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A-Level Biology AQA > Populations and Ecosystems > Flashcards

Populations and Ecosystems Flashcards

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1
Q

what is a population?

A

a group of organisms of the same species living in the same habitat

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2
Q

what is a habitat?

A

the part of an ecosystem where an organism lives

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3
Q

what is a community?

A

all the populations of different species living in the same habitat at the same time

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4
Q

what is an ecosystem?

A

a community of all living and non living components of an environment (the biotic and abiotic factors)

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5
Q

what is a niche?

A

the role of a species within an ecosystem and their habitat, including their position in the food web and what they eat. no two species can have the same niche

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6
Q

what is the carrying capacity?

A

the maximum population size an ecosystem can support

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7
Q

what are the abiotic factors?

A

the non living features of an ecosystem eg the temperature and the water availability

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8
Q

what are the biotic factors?

A

the living factors eg. the presence of predators and food

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9
Q

the niche a species occupies within a population includes what?

A

its biotic interactions - what it eats and what its eaten by
its abiotic interactions - eg the oxygen it breaths in and the co2 it breaths out

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10
Q

what is a species?

A

organisms that can interbreed to produce fertile offspring

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11
Q

give 6 examples of abiotic factors

A
  • temperature
  • oxygen
  • carbon dioxide concentration
  • light intensity
  • pH
    -soil conditions
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12
Q

what is an adaptation?

A

a feature that increases an organisms chance of survival and reproduction

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13
Q

state and describe the three types of adaptation

A

behavioural = the way the organism acts, such as migrating to find food
physiological = internal biological functions helping the organism survive
structural = features of an organisms body that help it survive

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14
Q

by what process do adaptations develop?

A

natural selection

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15
Q

explain how natural selection increases an organisms chances of survival

A
  • organisms better adapted to the environment are more likely to survive and reproduce
  • by doing this, they will pass on their alleles
  • thus, the frequency of this allele will become increase within the population
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16
Q

give two examples of biotic factors that can affect population size

A

competition and predation

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17
Q

what is interspecific competition?

A

when members of different species compete for the same resources that are in limited supply.
(the individual better adapted to the environment is more likely to succeed in the competition)

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18
Q

what is intraspecific competition?

A

when members of the same species compete for resources and a mate. (individuals that are fitter, have more energy or are in better condition are more likely to attract the mate)

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19
Q

state 4 things that species may compete for

A
  • space
  • food
  • water
  • a mate
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20
Q

what is the general strategy for taking a random sample?

A
  • chose a random area to sample to avoid bias by dividing the field into a grid, and then using a random number generator to select coordinates
  • chose an appropriate technique to take a sample (eg. quadrats or transects)
  • repeat the process, taking as many samples as possible (reducing the likelyhood results are down to chance)
  • number of individuals in the whole area can be estimated by taking a mean of the data in each sample and then multiplying it by the size of the whole area
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20
Q

describe the population relationship between predators and prey

A
  • as the prey population increases, theres more food for the predators, so the predator population increases.
  • however, as the predator population increases, more prey is eaten, so the prey population begins to fall.
  • this means theres less food for the predators, so their population decreases too.
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21
Q

how to ensure samples accuratley represent the population?

A

random sampling in uniform areas to eliminate bias
- line transects to examine a change over distance
- a large number of samples (30+) to ensure your accuratley representing the population

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22
Q

when is it appropriate to use a quadrat?

A
  • when the sample contains slow/non moving organisms
  • when the organisms are uniformly distributed in the area
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23
Q

when do we use a line transect?

A
  • when there is uneven distribution of organisms in the area (populations that change over distance)
  • when the sample contains slow/non moving organisms
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24
Q

with moving organisms, what sampling technique do we use?

A

mark-release-recapture method

25
Q

how would a student use a quadrat to estimate a sample population on a uniformly distributed field of daisies? (6)

A
  1. lie two tape measures at a right angle to create a gridded area
  2. use a random number generator to generate two coordinates
  3. place the quadrat and collect the data (calculate the percentage cover or the frequency of the daisies)
  4. repeat this process at least 30 times and then calculate a mean, before multiplying by the size of the field.
26
Q

what are the two different types of line transect?

A

the belt transect and the interrupted belt transect

27
Q

how does a belt transect work?

A

the quadrats are placed next to eachother along the transect

28
Q

how does an interrupted belt transect work?

A

the quadrat is placed at uniform intervals along the tape measure with spaces in between them eg. every five metres (to cover a larger distance OR if not much distance will be observed using a belt transect)

29
Q

describe a method as to how a student would set up and conduct a sampling experiment using a line transect (4-6)

A
  • place a tape measure at a right angle to the shore line
  • take a 1m quadrat divided into 100 squares and place it next to the tape measure every 5 meters/ next to eachother
  • count the squares containing organism and calculate the percentage cover, then record this in a table
  • repeat by placing another 30 transects at right angles to the shore line along your sampling area
30
Q

state and describe the different methods that can be used to estimate the abundance of a species

A
  1. local frequency = the % of squares in the quadrat with the species present
  2. density = count how many of one species you have within the quadrat (eg how many daisies) and then apply this to the area of the field
  3. percentage cover = the % of full squares occupied within the quadrat
31
Q

what are the advantages and disadvantages of using the local frequency method?

