Exam questions · Biology
Evolution and Natural Selection
- 42 exam questions
- 146 marks
- 63 quick checks
Darwin and Wallace
Just this lesson-
1 State [2 marks]
State the names of the two scientists who put forward the theory of evolution by natural selection.
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Model answer
Charles Darwin and Alfred Russel Wallace.
Mark scheme
- Darwin — 1 mark
- Wallace — 1 mark
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2 Describe [3 marks]
Describe how Darwin collected evidence for his theory.
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Model answer
Darwin travelled round the world on HMS Beagle, collecting plants, animals and fossils. He studied the animals of the Galápagos Islands, such as finches and tortoises, and noticed differences between the islands. He also studied selective breeding by pigeon breeders.
Mark scheme
- Voyage on the Beagle — 1 mark
- Galápagos species — 1 mark
- Selective breeding — 1 mark
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3 Explain [3 marks]
Explain why Darwin delayed the publication of his theory.
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Model answer
He wanted to collect more evidence and to check his ideas thoroughly. He also knew that the theory would upset many people because it contradicted religious beliefs about creation.
Mark scheme
- Wanted more evidence — 1 mark
- Aware it would upset people — 1 mark
- Contradicted beliefs about creation — 1 mark
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4 Explain [4 marks]
Explain why the theory of evolution by natural selection was not accepted by everyone when it was first published.
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Model answer
Many people believed that species had been created separately, and the theory conflicted with religious teaching. The idea that humans shared an ancestor with apes was offensive to some people. Evolution is very slow, so the evidence could not be seen directly, and there was no mechanism to explain how characteristics are inherited.
Mark scheme
- Religious beliefs — 1 mark
- Humans and apes — 1 mark
- Too slow to observe — 1 mark
- No mechanism for inheritance — 1 mark
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5 Explain [4 marks]
Explain how the discovery of genes and DNA made the theory of evolution more convincing.
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Model answer
Darwin could not explain how features are passed from parents to offspring. Genetics showed that characteristics are controlled by genes, which are passed on in gametes, and that DNA can mutate to produce new variation. This gave the mechanism for both inheritance and variation, which supports natural selection.
Mark scheme
- Darwin had no mechanism of inheritance — 1 mark
- Genes pass on characteristics — 1 mark
- Mutations give new variation — 1 mark
- This supports natural selection — 1 mark
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6 Evaluate [6 marks]
Evaluate the importance of the work of Darwin and Wallace to modern biology.
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Model answer
Darwin and Wallace independently developed the idea that species change over time by natural selection. Darwin supported it with a large amount of evidence from the Beagle voyage, the Galápagos and selective breeding, and Wallace added evidence from his collecting. The theory explained the variety of life and the fact that all organisms are related by common ancestors, and it is now the basis of biology. When genetics and DNA were discovered, they supplied the missing mechanism of inheritance and variation. The theory also helps to explain modern problems such as antibiotic resistance. It is therefore the unifying idea of the subject.
Mark scheme
- They developed natural selection — 1 mark
- Evidence from Darwin — 1 mark
- Wallace's independent work — 1 mark
- Explains common ancestry — 1 mark
- Genetics supplied the mechanism — 1 mark
- A modern application, such as antibiotic resistance — 1 mark
Quick check
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1
Which scientist sailed on HMS Beagle?
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B: Darwin
Charles Darwin sailed on HMS Beagle from 1831 to 1836.
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2
In which year was On the Origin of Species published?
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C: 1859
Darwin published his book in 1859.
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3
Which scientist independently came up with the idea of natural selection?
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A: Alfred Russel Wallace
Alfred Russel Wallace reached the same conclusion on his own, and sent it to Darwin in 1858.
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4
On which group of islands did Darwin study finches?
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D: The Galápagos Islands
Darwin studied finches and other animals on the Galápagos Islands.
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5
Which was a reason why many people rejected Darwin's theory?
