Ecology and environment for O-Level Biology (SEAB 6093): ecosystems and food chains, energy flow and the role of decomposers, the carbon cycle, and human impact on the environment

What this module covers

Ecology and environment looks at how organisms interact with each other and their surroundings, and how humans affect the natural world. In O-Level Biology (SEAB 6093) you must describe ecosystems and feeding relationships using food chains and webs, explain the flow of energy and the role of decomposers in recycling nutrients, describe the carbon cycle, and account for the effects of pollution and deforestation along with ways to conserve the environment. This module draws together photosynthesis, respiration and nutrition at the scale of whole communities.

This overview links every dot point in the module; work through them, then test yourself at the end. See the full set at /sg-o-level/biology/syllabus.

Ecosystems and food chains

Start with how organisms feed. The page on ecosystems and food chains sets out the key ecological terms, the trophic levels of a food chain, how food webs link chains, and the effect of removing an organism. Learn producer, consumer and decomposer, and be able to read the direction of the arrows (energy flows from the eaten to the eater).

Energy flow and decomposers

Next, follow the energy. The page on energy flow and nutrient cycles explains why energy is lost between trophic levels, why food chains are short, and how decomposers recycle nutrients back to producers. The ten percent idea, that only about a tenth of the energy passes to the next level, explains the shape of pyramids of energy.

The carbon cycle

Then the recycling of carbon. The page on the carbon cycle describes how photosynthesis, respiration, decomposition and combustion move carbon between the air, living things and fossil fuels. Learn which processes remove carbon dioxide (photosynthesis) and which add it (respiration, decomposition, combustion).

Human impact on the environment

Finally, our effect. The page on human impact on the environment describes the effects of water and air pollution, the enhanced greenhouse effect, the consequences of deforestation, and ways to conserve the environment. Be ready to link a human activity to its effect and then to a conservation measure.

How this module is examined

• Arrows show energy flow. In food chains and webs the arrow points from the organism eaten to the one that eats it; getting the direction right is often a mark.
• Reason and consequence. For short food chains, state where energy is lost and that too little remains for more levels.
• Add versus remove. Carbon cycle questions reward sorting processes into those that add carbon dioxide (respiration, decomposition, combustion) and those that remove it (photosynthesis).
• Activity to effect to solution. Human impact questions reward linking an activity to its environmental effect and then to a conservation measure.

Check your knowledge

A mix of definition, explanation and application questions. Attempt them, then check against the solutions.

1. Define the terms producer and decomposer. (2 marks)
2. Explain why food chains usually have only a few links. (3 marks)
3. State one process that removes carbon dioxide from the air and two that add it. (3 marks)
4. State one effect of deforestation and one way to conserve the environment. (2 marks)