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A Level H1 Biology Practice Paper 3

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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 3
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 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 hour on Section A and 30 minutes on Section B.

Section A: Structured Questions

Answer all questions in this section.

1. Fig. 1.1 shows a diagram of a phospholipid molecule.

(a) Label the hydrophilic and hydrophobic regions of the molecule in Fig. 1.1. [2]

(b) Explain how phospholipids arrange themselves when placed in an aqueous environment to form a cell membrane. [2]

(c) State one property of the phospholipid bilayer that allows small, non-polar molecules (such as oxygen) to pass through easily, while preventing ions from passing through. [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	12
20	25
30	45
40	58
50	30
60	5
70	0

(a) Describe the trend in enzyme activity as the temperature increases from 10°C to 40°C. [2]

(b) Explain the decrease in enzyme activity observed at temperatures above 50°C. [3]

(c) Suggest why the rate of reaction is zero at 70°C. [1]

3. Fig. 3.1 shows a simplified diagram of a cell membrane with two transport mechanisms, A and B.

(a) Identify mechanism A and mechanism B. [2]

Mechanism A: __________________________
Mechanism B: __________________________

(b) State one difference between mechanism A and mechanism B in terms of energy requirement. [1]

(c) Glucose enters red blood cells via facilitated diffusion. Explain why glucose cannot enter cells by simple diffusion. [2]

4. Haemoglobin is a globular protein found in red blood cells.

(a) Describe the quaternary structure of haemoglobin. [2]

(b) Explain how the specific shape of haemoglobin allows it to function effectively in oxygen transport. [2]

(c) Sickle cell anaemia is caused by a mutation in the gene for haemoglobin, resulting in the substitution of valine for glutamic acid in the primary structure. Explain how this change in primary structure affects the tertiary structure and function of haemoglobin. [3]

5. Water is essential for life.

(a) Define the term water potential. [1]

(b) A plant cell is placed in a solution with a higher water potential than the cell sap. (i) State the direction of net water movement. [1] (ii) Describe the appearance of the cell after 30 minutes. [2]

(c) Explain why water is described as a "universal solvent" and why this property is important for metabolic reactions in cells. [2]

6. Triglycerides and phospholipids are both lipids.

(a) State the molecular components of a triglyceride. [2]

(b) Compare the structure of a triglyceride with that of a phospholipid. [2]

(c) Explain why triglycerides are suitable for energy storage in animals, whereas phospholipids are not. [2]

7. Fig. 7.1 shows the structure of a mitochondrion.

(a) Identify the structure labelled X. [1]

(b) The inner membrane of the mitochondrion is folded into cristae. Explain the significance of this folding for cellular respiration. [2]

(c) State the process that occurs in the matrix of the mitochondrion. [1]

8. DNA and RNA are nucleic acids.

(a) Complete Table 8.1 to show three differences between DNA and RNA. [3]

Feature	DNA	RNA
Sugar
Bases
Structure

(b) Explain the role of mRNA in protein synthesis. [2]

9. Enzyme inhibitors can be competitive or non-competitive.

(a) Describe how a competitive inhibitor affects the rate of an enzyme-catalysed reaction. [2]

(b) Explain how increasing the substrate concentration affects the inhibition caused by a competitive inhibitor. [2]

(c) State one way in which a non-competitive inhibitor differs from a competitive inhibitor in terms of where it binds to the enzyme. [1]

10. Collagen is a fibrous protein.

(a) Describe the structural features of collagen that give it high tensile strength. [3]

(b) State one location in the human body where collagen is found and relate its structure to its function in that location. [2]

Section B: Free Response Questions

Answer all questions in this section.

11. Discuss the importance of the properties of water to living organisms. In your answer, refer to:

Thermal properties
Solvent properties
Cohesion and adhesion

[8]

<br...... *(Space reserved for student answer)*

12. Compare and contrast the structures and functions of starch, glycogen, and cellulose. Explain how the structure of each polysaccharide relates to its specific role in plants or animals.

[10]

End of Paper

Answers

TuitionGoWhere Practice Paper - Biology H1 A-Level

Answer Key & Marking Scheme - Version 3

Subject: Biology H1
Topic: Cells & Biomolecules

Section A: Structured Questions

1. Phospholipids

(a) [2]
- Head: Hydrophilic (1)
- Tails: Hydrophobic (1)
(b) [2]
- Phospholipids form a bilayer (1).
- Hydrophilic heads face outward towards the aqueous environment (cytoplasm/tissue fluid), and hydrophobic tails face inward, away from water (1).
(c) [1]
- The interior of the membrane is hydrophobic/non-polar (1).
- Note: Accept "impermeable to charged/polar molecules".

2. Enzyme Kinetics

(a) [2]
- Rate of reaction increases as temperature increases (1).
- More kinetic energy leads to more frequent successful collisions between enzyme and substrate (1).
(b) [3]
- High temperature breaks hydrogen bonds/ionic bonds holding the tertiary structure (1).
- The enzyme denatures (1).
- The active site changes shape and is no longer complementary to the substrate (1).
(c) [1]
- The enzyme is fully denatured (1).

3. Membrane Transport

(a) [2]
- Mechanism A: Active Transport (1)
- Mechanism B: Facilitated Diffusion (1)
- Note: Accept Simple Diffusion for B if diagram shows no protein, but typically B implies protein channel/carrier in these diagrams. If diagram shows movement against gradient for A and down for B via protein, this is the standard answer.
(b) [1]
- Mechanism A requires ATP/energy; Mechanism B does not (1).
(c) [2]
- Glucose is a large/polar molecule (1).
- It cannot pass through the hydrophobic fatty acid tails of the phospholipid bilayer (1).