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B: It conflicted with the belief that species were created separately
It went against the religious belief that each species had been created separately.
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6
What did Darwin not know about?
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C: Genes and how inheritance works
Darwin did not know how characteristics are inherited, because genes had not yet been discovered.
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7
Which discovery later provided the mechanism of inheritance?
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D: Genetics
Genetics, including Mendel's work and the discovery of DNA, explained inheritance.
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8
Why did Darwin study pigeon breeders?
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A: Selective breeding produces new varieties, like natural selection
Breeders choose parents to produce new varieties, which gave Darwin an idea of how nature might select.
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9
Why was it important that Wallace reached the same idea independently?
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B: It supported the idea and pushed Darwin to publish
Two scientists arriving at the same conclusion from different evidence gave the idea more support, and pushed Darwin to publish.
Natural Selection
Just this lesson-
1 State [2 marks]
State two things that organisms in a habitat may compete for.
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Model answer
Any two from: food, water, light, space, mates, shelter.
Mark scheme
- First — 1 mark
- Second — 1 mark
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2 Define [2 marks]
Define the term adaptation.
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Model answer
A feature of an organism that helps it to survive and reproduce in its environment.
Mark scheme
- A feature of an organism — 1 mark
- Helps survival / reproduction in its environment — 1 mark
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3 Describe [3 marks]
Describe what happened to the proportions of dark and pale peppered moths during the Industrial Revolution.
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Model answer
The proportion of dark moths increased, from about 2% in 1848 to about 98% in 1895, and the proportion of pale moths fell from about 98% to about 2%.
Mark scheme
- Dark moths increased — 1 mark
- Pale moths decreased — 1 mark
- Figures to support — 1 mark
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4 Explain [4 marks]
Explain why dark peppered moths became more common in industrial areas.
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Model answer
Soot from factories made the tree trunks dark. Dark moths were better camouflaged, so birds were less likely to eat them. They were more likely to survive and reproduce, and passed on the allele for dark colour to their offspring. So the proportion of dark moths increased.
Mark scheme
- Soot blackened the trees — 1 mark
- Dark moths were camouflaged and less likely to be eaten — 1 mark
- They survived and reproduced — 1 mark
- Passed on the allele for dark colour — 1 mark
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5 Explain [4 marks]
A giraffe's neck is long. Use Darwin's theory to explain how this may have evolved.
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Model answer
There was variation in neck length in the ancestors of giraffes. Those with longer necks could reach leaves higher up in the trees, and so had more food and were more likely to survive and reproduce. They passed on the alleles for long necks to their offspring, so over many generations the average neck length increased.
Mark scheme
- Variation in neck length — 1 mark
- Longer necks could reach more food and survive — 1 mark
- Passed on the alleles — 1 mark
- The average length increased over generations — 1 mark
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6 Evaluate [6 marks]
A student says: "The giraffe grew a longer neck because it needed to reach the leaves, and its babies inherited the longer neck." Explain why this idea is incorrect, and give the correct explanation.
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Model answer
This is Lamarck's idea, that a characteristic acquired during a lifetime is passed on. It is wrong because stretching a neck does not change the genes in the gametes, so the babies would not inherit a longer neck. A giraffe cannot change its genes because it needs to. The correct explanation is natural selection. There was variation in neck length because of different alleles. Giraffes with longer necks could reach more food, so they survived and reproduced more, and passed on their alleles. Over many generations, the alleles for long necks became more common in the population.
Mark scheme
- Describes the incorrect idea — 1 mark
- Acquired characteristics are not inherited — 1 mark
- Variation due to alleles — 1 mark
- Longer necks survive and breed more — 1 mark
- Pass on alleles — 1 mark
- Proportion increases over generations — 1 mark
Quick check
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1
What does natural selection act on?
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C: Variation in a population
Natural selection acts on the variation that is already present in a population.
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2
Which is the correct first step of natural selection?