A

advantages = quick method to sample a large area, and useful if its too difficult to identify individual organism or too many to count

disadvantages = poor accuracy as it doesnt consider overlapping plants or the size of the plant

32
Q

what are the advantages and disadvantages of using the density method?

A

more accurate if you can easily distinguish an individual plant, and there are not too many to count. can be used to estimate species richness

more time consuming

33
Q

what are the advantages and disadvantages of using the percentage cover method

A

advantages = quicker method than density, and useful if its too difficult to identify the individual organism or if theres too many to count

disadvantages = subjective, which limits accuracy. and doesnt consider overlapping plants or the size of the plant

34
Q

describe how you could estimate the size of a population of sundews (motile species) in a small marsh

A
  • capture sample, mark them and release them back into the environment
  • leave time for them to disperse before the second collection
  • the population is equal to (number marked in first sample x the total number in second sample) / the number marked in second sample
35
Q

state the four different phases of a sample population growth curve

A

lag phase
log phase
stationary phase
death phase

36
Q

recall six events that occur during the lag phase on a population growth curve

A

genes switch on
enzyme synthesis
dna replication
protein synthesis
digestion and absorption

37
Q

recall four events that occur during the log (exponential) phase on a population growth curve

A

high nutrient availability
high oxygen levels
less intra-specific competition
waste products havent yet reached a toxic level

38
Q

recall what happens during the stationary and death phases on a population growth cure

A

stationary = the birth rate is equal to the death rate
death = the birth rate is lower than the death rate

39
Q

why is a log scale used to record the number of cells?

A

because there is a large range / increase in numbers

40
Q

define succession

A

the gradual directional change in an ecological community over time

41
Q

what are each of the stages during succession called?

A

the seral stages

42
Q

what is the final seral stage of succession? (the end result)

A

the climax community

43
Q

what are the two types of succession?

A

primary and secondary succession

44
Q

when does primary succession occur?

A
  • happens on land thats been newly formed or exposed - eg where a volcano has just erupted or where sea level has dropped exposing land
  • theres no soil or organic material to begin with, just bare rock
45
Q

what is the first species to ever colonise bare rock or sand called?

A

the pioneer species

46
Q

what are pioneer species adapted to do?

A

survive in harsh abiotic factors

47
Q

describe and explain how succession occurs

A
  • pioneer species colonise the area
  • they then change the environment and make it less hostile by decaying, leaving behind a soil called humus that contains nutrients
  • this enables other species colonise the area and survive
  • some new species change the environment, which makes it les suitable for the previous species
  • the soil becomes more fertile, so a range of plants can grow which increases the habitats for other organisms
  • biodiversity changes (increases)
  • the environment becomes more stable, and the climax community forms after a few hundred years
48
Q

when does secondary succession occur?

A

when a primary succession becomes disrupted - eg. the present community becomes destroyed.
- so, succession starts again, but the soil is already created so it does not start from the bare rock seral stage.

49
Q

what happens during secondary succession?

A

species richness and number of organisms increases (biodiversity increases)
- as succession occurs, larger plant species and animals colonise the area
- therefore food webs become more complex

50
Q

define what is meant by conservation

A

the maintenance of biodiversity and genetic diversity within a species and also the variety of habitats and ecosystems

51
Q

what is typically the reason for the destruction of habitats, and what does this lead to?
what is done because of this?

A

human activity
a loss of food and space for organisms and can lead to extinction

to conserve habitats, succession is often managed.

52
Q

what are the advantages of maintaining earlier stages of succession and preventing the climax community?

A

a greater variety of habitats are conserved and therefore a greater range of species

53
Q

what is speciation?

A

the process that results in the creation of a new species

54
Q

why does speciation occur?

A

because one original population of the same species becomes reproductivley isolated, which means there are now two populations of the same species that cannot breed together

55
Q

what is the consequence of speciation

A

the accumulation of differences in their gene pools, causing a change in phenotype - to the extent that the two populations would be unable to interbreed to produce fertile offspring - and therefore classed as two different species

56
Q

what are the two ways organisms can become reproductivley isolated?

A

allopatric speciation
sympatric speciation

57
Q

what is allopatric speciation and explain how it works

A

when populations are separated georgraphically, by a physical barrier.
this means the populations will experience slightly different conditions, and therefore different selection pressures. so, different changes in allele frequencies occur. different alleles will become more advantageous in different populations. the changes in allele frequency will lead to changes in the gene pools of the separated populations, causing changes in phenotype frequencies. over generations, individuals from the different populations will have changed so much that they wont be able to breed with eachother to produce fertile offspring, so they have become reproductivley isolated.

58
Q

what is sympatric speciation and explain how it works

A

occurs when two populations are geographically in the same location, but random mutations occur within the population, preventing members of that population breeding with the other members of the species. this can be due to differences in behaviour (eg the mutation affected the courtship ritual) or even changes in when individuals become fertile. these would mean they would not be able to reproduce together and there will be no gene flow between the two groups of organisms. over generations, these reproductivley isolated populations will accumulate different mutations to the extent their DNA is so different they cannot interbreed to create fertile offspring and therefore are classed as two different species.

59
Q

what is genetic drift? and why does it affect smaller populations more than larger populations?

A

the change in allele frequency within a population between generations.
- it only has an impact on smaller populations.
- only substantial genetic drift results in evolution.
- however in smaller populations, even the slightest change in allele frequency has a large impact.

A-Level Biology AQA (5 decks)

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