1
Q
What are species
A
a group of similar organisms that can reproduce to give fertile offspring
2
Q
what is a Population
A
is a group of organisms of the same species living in a particular habitat at a particular time, so they have the potential to interbreed
3
Q
What is community
A
consist of populations of ALL different species within an area.
4
Q
whats an ecosystem
A
is the community (biotic), plus all the abiotic (non-living) conditions in that area
5
Q
whats habitat
A
is a small part of the ecosystem where a population lives
6
Q
whats a niche
A
- Niche is the role that a species plays in within a community; 2. Includes food resources; 3. No two species can occupy identical niche;
7
Q
Whatre abiotic factors
A
the non-living features of the ecosystem eg temperature, availability of water
8
Q
whatre biotic factors
A
- the living features of then ecosystem eg predators, parasites, prey
9
Q
suggest 2 reasons for conserving rainforests
A
maintain biodiversity
preserve habitats
10
Q
Habitat vs niche
A
Within an ecosystem, the biotic and abiotic factors determine the habitat for each population. More than one species may occupy the same habitat however only one species has its own unique niche. This is governed by its adaptations to the biotic and abiotic factors in that niche.
A niche is the role of a species within its ecosystem or community – what it eats, where it eats and when it eats. Niches
can be separated by time, location, or behaviour.
If two species tried to occupy the same niche, the most successful would outcompete the other and only one would
remain.
11
Q
what’s an allele
A
one of a number of alternative forms of a gene
12
Q
whats a locus
A
the location of a gene on a chromosome.
13
Q
what’s diploid
A
nucleus contains 2 sets ofchromosomes.
14
Q
whats haploid
A
cells that contain only a single copy of each chromosome, e.g. (usually) the sex cells or gametes.
15
Q
Define phenotype
A
- Expression of genetic constitution of a genotype; And its interaction with the environment;
16
Q
Define genotype.
A
The genetic constitution of an organism
17
Q
If a gene is sex-linked on the X chromosome, why
is the phenotype more common in XY organisms
A
Males have one allele; Females need two recessive alleles
18
Q
Mutation is one cause of genetic variation in
organisms.
Give two other causes of genetic variation.(2)
A
1. Crossing over; 2. Independent segregation of homologous chromosomes
3. Random fertilisation
19
Q
In genetic crosses, the observed phenotypic ratios
obtained in the offspring are often not the same
as the expected ratios.
Suggest two reasons why
A
1. Small sample size; 2. fertilisation of gametes is random;
3. Linked Genes; 4. Epistasis; 5. Lethal genotypes;
20
Q
Name the relationship between two alleles when both alleles appear in the phenotype
A
Co-dominance
21
Q
Name the type of gene interaction when one gene
affected the expression of another
A
epistasis
22
Q
Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results?
Give the reason for your choice of statistical test.
A
1. Chi squared test; 2. Categorical data.
23
Q
whats homozygous and heterozygous
A
Heterozygous: when the alleles are
different for a particular gene eg Bb.
Homozygous: when the alleles are the
same for a particular gene eg BB or bb
24
Q
whatre recessive and dominant alleles.
A
Recessive allele: only
expressed in the when 2 copies are present
Dominant allele: always shown
25
what do mohybrid crosses show?
inheritance of the alleles of one gene
26
whats sex linkage?
when a gene is sex linked if its located on a sex chromosome. often recessive Allele written as X with a superscript eg 2
X
27
What do dihybrid crosses show
inheritance of the alleles of 2 genes.
the 2 genes may be located on separate chromosomes and act completely independently or
they may be linked. In this case it is called AUTOSOMAL LINKAGE and it means that the 2
genes are on the same chromosome and so the alleles of the 2 genes on the chromosome
will be inherited together unless crossing over has separated them. These will give very
different expected phenotype ratios to unlinked genes.
if the 2 genes are on sep chrosomes an allele from one pair of chromosomes can enter a gamete w either allele from the other pair.
28
whats codominance
both alleles are expressed in the phenotype
29
explain why males are more likely to express a recessive x linked allele
females (XX) have 2 alleles, only express allele if homozygous recessive.
males (XY) have 1 allele, recessive allele always expressed
30
whats epistasis
when the expression of one gene may supress the expression of another gene.
31
explain how autosomal linkage affects inheritance of alleles
2 genes located on same autosome
so alleles on same chromosome inherited together. stay together during independent segregation of homologous chromosomes during meiosis
but crossing over between homologous chromosomes can create new combinitation of alleles. if the genes are closer together on an autosome, theyre less likely to be split by crossing over
31
whats autosomal linkage
when 2 genes are linked on the same chromosome, the alleles
of the genes present on that chromosome will always be inherited together unless they are separated by crossing over.
The closer the gene loci are the less likely that crossing over will
occur between them and separate them.
When two genes are on different chromosomes then all
combinations of the alleles of both genes are possible because of
independent segregation.
