SB4 - Natural Selection and Genetic Modification

Question 1

What is evolution?

Answer 1

The gradual change in the characteristics of a species over a long period of time.

Question 2

How can fossils be formed?

Answer 2

Mineral replacement - minerals replace hard parts of organism (bones) and solidify
Soft materials hardening - dead organism is encased in soft material (e.g. clay) which hardens
Preservation where decay is not possible - e.g. in a glacier or peat bog (highly acidic)

Question 3

What are some problems with using fossils as evidence for evolution?

Answer 3

There are gaps in fossil record due to some fossils not being discovered yet and many more being destroyed by geological events such as volcanic eruptions or earthquakes, so you cannot prove that one species evolved from another using fossil records.

Question 4

Describe ardipithecus ramidus.

Answer 4

Ardi lived 4.4 million years ago. Discovered in 1992, Ardi had long arms and feet adapted to climbing trees (one toe splayed out to one side to allow it to grip the tree trunk), leg bones suggest it could have walked upright, weighed 50kg, was 1.2m tall, skull volume 350 cm3.

Question 5

Describe Australopithecus afarensis.

Answer 5

Lucy lived 3.9-3.0 million years ago. Discovered in 1974, Lucy was 1.07m tall and most likely walked upright, the toe bones were arranged the same way as a human’s, though much more curved, skull volume 400 cm3.

Question 6

Describe homo habilis.

Answer 6

Homo habilis lived 2.4-1.4 million years ago. Discovered in the 1960s, it was quite short with long arms and walked upright, skull volume 500-600 cm3.

Question 7

Describe homo erectus.

Answer 7

Homo erectus lived 1.8-0.5 million years ago. It was quite tall at 1.79m and strongly built, skull volume 850 cm3.

Question 8

Describe Homo sapiens (humans).

Answer 8

Lived 195000 years ago to present. Average height 1.7m, skull volume 1450 cm3.

Question 9

How can fossils be used as evidence for human evolution?

Answer 9

Human-like fossils show an increase in skull volume over time, which corresponds to increasing complexity of stone tools. However, the issue with using this as evidence is that it assumes the brain fills the whole skull and gaps in fossil record means we cannot be sure if one human-like species evolved into the next.

Question 10

How can stone tools be used as evidence for human evolution?

Answer 10

The first stone tools were made 3.3 million years ago. They were very basic (pretty much just sharp rocks), but over time, they became more sophisticated and fit for a purpose (e.g. spearheads for hunting and knives for cutting things). This shows that human-like species increased in intelligence over time, which is supported by fossil record showing larger skulls over time.

Question 11

What are some ways to track evolution?

Answer 11

-analyse fossil records
-stone tools
-genetic analysis

Question 12

What is Darwin’s theory?

Answer 12

Darwin proposed that animals evolved in a series of stages (GENIE):
- Genetic variation - the characteristics of individuals vary due to differences in genes.
- Environmental change - conditions in the area change (e.g. food shortage leads to competition)
- Natural selection - the variations of some individuals make them better at coping with the new environment and so are more likely to survive
- Inheritance - those that survive can reproduce and they pass on their advantageous traits to their offspring
- Evolution - over time the advantageous trait spreads through the population until all individuals have it. The species has now evolved.

Question 13

How can antibiotic resistant bacteria be used as evidence for Darwin’s theory?

Answer 13

Some bacteria in a population are naturally more resistant to antibiotics than others (genetic variation), when the person starts taking antibiotics (environmental change), those that are the least resistant die off first and if the antibiotic course is finished early, the most resistant will remain (natural selection), they will then divide and produce clones with the same DNA as them (inheritance), so the antibiotic-resistance gene will be spread throughout the population until all have it. The bacteria have now evolved.

Question 14

Where did Darwin go and what did he do there?

Answer 14

He went to the Galápagos Islands and noticed differences in mockingbirds on different islands. This led him to begin thinking about evolution and how this could be.

