2025 Cambridge IAL Biology (9700) Practice Paper with Answers

The Michaelis-Menten constant (\(K_m\)) and maximum velocity (\(V_{max}\)) of an enzyme-catalysed reaction were determined in the absence and presence of two different inhibitors, X and Y, at the same concentration. With inhibitor X, the \(V_{max}\) was decreased but the \(K_m\) remained the same. With inhibitor Y, the \(V_{max}\) remained the same but the \(K_m\) increased. Which statement correctly describes the modes of action of inhibitors X and Y?

In a biochemical reaction, the energy level of the substrate is \(+20\text{ kJ mol}^{-1}\) and the energy level of the products is \(-10\text{ kJ mol}^{-1}\). The activation energy of the uncatalysed reaction is \(+60\text{ kJ mol}^{-1}\). When an enzyme is added, the activation energy is reduced by \(35\text{ kJ mol}^{-1}\). What is the activation energy of the enzyme-catalysed reaction and the overall energy change (\(\Delta H\)) for the reaction?

An ecologist sampled three different areas of a woodland to determine the species diversity of ground-nesting beetles. The data collected was used to calculate Simpson's Index of Diversity (\(D\)) for each area: Area 1: \(D = 0.85\); Area 2: \(D = 0.45\); Area 3: \(D = 0.12\). Which statement is a correct interpretation of these results?

A student wants to investigate the change in distribution and abundance of plant species across a transition zone from a salt marsh to a sand dune. Which sampling method and tool should the student use to obtain the most valid data?

A geneticist crosses two heterozygous fruit flies (\(AaBb \times AaBb\)) and obtains 160 offspring. The observed phenotypic ratio is compared to the expected Mendelian ratio of 9:3:3:1 using a chi-squared (\(\chi^2\)) test. The calculated \(\chi^2\) value is 5.82. The critical values of \(\chi^2\) at different degrees of freedom (df) and probability levels (p) are: df = 3 (p = 0.05 is 7.82; p = 0.01 is 11.34); df = 4 (p = 0.05 is 9.49; p = 0.01 is 13.28). What is the correct conclusion of this statistical test?

The lac operon in Escherichia coli regulates the expression of genes required for lactose metabolism. Under which combination of conditions will the transcription of the structural genes (lacZ and lacY) be at its highest level?

The polymerase chain reaction (PCR) is used to amplify DNA. Which row correctly identifies the function of each component in a PCR mixture?

When the water potential of the blood decreases, antidiuretic hormone (ADH) is released. Which row correctly describes the molecular effects of ADH binding to receptors on the collecting duct cells?

An investigation was carried out into the effect of two different inhibitors, X and Y, on an enzyme-catalysed reaction. The maximum velocity (\(V_{\max}\)) and Michaelis-Menten constant (\(K_m\)) were determined for the reaction without inhibitors, and in the presence of inhibitor X and inhibitor Y.

The results are shown in the table.

| Reaction mixture | \(V_{\max}\) / arbitrary units | \(K_m\) / \(\text{mmol dm}^{-3}\) |
|---|---|---|
| Enzyme + substrate | 120 | 1.5 |
| Enzyme + substrate + inhibitor X | 120 | 4.8 |
| Enzyme + substrate + inhibitor Y | 50 | 1.5 |

Which statement correctly identifies the types of inhibition shown by inhibitor X and inhibitor Y?

The energy profile of a biochemical reaction is analysed. The energy levels of the key stages of the reaction are as follows:

- Initial energy level of reactants = \(150\text{ kJ mol}^{-1}\)
- Energy of the transition state without enzyme = \(350\text{ kJ mol}^{-1}\)
- Energy of the transition state with enzyme = \(220\text{ kJ mol}^{-1}\)
- Final energy level of products = \(80\text{ kJ mol}^{-1}\)

Which row correctly shows the activation energy for the enzyme-catalysed reaction and the overall energy change (\(\Delta H\)) for this reaction?

| | Activation energy of catalysed reaction / \(\text{kJ mol}^{-1}\) | Overall energy change (\(\Delta H\)) / \(\text{kJ mol}^{-1}\) |
|---|---|---|
| A | +70 | -70 |
| B | +70 | +70 |
| C | +220 | -70 |
| D | +120 | -150 |

Which of the factors could explain a decrease in the rate of an enzyme-catalysed reaction over time when the reaction is carried out at the enzyme's optimum temperature of \(30^\circ\text{C}\)?

