2023 Cambridge IAS-Level Biology (9700) Practice Paper with Answers

An immunoglobulin G (IgG) antibody molecule is treated with a chemical reagent that selectively breaks only the disulfide bonds linking the light chains to the heavy chains, while leaving the heavy-to-heavy chain disulfide bonds fully intact. Which of the following describes the fragments that would be produced after this treatment?

An enzyme-catalysed reaction was studied under different conditions. The Michaelis-Menten constant (\(K_m\)) and maximum velocity (\(V_{\max}\)) were determined under control conditions and in the presence of two chemical substances, X and Y:

* Control: \(K_m = 2.0 \text{ mmol dm}^{-3}\), \(V_{\max} = 100 \mu\text{mol dm}^{-3} \text{ s}^{-1}\)
* With substance X: \(K_m = 5.5 \text{ mmol dm}^{-3}\), \(V_{\max} = 100 \mu\text{mol dm}^{-3} \text{ s}^{-1}\)
* With substance Y: \(K_m = 2.0 \text{ mmol dm}^{-3}\), \(V_{\max} = 45 \mu\text{mol dm}^{-3} \text{ s}^{-1}\)

Which statement correctly describes the binding sites of substances X and Y on the enzyme?

Which row correctly describes structural features of collagen and haemoglobin?

A student calibrated an eyepiece graticule using a stage micrometer. The stage micrometer had scale divisions spaced exactly \(0.1 \text{ mm}\) apart. At a magnification of \(\times 100\), 20 divisions of the eyepiece graticule coincided exactly with 4 divisions of the stage micrometer. The student then replaced the stage micrometer with a slide of plant cells and viewed it at \(\times 400\) magnification. An individual chloroplast was measured to be 3 eyepiece graticule divisions in length. What is the actual length of the chloroplast in micrometres (\(\mu\text{m}\))?

Which statement correctly describes the mechanism of action of penicillin on bacteria?

Which of the following correctly describes the movement of water and dissolved mineral ions through the apoplast pathway in the root of a herbaceous plant?

Carbon dioxide produced by actively respiring tissues diffuses into capillaries and enters red blood cells. Which sequence of events correctly describes what happens to this carbon dioxide inside a red blood cell in a systemic capillary?

A diploid animal cell has a chromosome number of \(2n = 16\). How many chromosomes, sister chromatids, and telomeres are present in this cell during metaphase of mitosis?

A student calibrated an eyepiece graticule using a stage micrometer. The stage micrometer had scale lines spaced at intervals of \(0.1\text{ mm}\). The student observed that \(50\) eyepiece graticule units coincided with \(15\) divisions on the stage micrometer. The student then replaced the stage micrometer with a slide of plant tissue and observed a xylem vessel element. At the same magnification, the diameter of the lumen of the xylem vessel element was measured as \(12\) eyepiece graticule units. What is the actual diameter of the lumen of the xylem vessel element?

Which description of the bonds that maintain the tertiary structure of a globular protein is correct?

In the presence of a certain inhibitor, the Michaelis-Menten constant (\(K_{\text{m}}\)) of an enzyme increases, but the maximum velocity (\(V_{\max}\)) of the reaction remains unchanged. Which statement is correct for this type of inhibition?

Which molecules in a cell surface membrane can act as receptors for cell signaling, and which can help to stabilize the membrane structure at high temperatures?

During DNA replication, both strands of the double helix act as templates. If a segment of the original DNA template strand has the base sequence \(3'\text{-ATCGGTACG-5'}\), which base sequence will be found in the newly synthesised complementary strand?

Which row correctly identifies features of a mature phloem sieve tube element compared to a xylem vessel element?

In red blood cells, carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen ions and hydrogencarbonate ions. Reaction 1 is catalysed by enzyme W. Hydrogencarbonate ions diffuse out of the red blood cell, and ions X enter the cell to maintain electrical neutrality. Hydrogen ions bind to oxyhaemoglobin, causing the release of oxygen (Y). Some carbon dioxide binds directly to the terminal amine groups of haemoglobin to form Z. Which row correctly identifies W, X, Y and Z?

