AS & A Level Biology - 9700 Paper 2 2023 Winter Zone 3

(a) With reference to Fig. 1.1, suggest how the presence of P. falciparum affects a red blood cell.

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(b) When P. falciparum divides there is unequal division of the cytoplasm to form small, genetically identical daughter cells.
Outline the events that occur in the cell of P. falciparum to form the daughter cells shown in Fig. 1.1.
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(c) Explain how antibodies will reduce the spread of the malarial pathogen through the bloodstream.
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(d) Some vaccination programmes have been more successful than others.
Discuss the factors that contribute to the success of a vaccination programme.
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(a) (i) Explain why the absorbance increases, as shown in Fig. 2.1.
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(ii) The students took their final sample at 12 minutes.
Predict the results for absorbance if the students had continued to take samples for a further 10 minutes. Explain your answer.
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(iii) State an advantage of using a colorimeter in determining the progress of the reaction.
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(b) The reaction catalysed by starch phosphorylase occurs at the ends of amylose molecules.
Describe the sequence of events that occurs when starch phosphorylase catalyses the addition of a molecule of glucose to the end of an amylose molecule.
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(a) (i) The shading represents the two different polypeptides that form a molecule of haemoglobin.
State the names of the two different polypeptides.
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(ii) Identify the structure labelled P in Fig. 3.1.
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(iii) Fig. 3.1 shows some of the levels of protein structure.
State the level of protein structure that is not shown in Fig. 3.1.
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(b) Haemoglobin is involved in the transport of carbon dioxide.
Molecules of carbon dioxide enter red blood cells as the cells travel in capillaries through muscle tissue. Some of these molecules are converted to carbonic acid.
Explain how haemoglobin is involved in the transport of carbon dioxide molecules that are not converted to carbonic acid.
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(c) When haemoglobin associates (binds) with oxygen it forms oxyhaemoglobin.
State the precise site in the mammalian body where haemoglobin molecules bind with oxygen.
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(d) The compound 2,3-diphosphoglycerate (2,3-DPG) is produced in red blood cells.
2,3-DPG binds to haemoglobin and stabilises it.
Fig. 3.2 shows oxygen dissociation curves when red blood cells have high and low concentrations of 2,3-DPG.
P₅₀ is the partial pressure of oxygen when haemoglobin is 50% saturated. The P₅₀ is used to compare the affinity of haemoglobin for oxygen under different conditions.
(i) Use the information in Fig. 3.2 to describe the effect of an increase in the concentration of 2,3-DPG on the oxygen dissociation curve.
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(ii) Blood is stored in blood banks for use in hospitals during operations.
The concentration of 2,3-DPG in red blood cells decreases when blood is stored in a blood bank.
State and explain the effect that the use of blood taken from a blood bank has on the supply of oxygen to the tissues of a person during an operation.
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(a) (i) Name the enzyme labelled A in Fig. 4.1. [1]
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(ii) Name the bond that forms between the nucleotides in the primary transcript. [1]
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(b) (i) State the number of amino acids that are coded for by the sequence of nucleotides on the primary transcript shown in Fig. 4.1. [1]
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(ii) Use the information in Fig. 4.1 to explain why one of the strands of DNA is not transcribed. [2]
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[Image_1: Fig. 4.1 shows the transcription of part of the COL1A2 gene.]

(c) (i) State two features of mitochondria that are visible in Fig. 4.2. [2]
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(ii) The line on Fig. 4.2 shows the diameter of one of the mitochondria. Calculate the actual diameter of the mitochondrion.
Give your answer to one significant figure. [1]
answer = ................................................... μm

(d) Mitochondrial DNA codes for some polypeptides of proteins used within the mitochondrion. Some of the proteins allow movement of ions into and out of the mitochondria. Outline the ways in which ions can move into mitochondria. [3]
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[Image_2: Fig. 4.2 is a transmission electron micrograph of a mitochondrion that is dividing.]

In flowering plants, transport of assimilates occurs in phloem tissue between sources and sinks.

(a) (i) Explain why a root can be a source and a sink.
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(ii) State two examples of assimilates that are transported in the phloem.
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(b) Describe and explain the mechanism that is responsible for the movement of phloem sap in sieve tubes.
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(c) Tobacco mosaic virus (TMV) infects many crop plants. The virus passes between cells in the leaves and can travel throughout plants in the phloem.

The enzyme pectin methylesterase (PME) is involved with the production of cell walls. The enzyme is also known to influence the movement of TMV through plants. Scientists investigated the effect of PME on the transport of TMV through plants.

The scientists used three varieties of tobacco plants. Two varieties, V1 and V2, have small quantities of PME. A third variety, C, has the normal quantity of PME and was used as the control in this investigation.

The plants in each group were infected with TMV at the same time. The accumulation of the virus particles transported to the leaves at the top of the plants was determined over 36 days.

The results are shown in Fig. 5.1. The arrow indicates when all the plants were infected with TMV.

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Compare the results for varieties V1 and V2 with the control group of plants, C.
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The mammalian heart consists of four chambers.

(a) Explain why the ventricles have thicker walls than the atria.
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(b) Complete Table 6.1 to identify the structure in the heart responsible for each function listed.

Table 6.1

| function | structure in the heart |
|---------------------|-------------------------|
| initiates the heartbeat | |
| delays the wave of depolarisation between the atria and the ventricles | |
| transmits the wave of depolarisation through muscles of the ventricle | |
| closes when the left ventricle contracts | |
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