• Created by: allie_99
  • Created on: 17-03-15 10:26

estimating population size


  • capture a sample of population and mark the animals
  • recapture another population, and count the amount of animals marked
  • estimate using equation: population size = (number in 1st sample x number in 2nd sample) / number in 2nd sample previously marked
    • have to assume that there are no changes in population size (from death/ immigration/ emigration)
    • sampling methods are identical
    • marking hasnt affected chance of survival (more identifiable by predators)

Scaling up from small sample size (quadrats)

  • quadrat(frame enclosing known area)
  • count all organisma=s in 1m2 quadrats
  • multiply number of organisms by the total area (in m2) of the habitat
    • sample size affects accuracy - bigger the sample size the more accurate
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Ecosystem and distribution of organisms

  • ecosystem - all organisms living in a particular area (and non living e.g. abiotic)
  • they are self supporting - contain everything they need to maintain themselves
  • only outside resource needed is an energy source (e.g. sun)
  • Transects are used to investigate the distribution (where organisms are found in a particular area) of organisms
  • to do a transect, you mark a line using a tape measure, and place quadrats next to each other all the way along the line. you then count the organisms you find in the quadrats

Kite diagrams - A kite diagram is a chart that shows the number of animals (or percentage cover for plants) against distance along a transect.

Kite chart (http://www.bbc.co.uk/staticarchive/ec2a189d7ecddde97c9de7878b547d490cc050a8.jpg)

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  • zonation is the gradual change in the distribution of species across a habitat

the distribution of organisms is affected by abiotic features (non-living physical factors in an environment)
this is because:

  • organisms are adapted to live in certain physical conditions meaning theyre more likely to survive in areas with these conditions
  • many organisms can only survive in the conditions theyre adapted to

changes in abiotic factors can lead to zonation of organisms in a habitat

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  • Photosynthesis is a chemical reaction that happens in the chloroplasts of plant cells.
  • uses energy from the sun to change carbon dioxide and water into glucose and oxygen

6CO2 + 6H2O Reaction (light energy, chlorophyll) (http://www.bbc.co.uk/staticarchive/d4149e85e49ab03413b90e1dfc6df9eee13a5689.gif) C6H12O6 + 6O2

  • Glucose is converted into other substances
    • Respiration - releases energy so they can convert rest of glucose into other substances
    • Cellulose - for making Cell walls, especially in fast growing plants
    • Lipids - storing in seeds (e.g. we get oil from sunflower seeds)
    • Starch - stored in roots, stems and leaves for when photosynthesis isnt happening (at night)
    • Combined with nitrates to make amino acids which are turned into proteins used for growth and repair
  • Two stages
  • light energy is used to split water, releasing oxygen gas and hydrogen ions
  • Carbon dioxide gas combines with the hydrogen to make glucose
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Understanding Photosynthesis

Jan Baptist van Helmont (1580-1644)

  • dried soil, weighed it and put it in a pot
  • planted a willow tree in the soil
  • added rainway to pot whenever it was dry
    • After five years, he discovered that the willow tree weighed about 74 kg more than it did at the start.
  • concluded that because weight of soil had changed so little, it must have gained mass from another source, and since he only added water - must have been water consumption
    • today we also know it is gained from CO2

Joseph Priestley (1733 - 1804)

  • put a mint plant in a closed container with a burning candle
  • The candle flame used up the oxygen and went out
  • After 27 days, Priestley was able to re-light the candle.
  • This showed that plants produce a gas that allows fuels to burn (oxygen)
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More on Photosynthesis

Three limiting factors:

rate of photosynthesis plotted against light intensity. the rate begins to slow as the light intensity continues to increase (http://www.bbc.co.uk/staticarchive/afa3f2b16b4d58d077943c96929c9a4020fea83a.gif)rate of photosynthesis plotted against carbon dioxide concentration. the rate begins to slow as the carbon dioxide concentration continues to increase (http://www.bbc.co.uk/staticarchive/020c4bb33ca143df87adc99bc1afa29bb95a1688.gif)rate of photosynthesis plotted against temperature. the rate begins to slow as the temperature continues to increase (http://www.bbc.co.uk/staticarchive/32b3b8ad49fe959ff58ac5611559c0c4480cc33b.gif)

  • Increasing the light intensity will increase the rate of photosynthesis.
  • Increasing CO2 will increase the rate of photosynthesis
    • for light and CO2 once the graph flattens out, it is no longer the limiting factor
  • If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot as the plants enzymes denature
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Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration

  • happens in both liquids and gases, as particles are free to move around randomly
    • in gases particles diffuse around each other (e.g. when perfume smell diffuses through air in a room)

The rate of diffusion is increased in Cell Membranes when:

  • The distance is decreased
  • The surface area is increased
  • The concentration difference (concentration gradient) is increased
  • particles flow through cell membrane from higher to lower concentration 
  • move randomly so can go either way, but overall movement to high concentration
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Structure of a leaf

