Key Concept: Photosynthesis converts light energy into chemical energy stored in glucose. It uses carbon dioxide and water, and produces glucose and oxygen.
Section A: Photosynthesis Basics
1. Define photosynthesis and explain why it is important. [3]
2. Write the word equation and balanced symbol equation for photosynthesis. [4]
Section B: Limiting Factors
3. State three factors that affect the rate of photosynthesis. [3]
4. Define a limiting factor and explain how it affects photosynthesis. [3]
Section C: Leaf Structure and Adaptations
5. Label the diagram with: cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, stomata, guard cells, xylem, phloem. [9]
[Leaf cross-section diagram]
6. Describe three adaptations of the leaf for photosynthesis. [3]
Section D: Mineral Ions
7. Explain why plants need magnesium and nitrate ions. [4]
Total marks: 29
Mark Scheme
1. Photosynthesis is the process by which plants convert light energy into chemical energy in glucose [2]; provides food/biomass and releases oxygen [1]
2. Word: carbon dioxide + water → glucose + oxygen [2]; Symbol: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light, chlorophyll) [2]
3. Light intensity, carbon dioxide concentration, temperature [3]
4. Limiting factor is the factor in shortest supply that restricts the rate [2]; increasing it increases rate until another factor becomes limiting [1]
5. Labels as listed (1 mark each) [9]
6. Any three: large surface area; thin leaf; palisade cells with many chloroplasts; stomata for gas exchange; spongy mesophyll air spaces; veins for water/sugar transport [3]
7. Magnesium needed for chlorophyll [2]; nitrate needed to make amino acids/proteins [2]