Secondary 3 Biology Practice Paper 3

TuitionGoWhere Practice Paper - Biology Secondary 3 (Answer Key)

Version: 3 of 5
Subject: Biology
Level: Secondary 3

Section A: Multiple Choice Answers

1. D
Reasoning: Cell walls, chloroplasts, and large permanent vacuoles are found in plant cells but not animal cells. Cell membranes, cytoplasm, and mitochondria are found in both.

2. B
Reasoning: Rough Endoplasmic Reticulum (RER) is involved in protein synthesis (due to ribosomes), and mitochondria provide the energy (ATP) required for synthesis and secretion. This suggests a secretory cell (e.g., pancreatic or glandular).

3. A
Reasoning: Proteins contain Carbon, Hydrogen, Oxygen, and Nitrogen (C, H, O, N). Some also contain Sulphur. Carbohydrates contain only Carbon, Hydrogen, and Oxygen (C, H, O).

4. A
Reasoning: High temperatures break the bonds holding the enzyme's tertiary structure, changing the shape of the active site. This is called denaturation. It is irreversible; cooling does not restore the shape.

5. C
Reasoning: Active transport moves substances against a concentration gradient and requires energy (ATP). Diffusion and osmosis are passive processes.

Section B: Structured Answers

6.
(a) Golgi apparatus [1]
(b) To release energy (ATP) through aerobic respiration for cellular activities. [1]
(c) Chloroplasts are required for photosynthesis, which needs light. Liver cells are internal organs and do not receive light; they do not perform photosynthesis. [2]
(1 mark for mentioning photosynthesis/light, 1 mark for liver function/location)

7.
(a) As pH increases from 3 to 7, the time taken for starch to disappear decreases. This indicates that the rate of reaction increases. [2]
(1 mark for describing time decrease, 1 mark for linking to rate increase)
(b) At pH 11, the enzyme is denatured. The high pH alters the shape of the active site. The substrate (starch) can no longer fit into the active site, so no enzyme-substrate complexes are formed. [3]
(1 mark for denatured, 1 mark for active site shape change, 1 mark for no complex formation)
(c) Temperature / Concentration of amylase / Concentration of starch / Volume of solution. [1]

8.
(a) Red blood cells have no nucleus (or are biconcave); White blood cells have a nucleus (or are irregular/amoeboid). [1]
(b) The biconcave shape increases the surface area to volume ratio. This allows for a faster rate of diffusion of oxygen into and out of the cell. [2]
(1 mark for surface area, 1 mark for diffusion rate)
(c) It provides more space for haemoglobin. This allows the cell to carry a maximum amount of oxygen. [2]
(1 mark for space/haemoglobin, 1 mark for oxygen capacity)

9.
(a)
(i) Blue-black / Black [1]
(ii) Amino acids [1]
(iii) Benedict’s solution [1]
(b)

1. Crush the food sample and mix with ethanol. [1]
2. Shake well to dissolve any fats. [1]
3. Pour the solution into water. A cloudy white emulsion indicates the presence of fat. [1]

10.
(a) Osmosis is the net movement of water molecules [1] from a region of higher water potential (dilute solution) [1] to a region of lower water potential (concentrated solution) [1] through a partially permeable membrane. [1]
(Max 3 marks. Must mention water, water potential gradient, and membrane)
(b) The distilled water has a higher water potential than the sugar solution inside the tubing. Water molecules move by osmosis from the beaker into the visking tubing. This increases the volume of liquid inside the tubing, causing the level in the funnel to rise. [3]
(1 mark for water potential gradient, 1 mark for direction of flow, 1 mark for volume/level increase)

Section C: Free Response Answers

11.
(a)

• The enzyme has a specific active site with a unique shape. [1]
• The substrate has a complementary shape to the active site. [1]
• The substrate fits into the active site like a key fits into a lock, forming an enzyme-substrate complex. [1]
• The reaction occurs, and products are released, leaving the enzyme unchanged and ready to be reused. [1]

(b)
Temperature:

• As temperature increases, kinetic energy increases, leading to more frequent collisions between enzyme and substrate, increasing the rate. [1]
• At the optimum temperature, the rate is maximum. [1]
• Above the optimum, the enzyme denatures (active site changes shape), and the rate drops rapidly to zero. [1]

Substrate Concentration:

• As substrate concentration increases, the rate of reaction increases because there are more substrate molecules to collide with enzyme active sites. [1]
• Eventually, the rate levels off (plateaus) because all enzyme active sites are saturated (occupied). Adding more substrate does not increase the rate further. [1]

(Comparison: Temperature causes a drop after optimum due to denaturation; Substrate concentration plateaus due to saturation.) [5 marks total allocated for depth of explanation]

12.
(a) A tissue is a group of similar cells [1] that work together to perform a specific function. [1]
(Note: Question asks for definition, usually 1-2 marks. "Group of similar cells" is key.) [1]

(b)

• Root hair cells have a long, hair-like projection. This increases the surface area for absorption of water and minerals. [1]
• They have a thin cell wall (and cell membrane), providing a short diffusion distance for water and ions. [1]
• They contain many mitochondria to provide energy (ATP) for active transport of mineral ions. [1]
• They have a large vacuole containing cell sap with a lower water potential than soil water, facilitating water uptake by osmosis. [1]

(c)

• Mineral ions are often present in lower concentration in the soil than inside the root hair cell. [1]
• Therefore, they must be moved against the concentration gradient. [1]
• This requires energy (ATP) from respiration, which is provided by active transport. [1]
• Water moves from the soil (higher water potential) into the root hair (lower water potential) down the water potential gradient. [1]
• This process is passive and does not require energy, so it occurs by osmosis. [1]
  (Max 4 marks)