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B: Variation
Variation between individuals is needed, so some are better suited than others.
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3
Why do dark peppered moths survive better in sooty areas?
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D: They are camouflaged on dark trees
They are camouflaged against the dark trees, so birds are less likely to see them.
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4
What is an adaptation?
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A: A feature that helps an organism survive in its environment
An adaptation is a feature that helps an organism to survive and reproduce in its environment.
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5
Which of these is an example of a behavioural adaptation?
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C: Migration of birds
Migration is something an organism does, so it is a behavioural adaptation.
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6
What does it mean to say that an adaptation is inherited?
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B: It is controlled by alleles passed to offspring
It is controlled by alleles that are passed from parents to offspring.
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7
Which idea is Lamarck's?
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A: Acquired characteristics are inherited
Lamarck suggested that features acquired during a lifetime are passed to offspring, which is not supported by evidence.
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8
How can a new species form?
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D: By isolation and different selection until they cannot interbreed
If groups are isolated and different characteristics are selected in each, they can become unable to interbreed.
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9
In an exam answer, which statement about natural selection is best?
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B: Giraffes with longer necks survive and reproduce more
Selection acts on variation that is already there. Organisms do not change because they need to.
Antibiotic Resistance
Just this lesson-
1 State [1 mark]
State what is meant by antibiotic resistance.
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Model answer
The ability of bacteria to survive an antibiotic that would normally kill them.
Mark scheme
- Bacteria survive the antibiotic — 1 mark
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2 Explain [2 marks]
Explain why antibiotics should not be used to treat a cold.
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Model answer
A cold is caused by a virus, and antibiotics do not kill viruses. Using them unnecessarily increases the chance that bacteria will become resistant.
Mark scheme
- Antibiotics do not kill viruses — 1 mark
- Increases the chance of resistance — 1 mark
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3 Calculate [3 marks]
A bacterium divides every 30 minutes. Calculate the number of bacteria produced from one bacterium after 5 hours, assuming no cells die.
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Model answer
5 hours is 300 minutes, so there are 300 ÷ 30 = 10 divisions. The number is 2 to the power 10, which is 1024 bacteria.
Mark scheme
- 10 divisions — 1 mark
- \(2^{10}\) — 1 mark
- 1024 — 1 mark
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4 Explain [4 marks]
Explain how the use of an antibiotic can lead to a population of bacteria becoming resistant.
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Model answer
There is variation in the bacteria, and by mutation a few are resistant. The antibiotic kills the non-resistant bacteria, but the resistant ones survive. They reproduce, passing on the resistance allele to their offspring, so the proportion of resistant bacteria in the population increases.
Mark scheme
- Mutation gives a resistant bacterium — 1 mark
- Non-resistant bacteria are killed — 1 mark
- Resistant bacteria survive and reproduce — 1 mark
- The proportion of resistant bacteria increases — 1 mark
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5 Explain [3 marks]
Explain why a patient should always finish a course of antibiotics.
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Model answer
Stopping early may leave some bacteria alive, including the ones that are least susceptible. These can reproduce, and the infection can return, with a greater chance that the surviving bacteria are resistant.
Mark scheme
- Some bacteria may survive — 1 mark
- They reproduce — 1 mark
- More likely to be resistant — 1 mark
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6 Evaluate [6 marks]
Hospitals use a number of measures to control MRSA. Evaluate how antibiotic resistance supports Darwin's theory of evolution, and suggest the ways it can be controlled.
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Model answer
Antibiotic resistance supports Darwin's theory because it shows all the steps of natural selection. There is variation, because a few bacteria have a mutation that makes them resistant. The antibiotic is the selection pressure, and the resistant bacteria are more likely to survive and reproduce. They pass on their resistance alleles, so the population changes over generations, and this can be seen in a short time because bacteria reproduce so quickly. It can be controlled by using antibiotics only when they are needed, and for the full course, so that fewer resistant bacteria are selected. Hospitals can also reduce the spread by handwashing and isolating infected patients. New antibiotics are also needed.
