AS & A Level Biology - 9700 Paper 2 2023 Summer Zone 2

(a) Fig. 1.1 is a summary of blood flow through the right side of the heart during one cardiac cycle. Three boxes in Fig. 1.1 are not complete.

Complete boxes 3, 5 and 7 in Fig. 1.1 using only the terms systole and diastole.

[Image_1: Fig. 1.1]

(b) Impulses sent out by the SAN pass to the AVN, where there is a short delay.

With reference to Fig. 1.1, explain why it is important for the control of the cardiac cycle that there is a short delay at the AVN after impulses have been sent out by the SAN.

........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................

(c) Changes in blood pressure occur in the heart during the cardiac cycle. These changes cause the opening and closing of the bicuspid and tricuspid (atrioventricular) valves and the aortic and pulmonary (semilunar) valves.

Explain how blood pressure changes:
• cause the opening of the tricuspid valve
• cause the opening of the pulmonary valve
• help the flow of blood through the heart.

........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................
........................................................................................................................................................................

(a) Describe three differences, visible in Fig. 2.1, between root apical meristem cells and root cap cells.
1 ......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
2 ......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
3 ......................................................................................................................................................
.......................................................................................................................................................
....................................................................................................................................................... [3]

(b) Mucilage acts as a glue to bind tiny soil particles together, forming small clumps close to the root. These small clumps help to maintain the soil water around the root tip and prevent the loss of water.
With reference to the cohesive and adhesive properties of water, suggest and explain how the formation of small clumps of soil helps to maintain the soil water around the root tip.
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
....................................................................................................................................................... [3]

(c) Enzymes present in mucilage catalyse the breakdown of organic compounds in the soil. This increases the presence of mineral ions in the soil.
State the term used to describe enzymes that act outside the cells that synthesise them.
....................................................................................................................................................... [1]

(d) The polysaccharides and amino acids present in the mucilage are a source of nutrients for soil microorganisms that live in the area surrounding the root. Some of these microorganisms can break down soil compounds to release mineral ions.
(i) Explain what is meant by a polysaccharide.
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
....................................................................................................................................................... [2]

(ii) The soil microorganisms use amino acids to synthesise proteins. All of the twenty different amino acids that are present in proteins have the same general structure.
Draw the general structure of an amino acid in the space provided and use this drawing to explain how it is possible to have many different amino acids.
.......................................................................................................................................................
.......................................................................................................................................................
....................................................................................................................................................... [2]

(iii) Mineral ions are usually present in the soil in very low concentrations. The action of mucilage enzymes and soil microorganisms can help to increase the presence of mineral ions.
Root hair cells are specialised for the uptake of these mineral ions and for the absorption of water from the soil.
Suggest and explain how the presence of mineral ions in the root hair cell can increase the absorption of water by the root hair cells.
.......................................................................................................................................................
.......................................................................................................................................................
....................................................................................................................................................... [3]

Cells of the immune system respond to the presence of non-self antigens.
(a) Outline the features of non-self antigens.
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
[3]

(b) Four different types of cells of the immune system are shown in Table 3.1.
Complete Table 3.1:
* use a tick (✓) if the description applies to the named cell of the immune system
* use a cross (✗) if the description does not apply.

[Table_1]
Table 3.1
\begin{align} \text{description of cell} & \quad \text{cell of the immune system} \\ & \text{B-lymphocyte} & \text{plasma cell} & \text{T-helper cell} & \text{T-killer cell} \\ \text{able to go through a number of cell cycles (clonal expansion)} & [] & [] & [] & [] \\ \text{main role is to secrete cytokine during an immune response} & [] & [] & [] & [] \\ \text{present during a primary immune response to a virus} & [] & [] & [] & [] \\ \end{align}
[4]

(c) The cell cycle can be divided into different parts.
Complete sentences A, B and C to provide more information about the mitotic cell cycle.
A The part of the cell cycle that occurs immediately after mitosis is
.............................................................................................................................
B The part of the cell cycle in which the S phase occurs is
.............................................................................................................................
C The main event that occurs during the S phase is
.............................................................................................................................
[3]

Trypanosoma brucei is a unicellular organism that causes the infectious disease known as sleeping sickness. Insects known as tsetse flies pass on the organism from infected people to uninfected people when male and female tsetse flies feed on human blood.

