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Secondary 4 Pure Biology Practice Paper 3
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TuitionGoWhere Practice Paper - Pure Biology Secondary 4
Answer Key & Marking Scheme
Version: 3 of 5
Topic: Cells and Biomolecules
Section A: Multiple Choice Questions
1. D
Reasoning: Cell walls are present in plant cells but absent in animal cells. Cell membranes, cytoplasm, and mitochondria are found in both. [1]
2. B
Reasoning: Rough ER synthesizes proteins, and mitochondria provide energy for synthesis and secretion. This profile fits secretory cells (e.g., pancreatic cells). [1]
3. B
Reasoning: Active transport moves substances against the concentration gradient (low to high) and requires energy (ATP). [1]
4. C
Reasoning: Benedict’s solution tests for reducing sugars. A positive result is a colour change from blue to green/yellow/orange/brick-red precipitate upon heating. [1]
5. D
Reasoning: Enzymes are proteins (not lipids), are denatured by high (not low) temperatures, lower activation energy, and are specific to substrates. [1]
6. C
Reasoning: Crenation occurs when water leaves the cell by osmosis. This happens when the external solution has a lower water potential (hypertonic) than the cell cytoplasm. [1]
7. C
Reasoning: Carbohydrates and fats contain C, H, O. Proteins contain C, H, O, N (and sometimes S). Nitrogen is the distinguishing element here. [1]
8. C
Reasoning: Glycogen is the storage form of glucose in animals, used for short-to-medium term energy release. Fats are for long-term storage. [1]
9. B
Reasoning: In the lock-and-key model, the enzyme is the lock, the active site is the keyhole, and the substrate is the key. [1]
10. B
Reasoning: The Golgi apparatus modifies, sorts, and packages proteins received from the Rough ER for secretion or use within the cell. [1]
Section B: Structured Questions
11. Cell Structure and Function
(a)
A: Nucleus [1]
B: Mitochondrion [1]
(b)
Function of Nucleus:
- Contains genetic material (DNA/chromosomes). [1]
- Controls cell activities / cell division / protein synthesis. [1]
(c)
Why muscle cells have many mitochondria:
- Muscle contraction requires a large amount of energy. [1]
- Mitochondria are the site of aerobic respiration, which releases energy (ATP). [1]
(Note: Do not accept "makes energy" without context of respiration/ATP)
12. Enzyme Activity
(a)
Calculation:
Rate = 1 / 30 [1]
Rate = 0.033 s⁻¹ (accept 0.03 or 3.3 x 10⁻²) [1]
(b)
Description and Explanation (10°C to 40°C):
- As temperature increases, the rate of reaction increases (time taken decreases). [1]
- Kinetic energy of enzyme and substrate molecules increases. [1]
- This leads to more frequent collisions and more enzyme-substrate complexes forming. [1]
(c)
Explanation for 60°C:
- The high temperature causes the enzyme to denature. [1]
- The shape of the active site changes / is destroyed. [1]
- The substrate can no longer fit into the active site (no enzyme-substrate complexes formed). [1]
13. Osmosis in Potato Cells
(a)
Definition of Osmosis:
- The net movement [1]
- of water molecules [1]
- from a region of higher water potential to a region of lower water potential [1]
- through a partially permeable membrane. [1]
(Max 2 marks. Must mention water, gradient, and membrane)
(b)
Explanation for Solution P (Mass Increase):
- Solution P has a higher water potential than the potato cell sap. [1]
- Water enters the potato cells by osmosis. [1]
- This causes the cells to become turgid / gain mass. [1]
(c)
Isotonic Solution:
Solution: R [1]
Reason: There is no net movement of water into or out of the cells because the water potential of the solution is equal to that of the cell sap. [1]
14. Biological Molecules
(a)
Building blocks: Amino acids [1]
(b)
Elements: Carbon, Hydrogen, Oxygen, Nitrogen [1]
(Must include Nitrogen. C, H, O are assumed but N is key)
(c)
Functions (any two):
- Growth and repair of tissues / muscles. [1]
- Formation of antibodies / hormones / hemoglobin. [1]
(Do not accept "enzymes" as the question excludes it)
(d)
Protein Test:
Reagent: Biuret solution [1]
Method/Result: Add Biuret solution to the food sample. [1] A positive result is a colour change from blue to purple/violet. [1]
15. Transport in Plants
(a)
Adaptation:
- Long hair-like projection / large surface area. [1]
(b)
Why osmosis does not require energy:
- Osmosis is a passive process. [1]
- It relies on the natural kinetic energy of water molecules moving down a water potential gradient. [1]
(c)
Mineral Ion Uptake:
(i) Process: Active transport [1]
(ii) Why energy is required:
- Ions are moved against the concentration gradient (from low to high concentration). [1]
- Energy (ATP) is needed to pump the ions across the cell membrane. [1]
End of Marking Scheme