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A Level H1 Biology Practice Paper 1
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Questions
TuitionGoWhere Exam Practice (AI) - Biology H1 A-Level
Subject: Biology
Level: H1
Paper: Practice Paper 1 (Version 1 of 5)
Topic: Cells & Biomolecules
Duration: 1 hour 15 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 in 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 (40 Marks)
1. Fig. 1.1 shows a diagram of a cell membrane as seen under an electron microscope.
(Note: In a real exam, Fig 1.1 would show a phospholipid bilayer with embedded proteins. Assume standard fluid mosaic model structure.)
(a) With reference to Fig. 1.1, describe the arrangement of the phospholipid molecules in the membrane. [2]
(b) Explain how the structure of phospholipids contributes to the stability of the cell membrane in an aqueous environment. [2]
2. A student investigated the effect of temperature on the activity of the enzyme amylase. The results are shown in Table 2.1.
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 simplified diagram of the cell cycle.
(Note: Fig 3.1 shows a circle divided into G1, S, G2, and M phases.)
(a) Identify the phase of the cell cycle in which DNA replication occurs. [1]
(b) Explain why it is essential for DNA replication to occur before the cell enters mitosis. [2]
4. Isolated mitochondria were incubated in a solution containing either glucose or pyruvate. Oxygen consumption was measured.
(a) State which substrate, glucose or pyruvate, would result in oxygen consumption by the isolated mitochondria. [1]
(b) Explain your answer to (a). [3]
5. Water is essential for life.
(a) Describe two properties of water that make it a good solvent for biological reactions. [2]
(b) Explain how the high specific heat capacity of water helps organisms maintain a stable internal temperature. [2]
6. Fig. 6.1 shows the structure of a triglyceride molecule.
(Note: Fig 6.1 shows one glycerol molecule bonded to three fatty acid chains.)
(a) Name the type of reaction that joins the fatty acids to the glycerol. [1]
(b) Explain why triglycerides are suitable for energy storage in animals. [2]
7. A protein molecule consists of a specific sequence of amino acids.
(a) Name the bond that links amino acids together in a polypeptide chain. [1]
(b) Explain how the primary structure of a protein determines its three-dimensional shape. [3]
8. Fig. 8.1 shows a pedigree chart for a genetic condition caused by a recessive allele.
(Note: Standard pedigree with affected and unaffected individuals.)
(a) Using the symbol A for the dominant allele and a for the recessive allele, state the genotype of individual 3 in Generation I. [1]
(b) Explain how you determined this genotype. [2]
9. Compare and contrast the structure of DNA and RNA.
Complete Table 9.1 by stating two differences and one similarity.
Table 9.1
| Feature | DNA | RNA |
|---|---|---|
| Sugar present | Deoxyribose | (i) ___________________ [1] |
| Number of strands | (ii) ___________________ [1] | Single |
| Nitrogenous bases | (iii) ___________________ [1] | Adenine, Uracil, Cytosine, Guanine |
10. Fig. 10.1 shows a plant cell placed in a concentrated sucrose solution.
(Note: Fig 10.1 shows a plasmolysed cell where the protoplast has shrunk away from the cell wall.)
(a) Name the process that causes water to leave the cell. [1]
(b) Explain, in terms of water potential, why water leaves the cell. [2]
Section B: Data Interpretation and Application (20 Marks)
11. Scientists investigated the effect of pH on the activity of two different enzymes, Enzyme X and Enzyme Y. The results are shown in Fig. 11.1.
(Note: Fig 11.1 is a graph. Enzyme X has an optimum pH of 2. Enzyme Y has an optimum pH of 8.)
(a) State the optimum pH for Enzyme X. [1]
(b) Suggest where in the human body Enzyme X is likely to be found. Explain your answer. [2]
(c) Explain why the activity of Enzyme Y decreases significantly at pH 4. [3]
12. Fig. 12.1 shows the structure of a phospholipid bilayer and the movement of three different substances, A, B, and C, across it.
- Substance A moves directly through the bilayer from high to low concentration.
- Substance B moves through a channel protein from high to low concentration.
- Substance C moves through a carrier protein from low to high concentration, using ATP.
(a) Identify the type of transport for Substance A, Substance B, and Substance C. [3]
Substance A: _________________________ Substance B: _________________________ Substance C: _________________________
(b) Explain why Substance C requires ATP for transport. [2]
(c) Substance A is oxygen. Explain why oxygen can move directly through the phospholipid bilayer without the aid of proteins. [2]
13. A student performed a biochemical test on a food sample. The results are shown in Table 13.1.
Table 13.1
| Test | Reagent Used | Observation |
|---|---|---|
| Test 1 | Benedict’s solution | Blue color remained after heating |
| Test 2 | Biuret reagent | Purple color formed |
| Test 3 | Iodine solution | Blue-black color formed |
(a) State which biological molecules are present in the food sample based on the results. [2]
(b) Describe how Test 1 should be performed correctly to ensure a valid result for reducing sugars. [2]
(c) The student repeated Test 1 with a new sample and observed a brick-red precipitate. State what this indicates about the new sample. [1]
14. Fig. 14.1 shows the structure of a nucleotide.
(Note: Fig 14.1 shows a phosphate group, a pentose sugar, and a nitrogenous base.)