1. The activation energy of the reaction increases as product accumulates.
2. The frequency of successful collisions between enzyme and substrate molecules decreases.
3. Product molecules act as competitive inhibitors by binding to the active sites.

In a woodland habitat, there are five species of beetle. An environmental change causes the population of the most abundant beetle species to decrease significantly, while the populations of the other four species increase, such that all five species now have approximately equal numbers of individuals. The total number of individual beetles in the habitat remains unchanged.

Which row correctly shows the effect of this change on the species richness, species evenness, and Simpson's Index of Diversity (\(D\)) of this habitat?

| | Species richness | Species evenness | Simpson’s Index of Diversity (\(D\)) |
|---|---|---|---|
| A | remains the same | increases | increases |
| B | remains the same | decreases | decreases |
| C | decreases | increases | increases |
| D | increases | increases | remains the same |

Which features of the domain Archaea distinguish its members from those of the domain Bacteria?

1. They have membrane lipids containing branched hydrocarbon chains linked by ether bonds.
2. They have 70S ribosomes.
3. Their cell walls lack peptidoglycan.
4. Their DNA is associated with histone proteins in some species.

In a species of sweet pea, the gene for flower colour (P/p) and the gene for pollen grain shape (L/l) are autosomal and linked. A heterozygous plant with the genotype PpLl was crossed with a double homozygous recessive plant (ppll).

The offspring phenotypes and their numbers were:
- Purple flowers, long pollen grains: 382
- Red flowers, round pollen grains: 368
- Purple flowers, round pollen grains: 128
- Red flowers, long pollen grains: 122

What is the recombination frequency between these two gene loci?

Which row correctly describes what occurs at each temperature phase during one cycle of the polymerase chain reaction (PCR)?

| | \(95^\circ\text{C}\) | \(55^\circ\text{C}\) | \(72^\circ\text{C}\) |
|---|---|---|---|
| A | Hydrogen bonds break to separate DNA strands | Primers bind to single-stranded DNA templates | Taq polymerase synthesises complementary strands |
| B | Phosphodiester bonds break to separate DNA strands | Primers bind to single-stranded DNA templates | Taq polymerase synthesises complementary strands |
| C | Hydrogen bonds break to separate DNA strands | Taq polymerase binds to single-stranded DNA | Primers synthesise complementary strands |
| D | Phosphodiester bonds break to separate DNA strands | Taq polymerase binds to single-stranded DNA | Primers synthesise complementary strands |

The table shows the concentrations of four substances in the blood plasma, the glomerular filtrate in the Bowman's capsule, and the urine of a healthy human.

| Substance | Concentration in blood plasma / \(\text{g dm}^{-3}\) | Concentration in glomerular filtrate / \(\text{g dm}^{-3}\) | Concentration in urine / \(\text{g dm}^{-3}\) |
|---|---|---|---|
| W | 80.0 | 0.0 | 0.0 |
| X | 1.0 | 1.0 | 0.0 |
| Y | 0.3 | 0.3 | 20.0 |
| Z | 3.0 | 3.0 | 6.0 |

Which row correctly identifies W, X, Y, and Z?

| | W | X | Y | Z |
|---|---|---|---|---|
| A | Protein | Glucose | Urea | Sodium ions |
| B | Glucose | Protein | Sodium ions | Urea |
| C | Protein | Sodium ions | Urea | Glucose |
| D | Sodium ions | Glucose | Protein | Urea |

An experiment was carried out to investigate the effect of two different inhibitors, X and Y, on the rate of an enzyme-controlled reaction. The concentration of the enzyme was kept constant in all trials. The kinetic parameters of the reaction under different conditions were determined as follows:

* **Enzyme alone**: \(V_{max} = 100\text{ a.u.}\), \(K_m = 2.0\text{ mmol dm}^{-3}\)
* **Enzyme + inhibitor X**: \(V_{max} = 100\text{ a.u.}\), \(K_m = 6.0\text{ mmol dm}^{-3}\)
* **Enzyme + inhibitor Y**: \(V_{max} = 50\text{ a.u.}\), \(K_m = 2.0\text{ mmol dm}^{-3}\)

Which statement is the correct conclusion about inhibitors X and Y?

Which statement correctly explains how an enzyme increases the rate of a metabolic reaction?

