OCR A Level Biology B (Advancing) Scientific literacy in biology June 2017 question paper H422/02

This question is based on the Advance Notice article TURBOCHARGED PHOTOSYNTHESIS which is an insert.

Use Fig. 1 on the insert to help you answer the following questions.

State the precise location of the photosystems involved in the light-dependent reaction of photosynthesis.

Describe how the structures containing the photosystems are arranged differently in plant cells and cyanobacteria.

State the precise location of Rubisco in:

unmodified plant cells........

Explain how cyanobacteria are able to almost eliminate oxygen (O₂) fixation by Rubisco.

Table 1 on the insert shows the results of experiments to measure carboxylase activity in wild type (WT) tobacco plants and two lines of modified tobacco plant at different concentrations of carbon dioxide (CO₂).

Explain why the units of carboxylase activity are ‘mol CO fixed per mol active sites s (i)₂ rather than just ‘mol CO₂ fixed s^–1’.

Plot a graph of these results on the grid below. Include error bars showing two standard deviations.

Using Table 1 and your graph in (b)(ii), analyse whether the researchers successfully demonstrated that replacing Rubisco in tobacco plants with the cyanobacterial enzyme increased the effectiveness of photosynthesis.

Explain your conclusions.

A student made the following statement:

“Photosynthesis is more effective in the M35 strain than the Rbcx strain.”

Use Table 1 and your graph in (b)(ii) to evaluate the validity of the student’s statement.

Explain your conclusions.

* Evaluate the risks and benefits of growing supercrops.

Oogenesis occurs in the ovaries of female mammals, resulting in the production of gametes.

Name the type of nuclear division that results in the production of secondary oocytes from primary oocytes during oogenesis.

Complete the table below to indicate the stage and type of nuclear division in which the events being described occur.

Fig. 2.1 shows how oestrogen production varies throughout life in human females.

Explain how the rapid increase in oestrogen production towards the end of the growth phase results in the release of secondary oocytes.

Changes occur to the cells within ovaries over the course of a woman’s lifetime.

Use the data in Fig. 2.1 to explain the role of oestrogen production in the changes to ovarian cells that occur during adulthood.

In your answer you should refer to the stages of nuclear division that occur.

Fig. 2.2 shows how the number of ovarian follicles changes from birth to 50 years of age.

Using the data in Fig. 2.2, describe and explain the relationship between the number of follicles and age.

Name the biological process that occurs as a result of changes in the number of follicles between 45 and 50 years of age.

Describe two symptoms that women may experience during this process.

There is evidence that heart rate increases when people experience pain. Heart rate is one physiological factor that is regulated tightly and kept within narrow limits.

Name the process by which the internal environment of an organism is kept within narrow limits.

A student made the following revision notes about the control of heart rate.

Complete the student’s notes using the most appropriate word(s).

‘The resting heart rate of an adult human is about 70 beats per minute. This is

known as the set point. There are two types of receptor that control heart

rate: ………………………………………………… in the walls of the carotid artery that detect

changes in blood pH and pressure receptors in the carotid artery and the

aorta. When blood pressure rises, pressure receptors transmit nervous impulses

to the ……………………………………………………… which decreases heart rate via the

……………………………………………………… nervous system. This is an example of

Some doctors who study pain ask patients to give an estimate of the level of their pain by using a scale of 1 to 10.

Explain why some researchers think that measuring heart rate is a more accurate way of determining the level of pain.

Neuropathic pain is a type of pain caused by neurones malfunctioning following nerve damage. When this happens, some voltage-gated sodium ion channels (VGSCs) in pain receptors open spontaneously.

Explain how the spontaneous opening of a VGSC in a pain receptor leads to the generation of a nerve impulse in the sensory neurone attached to the pain receptor.

Three different types of VGSC in different parts of the nervous system have been linked to neuropathic pain. Drugs to treat neuropathic pain are now being developed that specifically block these types of VGSC.

Suggest why it is important to develop drugs that only block these three types of VGSC.

Single nucleotide polymorphisms (SNPs) have been detected in the genes coding for several types of VGSC. It is thought that these SNPs might alter the response of different patients to drugs that block VGSCs.

Describe the steps involved in identifying the SNPs present in a DNA sample from a patient.

Screening for other SNPs is used in the study, diagnosis, and treatment of cancer.

