OCR GCSE Combined Science: Ecosystems and Photosynthesis

GCSE Combined Science: Ecosystems & Photosynthesis

1. What is an Ecosystem?

An ecosystem is a community of living organisms (biotic factors) interacting with their non-living surroundings (abiotic factors). These interactions create a complex web of relationships.

Key concepts:

• Biotic Factors: Plants, animals, fungi, bacteria, etc.
• Abiotic Factors: Temperature, light, water, soil, pH, etc.

Examples of Ecosystems:

• Forest: Trees, animals, insects, soil, sunlight, rainfall.
• Ocean: Fish, plankton, coral reefs, salt water, currents, sunlight.
• Grassland: Grasses, herbivores, predators, soil, sunlight, rainfall.

2. Food Webs and Nutrient Cycles

Food Webs:

• Show the feeding relationships between organisms in an ecosystem.
• Arrows indicate the direction of energy flow.
• Producers (plants) form the base of the food web.
• Consumers (animals) feed on producers or other consumers.
• Decomposers (bacteria and fungi) break down dead organisms, returning nutrients to the soil.

Nutrient Cycles:

• Describe how essential nutrients are recycled within an ecosystem.
• Key cycles include the carbon cycle, nitrogen cycle, and water cycle.
• Understanding nutrient cycles is vital for maintaining ecosystem health.

3. Photosynthesis: The Basis of Life

What is Photosynthesis?

• The process by which plants convert light energy from the sun into chemical energy (glucose) and oxygen.
• Occurs in chloroplasts, containing chlorophyll (green pigment).
• Equation: Carbon Dioxide + Water + Light Energy ? Glucose + Oxygen

Factors Affecting Photosynthesis:

• Light Intensity: Higher light intensity leads to faster photosynthesis.
• Carbon Dioxide Concentration: Increased CO2 levels enhance photosynthesis.
• Temperature: Optimal temperature range for photosynthesis exists.
• Water Availability: Water is essential for the process.

4. Cellular Respiration: Energy Release

What is Cellular Respiration?

• The process by which organisms break down glucose to release energy (ATP).
• Occurs in the mitochondria of cells.
• Equation: Glucose + Oxygen ? Carbon Dioxide + Water + Energy

Relationship with Photosynthesis:

• Photosynthesis and cellular respiration are interconnected processes.
• Photosynthesis produces glucose, which is used in cellular respiration.
• Cellular respiration releases CO2, which is used in photosynthesis.

5. Practical Investigations

Measuring Photosynthesis Rates:

• Experiment: Using aquatic plants (e.g., Elodea) and measuring the rate of oxygen production.
• Variables: Light intensity, temperature, CO2 concentration.
• Data Collection: Measuring gas production using a syringe or measuring the amount of oxygen released.

Examining Food Web Models:

• Activity: Creating food web models using different organisms.
• Analysis: Identifying producers, consumers, and decomposers.
• Discussion: The impact of changes within the food web on different populations.

6. Environmental Impact on Ecosystems

Human Activities and Ecosystem Changes:

• Pollution: Air, water, and land pollution can harm organisms and ecosystems.
• Deforestation: Loss of trees reduces habitats and disrupts nutrient cycles.
• Climate Change: Rising temperatures and altered weather patterns impact ecosystems.

Sustainability and Conservation:

• Reducing our impact on ecosystems is vital for their survival.
• Conservation Efforts: Protecting habitats, managing resources, and promoting biodiversity.

7. Revision Tips

• Keywords: Understand the definitions of key terms related to ecosystems and photosynthesis.
• Diagrams: Use diagrams to illustrate concepts, such as food webs, nutrient cycles, and photosynthesis.
• Practical Applications: Apply your knowledge to real-world scenarios and understand the impact of human activities.
• Past Papers: Practice answering exam-style questions to assess your understanding.

Remember: This tutorial is a starting point for your study. Refer to your textbook and other resources for more detailed information.