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AQA A Level Biology > Populations and Evolution > Flashcards

Populations and Evolution Flashcards

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1
Q

Define species

A

Organisms that can reproduce to produce fertile offspring

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2
Q

Define population

A

All the organisms of a single species in one place at one time, species can exist as more than one population

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3
Q

Define community

A

All the organisms of all the species in one place at one time

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4
Q

Define gene pool

A

All the alleles present in a population

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5
Q

Define allele frequency

A

How common an allele is in the population

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6
Q

Define evolution

A

A change in allele frequency over time

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7
Q

Define differential reproductive success

A

Organisms with a phenotype better adapted to their environment have a selective advantage and are more likely to survive and reproduce

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8
Q

Define speciation

A

The process of forming a new species

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9
Q

What is the Hardy-Weinberg principle?

A

A model that predicts the frequency of alleles, genotypes and phenotypes in a population

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10
Q

What does the Hardy-Weinberg principle assume?

A
  • No mutations- No selection- Random mating- Large population (no genetic drift)- Population is genetically isolated- No migration
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11
Q

What does the Hardy-Weinberg principle predict?

A

That the frequency of alleles of a gene will stay constant over generations

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12
Q

What are the two Hardy-Weinberg equations?

A
  • p + q = 1- p^2 + 2pq + q^2
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13
Q

What is intraspecific variation?

A

Individuals of the same species have the same genes but different alleles and therefore variation in their phenotype

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14
Q

What is interspecific variation?

A

Individuals of different species have different genes and live in different environments leading to variation in their phenotypes

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15
Q

What is continuous variation?

A
  • Variation is smooth and continuous- Represented on a line graph- e.g. height and weight
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16
Q

What is discontinuous variation?

A
  • Individuals fall into discrete groups with no intermediates- Bar chart- e.g. blood type- Controlled by a single gene with a few alleles
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17
Q

What are the genetic causes of variation?

A
  • Mutation- Meiosis (crossing over/independent segregation)- Random fertilisation - Inherited
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18
Q

What are the environmental causes of variation?

A
  • Environment affects the phenotype constantly across an organisms lifespan- e.g. accent
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19
Q

How can variation be effected by both the environment and genetics?

A
  • Most variation is a result of both environmental and genetic variation- e.g. height, height is controlled genetically but can be affected by childhood nutrition
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20
Q

What does genetic variation result in?

A

Evolution

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21
Q

What is speciation?

A

The process of forming a new species

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22
Q

When does speciation happen?

A

When populations become reproductively isolated therefore preventing gene flow

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23
Q

What is allopatric speciation?

A

Geographical isolation provides a geographical selection pressure which results in reproductive isolation preventing gene flow

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24
Q

What is sympatric speciation?

A

Non geographical selection pressures result in reproductive isolation preventing gene flow

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25
Q

What are the non-geographical isolation mechanisms that cause sympatric speciation?

A
  • Morphological (different shaped genetalia)- Seasonal (reproductively active at different times of the year)- Behavioural (different courtship behaviour)- Hybrid sterility (hybrids of two parents are sterile
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26
Q

Why does speciation happen?

A
  • Variation exists in the population due to mutations- Different selection pressures lead to the directional selection of different phenotypes- Differential reproductive success causes a change in allele frequency over many generations
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27
Q

What is genetic drift?

A

Change in allele frequency between generations due to random change e.g. random fertilisation

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28
Q

What size population does genetic drift have the biggest effect on?

A

Smaller populations

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29
Q

What does genetic drift change?

A

Allele frequency

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30
Q

What does genetic drift cause?

A

Evolution

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31
Q

Does genetic drift depend on the environment?

A

No

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32
Q

What does random fertilisation mean?

A

It is random which allele passes to the zygote

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33
Q

What is evolution?

A

The change in heritable traits of a population over generations

34
Q

What are examples of genetic drift?

A

The bottleneck effect and the founder effect

35
Q

What happens in disruptive selection?

A

Both phenotype extremes are more likely to survive and reproduce than the mean phenotype therefore the environment selects for two different phenotypes

36
Q

What is disruptive selection the opposite of?

A

Stabilising selection

37
Q

What does disruptive selection contribute to?

A

sympatric speciation

38
Q

What is abundance?

A
  • The number of individuals of a single species in an ecosystem/habitat - Population size
39
Q

What is distribution?

A

Where a species is found in an ecosystem/habitat

40
Q

What effects an organisms distribution and why?

A

Interspecific competition and predators will affect an organisms distribution because organisms will only exist where they can survive

41
Q

How does intraspecific competition effect abundance?

A

Members of the same species occupy the same niche and therefore compete for everything

42
Q

What is the carrying capacity?

A

The max stable population an ecosystem can support

43
Q

What does abundance vary with?

A

Biotic and abiotic factors

44
Q

What is a biotic factor?

A
  • Living factor- e.g. food competition
45
Q

What is an abiotic factor?