At day 0, an individual is injected with an antigen for the first time. At day 30, the individual is injected with the same antigen for a second time. Which statement explains the differences between the primary immune response (after day 0) and the secondary immune response (after day 30)?

Four statements about protein structure are listed. 1. The secondary structure is stabilized solely by hydrogen bonds between peptide group atoms. 2. The tertiary structure is stabilized by interactions between R-groups. 3. Disulfide bonds can form between any two sulfur-containing amino acids (methionine and cysteine). 4. Quaternary structure is only present in proteins composed of more than one polypeptide chain. Which statements are correct?

If a competitive inhibitor is added to an enzyme-catalysed reaction, how do the Michaelis-Menten constant (\(K_m\)) and the maximum velocity (\(V_{\max}\)) of the reaction change?

A specimen is viewed under a light microscope. An eyepiece graticule has scale divisions calibrated to \(1.5\ \mu\text{m}\) at a magnification of \(\times 400\). A mitochondrion is measured to be \(4\) eyepiece graticule units in length. If the student changes the objective lens to increase the magnification to \(\times 1000\), what is the physical length of the mitochondrion and how many eyepiece graticule units long will it appear?

Which row correctly matches the mitotic stage with the cellular events occurring during that stage in a dividing plant cell?

A child is bitten by a venomous snake and immediately receives an injection of antivenom (containing specific antibodies). Three months later, the child is bitten by the same species of snake but is not immune and requires another injection of antivenom. Which row correctly describes the type of immunity provided and the reason why there was no long-term protection?

Which component of the cell surface membrane is responsible for maintaining membrane fluidity at low temperatures, and which component acts as a receptor for cell signalling molecules?

The sequence of a section of the DNA template strand is \(3'\text{-TACGGCATC}-5'\). What is the sequence of the complementary mRNA strand transcribed from this DNA sequence?

Carbon dioxide is transported in the blood in several forms. Which row correctly identifies the form in which the largest percentage of carbon dioxide is transported, and the enzyme that catalyses its conversion inside red blood cells?

Which components of cell membranes are involved in maintaining the stability of the membrane at low temperatures and in cell-to-cell recognition respectively?

A micrograph of a plant cell shows a chloroplast with a length of 40 mm. The actual length of the chloroplast is 5 \(\mu\)m. What is the magnification of this micrograph?

An enzyme-controlled reaction was carried out in the presence and absence of an inhibitor. The rate of reaction was plotted against substrate concentration. It was found that at very high substrate concentrations, the rate of reaction with the inhibitor was identical to the rate of reaction without the inhibitor. Which statement about the inhibitor is correct?

A portion of a template strand of DNA has the sequence: 3'- TAC GGC TTA CTA -5'. During transcription, this sequence is copied to produce mRNA, which is then translated. What is the correct sequence of anticodons on the tRNA molecules that bind to the codons of this mRNA sequence?

Which of the following describes the effect of an increase in carbon dioxide concentration on the oxygen dissociation curve of haemoglobin and its physiological consequence in respiring tissues?

Which structural features of xylem vessel elements adapt them for the efficient transport of water? 1. Lignified cell walls to prevent collapse under tension. 2. Absence of protoplasm to reduce resistance to water flow. 3. Presence of sieve plates to allow rapid flow. 4. Pits in the walls to allow lateral movement of water.

A person is bitten by a venomous snake and receives an immediate injection of antivenom containing specific antibodies. Two months later, the person is bitten by the same species of snake but does not have immunity and requires another injection. What type of immunity is provided by the antivenom, and why is it not long-lasting?

During which stage of the mitotic cell cycle do centromeres divide to separate sister chromatids, and which stage immediately follows this event?

A student calibrated an eyepiece graticule using a stage micrometer. The stage micrometer had divisions that were \(0.1\text{ mm}\) apart. At a magnification of \(\times 100\), 50 divisions of the eyepiece graticule aligned with 10 divisions of the stage micrometer. Under this same magnification, a plant cell was measured to be 3.5 eyepiece graticule units in length. What is the actual length of the plant cell?