A student measured the volume of oxygen released during the breakdown of hydrogen peroxide by catalase at regular intervals. The results are shown below:

* At \(0\text{ s}\): \(0.0\text{ cm}^3\)
* At \(10\text{ s}\): \(15.0\text{ cm}^3\)
* At \(20\text{ s}\): \(25.0\text{ cm}^3\)
* At \(30\text{ s}\): \(31.0\text{ cm}^3\)

What is the average initial rate of reaction over the first 10 seconds, and what is the main reason for the subsequent decrease in the rate of reaction?

A student sampled a community of soil invertebrates in a woodland habitat and recorded the abundance of three species as shown in the table:

| Species | Number of individuals (\(n\)) |
| :--- | :--- |
| Woodlouse | 10 |
| Earthworm | 6 |
| Beetle | 4 |

Using the formula for Simpson's Index of Diversity: \(D = 1 - \Sigma \left(\frac{n}{N}\right)^2\)

What is the calculated value of Simpson's Index of Diversity (\(D\)) for this community?

Which of the following describes features that are found in the domain Archaea but NOT in the domain Bacteria?

In a plant species, two genes, A/a and B/b, control flower color. At least one dominant allele of each gene (genotype A_B_) is required to produce red flowers. All other genotypes result in white flowers.

A cross is carried out between two double heterozygous red-flowered plants (AaBb \(\times\) AaBb).

What is the expected ratio of phenotypes in the offspring?

A student set up a PCR reaction mixture to amplify a specific sequence of DNA.

Which row correctly identifies the function of each component added to the reaction tube?

When blood glucose concentration decreases below the normal set-point, glucagon is secreted by the alpha cells of the pancreas.

Which sequence of events describes the mechanism of action of glucagon on liver cells?

An enzyme-catalysed reaction is carried out at two different temperatures, \(25^\circ\text{C}\) and \(35^\circ\text{C}\), across a range of substrate concentrations. Assume that the enzyme is not denatured at either temperature.

Which parameter(s) of the reaction will change at \(35^\circ\text{C}\) compared to \(25^\circ\text{C}\)?

1. \(V_{\max}\)
2. \(K_m\)
3. Activation energy of the reaction (\(E_a\))

An experiment was conducted to investigate the effect of a specific inhibitor on the rate of an enzyme-catalysed reaction.

In the presence of a constant concentration of the inhibitor, the following observations were made:
- At very high substrate concentrations, the rate of reaction approaches the maximum rate (\(V_{\max}\)) observed without the inhibitor.
- The concentration of substrate required to reach half of this maximum rate is doubled.

Which statement about this inhibitor is correct?

An ecologist sampled two different meadows, Meadow X and Meadow Y, to determine their plant diversity. The results of the sampling are shown in the table:

| Species | Number of individuals in Meadow X | Number of individuals in Meadow Y |
| :--- | :---: | :---: |
| Species A | 80 | 30 |
| Species B | 10 | 25 |
| Species C | 5 | 25 |
| Species D | 5 | 20 |

Which statement correctly compares Meadow X and Meadow Y?

In a species of sweet pea, flower colour is controlled by two genes, \(A/a\) and \(B/b\), which assort independently.

- The presence of at least one dominant allele of both genes (\(A\_B\_\)) results in purple flowers.
- All other genotypes (\(A\_bb\), \(aaB\_\), or \(aabb\)) result in white flowers.

A plant with purple flowers of genotype \(AaBb\) is self-pollinated.

What is the expected phenotypic ratio in the offspring?

During a single cycle of the Polymerase Chain Reaction (PCR), the mixture is subjected to three different temperatures in sequence: \(95^\circ\text{C}\), then \(55^\circ\text{C}\), and finally \(72^\circ\text{C}\).

Which row correctly describes the main event occurring at each temperature?

| | \(95^\circ\text{C}\) | \(55^\circ\text{C}\) | \(72^\circ\text{C}\) |
| :--- | :--- | :--- | :--- |
| **A** | Denaturation of DNA double helix | Annealing of primers to single strands | Optimum temperature for Taq polymerase extension |
| **B** | Denaturation of DNA double helix | Activation of Taq polymerase | Annealing of primers to single strands |
| **C** | Synthesis of complementary strands | Annealing of primers to single strands | Denaturation of DNA double helix |
| **D** | Activation of Taq polymerase | Denaturation of DNA double helix | Synthesis of complementary strands |

What is the correct sequence of intracellular events that occurs immediately after antidiuretic hormone (ADH) binds to cell surface receptors on the collecting duct cells of a nephron?

