Classification & Evolution (OCR A Level Biology)

Many algal species are unicellular organisms. Some occur in colonies of more than one cell.

Fig. 21.2 shows a typical algal cell.

Fig. 21.2

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The cheetah, Acinonyx jubatus, is a member of the cat family, Felidae.

Cheetahs display less intraspecific variation than other members of the family Felidae.

Fig. 20.1 shows the mean body length of a population of cheetahs from southern Africa.

The error bars on Fig. 20.1 show the standard deviation of mean body length.

Fig. 20.1

The population of cheetahs has been declining for the past 100 years and is estimated to be between 6000 and 7000.
Within the remaining cheetah population, intraspecific genetic diversity is very low.
One isolated population of cheetahs in Iran has fewer than 100 individuals.

Madagascar is a large island off the coast of Africa that once formed part of the mainland.

The fossa, Cryptoprocta ferox is the top predator on Madagascar.

The fossa shares many physical similarities with cats but it is not a member of the family Felidae. It is related to the mongoose.

The mongoose is a much smaller mammal that lives on the African mainland.
Fig. 20.2 shows a fossa and a mongoose.

State three other conditions that must be present in order for speciation to occur.

1 ...............................................
2 ...............................................
3 ...............................................

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Bacteria that are able to digest and metabolise the hydrocarbons in crude oil are more common in areas, such as around the coast of Alaska and the Gulf of Mexico, where oil spillages are common.

Suggest an explanation for this observation.

The effect of wave action on the height of the shells of the dog whelk (Nucella lapillus) was investigated by comparing an exposed shore and a sheltered shore.

• A random sampling technique was used to collect 50 shells from an exposed shore.
• The shell height was measured from the base to the conical tip. The whelk was returned to its location.
• The process was repeated for the sheltered shore.
• All the results were recorded in Table 3.1.

Table 3.1

The t test can be used to determine the significance of the differences between shell height on the exposed shore and the sheltered shore.

Calculate the t value for the data using the formula:

where,

is the difference in mean values of sample 1 and sample 2

and are the squares of the standard deviations of the samples

n₁ and n₂ are the sample sizes.

Give your answer to two decimal places.

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The null hypothesis is that there is no difference between the means of the two shell populations.

The critical values at 98 degrees of freedom are shown in Table 3.2.

Table 3.2

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The students organised the data from Table 3.1 into classes.

The organised data is shown in Table 3.3.

Sheltered shore			Exposed shore
Height (mm)	Tally	Total	Height (mm)	Tally	Total
23–26		5	11–14		4
27–30		22	15–18		7
31–34		11	19–22		12
35–38		9	23–26		12
39–42		3	27–30		4

Plot the most suitable graph of the data given in Table 3.3.

Use the data and graph to discuss any correlation between the height of the whelk shell and the type of shore.

Suggest explanations for your findings.

Suggest a limitation of the procedure used to gather the data in this experiment and recommend how you could improve this.

How could the students improve the accuracy of their data?

Discuss the validity of the conclusions you have made during this experiment.

Termites are highly social insects. They are thought to have evolved from earlier forms of insect at least 150 million years ago, in the Jurassic geological period. They are related to cockroaches.

Fig. 5.1, shows a termite mound, the nest of approximately one million individuals.

Fig. 5.1

The photograph was taken in Queensland Australia, about 3000 kilometres south of the equator.

In Africa, closer to the equator, the mounds built by some species of termite are blade-shaped, with the long axis pointing North–South. Fig. 5.2, shows an example of a termite mound in Africa.

Most termites eat only dead vegetable material, so their principle food source is cellulose.

Cellulose is a polymer.

State the name of the monomer in cellulose.

Use the information given to state one argument that supports this statement and one argument that does not.

Two species of chimpanzees, the chimpanzee and the bonobo, are the closest living relatives of humans.

Fig. 19.1 is a diagram representing the current classification of chimpanzees and humans within the Family Hominidae.

Fig. 19.1

Humans and chimpanzees are currently classified within the same family.

Chimpanzees were once classified separately from humans in the Family Pongidae along with gorillas and orang utans.

Fig. 19.2 shows a human hand and a chimpanzee hand.

Describe two differences between the two images that could have been used to classify humans and chimpanzees in separate families.

Differences between the nucleotide base sequences can be used to estimate the length of time since two species diverged from one another.

The greater the number of differences, the greater the length of time that has elapsed since the two organisms were part of the same species.

