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A Level H1 Biology Practice Paper 4
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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 4 of 5)
Topic Focus: Cells & Biomolecules
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 on this question paper.
- 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 simplified diagram of a phospholipid bilayer forming a cell membrane.
(a) Identify the components labelled A and B in Fig. 1.1. [2] A: _______________________________________________________ B: _______________________________________________________
(b) Explain why phospholipids spontaneously arrange themselves into a bilayer in an aqueous environment. [2]
(c) Cholesterol is another component of the cell membrane. State two functions of cholesterol in the membrane. [2]
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 | 1.8 |
| 60 | 0.0 |
(a) Explain the increase in the rate of reaction between 10°C and 40°C. [2]
(b) Explain why the rate of reaction is zero at 60°C. [2]
(c) The student repeated the experiment at pH 3. The rate of reaction was significantly lower at all temperatures. Explain why. [2]
3. Fig. 3.1 shows a diagram of a mitochondrion.
(a) Name the structures labelled C and D. [2] C: _______________________________________________________ D: _______________________________________________________
(b) The matrix of the mitochondrion contains enzymes for the Krebs cycle. State two products of the Krebs cycle (other than ATP) that are used in the electron transport chain. [2]
(c) Explain why the inner mitochondrial membrane is highly folded into cristae. [2]
4. Water is essential for life.
(a) Describe the property of water that allows it to act as a solvent for polar molecules. [2]
(b) Explain the significance of the high specific heat capacity of water for living organisms. [2]
5. Fig. 5.1 shows the structure of a triglyceride molecule.
(a) Name the molecules labelled E and F. [2] E: _______________________________________________________ F: _______________________________________________________
(b) Triglycerides are used as energy storage molecules in animals. Explain two properties of triglycerides that make them suitable for this function. [2]
(c) Describe the test used to identify the presence of lipids in a food sample. [2]
6. Active transport and facilitated diffusion are both methods of moving substances across cell membranes.
(a) State two differences between active transport and facilitated diffusion. [2]
(b) Explain why root hair cells use active transport to absorb mineral ions from the soil. [2]
7. Proteins have complex structures.
(a) Define the term 'primary structure' of a protein. [1]
(b) Explain how the primary structure of a protein determines its tertiary structure. [3]
8. Fig. 8.1 shows a cell undergoing mitosis.
(a) Identify the stage of mitosis shown in Fig. 8.1. [1]
(b) Describe what happens to the chromosomes during this stage. [2]
(c) State the significance of mitosis for multicellular organisms. [2]
9. DNA and RNA are nucleic acids.
(a) State two structural differences between DNA and RNA. [2]
(b) Explain the role of mRNA in protein synthesis. [2]
10. Enzymes are biological catalysts.
(a) Define the term 'activation energy'. [1]
(b) Explain how enzymes lower the activation energy of a reaction. [2]
Section B: Data Interpretation and Application
Answer all questions in this section.
11. Fig. 11.1 shows the results of an experiment investigating the effect of sucrose concentration on the mass of potato cylinders.
[Graph Description: X-axis = Sucrose Concentration (mol dm⁻³), Y-axis = % Change in Mass. The line starts positive at 0.0 mol dm⁻³, crosses the x-axis at 0.3 mol dm⁻³, and becomes negative at higher concentrations.]
(a) Determine the water potential of the potato cells relative to the sucrose solutions. Explain your answer. [2]
(b) Explain why the potato cylinders gained mass in the 0.1 mol dm⁻³ sucrose solution. [3]
(c) Predict what would happen to the potato cylinders if they were placed in a 1.0 mol dm⁻³ sucrose solution for a further 2 hours. Explain your prediction. [2]
12. Fig. 12.1 shows the structure of hemoglobin.
(a) Hemoglobin is a globular protein. Explain how its structure is related to its function of transporting oxygen. [3]
(b) Sickle cell anemia is caused by a mutation in the gene for hemoglobin. This mutation changes one amino acid in the primary structure. Explain how this change affects the tertiary structure and function of hemoglobin. [3]
