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A Level H2 Biology Practice Paper 4

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TuitionGoWhere Practice Paper - Biology H2 A-Level

TuitionGoWhere Practice Paper (AI)

Subject: Biology H2
Level: A-Level
Paper: Practice Paper (Version 4 of 5)
Topic Focus: Cells & Biomolecules
Duration: 1 hour 15 minutes
Total Marks: 40

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 45 minutes 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 bilayer forming a cell surface membrane.

(Note: In a real exam, Fig 1.1 would show a bilayer with hydrophilic heads and hydrophobic tails, and a transmembrane protein.)

(a) State the property of phospholipids that allows them to form a bilayer in an aqueous environment. [1]

(b) Explain why small non-polar molecules, such as oxygen, can diffuse rapidly through the membrane, whereas ions, such as sodium, cannot. [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
20	12
30	28
40	45
50	30
60	5

(a) Explain the increase in the rate of reaction between 20°C and 40°C. [3]

(b) Explain the decrease in the rate of reaction between 40°C and 60°C. [3]

3. Fig. 3.1 represents the structure of a triglyceride molecule.

(a) Identify the type of reaction that joins the glycerol molecule to the fatty acids. [1]

(b) State one structural difference between a phospholipid and a triglyceride. [1]

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

(a) Describe the structural levels of organisation in a haemoglobin molecule. [4]

(b) Suggest why a change in a single amino acid in the primary structure of haemoglobin (as seen in sickle cell anaemia) can affect its function. [2]

5. Mitochondria are often described as the "powerhouses" of the cell.

(a) Name 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 B: Data Interpretation and Extended Response

Answer all questions in this section.

6. Fig. 6.1 shows the results of an experiment using dialysis tubing to model absorption in the small intestine. Two substances, Glucose and Starch, were placed inside the tubing, which was submerged in water.

(Note: Fig 6.1 would show test results for Benedict’s test and Iodine test for the water outside the tubing at time 0 and time 30 mins.)

At time 0, the water outside tested negative for both. At time 30 mins, the water outside tested positive for Glucose but negative for Starch.

(a) Explain these results in terms of membrane permeability and molecular size. [3]

(b) If the experiment were repeated at 5°C, predict and explain how the time taken for glucose to appear outside the tubing would change. [2]

7. DNA and RNA are nucleic acids essential for life.

(a) Complete Table 7.1 to show three differences between DNA and RNA. [3]

Table 7.1

Feature	DNA	RNA
Sugar
Bases
Structure

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

8. The fluid mosaic model describes the structure of cell membranes.

(a) Define the term "fluid mosaic". [2]

(b) Explain the difference between facilitated diffusion and active transport. [3]

9. Enzymes are biological catalysts.

(a) Define the term "activation energy". [1]

(b) Explain how an enzyme reduces activation energy. [2]

10. Cell division is vital for growth and repair.

(a) State the phase of the cell cycle where DNA replication occurs. [1]

(b) Explain why it is important for DNA replication to be semi-conservative. [2]

End of Practice Paper

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Answers

TuitionGoWhere Practice Paper - Biology H2 A-Level

Answer Key and Marking Scheme (Version 4)

Topic: Cells & Biomolecules

Section A: Structured Questions

1. Membrane Structure (a) Phospholipids are amphipathic / have hydrophilic heads and hydrophobic tails. [1] (b)

The interior of the bilayer is hydrophobic / non-polar. [1]
Non-polar molecules (oxygen) can dissolve in/pass through the lipid layer. [1]
Ions are charged/polar and are repelled by the hydrophobic core / cannot pass through the lipid bilayer without a protein channel. [1] (Max 2 marks) (c)
Cholesterol restricts the movement of phospholipid fatty acid tails. [1]
This reduces membrane fluidity / prevents the membrane from becoming too fluid at high temperatures. [1]

2. Enzyme Kinetics (a)

As temperature increases, 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. [1] (b)
High temperature breaks hydrogen bonds (and other bonds) maintaining the tertiary structure. [1]
The enzyme denatures / changes shape. [1]
The active site is no longer complementary to the substrate / substrate cannot bind. [1]

3. Lipids (a) Condensation / Esterification. [1] (b)

Phospholipids contain a phosphate group; triglycerides do not. [1]
OR: Phospholipids have two fatty acids; triglycerides have three. [1] (c)
Triglycerides have a high ratio of energy-storing C-H bonds to carbon atoms (high energy yield per gram). [1]
They are insoluble in water, so they do not affect the water potential of cells / can be stored compactly. [1]

4. Proteins (a)

Primary: Sequence of amino acids held by peptide bonds. [1]
Secondary: Folding into alpha-helices or beta-pleated sheets held by hydrogen bonds. [1]
Tertiary: 3D folding held by ionic, hydrogen, disulfide bonds, and hydrophobic interactions. [1]
Quaternary: Association of multiple polypeptide chains (haemoglobin has 4). [1] (b)
The change in amino acid changes the primary structure, which alters the tertiary structure / shape of the protein. [1]
This may alter the shape of the active site (if enzymatic) or binding site (e.g., oxygen binding in haemoglobin), affecting function. [1]

5. Mitochondria (a) Krebs Cycle / Link Reaction. [1] (Accept either, though Krebs is the main matrix process) (b)

The inner membrane is folded into cristae, increasing surface area. [1]
This allows for more electron transport chain carriers / ATP synthase enzymes. [1]
It creates a small intermembrane space to maintain a steep proton gradient for chemiosmosis. [1]

Section B: Data Interpretation and Extended Response

6. Dialysis Modelling (a)

Glucose molecules are small / monomers. [1]
They can pass through the pores of the dialysis tubing. [1]
Starch molecules are large / polymers / macromolecules. [1]
They are too large to pass through the pores. [1] (Max 3 marks) (b)
Time taken would increase / rate would decrease. [1]
Lower temperature means less kinetic energy, so slower diffusion rate. [1]

7. Nucleic Acids (a)

Sugar: DNA has Deoxyribose; RNA has Ribose. [1]
Bases: DNA has Thymine; RNA has Uracil. (Both have A, C, G). [1]
Structure: DNA is double-stranded/helix; RNA is single-stranded. [1] (b)
Ensures that the new strand is an exact copy / complementary to the template. [1]
Maintains genetic information / fidelity during cell division. [1]

8. Fluid Mosaic Model (a)

Fluid: Phospholipids and proteins can move laterally within the layer. [1]
Mosaic: Proteins are embedded in the bilayer in a scattered pattern. [1] (b)
Facilitated Diffusion: Moves down concentration gradient; does not require ATP/energy. [1]
Active Transport: Moves against concentration gradient; requires ATP/energy. [1]
Both use carrier proteins, but active transport involves a conformational change driven by energy. [1]

9. Enzymes (a) The minimum amount of energy required for a reaction to occur / for substrates to reach the transition state. [1] (b)

The enzyme binds to the substrate to form an enzyme-substrate complex. [1]
This stabilises the transition state / strains bonds in the substrate, lowering the energy barrier. [1] (c)
Competitive: Inhibitor has a similar shape to substrate; binds to the active site. [1]
Effect can be overcome by increasing substrate concentration. [1]
Non-competitive: Inhibitor binds to an allosteric site (not the active site). [1]
Changes the shape of the active site; cannot be overcome by increasing substrate concentration. [1]

10. Cell Division (a) S Phase (Synthesis phase) of Interphase. [1] (b)

Each new DNA molecule contains one original (parental) strand and one new strand. [1]
This ensures genetic continuity / accuracy of genetic information passed to daughter cells. [1]