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Leaving Cert Biology Revision: Photosynthesis


What is Photosynthesis?

  • Photosynthesis is the process by which green plants, algae, and some bacteria make their food.

  • It converts light energy from the sun into chemical energy in the form of glucose (a type of sugar).

Where Does Photosynthesis Occur?

  • Takes place in the chloroplasts of plant cells.

  • Chloroplasts contain a green pigment called chlorophyll, which captures light energy.

Ingredients Needed for Photosynthesis

1. Light Energy: Usually from the sun.

2. Carbon Dioxide (CO2): From the air.

3. Water (H2O): Absorbed by roots from the soil.

Main Steps of Photosynthesis

Light Reactions

  •   Occur in the thylakoid membranes of the chloroplasts.

  •   Convert light energy into chemical energy (ATP and NADPH).

Calvin Cycle (Dark Reactions)

  •    Occurs in the stroma of the chloroplasts.

  •    Uses ATP and NADPH to convert CO2 into glucose.

Key Outputs of Photosynthesis

  • Glucose (C6H12O6): Used by the plant for energy and growth.

  • Oxygen (O2): Released into the air as a byproduct.

Importance of Photosynthesis

  • Provides food and energy for plants.

  • Produces oxygen necessary for most living organisms to breathe.

  • Removes CO2 from the atmosphere, helping to regulate Earth's climate.

Fun Facts

  • Plants are often called "producers" because they produce their food.

  • The process of photosynthesis is crucial for the survival of almost all life on Earth.

Factors Affecting Photosynthesis

1. Light Intensity: More light increases the rate of photosynthesis up to a point.

2. Carbon Dioxide Concentration: Higher CO2 levels can enhance the rate.

3. Water Availability: Essential for the light reactions.

4. Temperature: Extreme temperatures (too hot or too cold) can slow down or stop photosynthesis.

Types of Photosynthesis

- C3 Photosynthesis: The most common form used by most plants.

- C4 Photosynthesis: Found in some grasses, more efficient under high light and temperature.

- CAM Photosynthesis: Used by desert plants, allows them to conserve water by opening their stomata at night.

Importance of Photosynthesis for Ecosystems

  1. Energy Source: Provides energy at the base of the food chain.

  2. Oxygen Production: Produces the oxygen we breathe.

  3. Carbon Cycle: Plays a critical role in the carbon cycle, helping to balance CO2 levels in the atmosphere.

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