Oxygen moves from the palisade layer to the air spaces in the spongy layer. (http://www.bbc.co.uk/staticarchive/11bd9bf22c2b7684a7fcdaedd7b39b423e589656.gif)

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Leaves and Diffusion

Plants carry out both photosynthesis and respiration

  • Photosynthesis - when it photosynthesises it uses up CO2 so theres hardly any in the leaf
    • this makes more CO2 move to the leaf by diffusion
    • at the same time, O2 is being made as a waste product of photosynthesis
    • some is used in respiration and the rest diffuses out of the leaf
  • Respiration - happens at night as there is no light for photosynthesis
    • lots of CO2 is made and O2 is used up
    • a lot of CO2 in the leaf and not a lot of O2, so now CO2 diffuses out and O2 diffuses in
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Leaves and Photosynthesis

Leaves are adapted for efficient photosynthesis:

  • broad - large surface area for gases to diffuse
  • broad - large area exposed to light
  • Chloroplasts in palisade layer - containing chlorophyll to absorb light energy near the top of the leaf where it can get most light
  • thin - CO2 and water vapour only diffuse short distance to reach photosynthesising cells
  • stomata filled lower surface - let gases (CO2/O2) in and out. also allow water to escape (transpiration
  • guard cells - control when stomata opens and closes allowing control of gas exchange
  • air gaps in spongy mesophyll layer - CO2 and o" can move between stomata and photosynthesising cells
  • upper epidermis is transparent so light can pass through to palisade layer
  • Vascular bundles(xylem & phloem)- support structure of leaf
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Net movement of water particles from a dilute solution to a concentrated solution accross a partially permeable membrane

  • turgid is when plants is watered, it takes in water by osmosis becoming plump and swollen.
  • the contents of of the cell wall push against the inelestic cell wall (turgor pressure). this supports the plant tissues
  • if there is no water in the soil a plant starts to droop as the cells lose water so lose the turgor pressure. theyre then said to be flaccid
  • if the plant is really short of water, the cytoplasm inside its cells start to shrink as the membrane pulls away from the cell wall. the cell is now plasmolysed

animal cells so not have inelastic cell walls therefore if it takes in to much water it bursts (lysis). If it loses to much water it shrivels up (crenation). This means that animals have to keep the amount of water in their cells constant - this is why plants are more tolerant to periods of drought.

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Transport Systems in Plants

(usually run along side each other in vascular bundles)


  • made of columns of living cells with perforated end-plates to allow food to flow through
  • transport food substances (e.g. sugars) up and down the stem for growing and storage tissues
  • movement of food substances is known as translocation


  • made of dead cells joined with no end walls between them and a hole (lumen) down the centre
  • thick side walls are made of cellulose. theyre strong and stiff which gives plant support
  • carry water and minerals from the roots u[ the shoot to the leaves in the transpiration stream
    • roots have to resist crushing as they push through soil. xylem in centre to give strength
    • stems need to resist bending so xylem forms "scaffolding". phloem is around outside of stem
    • xylem and phloem make up network of veins in the leaf to support the leaves
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Water Flow Through Plants

  • Root Hairs - cells on plant roots grow into "hairs" which stick to soil. each branch of a root will be covered in millions of microscopic hairs. this gives the plant a big surface area for water absorption.
  • There is usually a higher concentration of water in the soil than there is inside the plant to the water is drawn into the root hair cell by osmosis.

Transpiration- caused by evaporation and diffusion of water vapour from inside the leaves resulting in a slight shortage of water in the leaf so more water is drawn up from the rest of the plant through the xylem vessels to replace it. this means more water is drawn up from the roots so there is a constant transpiration stream of water through the plant.

transpiration is a side effect of leaf adaptations of photosynthesis. as there is more water inside the plant then outside, the water escapes from the leaves through stomata.

There are some benefits:

  • constant stream of water from ground keeps plants cool
  • provides plant with constant supply of water for photosynthesis
  • water creates turgor pressure in cells, helping to support and stop it wilting
  • minerals needed by the plant can be brought in from the soil along with the water
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Transpiration Factors

Transpiration is increased by 4 main factors:


In bright light transpiration increases The stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis Temperature Transpiration is faster in higher temperatures Evaporation and diffusion are faster at higher temperatures Wind Transpiration is faster in windy conditions Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf Humidity Transpiration is slower in humid conditions

Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air

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Water Flow Through Plants (cont.)