Mark scheme
- Variation from mutation — 1 mark
- Antibiotic as selection pressure — 1 mark
- Resistant survive and reproduce — 1 mark
- Population changes, over a short time — 1 mark
- Use antibiotics carefully / complete course — 1 mark
- Hygiene or isolation — 1 mark
Quick check
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1
How do bacteria become resistant to an antibiotic?
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C: By random mutation, and the resistant ones survive
A random mutation gives a bacterium resistance, and it then survives and reproduces.
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2
What is the selection pressure in antibiotic resistance?
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A: The antibiotic
The antibiotic kills non-resistant bacteria, so it selects for the resistant ones.
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3
Why do bacteria evolve so quickly?
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B: They reproduce very rapidly
They reproduce rapidly, so there are many generations in a short time.
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4
Why should antibiotics not be given for viral infections?
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D: They do not work on viruses and increase resistance
Antibiotics do not kill viruses, and unnecessary use makes resistance more likely.
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5
What does MRSA stand for?
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C: Methicillin-resistant Staphylococcus aureus
MRSA is methicillin-resistant Staphylococcus aureus.
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6
What happens to non-resistant bacteria when an antibiotic is used?
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A: They are killed
They are killed or stopped from growing.
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7
A bacterium divides every 20 minutes. How many bacteria are there after 2 hours, from one cell?
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D: 64
There are 6 divisions in 2 hours, so \(2^6 = 64\) bacteria.
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8
Which action helps to slow the development of antibiotic resistance?
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B: Finishing the course of antibiotics
Finishing the course makes sure that all the bacteria are killed, instead of leaving resistant ones.
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9
A student says that "antibiotics cause bacteria to mutate and become resistant". What is wrong with this?
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C: Mutations occur at random, and the antibiotic selects resistant bacteria
Mutations happen at random. The antibiotic does not cause them, it selects the bacteria that already have the resistance allele.
Fossil Evidence for Human Evolution
Just this lesson-
1 State [2 marks]
State two features that the fossil Lucy shows about how her species moved.
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Model answer
She walked upright on two legs, shown by her pelvis and knee, and she could still climb trees, shown by her long arms.
Mark scheme
- Walked upright — 1 mark
- Could still climb — 1 mark
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2 State [2 marks]
State the age of the fossils of (a) Ardi and (b) Lucy.
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Model answer
(a) 4.4 million years. (b) 3.2 million years.
Mark scheme
- 4.4 million years — 1 mark
- 3.2 million years — 1 mark
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3 Calculate [3 marks]
The brain volume of Ardi was 325 cm³ and the brain volume of a modern human is 1350 cm³. Calculate the percentage increase in brain volume. Give your answer to the nearest whole number.
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Model answer
The increase is 1350 − 325 = 1025 cm³. The percentage increase is 1025 ÷ 325 × 100 = 315%.
Mark scheme
- Increase of 1025 — 1 mark
- Divide by 325 and multiply by 100 — 1 mark
- 315% — 1 mark
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4 Describe [3 marks]
Describe how the brain volume changed from Ardi to the Homo erectus fossils from 1.6 million years ago.
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Model answer
The brain volume increased from about 325 cm³ in Ardi to about 400 cm³ in Lucy, and then to about 880 cm³ in Homo erectus. The increase was larger in the later period.
Mark scheme
- Increased — 1 mark
- Values for the fossils — 1 mark
- Larger increase between Lucy and Homo erectus — 1 mark
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5 Explain [4 marks]
Explain how the fossils of Ardi and Lucy provide evidence that walking upright evolved before large brains.
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Model answer
Both Ardi and Lucy had features such as a pelvis and leg bones that show they could walk upright. Their brain volumes were small, at about 325 and 400 cm³, similar to those of a chimpanzee. So the ability to walk upright was present millions of years before the brain became much larger, as shown by the later Homo erectus.
