A Level H2 Biology Practice Paper 2

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TuitionGoWhere Exam Practice (AI) - Biology H2 A-Level

Subject: Biology
Level: H2
Paper: Practice Paper (Version 2 of 5)
Duration: 1 hour 30 minutes
Total Marks: 60
Name: __________________________
Class: __________________________
Date: __________________________

INSTRUCTIONS TO CANDIDATES

• Write your name, class, and date in the spaces provided.
• Answer all questions.
• Write your answers in the spaces provided in this booklet.
• The number of marks is given in brackets [ ] at the end of each question or part question.
• You are advised to spend approximately 15 minutes on Section A and 75 minutes on Section B.

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Section A: Structured Questions (30 Marks)

Answer all questions in this section.

1. Fig. 1.1 shows a schematic representation of the fluid mosaic model of a cell surface membrane, highlighting the movement of a specific solute.

(Note: In a real exam, Fig 1.1 would show a phospholipid bilayer with a carrier protein undergoing conformational change, moving solute X from high to low concentration.)

(a) With reference to Fig. 1.1, identify the type of transport occurring. [1] ........................................................................................................................................

(b) Explain why this process does not require ATP. [2] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

(c) State one structural feature of the protein shown in Fig. 1.1 that allows it to be specific to solute X. [1] ........................................................................................................................................

2. A student investigated the effect of temperature on the activity of the enzyme amylase. The results are shown in Table 2.1.

Temperature / °C	Rate of Reaction / arbitrary units
20	12
30	28
40	45
50	38
60	10
70	0

(a) Describe the trend in enzyme activity between 20°C and 40°C. [2] ........................................................................................................................................ ........................................................................................................................................

(b) Explain the result observed at 70°C. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

3. Fig. 3.1 shows the structure of a triglyceride molecule.

(a) Name the two types of molecules that combine to form a triglyceride. [1] ........................................................................................................................................

(b) Triglycerides are used as energy storage molecules in animals. Explain two properties of triglycerides that make them suitable for this function. [4]

1. .................................................................................................................................... ........................................................................................................................................
2. .................................................................................................................................... ........................................................................................................................................

4. Mitochondria are often described as the "powerhouses" of the cell.

(a) Describe the role of the inner mitochondrial membrane in ATP synthesis. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

(b) Cyanide is a poison that inhibits the electron transport chain. Explain why this leads to a cessation of ATP production. [2] ........................................................................................................................................ ........................................................................................................................................

5. Fig. 5.1 shows the results of gel electrophoresis performed on DNA samples from four individuals (A, B, C, and D) for a specific gene locus.

(Note: Fig 5.1 would show lanes. Lane A: 1 band. Lane B: 2 bands. Lane C: 1 band (different position to A). Lane D: 2 bands (same positions as B).)

(a) Identify which individual(s) are heterozygous for this gene. [1] ........................................................................................................................................

(b) Explain how gel electrophoresis separates DNA fragments. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

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Section B: Long Structured Questions (30 Marks)

Answer all questions in this section.

6. The lac operon in E. coli is a classic example of gene regulation in prokaryotes.

(a) Define the term 'operon'. [1] ........................................................................................................................................

(b) Describe the role of the following components in the lac operon when lactose is absent from the environment: (i) The regulator gene (lacI) [2] ........................................................................................................................................ ........................................................................................................................................ (ii) The operator region [2] ........................................................................................................................................ ........................................................................................................................................

(c) Explain the metabolic advantage to E. coli of having an inducible operon like the lac operon, rather than constitutively expressing the enzymes for lactose digestion. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

7. Protein structure determines function. Misfolding of proteins can lead to serious diseases such as Alzheimer’s disease and Bovine Spongiform Encephalopathy (BSE).

