2025 Cambridge IAS-Level Biology (9700) Practice Paper with Answers

A student calibrates an eyepiece graticule using a stage micrometer. At \( \times 100 \) magnification, 100 eyepiece units (epu) align exactly with 25 stage micrometer divisions (smd). Each smd is 0.1 mm. The student then replaces the stage micrometer with a slide of plant tissue and, at \( \times 400 \) magnification, measures a palisade mesophyll cell to be 12 epu wide. What is the actual width of this palisade mesophyll cell?

A student performs three biochemical tests on an unknown liquid food extract. Test 1: Heating with Benedict's solution after boiling with dilute hydrochloric acid and neutralizing with sodium hydrogencarbonate gives a brick-red precipitate. Test 2: Heating directly with Benedict's solution (without prior treatment) gives a blue solution. Test 3: Adding biuret reagent gives a purple colour. What does the food extract contain?

Which row correctly matches the level of protein structure with the type of bonds that stabilize it and whether it is affected by denaturation?

An enzyme-catalyzed reaction is investigated in the presence and absence of an inhibitor. In the presence of the inhibitor, the maximum rate of reaction (\( V_{max} \)) remains unchanged, but the value of the Michaelis-Menten constant (\( K_m \)) is increased. Which statement about this inhibitor is correct?

A student observes plant root tip cells under a light microscope. In one cell, the chromosomes are aligned individually along the equator of the spindle, with sister chromatids still joined at their centromeres. Which stage of mitosis is this cell in, and what event occurs next?

A polypeptide consists of 120 amino acids. During protein synthesis, a mutation occurs in the DNA gene coding for this polypeptide. A base substitution changes the mRNA codon at position 81 from \( 5'\text{-UAC-3'} \) to a stop codon \( 5'\text{-UAA-3'} \). How many peptide bonds will there be in the truncated polypeptide that is synthesized?

Which row correctly matches a structural feature of xylem vessel elements or phloem sieve tube elements to its functional significance?

A person is bitten by a venomous snake and is immediately given an injection of antivenom containing antibodies. Three months later, the person is bitten by the same species of snake and is surprised to find they require another injection of antivenom to survive. Which row correctly describes the type of immunity provided by the first injection, and explains why the person is not immune to the second bite?

An eyepiece graticule is calibrated using a stage micrometer. At a magnification of \(\times 100\), 12 divisions of the stage micrometer (where each division is \(0.1\text{ mm}\) apart) align exactly with 60 divisions of the eyepiece graticule. The stage micrometer is then replaced with a slide of plant tissue, and the magnification is increased to \(\times 400\). A cell is measured and found to span 18 divisions of the same eyepiece graticule. What is the actual width of this plant cell?

An unknown aqueous sample was tested for the presence of biological molecules. The results of the tests were: 1. Addition of iodine in potassium iodide solution: remains yellow-brown. 2. Biuret test: solution turns purple. 3. Benedict's test on raw sample: remains blue. 4. Benedict's test on the sample after boiling with hydrochloric acid and neutralizing: turns orange-red. 5. Emulsion test: a cloudy white emulsion layer forms. Which combination of biological molecules is present in the sample?

An enzyme-controlled reaction was carried out in three different conditions: with enzyme alone, with enzyme and Inhibitor X, and with enzyme and Inhibitor Y. The values of \(K_m\) and \(V_{\max}\) were determined for each condition: 1. Enzyme alone: \(K_m = 2.0\text{ mmol dm}^{-3}\), \(V_{\max} = 100\text{ au}\). 2. Enzyme + Inhibitor X: \(K_m = 5.5\text{ mmol dm}^{-3}\), \(V_{\max} = 100\text{ au}\). 3. Enzyme + Inhibitor Y: \(K_m = 2.0\text{ mmol dm}^{-3}\), \(V_{\max} = 45\text{ au}\). What type of inhibition is exhibited by Inhibitor X and Inhibitor Y?

Plant cells with an initial water potential (\(\psi\)) of \(-600\text{ kPa}\) and a solute potential (\(\psi_s\)) of \(-800\text{ kPa}\) are placed in a solution of sucrose with a water potential of \(-400\text{ kPa}\). Assuming the solute potential of the cell remains constant, what is the turgor pressure (\(\psi_p\)) of the cells once they have reached equilibrium with the solution?

