sample answer:

• Adaptation 1: Biconcave/disc shape
• Explanation: Increases surface area to volume ratio for efficient oxygen loading and unloading
• Adaptation 2: No nucleus or organelles
• Explanation: Provides more space for haemoglobin to carry oxygen

Alternative acceptable adaptations: flexible membrane for passage through capillaries, contains haemoglobin

6. (c) [3 marks]

• Structure: Long projection/hair-like extension from cell surface [1]
• Function: Increases surface area for absorption of water and mineral salts [2]

7. (a) 40°C [1 mark]

7. (b) [3 marks] As temperature increases from 10°C to 40°C, enzyme activity increases because:

• Molecules have more kinetic energy [1]
• More frequent collisions between enzyme and substrate [1]
• Faster rate of enzyme-substrate complex formation [1]

7. (c) [3 marks] After 40°C, enzyme activity decreases because:

• High temperature causes enzyme denaturation [1]
• Active site shape changes [1]
• Substrate can no longer bind to active site/enzyme becomes non-functional [1]

7. (d) [1 mark] Sample answers:

• Repeat the experiment multiple times and calculate average
• Use same volume/concentration of hydrogen peroxide
• Use same amount of catalase
• Control other variables (pH, pressure)

8. (a) [2 marks - 1 mark each] Sample similarities:

• Both involve movement of substances across cell membranes
• Both are essential for cell survival/function
• Both can be selective for certain substances

8. (b) [4 marks - 2 marks per difference]

Alternative differences: speed, use of carrier proteins, selectivity

9. (a) [2 marks]

• A: Cell wall [1]
• B: Chloroplast [1]

9. (b) [2 marks] Function of cell wall:

• Provides structural support/protection [1]
• Prevents over-expansion when cell absorbs water/maintains cell shape [1]

Section C: Extended Response [15 marks]

10. [8 marks total]

Expected content for full marks:

Red Blood Cell (4 marks):

• Function: Transport oxygen from lungs to body tissues [1]
• Adaptation 1: Biconcave shape increases surface area for gas exchange [1]
• Adaptation 2: No nucleus provides more space for haemoglobin [1]
• Adaptation 3: Flexible membrane allows passage through narrow capillaries [1]

Root Hair Cell (4 marks):

• Function: Absorb water and mineral salts from soil [1]
• Adaptation 1: Hair-like projection increases surface area for absorption [1]
• Adaptation 2: Thin cell wall allows rapid diffusion [1]
• Adaptation 3: Many mitochondria provide energy for active transport of minerals [1]

Marking notes: Award marks for clear structure-function relationships. Accept alternative valid adaptations.

11. (a) [3 marks] In 0% salt solution (pure water):

• Water moves into potato cells by osmosis [1]
• Water potential outside cell is higher than inside cell [1]
• Cells gain water and increase in mass [1]

11. (b) [4 marks] Conclusion and explanation:

• The cell sap concentration is equivalent to approximately 1.0% salt solution [1]
• This is where there is no net change in mass (equilibrium point) [1]
• At this concentration, water potential inside and outside cells is equal [1]
• No net movement of water occurs by osmosis [1]

Marking Guidelines:

• Award marks for scientific accuracy and appropriate use of terminology
• Accept alternative valid explanations that demonstrate understanding
• Deduct marks for incorrect scientific terminology or concepts
• Award partial marks for incomplete but correct responses