Ecosystems

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Components of Ecosystems:

Producers - plants which photosynthesise to produce food

Consumers - animals which eat plants or other animals

Decomposers - decay dead material and help in recycling nutrients

Physical environment - sum total of non-biological components of ecosystem - E.G. water and soil in pond, soil and air in forest

Each ecosystem has many habitats - places where specific organisms live - some given by physical environment or organisms themselves (dead vegetation gives habitat for decomposers)

All organisms of particular species in an ecosystem at any time are population of that species in that ecosystem

Population of all species (animals, plants, decomposers, etc.) found in particular ecosystem are the community of the ecosystem

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Quadrats to Sample from a Habitat:

Sample - smaller representative part of the population

Quadrats - used to sample plants or animals which don’t move much, E.G. snails

Sampling should be random to avoid bias

Experiment: The plant community in Area A is different from the Plant community in Area B

Area A - Lay out two measure tapes to form the sides of a square

Randomly generate a pair of numbers from the random number function on a calculator - the numbers are coordinates to position the quadrats in the large square

Numbers of each plant species in quadrat counted

Repeat process for nine more quadrats

Move tape measure to Area B and repeat process to sample 10 quadrats

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Interactions in Ecosystems:

Organisms in ecosystem interact with each other and physical environment in such ways:

Feeding among organisms - plants, animals, decomposers recycle same nutrients through ecosystem

Competition among organisms - animals: food, shelter, nesting sits, mates; plants: carbon dioxide, mineral ions, light, water

Interaction between organisms and environment - plants absorb mineral ions, CO2, H2O from environment, give off water vapour, O2 into environment; animals use materials from environment to build shelter, environment temperature affects organism processes and processes in organism affect temperature of environment

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Feeding Relationships:

Food chain for diagram below:

Grass - producer

Grasshopper - primary consumer - animal which eats producer and is a herbivore

Lizard - secondary consumer - eats primary consumer so carnivore

(Tertiary consumer - fourth stage)

Microorganisms play key role in recycling - break down complex organic molecules in bodies of dead animals and plants into simpler substances which they release into environment.

Trophic levels - different stages in food chain

Plankton --> Crustacean --> Fish --> Ringed seal --> Polar bear

Polar bear - quaternary consumer - nothing eats it, so also the top carnivore

Food web - different food chains and how they link

Food web of salmon below:

If leech population decreased,

Less leeches to eat midge larvae -- more midge larvae -- more for stonefly nymph population to feed on -- population increases

Fewer leeches for mature salmon to eat -- mature salmon feed more on stonefly nymph population -- stonefly nymph population decreases

Numerous could stay static due to combination of above

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Ecological Pyramids:

Diagrams representing relative amounts of organisms at each trophic level.

Pyramids of numbers - numbers of organisms in each trophic level in food chain, irrespective of their mass

Pyramids of biomass - total mass of organisms in each trophic level, irrespective of numbers

Why feeding relationship diagrams give a pyramid shape:

There are losses at each trophic level:

Some parts of the grass aren’t eaten E.G. roots

Some parts aren’t digested so not absorbed and therefore egested

Some materials which are absorbed form excretory products

Many metals are respired to release energy, with the loss of CO2 and H2O

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Flow of Energy Through Ecosystems:

Feeding is a way of transferring energy between organisms on various trophic levels.

Energy flow diagram

Photosynthesis ‘fixes’ sunlight energy into glucose and starch

Respiration releases energy from organic compounds E.G. glucose

Most biological processes E.G. muscle contraction, growth, reproduction, etc.) use energy released in respiration

If energy released in respiration used to produce new cells, then energy remains ‘fixed’ in molecules in that organism - can be passed on to next trophic level through feeding

If energy released in respiration used for other processes then it will, once used, escape as heat from organism -- therefore, energy is lost from food chains and webs at each trophic level

Only around 10% of energy entering trophic level passed on to the next level, which is why not many food chains have more than 5 trophic levels.

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The Carbon Cycle:

Carbon - major biological component - carbohydrates, lipids, vitamins, proteins, etc. all have carbon.

These processes important in cycling carbon through ecosystem:

Photosynthesis - ‘fixes’ carbon atoms from CO2 into organic compounds E.G. C6H12O6

Feeding and Assimilation - pass carbon atoms already present in organic compounds, along the food chain

Respiration - produces inorganic carbon dioxide from organic compounds (mostly carbohydrates) as they are broken down to release energy

Fossilisation - sometimes living things don’t fully decay at death due to soil conditions (E.G. if too acidic) and fossil fuels (coal, oil, gas) formed

Combustion - releases carbon dioxide into atmosphere when fossil fuels burned

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The nitrogen cycle:

Processes of cycling nitrogen through ecosystem:

Feeding and assimilation - pass nitrogen atoms already in organic compounds along the food chainD

Decomposition - produces ammonia from nitrogen in compounds E.G. proteins, DNA, vitamins

Nitrification - Ammonia oxidised to nitrite and then nitrate by nitrifying bacteria

Plant roots absorb nitrates and combine with carbohydrates from photosynthesis to form amino acids, then proteins and other nitrogen-containing compounds

Nitrogen cycle:

Denitrification - reduces amount of nitrate in soil as denitrifying bacteria use nitrates as energy source and convert into nitrogen gas

Free-Living nitrogen-fixing bacteria in soil - convert nitrogen gas to ammonia - used by bacteria to make a.a and proteins - when bacteria die, proteins decompose and ammonia back in soil

Nitrogen-fixing bacteria in root nodules - make ammonia but converted by plant into a.a - death and decomposition of plants returns nitrogen to soil as ammonia

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The water cycle:

Water cycled between atmosphere, rivers and lakes, organisms, back to sea

Heat from Sun evaporates water from surface of oceans, lakes, rivers

Plant transpiration and organism respiration releases water vapour in the air

Clouds rise over mountains and high ground - cool and water condenses into rain or snow

Precipitation falls on Earth, taken up by animals or plants or enters rivers and flows to sea to start cycle again