evolution and populations in ecosystems

Question 1

what genetic factors cause variation within a species

Answer 1

mutation

random segregation of alleles in metaphase I meiosis

crossing over between chromatids of homologous chromosomes

random mating of organisms within a species

random fertilisation

Question 2

what is mutation

Answer 2

mutation is a change to the DNA

mutations can either be a gene mutation or a chromosome mutation

Question 3

what environmental factors could cause variation

Answer 3

diet
disease
predators

Question 4

explain how natural selection causes a change in allele frequency

Answer 4

organisms produce more offspring than are needed to replace the parents. most population numbers remain the same

this causes competition for existence

individuals in a species show variation.

those with advantageous alleles will survive. (survival of the fittest)

these individuals reproduce, passing on their advantageous allele

this will shift the allele frequency within the gene pool

Question 5

what are the three types of natutral selection

Answer 5

Stabilising selection
directional selection
disruptive selection

Question 6

explain stabilising selection

Answer 6

stabilising selection is the elimination of extreme variations in a population
e.g bettle colour- light and dark beetles may be easy to see but all those in th middle may camouflage well

Question 7

define natural selection

Answer 7

the process by which heritable traits become either more or less common in a population due to pressures from the environment

Question 8

directional selection

Answer 8

if an environment changes one extreme form of a trait may be favoured
e.g peppered moth frequency in industrial revolution. darker moths became harder to see so were selected for.

Question 9

disruptive selection

Answer 9

both extremes in a trait are selected for but the middle is disadvantageous so is selected against

opposite of stabilising

e.g salmon male size
large fish can fight off opponents to fertilise eggs, small ones are fast enough to sneak in and fertilise the eggs, medium fish are selected against

Question 10

evolution

Answer 10

is the shift of allele frequency in a gene pool caused by selection pressure

Question 11

what is speciation

Answer 11

the formation of new species

Question 12

what are the 2 forms of speciation

Answer 12

Allopatric

sympatric

Question 13

describe allopatric speciation

Answer 13

the developement of new species due to a physical seperation of a species

population seperated by geographical isolation e.g sea, mountain range etc

isolated populations subjected to different selection pressures.

natural selection causes a shift in the gene pool, resulting in the two populations being reproductively isolation and therefore a new species has evolved

Question 14

describe sympatric speciation

Answer 14

new species formed when there are no physical barriers- reproductive isolation due to:

• behaviour- mates attracted by calls and dances etc
• structure- sex organs incompatible
• gamete mortality
• hybrid inviability- may result in a zygote that cant divide
• hybrid sterility- two species mate to form a hybrid but this cant reptroduce
• polyploidy- failure of separation of chromosomes in meiosis

Question 15

genetic drift

Answer 15

changing of allele frequency due to chance.
e.g forest fire wipes out large proportion of population but at random- not due to an advantage that they have

this has a larger affect on a smaller population

Question 16

what is the founder effect

Answer 16

organisms that start a new population may not be representative of original population

Question 17

what is a community

Answer 17

all living things in a particular habitat

Question 18

what makes up an ecosystem

Answer 18

the community (biotic) and the habitat (abiotic)

Question 19

what is the carrying capacity

Answer 19

the maximum size of a population an ecosystem can support

Question 20

what factors can affect the population size

Answer 20

Abiotic factors- climate factors, lack of shelter, pollution

biotic factors:

• competition within speciesfor resources e.g light, water, food etc
• competition between species for resources e.g light, water, food etc
• predators

Question 21

How would you estimate a population size

Answer 21

two different ways
Quadrats- for slow moving or non motile organisms.
divide the area into quadrats, pick a sample of quadrats,
count how many organisms are in the sampled quadrats and multiply up for the total area

mark-release-recapture
capture a population and mark them then release them.
recapture a sample from the number of marked organisms in the 2nd sample an estimation of the total population can be made

using the equation:
P=MxS/R

P-population size
M-number of animals marked captured and released
S-animals captured in second sample
R-number of marked animals recaptured

Question 22

what is succession

Answer 22

succession is the change in structure and species composition of a community over time

Question 23

what is primary succession

Answer 23

newly formed habitats that have not previously supported a community

Question 24

what is the pioneer species

Answer 24

the first organism to colonise a new habitat

e.g lichen and algae on bare rock

Question 25

what is secondary succession

Answer 25

the repopulation at sites that have previously supported a community, usually after a major environmental disturbance e.g forest fire

Question 26

what is the climax community

Answer 26

when the community reaches and equilibrium with its environment and no further changes occur