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A-Level Biology AQA > 7. Genetics Populations and Ecosystems > Flashcards

7. Genetics Populations and Ecosystems Flashcards

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1
Q

what is a population?

A

a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

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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. governed by adaptation to abiotic and biotic factors. no two species 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 (can exist as one or more populations)

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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 evolution?

A

the change in the allele frequencies in a population

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13
Q

what are the three types of selection?

A

directional
stabillising
disruptive

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14
Q

what is directional selection?

A

when the extreme trait has the selective advantage, so organisms with alleles that code for an extreme trait are more likely to survive and reproduce. this is in response to an environmental change.

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15
Q

what is stabilising selection?

A

when the modal trait (organisms with alleles that code for characteristics towards the middle of the range) are more likely to survive and reproduce. occurs when there is no environmental change.

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16
Q

what is disruptive selection?

A

when extreme traits on both ends of the range have the selective advantage

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17
Q

what is an adaptation?

A

a feature that increases an organisms chance of survival and reproduction

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18
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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19
Q

by what process do adaptations develop?

A

natural selection

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20
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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21
Q

give two examples of biotic factors that can affect population size

A

competition and predation

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22
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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23
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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24
Q

state 4 things that species may compete for

A
  • space
  • food
  • water
  • a mate
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25
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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26
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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27
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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28
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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29
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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30
Q

with moving organisms, what sampling technique do we use?

A

mark-release-recapture method

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31
Q

describe how the mark-release-recapture method works

include the equation

A
  • an initial sample of the population is captured
  • these individuals are marked and then released back into the wild, and the number of marked individuals is recorded (mark must be weather resistant)
  • marked individuals are then left for a period of time to allow them to randomly disperse throughout the habitat
  • the second sample is then captured
  • the total number captured in the second sample is recorded, and the number recaptured is also recorded
  • the process is repeated multiple times, and a mean is then calculated for more reliable results

population size = (number initially captured x number in second sample) / number marked in second sample

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32
Q

what are the ethics to consider when doing the capture-recapture method?

A
  • how organisms are captured and marked must not cause permanent harm
  • the mark must be non toxic
  • mark must not increase chances of predation or reduce chances of reproduction
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33
Q

what are the assumptions associated with the capture recapture method?

A
  • that the population size is constant (no birth/death or migration)
  • that the animals always distribute evenly (they may all huddle near food in reality)
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34
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.
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35
Q

what are the two different types of line transect?

A

the belt transect and the interrupted belt transect

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36
Q

how does a belt transect work?

A

the quadrats are placed next to eachother along the transect

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37
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)

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38
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
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39
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
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40
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

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41
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

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42
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

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43
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
44
Q

state the four different phases of a sample population growth curve

A

lag phase
log phase
stationary phase
death phase

45
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

46
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

47
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

48
Q

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

A

because there is a large range / increase in numbers

49
Q

define succession

A

the gradual directional change in an ecological community over time

50
Q

what are each of the stages during succession called?

A

the seral stages

51
Q

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

A

the climax community

52
Q

what are the two types of succession?

A

primary and secondary succession

53
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
54
Q

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

A

the pioneer species

55
Q

what are pioneer species adapted to do?

A

survive in harsh abiotic factors

56
Q

describe and explain how primary 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
57
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.

58
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

59
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

60
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.

61
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

62
Q

what is speciation?

A

the process that results in the creation of a new species

63
Q

what is the primary source of genetic variation?

A

mutation

64
Q

name two other factors that produce further genetic variation

A
  • meiosis
  • random fertilisation of gametes
65
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

66
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

67
Q

what are the two ways organisms can become reproductivley isolated?

A

allopatric speciation
sympatric speciation

68
Q

what is allopatric speciation and explain how it works

A

when populations are separated geographically, 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.

69
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.

70
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.

71
Q

what is the gene pool?

A

the complete range of alleles present in a population

72
Q

what is a locus?

A

the fixed location of a gene on a chromosome

73
Q

define diploid

A

term applied to cells in the nucleus that have two sets of chromosomes

74
Q

define haploid

A

a term applied to cells in the nucleus that only contain a single copy of each chromosome

75
Q

what is an allele?

A

one of a number of alternatives forms of a gene

76
Q

what is a recessive allele?

A

an allele that is only expressed in the phenotype when both alleles are recessive/no dominant allele

77
Q

what is a dominant allele?

A

an allele that is always expressed in the phenotype of an organism

78
Q

define codominant?

A

when both alleles are expressed in the phenotype

79
Q

define homozygous

A

when the alleles are the same for a particular gene

80
Q

define heterozygous

A

when the alleles are different for a particular gene

81
Q

define genotype

A

the genetic constitution of an organism

82
Q

define phenotype

A

the physical characteristics of an organism due to its genotype and its interaction with the environment

83
Q

what letter chromosomes do males have?

what letter chromosomes do females have?