(a) Distinguish between the secondary and tertiary structures of a protein. [4] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

(b) With reference to the chemical bonds involved, explain how a change in pH can cause a protein to denature. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

(c) Suggest why misfolded proteins tend to aggregate within cells, referring to the properties of amino acid side chains. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

8. Cell division is essential for growth and repair.

(a) Compare the outcomes of mitosis and meiosis in terms of: (i) The number of daughter cells produced. [1] ........................................................................................................................................ (ii) The genetic composition of the daughter cells. [2] ........................................................................................................................................ ........................................................................................................................................

(b) During prophase I of meiosis, crossing over occurs. Explain the significance of crossing over for genetic variation. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

(c) Uncontrolled cell division can lead to tumour formation. Describe how a mutation in a tumour suppressor gene (such as p53) can contribute to cancer development. [3] ........................................................................................................................................ ........................................................................................................................................ ........................................................................................................................................

9. Water is vital for life due to its unique physical and chemical properties.

(a) Explain how the polarity of water molecules leads to the formation of hydrogen bonds. [2] ........................................................................................................................................ ........................................................................................................................................

(b) Discuss the importance of the following properties of water to living organisms: (i) High specific heat capacity [2] ........................................................................................................................................ ........................................................................................................................................ (ii) Solvent properties [2] ........................................................................................................................................ ........................................................................................................................................

10. The cell cycle consists of interphase and the M phase.

(a) Describe the events that occur during the S phase of interphase. [2] ........................................................................................................................................ ........................................................................................................................................

(b) Explain why checkpoints are important in the cell cycle. [2] ........................................................................................................................................ ........................................................................................................................................

(c) A drug used in chemotherapy targets microtubules. Suggest how this drug stops cell division. [2] ........................................................................................................................................ ........................................................................................................................................

*** END OF PAPER ***

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TuitionGoWhere Exam Practice (AI) - Biology H2 A-Level

Marking Scheme & Answer Key (Version 2)

Subject: Biology H2
Paper: Practice Paper (Version 2 of 5)
Total Marks: 60

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Section A: Structured Questions

1. Membrane Transport (a) Facilitated diffusion. [1] (b)

• Movement is down the concentration gradient (from high to low concentration); [1]
• Therefore, no additional energy (ATP) is required to move the solute. [1] (c)
• The specific shape/tertiary structure of the binding site; [1]
• Accept: Complementary shape to solute X.

2. Enzyme Activity (a)

• As temperature increases from 20°C to 40°C, the rate of reaction increases; [1]
• This is due to increased kinetic energy of molecules, leading to more frequent successful collisions between enzyme and substrate. [1] (b)
• At 70°C, the enzyme is denatured; [1]
• High heat breaks the hydrogen bonds (and ionic bonds) holding the tertiary structure together; [1]
• The active site changes shape and is no longer complementary to the substrate, so no enzyme-substrate complexes can form. [1]

3. Lipids (a) Glycerol and fatty acids. [1] (b)

• High energy content: Triglycerides have a high ratio of carbon-hydrogen bonds, which release much energy when oxidised (more than twice the energy per gram compared to carbohydrates); [2]
• Hydrophobic/Insoluble: They do not affect the water potential of cells/osmotic balance, allowing them to be stored in large quantities without causing water to enter cells by osmosis. [2]
  • Note: Award 1 mark for each property explained. Max 4 marks.

4. Mitochondria (a)

• The inner membrane contains the electron transport chain (ETC) and ATP synthase; [1]
• It is impermeable to protons ($H^+$), allowing a proton gradient to be established across it; [1]
• Protons flow back into the matrix through ATP synthase, driving the synthesis of ATP from ADP and Pi (chemiosmosis). [1] (b)
• Cyanide blocks the transfer of electrons to oxygen (the final electron acceptor); [1]
• This stops the flow of electrons through the ETC, preventing the pumping of protons and the establishment of the proton gradient required for ATP synthesis. [1]

5. Gel Electrophoresis (a) Individuals B and D. [1] (b)

• DNA fragments are negatively charged (due to phosphate groups); [1]
• When an electric field/potential difference is applied, DNA moves towards the positive anode; [1]
• Smaller fragments move faster/further through the gel matrix than larger fragments, separating them by size. [1]

