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Question 1

Describe how the mark-release-recapture method can be used for estimating the size of population

Answer 1

> Capture a large sample of organisms being studied + count
Mark each organism without causing harm
Release marked organisms back into habitat
Capture a second large sample from the same population after a certain time
Count the total no. caught + total no. marked

Question 2

Describe predation

Answer 2

> An organism (predator) feeds on another organism (prey)

>Predator and prey populations linked

Question 3

Describe stabilising selection

Answer 3

> Selection in favour of individuals with mean phenotypes; selection against extremes
Occurs in unchanging environment
Reduces range of possible phenotypes, and SD from mean

Question 4

Describe the log phase of population growth

Answer 4

> Period of rapid growth
Exponential increase, rather than arithmetic
Growth is rapid due to lack of limiting factors

Question 5

Different species occupy different ecological niches.

Answer 5

Explain the advantage of species occupying different niches.

Less competition for food / resource

Question 6

Explain how evolutionary change over time has resulted in a great diversity of organisms

Answer 6

> Diversity of life is the result of speciation + evolutionary change over millions of years
Original population of organisms divided, became separate species

Question 7

Explain how microorganisms contribute to the increase in temperature during processing of organic waste

Answer 7

> Respiration / metabolism / ammonification

>Releases heat

Question 8

Explain how natural selection is a method by which evolution occurs

Answer 8

> Organisms with phenotype that increases their chance of survival
More likely to survive, reproduce + pass on advantageous alleles to offspring
Leads to change in allele frequency over time/many generations

Question 9

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium

Answer 9

> Frequent use of antibiotic creates selection pressure
Bacteria with mutation / resistance have selective advantage over others
Great chance of survival -> reproduce + pass on advantageous allele in great numbers
Frequency of advantageous allele increases in subsequent generations
Frequency of resistant bacteria increases in subsequent generations

Question 10

Explain why actual numbers of offspring may be different from expected

Answer 10

> Offspring ratios are a probability / arise by chance
Gametes not produced in equal numbers
Fertilisation / fusion of gametes is random
Small sample

Question 11

Give an example of codominance

Answer 11

> Alleles for Hb (HN) and sickle-cell anaemia (HS)
HNHN = normal Hb, HSHS = sickle-cell anaemia
HNHS = sickle-cell trait, mixture of normal Hb and sickle Hb

Question 12

Give an example of multiple alleles

Answer 12

> ABO blood group system - three alleles for blood type

>Codominant IA and IB, recessive IO

Question 13

Give the differences between X and Y chromosomes

Answer 13

> Y c/s = smaller, carries few genes + shaped differently
Most genes on sex c/s only carried on X c/s (i.e. are X-linked genes)
Most of X and Y not homologous i.e. short pairing region

Question 14

How do multiple alleles of a gene arise?

Answer 14

> Mutations

>Occuring at different positions in gene

Question 15

How does interspecific competition arise?

Answer 15

> When two different species in the same habitat require the same resource
Resource is in short supply
If niches of two species are similar, more likely for interspecific competition to occur

Question 16

How does meiosis further genetic variation?

Answer 16

> Chromosomal crossover - sections of chromatids exchanged between bivalents = chromosome with new allele combo
Independent assortment - maternal + paternal chromosomes randomly shuffled; results in different combo of alleles in gamete

Question 17

How is the data from the mark-release-recapture method used to estimate the total population size

Answer 17

> Lincoln index

>Total no. of animals in population = (no. sample 1)(no. sample 2) / (no. marked sample 2)

Question 18

How many alleles for each gene do gametes carry compared to diploid cells?

Answer 18

> Only one -> when gametes from each parent fuse, alleles form genotype of offspring
Diploid cells -> two

Question 19

How many antigen-determining alleles will be present in a white blood cell? Give a reason for your answer

Answer 19

> Two

>White blood cells are diploid / alleles are present on each chromosome of a homologous pair

Question 20

How may differences in the gene pools of two population accumulate?

Answer 20

Reproductive separation/isolation

Question 21

How may reproductive isolation occur?

Answer 21

> Seasonal - individuals within the same population have different flowering/mating seasons or sexually active at different times
Mechanical - changes in reproductive organs, prevent successful mating
Behavioural - group of individuals develop courtship rules, aren’t attractive to main population

Question 22

How may the results of a genetic cross show autosomal linkage?

Answer 22

> Expected ratio not seen
Parental phenotypes overrepresented / more offspring with same genotypes as present
Non-parental phenotypes underrepresented / fewer recombinants / offspring with new combinations of parental alleles
Evidence that genes do not assort independently i.e. not separated by independent segregation during meiosis

Question 23

If two genes are closer together on an autosome, what is their relationship?

Answer 23

> More closely linked

>Less likely to be split during chromosomal crossover

Question 24

In a diploid organism, what may the alleles at a specific locus be?

Answer 24

> Homozygous or heterozygous

>e.g. in sister chromatid pair (i.e. chromosome), one chromatid has H allele, other has h allele

Question 25

In mammals, how is sex determined?

Answer 25

>Females = two X chromosomes (XX)
>Males = one X, one Y (XY)

Question 26

List examples of abiotic factors

Answer 26

> Temperature
Light intensity
Availability of water / NaCl / carbon dioxide / oxygen
Mineral content / pH / water-holding and drainage capacities of soil

Question 27

On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.

Answer 27

>Geographical isolation
>Separate gene pools / no interbreeding / gene flow (between populations)
>Variation due to mutation
>Different selection pressures
>Differential reproductive success
>Leads to change in allele frequency

Question 28

Scientists may use percentage cover rather than frequency to record the abundance of a particular species present. Suggest why

Answer 28

> Difficult / too many to count

>Individual organisms not identifiable / too small to identify

Question 29

State two factors which causes variation in population size

Answer 29

> Effect of abiotic factors

>Interactions between organisms

Question 30

Suggest economic consequences of the spread of a major pest species

Answer 30

> Cost of control / removal
Cost of restoring habitat / conservation
Loss of income from tourism / recreation