The Role of Light, Water, CO₂ and Chlorophyll

• The sun is the main source of energy for life on Earth.
• Plants can trap light energy and convert it to chemical energy.
• The chemical energy is passed along the food chain.
• Photosynthesis occurs in the chloroplasts of plant cells.

Chloroplast

• Chloroplasts are small structures in plant cells where photosynthesis happens.
• Chloroplasts are found mainly in the upper layers of leaf cells and in ground tissue.
• Parts of the Chloroplast:
  1. Thylakoids: Flat, disc-shaped membranes where light energy is absorbed.
  2. Grana: Stacks of thylakoids.
  3. Stroma: The liquid part around the grana, where glucose is made.
• Chloroplasts contain chlorophyll, which absorbs sunlight for photosynthesis.

Essential Requirements for Photosynthesis

There are four requirements for photosynthesis:

1. Light
2. Water
3. Carbon dioxide
4. Chlorophyll

1. Light

• Plants get energy from the sun.
• Chloroplasts absorb all colours of light except green, which they reflect. This is why plants look green.

2. Water

• Water is absorbed by the root hairs of plants through osmosis.
• Root hairs increase the surface area for water absorption.
• Water travels through the xylem from the roots, up the stem, and into the leaves.
• In photosynthesis, water is split to provide electrons, hydrogen (H⁺) ions, and oxygen.

3. Carbon Dioxide (CO₂)

• CO₂ enters the plant through tiny openings called stomata.
• They are located on the underside of leaves.
• CO₂ moves into the leaf by diffusion from the atmosphere.
• Plants also produce CO₂ during respiration.

4. Chlorophyll

• Chlorophyll is the green pigment in chloroplasts.
• It traps sunlight (light energy) and converts it into energy for photosynthesis.

How to Increase the Rate of Photosynthesis

1. Artificial Light: Extra light in greenhouses provides more energy for photosynthesis.
2. Carbon Dioxide Enrichment: Pumping CO₂ into greenhouses makes photosynthesis faster.
3. Temperature Control: Warmer temperatures (up to an optimal point) increase the rate of photosynthesis. If the temperature is too high, the enzymes will be denatured and the process will stop.