AQA Unit Four Biology Exam questions

A range of exam question for unit 4 biology past papers, along with mark scheme answers for revision. 

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Why is growing crops more efficient in terms of food production?
Fewer tropic levels therefore
Less energy lost between tropic levels
If a piece of land was left bare how would succession be measured?
Use coordinates/random numbers/permanent quadrats
(reject transect)
Use a large number of Quadrats
Count number of (each) species of plant/percentage cover
Repeat at regular time intervals/stated time interval
Use data/ statistics to make a comparison
Explain how grass land can become replaced by a woodland community ( 3 Marks)
Mowing grassland kills other plants/prevents succession
(Once mowing stops) competition occurs
Changes in community lead to changes in abiotic/edaphic factors
Allowing trees/woodland/climax community to become established
Name and describe three abiotic factors, which could affect the distribution of bluebells in a
woodland ( 3 Marks )
Temperature (of air) may affect transpiration/enzymes/temperature of soil as
this may affect enzymes
Wind speed as this may affect rate of transpiration / seed/pollen dispersal
Light intensity as this may affect (LDR of) photosynthesis
Edaphic factors/named factor as this may affect nutrient availability / soil
organisms
(Accept pH of soil affecting enzymes, reject pH alone)
Humidity as this may affect rate of transpiration/water loss
Explain the changes in oxygen concentration in the water ( 4 marks )
(Organic material) allows rapid growth/increase of bacteria
(Aerobic) bacteria take up oxygen (for respiration)/respire aerobically
Further downstream, organic material decomposed/diluted
So bacterial numbers drop (and so does their oxygen uptake)
Increase in plants/algae releases O2
Turbulence causes increase O2 from air

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Fish eating birds died from D.D.T. poisoning (2 marks)
Each organism at higher levels in the food chain eats many organisms lower
in the food chain
As DDT isn't excreted it accumulates in the body/fatty tissue
Many insect populations become resistant to D.D.T.…read more

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Not adapted to water loss (Allow other abiotic factors with explanation e.g.…read more

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