A mutation in either the BRCA1 or BRCA2 gene increases the risk of breast cancer.

Explain why screening for these mutations is only offered to individuals with a strong family history of breast cancer and a living relative with breast cancer.

Fig. 4 shows a simplified diagram of part of a DNA molecule.

Fig. 4

Identify the parts of the DNA molecule labelled A to C in Fig. 4.

The table below shows the results of an analysis of the base composition for each strand of a DNA molecule.

Complete the table by adding the missing values for strands 1 and 2.

Hydrogen bonding is central to the function of nucleic acids.

Explain how hydrogen bonding contributes to the process of semi-conservative replication of DNA.

Hereditary non-polyposis colorectal cancer (HNPCC) is a type of bowel cancer caused by a mutation in genes that normally repair DNA.

Explain why mutations in DNA repair genes lead to development of cancer in the bowel and other organs.

The MenB vaccine was developed to protect against disease caused by the bacterium Neisseria meningitidis. Infection with this bacterium (meningococcal infection) is a major cause of meningitis and blood poisoning, particularly in babies and young children.

The MenB vaccine was introduced into the routine UK vaccination schedule on 1st September 2015. It is available to all new babies born on or after 1st July 2015.

The MenB vaccine is a subunit vaccine.

Explain what is meant by a subunit vaccine.

Parents have been reassured that the MenB vaccine cannot cause meningitis in their children.

Explain why the MenB vaccine cannot cause the disease.

The MenB vaccine has also been shown to be effective against other types of meningococcal infection.

Suggest why.

* Evaluate the importance of herd immunity in the prevention of epidemics.

Patients with chronic anaemia have reduced levels of haemoglobin in their blood. When anaemia develops over a long period of time, the concentration of the compound 2,3-bisphosphoglycerate (2,3-BPG) in the blood increases.

Fig. 6 shows the oxygen dissociation curves of haemoglobin from two individuals, one suffering from chronic anaemia and the other a normal control.

P₅₀ is the partial pressure of oxygen at which haemoglobin is 50% saturated.

Using Fig. 6, calculate the percentage increase in P₅₀ in the anaemic patient compared with the normal control.

Show your working. Give your answer to three significant figures.

Using the data in Fig. 6, describe the effect of 2,3-BPG on the oxygen affinity of haemoglobin.

Explain how this effect might partially compensate for the reduction in levels of haemoglobin that occur in anaemic patients.

Haemoglobin is contained in erythrocytes. While studying oxygen transport, a student investigated the water potential of erythrocytes. They wrote the following description in their laboratory notebook:

I placed a drop of blood on a microscope slide and covered it with a coverslip, then added a drop of distilled water on one side of the coverslip. I immediately observed the slide under high power. I repeated the procedure with sodium chloride solutions of two different concentrations to find the one that caused plasmolysis to occur.

Explain why the term ‘plasmolysis’ is used incorrectly in this student’s description.

State two ways in which the experimental procedure described by the student could be improved.

Fig. 7.1 shows the structures visible in a light micrograph of a generalised animal cell.

Identify the structures labelled D to H in Fig. 7.1.

Describe two functions of structure H and one function of structure J.

The route taken by proteins that are secreted from the cell has been worked out by many different experiments. One series of experiments involved the following steps:

• A virus was modified so that one of its proteins (VSVG) was tagged with green fluorescent protein (GFP).

• Cells were infected with the modified virus.

• The virus produced the tagged protein, VSVG-GFP, using the cells’ organelles, but only when the temperature was reduced from 40 °C to 32 °C.

• This allowed the path through the cell taken by the VSVG-GFP to be followed by fluorescence microscopy from the time the temperature was reduced.

Fig. 7.2 shows the results of one experiment where the distribution of fluorescence within individual cells was followed for up to 600 minutes.

Using Fig. 7.2 and your knowledge of the synthesis and secretion of proteins, identify the organelles corresponding to curves K, L and M on Fig. 7.2.

Give reasons for your answers.

Using Fig. 7.2, estimate the time taken for secretion of VSVG-GFP to reach a maximum.

Vinblastine is a drug used in the treatment of cancer. It inhibits the assembly of microtubules.

Another experiment similar to that described in part (b) was carried out, but the cells were treated with vinblastine before the temperature was reduced from 40° C to 32° C.

When VSVG-GFP fluorescence was followed through the treated cells, only curve M disappeared.

Suggest why.