(a) Fig. 4.1 is a transmission electron micrograph of the form of T. brucei found in human blood.



Fig. 4.1

(i) Draw an arrow on Fig. 4.1 to indicate the location in the cell where ribosomal RNA (rRNA) and proteins are assembled to make ribosomal subunits. [1]

(ii) With reference to Fig. 4.1, explain how the structure labelled X provides evidence that T. brucei is motile (able to move).

...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
........................................................................................................................................................... [2]

(iii) With reference to Fig. 4.1, explain whether T. brucei is a eukaryote or prokaryote.

...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
........................................................................................................................................................... [3]

(b) Malaria is an infectious disease caused by organisms belonging to the genus Plasmodium.

(i) State the term used to describe an organism that causes disease.

........................................................................................................................................................... [1]

(ii) Name one of the species of Plasmodium that causes malaria.

Plasmodium .......................................................... [1]

(c) Outline the similarities and differences between the modes of transmission of malaria and sleeping sickness.

...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
...........................................................................................................................................................
........................................................................................................................................................... [3]

Nucleotide and nucleoside analogues are therapeutic drugs that have a similar structure to nucleotides or nucleosides of RNA and DNA. A nucleoside is composed of a nitrogenous organic base (base) and a pentose sugar.

(a) The names of the bases present in RNA and DNA nucleotides can be abbreviated using a single letter. These are shown in Table 5.1.

Complete Table 5.1 by stating:
• the name of each base
• whether the base is a purine or pyrimidine
• whether the base is present
– only in an RNA molecule (write RNA in the table)
– only in a DNA molecule (write DNA in the table)
– in RNA and in DNA molecules (write the word both in the table).

[Table_1]

[4]

(b) Abacavir is an analogue drug used in the treatment of some viral diseases. It enters a cell infected by a virus and is metabolised to the analogue carbovir triphosphate.

Fig. 5.1 shows the molecular structure of abacavir and carbovir triphosphate.



Carbovir triphosphate can be inserted into an elongating polynucleotide chain instead of a nucleotide. This interferes with the action of DNA polymerase during the synthesis of viral DNA.

(i) With reference to Fig. 5.1, explain whether carbovir triphosphate will replace a purine or a pyrimidine nucleotide in the elongating polynucleotide chain.
.......................................................................................................................................
.......................................................................................................................................
....................................................................................................................................... [1]

(ii) With reference to Fig. 5.1 and the action of DNA polymerase, suggest why the conversion of abacavir to carbovir triphosphate increases the chance of the analogue being added to the viral polynucleotide chain.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
....................................................................................................................................... [2]

(iii) Suggest and explain how carbovir triphosphate interferes with the action of DNA polymerase and how this may prevent the synthesis of viral DNA.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
....................................................................................................................................... [4]

(a) The Weibel Lung model describes how each airway divides into two.

Name the airways in generation 1, labelled X in Fig. 6.1, that branch from generation 0.
............................................................................................................................. [1]

(b) The airways are well supplied with blood. However, the airways from generation 0 to generation 16, shown in Fig. 6.1, are not able to carry out gas exchange.

Suggest why the airways from generation 0 to generation 16 are not able to carry out gas exchange.
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
...................................................... [2]

(c) High-resolution computed tomography (HRCT) is an imaging technique that is used to obtain measurements of airway diameters in people with a pulmonary (lung) disease. Regular, repeated imaging must be avoided because it involves exposure to harmful radiation.

Scientists researched the use of a different technique, HP gas MRI, that does not involve harmful radiation. Two types of MRI image, known as projection and multi-Slice, were used to obtain measurements of airway diameters.

Fig. 6.2 shows the results of the HP gas MRI study compared with the Weibel Lung model, for generations 0 to 5. The Weibel Lung model was used as a standard reference for airway diameters.



(i) State the relationship shown in Fig. 6.2 between airway diameter and airway generation for the Weibel Lung model data.
............................................................................................................................. [1]

(ii) With reference to the data in Fig. 6.2, explain whether HP gas MRI could be a useful alternative to HRCT in obtaining airway diameter measurements.
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
............................................................................................................................. [3]