An enzyme-controlled reaction is carried out in the presence of a competitive inhibitor. Which statement correctly describes the effect of this inhibitor on the maximum rate of reaction (\(V_{max}\)) and the Michaelis-Menten constant (\(K_m\)) of the enzyme?

Which statements about the structure of a collagen molecule are correct? 1. It has a primary structure in which glycine occurs as every third amino acid. 2. Hydrogen bonds stabilize the triple helix structure formed by three polypeptide chains. 3. Covalent bonds form cross-links between adjacent triple helices to form a collagen fibril.

A child is bitten by a venomous snake and is immediately given an injection of antivenom containing specific antibodies. Six months later, the child is bitten by the same species of snake and again requires antivenom treatment. Which statement explains why the child did not have immunity to the snake venom during the second bite?

During intensive physical exercise, the partial pressure of carbon dioxide in actively respiring muscle tissue increases. What is the effect of this change on the plasma pH, the affinity of haemoglobin for oxygen, and the position of the oxygen dissociation curve?

Water moves from the soil to the xylem of a plant root. Which sequence of structures shows the correct pathway of water that travels mainly via the apoplast pathway in the cortex?

Which row correctly shows the presence (+) or absence (-) of tissues in the bronchus and alveolus of a healthy human lung? (Row A: Cartilage in bronchus: +, Smooth muscle in bronchus: +, Elastic fibres in alveolus: +, Cilia in alveolus: -) (Row B: Cartilage in bronchus: +, Smooth muscle in bronchus: -, Elastic fibres in alveolus: +, Cilia in alveolus: +) (Row C: Cartilage in bronchus: -, Smooth muscle in bronchus: +, Elastic fibres in alveolus: -, Cilia in alveolus: -) (Row D: Cartilage in bronchus: +, Smooth muscle in bronchus: +, Elastic fibres in alveolus: -, Cilia in alveolus: +)

A strand of mRNA has the codon sequence 5'-AUG-CCG-AAA-UGC-3'. Which tRNA anticodons will bind to these codons during translation?

Trypsin is a protease enzyme secreted by the pancreas that hydrolyses peptide bonds in proteins. (a) Describe the mechanism of action of trypsin in terms of the lock-and-key or induced-fit hypothesis, explaining how it lowers the activation energy of the reaction. [4] (b) In an investigation, the rate of trypsin activity was measured at different concentrations of a competitive inhibitor, benzamidine, while keeping substrate concentration constant. (i) Explain how a competitive inhibitor like benzamidine decreases the rate of trypsin activity. [3] (ii) State three variables, other than the concentration of the inhibitor, that must be kept constant in this investigation to obtain valid results. [3]

Active loading of sucrose into the phloem sieve tubes is essential for translocation in plants. (a) Explain how companion cells are adapted to actively load sucrose into sieve tube elements. [4] (b) Describe how the accumulation of sucrose in sieve tubes leads to the movement of phloem sap from source to sink. [4] (c) State two differences in structure between a companion cell and a phloem sieve tube element. [2]

Monoclonal antibodies are highly specific antibodies produced from a single clone of hybridoma cells. (a) Describe the steps involved in the production of monoclonal antibodies using the hybridoma method. [5] (b) Explain why monoclonal antibodies are useful in the diagnosis of diseases. [3] (c) Distinguish between active immunity and passive immunity. [2]

The investigation of cell structure relies on microscopy. (a) Distinguish between the terms magnification and resolution. [2] (b) An organelle has an actual diameter of 2.5 \(\mu\)m. In a micrograph, its image measures 5.0 cm. Calculate the magnification of this image. Show your working and state your final answer. [3] (c) Explain why internal structures of organelles, such as the grana in chloroplasts, can be seen with an electron microscope but not with a light microscope. [3] (d) State two structures visible in a plant cell under a light microscope that are not present in an animal cell. [2]

