gcse science biology unit B4 cards

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  • Created by: charlie
  • Created on: 06-06-13 12:50

equation for capture-recapture

pop. size= number first sample x number second sample / number in second sample previously marked 

assumptions to make- capture recapture 

  • no changes in pop. size (death, immigration), 
  • sampling methods both time identical, 
  • mark hasnt affected chance of survival 
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  • all organisms living in a particular area with abiotic factors factors, 
  • self supporting except energy source (sun) 

abiotic factors 

  • non-lving (light, temp, water, salinity) 
  • affect distibution- organisms adapted and can only survive in these places 
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distribution of organisms in an ecosystem

  • distribution is where an organism are found in particular area 
  • investigate distibution using transect lines 

kite diagrams 

  • show distibution (m) and % abundance (number) of organisms 


  • gradual change in the distibution of species across a habitat due to change in abiotic factors
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  • variation between individuals of the same species in an area 
  • number of diff. species and diff. habitats in area 

more biodiversity the healthier the ecosystem as they can adapt to changes 

natural ecosystmes have higher biodiversity than artificial ones 

  • native woodlands have more variety of species, plants, animals habitats, different sizes+ages, 
  • forestry plantation have one species, fewer pleant species, habitats+animals, all planted same time - same age 
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happens in two main satages 

  • light energy splits water into O2 gas + H2 ions 
  • CO2 gas combines with H2 ions making glucose + water 
  • water isnt overall product as more is used up in first stage than the second 

glucose can be converted into other substances 

  • used for respiration 
  • turned into lipids for storage 
  • turned into cellulose to make cell wall 
  • combined with nitrates to make amino acids which make proteins 
  • stored as starch when photo. isnt happening at night- insoluble:

-cant dissolve in water and move away in solution

-doesnt affect water concen. in cells- doesnt bloat 

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more on photosynthesis

history- 350BC (greek scientists):

  • only thing touching plant was soil- plants must grow and gain mass form minerals in soil 

1648- Jan Van Helmont: 

  • dried soil- weighed it- put in pot with willow tree (2.2kg)- added rainwater
  • 5 years later- tree was 76.7kg(gained weight)- soil weight hadnt changed- must be water 
  • today we know it also gains mass from CO2

priestley's experiments 

  • 1770's- burning candle- sealed container- burnt out, added plant- relit 
  • exhaled air- sealed container- mouse died, added plant- survived few seconds 

oxygen produced comes from water 

  • plant supplied with water isotope O-18+ CO2 isotope O-16 = produced O-18 

three limiting factors 

  • light intensity- increase only to certain point 
  • CO2- increase to a certain point 
  • temp- limiting factor when too low- optimum temp (45d.c)- denatures when too high 
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diffusion and leaves

diffusion: net movement of particles from and area of higher concen. to an area of lower concen.

cell membranes: hold stuff togeth but let small stuff in and out (simple sugars, water, ions)

rate of diffusion depends on:

  • distance- diffuse more quickly when havent as far to move 
  • concentration difference (gradient)- faster when bigger difference 
  • SA- more SA the faster diffusion 

plants carry out photosynthesis and respiration 

photo.- during day- uses up CO2 (so moves into leaf via diffusion) + O2 (some used in resp some diffuses out)

resp- all the time- CO2 (diffuse out) + O2 (diffuse in) 

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leaves and photosynthesis

leaves adapted for efficient photo.:

  • broad+large SA+thin for diffusion of gases 
  • stomata holes let gases in+out + water- guard cells control gas exchange 
  • air spaces in spongy m. layer- gases move+large SA (big internal SA to vol. ratio)

leaves adapted to absord light- chloroplasts contain diff. pigments absorb diff. wavelengths:

  • chlorophyll a- 400-450+650-700 nm
  • chlorophyll b- 450-500+600-650 nm
  • carotene- 400-550 nm
  • xanthophyll- 400-530 nm 

chloroplasts in palisade layer (top of leaf) so can access most light + upper epidermis transparent

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net movement of water molecules across a partially permeable membrane from region of higher water  concen. to region of lower water concen. 

partially permeable has tiny holes- only water can pass throught no sucrose solution 

water in plant cells:

  • turgid- well watered 
  • turgor pressure- contents push against inelastic cell wall for support 
  • flaccid- no water wilts and droops 
  • plasmolysed- cytoplasm inside shrink and cell membrane pulls away 

water in animals cells: 

