Unit 7

Question 1

Community

Answer 1

All the populations of different species living in the same place (habitat) at the same time.

Question 2

Ecosystem

Answer 2

A community and the non-living (abiotic) components of its environment.

Question 3

Niche

Answer 3

-The specific role of a species within its habitat.
-Governed by its adaptation to both abiotic and biotic conditions.

Question 4

Advantage of species occupying different niches

Answer 4

-Less competition for food/ resources.
-If two species tried to occupy the same niche, one would outcompete the other.

Question 5

Carrying capacity

Answer 5

Maximum (stable) population size of a species that an ecosystem can support.

Question 6

Factors that influence carrying capacity

Answer 6

-Abiotic factors
-Interspecific competition (between different species)
-Intraspecific competition (between same species)
-Predation

Question 7

How abiotic factors affect pop size/ carrying capacity?

Answer 7

-If conditions are favourable, organisms are more likely to survive and reproduce.
-Increases carrying capacity.

Question 8

How interspecific competition may affect pop size/ carrying capacity?

Answer 8

-Reduced resources available to both species, limiting their chances of survival and reproduction.
-Reduces population size of both species.
-If one species is better adapted, it will outcompete the other.
-So pop size of less adapted reduces, leading to extinction.

Question 9

How intraspecific competition may affect pop size/ carrying capacity?

Answer 9

-As pop size increases, resources availability per organism decreases, so competition increases.
-Chances of survival and reproduction decreases, pop size decreases.
-As pop size decreases, resource availability per organism increases, so competition decreases.
-Chances of survival and reproduction increases, pop size increases.

Question 10

Explain pop change of predator and prey

Answer 10

-Prey increase so predators have more food, more predators survive and reproduce.
-Predator increase so more prey likely to be killed and eaten, less prey survive and reproduce.
-Prey decreases so predators have less food, less predators survive and reporduce.
-Predator decreases so less prey killed and eaten, so more prey survive and reproduce.
-Cycle repeats.

Question 11

Pop of slow-moving/ non-motile organisms

Answer 11

-Divide area into grid/squares.
-Generate a pair of co ordinates using a random number generator.
-Place quadrat here and count frequency of species.
-Repeat for a large number of times and calculate a mean per quadrat.
-Pop size= (total area of habitat/ quadrat area) x mean per quadrat.

Question 12

Mark-release-recapture for motile organisms

Answer 12

-Capture sample of species, mark and release.
-Ensure marking isn’t harmful/ doesn’t affect survival.
-Allow time for organisms to randomly distribute before collecting second sample.
Pop= (Number in S1 x Number in S2) / Number marked in S2

Question 13

Assumptions of mark-release-recapture

Answer 13

-Sufficient time for marked individuals to distribute evenly in pop.
-Marking not removed and doesn’t affect chances of survival/ predation.
-Limited immigration/emigration.
-No/few births/deaths/breeding/changes in pop size.

Question 14

Reliability of mark-release-recapture

Answer 14

-Unlikely that organisms distribute evenly.
-Less chance of recapturing organisms.

Question 15

Succession

Answer 15

Change in community over time due to change in abiotic factors.

Question 16

Primary succession

Answer 16

-Colonisation by pioneer species (first to colonise).
-Pioneer species change abiotic conditions (die and decompose to form soil).
-So environment becomes less hostile for other species with different adaptations and less suitable for previous species.
-Better adapted species outcompete previous species.
-As succession goes on, biodiversity increases.
-Climax community reached- final stable community.

Question 17

Climax community- features

Answer 17

-Same species present over a long time.
-Abiotic factors remain constant.
-Pop stable

Question 18

Management of succession- conservation of habitats

Answer 18

-Further succession can be prevented to stop climax community forming.
-By removing/ preventing growth of species associated with later stages.
-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.

Question 19

Managing conservation- human needs

Answer 19

-Human demand for natural resources 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.

Question 20

Genotype

Answer 20

Genetic constitution of an organism.

Question 21

Phenotype

Answer 21

The expression of this genetic constitution (genotype) and its interaction with the environment.

Question 22

Allele

Answer 22

Variations of a particular gene- arise by mutation (change in DNA base sequence).

Question 23

How many alleles of a gene can be found in diploid organisms?

Answer 23

-2 as diploid organisms have 2 sets of chromosomes- homologous pairs.
-May be many alleles of a single gene in a population.

Question 24

Dominant allele

Answer 24

Always expressed- shown in the phenotype

Question 25

Recessive allele

Answer 25

Only expressed when 2 copies present (homozygous recessive), not expressed when dominant allele present (heterozygous).

Question 26

Codominant alleles

Answer 26

Both alleles expressed and contribute to phenotype.