1. Vesicles containing aquaporins fuse with the luminal (apical) membrane.
2. Adenylyl cyclase is activated, converting ATP to cyclic AMP (cAMP).
3. Cyclic AMP acts as a second messenger to activate a kinase cascade.
4. Active G-protein is produced following receptor conformational change.
5. Water permeability of the luminal membrane increases, allowing water to enter by osmosis.

Which statement about the Michaelis-Menten constant (\(K_m\)) of an enzyme is correct?

Which features are characteristic of organisms in both the Domain Archaea and the Domain Bacteria, but are NOT characteristic of organisms in the Domain Eukarya?

1. Ribosomes that are 70S
2. Absence of a nucleus surrounded by a nuclear envelope
3. Cell walls containing peptidoglycan

The Michaelis-Menten constant (\(K_m\)) and the maximum velocity (\(V_{\max}\)) of an enzyme-catalyzed reaction were measured in both the absence and presence of an inhibitor.

- In the absence of the inhibitor: \(K_m = 1.5\text{ mmol dm}^{-3}\) and \(V_{\max} = 50\text{ \mu mol min}^{-1}\)
- In the presence of the inhibitor: \(K_m = 4.5\text{ mmol dm}^{-3}\) and \(V_{\max} = 50\text{ \mu mol min}^{-1}\)

Which statement describes the mechanism of this inhibitor?

Which of the following describe how an enzyme lowers the activation energy of a metabolic reaction?

1. Aligning substrate molecules in the correct orientation for reaction.
2. Changing the overall energy change (\(\Delta H\)) of the reaction.
3. Putting physical strain on specific bonds in the substrate.
4. Providing temporary alternative chemical pathways through active site residues.

The initial rate of an enzyme-controlled reaction is measured at \(20^\circ\text{C}\) and is found to be \(1.2\text{ mmol dm}^{-3}\text{ s}^{-1}\).

The temperature coefficient (\(Q_{10}\)) of this reaction is \(2.0\) between \(20^\circ\text{C}\) and \(40^\circ\text{C}\).

Assuming that the enzyme is not denatured at \(40^\circ\text{C}\), what is the expected rate of reaction at \(40^\circ\text{C}\)?

An ecological survey compared the plant biodiversity of two grassland communities, X and Y.

- Grassland X: Simpson's Index of Diversity (\(D\)) = 0.82
- Grassland Y: Simpson's Index of Diversity (\(D\)) = 0.24

Which statement is a correct conclusion based on these results?

Which of the following conservation methods are correctly classified as *ex situ* conservation?

1. Captive breeding of endangered animals in a zoological park.
2. Controlled burning to maintain a specific successional stage in a nature reserve.
3. Storing seeds of wild crop relatives in a temperature-controlled seed bank.
4. Eradicating invasive alien species from an offshore island sanctuary.

In a species of sweet pea, flower color is controlled by two genes, \(A/a\) and \(B/b\), which assort independently.

The production of purple pigment requires the presence of at least one dominant allele of both genes (genotype \(A\_B\_\)). All other genotypes (such as \(A\_bb\), \(aaB\_\), or \(aabb\)) result in white flowers.

If two plants with the genotype \(AaBb\) are crossed, what is the expected ratio of phenotypes in the offspring?

The table shows steps in one cycle of the polymerase chain reaction (PCR).

Which row correctly identifies the temperature and molecular event occurring at each step of the cycle?

The following events occur in the cells of the collecting duct when antidiuretic hormone (ADH) regulates water reabsorption in the mammalian kidney.

1. Aquaporins are inserted into the luminal membrane.
2. Active protein kinase A phosphorylates proteins that trigger vesicle movement.
3. Intracellular cyclic AMP (cAMP) levels increase.
4. ADH binds to G-protein coupled receptors on the cell surface membrane, activating adenylyl cyclase.
5. Water enters the cell by osmosis from the lumen of the collecting duct.

What is the correct sequence of these events?

