Evolution

Question 1

What is variation?

Answer 1

The presence of variety; physical and genetical differences between members of different species as well as members of the same species.

Question 2

What types of variation are there?

Answer 2

1. Continuous variation.
2. Discontinuous variation.
3. Intraspecific variation.
4. Interspecific variation.

Question 3

What is intraspecific variation?

Answer 3

Variation between members of the same species.

Question 4

What is interspecific variation?

Answer 4

Variation between members of different species.

Question 5

What is continuous variation?

Answer 5

Variation in which there is a full range of intermediate phenotypes between 2 extremes.

Question 6

What are the characteristics of continuous variation?

Answer 6

• Significantly affected by environmental influences.
• Quantitative.
• Combined effect of many genes (polygenetic inheritance) with different alleles, each having a small effect.
• Complete range of measurements from one extreme to another.
• Data can be plotted on frequency histogram.
• Data plotted usually forms a typical bell shaped curve (normal distribution).

Question 7

What is discontinuous variation?

Answer 7

Variation in which there are discrete groups of phenotypes with no or very few individuals in between.

Question 8

What are the characteristics of discontinuous variation?

Answer 8

• Controlled by alleles of a single gene or small number of genes.
• Features cannot be measured across a complete range.
• Qualitative.
• Individuals fall into a distinct category.
• None/little environmental influences.
• Data can be plotted as bar charts.
• Data is discrete/categorical.

Question 9

What are some examples of continuous variation?

Answer 9

Humans:
- Height.
- Mass.
Plants: 
- Width of leaves.
- Mass of fruit.
Microorganisms:
- Diameter.
- Lifetime.
- Length of flagellum.

Question 10

What are some examples of discontinuous variation?

Answer 10

Humans:
- Blood group.
- Hair colour.
- Eye colour.
Plants:
- Colour of flower.
- Flowering/non-flowering.
Microorganisms:
- Presence of flagellum.
- Parasitic/free-living.

Question 11

What causes variation?

Answer 11

Genetics: Many of our characteristics (phenotypes) are determined by the genes we have (genotype). A lot of the time, a combination of genes are responsible for one characteristic. Within this combination are different alleles of the same gene that create variation.
Environment: Environmental factors can influence which genes are active at a particular time. For example, a person exposed to sunlight regularly may become tanned as a result of the sunlight activating a gene responsible for producing dark pigments in the skin.

Question 12

What is a adaptation?

Answer 12

A variation which helps an organism survive and thrive in the environment they live in.

Question 13

What are the features of a well-adapted organism?

Answer 13

They are able to:

• Gather enough food by autotrophic or heterotrophic means.
• Find enough water.
• Defend itself from predators and diseases.
• Survive the physical conditions of the environment, e.g. temperature, light, amount of water…
• Respond quickly to changes.
• Have enough energy and nutrients in excess to reproduce successfully.

Question 14

What are behavioural adaptations?

Answer 14

Things that an organism chooses to do which enhances their chances of survival. For example, killer whales hunt in packs in order to increase chances of success against preys.

Question 15

What are physiological adaptations?

Answer 15

Things that the body/cells in the body of the organism does in order to enhance their chances of survival. For example, chemical reaction in lure of anglar fish produces a light used to attract their prey.

Question 16

What are anatomical adaptations?

Answer 16

Feature of the body of the organism that are adapted especially to enhance the chances of survival. For example, killer whales have fat layer of blubber underneath skin used as insulation in the cold.

Question 17

What were Darwin’s 4 observations?

Answer 17

1. No two individuals are identical.
2. Populations in nature tend to remain fairly stable in size.
3. Offsprings generally appear similar to their parents.
4. Organisms have the ability to produce large numbers of offsprings.

Question 18

What were Darwin’s 3 conclusions?

Answer 18

1. There is a struggle to survive: Too many offsprings are produced each generation (Organisms have the ability to produce large numbers of offspring), so there is fierce competition for food and resources; only a small proportion of offsprings live to reproduce (Populations in nature tend to remain fairly stable in size).
2. Better adapted individuals survive and pass on their characteristics: Some individuals are more adapted to the environment than others due to chance mutations (No two individuals are identical), so they outcompete the less well adapted and live to reproduce, passing on their characteristics to their offsprings (Offsprings generally appear similar to their parents).
3. Over time, a number of changes may give rise to a new species: Over a long time, these small variations may accumulate in a group of organisms of the same species until they become so different that they are no longer able to interbreed with the rest of the population, and become a new species.

