NATURAL SELECTION

Question 1

define natural selection

Answer 1

“survival of the fittest”
organisms that are best suited to their environment survive and pass on their genes.

Question 2

variation caused by meiosis, sexual reproduction and mutations.

Answer 2

in a population there is variation that is caused by meiosis, sexual reproduction and mutations. Many species produce more offspring then could possibly survive, due to competition of resources.
- The best adapted have a selective advantage that makes it more likely they will survive to breed and pass on their genes.

Question 3

abiotic and biotic factor

Answer 3

the change can be brought about by an abiotic factor (non living e.g temperature) or biotic (Living).

Question 4

example - peppered moth

Answer 4

two forms of moth - light & dark form
in the industrial revolution the dark (melanic) form was prevalent.
in non industrial environments the light (peppered) form was more prevalent.
In each case the form was better camouflaged against the background and not seen by predators.
Whatever moth has the selective advantage survives and passes on its genes.

Question 5

sickle cell anemia

Answer 5

Genetic disorder caused by abnormal haemoglobin S.
The normal allele is incompletely dominant to haemoglobin S. There is an in between state which leads to sickle cell trait.
- sickle cell trait have a selective advantage in countries with malaria

Question 6

Resistance to antibiotics

Answer 6

some bacteria can build up resistance to antibiotics. - They can pass this onto others by the process conjugation.
Already bacteria that are resistant to all but one antibiotic “super strath” staphyloccus avelus.
Also a species of salmonella resistant to 7 antibiotics

Question 7

resistance insects

Answer 7

insects have resistance to various insecticides e.g DDT
Insects can also become resistant to heavy metal which allows them to colonise areas that many plants cannot grow.