The enzyme urease catalyses the hydrolysis of urea into ammonia and carbon dioxide. (a) Explain the term activation energy and describe how enzymes such as urease lower it. [3] (b) An investigation was carried out to determine the effect of lead ions \(Pb^{2+}\) on the rate of urease activity at different substrate concentrations. The results showed that the maximum rate of reaction \(V_{max}\) remained unchanged, but the Michaelis-Menten constant \(K_m\) increased. (i) State the independent and dependent variables in this investigation. [2] (ii) State, with a reason, the type of inhibition caused by lead ions. [2] (c) Explain how an increase in temperature up to the optimum increases the rate of an enzyme-catalysed reaction, and why exceeding the optimum temperature decreases the rate. [3]

Lactase is an enzyme used to produce lactose-free milk by hydrolysing lactose into glucose and galactose. The enzyme can be used in its free state or immobilised in alginate beads. (a) Describe how lactase is immobilised using alginate beads. [3] (b) Explain three advantages of using immobilised lactase compared to free lactase in the food industry. [3] (c) Suggest and explain how the process of immobilisation might affect the Michaelis-Menten constant \(K_m\) of lactase for its substrate, lactose. [4]

Ecologists studied the biodiversity of two marine habitats: a seagrass meadow and a coral reef. (a) Define the terms species richness and species evenness. [2] (b) The formula for Simpson's Index of Diversity is: \(D = 1 - \sum \left(\frac{n}{N}\right)^2\). In a sample from the seagrass meadow, four species (A, B, C, and D) were identified with the following individual counts: Species A = 45, Species B = 15, Species C = 30, Species D = 10. Calculate the Simpson's Index of Diversity (D) for the seagrass meadow. Show your working. [3] (c) The coral reef had a calculated D value of 0.88. Compare the biodiversity of the seagrass meadow and the coral reef, and explain what a higher D value indicates about the stability of the ecosystem. [3] (d) State two reasons why it is important to conserve marine ecosystems such as coral reefs. [2]

Coat color in a rodent species is determined by two independently assorting genes, Gene A and Gene B. Gene A determines pigment production; the dominant allele A allows pigment production, whereas the recessive allele a prevents pigment production, resulting in an albino coat. Gene B determines the distribution of pigment; the dominant allele B produces an agouti coat, while the recessive allele b produces a solid black coat. (a) Explain what is meant by the term epistasis. [2] (b) State the phenotypes of rodents with the following genotypes: (i) AaBb, (ii) Aabb, (iii) aaBB. [3] (c) Two heterozygous agouti rodents (AaBb) are crossed. Draw a genetic diagram to determine the expected phenotypic ratio of their offspring. [4] (d) State the statistical test that should be used to determine if the observed ratio of offspring phenotypes differs significantly from the expected ratio. [1]

Recombinant DNA technology is used to produce human proteins, such as human growth hormone (hGH), in bacterial cells. (a) Outline why complementary DNA (cDNA), rather than genomic DNA, is used when expressing eukaryotic genes in prokaryotic host cells such as Escherichia coli. [2] (b) Describe the roles of the following enzymes in the production of recombinant plasmids: (i) restriction endonuclease [2] (ii) DNA ligase [2] (c) Plasmids often contain marker genes, such as those coding for green fluorescent protein (GFP) or antibiotic resistance. Explain the purpose of including marker genes in recombinant plasmids and how they are used. [4]

The regulation of blood glucose concentration is a key homeostatic mechanism in mammals. (a) Describe how a rise in blood glucose concentration is detected by the pancreas and how insulin is subsequently secreted by the beta cells of the islets of Langerhans. [4] (b) Explain how insulin acts on liver cells (hepatocytes) to decrease blood glucose concentration. [4] (c) Distinguish between the terms glycogenesis and gluconeogenesis. [2]

Paper 32 Advanced Practical Skills 2

**Question 1**

You are required to investigate the effect of the concentration of an inhibitor, copper sulfate solution (\textbf{I}), on the activity of the enzyme amylase.

You are provided with:
- \(1.0\%\) amylase solution, labelled \textbf{E}
- \(1.0\%\) starch suspension, labelled \textbf{S}
- \(2.0\%\) copper sulfate solution, labelled \textbf{I}
- Distilled water, labelled \textbf{W}
- Iodine in potassium iodide solution, labelled \textbf{Iodine}

(a) (i) Complete Table 1.1 to show how you would dilute the stock \(2.0\%\) copper sulfate solution to prepare five different concentrations of copper sulfate solution: \(2.0\%\), \(1.5\%\), \(1.0\%\), \(0.5\%\), and \(0.0\%\), each with a final volume of \(10.0\text{ cm}^3\).

