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A Level H1 Biology Practice Paper 2
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TuitionGoWhere Practice Paper - Biology H1 A-Level
TuitionGoWhere Practice Paper (AI)
Subject: Biology H1
Level: A-Level
Paper: Practice Paper (Version 2 of 5)
Topic Focus: Cells and Biomolecules
Duration: 1 hour 30 minutes
Total Marks: 60
Name: _________________________
Class: _________________________
Date: __________________________
Instructions to Candidates
- Write your Name, Class, and Date in the spaces above.
- 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 1.5 minutes per mark.
Section A: Structured Questions
Answer all questions in this section.
1. Fig. 1.1 shows a diagram of a phospholipid molecule.
(a) Identify the parts labelled A and B. [2] A: _______________________________________________________ B: _______________________________________________________
(b) Explain how phospholipids arrange themselves when placed in an aqueous environment to form a membrane. [2]
(c) State one property of the phospholipid bilayer that allows small, non-polar molecules (such as oxygen) to pass through easily. [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) |
|---|---|
| 10 | 0.5 |
| 20 | 1.2 |
| 30 | 2.8 |
| 40 | 3.5 |
| 50 | 1.1 |
| 60 | 0.0 |
(a) Explain the increase in the rate of reaction between 10°C and 40°C. [3]
(b) Explain why the rate of reaction is zero at 60°C. [2]
3. Fig. 3.1 shows a cross-section of a mitochondrion.
(a) Name the structures labelled X and Y. [2] X: _______________________________________________________ Y: _______________________________________________________
(b) Explain why mitochondria are abundant in muscle cells. [2]
(c) State the process that occurs in the matrix of the mitochondrion. [1]
4. Hemoglobin is a globular protein found in red blood cells.
(a) Describe the quaternary structure of hemoglobin. [2]
(b) Explain how the specific shape of hemoglobin allows it to function effectively in oxygen transport. [2]
5. Fig. 5.1 shows a cell undergoing mitosis.
(a) Identify the stage of mitosis shown in Fig. 5.1. [1]
(b) Describe two events that occur during this stage. [2]
(c) Explain the importance of mitosis in multicellular organisms. [2]
6. Glycogen and cellulose are both polysaccharides made from glucose monomers.
(a) State one structural difference between glycogen and cellulose. [1]
(b) Explain how the structure of glycogen makes it suitable for energy storage in animals. [2]
(c) Explain why humans cannot digest cellulose. [1]
7. Fig. 7.1 shows the fluid mosaic model of a cell membrane.
(a) Name the component labelled Z which spans the membrane. [1]
(b) Explain the term "fluid mosaic" with reference to the structure of the membrane. [2]
8. Water is essential for life.
(a) Define the term water potential. [1]
(b) Explain why water is described as a universal solvent. [2]
9. A student placed potato cylinders in sucrose solutions of different concentrations.
(a) Define osmosis. [2]
(b) If a potato cylinder gains mass, state the relationship between the water potential of the potato cells and the sucrose solution. [1]
10. DNA and RNA are nucleic acids.
(a) State two differences between DNA and RNA. [2]
(b) Describe the role of mRNA in protein synthesis. [2]
Section B: Data Interpretation and Application
Answer all questions in this section.
11. Fig. 11.1 shows the effect of substrate concentration on the rate of an enzyme-catalyzed reaction.
(a) Describe the shape of the curve between point A and point B. [2]
(b) Explain why the rate of reaction levels off at point C. [2]
(c) Sketch on Fig. 11.1 the expected curve if a competitive inhibitor was added. Label this curve I. [1]
12. Table 12.1 compares prokaryotic and eukaryotic cells.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nucleus | Absent | Present |
| Ribosomes | 70S | 80S |
| DNA form | Circular, naked | Linear, associated with histones |
(a) Explain the significance of DNA being associated with histones in eukaryotic cells. [2]
(b) State one other structural difference between prokaryotic and eukaryotic cells not mentioned in the table. [1]
