Key Words

Habitat > the place where an organism lives

Population > all the organisms of one species living in a habitat

Community > the populations of different species

Abiotic factors > non-living factors on the environment (eg. temperature)

Biotic factors > living factors on the environment (eg. food)

Ecosystem > the interaction of a community of living organism with non-living organisms parts of the environments 

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Plants compete for:

  • light
  • space
  • water & minerals


  • space (territory)
  • food
  • water
  • mating partners
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Competition (continued)

Ecosystems are interdependent (rely on each other for food, shelter, pollination)

If one animal/plant dies or increases it can affect the entire ecosystem

Stable communities > the population size is roughly consistent

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Abiotic & Biotic Factors

Abiotic > moisture levels, light intensity, temperature, carbon dioxide levels, wind intensity, oxygen levels, soil pH & mineral content

Different organism adapt to different abiotic conditions


Decrease in light intensity > decrease rate of photosynthesis > affect plant growth > decrease population size

Biotic > new predators, competition, new pathogens, availability of food

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Structural :

  • arctic animals > white fur so prey/predators can't see them
  • cold water > low surface to volume ratio to retain heat
  • hot places > have a large surface to volume ratio to loose heat & large ears


  • birds migrate to escape cold conditions 

Functional: (on inside of body eg, reproduction, metabolism) 

  • desert animals > produce little sweat 
  • brown bears > hibernate so lower metabolism & conserve energy

Extremophiles > live in extreme conditions 

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Food chains

Dandelions > rabbit > fox

> = energy transferred

Populations are limited by the food available 

Prey increases = predators increase

but. predators increase = prey decrease 

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Using Quadrants (practical)

Distribution of organism > where an organism is found

Where an organism is found is affected by environmental factors

Can study distribution by:

  • take two sample areas
  • measure the change over a larger area

To use quadrant:

  • place 1m2 quadrant randomly on the floor
  • count desired organism
  • repeat 3 times or as many as possible 
  • calculate mean
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Using Transects (practical)

Work out how an organism is distributed over an area

  • mark out a line in the study area using a tape measure
  • collect data along line
  • can either count number of organisms along the line or use quadrant

Instead of counting quadrant can estimate percentage cover

Only count a quadrant square if more than half is covered

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Environmental Change

Why does distribution (where an animal lives) change over time?

Environmental changes:

  • temperature - European bee-eater birds have moved from Mediterranean to parts of Germany
  • availability of water -  giant wildebeest migrate with the rainfall patterns
  • the composition of atmospheric gases - some species of lichen can't grow in areas where sulfur dioxide is present due to industrial processes 

these factors can be caused by seasonal, geographic or man-made factors

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The water cycle

water moves between rivers, lakes, oceans & the atmosphere 

1. energy from sun makes water evaporate from land, plants (transpiration) & sea

2. warm water vapour is carried upwards & condenses into clouds

3. water falls from clouds as rain, snow or hail & provides fresh water for plants & animals

4. the excess drains into oceans so cycle repeats

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The carbon cycle

living things are made up from materials around them 

  • a plant uses carbon, oxygen, hydrogen & nitrogen to make complex compounds which are then passed up the food chain
  • these are then returned in waste products or when organisms die & decay
  • materials decay as they are digested by other microorganisms (happens fastest in warm, moist, aerobic conditions) 
  • decay puts the minerals back into the soil that plants need to grow
  • when a community is stable the cycle is balanced
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Carbon cycle (continued)

1. CO2 is removed from atmosphere via photosynthesis - this is used to make glucose which can be turned into carbohydrates, fats & proteins (this energy is moved up the food chain)

2. when plants respire some carbon is given out back into atmosphere CO2

3. when plants are eaten carbon becomes fat & protein in the animal's body

4. when animals respire some carbon is returned as CO2 to the atmosphere

5. when plants die other microorganisms (detritus feeders) feed on them producing CO2 as they respire putting CO2 back into the atmosphere