Haemoglobin is a globular protein that transports oxygen in the blood. (a) Describe how the quaternary structure of haemoglobin enables it to perform its function of oxygen transport. [3] (b) At high partial pressures of carbon dioxide (\(p\text{CO}_2\)), the oxygen dissociation curve of haemoglobin shifts to the right (the Bohr shift). Explain the physiological significance of the Bohr shift in respiring tissues. [5] (c) Explain the role of the enzyme carbonic anhydrase in the transport of carbon dioxide. [2]

Cholera and tuberculosis (TB) are two major infectious diseases that affect human populations globally. (a) Complete the comparison of these two diseases by identifying: (i) the genus of the pathogen that causes cholera, [1] (ii) the genus of the pathogen that causes tuberculosis, [1] (iii) the primary mode of transmission of cholera, [1] (iv) the primary mode of transmission of tuberculosis. [1] (b) Explain why tuberculosis is more difficult to control and eradicate globally compared to other bacterial diseases. [4] (c) State how cholera is treated to prevent death from dehydration. [2]

Amylase is an enzyme that catalyses the hydrolysis of starch into maltose. You are required to investigate the effect of different concentrations of a plant extract, solution I, on the activity of amylase. Solution I acts as an inhibitor.

You are provided with:
- \(10\text{ cm}^3\) of \(1.0\%\) solution of the inhibitor, I
- \(50\text{ cm}^3\) of distilled water, W
- \(20\text{ cm}^3\) of \(1.0\%\) amylase solution, A
- \(20\text{ cm}^3\) of \(1.0\%\) starch solution, S
- Iodine in potassium iodide solution (in a dropper bottle)

(a) You are required to prepare a range of concentrations of the inhibitor solution, I, using simple dilution of the stock \(1.0\%\) solution I with distilled water, W.
Prepare five concentrations of I: \(1.0\%\), \(0.8\%\), \(0.6\%\), \(0.4\%\), and \(0.2\%\). The total volume of each solution should be \(10.0\text{ cm}^3\).
Complete Table 1.1 to show the volumes of \(1.0\%\) solution I and distilled water, W, required to prepare each concentration. [4]

Table 1.1
| Concentration of inhibitor I / % | Volume of 1.0% inhibitor solution I / \(\text{cm}^3\) | Volume of distilled water, W / \(\text{cm}^3\) |
|---|---|---|
| 1.0 | | |
| 0.8 | | |
| 0.6 | | |
| 0.4 | | |
| 0.2 | | |

(b) Carry out the investigation using the following instructions:
1. Label five test-tubes with the concentrations of I prepared in (a).
2. Pipette \(2.0\text{ cm}^3\) of each concentration of I into its respective test-tube.
3. Add \(2.0\text{ cm}^3\) of amylase solution A to each test-tube and mix gently.
4. Leave the mixtures for 2 minutes to allow interaction.
5. Put one drop of iodine solution into each well of a spotting tile.
6. Add \(2.0\text{ cm}^3\) of starch solution S to the first test-tube (containing \(1.0\%\) I and A), mix quickly, and start a timer.
7. Every 30 seconds, use a clean dropper pipette to remove a drop of the mixture and add it to a well containing iodine solution on the spotting tile.
8. Record the time when the starch is completely hydrolysed (when the blue-black colour no longer appears and the iodine remains yellow-brown). If the starch is not hydrolysed after 300 seconds, stop timing and record 'more than 300'.
9. Repeat steps 6 to 8 for the remaining four concentrations of I.

Record your results in an appropriate table. [6]

(c) In another investigation, a student measured the rate of amylase activity at different pH values, with no inhibitor present. The results are shown in Table 1.2.

Table 1.2
| pH | Rate of reaction / arbitrary units (a.u.) |
|---|---|
| 4.0 | 1.2 |
| 5.0 | 3.5 |
| 6.0 | 6.8 |
| 7.0 | 8.5 |
| 8.0 | 4.2 |
| 9.0 | 0.8 |

(i) Plot a line graph of the data in Table 1.2 on a grid. [4]
(ii) State and explain the effect of pH on the activity of amylase shown in the graph. [2]

(d) (i) Identify two sources of error in the method you used in (b). [2]
(ii) Suggest how you would modify the method in (b) to investigate the effect of temperature on the rate of starch hydrolysis. [4]