A Level H2 Biology Cells Biomolecules Quiz

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A-Level Biology H2 Quiz - Cells Biomolecules

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 60

Duration: 90 Minutes
Total Marks: 60
Instructions: Answer all questions. Use precise scientific terminology. For figure-based questions, ensure your answers refer specifically to the provided descriptions or labels.

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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. [1]
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2. Explain why the presence of cholesterol in the plasma membrane is important for maintaining membrane fluidity at varying temperatures. [2]
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3. Describe the role of the nucleolus within the nucleus. [2]
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4. Distinguish between the functions of smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER). [2]
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5. Define the term "water potential" and state its unit of measurement. [2]
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6. Explain why a cell with a high surface area to volume ratio is more efficient in nutrient uptake. [2]
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7. State the bond formed between two amino acids during the synthesis of a polypeptide. [1]
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Section B: Structured Response & Data Interpretation (Questions 8-15)

8. Figure 1 shows a diagram of a protein misfolding event where a normally alpha-helical region becomes a beta-pleated sheet, exposing hydrophobic residues. (a) Suggest why these misfolded proteins tend to aggregate within the cell. [2]
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   (b) Explain the consequence of such aggregation on cellular function. [2]
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9. A researcher uses gel electrophoresis to analyze the haemoglobin of four patients. (a) Describe how gel electrophoresis separates different variants of haemoglobin. [3]
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   (b) If Patient A shows two distinct bands while Patient B shows one band at the position of normal HbA, interpret the genotypes of both patients. [2]
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10. Figure 2 illustrates 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. [2]
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11. A suspension of mitochondria was placed in a buffer containing ADP and inorganic phosphate (Pi). (a) Explain the relationship between the rate of oxygen consumption and the availability of ADP in this system. [3]
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    (b) Predict the effect on oxygen uptake if a chemical inhibitor that blocks the cytochrome c oxidase complex is added. Explain your answer. [3]
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12. Compare and contrast the structures of DNA and RNA. [4]
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13. Describe the process of facilitated diffusion and explain how it differs from active transport. [4]
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14. Explain the importance of the tertiary structure of an enzyme in determining its substrate specificity. [3]
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15. Describe the role of ATP as the "universal energy currency" in the cell, focusing on the hydrolysis of its phosphate bonds. [3]
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Section C: Extended Response & Synthesis (Questions 16-20)

16. Discuss the structure and function of the mitochondrial inner membrane, specifically referring to the cristae and the electron transport chain. [5]
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17. Explain the mechanism of the sodium-potassium pump ($\text{Na}^+/\text{K}^+$-ATPase) and its significance in maintaining the resting membrane potential of a neuron. [5]
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18. Describe the biochemical properties of phospholipids that allow them to form a bilayer spontaneously in an aqueous environment. [4]
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19. Compare the regulation of an inducible operon (e.g., lac) with a repressible operon (e.g., trp). Explain the biological logic behind each. [5]
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20. Evaluate the impact of a mutation that replaces a polar amino acid with a non-polar amino acid in the core of a globular protein. [4]
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Answer Key - A-Level Biology H2 Quiz: Cells Biomolecules

Section A

1. Prokaryotes have circular DNA (naked/no histones) located in a nucleoid region; Eukaryotes have linear DNA associated with histones located within a membrane-bound nucleus. [1]
2. Cholesterol acts as a temperature buffer; at high temps, it restricts phospholipid movement (reducing fluidity); at low temps, it prevents tight packing (preventing solidification). [2]
3. Site of ribosomal RNA (rRNA) synthesis and assembly of ribosomal subunits. [2]
4. RER: Studded with ribosomes, involved in synthesis and transport of proteins for secretion or membranes. SER: No ribosomes, involved in lipid/steroid synthesis and detoxification. [2]
5. The potential energy of water per unit volume relative to pure water; measured in kilopascals (kPa) or megapascals (MPa). [2]
6. High SA:Vol ratio means more membrane area available for transport relative to the volume of cytoplasm that needs nutrients, reducing diffusion distance. [2]
7. Peptide bond. [1]

Section B

8. (a) Misfolding exposes hydrophobic R-groups normally buried in the core; these hydrophobic regions interact with each other to avoid the aqueous cytosol, driving aggregation. [2]
9. (b) Patient A is heterozygous (two bands = two different alleles/variants); Patient B is homozygous for the normal allele (one band at HbA position). [2]
10. (a) The operon is normally "off" (repressed) and is only turned "on" (induced) when a specific inducer molecule (e.g., allolactose) binds to the repressor. [2] (b) Prevents waste of energy and amino acids by only synthesizing enzymes when the substrate they act upon is present in the environment. [2]
11. (a) Oxygen consumption is coupled to ATP synthesis; as ADP is converted to ATP, the proton gradient is dissipated, allowing the ETC to move electrons to $O_2$ faster. [3] (b) Oxygen uptake will decrease/stop. Inhibitor blocks the final step of ETC; electrons cannot be transferred to $O_2$, halting the entire chain. [3]
12. DNA: Double-stranded, deoxyribose sugar, Thymine, very long. RNA: Single-stranded, ribose sugar, Uracil, shorter. Both have phosphate backbone and A, C, G bases. [4]
13. Facilitated diffusion: Passive movement of polar/charged molecules via channel/carrier proteins down a concentration gradient. Active transport: Movement against gradient requiring ATP and carrier proteins. [4]
14. Tertiary structure creates a specific 3D shape of the active site; complementary in shape and chemical properties (charge/polarity) to the substrate. [3]
15. ATP stores energy in high-energy phosphoanhydride bonds; hydrolysis of the terminal phosphate releases energy ($\approx 30.5$ kJ/mol) used to power endergonic reactions. [3]

Section C

16. Inner membrane is highly folded into cristae to increase surface area for ETC complexes and ATP synthase. ETC creates a proton gradient in the intermembrane space; ATP synthase uses this gradient (chemiosmosis) to synthesize ATP. [5]
17. Pump uses ATP to move $3\text{Na}^+$ out and $2\text{K}^+$ in against gradients. This creates a concentration gradient and a net loss of positive charge from the interior, contributing to the negative resting potential. [5]
18. Amphipathic nature: Hydrophilic phosphate heads face aqueous environment; hydrophobic fatty acid tails face inward, away from water. This minimizes free energy and forms a stable bilayer. [4]
19. Inducible: Repressor active by default; inducer inactivates repressor (e.g., lac). Logic: Catabolic enzymes made only when substrate present. Repressible: Repressor inactive by default; co-repressor activates it (e.g., trp). Logic: Anabolic enzymes stopped when product is sufficient. [5]
20. Non-polar amino acid in the core is normal; however, if the mutation disrupts a specific interaction or if it was a polar residue essential for a hydrogen bond, it may destabilize the protein. If it causes misfolding, it may expose hydrophobic regions, leading to aggregation and loss of function. [4]