Question 1: Define the term 'chloroplast' and explain its role in a leaf.

Answer: Chloroplasts are organelles within plant cells that contain chlorophyll and are the site of photosynthesis, converting light energy into chemical energy.

Question 2: Describe the function of the stomata in a leaf.

Answer: Stomata are small openings on the leaf surface that allow gases such as carbon dioxide and oxygen to diffuse in and out of the leaf.

Question 3: What is the primary pigment responsible for photosynthesis in leaves?

Answer: Chlorophyll

Question 4: Explain how the arrangement of palisade mesophyll cells benefits photosynthesis.

Answer: Palisade mesophyll cells are tightly packed and contain many chloroplasts, maximising light absorption for efficient photosynthesis.

Question 5: Calculate the surface area to volume ratio of a leaf measuring 10 cm by 5 cm with a thickness of 0.2 cm. Use the formula: Surface Area / Volume.

Answer: Surface Area = 2*(length*width + length*thickness + width*thickness) = 2*(10*5 + 10*0.2 + 5*0.2) = 2*(50 + 2 + 1) = 2*53 = 106 cm². Volume = length * width * thickness = 10 * 5 * 0.2 = 10 cm³. Ratio = 106 / 10 = 10.6.

Question 6: Identify two adaptations of leaves that help reduce water loss in dry environments.

Answer: Thick cuticle and fewer stomata or stomata located on the underside of the leaf.

Question 1: Describe a simple experiment to investigate the effect of light intensity on the rate of photosynthesis in leaves.

Answer: Place identical leaves in a setup exposed to different light intensities. Measure oxygen production or the amount of oxygen bubbles released over a fixed time period. Ensure all other variables such as CO₂ concentration and temperature are controlled.

Question 2: List two safety precautions to consider when performing experiments involving plant tissues and chemicals.

Answer: Wear gloves and eye protection to prevent chemical contact; handle sharp tools carefully when preparing plant samples.

Question 1: A study shows that leaves with a thicker cuticle are less effective at gas exchange but better at conserving water. Explain how this trade-off might affect plants in different environments.

Answer: In dry environments, a thicker cuticle helps prevent water loss, which is beneficial for survival. However, it may reduce gas exchange efficiency, potentially limiting photosynthesis. In moist environments, thinner cuticles allow more gas exchange, supporting higher photosynthesis rates but increasing water loss, which may be disadvantageous.

Question 2: Discuss how understanding leaf structure can aid in developing drought-resistant crops.

Answer: Knowledge of leaf adaptations such as thicker cuticles, fewer stomata, or sunken stomata can inform breeding programmes aimed at developing crops that retain water more effectively. Genetic modification or selective breeding can enhance these traits, improving crop resilience in drought-prone areas.