6. animals' waste is also broken down by detritus feeders

7. the combustion of wood & fossil fuels also puts CO2 into the atmosphere

8. carbon & energy are constantly being cycled from air, through food chains & back to the air

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Compost > decomposed organic matter used as a natural fertilizer (farmers & gardener try to produce perfect conditions for decay to make compost) 

Decay happens because of microorganisms, bacteria, fungi & detritus feeders 

Factors affect such as:

  • temperature > warmer conditions are better as enzymes work quicker but too cold or hot enzymes are denatured 
  • water availability > is faster in moist areas as organism involved with decay need water for biological functions
  • oxygen availability > need oxygen to respire (aerobic decay)
  • number of decay organisms > the more decay organisms the faster it happens 
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Biogas - using decay to make a fuel

Made of methane which can be burnt as a fuel

Sludge waste from sewage is used to make biogas on a large scale

Digester/generator > makes biogas (must be kept at constant temp for decay to occur)

Has to be used straight away as can't be stored as liquid (can be used for heating, cooking, lighting, power a turbine to generate electricity

Two types > batch generators (loaded with waste & left to digest, produce small-scale, cleaned after every session)

                 > continuous generators (waste continuously put in & fed                    out better for large scale)

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Investigating Decay (practical)

observing the reaction between lipase & milk that is alkaline (when the milk is broken down the pH decreases)

This practical looks at how temp affects decay, an indicator dye called phenolphthalein is used (pink when pH is 10 & colourless when below 8.3) 

1. measure out 5cm3 of lipase solution into test tube, label L

2. measure out 5cm3 of milk add to different test tube

3. add 5 drops of indicator to milk

4. measure out 7cm3 of sodium carbonate solution add to milk - solution will turn pink

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Investigating decay (continued)

5. put both tubes into 30.C water bath & leave till temp reached

6. put 1cm3 (use calibrated dropping pipette as has scale) of lipase into milk tube & start stopwatch straightaway

7. stir contents with glass rod & enzymes will start to decompose milk

8. once solution looses pink colour stop stopwatch & record time 

9. repeat the experiment at different temps then calculate mean time

10. calculate rate of decay by > rate = 1000/time (s-1)

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Biodiversity & waste management

Biodiversity > the variety of species on Earth or within an ecosystem 

High biodiversity ensures stability of ecosystem & maintains the physical environment of an ecosystem

For humans to survive we need a high biodiversity

Factors decreasing:

  • deforestation
  • waste production
  • global warming 

The population has increased > modern medicine & farming techniques 

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Biodiversity & waste management (continued)

Demands on the environment:

  • increasing population
  • increasing standard of living 
  • using resources quicker than replacing 

Producing more waste:

  • waste chemicals > pollution > decreases biodiversity
  • sewage & toxic chemicals pollute lakes etc.
  • pesticides etc. used on land wash into lakes
  • burying nuclear waste underground
  • landfill sites (increase due to population) produce methane & dangerous chemicals which pollute the land
  •  smoke & acidic gases pollute ai causing acid rain, global warming & global dimming
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Global warming

Gases in atmosphere insulate earth so life can happen

Greenhouses gases:

  • methane (cattle, landfill, swamps)
  • carbon dioxide (burning fossil fuels, deforestation)
  • water vapour (rise in temp = sea evaporates more)

The sun emits heat energy which reflects of the earth & some is absorbed by greenhouse gases in the atmosphere

More greenhouse gases = more heat energy absorbed = rise in temp

Global warming leads to:

  • change in weather patterns eg. rainfall (affects food production)
  • more extreme weather eg. hurricanes 
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Global warming (continued)

Sea levels rise:

  • high temps > sea water expands & ice melts
  • lead to flooding & higher levels of water vapor

Changes in species distribution:

  • temperature increases & rainfall changes causing wild animals to migrate
  • may become more widely or less distributed
  • could affect natural ecosystems/food chains > reduction in biodiversity 
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Maintaining ecosystems & biodiversity

Breeding programmes:

  • prevent endagengered species becoming exstinct
  • animals are bred in captivity
  • individuals are sometimes released to boost or reastablish population