Which row correctly associates a process in the cell cycle with the stage in which it first occurs?

A template strand of DNA has the sequence: \(3'\text{- TAC GGC TTA CTA ACT -}5'\). During protein synthesis, transcription and translation occur. What is the correct sequence of anticodons on the tRNA molecules that bind to the transcribed mRNA?

Which row correctly identifies the presence of a nucleus, cytoplasm, and a lignified cell wall in mature transport cells of a flowering plant?

In an actively respiring skeletal muscle tissue, local physiological conditions change. Which set of changes correctly describes the environment of the tissue and its subsequent effect on hemoglobin's affinity for oxygen and the oxygen dissociation curve (the Bohr effect)?

A student calibrated an eyepiece graticule using a stage micrometer. The stage micrometer has divisions spaced \(0.01\text{ mm}\) apart. At a magnification of \(\times 100\), 40 eyepiece graticule divisions coincided with 12 divisions of the stage micrometer. Under the same magnification, a chloroplast was measured to be 3 eyepiece graticule divisions in length. What is the actual length of the chloroplast?

A solution of unknown biological molecules was subjected to several biochemical tests. The results were as follows: Benedict's test (direct heating): blue color; Benedict's test (heating after acid hydrolysis and neutralization): green precipitate; Biuret test: purple color; Iodine in potassium iodide solution: yellow-brown color. Which biological molecules are present in this solution?

An experiment is carried out to investigate the effect of an inhibitor on an enzyme-catalyzed reaction. It is found that at high substrate concentrations, the rate of reaction in the presence of the inhibitor reaches the same maximum velocity (\(V_{\max}\)) as the control without the inhibitor. Which statement correctly explains this observation?

Plant cells with a water potential of \(-500\text{ kPa}\) are placed in a solution with a water potential of \(-200\text{ kPa}\). Which statement correctly describes the net movement of water and the state of the plant cells at equilibrium?

Which row correctly identifies the behavior of chromosomes and spindle microtubules during anaphase of mitosis?

A template DNA strand contains the sequence: 3'-TAC GGC-5'. During protein synthesis, what is the sequence of codons on mRNA, and the corresponding anticodons on tRNA (written in the 3' to 5' direction)?

Which features correctly describe mature xylem vessel elements compared to mature sieve tube elements?

Which statement correctly describes the differences between active immunity and passive immunity?

At \(\times 10\) objective magnification, 10 eyepiece graticule units align with 2.5 divisions of a stage micrometer. The stage micrometer has divisions spaced at \(0.1\text{ mm}\) intervals. An epidermal cell is measured using the same objective lens and is found to be 12 eyepiece graticule units long. What is the actual length of the cell?

A liquid food sample of unknown composition is subjected to three biochemical tests. The results are as follows: Test 1: Biuret test yields a purple solution. Test 2: Iodine in potassium iodide solution yields a yellow-brown solution. Test 3: Benedict's test on the raw sample yields a blue solution, but after heating with dilute hydrochloric acid and neutralizing, it yields a brick-red precipitate. Which biological molecules are present in this food sample?

An experiment was carried out to investigate the effect of two different inhibitors, X and Y, on the rate of an enzyme-catalyzed reaction at different substrate concentrations. With inhibitor X, the maximum rate of reaction (\(V_{\max}\)) was reached at high substrate concentrations. With inhibitor Y, the maximum rate of reaction (\(V_{\max}\)) was significantly lower than the control, even at very high substrate concentrations. Which statement about these inhibitors is correct?

A student calculated the mitotic index of an onion root tip tissue sample. Out of 800 cells observed, 720 cells were in interphase, 45 in prophase, 12 in metaphase, 15 in anaphase, and 8 in telophase. If the complete cell cycle for these cells takes 20 hours, what is the expected duration of metaphase in minutes?

During exercise, the concentration of carbon dioxide in active muscle tissues increases, leading to a decrease in blood pH. Which statement correctly describes how this affects oxygen transport and release by hemoglobin?

Which row correctly identifies the type of pathogen and the primary method of transmission for cholera?

