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A Level H1 Biology Practice Paper 2

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Questions

TuitionGoWhere Exam Practice (AI)

Subject: Biology H1
Level: A-Level
Paper: Practice Paper 2 (Version 2 of 5)
Duration: 2 Hours
Total Marks: 80

Name: __________________________ Class: __________ Date: __________

Instructions to Candidates

Answer all questions in the spaces provided.
Write your answers clearly and concisely.
Use biological terminology accurately.
For questions involving figures, refer specifically to the labels and data provided in the diagrams.

Section A: Structured Questions (40 Marks)

Question 1 Fig. 1 shows a diagram of the cell cycle of a mammalian cell. (Imagine Fig. 1: A circular diagram showing G1, S, G2, and M phases)

(a) If radioactive thymidine was added to the culture medium, identify which period of the cell cycle in Fig. 1 would first show an increase in radioactivity. Justify your answer. [3]

(b) Describe the arrangement of phospholipids in the cell membrane of this mammalian cell. [2]

Question 2 Fig. 2 shows a cross-section of a specialized secretory cell containing various organelles. (Imagine Fig. 2: A cell with prominent RER, Golgi apparatus, and secretory vesicles)

(a) Name the structure labeled X (Rough Endoplasmic Reticulum) and describe its specific role in this secretory cell. [2]

(b) Explain the sequence of events that occurs after a protein is synthesized at structure X before it is secreted from the cell. [4]

Question 3 A researcher incubated isolated mitochondria with two different substrates: Pyruvate and Glucose. (a) Explain why carbon dioxide is produced when mitochondria are incubated with pyruvate, but not when incubated with glucose. [3]

(b) State the specific location within the mitochondrion where the decarboxylation reactions producing $\text{CO}_2$ occur. [1]

Question 4 Fig. 3 illustrates the movement of a specific ion, $\text{K}^+$ , across a plasma membrane. (Imagine Fig. 3: A membrane with a protein pump moving $\text{K}^+$ against a concentration gradient using ATP)

(a) With reference to Fig. 3, describe how $\text{K}^+$ ions move across the membrane. [3]

(b) Distinguish between the movement of $\text{K}^+$ ions as shown in Fig. 3 and the movement of water molecules across the same membrane. [3]

Question 5 Table 1 shows the optimal pH and temperature for the activity of three different enzymes found in a specific soil bacterium. (Imagine Table 1: Enzyme A (pH 5, 30°C), Enzyme B (pH 7, 30°C), Enzyme C (pH 9, 30°C))

(a) With reference to Table 1 and your knowledge of enzymes, explain why a soil environment with a pH of 5.5 and a constant temperature of 30°C would be most suitable for the growth of this bacterium. [3]

(b) Describe the effect on the tertiary structure of Enzyme B if the soil pH were to drop to 4.0. [2]

Question 6 (a) Describe the structure of a triglyceride molecule. [3]

(b) Explain why lipids are more suitable than carbohydrates for long-term energy storage in animals. [3]

Question 7 (a) Describe the structure of the DNA double helix. [4]

(b) Explain the significance of complementary base pairing during DNA replication. [3]

Section B: Free Response and Extended Questions (40 Marks)

Question 8 (a) Discuss the significance of the movement of substances across membranes to the process of photosynthesis in plants. [8]

Question 9 (a) Describe how mitosis maintains genetic stability in a multicellular organism. [7]

(b) Explain the importance of this genetic stability in the context of tissue repair and asexual reproduction. [5]

Question 10 (a) Compare and contrast the structures and functions of prokaryotic and eukaryotic cells. [10]

(b) Explain how the structure of the cell membrane allows it to be "selectively permeable." [10]

Answers

TuitionGoWhere Exam Practice (AI) - Answer Key

Subject: Biology H1 | Paper: Practice Paper 2 (Version 2)

Section A: Structured Questions

Question 1 (a) S phase. [1] Radioactive thymidine is a nucleotide analogue incorporated into DNA during synthesis/replication. [1] S phase is the specific period of the cell cycle where DNA replication occurs. [1] (b) Phospholipids are arranged in a bilayer. [1] Hydrophilic heads face the aqueous environments (extracellular and intracellular), while hydrophobic tails face inward, away from water. [1]

Question 2 (a) Rough Endoplasmic Reticulum (RER). [1] Site of synthesis of proteins destined for secretion or membrane insertion (via ribosomes). [1] (b) Proteins are transported via vesicles from RER to the Golgi apparatus. [1] In the Golgi, proteins are modified (e.g., glycosylation) and packaged. [1] They are then sorted into secretory vesicles. [1] Vesicles move toward the cell surface and fuse with the plasma membrane (exocytosis) to release contents. [1]