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Section B: Long Structured Questions

6. The lac Operon (a) A cluster of structural genes controlled by a single promoter/operator region. [1] (b) (i)

• The regulator gene (lacI) is constitutively expressed to produce the repressor protein; [1]
• In the absence of lactose, the repressor protein is active. [1] (ii)
• The active repressor protein binds to the operator region; [1]
• This physically blocks RNA polymerase from binding to the promoter/transcribing the structural genes (lacZ, lacY, lacA). [1] (c)
• It prevents the wasteful synthesis of enzymes (beta-galactosidase, permease) when the substrate (lactose) is not available; [1]
• This conserves energy and resources (amino acids/ATP) for the cell; [1]
• Allows the bacterium to respond rapidly to changes in environmental nutrient availability. [1]

7. Protein Structure and Misfolding (a)

• Secondary structure: Local folding of the polypeptide chain into alpha-helices or beta-pleated sheets, stabilised by hydrogen bonds between the backbone atoms (C=O and N-H groups); [2]
• Tertiary structure: The overall 3D shape of the entire polypeptide chain, stabilised by interactions between R-groups (side chains), including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions. [2] (b)
• Changes in pH alter the concentration of $H^+$ ions; [1]
• This affects the ionisation of charged R-groups (e.g., carboxyl and amino groups); [1]
• Disruption of ionic bonds and hydrogen bonds causes the tertiary structure to unfold/denature. [1] (c)
• In correctly folded proteins, hydrophobic R-groups are buried in the core; [1]
• Misfolding exposes these hydrophobic regions to the aqueous cytoplasm; [1]
• Hydrophobic interactions cause these exposed regions to clump together with other misfolded proteins to avoid water, leading to aggregation. [1]

8. Cell Division (a) (i) Mitosis: 2 daughter cells; Meiosis: 4 daughter cells. [1] (ii)

• Mitosis: Daughter cells are genetically identical to the parent cell (clones); [1]
• Meiosis: Daughter cells are genetically unique/different from the parent and each other (haploid). [1] (b)
• Crossing over involves the exchange of genetic material between non-sister chromatids of homologous chromosomes; [1]
• This creates new combinations of alleles on the chromatids (recombinants); [1]
• Increasing genetic variation in the gametes/offspring. [1] (c)
• Tumour suppressor genes normally inhibit cell division or promote apoptosis (cell death) if DNA is damaged; [1]
• A mutation in p53 can lead to a non-functional protein; [1]
• Cells with damaged DNA are not stopped from dividing or destroyed, leading to uncontrolled mitosis and tumour formation. [1]

9. Properties of Water (a)

• Oxygen is more electronegative than hydrogen, creating a partial negative charge ($\delta-$) on oxygen and partial positive charge ($\delta+$) on hydrogen; [1]
• The $\delta+$ hydrogen of one molecule is attracted to the $\delta-$ oxygen of another, forming a hydrogen bond. [1] (b) (i)
• Water can absorb a large amount of heat energy with only a small rise in temperature; [1]
• This helps organisms maintain a stable internal body temperature (homeostasis) despite environmental fluctuations. [1] (ii)
• Water is a polar solvent and dissolves many polar/ionic substances (e.g., glucose, salts, amino acids); [1]
• This allows metabolic reactions to occur in solution and facilitates the transport of nutrients and waste products in blood/plasma. [1]

10. Cell Cycle (a)

• DNA replication occurs; [1]
• Each chromosome is replicated to form two sister chromatids joined at the centromere. [1] (b)
• Checkpoints ensure that the cell only proceeds to the next stage if specific conditions are met (e.g., DNA is undamaged, chromosomes are attached to spindle fibres); [1]
• This prevents the propagation of mutations or chromosomal abnormalities to daughter cells. [1] (c)
• Microtubules form the spindle fibres required to separate chromosomes during mitosis; [1]
• Inhibiting microtubule formation prevents chromosome segregation, arresting the cell in metaphase and triggering apoptosis or stopping division. [1]