Pearson Science Double Award Biology 4: Ecology and the Environment

Ecology studies organisms in relation to one another and their physical surroundings. Pearson Double Award Topic 4 links population distribution, feeding relationships, carbon cycling and human pollution. Strong answers follow matter or energy through a named pathway.

These notes use the exact 4SD0 Issue 4 points. Practical sampling is owned by the separate practical hub.

Organisms in their environment

A population is all organisms of one species in an area. A community contains populations of different species. A habitat is the place where an organism lives. An ecosystem includes the community and its non-living environment interacting together.

Population size and distribution respond to abiotic factors such as temperature, light, water, pH and mineral availability, and biotic factors such as food, competition, predation and disease. A correlation between abundance and one factor does not prove causation because several factors may vary across the same site.

Quadrats can compare abundance in two areas when positions are selected objectively and the counting rule is consistent. Method and evaluation belong in the practical hub; theory explains why a factor could affect an organism.

Feeding relationships and energy

Producers capture energy and make organic material. Primary consumers feed on producers; secondary and tertiary consumers feed at later trophic levels. Decomposers break down dead material and waste.

Food-chain arrows point in the direction of energy and substance transfer, from food to feeder. Food webs show interconnected chains. A pyramid of numbers displays organism counts, a pyramid of biomass displays living material, and a pyramid of energy transfer shows energy passed between levels.

Only about 10% of energy is commonly transferred to the next trophic level. Energy is lost through respiration as heat, movement, excretion and material that is not eaten or digested. This limits food-chain length and means less biomass can usually be supported at higher trophic levels.

Carbon cycle

Photosynthesis removes carbon dioxide from the atmosphere and incorporates carbon into organic compounds. Feeding transfers carbon through food chains. Respiration by plants, animals and decomposers releases carbon dioxide. Decomposition transfers carbon from dead organisms and waste, and combustion of biomass or fossil fuels releases stored carbon dioxide.

Matter cycles, but energy flows through the ecosystem and is ultimately dissipated as heat. Do not draw energy returning from decomposers to producers.

Human influences

Sulfur dioxide can damage leaves and acidify environments. Carbon monoxide binds to haemoglobin and reduces oxygen transport. Sewage adds organic material and microorganisms to water; decomposition can lower dissolved oxygen and harm aquatic organisms.