32
what are the 3 statistical tests in biology
Chi-squared test when the data are categoric (frequencies) – used in inheritance to test whether the
expected phenotypic ratios are significantly different from the observed ratios
Student’s t test when comparing the mean values of two data sets
A correlation coefficient when examining an association between two sets of data
33
Describe when you would accept the null hypothesis for the 3 statistical tests used in biology
chi squared- no sig difference between observed/exp results
t test- no sig diff between the means being compared
correlation coefficient - no sig dif between 2 values.
34
whats a gene pool
total number of alleles in a population. species with a more diverse gene pool more stable and more likely to survive if selection pressures change.
35
whats allele frequency
proportion of an allele in a gene pool
36
what can change the gene pool and allele frequency?
Natural selection and speciation due to selection pressures.
genetic drift can also alter the gene pool by chance, has larger effect in smaller populations
37
what are selection pressures
act on certain genes and can change allelic frequency and gene pool
38
what does the hardy weinberg principle state and what are the conditions under which the principle applies
allele frequencies will not change from generation to generation given:
large population
no immigration/emigration
no mutations
no selection for/against alleles
mating is random.
39
explain why individuals within a population may show a wide range of variation in phenotype.
mutations, crossing over between homologous pairs of chromosomes during meiosis, independent segregation of homologous chromosomes during meiosis, random fertilisation of gametes during sexual reproduction, env factors
40
whats evolution
Evolution is a change in allele frequencies in populations over time. This can occur through the process of
1. Natural Selection or
2. Genetic Drift
41
principles of natural selection
MUTATION - creates new alleles increasing the genetic diversity of the individuals within a population.
ADAPTED - selection pressures eg disease, predation and competition create a struggle for survival with some individuals being better adapted than others
REPRODUCE - those better adapted survive to reproduce and pass on their beneficial alleles
INHERIT - a greater proportion of the next generation inherit those alleles and they then survive,
reproduce and pass on those alleles
ALLELE FREQUENCY - there is an increase in that allele frequency
42
describe the effects of stabilising selection
organisms with alleles coding for average variations of a trait have a selective advantage
so frequency of alleles coding for average variations of a trair increase and those coding for extreme variations of a trait decrease
so range is reduced
43
Explain the effects of directional selection
Organisms with alleles coding for one extreme
variation of a trait have a selective advantage
(eg. bacteria with high resistance to an antibiotic)
● So frequency of alleles coding for this extreme
variation of the trait increase and those coding for
the other extreme variation of the trait decrease
44
Explain the effects of disruptive selection
Organisms with alleles coding for either extreme
variation of a trait have a selective advantage
● So frequency of alleles coding for both extreme
variations of the trait increase and those coding for
the average variation of the trait decrease
● This can lead to speciation
45
Describe speciation (how new species arise from existing species
1. Reproductive separation of two populations (of the same species)
2. This can result in accumulation of differences in their gene pools
3. New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring
46
Describe allopatric speciation
1. Population is split due to geographical isolation
2. This leads to reproductive isolation, (separating gene pools by preventing interbreeding & seperate gene pools form)
3. Different selection pressures (act on each population)
4. variation due to mutations
5. So different advantageous alleles are passed on in each population
6. Eventually different species cannot (inter)breed to produce fertile offspring
47
Describe sympatric speciation
1. Not geographically isolated; / same habitat
2.mutation causes reproductive isolation
3.Gene pools kept separate
4.Different alleles passed on
5.Cannot breed to produce fertile offspring;
disruptive selection
48
List the factors that influence carrying capacity
The maximum (stable) population size of a species that an ecosystem can support
Abiotic factors Eg. light intensity, temperature, soil pH & mineral content, humidity
Interactions between organisms
a. Interspecific competition - between organisms of different species
b. Intraspecific competition - between organisms of the same species
c. Predation (predators kill and eat other animals, called prey
49
Explain how abiotic factors may affect population size / carrying capacity
If conditions favourable, organisms more likely to survive & reproduce → increasing carrying capacity
● Eg. increasing light intensity increases rate of photosynthesis, increasing nitrates increases protein
production and increasing phosphates increases phospholipid production in plants
○ This increases carrying capacity of a variety of plant species
○ So increases the number and variety of habitats, niches and food sources for animals
○ So increasing carrying capacity of a variety of animal species
50
Explain how interspecific competition may affect population size
Reduces [named resource] available to both species, limiting their chances of survival & reproduction
○ So reduces population size of both species
● If one species is better adapted, it will outcompete the other
○ So population size of less well adapted species declines, potentially leading to extinction
51
Explain how intraspecific competition may affect population size
1. As population size increases, resource availability per organism decreases, so competition increases
○ So chances of survival & reproduction decrease → population size decreases
2. As population size decreases, resource availability per organism increases, so competition decreases
○ So chances of survival & reproduction increase → population size increases
52
Explain the changes which occur in populations of predators & prey
1. Prey population increases so predators have more food
○ So more predators survive & reproduce
2. Predator population increases so more prey killed & eaten
○ So less prey survive & reproduce
3. Prey population decreases so predators have less food
○ So less predators survive & reproduce
4. Predator population decreases so less prey killed & eaten
○ So more prey survive & reproduce (cycle repeats)
53
Describe how the size of a population of slow-moving or non-motile organisms can be estimated
1. Divide area into a grid / squares eg. place 2 tape measures at right angles
2. Generate a pair of coordinates using a random number generator (eg. on a calculator)
3. Place a quadrat here and count number / frequency of [named species]
4. Repeat a large number of times (10 or more) and calculate a mean per quadrat
5. Population size = (total area of habitat / quadrat area) x mean per quadrat
54
What assumptions does the mark-release-recapture method make?
