Chapter 18 — Population And Evolution

Question 1

How does genetic variation occur?

Answer 1

Genetic variation can occur in 3 ways:

• mutations
• meiosis
• random fertilization of gametes

Question 2

What are selection pressures?

Answer 2

Selection pressures are the environmental factors that affect an organism’s chance of survival and reproduction

Question 3

What is stabilising selection?

Answer 3

• organisms with middle range characteristics are more likely to survive and reproduce
• occurs in a stable environment

Question 4

Give a definition of variation.

Answer 4

Variation is essentially the differences that exist between individuals, occuring within species and between species.

Question 5

What is directional selection?

Answer 5

when one of the extremes are favoured

individuals with allele for one

Question 6

What is disruptive selection

Answer 6

• when extreme characteristics on both ends of the range are favoured
• and more likely to survive

Question 7

Give 2 types of factors that cause phenotypic variation.

Answer 7

genetic factors and environmental factors both cause phenotypic variation

Question 8

What is allopatric speciation?

Answer 8

A type of speciation where new species form from different populations that are found in different areas

Question 9

Describe how you could use the mark-release-recapture method to estimate the number of lizards on an island.

Answer 9

• collect sample 1 by capturing, marking and releasing the lizards
• marking should be in a way that doesn’t make them obvious to predators
• release them back into the wild
• leaving sufficient time for them to randomly distribute over area
• and then collecting sample 2 by recapturing them
• population = (number in sample 1 × number in sample 2) divided by number of marked in sample 2

Question 10

Habitat

Answer 10

Where an organism lives

Question 11

Population

Answer 11

all the organisms of one species in a habitat

Question 12

Community

Answer 12

Groups of different species in an area

Question 13

Ecosystem

Answer 13

A community, including all the biotic features (predators, prey​) and all the abiotic conditions (temp, water availability)

Question 14

Abiotic factors

Answer 14

The non-living physical or chemical features of an ecosystem that affect an organism’s survival and reproduction

• temperature
• climate
• water
• nutrients
• oxygen concentrations
• pollution
• light intensity
• moisture
• pH

Question 15

Biotic factors

Answer 15

All the living organisms of an ecosystem

• plants
• fungi
• animals
• predators
• prey
• food
• bacteria

Question 16

Niche

Answer 16

The role of a species within its habitat

Question 17

Adaptation

Answer 17

A feature that members of a species have that increases their chance of survival and reproduction.

Question 18

What is speciation?

Answer 18

Speciation is the development of a new species from an existing species, occuring when populations of the same species become reproductively isolated.

Question 19

What is the difference between allopatric and sympatric speciation?

Answer 19

Allopatric speciation occurs when a population is geographical isolated and sympatric speciation occurs when there is no physical separation.

Question 20

Describe the process of allopatric speciation.

Answer 20

• physical barrier stops interbreeding between two populations of the same species
• each side of the physical barrier will have slightly different conditions
• and thus each population will experience different selection pressures
• each population adapts to its new environment and conditions
• allele and phenotype frequency change leading to the development of new species

Question 21

Genetic drift

Answer 21

When chance determines which allele for one genotype is passed on to offspring more often than the others. The number of individuals with the allele increases. This could eventually lead to reproductive isolation.

Question 22

the frequency of the beneficial alleles in the gene pool increases from generation to generation

Answer 22

…

Question 23

Interbreeding

Answer 23

When organisms of the same species breed

Question 24

Crossbreeding

Answer 24

When organisms of different species breed

Question 25

Carrying capacity

Answer 25

The maximum size of a population that an ecosystem can support

Question 26

Succession

Answer 26

the process by which ecosystems change overtime, of which there are two types: primary succession and secondary succession

can also be describes as the process by which communities of animals and plants colonise an area and then over time are replaced by other usually more varied communities

Question 27

Primary succession

Answer 27

1- occurs when there is just an empty inorganic surface such as bare rock

• due to volcanic eruptions, landslides etc.
• opportunists or pioneer species (mosses, lichens) are the first to colonise because they are hardy, don’t dry out easily
• help to form humus by breaking down rock surfaces into organic material
• when these plants die and decompose they form soil allowing other species (grasses, ferns) to take root
• these also add to the soil when they die and decay
• as more nutrients and water are retained in the soil, it us able to support larger species of plants
• animal species make these plants their home and source of food
• diversity increases
• a climax community is reached at some point: the biodiversity of the ecosystem stays constant, the community is self-sustaining, the most productive group of organisms that environment can support

Question 28

Secondary succession

Answer 28

• occurs when soil is present but free of vegetation
• due to forest fires, floods, human disturbances etc.
• the new climax community can be different from the original climax community