Populations and ecosystems

Question 1

What is a habitat

Answer 1

a place where a particular population or community live e.g. a lake

Question 2

What is an environment

Answer 2

the surroundings of an organism, composed of living and non living components

Question 3

What does abiotic mean

Answer 3

factors that relate to the non living part of the environment e.g. flow of water through a lake

Question 4

What does biotic mean

Answer 4

factors that relate to the living part of the environment

Question 5

What is a community

Answer 5

all the populations of different species living in a particular space at the same time

Question 6

What is a population

Answer 6

a group of organisms belonging to the same species living in a particular place at the same time

Question 7

What is an ecosystem

Answer 7

the basic unit of ecology, consisting of a community (biotic) of living organisms and their environment (abiotic)

Question 8

What is a niche

Answer 8

how an organism fits into its environment, the place where it is found and what it does there

Question 9

What genetic factors cause variation within a species

Answer 9

• mutation
• random segregation of alleles in metaphase in meiosis
• crossing over between chromatids of homologous chromosomes
• random mating of organisms within a species
• random fertilisation

Question 10

What is mutation

Answer 10

• mutation is a change to the DNA

- mutations can either be a gene mutation or a chromosome mutation

Question 11

What environmental factors could cause variation

Answer 11

• diet
• disease
• predators

Question 12

Explain how natural selection causes a change in allele frequency

Answer 12

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
• these individuals reproduce, passing on their advantageous allele
• this will shift the allele frequency within the gene pool

Question 13

What are the three types of natural selection

Answer 13

• stabilising selection
• directional selection
• disruptive selection

Question 14

Define stabilising selection

Answer 14

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

Question 15

What is natural selection

Answer 15

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

Question 16

Define directional selection

Answer 16

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 17

Define disruptive selection

Answer 17

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 18

Define evolution

Answer 18

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

Question 19

What is speciation

Answer 19

the formation of new species

Question 20

What is allopatric speciation

Answer 20

• the development of new species due to a physical separation of a species
• population separated 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 21

What is sympatric speciation

Answer 21

-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 22

What is genetic drift

Answer 22

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 23

What is the founder effect

Answer 23

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

Question 24

What factors can affect the population size

Answer 24

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 25

What two methods can be used to estimate a population size

Answer 25

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

Question 26

What is succession

Answer 26

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

Question 27

What is primary succession

Answer 27

newly formed habitats that have not previously supported a community

Question 28

What is the pioneer species

Answer 28

the first organism to colonise a new habitat

e.g lichen and algae on bare rock

Question 29

What is secondary succession

Answer 29

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

Question 30

What is the climax community

Answer 30

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