Mark scheme
- Pelvis and leg shape show walking upright — 1 mark
- Both were old fossils (4.4 and 3.2 million years) — 1 mark
- Brain was small — 1 mark
- Large brain appeared later — 1 mark
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6 Evaluate [6 marks]
Evaluate the use of fossils as evidence for human evolution.
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Model answer
Fossils provide direct evidence of the structure of our ancestors. The finds of Ardi, Lucy and the Leakey fossils show a gradual change from small brains and a mixed walk and climb to large brains and an efficient upright walk, over millions of years. The fossils can also be dated, so the order of changes can be worked out. However, the fossil record is incomplete because fossilisation is rare, and many species may be missing. Often only a few bones are found, so scientists can disagree about how to interpret them. The dating methods have some uncertainty. Overall, fossils are strong evidence, particularly when they are supported by DNA evidence.
Mark scheme
- Direct evidence of structure — 1 mark
- Shows gradual change — 1 mark
- Can be dated — 1 mark
- Record is incomplete — 1 mark
- Interpretation is uncertain — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
Which fossil is about 3.2 million years old?
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B: Lucy
Lucy lived about 3.2 million years ago.
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2
Which fossil is the oldest?
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A: Ardi
Ardi, at about 4.4 million years, is older than Lucy and the Homo erectus fossils.
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3
What does the pelvis of Lucy show?
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C: That she walked upright
The shape of her pelvis shows that she walked upright on two legs.
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4
Which fossil had the largest brain?
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D: Homo erectus
The Homo erectus fossil, with about 880 cm³, had a bigger brain than Lucy or Ardi.
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5
In which country were Ardi and Lucy found?
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B: Ethiopia
Both were found in Ethiopia, in East Africa.
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6
What evolved first in human ancestors?
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A: Walking upright
Fossils such as Ardi and Lucy show that walking upright came before large brains.
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7
Why is the fossil record incomplete?
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C: Few organisms become fossils
Fossilisation is rare, so most organisms never form fossils.
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8
Lucy's brain was 400 cm³ and the Homo erectus boy's was 800 cm³. What is the percentage increase?
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D: 100%
The increase is 400, and \(400 \div 400 \times 100 = 100\%\).
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9
Scientists sometimes disagree about how a fossil fits into human evolution. Why?
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B: Only a few bones are often found, so they are hard to classify
Often only a few bones are found, so the fossil is hard to classify, and different scientists interpret them differently.
Stone Tools and Human Evolution
Just this lesson-
1 State [2 marks]
State two ways in which stone tools changed over time.
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Model answer
Any two from: they became more complex; they became more symmetrical and finely shaped; they were made for specific purposes; they were made of more materials, such as bone.
Mark scheme
- First change — 1 mark
- Second change — 1 mark
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2 Explain [3 marks]
Explain what a hand axe shows about the person who made it.
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Model answer
It had to be shaped on both sides to a symmetrical design, so the maker had to plan the shape in advance and carry out many steps. This suggests skill, a larger brain and the ability to learn from others.
Mark scheme
- Had to plan the shape — 1 mark
- Skill / dexterity — 1 mark
- Larger brain / learning — 1 mark
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3 Describe [3 marks]
Describe how a stone tool found between two layers of volcanic ash can be dated.
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Model answer
The age of each layer of ash is found, using radioactive dating. The tool is younger than the lower layer and older than the upper layer. So its age lies between the ages of the two layers.
Mark scheme
- Ash layers are dated — 1 mark
- Tool is younger than the layer below — 1 mark
- And older than the layer above — 1 mark
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4 Calculate [3 marks]
Sediment builds up at 1 cm every 500 years. A stone tool is found 60 cm below a layer that is 2.0 million years old. Calculate the age of the tool.
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Model answer
60 cm × 500 years = 30 000 years. The age is 2 000 000 + 30 000 = 2 030 000 years.
