AQA A Level Biology: Populations - Past Paper Questions and Answers, Exams of Advanced Education

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AQA A level biology; populations

past paper Qs

Define niche. - How an organism fits into its environment, including where it lives, its role and all abiotic and biotic factors. Define ecosystem - A group of interrelated organisms and their physical environment in a particular area. Define population - All the organisms of one species living in a particular habitat at the same time. Define community. - All the populations of all the species that live together in a particular ecosystem or habitat. Define abiotic factors. - The non-living physical conditions in an ecosystem. Define biotic factors. - The effects of all the activities of living organisms on other organisms. Define habitat. - The part of an ecosystem in which particular ecosystems live. Explain the difference between interspecific and intraspecific competition. - Inter is between two different species, whereas intra is within a species. What should be considered to maintain reliability of results provided by the Lincoln Index? - 1. Large sample size

2. No significant migration between collections
3. Marked animals are not more or less likely to die
4. Marked animals mix fully and randomly when returned to population
5. No significant change in population size between collections

Explain how using the sterile insect technique could reduce transmission of a disease caused by a virus spread by mosquitos. - 1. Compete (with fertile males) to mate/for food/resources OR intraspecific competition

2. Do not reproduce/breed OR Reduces population (of mosquitoes) Describe how the mark-release-recapture method could be used to determine the population of a mosquito at the start of an investigation. - 1. Capture/collect/sample, mark and release
   2. Leave time for mosquitoes to disperse before second sampling/collection
3. (Population =) number in first sample × number in second sample divided by number of marked in second sample/number recaptured Describe how you would perform an investigation to determine whether the frequency of lawn mowing influences the population density of plantains in a lawn. - 1. select similar lawns/areas of the same lawn
4. mown at different frequencies/once, twice, three times a month or similar
5. sample using quadrats
6. 1 metre2 size
7. generate random numbers to set up random coordinates (to place quadrats)
8. count number of plantains in each quadrat
9. at least five quadrats per area
10. work out population density/number of plantains per square metre
11. repeat sampling every week for about three months
12. standard procedure adopted about counting plantains touching sides of quadrats Explain how geographical isolation can cause the evolution of many species from just one. - 1. Separate gene pools / no interbreeding / gene flow (between populations)
13. Variation due to mutation
14. Different selection pressures / different abiotic / biotic conditions / environments / habitats
15. Different(ial) reproductive success / selected organisms (survive and)
16. Leads to change / increase in allele frequency

Describe how you could use the mark-release-recapture method to estimate the number of a particular lizard species on an island. - 1. Capture / collect sample, mark and release

2. Method of marking does not harm lizard / make it more visible to predators
3. Leave sufficient time for lizards to (randomly) distribute (on island) before collecting a second sample
4. (Population =) number in first sample × number in second sample divided by number of marked lizards in second sample / number recaptured. Suggest one reason for conserving woodlands. - 1. Conserving / protecting habitats / niches
5. Conserving / protecting (endangered) species / maintains / increases (bio) diversity
6. Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide
7. Source of medicines / chemicals / wood
8. Reduces erosion / eutrophication. Explain the following terms. (i) interspecific competition. (ii) ecological niche. - (i) competition between different species for food/nesting sites/display sites (ii) describes habitat and role of species e.g. sparrowhawk lives in large woods where it is a top carnivore Explain why bird conservation and maximum timber production may be conflicting management objectives. - some bird species require glades/open areas/dead wood these reduce timber production Why is it important to maintain a diversity of trees within a woodland? - increases diversity of other types of organism/non-tree species different trees provide microhabitats attracting a wider variety of insects/birds What is meant by the term 'pioneer species'? - first species to colonise/can colonise bare ground usually lichens/algae

have adaptations to survive in extreme conditions can initiate a plant succession Why is species diversity considered to be an important measure? - Indicates complexity/stability/allows comparisons of different ecosystems/communties Suggest one reason why species diversity often declines once the climax stage has been reached. - trees/conifers may shade other species acidify soils/reduce water/salt availability Outline the sequence of events by which a hydrophytic community develops into a mesophytic community such as a woodland. - dead plant material/humus/organic matter accumulates site dries/soil rises above water level conditions become less favourable/unfavourable for hydrophytes/more favourable for mesophytes reference to colonisation by herbaceous plants, shrubs, trees reference to correct/qualified change in conditions/light regime/water availabilty Describe how a student would use quadrats to obtain data about the relationship between two different plants. - generate random numbers from tables/by computer use them as random coordinates for placing quadrats use 1.0/0.5 metre2 quadrats no need to count numbers of plants/% cover, just need to record presence or absence use standard method for recording plants which touch quadrat sides comment on need for many replicates Outline a suitable procedure for randomly selecting sampling points in an investigation. - set up coordinate grid/use tapes along 2 sides generate random numbers for co-ordinates co-ordinate indicates centre of sampling quadrat

