Populations, evolution and ecosystems.

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What is the gene pool?
The complete range of alleles for all genes in the organisms of a population.
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What is allele frequency? *
The proportion of a particular type of allele in a population.
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What is evolution? (in terms of alleles)
A change in the allele frequencies in a population.
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What is genotype frequency?
The proportion of a particular allele combination in a population.
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What is phenotype frequency?
The proportion of a particular characteristic in a population.
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What is the Hardy - Weinberg principle?
That the allele frequency in a population will remain constant over time.
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What conditions must be met if the Hardy - Weinberg principle is to be true? *
There are no mutations, no immigration/emigration, no natural selection (no selection pressures), mating is random and the population is large.
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Which equation can be used to find allele frequency?
p+q=1, where p = frequency of dominant allele and q = frequency of recessive allele.
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Which equation can be used to find genotype/phenotype frequency?
p^2+2pq+q^2=1, where p^2 = homozygous dominant frequency, 2pq = heterozygous frequency, q^2 = homozygous recessive frequency.
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Give 3 conditions needed for reproductive success. *
1) All organisms produce more offspring than can be supported. 2) The gene pool of a population contains a wide variety of alleles. 3) All organisms face selection pressures that determine their ability to survive.
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What are the two sources of variation?
Genetic and environmental.
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Which two factors cause genetic variation? *
Mutations and sexual reproduction.
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What are the two main ways in which mutations can cause genetic variation? *
Chromosome mutations (e.g. non - disjunction) or gene mutations.
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In which 3 ways can sexual reproduction provide genetic variation?
1) Random assortment (independent segregation). 2) Crossing over of homologous chromosomes. 3) Random fertilisation of gametes.
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What are the 2 types of variation?
1) Continuous 2) Discontinuous
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What are the 3 main features of continuous variation? Give 2 examples. *
1) No categories to place individuals. 2) Controlled by a large number of genes. 3) Are significantly affected by the environment. E.g. weight, hair colour, rate of photosynthesis, intelligence.
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What are the 3 main features of discontinuous variation? Give 2 examples. *
1) Distinct categories with no overlap between categories. 2) Controlled by a small number of genes. 3) Largely unaffected by the environment. E.g. blood group, attachment of ear lobes, pea seed colour.
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How do we know that speciation has taken place?
When 2 previously separated populations come back into contact and can no longer interbreed to produce fertile offspring.
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What are the 2 main types of species isolation?
1) Geographical isolation (allopatric). 2) Reproductive isolation (sympatric).
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What is sympatric isolation?
When a group of organisms inhabiting the same area become reproductively isolated into two groups where there are no physical barriers.
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What are the three main mechanisms of sympatric isolation?
1) Behavioural isolation. 2) Morphological isolation. 3) Gametic isolation
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What is behavioural isolation?
Where different courtship methods/other behaviours are adopted by separate groups. Members of the separate groups may therefore not interbreed.
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What is morphological isolation?
Differences in body shape mean that certain individuals are not physically able to breed.
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What is gametic isolation? *
Where some or all of the chromosomes in the male and female gametes cannot form homologous pairs. This results in hybrid sterility/inviability.
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What is genetic drift?
When variations in small/isolated populations occur by chance.
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Why is genetic drift only significant in small populations? *
Small number of different alleles (gene pool) > alleles which are more favourably passed on increase in proportion relative to whole gene pool > any mutations to one of the selectively favoured alleles more quickly affect the whole population.
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Why do we use sampling to study the distribution of organisms?
It is often impossible to count, measure and/or weigh every organism in a habitat.
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What are the 3 main types of sampling? *
1) Random. 2) Systematic. 3) Mark - release - recapture.
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What percentage of the total area must samples be taken from in random sampling? *
Sufficient samples for 10% of the area.
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Which sized quadrats are used to measure gradual change?
Small
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Which sized quadrats are used to measure wider variance?
Large
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What is used to identify different species when conducting experiments?
Field guide.
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Which scale is used to measure the frequency of an organism?
DAFOR - dominant > abundant > frequent > often > rare.
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What must be calculated for each section of area to compare species distribution across the whole area?
Mean average
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When is transect (systematic) sampling used?
To test spatial variation (change across an area).
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How can the change be measured across the whole area using transects?
Use multiple transects as different positions and calculate the average number of organisms at each distance.
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What are the two types of transect? *
1) Intermittent - quadrat placed at intervals. 2) Continual - quadrat 'flipped over' so samples are taken across the whole length of the transect.
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How can bias be avoided when using quadrats?
Ensure that placing of the quadrats is random - random coordinate generator.
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How can a representative sample be obtained?
Use many quadrats/transects.
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Why is it important to assess species diversity? *
To monitor environmental change, damage and the success of conservation efforts.
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What is species richness?
Number of different species.
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What is species diversity?
Number of species and number of individuals of each species.
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What is the formula for Simpson's diversity index? *
N(N-1) divided by the sum of n(n-1), where N = total number of organisms of all species and n = total number of organisms of each species.
