OCR GCSE Biology: Ecosystems and Photosynthesis

OCR GCSE Biology: Ecosystems and Photosynthesis

1. What are Ecosystems?

• Ecosystems are communities of living organisms (biotic factors) interacting with their non-living surroundings (abiotic factors).
• Biotic factors: Plants, animals, fungi, bacteria
• Abiotic factors: Temperature, light intensity, water availability, pH, soil nutrients
• Interdependence: Organisms within an ecosystem rely on each other for survival.

2. Food Chains and Food Webs

• Food chains show the flow of energy through an ecosystem, starting with a producer (e.g., plant) and moving to a series of consumers (e.g., herbivore, carnivore).
• Food webs are interconnected food chains, showing the complex relationships between organisms within an ecosystem.

3. Photosynthesis: The Basis of Life

• Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy (glucose) and oxygen.
• Word equation: Carbon dioxide + Water ? Glucose + Oxygen
• Chemical equation: 6CO2 + 6H2O ? C6H12O6 + 6O2
• Chlorophyll is a green pigment found in chloroplasts that absorbs light energy for photosynthesis.
• Factors affecting photosynthesis:
  • Light intensity: Higher intensity, faster photosynthesis (up to a point).
  • Carbon dioxide concentration: Higher concentration, faster photosynthesis (up to a point).
  • Temperature: Optimum temperature for each plant species, too high or too low slows down photosynthesis.

4. Nutrient Cycling: Carbon, Oxygen, and Nitrogen

• Carbon cycle: The continuous movement of carbon atoms between the atmosphere, biosphere, geosphere, and hydrosphere.
• Oxygen cycle: The continuous movement of oxygen atoms between the atmosphere and living organisms.
• Nitrogen cycle: The continuous movement of nitrogen atoms through the atmosphere, soil, and organisms.

5. Practical Work: Measuring Photosynthesis

• Experiment: Investigate the effect of light intensity on the rate of photosynthesis using a pondweed and a light source.
• Method:
  1. Set up a beaker with pondweed and water.
  2. Expose the beaker to different light intensities.
  3. Measure the rate of oxygen production (using a gas syringe or counting bubbles).
• Results: Higher light intensity generally leads to a higher rate of photosynthesis.

6. Understanding Interdependence in Ecosystems

• Environmental changes: Human activities can significantly impact ecosystems.
• Pollution: Can disrupt nutrient cycles and harm organisms.
• Climate change: Rising temperatures, altered precipitation patterns, and more extreme weather events can disrupt ecosystems.
• Habitat loss: Destruction of habitats reduces biodiversity and can lead to extinction.

7. Key Concepts to Remember

• Ecosystems are complex, interconnected systems.
• Photosynthesis is the foundation of life on Earth.
• Nutrient cycles ensure the continuous flow of essential elements within ecosystems.
• Human activities have a profound impact on ecosystems.
• Understanding ecological principles is crucial for maintaining healthy ecosystems.