gcse science biology unit B4 cards

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 

• 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 

• 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 

zonation 

• gradual change in the distibution of species across a habitat due to change in abiotic factors

includes:

• 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 

6CO2+6H2O=C6H12O6+6O2

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 

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 

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) 

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

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 

phloem:

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

xylem 

• 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 

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

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 

3)potassium

• 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 

.

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 

detritivores 

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

saprophytes

• 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 

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

hydrophonics 

• 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

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