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A Level H1 Biology Cells Biomolecules Quiz

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A-Level Biology H1 Quiz - Cells Biomolecules

Name: __________________________
Class: __________________________
Date: __________________________
Score: _______ / 50

Duration: 45 minutes
Total Marks: 50

Instructions:

Answer all questions in the spaces provided.
The number of marks is given in brackets [ ] at the end of each question or part question.
Use clear scientific terminology. Diagrams should be drawn with sharp pencil lines and labelled clearly.

Section A: Biological Molecules (Questions 1–5)

1. Water is essential for life due to its unique chemical properties.
(a) Explain how the polarity of water molecules contributes to its effectiveness as a solvent for ionic compounds. [2]

(b) State one property of water that helps to buffer changes in temperature in living organisms and explain its biological significance. [2]

2. Fig. 1.1 represents a dipeptide formed from two amino acids.

(Imagine Fig 1.1 showing two amino acids joined by a peptide bond, with R-groups R1 and R2)

(a) Name the type of reaction that occurs when two amino acids join to form a dipeptide. [1]

(b) Identify the bond labelled X in Fig. 1.1. [1]

(c) Explain how the sequence of amino acids in a polypeptide determines the three-dimensional structure of a protein. [3]

3. Carbohydrates serve different functions in organisms depending on their structure.
(a) Compare the structural features of starch and cellulose. Include references to:

The monomer units
The type of glycosidic bonds
The arrangement of chains
[4]

(b) Explain why glycogen is a more suitable storage molecule in animals than starch. [2]

4. Lipids are a diverse group of biological molecules.
(a) Describe the test for lipids and the positive result observed. [2]

(b) Triglycerides and phospholipids have different structures and functions.
(i) State the structural difference between a triglyceride and a phospholipid. [1]

(ii) Explain how this structural difference allows phospholipids to form cell membranes. [2]

5. Hemoglobin is a globular protein with a quaternary structure.
(a) Define the term quaternary structure. [1]

(b) Explain the significance of the prosthetic group (haem) in hemoglobin. [2]

Section B: Cell Structure and Membranes (Questions 6–10)

6. Fig. 2.1 shows an electron micrograph of a liver cell.

(Imagine Fig 2.1 showing a eukaryotic animal cell with labelled organelles A, B, C, D)

(a) Identify organelles A, B, and C. [3]
A: __________________________
B: __________________________
C: __________________________

(b) Organelle D is the nucleus. State the function of the nucleolus found within the nucleus. [1]

7. Prokaryotic and eukaryotic cells differ in their internal organization.
(a) State two structural differences between a prokaryotic cell and a eukaryotic cell. [2]

(b) Explain why ribosomes are found in both prokaryotic and eukaryotic cells. [1]

8. The fluid mosaic model describes the structure of cell membranes.
(a) Explain the meaning of the terms fluid and mosaic in this model. [2]
Fluid: ____________________________________________________________________
Mosaic: ___________________________________________________________________

(b) Cholesterol is present in animal cell membranes. Describe its role in membrane stability. [2]

9. Substances cross cell membranes by various mechanisms.
(a) Define active transport. [2]

(b) Explain why active transport is necessary for the uptake of mineral ions by root hair cells from the soil. [2]

10. Fig. 3.1 shows the effect of temperature on the rate of diffusion of a substance across a membrane.

(Imagine Fig 3.1 showing a curve increasing with temperature then plateauing or dropping sharply if proteins denature, but for simple diffusion it just increases)

(a) Explain the shape of the curve between 10°C and 40°C. [2]

(b) If the substance was entering via facilitated diffusion, explain what might happen to the rate above 45°C. [2]

Section C: Enzymes and Cellular Processes (Questions 11–15)

11. Enzymes are biological catalysts.
(a) Describe the 'induced fit' model of enzyme action. [3]

(b) Explain how enzymes lower the activation energy of a reaction. [2]

12. Fig. 4.1 shows the effect of substrate concentration on the rate of an enzyme-controlled reaction.

(Imagine Fig 4.1 showing a hyperbolic curve reaching Vmax)