13. Fig. 13.1 shows a dipeptide formed from two amino acids.
(a) Name the bond labelled W. [1]
(b) Name the type of reaction that forms this bond. [1]
(c) Explain what is meant by the primary structure of a protein. [2]
14. Cholesterol is a lipid found in animal cell membranes.
(a) State one function of cholesterol in the cell membrane. [1]
(b) Explain why cholesterol is classified as a lipid despite not having fatty acid tails like triglycerides. [2]
15. Fig. 15.1 shows the results of an experiment investigating the effect of pH on enzyme activity.
(a) Identify the optimum pH for this enzyme. [1]
(b) Explain how a change in pH away from the optimum affects enzyme activity. [3]
Section C: Extended Response
Answer all questions in this section.
16. Discuss the importance of water’s thermal properties to living organisms. [4]
17. Explain the process of facilitated diffusion and active transport. Compare and contrast these two methods of transport across cell membranes. [6]
18. Describe the structure of a named fibrous protein and explain how its structure is related to its function. [5]
19. Explain the significance of the complementary base pairing in DNA structure. [4]
20. Discuss the role of membranes in compartmentalizing cellular activities. Use specific examples of organelles to support your answer. [6]
End of Paper
Answers
TuitionGoWhere Practice Paper - Biology H1 A-Level
Answer Key and Marking Scheme Topic: Cells and Biomolecules Version: 2 of 5
Section A: Structured Questions
1. (a) A: Phosphate head (hydrophilic) [1]; B: Fatty acid tails (hydrophobic) [1] (b) Phospholipids form a bilayer [1]; Hydrophilic heads face outward towards the aqueous environment, while hydrophobic tails face inward, away from water [1]. (c) It is permeable to non-polar molecules / The interior is hydrophobic [1].
2. (a) As temperature increases, kinetic energy of enzyme and substrate molecules increases [1]; This leads to more frequent collisions [1]; More enzyme-substrate complexes are formed per unit time [1]. (b) High temperature breaks hydrogen/ionic bonds holding the tertiary structure [1]; The active site changes shape (denaturation), so the substrate no longer fits [1].
3. (a) X: Cristae (inner membrane fold) [1]; Y: Matrix [1] (b) Muscle cells require large amounts of ATP for contraction [1]; Mitochondria are the site of aerobic respiration/ATP production [1]. (c) Krebs cycle (Citric Acid Cycle) / Link Reaction [1].
4. (a) Hemoglobin consists of four polypeptide chains (subunits) [1]; These chains are held together by bonds (e.g., hydrogen bonds) to form a specific 3D shape [1]. (b) The specific 3D shape creates a binding site for heme groups/oxygen [1]; This allows reversible binding of oxygen for transport [1].
5. (a) Metaphase [1] (b) Chromosomes align at the equator/center of the cell [1]; Spindle fibers attach to the centromeres of chromosomes [1]. (c) Produces genetically identical cells for growth [1]; Replaces damaged/dead cells for repair [1].
6. (a) Glycogen is branched/helical; Cellulose is straight/unbranched [1] OR Glycogen has alpha-glucose; Cellulose has beta-glucose [1]. (b) Branched structure provides many ends for enzymes to act on, allowing rapid release of glucose [1]; Compact structure allows storage of many glucose units in a small space [1]. (c) Humans lack the enzyme (cellulase) to hydrolyze beta-1,4-glycosidic bonds [1].
7. (a) Transmembrane protein / Channel protein / Carrier protein [1] (b) "Fluid": Phospholipids and proteins can move laterally within the layer [1]; "Mosaic": Proteins are embedded in the bilayer in a scattered pattern [1].
8. (a) The tendency of water molecules to move from one region to another / Measure of the free energy of water molecules [1]. (b) Water is a polar molecule [1]; It forms hydrogen bonds with ions and other polar molecules, surrounding them and keeping them in solution [1].
9. (a) The net movement of water molecules [1] from a region of higher water potential to a region of lower water potential [1] through a partially permeable membrane. (b) Water potential of potato cells is lower (more negative) than the sucrose solution [1].