State one advantage and one disadvantage of random sampling. - Advantage: unbiased/allows statistical testing Disadvantage: coverage may be uneven/unrepresentative/large areas may be missed Suggest two adaptations which may be seen in the leaves of plants growing in low light intensities. - thinner epidermis large/many chloroplast chloroplasts concentrated towards upper/adaxial surface high chlorophyll concentration larger leaves Suggest two ways in which stream pH may influence the number of invertebrate species in a stream. - may influence ion activity eg Ca2+/Al3+ may influence solubility of toxins/metals may effect physiology/named process in a species/enzyme action may be inhibited/enhanced State two abiotic stream factors, other than pH, which may have influenced the number of invertebrate species in a stream. - Temperature light intensity concentrations of metals oxygen concentration Suggest explanations for each of the following aspects of recent forestry practice: (i) the use of coniferous tree species which bear needles (leaves) all year round. (ii) planting trees very close together. - (i) effectively increases length of growing season greater photosynthesis increased growth/yield/profit (ii) inhibits branches/encourages apical growth reduces light reaching ground/reduces growth of ground flora/competition

State three assumptions of the capture-recapture technique. - marking does not affect probability of recapture marking persists over trapping period/marks do not wear/wash off the population remains constant over the sampling period the samples consitute an accurate cross section of the population/sexes/ages etc Explain why 'throwing quadrats' is not an acceptable sampling technique. - will not provide a random sample because of 'handedness'/subjectivity/bias/differences between samplers' throwing ability Outline how you would use random sampling to estimate the number of dandelion flowers in a square lawn. - set up grid using tapes at right angles/along two sides of lawn generate random/numbers for use as co-ordinates using accurate technique e.g. computer/tables place quadrat at intersection count number of dandelions in the quadrat repeat at least 10 times and calculate the mean density per quadrat area calculate daisy population in total lawn area Describe how the surface area of a leaf can be measured. - lay leaf flat on graph paper and draw round margin count up total number of squares included count up total number of ½ squares included and add into total multiply by two to get total surface area (both sides of leaf) Samples of mud were collected using large spoons. Nets were used to sample organisms in the open water and in the weeds. Suggest two possible sources of error in the sampling methods used. - unequal sampling intensity/unequal sample sizes/only part of microhabitat sampled To determine total biomass, quadrats were used to collect the heather samples. Describe the procedure you would have used to place these quadrats. - Placing quadrats at random

(method of) marking area out with grid/using tapes acceptable method of generating random numbers e.g. table/calculator Give one organic compound in which the nitrogen will be found in the heather plants. Give one ion in which the nitrogen will be found in the soil. - (i) proteins/nucleic acids/amino acids/ATP/nucleotides (ii) ammonium/nitrate/nitrite Explain how bare ground may, over a long period of time, become forest. - Colonisation/pioneer species/examples from fig/seeds/fruits soil formation/improvement/change by organism succession/ process repeated to climax community/forest diversity is reduced Explain how bare, cleared land could once again become forest. - (Before clearing) soil exists / already produced (After clearing) recolonisation by new plants / seeds (Brings about) change in environment / soil (Allows) succession (Leading to) climax (community) Some of the soil used to determine bacterial numbers was collected from the surface of the soil store. Describe how you would ensure that this soil was collected at random. - Tapes / string / axes laid out at right angles / grid area Method of obtaining random co-ordinates Explain why one community is gradually replaced by another during succession. - change in habitat/environmental conditions by the species present making it less suitable for existing species/more suitable for other species reference to competition

Describe how each of the following farming practices influences the process of succession. (i) regular grazing by sheep (ii) ploughing fields each year - (i) succession stopped (at herbaceous perennial stage) young trees/shrubs eaten (ii) succession stopped due to destruction/burial of all vegetation present succession begins again each year Under natural and suitable conditions, bare soil would eventually become covered by a woodland community. Explain how farming practices prevent this from happening. - crops are planted (not native plants) these compete with native plants ploughing returns to bare soil destroys herbaceous plants/tree/shrub seedlings grazing by farm animals destroys herbaceous/shrub seedlings/communities. Explain how a frame quadrat is used to find percentage cover of a species of plant in a habitat. - suitable number of quadrats used (many/ large number/ 10 minimum) count all the squares occupied (by the leaves of) one species reference to randomising description of a method of randomising