10.8 Changing Popn. Characteristics

Question 1

Natural Selection

Answer 1

All organisms are exposed to SELECTION PRESSURES. These are factors that affect the organisms’ chance of survival or reproductive success.

Organisms that are best adapted to their environment are more likely to survive and reproduce. As a result of natural selection these adaptations will become more common in the popn.

Question 2

How Natural Selection Happens

Answer 2

1. organisms within a species show variation in their characteristics that are caused by genetic variation.
2. organisms whose characteristics are best adapted to a selection pressure, such as predation, competition, or disease, have an increased chance of surviving and reproducing. Less well adapted die or fail to reproduce (‘survival of the fittest’).
3. successful organisms pass the allele encoding the advantageous characteristic onto their offspring.
4. process is repeated for every generation and the advantageous characteristic increases.
5. over generations, this leads to the evolution of a new species.

Question 3

Peppered Moths Example of Natural Selection

Answer 3

Peppered moths were were white, providing camouflage against the light-coloured bark of trees.

Industrial Revolution happened and produced a lot of soot which rested on the trees, turning them darker (SELECTION PRESSURE).

The white moths were now exposed to predators.

The few black moths are now camouflaged and survive/reproduce.

More black moths occur and produces a new species.

This is now changing as the environment is becoming cleaner and white moths are increasing again.

Question 4

Sheep Blowflies

Answer 4

Sheep Blowflies lay their eggs in faecal matter around a sheep’s tail, then the larvae hatch and cause sores - condition known as ‘flystrike’.

In the 1950s, a pesticide was used to kill the flies but within 6 years, they had developed a high level of resistance to the chemical, which was passed on to their offspring and caused the species to evolve.

When scientists studied them to find out when the resistance adaptation happened, it was revealed the species had pre-existing resistance.

Question 5

Flavobacterium

Answer 5

Most evolution happens as a negative result of selection pressures. However, some organisms have evolved due to opportunities that have arisen in their environment.

Flavobacterium has been found in waste water from factories and produce nylon 6; nylon 6 is used to make toothbrushes and violin strings.

This strain of bacteria can be useful to us because they help clean factories and digest nylon.