Mark scheme
- 60 × 500 = 30 000 — 1 mark
- Adds to 2 000 000 — 1 mark
- 2 030 000 years — 1 mark
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5 Explain [4 marks]
Explain how stone tools provide evidence that humans evolved over a long period of time.
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Model answer
The oldest tools are simple choppers, and later tools such as hand axes are more complex and symmetrical. Later still there are finely made blades and tools of bone. This gradual increase in complexity matches the increase in brain size seen in fossils, suggesting that the skills and intelligence of our ancestors developed over millions of years.
Mark scheme
- Simple tools are oldest — 1 mark
- Tools became more complex — 1 mark
- Matches increase in brain size — 1 mark
- Gradual change over millions of years — 1 mark
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6 Evaluate [6 marks]
Evaluate the use of stone tools as evidence for human evolution, compared with fossil bones.
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Model answer
Stone tools last much longer than bones and are more common, so they give a more continuous record. They show the skills, behaviour and planning of the maker, which bones cannot. However, the tools do not show what the maker looked like, and they may be found without fossils, so it can be unclear which species made them. Tools made from wood or bone rot away, so the record is biased, and layers can be disturbed so that dating is wrong. Fossils show the structure, such as brain size and body shape, but they are rare and incomplete. Used together, they give much better evidence than either alone.
Mark scheme
- Tools last and are common — 1 mark
- Show behaviour and skills — 1 mark
- Do not show structure, maker unknown — 1 mark
- Perishable tools / disturbed layers — 1 mark
- Fossils show structure but are rare — 1 mark
- Together they give better evidence — 1 mark
Quick check
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1
Which are the oldest well-known stone tools?
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A: Oldowan choppers
Oldowan tools, made about 2.6 million years ago, are the oldest well-known stone tools.
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2
Which hominid made hand axes?
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C: Homo erectus
Homo erectus made symmetrical hand axes.
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3
What do more complex tools suggest?
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D: Greater skill, planning and a larger brain
Complex tools need planning and skill, which suggest a larger brain.
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4
In undisturbed rock layers, which layer is the oldest?
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B: The bottom layer
Sediments build up on top of each other, so the lowest layers are the oldest.
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5
A tool is found between two ash layers dated 1.0 and 1.8 million years. How old is the tool?
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C: Between 1.0 and 1.8 million years
It is younger than the lower layer and older than the upper layer, so its age is between 1.0 and 1.8 million years.
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6
What can be dated by radiocarbon dating?
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A: Charcoal younger than about 50 000 years
Carbon-14 can be used to date organic material, such as charcoal or bone, up to about 50 000 years old.
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7
Which is a limitation of stone tools as evidence?
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D: The maker is often unknown
The maker is often unknown, and tools made of wood rot away.
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8
Why do scientists use several different dating methods?
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B: To make the result more reliable
Cross-checking the results makes the age more reliable.
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9
The Lomekwi tools are older than any known Homo fossils. What does this suggest?
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A: Tool making began earlier than thought, perhaps before Homo
It suggests that tool making began earlier than the genus Homo, perhaps by an earlier hominid.
The Pentadactyl Limb
Just this lesson-
1 Name [3 marks]
Name the three groups of bones that are found in the limb of a human, a bat and a whale, apart from the humerus.
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Model answer
The radius and ulna, the carpals, and the metacarpals and phalanges.
Mark scheme
- Radius and ulna — 1 mark
- Carpals — 1 mark
- Metacarpals and phalanges — 1 mark
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2 State [2 marks]
State what is meant by the term pentadactyl limb.
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Model answer
A limb with five digits, which has the same basic pattern of bones in many vertebrates.
Mark scheme
- Five digits — 1 mark
- Same basic pattern of bones — 1 mark
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3 Explain [3 marks]
Explain why the human arm and the bat wing are described as homologous structures.
