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The abundance and distribution of organisms in an ecosystem is determined by biotic and abiotic factors. Animals and plants have adaptations to allow them to compete for resources.

The feeding relationships between organisms in an ecosystem can be seen in food chains. Sampling allows us to measure the abundance and distribution of these species.

Decomposition, or decay, is the breakdown of dead matter. The rate at which this happens depends upon the number of decomposing microorganisms, the temperature, and water and oxygen availability.

Biodiversity is a measure of how many different species live in an ecosystem. Human activities like changing land use, deforestation and peat bog destruction reduce this.

Feeding relationships are shown in food chains. Each stage is a trophic level. Biomass is a measure of the total mass of living material in each trophic level.

Factors such as the increase in human population, new pests and pathogens, overhunting and armed conflict, can result in food scarcity in some countries.

Understanding how to approach exam questions helps to boost exam performance. Question types will include multiple choice, structured, mathematical and practical questions.