Topic 5.2 Natural Selection

Question 1

Natural Selection

Answer 1

‘survival of the fittest’ / The strongest or most intelligent doesn’t always survive, instead it’s the ones that are most responsive to change that survive the best

Question 2

Key components of natural seleciton

Answer 2

I - Inherited variation exists within the population
C - Competition results from an overproduction of offspring
E - Environmental pressures lead to differential reproduction

A - Adaptations which benefit survival are selected for
G - Genotype frequency changes across generations
E - Evolution occurs within the population

Question 3

Three main mechanisms by which genetic variations could occur

Answer 3

Mutations – Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring

Meiosis – Via either crossing over (prophase I) or independent assortment (metaphase I)

Sexual reproduction – The combination of genetic material from two distinct sources creates new gene combinations in offspring

Question 4

The Malthusnian dilemma

Answer 4

Species population increases geometrically while resources only increase arithmetically

Question 5

If left to follow course, a stable population will inevitably outgrow its resource base, leading to competition for survival

Answer 5

When there is an abundance of resources, a population will grow according to its biotic potential (exponential J-curve)

With more offspring, there are less resources available to other members of the population (environmental resistance)

This will lead to a struggle for survival and an increase in the mortality rate (causing population growth to slow and plateau)

Question 6

Adaptations

Answer 6

features of an organism that aid their survival by allowing them to be better suited for an environment

Question 7

Adaptation Classification

Answer 7

Structural: Physical differences in biological structure (e.g. neck length of a giraffe)

Behavioural: Differences in patterns of activity (e.g. opossums feigning death when threatened)

Physiological: Variations in detection and response by vital organs (e.g. homeothermy, colour perception)

Biochemical: Differences in molecular composition of cells and enzyme functions (e.g. blood groups, lactose tolerance)

Developmental: Variable changes that occur across the life span of an organism (e.g. patterns of ageing / senescence)

Question 8

Adaptive radiation

Answer 8

Rapid evolutionary diversification of a single similar ancestral line