A Level H2 Biology Practice Paper 5

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A-Level Biology H2 Quiz - Cells Biomolecules

Name: ____________________ Class: ____________________ Date: ____________________ Score: / 55

Duration: 60 minutes
Total Marks: 55
Instructions: Answer all questions. Use precise biological terminology. For figure-based questions, refer specifically to the details provided in the descriptions.

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Section A: Short Answer & Knowledge (Questions 1-7)

1. State the primary difference between the structure of a prokaryotic cell and a eukaryotic cell regarding genetic material storage. [1]
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2. Describe the role of the Golgi apparatus in the processing of proteins synthesized by the rough endoplasmic reticulum. [2]
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3. Explain why the inner mitochondrial membrane is highly folded into cristae. [2]
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4. Define the term 'amphipathic' in the context of phospholipid molecules in the plasma membrane. [1]
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5. Distinguish between the functions of the smooth endoplasmic reticulum and the rough endoplasmic reticulum. [2]
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6. State the bond formed between two amino acids during the synthesis of a polypeptide chain. [1]
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7. Explain why ATP is considered a high-energy molecule. [2]
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Section B: Structured Response & Data Interpretation (Questions 8-15)

8. Figure 1 shows a diagram of a protein that has undergone misfolding. (a) Suggest why misfolded proteins tend to aggregate within the cytoplasm of a cell. [2]
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   (b) Explain how such protein aggregation can lead to cellular dysfunction. [2]
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9. A researcher uses gel electrophoresis to analyze the haemoglobin of four patients suspected of having sickle cell anaemia. (a) Describe how gel electrophoresis separates different variants of the haemoglobin protein. [3]
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   (b) If Patient A shows two distinct bands on the gel, interpret this result in terms of their genotype. [2]
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10. Figure 2 depicts the lac operon in E. coli. (a) Explain why the lac operon is described as an "inducible" system. [2]
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    (b) Suggest the metabolic advantage for a prokaryote to utilize an inducible operon rather than constitutive expression of these genes. [2]
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11. A suspension of mitochondria was placed in a buffer. (a) Describe the effect on oxygen consumption if ADP is depleted from the buffer. [2]
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    (b) Explain the link between oxygen consumption and the synthesis of ATP via chemiosmosis. [3]
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12. Compare the structural properties of saturated and unsaturated fatty acids. [3]
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13. Describe the mechanism of facilitated diffusion and explain how it differs from active transport. [3]
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14. Figure 3 shows the structure of a DNA molecule. (a) Explain the significance of the complementary base pairing in DNA replication. [2]
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    (b) Describe the role of DNA polymerase in the synthesis of a new strand. [2]
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15. Explain how the primary structure of a protein determines its tertiary structure. [3]
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Section C: Extended Response & Application (Questions 16-20)

16. Discuss the role of the sodium-potassium pump in maintaining the resting potential of a neuron. [4]
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17. Using the example of the trp operon, explain the mechanism of a repressible operon. [4]
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18. Explain the process of oxidative phosphorylation, specifically focusing on the role of the electron transport chain and ATP synthase. [5]
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19. Compare and contrast the structure and function of cellulose and glycogen. [4]
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20. A drug is developed that binds to the active site of a specific enzyme, preventing the substrate from binding. (a) Identify the type of inhibition occurring. [1] (b) Explain how increasing the substrate concentration would affect the rate of reaction in the presence of this drug. [3]
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A-Level Biology H2 Quiz - Cells Biomolecules (Answer Key)

Section A

1. Prokaryotes have circular DNA located freely in the cytoplasm (nucleoid), whereas eukaryotes have linear DNA enclosed within a membrane-bound nucleus. [1]
2. Modifies proteins (e.g., glycosylation), sorts them, and packages them into vesicles for secretion or delivery to other organelles. [2]
3. To increase the surface area of the inner membrane, allowing for more electron transport chain complexes and ATP synthase molecules, thereby increasing ATP production. [2]
4. A molecule possessing both a hydrophilic (polar) head and a hydrophobic (non-polar) tail. [1]
5. RER is studded with ribosomes and is involved in protein synthesis/transport; SER lacks ribosomes and is involved in lipid synthesis and detoxification. [2]
6. Peptide bond. [1]
7. Contains high-energy phosphate bonds (phosphoanhydride bonds); hydrolysis of the terminal phosphate releases a significant amount of free energy. [2]

Section B

8. (a) Misfolding exposes hydrophobic amino acid residues that are normally buried in the core; these hydrophobic regions interact with each other to minimize contact with water. [2] (b) Aggregates form insoluble clumps (plaques) that can disrupt cellular transport, interfere with organelle function, or trigger apoptosis. [2]
9. (a) An electric field/potential difference is applied; proteins migrate through the gel matrix based on their net charge and molecular mass/size. [3] (b) Patient A is heterozygous; they possess two different alleles of the haemoglobin gene, resulting in two different protein variants with different migration rates. [2]
10. (a) The genes are normally "off" (repressed) but can be "induced" or turned on when a specific inducer (e.g., allolactose) binds to the repressor protein. [2] (b) Prevents the waste of energy and resources (ATP/amino acids) by only synthesizing enzymes when the substrate (lactose) is actually present in the environment. [2]
11. (a) Oxygen consumption will decrease/stop. [1] Because ATP synthase cannot function without ADP, the proton gradient builds up, inhibiting the electron transport chain. [1] (b) Oxygen acts as the final electron acceptor in the ETC; its consumption is coupled to the pumping of protons into the intermembrane space; this gradient drives ATP synthesis via ATP synthase. [3]
12. Saturated fatty acids have no double bonds in the hydrocarbon chain (straight chain, pack closely); unsaturated fatty acids have one or more cis-double bonds (kinked chain, pack less closely). [3]
13. Facilitated diffusion uses channel or carrier proteins to move molecules down a concentration gradient (passive); active transport moves molecules against a gradient using energy (ATP) and carrier proteins. [3]
14. (a) Ensures that the sequence of bases in the new strand is an exact complement of the template strand, maintaining genetic fidelity. [2] (b) Catalyses the formation of phosphodiester bonds between the 3' OH group of the existing strand and the 5' phosphate of the incoming nucleotide. [2]
15. The sequence of amino acids (primary) determines the specific R-group interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions) that fold the protein into its 3D shape. [3]

Section C

16. The pump uses ATP to actively transport 3 $\text{Na}^+$ ions out of the cell and 2 $\text{K}^+$ ions into the cell; this creates a concentration gradient and contributes to the net negative charge inside the membrane. [4]
17. The operon is normally "on"; when the end-product (tryptophan) accumulates, it acts as a co-repressor, binding to the repressor protein; the repressor-corepressor complex binds to the operator, blocking RNA polymerase and stopping transcription. [4]
18. Electrons from NADH/$\text{FADH}_2$ pass through the ETC; energy released is used to pump $\text{H}^+$ from matrix to intermembrane space; this creates a proton motive force; $\text{H}^+$ flow back into the matrix through ATP synthase, driving the phosphorylation of ADP to ATP. [5]
19. Cellulose: $\beta$-glucose, linear/unbranched, forms microfibrils for cell wall strength. Glycogen: $\alpha$-glucose, highly branched, stored in animals for rapid glucose mobilization. [4]
20. (a) Competitive inhibition. [1] (b) Increasing substrate concentration increases the likelihood that a substrate molecule will bind to the active site instead of the inhibitor; this displaces the inhibitor and increases the reaction rate toward $V_{max}$. [3]