10. (a) DNA contains deoxyribose sugar; RNA contains ribose sugar [1]; DNA is double-stranded; RNA is single-stranded [1] OR DNA contains Thymine; RNA contains Uracil [1]. (b) mRNA carries the genetic code from DNA in the nucleus [1] to the ribosomes in the cytoplasm for translation [1].
Section B: Data Interpretation and Application
11. (a) The rate of reaction increases linearly/proportionally with substrate concentration [1]; Because there are more substrate molecules available to collide with active sites [1]. (b) All active sites are saturated/occupied [1]; Adding more substrate does not increase the rate because enzymes are working at maximum capacity () [1]. (c) Curve should start at the same origin, rise more slowly, and plateau at the same as the original curve [1].
12. (a) Histones allow DNA to be packed tightly into chromosomes [1]; This protects DNA and regulates gene expression [1]. (b) Prokaryotes have cell walls made of peptidoglycan (murein) [1] OR Prokaryotes lack membrane-bound organelles [1].
13. (a) Peptide bond [1] (b) Condensation [1] (c) The specific sequence of amino acids in the polypeptide chain [1]; Determined by the sequence of bases in DNA/gene [1].
14. (a) Regulates membrane fluidity / Stabilizes the membrane at high temperatures [1]. (b) Cholesterol is insoluble in water (hydrophobic) [1]; Like other lipids, it is soluble in organic solvents [1].
15. (a) pH 7 (or value indicated by peak on graph) [1] (b) Change in pH alters the charge on amino acid R-groups [1]; This disrupts ionic/hydrogen bonds maintaining the tertiary structure [1]; The active site changes shape, reducing enzyme-substrate complex formation [1].
Section C: Extended Response
16. Marking Points (Max 4):
- High specific heat capacity: Water absorbs/releases large amounts of heat with little temperature change [1]; Helps organisms maintain stable internal temperature/homeostasis [1].
- High latent heat of vaporization: Evaporation of water (sweating/transpiration) removes large amounts of heat [1]; Provides an effective cooling mechanism for organisms [1].
- Note: Accept other valid thermal properties such as high boiling point allowing liquid state over a wide range.
17. Marking Points (Max 6):
- Facilitated Diffusion: Movement of molecules down a concentration gradient [1]; Requires channel or carrier proteins [1]; Does not require energy (ATP) [1].
- Active Transport: Movement of molecules against a concentration gradient [1]; Requires carrier proteins (pumps) [1]; Requires energy (ATP) from respiration [1].
- Comparison: Both involve specific membrane proteins; Both are selective/specific to certain molecules.
- Contrast: Direction of gradient (down vs. against); Energy requirement (none vs. ATP).
18. Marking Points (Max 5):
- Named Protein: e.g., Collagen [1].
- Structure: Three polypeptide chains wound into a triple helix [1]; Held together by hydrogen bonds [1]; Cross-links between chains provide strength [1].
- Function: Provides tensile strength to tissues (e.g., tendons, skin, bone) [1]; Resists pulling forces [1].
- Alternative: Keratin (alpha-helix, disulfide bonds, waterproofing/protection).
19. Marking Points (Max 4):
- Adenine pairs with Thymine (2 H-bonds); Guanine pairs with Cytosine (3 H-bonds) [1].
- Ensures the two strands are held together securely but can be separated for replication/transcription [1].
- Ensures accurate replication: Each strand serves as a template for the new strand [1].
- Maintains the constant width of the DNA double helix [1].
20. Marking Points (Max 6):
- Membranes create separate compartments allowing incompatible reactions to occur simultaneously [1].
- Example 1: Lysosomes: Contain hydrolytic enzymes [1]; Membrane prevents enzymes from digesting the cell itself [1]; Maintains acidic pH for enzyme activity [1].
- Example 2: Mitochondria: Inner membrane creates compartments for electron transport chain [1]; Establishes proton gradient for ATP synthesis [1].
- Example 3: Nucleus: Nuclear envelope separates transcription (DNA to RNA) from translation (RNA to Protein) [1]; Allows for regulation of gene expression [1].
- General: Concentrates substrates/enzymes to increase reaction efficiency [1].