Habitat protection:

  • to protect & regenerate rare habitats 
  • help to protect & preserve ecosystem
  • programmes to reintroduce hedgerows as field borders on farms

Preventing global warming:

  • deforestation increase carbon dioxide in area (some government trying to reduce)
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Maintaining ecosystem & biodiversity (continued)


  • governments pay farmers to reintroduce hedge rows
  • regulating designed to record & maintain biodiversity is expensive
  • money often prioritised
  • could affect local economy also ie. people who benefit from deforestation 

Food security:

  • using pesticides can affect ecosystems but benefit food production

Development of society:

  • land is in high demand due to rise in population
  • land used to promote high biodiversity may also be needed for other uses
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Trophic Levels

The different stages of a food chain

Each is level is numbered on how far along the chain they are

Trophic level 1 = producers (plants)

Trophic level 2 = primary consumers (herbivores)

Trophic level 3 = secondary consumers (carnivores)

Trophic level 4 - tertiary consumers (carnivores at top of food chain > apex predators)

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Pyramid of Biomass

Always in a pyramid


                        ^                                   fleas

                  ^^^^^^^                              fox

          ^^^^^^^^^^^^^^^^                      rabbits

^^^^^^^^^^^^^^^^^^^^^^^^^^       dandelions

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Biomass transfer

Only 10% of energy is passed on between each level of the food chain

  • animals don't eat every bit of an organism eg. bones
  • animals don't absorb everything they eat some is excreted
  • a lot of energy is used in respiration & to heat the body rather than put on as mass
  • waste products like carbon dioxide & urea (urine) are made

Efficency of biomass transfer can be calculated

efficency = (biomass transferred to the next level / biomass available at previous level) x 100

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Food security & farming

Food security > having enough food to feed a population

  • an excessively increasing population can affect food security
  • new pests/pathogens or changes in weather patters affecting crops or livestock
  • due to the prices of food production there might not be enough people producing food
  • confilcts can affect water availibility & food production

Sustainable food production is important so that food can be continually produced & won't run out

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Food security & farming (continued)


  • affects food chains as there are less fish to eat
  • we need to sustainably fish so fish are at levels where they can still breed
  • cod are at risk of disappearing form the north west Atlantic

Fish quotas > limit the number of fish that can be caught in certain areas

Net size > restrictions based on fish being caught (means unwanted or yound fish can escape)

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Efficent food production

Limiting movement of livestock & controling temperatures so less energy is wasted means more energy is used for growth

High protein food can be given so animals grow quicker

Some of these factory farming methods are controversial as it is unnatural for the animal & there is a higher risk of disease (so some will be given antibiotics 'just incase')

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Living things are manipulated through a biological process to make them more useful

Genetic engineering to produce human insulin:

  • a plasmid (loop of DNA) is removed from a bacterium
  • insulin gene is cut out of a human chromosome using a restriction enzyme (recognize specific sequences of DNA & cut)
  • the DNA strand left with an unpaired base is called a sticky end
  • the plasmid is cut open with same restriction enzyme leaving the same sticky end
  • the plasmid & human insulin genes are mixed 
  • ligase (enzyme) is added to join sticky ends to produce recombinant DNA (two different bits of DNA  stuck together)
  • recombinant DNA is inserted into a bacterium
  • grown in a vat so can be harvested & purified for use in humans 
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Biotechnology (continued)


  • use modern biotechnology > a lot of microorganisms are cultured under controlled conditions in large vats
  • used to make high protein substitutes to meat eg. Quorn
  • made from Fusarium (fungus) & grown in aerobic conditions with glucose syrup for food
  • the fungus is harvested & purified

Genetically modified crops:

  • can be GM so resistant to pests, grow better in drought or be higher in certain nutrients (eg. golden rice high in a chemical which can be made into Vitamin A)
  • some people argue that people can't afford to buy food not grow it
  • countries may become dependent on GM
  • poor soil means even GM crops cant survive
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So useful and convenient for me, thank u very much :)

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