(a) Explain why the rate of reaction increases as substrate concentration increases from point P to point Q. [2]

(b) Explain why the rate of reaction remains constant at point R. [2]

13. Competitive and non-competitive inhibitors affect enzyme activity differently.
(a) State how a competitive inhibitor affects the $V_{max}$ and $K_m$ of an enzyme. [2]
$V_{max}$ : __________________________
$K_m$ : __________________________

(b) Explain how increasing the substrate concentration can overcome the effect of a competitive inhibitor but not a non-competitive inhibitor. [3]

14. ATP is the universal energy currency of cells.
(a) Describe the structure of an ATP molecule. [2]

(b) Explain why ATP is a suitable immediate source of energy for cellular processes. [2]

15. Mitochondria are the site of aerobic respiration.
(a) State the process that occurs in the mitochondrial matrix. [1]

(b) Explain how the structure of the inner mitochondrial membrane is adapted for its function in ATP synthesis. [3]

Section D: Nucleic Acids and Synthesis (Questions 16–20)

16. DNA and RNA are nucleic acids.
(a) State two differences between DNA and RNA. [2]

(b) Describe the structure of a nucleotide. [2]

17. DNA replication is semi-conservative.
(a) Explain what is meant by semi-conservative replication. [2]

(b) State the role of DNA helicase in replication. [1]

18. Protein synthesis involves transcription and translation.
(a) Describe the process of transcription. [3]

(b) Explain the role of tRNA in translation. [2]

19. Fig. 5.1 shows a section of a DNA molecule.

(Imagine Fig 5.1 showing a double helix with base pairs)

(a) If the base sequence on one strand is A-T-G-C, state the complementary sequence on the other strand. [1]

(b) Explain the importance of complementary base pairing in DNA replication. [2]

20. Mutations can occur in DNA sequences.
(a) Define the term mutation. [1]

(b) Explain why a substitution mutation may not always result in a change to the amino acid sequence of a protein. [2]

End of Quiz

Answers

A-Level Biology H1 Quiz - Cells Biomolecules - Answer Key

Total Marks: 50

Section A: Biological Molecules

1.
(a) Water molecules are polar / have a dipole; Oxygen is slightly negative ( $\delta-$ ) and Hydrogen is slightly positive ( $\delta+$ ); These charges attract oppositely charged ions (cations/anions); Surrounding ions prevents them from re-associating / keeps them in solution. [2]
(b) High specific heat capacity; Requires large amount of energy to raise temperature; Buffers temperature changes in organisms/environments; Prevents denaturation of enzymes/maintains homeostasis. [2]
(Accept High latent heat of vaporization for cooling effect)

2.
(a) Condensation. [1]
(b) Peptide bond. [1]
(c) Sequence of amino acids determines primary structure; R-groups interact (H-bonds, ionic, disulfide, hydrophobic); Causes folding into specific tertiary structure; Specific shape determines function (e.g., active site). [3]

3.
(a) Starch: Monomer is $\alpha$ -glucose; Glycosidic bonds are $\alpha$ -1,4 (and $\alpha$ -1,6 in amylopectin); Coiled/helical structure (amylose) or branched (amylopectin). Cellulose: Monomer is $\beta$ -glucose; Glycosidic bonds are $\beta$ -1,4; Straight/unbranched chains; Chains linked by H-bonds to form microfibrils. [4]
(1 mark for each correct comparison point, max 4)
(b) Glycogen is more highly branched than starch; More ends available for enzyme action; Faster hydrolysis/release of glucose for respiration. [2]

4.
(a) Emulsion test; Add ethanol then water; White cloudy emulsion forms. [2]
(b) (i) Phospholipid has a phosphate group (hydrophilic head) replacing one fatty acid; Triglyceride has 3 fatty acids. [1]
(ii) Hydrophilic heads face aqueous environment; Hydrophobic tails face inward; Forms a bilayer; Acts as a barrier to water-soluble substances. [2]

5.
(a) Structure formed by more than one polypeptide chain joined together. [1]
(b) Contains iron ( $Fe^{2+}$ ); Binds oxygen reversibly; Allows hemoglobin to transport oxygen. [2]