13. Fig. 13.1 shows a diagram of the fluid mosaic model of the cell membrane.
(a) Explain why the membrane is described as 'fluid'. [2]
(b) Explain why the membrane is described as a 'mosaic'. [2]
(c) Some substances can pass through the membrane by simple diffusion, while others require channel proteins. Explain this difference with reference to the properties of the substances. [3]
14. Table 14.1 shows the percentage composition of bases in the DNA of three different organisms.
| Organism | Adenine (%) | Guanine (%) | Cytosine (%) | Thymine (%) |
|---|---|---|---|---|
| Human | 30 | 20 | 20 | 30 |
| Wheat | 27 | 23 | 23 | 27 |
| Bacterium | 15 | 35 | 35 | 15 |
(a) State the relationship between the percentages of Adenine and Thymine in these organisms. [1]
(b) Explain this relationship with reference to the structure of DNA. [2]
(c) Calculate the percentage of Guanine in the DNA of a virus that has single-stranded DNA and contains 20% Adenine. Explain your answer. [2]
15. Fig. 15.1 shows the effect of substrate concentration on the rate of an enzyme-catalyzed reaction.
[Graph Description: Hyperbolic curve rising steeply then plateauing at Vmax.]
(a) Explain the shape of the curve between point A (low substrate concentration) and point B (high substrate concentration). [3]
(b) A competitive inhibitor is added to the reaction. Sketch the expected change in the curve on Fig. 15.1 and explain your sketch. [3]
Section C: Extended Response
Answer all questions in this section.
16. Discuss the importance of water properties to living organisms. [6]
17. Compare and contrast the structures and functions of starch, glycogen, and cellulose. [6]
18. Explain how the structure of the cell membrane allows it to control the movement of substances into and out of the cell. [6]
19. Describe the process of aerobic respiration, including the locations and main products of each stage. [6]
20. Explain the role of enzymes in metabolic pathways and how their activity is regulated. [6]
End of Paper
Answers
TuitionGoWhere Practice Paper - Biology H1 A-Level
Answer Key and Marking Scheme
Subject: Biology H1
Paper: Practice Paper (Version 4 of 5)
Topic Focus: Cells & Biomolecules
Section A: Structured Questions
1. (a) A: Hydrophilic head (phosphate group) [1]; B: Hydrophobic tail (fatty acid) [1]. (b) Heads are polar/hydrophilic and attract water [1]; Tails are non-polar/hydrophobic and repel water [1]; Therefore, heads face outward towards aqueous environment and tails face inward [1]. (Max 2) (c) Any two: Regulates membrane fluidity [1]; Stabilizes the membrane at high temperatures [1]; Prevents packing of phospholipids at low temperatures [1]; Reduces permeability to small water-soluble molecules [1].
