Photosynthesis

Definition

Photosynthesis is the process by which green plants manufacture food (glucose) using carbon dioxide, water, and light in the presence of chlorophyll.

Importance of Photosynthesis

• Provides food for plants and animals.
• Releases oxygen essential for respiration.
• Removes carbon dioxide from the atmosphere.
• Forms the basis of food chains.

Equation

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Process of Photosynthesis

• Light stage: Occurs in the thylakoid; light energy splits water to release oxygen, ATP, and NADPH.


• Dark stage (Calvin cycle): Occurs in the stroma; CO₂ is fixed to produce glucose using ATP and NADPH.

Adaptations of the Leaf for Photosynthesis

• Numerous stomata in the lower epidermis allow CO₂ entry and O₂ exit.


• Xylem vessels transport water to the leaves.


• Phloem vessels transport manufactured food (glucose) to other parts of the plant.


• Palisade cells are cylindrical and closely packed to maximize sunlight absorption.


• Transparent cuticle allows light to reach mesophyll cells.


• Palisade cells contain well-positioned chloroplasts for maximum light capture.


• Waxy cuticle on top prevents water loss (desiccation).


• Thin leaves provide a short diffusion path for CO₂.


• Broad, flat surface area absorbs sunlight efficiently.


• Large air spaces in spongy mesophyll allow circulation of gases.

Factors Affecting Photosynthesis

• Light intensity
• Carbon dioxide concentration
• Temperature
• Water availability
• Chlorophyll concentration

Practice Questions

• Define photosynthesis and state two importance. (4 marks)
• Write the photosynthesis equation and label reactants and products. (3 marks)
• Explain the light and dark stages of photosynthesis. (6 marks)
• List and explain five adaptations of a leaf to photosynthesis. (5 marks)
• Describe three factors that affect the rate of photosynthesis. (3 marks)