Question 3 (a) Pyruvate can be converted to Acetyl-CoA and enter the Krebs cycle directly within the mitochondrial matrix. [1] The Krebs cycle produces $\text{CO}_2$ as a byproduct. [1] Glucose cannot enter the mitochondria; it must first undergo glycolysis in the cytoplasm to become pyruvate. [1] Isolated mitochondria lack the cytoplasmic enzymes for glycolysis. [1] (Any 3) (b) Mitochondrial matrix. [1]

Question 4 (a) $\text{K}^+$ ions move via active transport. [1] They move against a concentration gradient (from low to high concentration). [1] This process requires a carrier protein/pump and the hydrolysis of ATP for energy. [1] (b) $\text{K}^+$ movement is active transport (requires ATP/protein pump), whereas water moves via osmosis. [1] Osmosis is a passive process (no ATP). [1] Water moves through the phospholipid bilayer or aquaporins down a water potential gradient. [1]

Question 5 (a) Enzyme A has an optimal pH of 5, which is closest to the soil pH of 5.5. [1] At 30°C, the enzymes are at their optimal temperature. [1] This ensures maximum enzyme activity/catalytic rate, supporting the metabolic needs for bacterial growth. [1] (b) The change in pH alters the charge of R-groups of amino acids. [1] This disrupts ionic/hydrogen bonds, leading to the denaturation of the protein/loss of the active site shape. [1]

Question 6 (a) Consists of one glycerol molecule [1] ester-bonded to three fatty acid chains. [1] The fatty acids can be saturated or unsaturated. [1] (b) Lipids have a higher energy density (more C-H bonds per unit mass) than carbohydrates. [1] Lipids are hydrophobic/insoluble in water, meaning they do not increase the osmotic pressure of the cell. [1] This allows for compact storage of energy. [1]

Question 7 (a) Two antiparallel polynucleotide strands. [1] Sugar-phosphate backbones on the outside. [1] Nitrogenous bases paired in the center via hydrogen bonds. [1] Twisted into a helix. [1] (b) Each base has only one complementary partner (A-T, C-G). [1] This ensures that the new strand is an exact copy of the template strand. [1] This maintains the genetic sequence across generations of cells. [1]

Section B: Free Response and Extended Questions

Question 8 (8 Marks)

$\text{CO}_2$ uptake: Diffuses from atmosphere into leaf through stomata and then across cell membranes into chloroplasts. [2]
Water uptake: Absorbed by root hair cells via osmosis; essential as a raw material for photolysis in the light-dependent reaction. [2]
Ion transport: Active transport of $\text{Mg}^{2+}$ (central atom of chlorophyll) and $\text{K}^+$ (stomata regulation). [2]
Product export: Triose phosphates/glucose transported out of chloroplasts/cells via facilitated diffusion or active transport to be used for energy or stored as starch. [2]

Question 9 (a) Mitosis & Stability (7 Marks):

S phase: DNA is replicated semi-conservatively to produce two identical sister chromatids. [2]
Metaphase: Chromosomes align at the equator. [1]
Anaphase: Sister chromatids are pulled apart by spindle fibers to opposite poles. [2]
Telophase/Cytokinesis: Two daughter nuclei form, each receiving an identical set of chromosomes. [2] (b) Importance (5 Marks):
Repair: Replaces damaged cells with identical cells to maintain tissue function and structure. [2]
Asexual Reproduction: Produces genetically identical clones, ensuring offspring are adapted to a stable environment. [2]
Growth: Increases cell number while maintaining the same genetic blueprint for organ development. [1]

Question 10 (a) Prokaryotic vs Eukaryotic (10 Marks):

Nucleus: Prokaryotes have no nucleus (nucleoid region); Eukaryotes have a membrane-bound nucleus. [2]
Organelles: Prokaryotes lack membrane-bound organelles (no mitochondria, Golgi, etc.); Eukaryotes possess them. [2]
DNA: Prokaryotes have circular DNA and plasmids; Eukaryotes have linear DNA associated with histones. [2]
Size: Prokaryotes are generally much smaller. [2]
Ribosomes: Prokaryotes have 70S; Eukaryotes have 80S. [2] (b) Selective Permeability (10 Marks):
Phospholipid Bilayer: Hydrophobic core prevents passage of large polar molecules and ions. [3]
Small Non-polar molecules: (e.g., $\text{O}_2, \text{CO}_2$ ) can diffuse directly through the bilayer. [2]
Channel Proteins: Allow specific ions or water (aquaporins) to pass via facilitated diffusion. [2]
Carrier Proteins: Bind to specific molecules (e.g., glucose) to transport them across. [2]
Active Transport: Pumps move specific substances against gradients using ATP. [1]