  • lysis- too much water and bursts as no cell wall 
  • crenation- loses too much water and shrivels 
  • animals have to keep water in cells constant 
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transport systems


  • living cells with perforated end-plates to allow stuff to flow through 
  • transport food up + down stem to growing+ storage tissues (translocation)


  • dead cells joined end to end hole (lumen) down the middle 
  • thick side walls made of cellulose (support)- carry water+min. from roots up to leaves in transpiration system 

run alongside eachother in vascular bundles 

where they are found relates to xylems other function support: roots, stem, leaves 

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water flow through plants

root hairs take in water by osmosis- millions of microscopic hairs for large SA

transpiration is loss of water from plant 

  • caused by evap.+diffusion of water vapour from inside leaves 
  • creates shortage in leaf- more water drawn up- constant system 
  • benefits: plant cool, constant water for photo., turgor pressure-support, min. needed travel with 

transpiration rate inc. by:

  • inc. in light intensity- stomata close when dark as photo cant happen+water cant escape 
  • inc. in temp- wamer the faster- particles more energy to evap+diffuse
  • inc. in air movement- wind creates low concen. of water outside leaf 
  • dec. in air humidity- so more diff. in gradient 

plants need to balance water loss with water uptake- adpated to reduce water loss (hot climate)

  • waxy cuticle- waterproof 
  • stomata found underside of leaf- darker+cooler 
  • fewer+smaller stomata - guard cells open/close  stomata when turgid/flaccid or day/night
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minerals needed for healthy growth

1) nitrates 

  • make amino acids + proteins- cell growth 
  • if none- poor growth + yellow older leaves 

2) phosphates 

  • resp.+growth - contain phosphorus for making DNA+cell membranes 
  • if none- poor root growth+discoloured older leaves 


  • help enzymes in photo.+resp. 
  • if none- poor flower/fruit growth+discoloured leaves 

*4) magnesium (*small amounts)

  • making chlorophyll 
  • if none- yellow leaves 

root hairs take in min. by active transport: concen. of min in soil is low

  • going against gradient+energy used is from respiration 
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things decay because of microorganisms (decomposers), rate of decay depends on:

  • temp- warm is faster as speeds up respiration 
  • amount of water- moist- microorganisms need water 
  • amount of O2- available- for aerobic respiration 


  • earthworms, maggots, woodlice- break up decaying material into smaller bits by feeding- smaller decomposers then work on 


  • feed on decay as well but extracellular- secreting digestive enzymes- break down- absorb

food preservation reduce rate of decay

  • canning- airtight                                        cooling- slows reproduction rate 
  • freezing- cant reproduce                            drying- decomposers need water 
  • adding salt/sugar- lose water by osmosis    adding vinegar- acid kills decomposers 
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intensive farming

produce as much food as possible from land, animals + plants- make energy transfer efficient:

  • herbicides to kill weeds- more energy from sun falling on field goes to crops 
  • pesticides to kill insects- no energy transferred into diff. food chain 
  • battery farming- close together- no energy lost through movement or warmth


  • plants grown in nutrient solution- mineral levels and diseases controlled more effectively 
  • however- lots of fertilisers need to be added and no support or achor for roots or plants 

intensive farming negatives- remove habitats, eutrophication, disturb food chains, ethical issues

alternatives: Organic Farming 

  • organic fertilisers- recycles- doesnt work as well but better for environment (no toxic chem.)
  • crop rotation- stops pests/disease building up- include nitrogn-fixing crops- legume plants
  • weeding- labour intesive but no nasty chemicals - cant grow as much food 
  • varying seed planting times- avoid major pests 
  • biological control- organic and no ethical issues however more space used for less crops
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pesticides and biological control

pesticides disturb food chains:

  • causes shortage of food further up food chains and kill animals if persistent+passed along
  • DDT 1960's- cant be excreted + otters ended up with highest concen.+died

biological control instead 

  • living things instead to control pests- predator, parasite, disease 
  • ladybirds introduced as a predator to aphids
  • wasps/flies produce larvae- develops in host insect- kills insect host 
  • myxomatosis- disease killing rabbits- myxoma disease released 

advantages- less pollution, food chain disruption, no need to repeat, humans not at risk 

disadvantages- might not eat pest, eat useful species, pop. inc. out of control + move to diff. area

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