2. (a) Increased kinetic energy of enzyme and substrate molecules [1]; More frequent collisions between enzyme and substrate [1]; More enzyme-substrate complexes formed [1]. (Max 2) (b) High temperature breaks hydrogen/ionic bonds holding the tertiary structure [1]; Active site changes shape/denatures [1]; Substrate no longer fits the active site [1]. (Max 2) (c) pH 3 is acidic/away from optimum pH [1]; Changes the charge of R-groups/ionic bonds in the enzyme [1]; Alters the shape of the active site/denatures enzyme [1]. (Max 2)
3. (a) C: Outer membrane [1]; D: Cristae (inner membrane) [1]. (b) Reduced NAD (NADH) [1]; Reduced FAD (FADH₂) [1]. (c) Increases surface area [1]; For attachment of electron transport chain proteins/ATP synthase [1]; Allows for more ATP production [1]. (Max 2)
4. (a) Water molecules are polar/dipolar [1]; Form hydrogen bonds with polar/charged solutes [1]; Surrounding solute molecules keeps them in solution [1]. (Max 2) (b) Water can absorb/lose large amounts of heat energy with little change in temperature [1]; Helps maintain stable internal body temperature/homeostasis [1]; Prevents overheating of cells [1]. (Max 2)
5. (a) E: Glycerol [1]; F: Fatty acids [1]. (b) High energy content per gram (more than carbohydrates) [1]; Insoluble in water (does not affect water potential/osmosis) [1]; Compact storage [1]. (Max 2) (c) Emulsion test [1]; Add ethanol and shake, then add water [1]; White cloudy emulsion indicates lipids [1]. (Max 2)
6. (a) Any two: Active transport requires energy (ATP) / Facilitated diffusion does not [1]; Active transport moves against concentration gradient / Facilitated diffusion moves down concentration gradient [1]; Active transport uses carrier proteins only / Facilitated diffusion uses channel or carrier proteins [1]. (b) Concentration of mineral ions is higher in root hair cells than in soil [1]; Ions must move against concentration gradient [1]; Requires active transport to accumulate ions [1]. (Max 2)
7. (a) The sequence of amino acids in the polypeptide chain [1]. (b) The sequence of amino acids (primary structure) determines the position of R-groups [1]; R-groups interact via hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions [1]; These interactions cause the polypeptide to fold into a specific 3D shape (tertiary structure) [1].
8. (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 [1]; Essential for growth, repair, and asexual reproduction [1].
9. (a) Any two: DNA is double-stranded / RNA is single-stranded [1]; DNA contains thymine / RNA contains uracil [1]; DNA contains deoxyribose sugar / RNA contains ribose sugar [1]. (b) Carries genetic code from DNA in nucleus to ribosomes in cytoplasm [1]; Template for translation/protein synthesis [1].
10. (a) The minimum amount of energy required for a reaction to occur [1]. (b) Enzyme binds to substrate to form enzyme-substrate complex [1]; Strains bonds in substrate or holds substrates in correct orientation [1]; Lowers the energy barrier for the reaction to proceed [1]. (Max 2)
Section B: Data Interpretation and Application
11. (a) 0.3 mol dm⁻³ [1]; This is the isotonic point where there is no net movement of water/no change in mass [1]. (b) Water potential of 0.1 mol dm⁻³ solution is higher (less negative) than potato cells [1]; Water enters cells by osmosis [1]; Through partially permeable membrane [1]; Down water potential gradient [1]. (Max 3) (c) Mass would decrease further/plasmolysis occurs [1]; Water potential of solution is much lower than cells [1]; Water leaves cells by osmosis [1]. (Max 2)
12. (a) Globular shape is compact/soluble in blood [1]; Contains heme group with iron to bind oxygen [1]; Quaternary structure (4 subunits) allows for cooperative binding [1]. (Max 3) (b) Change in amino acid changes primary structure [1]; Alters R-group interactions/tertiary structure [1]; Hemoglobin becomes insoluble/forms fibers/distorts red blood cell shape [1]; Reduced oxygen carrying capacity [1]. (Max 3)
13. (a) Phospholipids and proteins can move laterally within the layer [1]; Due to weak hydrophobic interactions between tails [1]. (b) Proteins are embedded in the bilayer like tiles in a mosaic [1]; Different types of proteins (channel, carrier, receptor) are scattered throughout [1]. (c) Small, non-polar/lipid-soluble substances (e.g., O₂, CO₂) can pass through the phospholipid bilayer by simple diffusion [1]; Large, polar, or charged substances (e.g., ions, glucose) cannot pass through the hydrophobic core [1]; Require channel/carrier proteins to facilitate movement [1].
