▶️ Answer/Explanation
(a)(i) Aerobic respiration.
Explanation: The diagram shows oxygen entering the cell and carbon dioxide leaving, which are characteristics of aerobic respiration. This process occurs in the presence of oxygen and is more efficient than anaerobic respiration.
(a)(ii) A: Glucose; B: Water.
Explanation: In aerobic respiration, glucose (A) is broken down to release energy, and water (B) is produced as a byproduct. The chemical equation for aerobic respiration is: \( C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy} \).
(a)(iii) Diffusion.
Explanation: Oxygen moves into the cell by diffusion, which is the passive movement of molecules from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell). This process does not require energy.
(b) Three processes that require energy from respiration:
- Active transport: Movement of molecules against their concentration gradient, such as the absorption of nutrients in the gut.
- Muscle contraction: Energy is needed for muscle fibers to contract, enabling movement.
- Protein synthesis: Building proteins from amino acids requires energy, especially for growth and repair.
(c) Effect of temperature on the rate of respiration in yeast:
The rate of respiration increases as the temperature rises from 0°C to 40°C, peaking at 40°C. This is because higher temperatures increase the kinetic energy of molecules, leading to more frequent enzyme-substrate collisions. Beyond 40°C, the rate decreases sharply due to enzyme denaturation, which alters their active sites and reduces their efficiency. At very high temperatures (70°C and above), respiration nearly stops as most enzymes are denatured.
Key observations:
- Optimum temperature for yeast respiration is around 40°C.
- Respiration is very slow at low temperatures (0°C–10°C).
- Enzyme activity is destroyed at temperatures above 60°C.