Plant nutrition
Plants require light, carbon dioxide, water, mineral ions, and a suitable temperature for healthy growth. Carbon dioxide enters through stomata, water is absorbed by roots, and mineral ions are taken up from the soil. Plants manufacture organic food rather than obtaining it by eating other organisms.
Photosynthesis
Photosynthesis is the process by which green plants use light energy to make glucose from carbon dioxide and water. Oxygen is released as a by-product.
carbon dioxide + water → glucose + oxygen
Light energy is absorbed by chlorophyll in chloroplasts. Glucose may be used in respiration, converted to starch for storage, or used to make cellulose, lipids, and proteins.
Leaf adaptations
- A broad surface provides a large area for light absorption.
- A thin shape gives a short distance for carbon dioxide to diffuse.
- Chloroplasts are concentrated in the palisade cells.
- Stomata allow gas exchange.
- Veins bring water and mineral ions and carry away manufactured food.
Factors affecting photosynthesis
Light intensity, carbon-dioxide concentration, and temperature can limit the rate. If one factor is below its optimum, increasing another factor may have little effect until the limiting factor is improved.
Translocation
Translocation is the movement of dissolved manufactured food, especially sucrose, through the phloem from sources such as leaves to sinks such as roots, fruits, seeds, and growing regions.
Revision questions
- Write the word equation for photosynthesis.
- State four adaptations of a leaf for photosynthesis.
- Name three factors that affect the rate of photosynthesis.
- Distinguish between photosynthesis and translocation.