(a) Name the three components labeled X, Y, and Z in Fig. 14.1. [3]
X: _________________________ Y: _________________________ Z: _________________________
(b) Explain how nucleotides join together to form a polynucleotide chain. [2]
15. Collagen is a fibrous protein found in connective tissues.
(a) Describe the structural features of collagen that give it high tensile strength. [3]
(b) State one function of collagen in the human body. [1]
END OF PAPER
Answers
TuitionGoWhere Exam Practice (AI) - Biology H1 A-Level
Answer Key and Marking Scheme
Topic: Cells & Biomolecules
Paper: Practice Paper 1 (Version 1 of 5)
Section A: Structured Questions
1. (a) Phospholipids are arranged in a bilayer [1]. The hydrophilic heads face outward towards the aqueous environment, and the hydrophobic tails face inward, away from water [1]. (b) The hydrophilic heads interact with water molecules (hydrogen bonding) [1], while the hydrophobic tails exclude water, creating a stable barrier that prevents water-soluble substances from passing freely [1].
2. (a) As temperature increases, the kinetic energy of enzyme and substrate molecules increases [1]. This leads to more frequent collisions between enzyme and substrate [1]. More enzyme-substrate complexes are formed per unit time, increasing the rate of reaction [1]. (b) At 60°C, the high temperature causes the hydrogen bonds holding the tertiary structure of the enzyme to break [1]. The active site changes shape (denaturation), so the substrate can no longer bind [1].
3. (a) S phase [1]. (b) DNA replication ensures that each daughter cell receives a complete and identical set of genetic information [1]. This maintains genetic stability and allows the daughter cells to function correctly [1].
4. (a) Pyruvate [1]. (b) Glycolysis occurs in the cytoplasm, not in the mitochondria [1]. Glucose must be broken down into pyruvate via glycolysis before it can enter the mitochondria [1]. Isolated mitochondria lack the enzymes for glycolysis, so they cannot use glucose. However, they contain the enzymes for the link reaction and Krebs cycle, so they can use pyruvate to produce reduced NAD/FAD, which drives the electron transport chain and oxygen consumption [1].
5. (a) Water is a polar molecule [1]. It can form hydrogen bonds with other polar or charged molecules, allowing them to dissolve [1]. (b) Water has a high specific heat capacity, meaning it can absorb or lose a large amount of heat energy with only a small change in temperature [1]. This helps buffer organisms against sudden temperature changes in the environment, maintaining homeostasis [1].
6. (a) Condensation [1]. (b) Triglycerides have a high ratio of carbon-hydrogen bonds, which release a large amount of energy when oxidized [1]. They are insoluble in water, so they do not affect the water potential of cells and can be stored compactly [1].
7. (a) Peptide bond [1]. (b) The primary structure is the specific sequence of amino acids [1]. This sequence determines the interactions between the R-groups (side chains) of the amino acids [1]. These interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions) determine the folding of the polypeptide into its specific tertiary structure [1].
8. (a) Aa [1]. (b) Individual 3 is unaffected (dominant phenotype) but has an affected child (aa) [1]. Therefore, individual 3 must carry one recessive allele to pass to the affected child, making them heterozygous [1].
9. (i) Ribose [1] (ii) Double-stranded (or double helix) [1] (iii) Adenine, Thymine, Cytosine, Guanine [1]
10. (a) Osmosis [1]. (b) The sucrose solution has a lower water potential (more negative) than the cell sap [1]. Water moves from a region of higher water potential (inside the cell) to a region of lower water potential (outside the cell) down a water potential gradient [1].
Section B: Data Interpretation and Application
11. (a) pH 2 [1]. (b) Stomach [1]. The stomach contains hydrochloric acid, creating an acidic environment (low pH) suitable for Enzyme X (pepsin) [1]. (c) At pH 4, the concentration of H+ ions is lower than the optimum for Enzyme Y (or higher than optimum for Enzyme X, but context implies Y is alkaline enzyme like trypsin). Correction based on graph description: Enzyme Y optimum is pH 8. At pH 4, the change in pH alters the charge on the amino acids in the active site [1]. This disrupts the ionic bonds holding the tertiary structure [1]. The active site changes shape, reducing the frequency of successful enzyme-substrate complex formation [1].
12. (a) Substance A: Simple Diffusion [1] Substance B: Facilitated Diffusion [1] Substance C: Active Transport [1] (b) Substance C moves against the concentration gradient (from low to high concentration) [1]. This requires energy (ATP) to pump the molecules [1]. (c) Oxygen is a small, non-polar (uncharged) molecule [1]. It can dissolve in the hydrophobic fatty acid tails of the phospholipid bilayer and pass through easily [1].
13. (a) Protein and Starch [1] (1 mark for each correct identification, max 2). Note: Benedict's was negative, so no reducing sugar. (b) Add Benedict’s solution to the sample [1]. Heat the mixture in a water bath at 80-100°C for a few minutes [1]. (c) The new sample contains reducing sugars [1].
14. (a) X: Phosphate group [1] Y: Pentose sugar (or Deoxyribose/Ribose) [1] Z: Nitrogenous base [1] (b) Nucleotides join via condensation reactions [1]. A phosphodiester bond forms between the phosphate group of one nucleotide and the sugar of the next nucleotide [1].
15. (a) Collagen consists of three polypeptide chains wound together in a triple helix [1]. Hydrogen bonds form between the chains, holding them together [1]. Covalent cross-links form between adjacent collagen molecules, providing high tensile strength [1]. (b) Provides strength to tendons/ligaments/bones/skin [1] (Any one valid connective tissue function).
END OF MARKING SCHEME