Which structural features are present in mature sieve tube elements of phloem but absent from mature xylem vessel elements? 1. Cytoplasm, 2. Plasmodesmata, 3. Sieve plates

An individual is bitten by a venomous snake and immediately receives an injection of antivenom (containing specific antibodies against the venom). Several months later, the same individual is bitten again by the same species of snake and must receive another injection of the same antivenom. Which row correctly describes the type of immunity provided by the antivenom and explains why the second injection is necessary?

A student calibrates an eyepiece graticule using a stage micrometer. The stage micrometer has scale divisions of \( 0.1\text{ mm} \). At a magnification of \( \times 100 \), 40 divisions of the eyepiece graticule coincide with 4 divisions of the stage micrometer. The student then replaces the stage micrometer with a slide of plant cells and observes them at a magnification of \( \times 400 \). A plant cell is measured to be 6 eyepiece graticule divisions in width. What is the actual width of this plant cell?

A student investigated the effect of a competitive inhibitor on an enzyme-controlled reaction. They plotted a graph of the rate of reaction against substrate concentration for the reaction with and without the inhibitor. Which of the following describes the curve for the reaction with the competitive inhibitor compared to the curve without the inhibitor?

An animal cell with a diploid number of 12 (\( 2n = 12 \)) undergoes mitosis. What is the number of chromosomes and the number of DNA molecules in the cell during metaphase, and in each of the two newly forming nuclei during telophase?

Which row in the table correctly identifies the enzyme involved in the conversion of carbon dioxide to hydrogencarbonate ions within red blood cells, and the direction of ion movement during the chloride shift?

Which features of xylem vessel elements are correct structural adaptations for their function of transporting water under tension? 1. Lignified walls to prevent inward collapse. 2. Absence of cytoplasm and end walls to form a continuous tube with low resistance. 3. Presence of pits to allow lateral movement of water. 4. Presence of sieve plates to allow rapid flow of water under pressure.

A segment of DNA has the template strand sequence: 3'-TAC GGC TTA CTA-5'. What is the correct sequence of anticodons on the tRNA molecules that bind to the mRNA transcribed from this DNA?

Which row correctly matches the pathogen type, the method of transmission, and a primary prevention method for cholera?

An individual is bitten by a venomous snake and is immediately injected with an antivenom containing specific antibodies. Two months later, the individual is bitten again by the same species of snake and requires another injection of antivenom to survive. Which statements explain why the individual did not have immunity against the venom during the second bite? 1. The antivenom provided artificial passive immunity. 2. No memory cells were produced because the individual's immune system was not stimulated by active antigens. 3. The injected antibodies were broken down by the body over time.

Fig. 1.1 shows a transmission electron micrograph of a plant cell. (a) Distinguish between the terms magnification and resolution. [3] (b) A student measures the diameter of a mitochondrion in Fig. 1.1 as 24 mm. The actual length of this mitochondrion is 1.2 micrometres. Calculate the magnification of the micrograph. Show your working and state your answer to three significant figures. [3] (c) Contrast the advantages and limitations of using a transmission electron microscope (TEM) compared to a light microscope for studying cell structure. [4]

A student is provided with two solutions of unknown carbohydrates, labelled P and Q. (a) Describe the steps the student should take to carry out a semi-quantitative Benedict's test to compare the concentration of reducing sugars in solutions P and Q. [4] (b) After testing, both P and Q remained blue. Describe how the student could confirm whether non-reducing sugars are present in these solutions. [4] (c) State the color change that would be observed in a positive Biuret test for proteins, and identify the specific covalent bond that is detected by this test. [2]

Enzymes are globular proteins that catalyse biochemical reactions. (a) Explain the effects of increasing temperature on the rate of an enzyme-catalysed reaction up to and beyond the optimum temperature. [4] (b) Outline the structural and functional differences between competitive and non-competitive enzyme inhibitors. [4] (c) Describe the effects of a non-competitive inhibitor on the maximum rate of reaction (Vmax) and the Michaelis-Menten constant (Km) of an enzyme. [2]

Water transport in plants relies on coordinated pathways and structures. (a) Compare the apoplast pathway with the symplast pathway for the movement of water across the root cortex. [3] (b) Explain the role of the Casparian strip in regulating the passage of water and inorganic ions into the xylem vessel. [3] (c) Describe and explain how an increase in external relative humidity affects the rate of transpiration. [4]