4. Haemoglobin

(a) [2]
- Consists of four polypeptide chains (1).
- Each chain is associated with a haem group (1).
(b) [2]
- Specific 3D shape creates a binding site for oxygen (1).
- Conformational change allows cooperative binding (loading/unloading) (1).
(c) [3]
- Change in amino acid sequence (primary structure) changes the R-group interactions (1).
- This alters the folding/tertiary structure (1).
- Haemoglobin becomes insoluble/fibrous and cannot carry oxygen effectively (1).

5. Water

(a) [1]
- The tendency of water molecules to move from one region to another (or measure of free energy of water molecules) (1).
(b)
- (i) [1] Into the cell (1).
- (ii) [2] The cell becomes turgid (1). The vacuole expands and pushes the cytoplasm against the cell wall (1).
(c) [2]
- Water is polar, allowing it to dissolve polar/ionic substances (1).
- This allows metabolic reactions to occur in solution/transport of nutrients (1).

6. Lipids

(a) [2]
- One glycerol molecule (1).
- Three fatty acid chains (1).
(b) [2]
- Triglyceride has 3 fatty acids; Phospholipid has 2 fatty acids and 1 phosphate group (1).
- Phospholipid has a hydrophilic head and hydrophobic tails; Triglyceride is entirely hydrophobic (1).
(c) [2]
- Triglycerides are insoluble in water, so they do not affect water potential/osmosis in cells (1).
- They have a high energy-to-mass ratio (more C-H bonds) (1).

7. Mitochondria

(a) [1]
- Cristae (or Inner Membrane) (1).
(b) [2]
- Increases surface area (1).
- Allows for more electron transport chain proteins/ATP synthase enzymes to be embedded (1).
(c) [1]
- Krebs Cycle (Link Reaction also occurs here, but Krebs is the main cycle) (1).

8. Nucleic Acids

(a) [3]
- Sugar: Deoxyribose (DNA) vs Ribose (RNA) (1).
- Bases: Thymine (DNA) vs Uracil (RNA) (1).
- Structure: Double stranded/helix (DNA) vs Single stranded (RNA) (1).
(b) [2]
- Carries genetic code from DNA in nucleus to ribosomes in cytoplasm (1).
- Serves as a template for translation/protein synthesis (1).

9. Inhibition

(a) [2]
- Competitive inhibitor has similar shape to substrate (1).
- Competes for the active site, reducing the number of enzyme-substrate complexes formed (1).
(b) [2]
- Increasing substrate concentration reduces the effect of inhibition (1).
- Substrate outcompetes the inhibitor for the active site (1).
(c) [1]
- Non-competitive inhibitors bind to an allosteric site (not the active site) (1).

10. Collagen

(a) [3]
- Three polypeptide chains wound into a triple helix (1).
- Held together by hydrogen bonds (1).
- Cross-links between molecules provide strength (1).
(b) [2]
- Location: Tendons/Ligaments/Bone/Skin (1).
- Function: Withstands pulling forces/tensile strength due to strong cross-links (1).

Section B: Free Response Questions

11. Properties of Water [8]

Thermal Properties (High Specific Heat Capacity):
- Water has a high specific heat capacity due to hydrogen bonds requiring energy to break (1).
- This allows water to buffer temperature changes, maintaining stable internal environments for organisms/homeostasis (1).
- High latent heat of vaporization allows for cooling via sweating/transpiration without excessive water loss (1).
Solvent Properties:
- Water is a polar molecule, making it an excellent solvent for ions and polar molecules (1).
- Metabolic reactions occur in aqueous solution (cytoplasm/blood) (1).
- Transport of nutrients (glucose, amino acids) and waste (urea, CO2) in blood/plasma (1).
Cohesion and Adhesion:
- Cohesion: Water molecules stick to each other via hydrogen bonds (1).
- Adhesion: Water molecules stick to other surfaces (e.g., xylem walls) (1).
- This creates a continuous column of water in plants, allowing transpiration pull to transport water to leaves against gravity (1).
- Surface tension supports small organisms (e.g., pond skaters) (1).
Marking Note: Award marks for clear explanation linking property to biological significance. Max 8 marks.

12. Polysaccharides: Starch, Glycogen, Cellulose [10]

Starch (Plants):
- Structure: Mixture of amylose (helical, unbranched) and amylopectin (branched). Made of $\alpha$ -glucose (1).
- Function: Energy storage in plants (1).
- Relation: Compact helical shape allows storage in small space; insoluble so doesn't affect water potential; branches allow rapid hydrolysis/release of glucose (1).
Glycogen (Animals):
- Structure: Similar to amylopectin but more highly branched. Made of $\alpha$ -glucose (1).
- Function: Energy storage in animals (liver/muscle) (1).
- Relation: Highly branched structure provides many ends for enzyme action, allowing rapid release of glucose for respiration during activity (1).
Cellulose (Plants):
- Structure: Straight, unbranched chains of $\beta$ -glucose. Chains linked by hydrogen bonds to form microfibrils (1).
- Function: Structural component of cell walls (1).
- Relation: High tensile strength due to hydrogen bonding between parallel chains; prevents cell bursting under turgor pressure; provides support for plant (1).
Comparison:
- Starch and Glycogen are $\alpha$ -glucose polymers (storage); Cellulose is $\beta$ -glucose (structural) (1).
- Starch/Glycogen are coiled/branched; Cellulose is straight/linear (1).
Marking Note: Award marks for accurate structural descriptions and clear links to function. Comparison points should be explicit. Max 10 marks.