4.3.9 natural selection & evolution

Question 1

theory of natural selection

Answer 1

• individual has characteristic which helps it survive in environment & lives long enough to reproduce
• evolution = selects individuals with adaptations who survive & reproduce
• adaptations passed on generations
• more & more have adaptive characteristic

Question 2

steps 1-6 of natural selection

Answer 2

1. mutation creates alternative versions of gene (allele)
2. creates genetic variation between individuals in species - intraspecific variation
3. now variety exists, the environment can ‘select’ - when resources are scarce, the environment selects those variations (characteristics) which provide an advantage = selection pressure
4. individuals with advantageous characteristic survive/reproduce
5. thus, they pass on advantageous characteristic = inheritance
6. next generation will have higher proportion of individuals with successful characteristics - over time, group of organisms become well adapted to environment = adaptation

Question 3

what must occur before evolution takes place

Answer 3

genetic variation

Question 4

pesticides

Answer 4

designed to kill pests

Question 5

insecticides

Answer 5

designed to kill specifically insects

Question 6

what does an insecticide apply

Answer 6

very strong selection pressure
- if insect susceptible = die
- if form of resistance = may survive & reproduce to pass on resistance characteristic so it quickly spreads

Question 7

when was resistance to pesticides first documented & describe

Answer 7

1914
- scale insects resistant to inorganic insecticides

Question 8

how short can resistance arise in

Answer 8

little as 2 years

Question 9

problem of resistance to pesticides by insects

Answer 9

• can accumulate in food chain
• if many resistant insects eaten by predator, they receive much larger dose
• can reach humans

Question 10

what pesticide has been banned in many areas

Answer 10

DDT

Question 11

problems associated with antibiotic resistance

Answer 11

• possible that some bacteria are resistant & survive
• many people stop taking antibiotics before end of course = resistant bacteria survives & reproduce creating resistant strain

Question 12

what has led to bacteria practically resistant to all antibiotics

Answer 12

overuse & incorrect use of antibiotics

Question 13

what does prescribing multiple antibiotics do

Answer 13

greatly reduces chance that any bacteria will survive

Question 14

selection of resistant microorganisms
- before selection
- directly after selection
- final population

Answer 14

before selection: variety of levels of resistance
- variation is caused by mutations which create genetic variation within species

directly after selection: least resistant individuals killed
- all that remains is individuals possessing some resistance

final population: partly resistant individuals reproduce
- next generation contains much higher proportion of resistant individuals

Question 15

example of bacteria which have gained wide range of resistance

Answer 15

MRSA
- developed resistance to increasing range of stronger drugs
- ‘evolutionary arms race’ = medical researchers struggling to develop new/effective drugs, but the bacterial populations rapidly become resistant to them