AQA GCSE FOUNDATION Biology: Photosynthesis

AQA GCSE Foundation Biology: Photosynthesis

Introduction

Photosynthesis is a vital process that plants, algae, and some bacteria use to convert light energy into chemical energy in the form of glucose. This glucose provides the organism with energy for growth and other life processes.

Understanding Light Absorption

Plants absorb light energy primarily through a pigment called chlorophyll, which gives plants their green colour. Chlorophyll absorbs light most effectively in the blue and red wavelengths of the electromagnetic spectrum, while reflecting green light.

• Chlorophyll is found in organelles called chloroplasts within plant cells.

• Light energy is absorbed by chlorophyll molecules within the chloroplasts, exciting electrons to a higher energy level.

The Photosynthesis Equation

The overall chemical equation for photosynthesis is:

6CO2 + 6H2O  ->  C6H12O6 + 6O2

• Carbon dioxide (CO2) and water (H2O) are the reactants.

• Glucose (C6H12O6) and oxygen (O2) are the products.

Steps of Photosynthesis

Photosynthesis can be divided into two main stages:

1. Light-dependent Reactions:

• Occur in the thylakoid membranes of chloroplasts.

• Light energy is absorbed by chlorophyll, exciting electrons.

• This energy is used to split water molecules, releasing oxygen as a by-product.

• ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) are produced, which act as energy carriers for the next stage.

2. Light-independent Reactions (Calvin Cycle):

• Occur in the stroma of chloroplasts.

• Carbon dioxide from the atmosphere is combined with a five-carbon compound (RuBP) using the energy from ATP and NADPH.

• This process forms glucose, which can be used by the plant for growth and other metabolic processes.

Factors Affecting Photosynthesis

• Light intensity: As light intensity increases, the rate of photosynthesis increases until a maximum rate is reached.

• Carbon dioxide concentration: Higher carbon dioxide concentrations increase the rate of photosynthesis up to a certain point.

• Temperature: Photosynthesis has an optimal temperature range. Too low or too high temperatures can reduce the rate of photosynthesis.

Importance of Photosynthesis

• Provides food for most living organisms: Photosynthesis is the primary source of energy for most ecosystems.

• Produces oxygen: Oxygen is essential for respiration, a process that releases energy from food.

• Reduces carbon dioxide levels: Photosynthesis removes carbon dioxide from the atmosphere, helping to regulate Earth's climate.

Conclusion

Photosynthesis is a complex process that is crucial for life on Earth. By understanding the mechanisms of photosynthesis, we can appreciate its significance and the role it plays in supporting our planet's ecosystem.