Question 19

What is natural selection?

Answer 19

The selection by the environment of particular individuals that show certain variations through selection pressure. These individuals will survive to reproduce and pass their variations to the next generation.

Question 20

What are some examples of selection pressures?

Answer 20

• Availability of food: Individuals that are able to eat the food available in the environment have the selective advantage.
• Predators: Individuals who can avoid being seen or are able to run away from predators have the selective advantage.
• Disease: Individuals that are resistant to a disease is more likely to survive during an outbreak.
• Environment: Individuals that are able to cope with the conditions in the environment have the selective advantage.

Question 21

What is speciation?

Answer 21

The formation of a new species.

Question 22

What conditions must be present in order for speciation to occur?

Answer 22

• There must be some form of a reproductive barrier.
• 2 groups of the same species are reproductively isolated from each other so that they are unable to interbreed and there are 2 gene pools.
• Variation in one gene pool cannot spread throughout the whole species.
• The 2 groups slowly change according to the different selection pressures present in the 2 environment.
• Eventually, the 2 groups may become so different from each other that they are no longer able to interbreed to produce fertile offsprings.

Question 23

What is allopatric speciation?

Answer 23

A geographic reproductive barrier that prevents 2 or more groups of the same species from breeding freely from each other. For example, different groups of the same species on different islands, separated by the ocean.

Question 24

What is sympatric speciation?

Answer 24

A reproductive barrier that arises within the population, for example:

• Behavioural: Different members may become active at different times of the year.
• Physical: Reproductive parts of individuals may become incompatible.

Question 25

What evidence is there for evolution?

Answer 25

• Fossils: Fossils have been found of animals that do not exist today but show many similarities with ones that do. For example, we have a good fossil record for the evolution of horses that shows the increase in size of the horse over time. We can deduce from this that the modern horse must be better adapted to the environments they live in compared to their ancestors which caused their ancestors to die out due to selection pressures.
• DNA: Parts of the DNA of different species that code for the same genes can be sequenced and compared. The more similar the base sequences of 2 species are to each other, the closer related they are to each other.
• Biological molecules: Certain proteins like cytochrome c are found in most living things in the world. This is good evidence that they are related to each other. However, the primary structure of these proteins can be analysed and compared to determine how closely related to each other they are.

Question 26

What is the overall process of evolution?

Answer 26

1. Variation within a species occurs due to chance mutations.
2. The environment applies selection pressures of which certain individuals with certain variations have the selective advantage.
3. Individuals with the advantage will survive and reproduce whereas the rest will die.
4. The advantageous variations are passed onto the next generation.
5. The next generation is slightly different from the last (they’ve evolved) to be better adapted to the environment they live in.

Question 27

How do insects become resistant to insecticides?

Answer 27

1. Selection pressure is the use of insecticides to kill insects.
2. Due to chance mutations, some individuals are resistant to the insecticide (they have enzymes to break down the chemical or modify target cell receptors).
3. These have the selective advantage and survive to reproduce while the rest of the population is killed by insecticides.
4. Characteristic passed onto offsprings who also become resistant to insecticides.
5. Insecticide resistant population spreads until the whole population becomes resistant to insecticides.

Question 28

What are the consequences of insecticide resistance for us?

Answer 28

• Insecticides used to spray mosquito nets to kill mosquitos carrying malaria are becoming redundant. As a result, more mosquitos live to spread malaria from person to person.
• Insecticides used to kill pests in agriculture are also becoming redundant. This leaves crops more vulnerable to pests and also reduces the yield of harvests; which is a problem for the growing human population.

Question 29

How do bacteria become resistant to antibiotics?

Answer 29

1. Selection pressure is the use of antibiotics to kill bacteria.
2. Due to chance mutations, some individuals are resistant to the antibiotic.
3. These have the selective advantage and survive to reproduce while the rest of the population are killed by the antibiotic.
4. Antibiotic resistant characteristic passed onto genetically identical offsprings of next generation.
5. Antibiotic resistant population spreads until the whole population is resistant to antibiotics.

Question 30

What are the consequences of antibiotic resistance for us?

Answer 30

Bacteria are becoming resistant to all the antibiotics we have available as a result of overuse or abuse (not finishing a course, taking the wrong antibiotics, antibiotics in agriculture…). This means that if nothing is done, we could have no effective antibiotics to treat bacterial infections within the next 50 years.