● Capture sample of species, mark and release
● Ensure marking is not harmful / does not affect survival
● Allow time for organisms to randomly distribute before collecting second sample
● Population = (number in sample 1 x number in sample 2) /number marked in sample 2
55
Suggest why the mark-release-recapture method can produce unreliable results in very large areas
● Unlikely that organisms will distribute randomly / evenly
● Less chance of recapturing organisms (that were marked initially)
56
Describe and explain how primary succession occurs
1. Colonisation by pioneer species (first to colonise)
2. Pioneer species change the environment
○ Eg. they die and decompose, forming soil which retains water (humus / organic matter)
3. Environment becomes less hostile for other species
(AND less suitable for previous species, so better adapted species outcompete previous species)
4. (As succession goes on,) Increase in biodiversity
5. Climax community
57
Describe features of a climax community
● Same species present over a long time
● Abiotic factors (fairly) constant over time
● Populations stable
58
Explain how conservation of habitats involves management of succession
Further succession can be prevented to stop a climax community forming
○ By removing or preventing growth of species associated with later stages eg. by allowing grazing
● This preserves an ecosystem at a certain point / in its current stage of succession (plagioclimax)
● So early species are not outcompeted by later species and habitats / niches are not lost
59
Describe the conflict between human needs and conservation as well as the importance of managing this
● Human demand for natural resources (eg. timber) is leading to habitat destruction / biodiversity loss
● Conservation is needed to protect habitats / niches / species / biodiversity
● Management of this conflict maintains the sustainability of natural resources
○ Meeting current needs without compromising the ability of future generations to meet theirs
60
mark release recapture assumptions
no immigration
no losses to predation
marking doesnt affect survival
birth rate and death rate equal
61
mark release recapture method
1. collect sample, mark and release;
2. Ensure marking doesn't affect survival
3. ensure mark is not removed
4. Allow time for x to distribute before collecting a second sample;
5. (Population =) number in first sample ×
number in second sample divided by number
of marked fish in second sample
62
Describe how you could estimate the size of a
population using random sampling
1. Use a grid
2. use a computer generator to obtain random coordinates
3. Count frequency in a quadrat
4. Large sample and calculate mean number (per quadrat);
5.multiply mean number of plants per m2 by area of a field.
63
The scientist used percentage cover rather
than frequency to record the abundance of
algae present. Suggest why
too many to accurately count
64
Describe use of systematic
sample to count plants
1. Systemic sampling at regular intervals along transect line;
2. Transect line from /to ……..;
3. Count frequency in a quadrat
4. Large sample and calculate mean
65
whats the carrying capacity
maximum stable population size that an ecosystem can supportt can be altered by
natural or human activity that alter the limiting factors
66
whats interspecific and intraspecific competitiom
Interspecific competition – between different species. The more similar the niches, the more competition.
Intraspecific competition – within a species. Animals often have their own territories to reduce this competition but there is usually competition for a mate
67
whats succession
the process by which an ecosystem changes
over time. The plant and animal communities change as the abiotic conditions change.
68
whats Primary succession
the starting point is land newly formed or exposed eg after a volcanic eruption or where sea level has dropped. There is no soil or organic material to start with, just bare rock
69
whats secondary succession
this happens on land that has been cleared of all the plants. There is soil eg after a forest fire or deforestation
This happens in the same way as primary succession, but soil is already present so succession begins at a later stage and the climax community is reached faster.
70
whats variation
variation results in individuals showing wide range of phenotypes. same genes different alleles. brought abt by
New alleles - due to random DNA mutations
* New combinations of alleles – due to crossing over and independent segregation in meiosis, and
also random fertilisation.
71
whats the bottleneck effect
A random reduction in population size alters the gene pool (allelic frequency) by chance.
The remaining population will increase over time yet some alleles have increased and others decreased
72
whats the founder effect
A migration of a small number of the population alters the gene pool (allelic frequency) by chance. The
new population will increase over time, yet
some alleles have increased, and others
decreased.
73
whats allopatric speciation
New species form from different populations from isolated populations
74
whats sympatric speciation
Formation of new species
From a population without geographical isolation
75
A Level Biology
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