Fig. 19.3 shows the line of best fit for the differences in DNA between pairs of primate species plotted against the number of years since the two species diverged from a common ancestor.

Fig. 19.3

Answer ............................% per million years [2]

Domesticated pigs are descended from Sus scrofa, sometimes called the ‘wild boar’.

• number the levels in the correct sequence and
• complete the name column.

Table 17.1

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The mean levels of human lactose intolerance vary in different parts of the world.

Table 18.1 shows the contrasting levels of lactose intolerance in two ethnic groups from different parts of the world.

Table. 18.1

The Hardy–Weinberg principle states that:

p + q = 1
p² + 2pq + q² = 1

Where p is the frequency of the dominant allele and q is the frequency of the recessive allele in the genotypes of a population.
  
The lactose intolerance allele is recessive to the mutant allele, which prevents lactose intolerance.
Calculate the frequency of the heterozygous genotype in the Australian aborigine population.

Read the following five statements.

Suggest how the lactose intolerance phenotype came to be present in only 5% of a population like the Europeans, but came to be present in 97% of the Australian aborigines. Use the information given above and knowledge of Darwin’s theory of evolution by natural selection.

An Iron Age farm was excavated by archaeologists. Some DNA was recovered from the tooth of an animal thought to be a type of domesticated milk cow.

A farmer keeps rare breed cows similar to those farmed on the Iron Age farm. DNA from the cows was obtained.

What technique would you plan to use, to compare digested and amplified fragments from the two DNA samples?

The heights of limpets (Patella vulgta) on exposed and sheltered rocky shores were measured to determine the effect of wave action. Ten shells were randomly collected and their height measured in each location.

 The results are shown below:

18, 16, 17, 18, 16, 20, 19, 17, 18, 17

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Suggest a limitation of the procedure used to gather the data in this investigation and explain how this limitation could be improved.

The investigation was repeated to improve the accuracy of the data.

Explain why this would not help.

A group of scientists investigated the relationship between the length and width of oak (Quercus robur) leaves.

Ten leaves were collected and their length and width measured with a ruler and recorded in the table below.

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The critical value of r_s at the 5% level (n = 10) is 0.65. The scientists conclude that there is a genuine positive correlation between the length and width of oak leaves.

Evaluate this conclusion.

In this investigation, the leaves were randomly selected from various oak trees.

Suggest three ways in which the validity of the sampling method could be improved.

The image below shows the leafy seadragon (Phycodurus eques), found along the southern and western coasts of Australia. The leafy seadragon has long leaf-like protrusions all over the body and small transparent fins which slowly undulate.

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Heliconius are a genus of butterflies commonly known as longwings or heliconians. They are found in tropical and subtropical areas and feed upon poisonous plants, making them toxic to predators. 

Heliconius exhibits brightly coloured wing patterns as shown in the image below.

The brightly coloured wing patterns signal the toxicity of the butterflies to predators and are controlled by one gene, named cortex, which was identified in 2016.

Over time, different species of Heliconius have evolved to have similar wing patterns. Explain how this is an example of natural selection.

The brightly coloured wing patterns of Heliconius are thought to have developed through the process of Mullerian mimicry where organisms sharing common predators mimic each other's warning signals to their mutual benefit.

Explain why this is an example of convergent evolution.

Clostridium difficile (C. diff) is a bacterium which is resistant to multiple antibiotics including penicillins and tetracyclines.

Genes for antibiotic resistance are often found outside the main bacterial chromosomes.

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The genomes of some bacteria change through conjugation; the exchange of genetic information between bacterial cells when they are in close contact. The DNA repair process of this genetic information is less effective than in chromosomal DNA.

[3]

Explain why the number of antibiotic-resistant populations of bacteria such as Clostridium difficile are increasing.

The image below shows a phylogenetic tree showing the relationship between primate species. It is based on the DNA sequence of the gene that codes for cytochrome c.

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Cytochrome C has a tertiary structure and plays an important role as an electron carrier in respiration. There is found to be one difference in the cytochrome c sequence between humans and rhesus monkeys and ten differences in the cytochrome c sequence between humans and kangaroos.

Explain how Cytochrome C is able to perform the same function in these different species despite the differences in gene sequence.

Cytochrome C is an integral protein to the oxidative phosphorylation stage of respiration.

Explain why this makes cytochrome C an important molecule used for DNA comparison between organisms.