Question 15

What did Malthus’ ‘A Principle of Population’ state and what did Darwin conclude from it?

Answer 15

That if people had too many children, some would die as there would not be enough food. Darwin concluded that organisms naturally produced more offspring than could survive and only those best suited to the surroundings would survive and reproduce to pass in their characteristics (natural selection).

Question 16

What did Darwin and Wallace do in 1858?

Answer 16

Wallace had noticed differences in the colouration of tiger beetles in Indonesia then read Malthus’ essay and come to the same conclusion. He wrote to Darwin, who produced a summary of his ideas which were published in a scientific paper alongside the letter.

Question 17

Why is Darwin famous but Wallace is not?

Answer 17

Darwin published his book, On the Origin of Species, before Wallace could publish, so Darwin was credited with the theory of evolution by means of natural selection.

Question 18

Why was Darwin’s theory slow to be accepted?

Answer 18

It challenged the belief in creation by a god. Darwin couldn’t explain how variation occurred or how traits were inherited as genes had not been discovered yet, so many viewed the evidence as inconclusive.

Question 19

What is the pentadactyl limb and what does it show about evolution?

Answer 19

A pentadactyl limb is a limb with 5 ‘digits’. All vertebrates have the pentadactyl limb, suggesting that they must have evolved from a common ancestor and changed shape over time to fit different purposes (running, swimming, flying).

Question 20

How are organisms classified?

Answer 20

KPCOFGS (KP Crisps Only Fry Good Spuds):
Kingdom
Phylum
Class
Order
Family
Genus
Species

Question 21

What is a binomial name?

Answer 21

Binomial name = genus species
E.g. African elephants:
genus = Loxodonta
species = africana
binomial name = Loxondonta africana.

Question 22

What is the problem with classifying organisms based solely on what they look like?

Answer 22

It means that organisms which look similar but evolved from different ancestors are thought to be closely related, when in fact, they are not.

Question 23

What are the 5 kingdoms (Linnaeus) and their characteristics?

Answer 23

Animals - multicellular, cells have nuclei, no cell walls
Plants - multicellular, have chloroplasts, cells have nuclei, cellulose cell walls
Fungi - multicellular (apart from yeast), live in or on the dead matter on which they feed, cells have nuclei, chitin cell walls
Protists - mostly unicellular, cells have nuclei, some have cell walls
Prokaryotes - unicellular, cells do not have nuclei, peptidoglycan cell walls

Question 24

What are the 3 domains (Woese) and their characteristics?

Answer 24

Archaea - cells with no nucleus, genes contain unused sections of DNA
Bacteria - cells with no nucleus, no unused sections of DNA in genes
Eukarya - cells with a nucleus, genes contain unused sections of DNA.
The 3 domain system was based on genetic analysis.

Question 25

What is selective breeding and how is it done?

Answer 25

Selective breeding (artificial selection) is when humans choose certain organisms to breed because of certain characteristics they have, such as sheep with thick wool. This is done by choosing the two individuals in the population which most strongly display the desired characteristic and breeding them. The two offspring who most strongly display the characteristic are then bred and this process is continued until the trait becomes more and more pronounced and a new breed (animals) or variety (plants) is produced.

Question 26

What are organisms often selectively bred for?

Answer 26

• disease resistance
• yield (larger plants)
• coping with certain environmental conditions
• fast growth
• flavour

Question 27

What are some problems with selective breeding?

Answer 27

Inbreeding - breeding closely related organisms often leads to genetic disorders in the offspring
Takes a long time - it takes many years for the desired characteristic to come up strongly.
Reduces the gene pool - selective breeding causes many alleles to disappear, meaning if there is an environmental change, the species is at much greater risk of not surviving it as there is less variation.

Question 28

What is genetic engineering?

Answer 28

It involves the changing of the DNA of one organism (its genome), often by inserting genes from another. This creates genetically modified organisms (GMOs).

Question 29

What is golden rice and what does it do?