Table 1.1
| Concentration of copper sulfate / % | Volume of 2.0% copper sulfate (I) / \(\text{cm}^3\) | Volume of distilled water (W) / \(\text{cm}^3\) |
| :---: | :---: | :---: |
| 2.0 | | |
| 1.5 | | |
| 1.0 | | |
| 0.5 | | |
| 0.0 | | |

[3]

(ii) State the independent variable and the dependent variable in this investigation. [2]

(b) A student performed this investigation by mixing \(1\text{ cm}^3\) of each copper sulfate solution with \(2\text{ cm}^3\) of amylase solution, incubating the mixture for 2 minutes, and then adding \(2\text{ cm}^3\) of starch suspension. Samples were tested with iodine solution on a spotting tile every 10 seconds. The results are shown in Table 1.2.

Table 1.2
| Concentration of copper sulfate / % | Time taken for starch to be completely hydrolyzed / s |
| :---: | :---: |
| 0.0 | 40 |
| 0.5 | 70 |
| 1.0 | 120 |
| 1.5 | 210 |
| 2.0 | No change after 300 s |

Process these data to calculate the rate of reaction in \(\text{s}^{-1}\) using the formula:
\[ \text{rate} = \frac{1000}{\text{time taken}} \]
For the \(2.0\%\) concentration, assume the rate of reaction is \(0\text{ s}^{-1}\).
Present the processed results in a suitable table, including both the concentration of copper sulfate and the calculated rate of reaction, to an appropriate number of significant figures. [4]

(c) Plot a graph of the rate of reaction (y-axis) against the concentration of copper sulfate (x-axis) on a grid. [4]

(d) Explain the effect of copper sulfate concentration on the activity of amylase, referencing the experimental data. [4]

(e) (i) The student identified that determining the "end point" (when the blue-black color of iodine no longer appears) is a major source of error. Suggest why this is a source of error. [1]
(ii) Suggest an improvement to the method that would allow more accurate and objective measurement of the rate of starch hydrolysis. [2]

Paper 32 Advanced Practical Skills 2

**Question 2**

Figure 2.1 is a photomicrograph of a transverse section through the stem of a typical herbaceous dicotyledonous plant, *Ranunculus*.

(a) Draw a large, low-power plan diagram of the segment of the stem shown in Figure 2.1, representing approximately one-quarter of the stem section. Your drawing should show the distribution of tissues (such as epidermis, cortex, vascular bundles, and pith) but should not show individual cells. Use a sharp pencil. [5]

(b) Figure 2.2 shows a high-power view of a single vascular bundle from the same stem section.

Make a large, detailed drawing of a group of three adjacent xylem vessel elements and two adjacent sclerenchyma (cap) fibres. Label one xylem vessel and one sclerenchyma cell on your drawing. [5]

(c) The actual diameter of a xylem vessel in the stem is \(60\ \mu\text{m}\). A student uses a light microscope with an eyepiece graticule to measure the same xylem vessel.

Under the high-power objective (\(\times 400\)), the stage micrometer calibration shows that \(1\) eyepiece graticule unit (\text{epu}) is equal to \(2.5\ \mu\text{m}\).

(i) Calculate the expected diameter of this xylem vessel in eyepiece graticule units (\text{epu}). Show your working. [2]

(ii) The student then measures the vessel in a drawing they made. The diameter of the vessel in the drawing is \(36\text{ mm}\). Calculate the magnification of the student's drawing compared to the actual size of the vessel (\(60\ \mu\text{m}\)). Show your working and state your answer to an appropriate number of significant figures. [3]

(d) Describe how the structure of a xylem vessel element is adapted to its function of transporting water and mineral ions under tension. [5]

Pyruvate kinase is a key enzyme in glycolysis that catalyses the final step of the pathway, converting phosphoenolpyruvate (PEP) to pyruvate with the concurrent production of ATP. It is allosterically regulated by fructose 1,6-bisphosphate (FBP), which acts as an activator, and by ATP, which acts as an inhibitor.

(a) Describe how pyruvate kinase lowers the activation energy of the reaction. [3]
(b) Explain how the binding of FBP (an allosteric activator) affects the activity of pyruvate kinase. [3]
(c) Distinguish between competitive and non-competitive inhibition of enzymes such as pyruvate kinase. [4]

An investigation was conducted to determine the effect of copper ions (\(Cu^{2+}\)), which act as non-competitive inhibitors, on the rate of starch hydrolysis by amylase.