14. (a) Percentage of Adenine equals percentage of Thymine [1]. (b) A pairs with T via hydrogen bonds in double helix [1]; Therefore, amount of A must equal amount of T [1]. (c) Cannot be determined / Not applicable [1]; In single-stranded DNA, base pairing rules (Chargaff's rules) do not apply [1]; OR if assuming double-stranded logic was mistakenly applied: 30% (but correct answer is that it's unpredictable without more data). Accept: "Cannot be calculated because it is single-stranded and bases do not pair." [2]
15. (a) At low substrate concentration, active sites are empty/available [1]; Increasing substrate concentration increases frequency of collisions/ES complex formation [1]; Rate increases proportionally [1]. (b) Sketch: Curve rises more slowly initially but reaches same Vmax [1]; Explanation: Inhibitor competes with substrate for active site [1]; At high substrate concentration, substrate outcompetes inhibitor [1]; Vmax is unchanged [1]. (Max 3)
Section C: Extended Response
16. Marking Guidance:
- Solvent: Polar nature allows dissolution of ions/polar molecules for metabolic reactions/transport [1].
- High Specific Heat Capacity: Buffers temperature changes, maintaining stable environment for enzymes [1].
- High Latent Heat of Vaporization: Cooling effect via sweating/transpiration [1].
- Cohesion/Adhesion: Transpiration stream in plants/column of water in xylem [1].
- Metabolite: Reactant in hydrolysis/photosynthesis [1].
- Incompressibility: Hydrostatic skeleton/turgor pressure in plants [1]. (1 mark per valid point explained, up to 6 marks.)
17. Marking Guidance:
- Starch (Amylose/Amylopectin): Alpha-glucose, helical/branched, compact storage in plants, insoluble [1].
- Glycogen: Alpha-glucose, highly branched, compact storage in animals/fungi, insoluble, rapid hydrolysis [1].
- Cellulose: Beta-glucose, straight chains, hydrogen bonds between chains form microfibrils, structural support in plant cell walls, high tensile strength [1].
- Comparison: Starch/Glycogen for storage vs Cellulose for structure [1]; Alpha vs Beta linkages [1]; Solubility/branching differences [1]. (1 mark per valid comparison/contrast, up to 6 marks.)
18. Marking Guidance:
- Phospholipid Bilayer: Hydrophobic core prevents passage of water-soluble/charged substances [1]; Allows passage of small non-polar molecules [1].
- Proteins: Channel proteins allow facilitated diffusion of ions/polar molecules [1]; Carrier proteins allow active transport/facilitated diffusion [1]; Specificity of proteins controls what enters/leaves [1].
- Cholesterol: Regulates fluidity and permeability [1].
- Glycoproteins/Glycolipids: Cell recognition/signaling [1].
- Selective Permeability: Membrane controls internal environment/homeostasis [1]. (1 mark per valid point explained, up to 6 marks.)
19. Marking Guidance:
- Glycolysis: Cytoplasm [1]; Glucose to Pyruvate [1]; Net gain 2 ATP, Reduced NAD [1].
- Link Reaction: Mitochondrial Matrix [1]; Pyruvate to Acetyl-CoA [1]; CO₂ released, Reduced NAD formed [1].
- Krebs Cycle: Mitochondrial Matrix [1]; Acetyl-CoA enters cycle [1]; CO₂ released, Reduced NAD/FAD, ATP formed [1].
- Oxidative Phosphorylation: Inner Mitochondrial Membrane/Cristae [1]; Electron Transport Chain pumps protons [1]; Chemiosmosis/ATP Synthase produces ATP [1]; Oxygen is final electron acceptor forming water [1]. (1 mark per valid point, up to 6 marks.)
20. Marking Guidance:
- Catalysis: Lower activation energy, speed up metabolic reactions [1].
- Specificity: Active site shape matches substrate [1].
- Metabolic Pathways: Series of enzyme-catalyzed reactions [1]; Product of one is substrate for next [1].
- Regulation (Inhibition): Competitive/Non-competitive inhibitors [1]; End-product inhibition (negative feedback) [1]; Prevents waste of resources [1].
- Regulation (Environmental): pH/Temperature affects enzyme activity [1].
- Compartmentalization: Enzymes in specific organelles (e.g., lysosomes) [1]. (1 mark per valid point explained, up to 6 marks.)