A

males = XY
females = XX

84
Q

are there any alleles on the Y chromosome?

A

no

85
Q

what is a carrier?

A

an individual who is heterozygous for a condition (caused by a recessive allele), but it is not expressed in their own phenotype, and can be passed on to their offspring

86
Q

explain why a trait caused by a recessive allele would be more common in men than in women

A
  • males are XY and females are XX /males only have one X chromosome, whereas females have two
  • males only have one allele of the gene, recessive allele is always expressed
  • whereas female needs two recessive alleles/recessive allele may be masked by a dominant allele
  • as there are no alleles on the Y chromosome
87
Q

when dealing with dihybrid parents, what method do we use to determine the gametes?

A

FOIL
first, outside, inside, last

88
Q

what ratio will offspring be produced in if organisms are heterozygous for both genes

A

9:3:3:1

89
Q

what ratio will offspring be produced in if organisms are heterozygous and linked?

A

3:1

90
Q

what is autosomal linkage?

A

when two genes are on the same chromosome

91
Q

what is an autosome?

A

any chromosome that ISNT a sex chromosome

92
Q

what would be the evidence for a recessive trait on a pedigree analysis chart?

A

two parents that do not have the trait but an offspring that does

  • this means the parents must be heterozygous carriers, as they have the recessive allele but its not expressed in their phenotype
93
Q

what would be the evidence for a dominant trait on a pedigree analysis chart?

A

two parents who do have the condition, and a child that does not

  • this is because the parents must be heterozygous dominant and therefore carriers of the recessive allele
94
Q

what is sex linkage?

A

when the gene is on the X or Y chromosome

95
Q

what is the evidence for a sex linked trait

A

always seen in males and not in females (only the case if trait is recessive)

96
Q

what is the evidence that a trait is not sex linked on a pedigree analysis chart?

A

males and their daughters = males always pass their X chromosome onto their daughters.
an affected male cannot have an unaffected daughter if condition is caused by a dominant allele

OR

mothers and their sons = if it was sex linked, sons always inherit their X chromosome from their mothers.
with a condition caused by a recessive allele, an affected mother cannot have an unaffected son.

97
Q

what is epistasis?

A

the interaction of different genes. when the gene at one locus influences the expression of another gene at another locus

98
Q

what is the general null hypothesis in genetics?

A

there is no significant difference in the phenotype ratio expected of___ and the phenotype ratio observed. Any deviation from the expected ratio is due to chance.

99
Q

what is the purpose of the chi squared experiment?

A

to compare how well the observed results match the expected results

100
Q

method for answering a chi-squared question

A
  • work out the expected number of organisms by applying the ratio to the actual number of organisms
  • take the observed values from the expected values (O-E)
  • square each value of O-E
  • divide (O-E)^2 by the expected values
  • then add together all the values from the previous step
  • choose your number of degrees of freedom by subtracting 1 from the total number of phenotypes
  • always use 0.05 probability
  • if the chi squared value is LESS than the critical value, you can accept the null hypothesis (difference isnt significant)
  • if the chi squared value is GREATER than the critical value, reject the null hypothesis as the difference IS significant

then answer the question like this : using __ degrees of freedom and 0.05 probability, the critical value was__. the chi squared value is __ which is less/more than the critical value, so we can accept/reject the null hypothesis as the difference is/isnt significant and there is a 0.05 probability the results are/arent due to chance

101
Q

what is allele frequency?

A

the proportion of a particular type of allele in a population

102
Q

what is genotype frequency?

what is phenotype frequency?

A
  • the proportion of a particular genotype combination in a population
  • the proportion of a particular physical characteristic in a population
103
Q

what does the hardy weinberg principle state?

A

the frequencies of dominant alleles, recessive alleles, and genotypes wont change in a population from one generation to the next if certain conditions are met

104
Q

what are the 5 conditions required for the hardy weinberg principle

A
  • very large population
  • no emmigration or immigration
  • no mutations
  • random mating
  • no selection pressures & natural selection
105
Q

what are the two hardy weinberg equations?

what do the different components of the equation mean?

A

p+q=1
p2 + 2pq + q2

p = frequency of the dominant allele
q = frequency of the recessive allele

p2 = frequency of dominant homozygous allele
2pq = frequency of dominant heterozygous genotype
q2 = frequency of recessive homozygous genotype

106
Q

in the hardy weinberg calculation, what is the frequency of dominant alleles (homozygous and heterozygous) represented by?

how would you rearrange the equation to find p2?

A

p2 + 2pq

take this from one and then square root

A-Level Biology AQA (7 decks)

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