Section B: Cell Structure and Membranes

6.
(a) A: Mitochondrion; B: Rough Endoplasmic Reticulum (RER); C: Golgi Apparatus. [3]
(b) Synthesis of ribosomal RNA (rRNA) / Assembly of ribosomes. [1]

7.
(a) Prokaryotes lack membrane-bound nucleus/organelles; Prokaryotes have circular DNA (nucleoid) / 70S ribosomes / murein cell wall. Eukaryotes have linear DNA / 80S ribosomes. [2]
(b) Protein synthesis is essential for all living cells. [1]

8.
(a) Fluid: Phospholipids and proteins can move laterally within the layer. Mosaic: Proteins are embedded in the bilayer in a scattered pattern. [2]
(b) Regulates membrane fluidity; Prevents packing of phospholipids at low temps (prevents freezing); Restricts movement at high temps (increases stability). [2]

9.
(a) Movement of substances against a concentration gradient; Requires energy (ATP); Requires carrier proteins. [2]
(b) Concentration of ions is higher in root cells than in soil; Must move against gradient; Active transport allows accumulation of essential minerals. [2]

10.
(a) Kinetic energy of molecules increases with temperature; Molecules move faster; More frequent collisions with membrane / faster diffusion rate. [2]
(b) Carrier/channel proteins denature; Change in tertiary structure/active site shape; Substance can no longer bind/pass through; Rate decreases. [2]

Section C: Enzymes and Cellular Processes

11.
(a) Substrate binds to active site; Active site changes shape slightly to fit substrate more closely; Induces strain on bonds / positions catalytic groups correctly; Forms enzyme-substrate complex. [3]
(b) Stabilizes the transition state; Lowers the energy required to break bonds / initiate reaction. [2]

12.
(a) More substrate molecules available; More frequent collisions with active sites; More enzyme-substrate complexes formed per unit time. [2]
(b) All active sites are saturated / occupied; Enzyme concentration is the limiting factor; Adding more substrate cannot increase rate further. [2]

13.
(a) $V_{max}$ : Unchanged; $K_m$ : Increases. [2]
(b) Competitive inhibitor binds to active site; Increasing substrate increases probability of substrate binding over inhibitor; Non-competitive inhibitor binds to allosteric site; Changes shape of active site; Substrate cannot bind regardless of concentration. [3]

14.
(a) Adenine (base); Ribose (sugar); Three phosphate groups. [2]
(b) Releases small, manageable amount of energy (hydrolysis of terminal phosphate); Soluble / easily transported; Regenerated quickly (ADP + Pi). [2]

15.
(a) Krebs Cycle (Citric Acid Cycle) / Link Reaction. [1]
(b) Folded into cristae; Increases surface area; Contains electron transport chain proteins / ATP synthase; Allows for maximum ATP production. [3]

Section D: Nucleic Acids and Synthesis

16.
(a) DNA has deoxyribose, RNA has ribose; DNA has Thymine, RNA has Uracil; DNA is double-stranded, RNA is single-stranded. [2]
(b) Pentose sugar; Phosphate group; Nitrogenous base. [2]

17.
(a) Each new DNA molecule contains one original (parental) strand and one newly synthesized strand. [2]
(b) Unzips DNA / Breaks hydrogen bonds between bases. [1]

18.
(a) DNA helicase unzips DNA; RNA polymerase binds to promoter; Joins RNA nucleotides complementary to DNA template strand; Forms mRNA; mRNA detaches and leaves nucleus. [3]
(b) Carries specific amino acid; Anticodon binds to complementary codon on mRNA; Ensures correct amino acid sequence. [2]

19.
(a) T-A-C-G. [1]
(b) Ensures accurate replication; Each strand serves as a template; Complementary bases pair specifically (A-T, C-G); Maintains genetic information. [2]

20.
(a) A change in the DNA base sequence. [1]
(b) Genetic code is degenerate/redundant; Multiple triplets code for the same amino acid; Substitution may result in same amino acid (silent mutation). [2]