A
  • Non-living factor- e.g. water, sunlight, soil, temp
46
Q

How does interspecific competition effect abundance?

A
  • Competition between species- Abundance of one species effects the abundance of another (predator-prey)
47
Q

How can niches effect abundance?

A

Species with a similar niche will compete for resources

48
Q

Where will the greatest population size be?

A

In an environment with optimal abiotic factors

49
Q

What is a niche?

A

The role that an organism plays in an ecosystem

50
Q

What is a biotic relationship?

A

Interspecific relationship e.g. what it eats and what eats it

51
Q

What are examples of abiotic relationships?

A
  • The shade it creates- The O2 it uses and the CO2 is produces - The use of minerals e.g. nitrates
52
Q

Why dont two species share a niche?

A

Because they would compete for everything

53
Q

Where species have similar niches, what happens?

A

Interspecific competition

54
Q

How will the abundance of a species be affected by niches?

A

Abundance will be effected my interspecific competition therefore the more similar niches there are the greater the competition and the greater the effect on abundance

55
Q

How will distribution be effected by niches?

A

Distribution will vary because an organism can only exist where its niche exists

56
Q

What are transects and quadrats used for?

A

They are used to survey slow moving or immobile organisms e.g. plants

57
Q

What are transects an example of?

A

systematic sampling

58
Q

What do transects record?

A

How the distribution of plants species changes in a line

59
Q

What is a line transect?

A
  • Run a tape measure between two points- Record all species that touch the tape
60
Q

What is a belt transect?

A

Use quadrats along the length of the transect

61
Q

What is an interrupted transect?

A

Use quadrats at fixed intervals along the transect

62
Q

What is a frame quadrat and how do you use it?

A
  • Square frame divided into 100 sections- Random sampling to record the abundance of a plant species- Record the number of individuals of each species in the quadrat
63
Q

What is the species frequency?

A

How often a species is found in each square

64
Q

What is percentage cover and when is it used?

A
  • Used if a square is more than 50% covered by a species- Faster- Dont have to count all individuals
65
Q

Why do we use sampling techniques?

A

It may be impossible to count all the organisms of a species so we want to do many repeats of different samples to make them representative of a whole habitat/ecosystem so we can use the data collected to estimate the total number of individuals in the ecosystem

66
Q

What factors go into deciding how many samples you carry out?

A
  • Want the data to be representative- Larger numbers are more reliable- Too many is a waste of time and resources- Enough to carry out statistical tests - Calculating a running mean and then stopping sampling when the mean levels off
67
Q

Why would you use random sampling?

A
  • Avoid bias
68
Q

How can you sample randomly?

A

Divide sampling area into a grid and pick co-ords with a . random number generator

69
Q

What is an example of non-random sampling?

A

Systematic sampling where samples are taken at fixed intervals (transects)

70
Q

What is mark - release - recapture?

A

A sampling method used to estimate the abundance of a mobile species

71
Q

What is the equation for mark - release - recapture?

A

( Total no. caught in 1st sample X Total no. caught in 2nd sample ) / ( no. of marked in the second sample)

72
Q

What is the method for mark - release - recapture?

A
  1. Capture organisms 2. Mark organisms in a way that will not harm them/ affect ability to feed/ increase chance of predation3. Wait long enough for them to mix with population but not too long (birth/death/immigration/emmigration)4. Take second sample using the same method5. Use equation
73
Q

What is succession?

A

A series of changes in species composition in a given place over time

74
Q

What starts succession?

A

An area is colonised by a pioneer species which changes the environment to make it less hostile e.g. by increasing the nutrients

75
Q

What does a pioneer species allow for?

A

Continuous outcompeting by preceding species until a climax community is reached

76
Q

What happens as succession takes place?

A
  • Soil depth (hummus) increases- Water and nutrient availability increases - Biodiversity increases- Plant height increases- Niches increase - Light intensity at the ground decreases
77
Q

What is a climax community?

A
  • A stable equilibrium of species- Dominated by a few species- Final stage of succession
78
Q

What are the four types of succession?

A
  • Primary succession- Secondary succession- Deflected succession- Climax communities
79
Q

What is primary succession?

A
  • Starts from newly formed land (volcanic rock)- Harsh abiotic conditions (no soil/hummus/little water.little nutrients)- Very slow
80
Q

What is secondary succession?

A
  • Starts from land where vegetation has been cleared (deforestation/forest fire)- Less harsh abiotic factors (soil exists with some water and nutrients available)- Much faster- Pioneer species can be larger
81
Q

What is a deflected succession?

A
  • A community that remains stable only because human activity prevents natural succession taking place (mowing/grazing)- Stops succession (full plants cant grow because tips cut off/ cannot out compete low growing grass)- Grassland becomes the climax community
82
Q

What is a climax community?

A
  • Different ecosystems have different abiotic conditions so they develop different climax communities- Tropical rainforest/temperature deciduous forest

AQA A Level Biology (13 decks)

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