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Which method is used to estimate the population size of motile organisms?
Mark - release - recapture
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How is the mark - release - recapture method carried out?
1) Sample of animals collected and counted. 2) Animals marked and released back into the population. 3) Marked animals given time to reintegrate. 4) Second sample caught, total number and number of marked individuals counted.
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How is population size estimated from the results of mark - release - recapture?
Lincoln index: P= (n1xn2)/nm, where: n1 = total no. of individuals in first sample, n2 = total no. of individuals in second sample, nm = number of marked individuals recaptured.
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Which factors must be true for mark - release - recapture to work? *
Sample size must be large so representative of whole population. Between collecting samples 1 & 2: little or no migration; little or no reproduction; organisms effectively re - mix with rest of population; marking doesn't increase predation.
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Which two methods can be used to sample aquatic animals?
1) Kick sampling. 2) Surber sampler.
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How is kick sampling carried out? *
Person 1 stood facing flow of water w/net - so fish flow into net. Person 2 stood set distance from 1 and kicks water - so fish clinging to rocks are released. Place sample in tray of water & count fish.
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What is a surber sampler?
A net placed in a river for a few hours. Measures natural flow of fish through river.
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Which two methods can be used to sample terrestrial animals? *
1) Pitfall trap. 2) Suction samplers (pooters).
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How is a pitfall trap set up? *
Dig into soil, place pot w/ food. Run soil upwards & place slabs at side of trap to prevent water flowing in. Check every 24h to see how many animals have fallen in. Standardise depth, length of time left for, amount of food. Different seasons.
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How are aerial animals sampled? What should be controlled?
Using sweep nets. Control the amount of sweeps, length of handle, person sweeping, net size.
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What are light traps used for?
To attract moths for sampling.
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Name 6 abiotic factors.
Temperature, pH, humidity, light intensity, wind velocity, water potential.
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Which abiotic factors can electronic meters be used to measure? *
pH, temperature, light, wind, humidity.
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What can a colorimeter be used to measure? *
Soil/river composition. Less light passing through (transmittance) = more pollution. May be measured as total suspended solids.
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What are the 4 main stages of population change? *
1) Lag phase, 2) Exponential growth phase, 3) Stationary/stable phase, 4) Death phase.
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What is the tolerance range?
The range of an abiotic factor over which animals of a given species are able to survive.
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What does an abiotic factor become once outside of the optimum range?
A limiting factor.
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What is the competitive exclusion principle? *
Where populations of two species have the same niche, one will normally have the competitive advantage. E.g. grey squirrels have out - competed red squirrels.
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Name an example of a pioneer species/primary coloniser.
Marram grass, lichens, moss.
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What are the 2 main features of pioneer species? *
1) Slow - growing, 2) Tolerant of extreme conditions.
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What happens when pioneer species die?
Microorganisms (saprobionts) decompose the dead organic matter into a thin soil.
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Which species can grow in thin soils?
Simple species such as grasses and ferns. Their roots accelerate soil formation.
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Why do tertiary colonisers (e.g. grass) grow faster than primary and secondary colonisers? *
They have a larger photosynthetic area. Faster growth means that they make more detritus, forming better soil which holds more water.
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What leads to the formation of a climax community?
Trees grow slowly, but eventually shade and out - compete the shrubs, which are replaced by shade - tolerant forest floor species.
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What is the climax community? *
The established, complex food web with many trophic levels and interactions.
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What is a lithosere?
A succession that starts from bare rock.
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What is a hydrosere?
A succession that begins in water.
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What is a psammosere?
A succession that starts on a sand dune.
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What is a plagioclimax?
An artificial climax community - common landscapes like farmland, grassland, moorland & gardens are all maintained at pre - climax stages by constant human interventions.
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What is secondary succession?
A succession starting with soil, but no or few species. E.g. in a forest clearing, following a forest fire, or when soil is deposited by a meandering river. Much more rapid than primary succession.
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Name 5 examples of human interventions to maintain a plagioclimax. *
1) Burning, 2) Grazing, 3) Mowing, 4) Coppicing (cutting trees at the base w/o removing stump), 5) Pollarding (cutting tree branches).
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What are the 4 main benefits of intervention to maintain & restore ecosystems & biodiversity?
1) Personal, 2) Ethical, 3) Economic, 4) Cultural & aesthetic.
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How might the population size of an endangered species be increased/maintained?
Captive breeding.
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What are seed banks used for?
Store the seeds of wild plants that are endangered or will become extinct if all wild plants disappear.
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Give 3 examples of schemes to protect certain areas/species. *
1) SSSI, 2) RAMSAR wetlands (protected by DEFRA), 3) Fishing quotas.
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Give 4 farming practices that have directly removed habitats and reduced species diversity. *
1) Removal of hedgerows 2) Monoculture 3) Filling in ponds & draining marsh 4) Over-grazing of land
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Give 3 farming practices that have indirectly reduced species diversity *
1) Use of pesticides and inorganic fertilisers 2) Escape of effluent from silage stores & slurry tanks into water courses 3) Absence of crop rotation & lack of intercropping.
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Card 2

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What is allele frequency? *

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The proportion of a particular type of allele in a population.

Card 3

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What is evolution? (in terms of alleles)

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Card 4

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What is genotype frequency?

Back

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Card 5

Front

What is phenotype frequency?

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