Question 27

Sex-linked gene

Answer 27

A gene with a locus on a sex-chromosome (normally X).

Question 28

Explain how autosomal linkage affects inheritance of alleles

Answer 28

-Two genes located on same autosome (non-sex chromosome). -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 combinations of alleles. -If the genes are closer together on an autosome, they are less likely to be split by crossing over.

Question 29

Worked example- autosomal linkage

Answer 29

-The two genes are linked/ autosomal linkage. -No crossing over occurs, genes are close together. -So only GL and gl gametes produced but Gl and gL gametes produced. -No Ggll and ggLl offspring produced.

Question 30

Epistasis

Answer 30

Interaction of products of non-linked genes where one masks/ suppresses the expression of the other.

Question 31

When can chi-squared test be used?

Answer 31

-When determining if observing results are significantly different from expected results (frequencies). -Data is categorical- can be divided into groups.

Question 32

Why are ratios not the same as offspring?

Answer 32

-Fusion/ fertilisation is random. -Autosomal linkage/ epistasis/ sex-linkage. -Small sample size- not representative of whole population. -Some genotypes may be lethal (cause death).

Question 33

Population

Answer 33

-A group of organisms of the same species in a particular space at a particular time. -That can potentially interbreed to produce fertile offspring.

Question 34

Gene pool

Answer 34

All the alleles of all the genes in a population at any one time.

Question 35

Allele frequency

Answer 35

Proportion of an allele of a gene in a gene pool.

Question 36

Hardy-Weinburg principle and conditions

Answer 36

Allele frequencies will not change from generation to generation, given: -Population is large -No immigration/ emigration (to introduce/ remove alleles) -No mutations to create new alleles -No selectin for/against particular alleles -Mating is random

Question 37

Hardy-Weinburg equation

Answer 37

p^2 +2pq +q^2 = 1 p= dominant allele q= recessive allele p^2= homozygous dominant genotype q^2= homozygous recessive genotype 2pq= heterozygous genotype

Question 38

How individuals show variation?

Answer 38

Genetics factors -Mutations -Crossing over between homologous chromosomes during meiosis -Independent segregation of homologous chromosomes during meiosis -Random fertilisation of gametes during sexual reproduction Environmental factors

Question 39

Evolution

Answer 39

-Change in allele frequency over time/ many generations in a population. -Occurring through the process of natural selection.

Question 40

Factors that drive natural selection

Answer 40

-Predation, disease and competition for the means of survival. -These results in differential survival and reproduction.

Question 41

Natural selection to evolution

Answer 41

GENIE

Question 42

Effects of stabilising selection

Answer 42

-Organisms with alleles coding for average modal variations of a trait have a selective advantage. -So frequency of alleles coding for average variations of a trait increase and those coding for extreme variations of a trait decrease. -So range/ standard deviation is reduced.

Question 43

Effects of directional selection

Answer 43

-Organisms with alleles coding for one extreme variation of a trait have a selective advantage. -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.

Question 44

Effects of disruptive selection

Answer 44

-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.

Question 45

Speciation

Answer 45

-Reproductive separation of two populations of the same species. -This can result in accumulation of differences in their gene pools. -New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring.

Question 46

Allopatric speciation

Answer 46

-Population is split due to geographical isolation. -This leads to reproductive isolation, separating gene pools by preventing interbreeding/ gene flow between populations. -Random mutations cause genetic variation within each population. -Different selection pressures/ environment act on each population. -So different advantageous alleles are selected for/ passed on in each population. -So allele frequencies within each gene pool change over many generations. -Eventually different populations cannot interbreed to produce fertile offspring.

Question 47

Sympatric speciation

Answer 47

-Population is not geographically isolated. -Mutations lead to reproductive isolation, separating gene pools by preventing interbreeding/ gene flow within one population (Gene incompatibility, different breeding seasons, different courtship behaviours prevent mating, body shape/ size changes preventing mating) -Different selection pressures act on each population. -So different advantageous alleles are selected for/ passed on in each population. -So allele frequencies within each gene pool change over many generations. -Eventually different populations cannot interbreed to produce fertile offspring.

Question 48

Genetic drift

Answer 48

A mechanism of evolution in which allele frequencies in a population change over generations due to chance (NOT natural selection).

Question 49

Importance of genetic drift in small populations

Answer 49

-Some alleles are passed onto offspring more/ less often by chance, regardless of selection pressures and whether alleles give a selective advantage. -So strongest effects in small populations with no interbreeding with other populations (no gene flow), as gene pool is small and chance has a greater influence. -Thus can reduce genetic diversity, some alleles have much higher frequencies, others are lost.