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Model answer
They have the same basic arrangement of bones, which is the humerus, radius and ulna, carpals and digits, but they have different functions. This is because they are inherited from a common ancestor.
Mark scheme
- Same arrangement of bones — 1 mark
- Different functions — 1 mark
- Inherited from a common ancestor — 1 mark
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4 Explain [4 marks]
Explain how the pentadactyl limb gives evidence for evolution from a common ancestor.
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Model answer
Animals as different as humans, bats and whales have limbs with the same arrangement of bones. If each had evolved separately, there would be no reason for them to share this pattern. The best explanation is that they inherited it from a common ancestor. Natural selection then changed the sizes and shapes of the bones to suit each way of life.
Mark scheme
- Same bones in different animals — 1 mark
- Would not be expected if separately evolved — 1 mark
- Inherited from common ancestor — 1 mark
- Natural selection adapted for function — 1 mark
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5 Explain [4 marks]
Explain how the bones of a bat's wing are adapted for flight.
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Model answer
The finger bones are very long and thin, so they can support a large wing surface. A thin membrane of skin is stretched between them, and this makes the wing light enough to be lifted. The thin bones also allow the wing to be folded away.
Mark scheme
- Long finger bones — 1 mark
- Support a wing membrane — 1 mark
- Light — 1 mark
- Can fold — 1 mark
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6 Evaluate [6 marks]
The wing of a bird and the wing of an insect have the same function. Evaluate whether this provides evidence of a common ancestor, and compare it with the pentadactyl limb.
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Model answer
The wings of a bird and an insect do the same job, but they have a completely different structure, because a bird's wing is made of bones, feathers and muscles, and an insect's wing is a thin membrane with veins. They are analogous structures, which evolved separately because flying is an advantage. This does not show a common ancestor. In contrast, the pentadactyl limb of a human, a bat and a whale has the same bones, despite different functions. They are homologous structures, so they provide evidence of a common ancestor. The structure, and not the function, is what shows a relationship.
Mark scheme
- Bird and insect wing have the same function — 1 mark
- Different structure — 1 mark
- Analogous, so no common ancestor — 1 mark
- Pentadactyl limb: same structure — 1 mark
- Homologous, so common ancestor — 1 mark
- Structure not function shows the relationship — 1 mark
Quick check
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1
How many digits does a pentadactyl limb have?
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C: Five
Pentadactyl means five digits.
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2
Which bone is in the upper part of the limb?
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A: Humerus
The humerus is the bone of the upper limb.
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3
What does the similar bone pattern in the arm of a human and the wing of a bat suggest?
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D: That they share a common ancestor
It suggests that they inherited the pattern from a common ancestor.
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4
What is the function of the whale's flipper?
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B: Swimming
The flipper is used for swimming and steering.
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5
Which structures are analogous?
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C: A bird wing and an insect wing
The wings of a bird and an insect have the same function but different structure and origin.
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6
Why is the horse's leg adapted for running?
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A: It is long with one digit and a hoof
It is long, with only one digit ending in a hoof, so it moves quickly.
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7
What has caused the bones of the limb to be different in different animals?
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D: Natural selection
Natural selection favoured different features in each species, according to their environment.
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8
What is divergent evolution?
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B: Related species evolving different features
It is the evolution of different features in related species from a common ancestor.
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9
A whale has a pentadactyl limb inside its flipper. What does this suggest?
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A: Whales evolved from land animals
It suggests that whales evolved from land animals with five-digit limbs.
Classification and the Three Domains
Just this lesson-
1 Name [3 marks]
Name the three domains of living things.
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Model answer
Bacteria, Archaea and Eukaryota.
Mark scheme
- Bacteria — 1 mark
- Archaea — 1 mark
- Eukaryota — 1 mark
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2 State [2 marks]
State two kingdoms of living things that are in the domain Eukaryota.
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Model answer
Any two from: animals, plants, fungi, protists.