(a) State three variable factors, other than the concentration of copper ions, that must be controlled in this investigation and suggest how each would be controlled. [3]
(b) Describe and explain the expected results as copper ion concentration increases from \(0\) to \(0.5\text{ mol dm}^{-3}\). [4]
(c) Explain why using immobilized amylase instead of free amylase is advantageous in industrial processes. [3]

Succinate dehydrogenase is an enzyme of both the citric acid (Krebs) cycle and the electron transport chain, located in the inner mitochondrial membrane. It catalyses the oxidation of succinate to fumarate. Malonate is a structural analogue of succinate and acts as a competitive inhibitor of this enzyme.

(a) Outline the role of succinate dehydrogenase in the Krebs cycle. [2]
(b) Suggest and explain the effect of adding an excess of succinate to a mitochondrial suspension containing a constant concentration of malonate. [3]
(c) Explain the role of NAD and FAD in the electron transport chain during aerobic respiration. [5]

An ecologist investigated the plant biodiversity of two grassland areas, Area X and Area Y, by counting the individuals of three species. The results are shown below:
Area X: Species A = 50, Species B = 30, Species C = 20 (Total \(N = 100\))
Area Y: Species A = 90, Species B = 8, Species C = 2 (Total \(N = 100\))

(a) Calculate the Simpson's Index of Diversity (\(D\)) for Area X and Area Y using the formula:
\(D = 1 - \sum \left(\frac{n}{N}\right)^2\)
Show your working. [4]
(b) Explain what the calculated values of \(D\) indicate about the biodiversity and stability of Area X compared to Area Y. [3]
(c) Describe how random sampling using quadrats can be used to estimate the abundance of plant species in a grassland. [3]

The black rhinoceros (*Diceros bicornis*) is critically endangered due to habitat loss and poaching. Conservation efforts involve both *in-situ* and *ex-situ* strategies.

(a) Distinguish between *in-situ* and *ex-situ* conservation, providing one example of each method used for the black rhinoceros. [3]
(b) Explain the role of captive breeding programmes in zoos in conserving endangered species such as the black rhinoceros, and discuss the difficulties associated with these programmes. [5]
(c) State two reasons why maintaining biodiversity is of economic importance to local human populations. [2]

In sweet peas (*Lathyrus odoratus*), the gene for flower colour has two alleles: purple (\(B\)) is dominant to red (\(b\)). The gene for pollen grain shape also has two alleles: long (\(L\)) is dominant to round (\(l\)). These two gene loci are autosomally linked. A cross was carried out between a dihybrid plant with purple flowers and long pollen (\(BbLl\)) and a homozygous recessive plant with red flowers and round pollen (\(bbll\)).

(a) Explain what is meant by the terms *autosomal linkage* and *crossing over*. [4]
(b) The offspring from the cross described above were:
Purple flowers, long pollen: 242
Purple flowers, round pollen: 28
Red flowers, long pollen: 32
Red flowers, round pollen: 238
Calculate the crossover value (recombination frequency) for these two genes. Show your working. [3]
(c) Explain how crossing over during meiosis produces recombinant phenotypes in the offspring. [3]

Recombinant DNA technology is used to produce human insulin in genetically modified *Escherichia coli* bacteria.

(a) Explain why complementary DNA (cDNA), synthesized using reverse transcriptase, is used to obtain the human insulin gene for expression in bacteria, rather than using genomic DNA. [3]
(b) Describe the role of restriction endonucleases and DNA ligase in the production of a recombinant plasmid. [4]
(c) Explain how marker genes, such as those coding for fluorescent proteins, are used to identify bacteria that have successfully taken up the recombinant plasmid. [3]

Osmoregulation is an essential homeostatic mechanism in mammals that maintains the water potential of the blood within narrow limits. When water potential decreases, antidiuretic hormone (ADH) is released.

(a) Explain how osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood and stimulate the release of ADH. [3]
(b) Describe the mechanism of action of ADH on the cells of the collecting duct of the kidney nephron. [5]
(c) Suggest the effect of a drug that blocks G-protein-coupled receptors in the collecting duct cells on urine volume and concentration. [2]

**(a)** Homeostasis relies on self-regulating mechanisms. Define the term *negative feedback* as used in homeostasis. [2]

**(b)** Osmoregulation is a key homeostatic process in mammals. When the water potential of the blood decreases below a set point, antidiuretic hormone (ADH) is released from the posterior pituitary gland. ADH travels in the blood and binds to specific receptors on the basolateral membranes of collecting duct cells in the kidney.
Describe the intracellular cell-signalling pathway that occurs within these cells after ADH binds to its receptor, leading to an increase in the permeability of the luminal membrane to water. [5]

