OCR A Level Biology A Unified Biology November 2020 question paper H420/03

A student dissected a kidney. Fig. 1.1 shows one half of the dissected kidney.

Draw a simple diagram of the kidney in Fig. 1.1 in the space below.

On your diagram, label the pelvis, medulla and cortex.

A photomicrograph of a stained section of kidney tissue is shown in Fig. 1.2.

State one function of the distal convoluted tubule.

Describe the function of the structures labelled A in Fig. 1.2.

Suggest which lumen, B or C, has the highest concentration of urea. Explain your answer.

* Water reabsorption in the kidney is controlled by the endocrine and nervous systems.

Aldosterone and ADH are hormones that act on the kidney.

Aldosterone causes sodium ions to be pumped from the collecting duct cells into tissue fluid.

Describe how the endocrine and nervous systems work together to increase water reabsorption from the collecting duct.

Additional answer space if required.

Diuretics are drugs that decrease the reabsorption of water into the blood from the kidney.

Diuretics can change the concentration of ions and other molecules in the blood.

Some diuretics are used to treat high blood pressure.

The table below lists three different diuretics, X, Y and Z, and some of their effects in the

Suggest which of the diuretics, X, Y or Z, would be the most effective at reducing a person’s blood pressure. Explain your choice.

Suggest which of the diuretics, X, Y or Z, would be the most appropriate for use by a person with type II diabetes. Explain your choice.

Valves control the flow of blood through the heart.

Complete the table below to show the roles of two valves in the heart.

A ventricular septal defect (VSD) is a hole in the septum of the heart.

The diagram below shows a heart with VSD.

Describe and explain why people with VSD can easily become tired.

Creatine kinase (CK) is an enzyme that catalyses reactions in heart muscle. High levels of CK in the blood indicate that a person may have had a heart attack.

Suggest why high levels of CK in the blood indicate that a person may have had a heart attack.

Mice are often used in laboratory studies to research treatments for heart conditions.

These mice are often clones.

Suggest one reason why clones are used in these studies.

Students investigated the effect of light on the growth of garden cress seedlings.

• A total of 120 seedlings were divided into 2 groups of 60.

• Group A was grown in darkness for 2 days.

• Group B was grown for 1 day in darkness and then for 1 day in white light using the set‑up shown in Fig. 3.1.

The results of the students’ experiment are shown in Tables 3.1 and 3.2.

* Describe and explain the results shown in Tables 3.1 and 3.2.

Additional answer space if required.

The students wanted to test whether there was a significant difference between the stem lengths of the seedlings in Group A and the seedlings in Group B.

State the name of the most appropriate statistical test for the students to use.

Justify your choice of statistical test given in part (ii).

Table 3.2 records the direction of growth as:

• away from light

• neither away from nor towards light

• towards light.

The students used the chi‑squared test to determine whether the direction of root growth was significantly different from their expectations.

Their null hypothesis was:

There is no difference between the expected direction of root growth and the observed direction of root growth.

The calculated chi‑squared value was 8.10.

The students compared their chi‑squared value of 8.10 to the values in Table 3.3.

What can the students conclude about their results based on a chi‑squared value of 8.10?

The solution in which the seedlings were grown contained various dissolved ions.

The table below lists two of the functions of these ions in the seedlings.

Complete the table below with the formula of each ion.

The students also investigated the effect of plant hormone concentration on root growth.

State the name of a plant hormone that would be expected to affect root growth.

In the investigation, the students controlled light, temperature and mineral concentration.

State one other factor that the students should have controlled in this investigation.

Prokaryotic cells have cytoskeletons. The molecules in prokaryotic cytoskeletons are different from the molecules in eukaryotic cytoskeletons.

Table 4.1 lists three molecules present in a prokaryotic cytoskeleton.

Suggest the function of Protein A.

Suggest the function of Protein C.

An antibiotic called A22 binds irreversibly to Protein B. Despite its antibiotic properties, A22 is not used in humans.

