OCR Biology A2 Unit 2 Module 3 Notes-Ecosystems & Sustainability

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ECOSYSTEM: any group of living organisms and non-living things occurring together, and the interrelationships between them. They are dynamic systems.

HABITAT: the place where an organism lives.

POPULATION: all of the organisms of one species, who live in the same place at the same time, and can breed together.

COMMUNITY: all the populations of different species who live in the same place at the same time, and can interact with each other.

NICHE: the role that each species plays in an ecosystem.

BIOTIC FACTORS: describe the effects of the living components of an ecosystem-food supply, predation, disease.

ABIOTIC FACTORS: describe the effects of non living components of an ecosystem-pH, temperature, soil type.

PRODUCER: supply chemical energy to all other organisms, at the bottom of the food chain/web.

CONSUMER: animal that feeds on producers or consumers.

DECOMPOSERS: feed on waste material or dead organisms.

TROPHIC LEVEL: the level at which an organism feeds in a food chain.

At each trophic level, some energy is lost from a food chain and is therefore unavailable to the organism at the next trophic level. At each trophic level, living organisms need energy to carry out life processes. Respiration releases energy from organic molecules like glucose. Some of this energy is eventually converted to heat. Energy remains stored in dead organisms and waste material includes part of animals and plants that cannot be digested.

PYRAMID OF NUMBERS: each bar proportional to the number of individuals.

PYRAMID OF BIOMASS: area of bars is proportional to dry mass of all the organisms at that trophic level-collect all organisms and put them in an oven at 80 degrees until all the water in them has been evaporated-destructive, so ecologists often use the wet mass and calculate dry mass from data.

PYRAMID OF ENERGY: burning organisms in calorimeter and working out how much heat energy is released per gram.

Limitations: only take a snapshot of ecosystem at one moment in time, may provide a distorted idea of the efficiency of energy transfer.

PRODUCTIVITY: the rate at which energy passes through each trophic level, MJ.

PRIMARY PRODUCTIVITY: the total amount of energy fixed by photosynthesis. It is the net flux of carbon from the atmosphere to plants, per unit time.

GROSS PRIMARY PRODUCTIVITY: the rate at which plants convert light energy into chemical energy.

NET PRIMARY PRODUCTIVITY: the rate at which carbohydrate accumulates in the tissue of plants of an ecosystem and is measured in dry organic mass. NPP = PP - R (respiratory heat loss). The amount of energy available to heterotrophs.

By manipulating environmental factors, humans can increase NPP-light levels, lack of water, temperature, available nutrients, pests, fungal disease, competition/

Improving secondary productivity: harvesting animals just before adulthood minimises loss of energy from the food chain, treated with steroids, selective breeding, treatment with antibiotics, zero grazing.

SUCCESSION: directional change in a community of organisms over time.

Island of Surtsey in Iceland: algae and lichens, pioneer community, erosion of rock, build-up of dead and rotting organisms produces enough soil for larger…


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