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Unit 2
Module 3…read more

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2.3.1 Ecosystems
· Any group of living organisms + non-living things occurring together, and the interrelationships between them, can be
thought of as an ecosystem.
· The components of an ecosystem:
­ 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.
· The role that each species plays in an ecosystem is called its niche.
Biotic + Abiotic
· Biotic factors describe the effects of the living components of an ecosystem ­ food supply, predation + disease.
· Abiotic factors describe the effects of the non-living components of an ecosystem ­ pH, temperature + soil type.
Ecosystems are Dynamic
· Population rises and falls.
· Can be very slightly or very noticeably.
· Any small changes in one species/population/community can affect another.
Energy + Ecosystems
· Matter is constantly recycled within an ecosystem. Energy is not recycled, it flows through the ecosystem.
· PRODUCERS ­ organisms that supply energy to all other organisms (eg. plants).
· CONSUMERS ­ animals and fungi are consumers. Primary consumers are herbivores and are eaten by carnivorous secondary
consumers which are eaten by tertiary consumers.
· DECOMPOSERS ­ living things that feed on waste material or dead organisms.…read more

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2.3.2 Understanding Energy Transfer
Transfer of Energy in an Ecosystem
· A food chain shows how energy is transferred from one living organism to another.
· The level at which an organism feed is called its trophic level.
· Within an ecosystem, living organisms are usually members of more than one food chain ­ food webs.
Efficiency of Energy Transfer
· At each trophic level, some energy is lost from a food chain from respiration (eg.).
· Energy remains stored in dead organisms + waste material ­ only available to decomposers.
· Less energy available to sustain living tissue at higher levels of the food chain, so less living tissue can be kept alive.
Measuring Efficiency of Energy Transfer
· Pyramids of Biomass:
­ The area of the bars is proportional to the dry mass of all the organisms at that trophic level.
­ Collect all the organisms and put them in an oven at 80°c until all the water in them has been evaporated.
­ Very destructive so the wet mass is usually measured to calculate the dry mass.
· Pyramids of Energy:
­ Different species may release different amounts of energy per unit mass.
­ Burning the organisms in a calorimeter + working out how much heat energy is released per gram.
­ This is calculated from the temperature rise of a known mass of water.
­ Also very destructive.
· Productivity:
­ Pyramids only take a snapshot of an ecosystem at one moment in time + population sizes fluctuate over time.
­ Look at the rate at which energy passes through each trophic level ­ pyramid of energy flow. The rate of energy flow is called productivity.
­ At the base of the food chain, the productivity of plants is called the primary productivity.
­ The gross primary productivity is the rate at which plants convert light energy into chemical energy.
­ Energy is lost when the plant respires, less energy is available to the primary consumer ­ the remaining energy is called the net primary
productivity (NPP).…read more

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2.3.3 Manipulating Energy Transfer
· Primary Productivity is the total amount of energy fixed by photosynthesis.
Improving Primary Productivity
· By manipulating environmental factors, humans can increase NPP ­ making energy conversion more efficient, reducing
energy loss and increasing crop yields:
­ Light levels can limit the rate of photosynthesis so some crops are planted early to provide a longer growing season to harvest more light,
others are grown under light banks.
­ Drought-resistant strains of plants have been bred for countries that experience lack of water.
­ Temperature can limit the speed of chemical reactions in a plant so greenhouses can provide a warmer temperature for growing plants and
increase NPP.
Improving Secondary Productivity
· It is possible for humans to manipulate energy transfer from producer to consumer:
­ A young animal invests larger proportion of its energy into grown than an adult does so harvesting animals just before adulthood minimises
loss of energy from the food chain.
­ Steroids can be used to make animals grow quicker (illegal now).
­ Selective breeding has been used to produce breed with faster growth rates, increased egg production + increased milk production.…read more

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2.3.4 Succession
· Succession is a directional change in a community of organisms over time.
How Does Succession Happen?
· The Island of Surtsey in Iceland was created by a volcanic eruption but is now home to a community of plants. Development
of such a community from bare ground is known as primary succession:
­ Algae + Lichens begin to live on the bare rock (PIONEER COMMUNITY).
­ Erosion of the rock + build up of dead organisms produces enough soil for larger plants to grow. These success the algae + lichens.
­ Larger plants success these smaller plants, until a final, stable community is reached (CLIMAX COMMUNITY).
· Secondary succession takes place on a previously colonised, but disturbed/damaged, habitat.…read more

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2.3.5 Studying Ecosystems
· It is impossible to count all the individuals in a habitat so they decided to sample small parts of the habitat using a quadrat.
· You can collect 2 types of data with a quadrat:
­ Presence/Absence of each species (DISTRIBUTION).
­ Estimate/Count the number of individuals (ABUNDANCE).
· Often hard to count certain species so scientists use percentage cover.
· To avoid bias + to get a representative sample, randomly position the quadrats across the habitat or take samples at regular
distances across the habitat.
· You may wants to look at the changes in abundance and distribution of species as you walk up a beach for example.
· A transect is a line taken across a habitat ­ take samples at regular intervals along the tape.
· LINE TRANSECT ­ at regular intervals, make a note of which species is touching the tape.
· BELT TRANSECT ­ at regular intervals, place a quadrat next to the line, studying each.…read more

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