Suggest why scientists have advised that A22 should not be used in humans.

Vancomycin is an antibiotic that has been used to treat bacterial infections for many decades. Several strains of bacteria have evolved resistance to vancomycin.

Oritavancin is an antibiotic with a similar structure to vancomycin.

Table 4.2 shows data obtained from treatments with the two antibiotics.

Use the data in Table 4.2 to evaluate the advantages and disadvantages of using oritavancin rather than vancomycin as an antibiotic.

Complete the diagram above by writing the missing words or phrases in the boxes labelled X, Y and Z.

........ Answer on the diagram........

Suggest why the scientists used a plasmid that contained an antibiotic resistance gene.

The scientists observed the following:

• 1 in 400 bacteria took up the plasmid

• 1 in 1000 of the plasmids taken up by bacteria contained the ‑galactosidase gene.

Calculate the percentage of bacteria that contained the ‑galactosidase gene.

A technique called quantitative PCR is used to check that the E. coli population is growing on the mice liver tumours rather than on healthy tissue.

Suggest how the scientists could use PCR to compare E. coli growth rates on cancerous liver tissue and healthy tissue.

Some people think that the genetic engineering of certain organisms is unethical.

However, there are very few ethical concerns about the genetic engineering of bacteria such as E. coli.

Suggest why there are very few ethical concerns about the genetic engineering of E. coli

Ecologists were studying an area that contained three different habitats. The area is shown in the diagram below.

The ecologists sampled the area to estimate insect biodiversity.

Describe how the ecologists should choose the number and locations of their samples to ensure that the sampling is representative.

Use a calculation to support your answer.

Two of the insect species that were sampled were the large heath butterfly and the bog hoverfly.

The ecologists used the capture‑mark‑recapture technique and estimated population sizes using two different calculations: the Lincoln estimate and the Chapman estimate.

The Lincoln and Chapman formulae give different estimates for population size.

Give two further conclusions about the difference in population estimates given by the Lincoln and Chapman formulae.

The peat bog habitat had been damaged by peat extraction and by management of the neighbouring farmland. Ecologists decided to treat the peat bog in the following way:

• A buffer region was created between the peat bog and the neighbouring farmland.

• No visitors were allowed on the land.

• Ditches were blocked to raise water levels.

• Peat extraction, tree planting and the use of fertilisers were banned.

A student suggested that this was an example of preservation.

Evaluate the student’s conclusion.

Conservation agreements can be national (within a particular country) or international.

Three conservation agreements are listed in the table below.

Place ticks (✓) in the correct boxes to indicate which features are true for each of the three

The oxygen dissociation curves for adult haemoglobin and fetal haemoglobin are shown in Fig. 6.1.

Outline why it is important that fetal haemoglobin has a higher oxygen affinity than adult haemoglobin.

Myoglobin is a protein found in muscles. Oxygen binds to myoglobin.

A student described the oxygen dissociation curve for myoglobin as follows:

• When oxygen first becomes available, myoglobin saturation increases at a constant rate of 8% per mmHg of oxygen.

• When there is a slightly higher partial pressure of oxygen, the rate of oxygen binding slows gradually until the myoglobin is 100% saturated.

• The partial pressure at which myoglobin reaches 100% saturation is the partial pressure at which adult haemoglobin is 80% saturated.

Sketch an oxygen dissociation curve for myoglobin on Fig. 6.1 based on the description provided above.

........ Answer on Fig. 6.1........

Haemocyanin is an oxygen‑binding pigment that is found in many invertebrate animals, including lobsters.

Fig. 6.2 shows the oxygen dissociation curves for haemoglobin and haemocyanin.

What can you conclude about the habitat of a lobster?

When old red blood cells are broken down, each haem group is converted to a molecule called bilirubin. Bilirubin passes through the digestive system. Bilirubin gives faeces their characteristic colour.

Explain why bilirubin production and processing is an example of excretion.