Structure and function are closely linked in plant transport tissues. (a) Describe how the structure of a xylem vessel is adapted to its function of transporting water and providing support. [4] (b) Companion cells play an essential role in the function of phloem sieve tube elements. Explain how companion cells are structurally adapted to support the active loading of sucrose into sieve tubes. [4] (c) State one difference in the structure of the cell walls of xylem vessels compared to phloem sieve tube elements. [2]

Cholera remains a major global health threat, particularly in regions with poor sanitation. (a) State the name of the pathogen that causes cholera, and describe how this pathogen is transmitted from one person to another. [3] (b) Once in the small intestine, the pathogen secretes a cholera toxin. Explain how this toxin leads to the development of severe watery diarrhoea. [4] (c) Smallpox was successfully eradicated worldwide, but cholera has not been eradicated. Discuss the factors that make cholera much more difficult to eradicate than smallpox. [3]

An investigation was carried out to study the effect of different concentrations of sucrose solution on the water potential of potato tissue. You are provided with a stock solution of 1.0 mol dm^{-3} sucrose solution, labeled S, and distilled water. (a) (i) Describe how you would prepare a simple dilution series of sucrose solutions of concentrations: 0.8, 0.6, 0.4, and 0.2 mol dm^{-3}, using stock solution S and distilled water, to give a final volume of 20.0 cm^3 for each concentration. Show your calculations. [3 marks] (a) (ii) Five potato cylinders of initial length 50 mm were weighed and placed into each of the sucrose concentrations. Table 1.1 shows the results of this experiment. Complete Table 1.1 by calculating the percentage change in mass for each concentration. Show your working for the 0.6 mol dm^{-3} concentration. [5 marks] Table 1.1: [Sucrose concentration / mol dm^{-3}: 0.2, Initial mass / g: 2.00, Final mass / g: 2.24] [Sucrose concentration / mol dm^{-3}: 0.4, Initial mass / g: 2.00, Final mass / g: 2.08] [Sucrose concentration / mol dm^{-3}: 0.6, Initial mass / g: 2.00, Final mass / g: 1.90] [Sucrose concentration / mol dm^{-3}: 0.8, Initial mass / g: 2.00, Final mass / g: 1.76] [Sucrose concentration / mol dm^{-3}: 1.0, Initial mass / g: 2.00, Final mass / g: 1.64] (b) Describe how you would plot a graph of the percentage change in mass against the concentration of sucrose solution, specifying the axes, scale selection, and plotting method. [4 marks] (c) (i) Estimate the concentration of sucrose solution that is isotonic to the potato tissue and explain how you determined this value. [3 marks] (c) (ii) Explain the results obtained for the 0.2 mol dm^{-3} and 1.0 mol dm^{-3} solutions in terms of water potential and movement of water. [3 marks] (d) State two sources of experimental error in this procedure and suggest one improvement for each error. [2 marks]

Fig. 2.1 shows a diagram of a transverse section of a dicotyledonous stem. (a) Describe the key rules and steps to produce a high-quality, low-power plan drawing of a sector of this stem, and identify the key tissues that must be represented and labeled. [6 marks] (b) Describe the key rules and features to produce a high-power drawing of three adjacent cells from the vascular bundle: one xylem vessel element and two surrounding parenchyma cells. [5 marks] (c) (i) A student calibrated an eyepiece graticule using a stage micrometer. Under the high-power objective lens (magnification x40), 40 eyepiece graticule units (egu) aligned exactly with 10 stage micrometer divisions. Each division on the stage micrometer is 0.1 mm. Calculate the actual length of one eyepiece graticule unit in micrometres (\mu m). Show your working. [3 marks] (c) (ii) Using the same microscope and objective lens, the student measured the internal diameter of a large xylem vessel, which was found to be 6 eyepiece graticule units. Calculate the actual diameter of this xylem vessel in micrometres (\mu m). Show your working. [2 marks] (d) Complete Table 2.1 to compare three structural features of xylem vessels and phloem sieve tube elements that can be observed in a transverse section under a light microscope. [4 marks]