Mark scheme
- First kingdom — 1 mark
- Second kingdom — 1 mark
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3 Describe [3 marks]
Describe how Carl Woese used genetic analysis to suggest the three domain system.
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Model answer
Woese compared the sequences of bases in the ribosomal RNA genes of many organisms. He found that the prokaryotes were not one group, because some, now called archaea, were very different from bacteria. This led him to propose three domains.
Mark scheme
- Compared gene sequences / rRNA — 1 mark
- Found two very different types of prokaryote — 1 mark
- Proposed three domains — 1 mark
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4 Explain [3 marks]
Explain why the use of genetic analysis changed the classification of living things.
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Model answer
Genetic analysis gives information about how closely related organisms are, which cannot always be seen from their appearance. It showed that the prokaryotes were two groups that were as different from each other as from the eukaryotes. So the classification had to be changed.
Mark scheme
- Genes show how closely related organisms are — 1 mark
- Appearance can be misleading — 1 mark
- Showed prokaryotes are two different groups — 1 mark
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5 Compare [4 marks]
Compare the five kingdoms system and the three domains system of classification.
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Model answer
The five kingdoms system was based mainly on the structure of organisms and the way they feed, whereas the three domains system is based on genetic analysis. In the five kingdoms system all the prokaryotes are in one kingdom, and in the three domains they are in two domains, Bacteria and Archaea. The eukaryotes are in the domain Eukaryota, which includes four of the kingdoms.
Mark scheme
- Structure and feeding / genetic analysis — 1 mark
- Prokaryotes in one group / two domains — 1 mark
- Five groups / three groups — 1 mark
- Eukaryota includes four kingdoms — 1 mark
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6 Evaluate [6 marks]
Evaluate why scientists changed from the five kingdoms to the three domains system, and why this shows how scientific ideas develop.
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Model answer
Woese used DNA sequencing to compare the genes of ribosomal RNA, a technique that was not available when the five kingdoms were developed. The results showed that archaea were as different from bacteria as they were from eukaryotes, which could not be seen from structure alone. This gave a more accurate picture of the evolutionary relationships. The idea was published and tested by other scientists, who found more evidence from other genes, so it became accepted. This shows that scientific ideas change when new technology gives new evidence, and that they are tested by others before they are accepted. Classification may change again as more genomes are sequenced.
Mark scheme
- DNA sequencing was new technology — 1 mark
- Compared rRNA genes — 1 mark
- Archaea very different from bacteria — 1 mark
- More accurate relationships — 1 mark
- Tested by other scientists — 1 mark
- Ideas change with new evidence — 1 mark
Quick check
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1
How many kingdoms are there in the five kingdoms system?
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B: Five
The five kingdoms are animals, plants, fungi, protists and prokaryotes.
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2
Which are the three domains?
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C: Bacteria, Archaea and Eukaryota
Living things are placed in the domains Bacteria, Archaea and Eukaryota.
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3
Who proposed the three domain system?
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A: Carl Woese
Carl Woese proposed it in 1977, using genetic evidence.
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4
In which domain are animals and plants?
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D: Eukaryota
Animals and plants have cells with a nucleus, so they are in Eukaryota.
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5
What evidence led to the three domain system?
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B: Genetic analysis
Comparing the base sequences of genes, such as those for ribosomal RNA, showed three main groups.
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6
Where are archaea often found?
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C: In extreme habitats, such as hot springs
Many live in extreme environments such as hot springs, salt lakes and deep-sea vents.
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7
Which statement about archaea is correct?
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A: They have no nucleus and differ genetically from bacteria
Archaea are prokaryotes with no nucleus, but they differ from bacteria in their genes and membranes.
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8
What is the binomial name for humans?
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D: Homo sapiens
The two-part name is Homo sapiens, with the genus first and the species second.
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9
Why can classification based on appearance be misleading?
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B: Unrelated organisms can look alike
Unrelated organisms may look alike because of similar functions, and related ones may look different, so genes give a better guide to relationships.