Topic 3.2 Natural Selection

Question 1

Darwins Theory of Evolution

Answer 1

-Living organisms produce more offspring than those that survive
-All organisms show variation due to mutation
-If conditions change then some organisms will be better suited to the new environment that others
-There will be competition, those which are better suited will survive (survival of the fittest)
-Those which survive will reproduce and pass on the allele to the next generation
-All the offspring will have the allele for the beneficial characteristic, there is an increase in the allele frequency
-Over time a new species may arise or evolve which is different to the original species.

Question 2

Niche

Answer 2

The role of an organism in an ecosystem based on the adaptations that have.

Question 3

Anatomical adaptations

Answer 3

Involve the form and structure of an organism (eg. the thick layer of blubber in seals).

Question 4

Physiological adaptations

Answer 4

Involve the way the body of the organism works and includes differences in biochemical pathways or enzymes (eg. diving mammals can stay underwater for longer that non-diving mammals without drowning, venom production).

Question 5

Behavioural adaptations

Answer 5

Involves changes to programmed or instinctive behaviour making organisms better adapted for survival (eg. many insects and reptiles orientate themselves to get maximum sunlight on their bodies when the air temperature is low, hibernation).

Question 6

Social behaviour

Answer 6

Social behaviour such as hunting as a team or huddling together for warmth can improve survival chances. Migrating to avoid harsh conditions and using tools are other examples of behavioural adaptations.

Question 7

Selection pressures

Answer 7

-A change in the environment means the selection pressure has changed
-The changes in selection pressure result in changes or evolution within the species.

Question 8

Directional pressure

Answer 8

-Is shown when there is a change from one dominant phenotype to the other
-This is in response to a change in the environment- one phenotype is elected for over all the others
-Speciation: eventually, over many generations a new species may arise.

Question 9

Natural selection in moths

Answer 9

……

Question 10

Antibiotic resistance

Answer 10

-Pathogens also show mutations adaptions and natural selection
-As a result they can becomes resistant to medicines especially antibiotics
-The antibiotic quickly becomes ineffective
-There is an evolutionary arms race to develop new antibiotics against pathogens

Question 11

Beating bacteria, Step 1

Answer 11

The Penicillin family of antibiotics affect gram-positive bacteria with their thick peptidoglycan walls, but do not affect other bacteria.
A range antibiotics were developed and for a short time it appeared that bacteria diseases would almost become a thing of the past.
Antibiotics were prescribed freely and everyone came to expect an antibiotic prescription when they went to doctors with an infection.

Question 12

Bacteria fight back

Answer 12

The presence of an enzyme called penicillinase that splits the penicillin molecule so it no longer works.
People became seriously ill and died from bacterial infections that were no longer effected by penicillin.

Question 13

Beating bacteria, Step 2

Answer 13

As penicillin resistance spread, scientists produced a new antibiotic called methicillin.
However this didn’t last long.
There are growing numbers of bacteria that are resistant to not just one but many antibiotics.

Question 14

Factors that contribute to bacteria resistance

Answer 14

-Antibiotics are too widely prescribed
-People do not complete courses of antibiotics
-A lack of basic hygiene in hospitals
-No financial incentive for pharmaceutical companies to develop new antibiotics

Question 15

How to overcome the problem of bacteria resistance

Answer 15

-Reducing the use of antibiotics
-Better education so people understand they don’t always need antibiotics
-DNA sequencing will help identify bacteria and find ways to target them
-Development of new antibiotics

Question 16

Bactericidal

Answer 16

Antibiotics are bactericidal meaning they kill the bacteria.

Question 17

Bacteriostatic

Answer 17

Meaning they slow the growth of bacteria (antibiotics can also be bacteriostatic).
They interfere with the process the bacteria need to multiply, such as protein production, DNA replication or metabolism.

Question 18

Example of bactericidal antibiotics

Answer 18

Penicillin is an example of a bactericidal antibiotics, which targets the peptidoglycan layer in the cell wall leading to cell death.

Question 19

Antibiotics spectrum

Answer 19

Antibiotics can be narrow spectrum, affecting only one or two species of bacteria, or a broad spectrum, affecting many different species of bacteria in the body.

Question 20

The important points to prevent resistance

Answer 20

-Antibiotics do not need to be taken for colds and flu as these usually get better on their own
-It is important to take the antibiotic exactly as instructed and complete the course
-Antibiotics are prescribed for a particular infection, they should not be taken for a different illness.

Question 21

Speciation

Answer 21

Speciation is the evolution of two different species from an existing one.
(The formation of a new species).

Question 22

Speciation in general

Answer 22

1. A population becomes separated into two groups that are reproductively isolated so that there is no gene flow between the groups
2. The two groups’ environment are different, so natural selection favours different characteristics
3. The allele frequencies in two groups will change in different ways
4. Eventually the two populations will be unable to interbreed, so will be different species.

Question 23

How does speciation occur?

Answer 23

Speciation occurs when gene flow has effectively stopped between populations where it has previously existed. This requires two populations of the same species to become reproductively isolated.

Question 24

Isolation leading to speciation

Answer 24

Isolation can be geographical, leading ti allopatric speciation, or due to changes in reproduction mechanism, leading to sympatric speciation.

Question 25

Geographic isolation

Answer 25

A physical barrier such as a river or a mountain range separates individuals from an original population.
When a species evolved in geographical isolation and is formed in only one place is said to be endemic.

Question 26

Ecological isolation

Answer 26

Two population inhabit the same region, but develop preferences for different parts of the habitat.

Question 27

Seasonal isolation (Or temporal isolation)

Answer 27

The timing of flowering or sexual receptiveness in some parts of a population drifts away from the norm of the group. This can eventually lead to the two groups reproducing several months apart.

Question 28

Behavioural isolation

Answer 28

Changes occur in the courtship ritual, display or mating pattern so that some animals do not recognise others as being potential mates. This might be due to a mutation that changes the colour or pattern of markings.

Question 29

Mechanical isolation

Answer 29

A mutation occurs that changes the genitalia of animals, making it physically possible for them to mate successfully with only some members of the group, or it changes the relationship between the stigma in flowers, making pollination between some individuals unsuccessful.

Question 30

Reproductive isolation

Answer 30

Reproductive isolation is the key factor in speciation.

Question 31

Allopatric speciation

Answer 31

Allopatric speciation takes place when populations are physically or geographically separated in some way.
The physical isolation of populations occur as a result of natural changes (eg. as islands form, as ice floes melt, rivers change and lakes dry up).

Question 32

Sympatric speciation

Answer 32

Sympatric speciation takes place between populations of a species living in the same place that become reproductively isolated by mechanical, behavioural or seasonal changes (a non-physical barrier eg. a mutation). Gene flow continues to some extent as speciation takes place.

Question 33

Cichlid speciation

Answer 33

Molecular phylogeny suggests that the great majority of the cichlid fish evolved much more recently than the lakes were formed.
The fish in the lake are more closely related to the other species of fish endemic in their own lake after they have become separated from each other.