AS & A Level Biology - 9700 Paper 2 2024 Winter Zone 3

(a) (i) Use the letters in Fig. 1.1 to identify the parts of the gas exchange system that contain cartilage.
................................................................. [1]
(ii) Describe the role of cartilage in the gas exchange system.
................................................................. [2]
(iii) Microscope slides were prepared from two regions of the gas exchange system.
Fig. 1.2 and Fig. 1.3 are photomicrographs of the two slides.
Complete Table 1.1.
• Use the letters from Fig. 1.1 to identify the regions of the gas exchange system from which the two slides were prepared.
• Identify one feature visible in Fig. 1.2 and one feature visible in Fig. 1.3.
• State one way in which each feature relates to its function.



Table 1.1
[Table_1]


[4]
(b) There is a regular and efficient supply of blood from the heart to the lungs. Describe the sequence of events that occurs in the heart to make sure that there is a regular and efficient supply of blood to the lungs.
................................................................. [5]
[Total: 12]

(a) (i) Explain why stem cells are required in places such as the lining of the small intestine.
.......................................................... [2]
(ii) Name the stage of mitosis shown in cell X in Fig. 2.1.
.......................................................... [1]
(iii) State the part of the cell cycle shown at Y in Fig. 2.1.
.......................................................... [1]
(b) Explain the role of centromeres in the cell cycle.
.......................................................... [2]

(c) Fig. 2.2 shows three types of specialised cell that develop from $Lgr5^+$ stem cells in the small intestine.
[Image]
The structural features of a cell indicate its likely function.
Suggest a function of each of the cells shown in Fig. 2.2, and explain how the structure of each cell supports your suggestion.
cell P function ..........................................................
explanation ..........................................................
cell Q function ..........................................................
explanation ..........................................................
cell R function ..........................................................
explanation ..........................................................[6]

The five bases found in nucleic acids are described as nitrogenous organic compounds. There are two types of base.

Fig. 3.1 shows the structure of the five bases.



(a) (i) State the name of the type of base that includes U, T and C.
................................................................................................................. [1]

(ii) State why it is not correct to say that all nucleic acids have five bases.
................................................................................................................. [1]

(b) Fig. 3.2 shows a stage in the replication of DNA. The circled part is enlarged in Fig. 3.3 to show the elongation of the DNA strand that is being synthesised.



Describe the sequence of events that occurs at the stage shown in Fig. 3.3 to extend the synthesised strand.
................................................................................................................. [4]

(c) The two strands in a molecule of DNA are described as antiparallel.

With reference to Fig. 3.2 and Fig. 3.3, state what is meant by antiparallel, and explain how the antiparallel arrangement of the strands determines how new strands are synthesised.
................................................................................................................. [3]
[Total: 9]

(a) Biofuels contain alcohols that are produced by the fermentation of sugars derived from crop waste. This waste contains cellulose and other organic compounds in cell walls.

Scientists investigated the production of sugars from crop waste for biofuel production. The scientists discovered that a strain of the fungus \textit{Penicillium citrinum}, isolated from soil, was a good source of three different extracellular enzymes, \textbf{M}, \textbf{N} and \textbf{O}. These enzymes break down polysaccharides in cell walls.

The scientists cultured \textit{P. citrinum} in a liquid medium containing cell wall material. Samples of the liquid were taken, and the three enzymes were separated from the medium. Each enzyme was placed in a reaction mixture with an appropriate substrate. The activity of each enzyme was determined to give a measurement of the quantity of enzyme produced by \textit{P. citrinum}.

The results are shown in Table 4.1.

[Table 4.1]

$$\begin{array}{|c|c|} \hline \text{enzyme} & \text{maximum activity / arbitrary units} \\ \hline M & 292.83 \\ \hline N & 111.72 \\ \hline O & 6.54 \\ \hline \end{array}$$

Optimum conditions for each enzyme were used to obtain the results in Table 4.1. The conditions were different for each enzyme.

The scientists carried out further research so that a solution containing the three enzymes (enzyme mixture) could be used for the most efficient production of sugars from crop waste.

Suggest what the scientists needed to find out in their research.
............................................................................................................................................................................................................................................. [4]

(b) Students investigated the composition of the cell wall of leaf cells of thale cress, \textit{Arabidopsis thaliana}. The students began by isolating the cell wall components from the rest of the cell material.

The students used enzymes extracted from a fungal pathogen of \textit{A. thaliana} to hydrolyse the cell wall components to smaller molecules.

The students prepared a reaction mixture containing the cell wall components and the enzymes.

After 24 hours, they separated and identified the smaller molecules found in the reaction mixture.

Four types of molecule were identified:

• short chains of \(\beta\)-glucose
• \(\beta\)-glucose
• peptides
• amino acids.

Explain the presence of these molecules in the reaction mixture after 24 hours of hydrolysis.
............................................................................................................................................................................................................................................. [4]

[Total: 8]

(a) (i) U4 and V4 are types of active T-lymphocyte. State the names given to these types of T-lymphocyte.
U4 ...........................................................
V4 ........................................................... [1]
(ii) Describe the roles of cells U4 and V4 in a primary immune response.
.............................................................. [4]
(b) Polio is a highly infectious viral disease. The virus infects the nervous system of humans. The disease can cause total paralysis within hours and can be fatal.
The Global Polio Eradication Initiative (GPEI) was started in 1988 by the World Health Organization. In 2022, polio had been successfully eradicated from most of the world. However, cases of the disease have been recorded in some countries.
Discuss the steps that must be taken by health authorities during a vaccination programme if an infectious disease, such as polio, is to be eradicated from the whole world.
........................................................................... [4]

(a) A student constructed a table to compare the structural features of a plant cell, a prokaryotic cell and a virus.
Complete Table 6.1.

Table 6.1
[Table_1]

(b) The cholera bacterium releases a protein toxin called cholera. The toxin causes the loss of chloride ions and water from epithelial cells into the lumen of the intestine.

Fig. 6.1 shows the events that occur in cells lining the intestine when cholera binds to the membrane of one of these cells.


(i) State one likely source of an outbreak of cholera. [1]

(ii) With reference to Fig. 6.1, state why cholera molecules are described as having quaternary structure. [1]

(iii) State the type of cell membrane component that forms the receptor for cholera. [1]

(iv) The process by which chloride ions leave the epithelial cell requires energy.
Name the phosphorylated nucleotide that is needed for this process. [1]

(v) Explain why water also moves from epithelial cells into the lumen of the intestine when cholera is present. [2]

[Total: 10]