Answer 29

Golden rice is a GMO with two genes inserted into its genome, one from a daffodil and one from a bacterium. They allow the rice to produce beta-carotene in its grains, which is needed in humans to make vitamin A, a lack of which can cause blindness. It is hoped that it can be grown in poorer countries where vitamin A deficiency is a problem to prevent blindness.

Question 30

What are some issues with genetic engineering?

Answer 30

‘Superweeds’ - GM crops could reproduce with wild plants to produce a ‘superweed’ which is resistant to herbicides
Affects food chains - many GM crops produce pesticides, meaning that the insects have no food to eat, so they die out and their predators have no food, and this continues up the food chain
Some people think eating GMOs is bad for their health (but there is no evidence for this)
GM bacteria produce insulin, but it is slightly different to insulin from mammals so not all diabetics can use it.

Question 31

How can bacteria be genetically modified to produce insulin?

Answer 31

• restriction enzymes make staggered cuts in DNA, producing sections with a few unpaired bases at each end (sticky ends), the human gene for making insulin is cut out in this way
• the same restriction enzymes are used to cut plasmids open (because the enzymes are the same, the sticky ends produced are the same as this on the insulin gene).
• the insulin genes and cut plasmids are mixed together and the complementary bases on the sticky ends match up, DNA ligase joins the ends together.
• the plasmids are inserted back into the bacteria (the vector), which are grown in huge tanks. The insulin they make is extracted.

Question 32

What is tissue culture?

Answer 32

The growing of cells or tissues in a liquid containing nutrients or on a solid medium (such as agar). It is a useful way to grow many identical cells and sometimes the cells are treated to make them differentiate.

Question 33

How is tissue culture done of animals?

Answer 33

• separate the cells in a small piece of tissue by mashing or using enzymes
• prepare a solid or liquid growth medium containing sugars and nutrients
• pour a thin layer of cells onto a sterile solid medium or suspend the cells in a sterile liquid medium
• store the cells in a warm place to encourage cell division and growth

Question 34

How is tissue culture done of plants?

Answer 34

• take a tiny piece of plant tissue from a rapidly growing area
• prepare a solid medium containing sugars, nutrients and growth hormones
• place a tiny piece of tissue on the sterile solid medium
• store in a bright warm place to encourage cell division, growth and differentiation.

Question 35

What are some uses of tissue culture of plants and animals?

Answer 35

A - could be used to produce replacement human organs
A - can be used for testing new medicines without risking harm to live animals or people
A/P - makes it easier to study how disease affects the way cells work
P - produces many identical individuals with desirable characteristics
P - produces individuals from species that do not grow well from seed (e.g. orchids)
P - can be used to produce many individuals of an endangered species

Question 36

Why is aseptic technique so important in tissue culture?

Answer 36

It ensures that the cultures will not be contaminated by microorganisms.

Question 37

What is biological control?

Answer 37

The use of organisms to control pests.

Question 38

What are the advantages and disadvantages of using biological control?

Answer 38

Advantages - it can increase yield by killing pests, does not damage environment as much as chemical control methods (pesticides, herbicides)
Disadvantages - it sometimes doesn’t work and can cause worse problems than before (e.g. the organism introduced as a control may become a new pest, or start preying in other local species)

Question 39

Why are fertilisers used?

Answer 39

Normally, plants take minerals and nutrients from the soil as they grow but when they die, the nutrients they contain are released back into the ground when they decompose. However, in farmland, the plants are harvested before they die, so the minerals are not replaced and the soil soon becomes mineral deficient. Fertilisers are used to supply the land with minerals.

Question 40

What are the two types of fertilisers + pros and cons of each?

Answer 40

• organic fertilisers are made from manure mixed with straw - they do not damage the environment however you can’t control the nutrients that are in it so it may give lower yields.
• inorganic fertilisers are made from chemicals such as sodium, potassium, phosphorus, nitrates and ammonia - they are bad for the environment and can get into water systems and kill aquatic life and harm animals/humans that drink it however you can control what nutrients are in it so they may produce higher yields.