Plants have adaptations to reduce water loss for if it hasnt rained in a while:

  • waxy cuticle covering upper epidermis making upper surface waterproof
  • stomata found on lower surface where darker and cooler slowing down diffusion of water out of leaf
  • hot climates - fewer and smaller stomata on the underside and no stomata on upper epidermis

Guard Cells: tugid = open stomata     flaccid = closed stomata

  • Stomata close automatically when supples of water from roots start to dry up
  • the guard cells have a kidney shape which opens and closes as they become turgid/flaccid
  • thin outer walls and thickened inner walls make this opening and closing function work properly
  • open stomata allow gases in and out for photosynthesis
  • theyre sensitice to light so they open in daylight and close at night. this allows for conservation of water.
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Minerals in Plants and Active Transport

  • Nitrates - contain nitrogen to make amino acids and proteins. these are needed for cell growth. if it doesnt get enough, it will have poor growth and will have yellow older leaves
  • Phosphates - contains phosphorus for making DNA and cell membranes and is needed for respiration and growth.without this they will have poor root growth and discoloured older leaves
  • Potassium - needed to help enzymes with photosynthesis and respiration. if there isnt enough potassium in the soil, plants have poor flower and fruit growth and discoloured leaves
  • Magnesium (a little) - needed for making chlorophyll (needed for photosynthesis). plants without this will have yellow leaves.
    • Root hairs have a big surface area for taking in minerals by active transport
    • (diffusion cant be used as the concentration of minerals in the soil is usually higher in the root hair cell then in the soil around it so diffusion wouldnt work)
    • Active transport energy from respiration to help the plant pull minerals into the root hair against the concentration gradient (from low to high concentration)
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Happens when dead animals and plants break down by soil bacteria or fungi (decomposers). The key factors involved are:

  • Temperature - warm makes things decay faster as it speeds up respiration in microorganisms
  • Amount of oxygen - faster when oxygen is available
  • Amount of water - faster when moist as microorganisms need water
    • then these are at optimum levels microorganisms reproduce quickly so there is more to decay living things.
  • Detritivores(earthworms, maggots and woodlice) - feed on dead and decaying material (detrius). they break if up into smaller buts giving a bigger surface area for smaller decomposers to work on so speeding up decay rate
  • Saptophytes - feed on decaying material by extracellular digestion (feed by secreting digestive enzymes on the material outside their cells). enzymes break down the material to smaller bits which can be absorbed by the saprophyte. these are mainly fungi
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Food Preservation

  • Canning The sealed can is heated to kill bacteria. When it cools, no more bacteria can enter.
  • Cooling The food is kept at a low temperature (4°C) so bacteria cannot reproduce (they are not killed).
  • Freezing Bacteria cannot reproduce at low temperatures and the water in the food is frozen.
  • Drying Removing water prevents the microorganisms from growing, or digesting the food.
  • Adding salt or sugar Removes water by osmosis
  • Adding vinegar Reduces the pH to prevent the enzymes in the microorganisms from working.
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Intensive Farming

  • Hydroponics - plants are grown in nutrient solutions (water and fertiliser) instead of soil
    • often used to grow glasshouse tomatoes and to grow plants in areas with barren soil
      • advantages - mineral levels can be controlled accurately and diseases can be controlled more effectively
      • disadvantages - lots of fertillisers need to be added. theres no soil to anchor the roots and support the plants.

Intensive farming is used to produce more food

  • Remove competing plants from the crop growing area Herbicide spray Allows more energy to be transferred to the crop Reduces biodiversity. May have harmful effect on health.
  • Remove animals/insects that feed on the crop Pesticide spray Prevents energy being transferred from the crop to consumers Reduces biodiversity. May poison helpful organisms.
  • Keep animals indoors 'Battery' farming Reduces energy transferred to environment so more energy available for growth Increased risk of disease. Lower quality product. Ethical concerns.
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Pesticides and Biological control

    • Pesticides disturb food chains:
  • pesticides sprayed onto crops to kill the creatures that damage them (pests) but they can also kill animals that arent pests
  • this causes shortage of food for animals further up food chain
  • some pesticides are persistent and stick around in the ecosystem - becoming hard to get rid of
  • danges of pesticised being passed along the food chain and killing animals further up
    • Bilogical control means using living things instead of chemicals to control a pest (predator, parasite or disease).
      • aphids are a pest as they east roses and wgetables. Ladybirds are Aphid predators so peaople release them to keep numbers down
      • some wasps and flies produce larvae which develop on a host insect killing the host
      • myxomatosis is a disease which kills rabbits
    • Advantages - no chamicals used so less pollution, disruption of food chains and risk to people eating food thats been sprayed/ no need to keep repeating treatment
    • Disadvantages - predator might not eat pest / predator could eat useful species/ predatiors population may increase and get out of control/ predator might not stay in area
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Organic Farming Methods

  • Manure| replaces Fertiliser| Recycles waste, improves soil structure |Difficult to apply and cannot control mineral content
  • Crop rotation |replaces Single crop| Reduces disease and damage to soil composition| Less productivity. Less efficient to grow different crops.
  • Weeding |replaces Herbicides| Less environmental damage, or health risk |Labour intensive
  • Nitrogen-fixing plants |replaces  Nitrogen fertilisers| Cheaper, longer lasting |Reduces area available for growing crops if part of a crop rotation
  • Biological control - previous card
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