Chapter 18

Question 1

variation

Answer 1

differences between individuals of the same species

Question 2

Continuous variation

Answer 2

Occurs as a range of phenotypes between two extremes, e.g. height in humans. Caused by both genetics and environmental factors.

Question 3

Discontinuous variation

Answer 3

Occurs in a limited number of phenotypes with no intermediates, e.g. tongue rolling. Mainly caused by genes alone.

Question 4

mutation

Answer 4

genetic change; the way in which new alleles are formed

Question 5

Effect of ionising radiation and some chemicals on the body

Answer 5

Increase the rate of mutation (causes cancer lol)

Question 6

Phenotypic variation

Answer 6

the variation in the features we can see, even with specialised equipment. It is effected by both genetics and environmental factors.

Question 7

Genetic variation

Answer 7

the variation between the genotypes of different individuals.

Question 8

gene mutation

Answer 8

a change in the base sequence of DNA

Question 9

Describe the symptoms of sickle cell anaemia

Answer 9

Sickle shaped red blood cells means less oxygen can be carried and they can cause difficulty breathing, tiredness, crises, delayed puberty, blockage of blood vessels and if the spleen destroys the sickle cells at a greater rate than r.b.c, causes anaemia

Question 10

Explain how a change in the base sequence of the gene for haemoglobin results in abnormal haemoglobin and sickle-shaped red blood cells

Answer 10

Sickle cell anaemia is caused by a single base substitution in the haemoglobin gene, Hb. A single A base is substituted by a T base. The normal allele Hb A becomes the sickle cell allele Hb S . The change causes haemoglobin to contain valine instead of glutamic acid, causing sickle cells to be produced.

Question 11

individuals with the sickle cell trait and their relationship with malaria

Answer 11

Due to the sickle cells having an abnormal shape, the parasite that is responsible for malaria can not enter the red blood cells. Therefore they are resistant to malaria.

Question 12

How the sickle cell allele is a selective agent

Answer 12

People who do not have the sickle cell trait die from malaria, the people who are homozygous with the sickle cell allele die young due to their condition and, as it is codominant, heterozygous individuals don’t suffer from sickle cell anaemia and are resistant to malaria. Therefore more likely to reproduce offspring with the same traits.

Question 13

Malaria distribution and the sickle cell allele distribution

Answer 13

majority of malaria is found in central Africa, where the sickle cell allele is also very prominent.

Question 14

adaptive feature

Answer 14

an inherited feature that helps an organism to survive and reproduce in its environment. (or in fancy terms, the inherited functional features of an organism that increase its fitness)

Question 15

fitness

Answer 15

the probability of an organism surviving and reproducing in the environment in which it is found

Question 16

adaptive features of hydrophytes

Answer 16

• little to no xylem tissue as there is no real need for water transport
• Roots, if present, is mainly for anchorage and not to absorb water or mineral ions (+ no root hair cells)
• leaves and stems are little or no cuticle, as they do not need to conserve water
• they have an extensive system of air spaces in their stems and leaves through which gases diffuse quickly
• air spaces also provide buoyancy to keep plants close to the light and are a reservoir of oxygen and carbon dioxide

Question 17

adaptive features of xerophytes

Answer 17

• leaves are reduced to spines to reduce the surface area to which water can be lost
• a thick way cuticle covers the plants surfaces to reduce transpiration
• they have swollen stems with water storage tissue
• they have a shallow spread out root system to quickly absorb any rain water or overnight condensation
• round compact shape reduces surface area to which water is lost
• their stomata are closed during the day to reduce water loss. they open up at night to absorb carbon dioxide which they store for photosynthesis.
• photosynthesis occurs only on the outer layer of their stems.

Question 18

Describe natural selection

Answer 18

• There is a variation within populations of a species that makes them more suitable for their environment, therefore more likely to live and produce offspring.
• Animals and plants produce many offspring, that ensure the survival of at least some offspring and gives a better chance for the stronger offspring to be produced with the weaker ones killed off.
• There is a competition for resources between a species in which the stronger ones would win and therefore are more likely to live and produce strong offspring. The term scientists use to describe the competition for resources is ‘struggle for survival. ‘
  Overall, the stronger and ‘genetically-varied-organism-which-is-better-suited-to-the-enivorment’ are more likely to survive and pass on their alleles to the next generation.

Question 19

Describe selective breeding

Answer 19

Selective breeding starts with humans. Humans decide on which desirable features they wish to be reproduced, they cross these individuals to produce the next generation and they select the offspring showing the desirable features. Rinse and repeat until you got the whole dang universe of heavy milk producing cows.

Question 20

process of adaptation

Answer 20

the process, resulting from natural selection, by which populations become more suited to their environment over many generations

Question 21

The development of strains of antibiotic resistant bacteria ….

Answer 21

…. are an example of evolution by natural selection. As their mutations made them better suited to their environment (aka, antibiotics) and they survived the competition of ‘who’s going to survive the antibiotic’ and reproduce offspring that are resistant to the antibiotic. Making a whole other generation of antibiotic-resistant bacteria.

Question 22

State the differences between natural and artificial selection: Natural selection

Answer 22

• selection due to environmental factors
• produces greater biodiversity
• may lead to new species
• outbreeding is common, leading to hybrid vigour
• a slow process
• proportion of heterozygous individuals remain high

Question 23

State the differences between natural and artificial selection: Artificial selection

Answer 23

• selection due to human influences
• produces varieties of organisms very different from their native generations
• does not result in new species
• inbreeding is common, loss of vigour in offspring
• a relatively fast process
• proportion of heterozygous individuals is reduced

Question 24

Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals

Answer 24

What can happen is two things: outbreeding and inbreeding. Humans can choose to have the desirable traits of species and the desirable traits of another species to create a stronger or ‘better’ animal/plant. This can lead to a stronger crop plant that is resistant to disease. This is outbreeding. However they can also choose to try and retain the desirable features of a animal/plant by breeding it with a similar or even related animal/plant. This can allow cows to to produce more milk. This is inbreeding.