**(c)** Nephrogenic diabetes insipidus (NDI) is a rare disorder that can be caused by an inherited mutation in the *AVPR2* gene, which codes for the ADH receptor (V2 receptor).
Explain how this mutation results in the production of large volumes of dilute urine, even when the individual is dehydrated. [3]

**(a)** Enzyme tools are essential in genetic engineering and research. Contrast the functions of *restriction endonucleases* and *reverse transcriptase*. [3]

**(b)** Microarray technology allows researchers to detect and measure the expression of thousands of genes simultaneously.
Describe how a microarray is used to compare the gene expression profiles of a cancerous lung cell and a normal, healthy lung cell. [5]

**(c)** Explain how the results of a microarray analysis can be used to assist in the development of personalized medical treatment for a patient with cancer. [2]

Alkaline phosphatase is an enzyme that catalyzes the hydrolysis of phosphate esters. In an investigation, the artificial substrate p-nitrophenyl phosphate (pNPP) is used. Alkaline phosphatase converts colorless pNPP into yellow p-nitrophenyl (pNP), which absorbs light at 405 nm.

A student wants to investigate the effect of different concentrations of a competitive inhibitor, phenylalanine, on the initial rate of this reaction.

The student is provided with:
- 10.0% (w/v) stock solution of phenylalanine (inhibitor)
- 1.0% (w/v) alkaline phosphatase enzyme solution
- 0.05 mol dm\(^{-3}\) pNPP substrate solution
- Buffer solution at pH 9.0
- Standard laboratory glassware and access to a colorimeter with a 405 nm filter.

(a) Describe a method the student could use to carry out this investigation.

Your description should be detailed enough to allow another person to follow it, and should include:
- the preparation of five different concentrations of phenylalanine using a simple or serial dilution of the stock 10.0% solution
- how the dependent variable will be measured
- how key confounding variables will be controlled
- a suitable control experiment
- the safety precautions that should be taken.
[9]

(b) (i) The student plotted a graph of the initial rate of reaction against substrate concentration at two different concentrations of phenylalanine. State how the student could use this graph to confirm that phenylalanine is a competitive inhibitor and not a non-competitive inhibitor. [2]

(ii) The student carried out 10 replicates at each inhibitor concentration and calculated the mean initial rate and standard deviation. Explain why calculating the standard deviation of the replicate data is more useful than finding the range. [2]

(iii) State the statistical test the student should use to determine whether there is a significant difference between the mean initial rates of reaction at two different inhibitor concentrations, and justify your choice. [2]

An ecological researcher wants to compare the species diversity of ground-dwelling beetles (Coleoptera) in two areas of a temperate deciduous forest:
- Area A: heavily grazed by wild deer.
- Area B: enclosed by a deer-exclusion fence for 10 years to prevent grazing.

(a) Describe a method the researcher could use to sample the beetle populations and collect the data required to calculate Simpson's Index of Diversity (\(D\)) for each area.

Your description should be detailed enough to allow another person to follow it, and should include:
- the sampling technique used to capture ground-dwelling beetles
- how sampling locations within each area are determined to prevent bias
- how standardisation is maintained to ensure the comparison between the two areas is valid
- how the beetles are identified and the data recorded
- safety and ethical considerations.
[8]

(b) The researcher calculated Simpson's Index of Diversity (\(D\)) for both areas using the formula:

\(D = 1 - \sum \left(\frac{n}{N}\right)^2\)

where \(n\) is the number of individuals of a particular species and \(N\) is the total number of individuals of all species.

(i) Explain what the values of Simpson's Index of Diversity (\(D\)) close to 1 and close to 0 indicate about the stability of the communities in these areas. [2]

(ii) In Area A, the total number of beetles caught (\(N\)) was 240. The sum of the squares of the proportions, \(\sum \left(\frac{n}{N}\right)^2\), was calculated as 0.382.
In Area B, the total number of beetles caught (\(N\)) was 310, and the sum of the squares of the proportions, \(\sum \left(\frac{n}{N}\right)^2\), was 0.145.

Calculate the Simpson's Index of Diversity (\(D\)) for Area A and Area B, and state which area has the higher species diversity. Show your working. [3]

(iii) Suggest two biotic factors, other than grazing by deer, that could influence the species diversity of beetles in these woodland areas. [2]