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A Level H1 Biology Practice Paper 1

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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 1 of 5)
Topic: Cells and Biomolecules
Duration: 1 hour 30 minutes
Total Marks: 60

Name: __________________________
Class: __________________________
Date: __________________________

Instructions to Candidates

Write your Name, Class, and Date in the spaces above.
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

Answer all questions in this section.

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

(a) Identify the parts labelled A and B. [2]
A: _________________________________________________________
B: _________________________________________________________

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

(c) State one property of the phospholipid bilayer that allows small, non-polar molecules (such as oxygen) to pass through easily. [1]

[Total: 5]

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	2.0
20	4.5
30	8.0
40	12.5
50	6.0
60	1.0
70	0.0

(a) Describe the trend in enzyme activity between 10°C and 40°C. [2]

(b) Explain the drop in enzyme activity observed at 60°C and 70°C. [3]

(c) Suggest why the rate of reaction at 50°C is lower than at 40°C, even though the enzyme is not yet fully denatured. [2]

[Total: 7]

3. Fig. 3.1 shows a simplified diagram of a cell membrane involved in the transport of glucose.

(a) Name the type of transport shown if glucose moves from a region of high concentration to low concentration via a carrier protein without the use of ATP. [1]

(b) Explain why glucose cannot simply diffuse through the phospholipid bilayer. [2]

(c) In some intestinal cells, glucose is absorbed against its concentration gradient. Name this process and state the energy source required. [2]
Process: _________________________________________________________
Energy Source: _________________________________________________________

[Total: 5]

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 one amino acid. Explain how a change in the primary structure can affect the tertiary structure of the protein. [3]

[Total: 7]

5. Compare and contrast the structures of glycogen and cellulose.

(a) State the monomer unit for both glycogen and cellulose. [1]

(b) Describe two structural differences between glycogen and cellulose. [2]

(c) Explain how the structure of cellulose makes it suitable for its function in plant cell walls. [2]

[Total: 5]

6. Fig. 6.1 shows an electron micrograph of a liver cell.

(a) Identify the organelle labelled X, which appears as a stack of flattened sacs. [1]

(b) State the function of organelle X in the context of a liver cell that synthesises plasma proteins. [2]

(c) Liver cells contain a high number of mitochondria. Explain why. [2]

[Total: 5]

7. Water is essential for life.

(a) Define the term high specific heat capacity. [1]

(b) Explain the biological significance of water’s high specific heat capacity for organisms. [2]

(c) Water is described as a universal solvent. Explain how this property facilitates metabolic reactions in cells. [2]

[Total: 5]

8. DNA and RNA are nucleic acids.

(a) State two structural differences between DNA and RNA. [2]

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

(c) A sample of DNA was analysed and found to contain 20% adenine. Calculate the percentage of cytosine in this sample. Show your working. [2]
Working:

Answer: _______________ %

[Total: 6]

9. Triglycerides are a type of lipid.

(a) Describe the chemical structure of a triglyceride. [2]

(b) Explain why triglycerides are efficient energy storage molecules compared to carbohydrates. [2]

(c) State one other biological function of lipids in mammals. [1]

[Total: 5]

10. Fig. 10.1 shows the fluid mosaic model of a cell membrane.

(a) Explain the term fluid in the context of the fluid mosaic model. [2]

(b) Explain the term mosaic in the context of the fluid mosaic model. [2]

(c) Cholesterol is present in animal cell membranes. State one function of cholesterol. [1]

[Total: 5]

Section B: Data Interpretation and Application

Answer all questions in this section.

11. A student placed strips of potato tissue in sucrose solutions of different concentrations. After 2 hours, the percentage change in mass was recorded. The results are plotted in Fig. 11.1.

(a) Determine the concentration of sucrose solution that is isotonic to the potato cell sap. [1]
Concentration: _______________ mol dm⁻³

(b) Explain the change in mass of the potato tissue in the 0.0 mol dm⁻³ sucrose solution. [3]

(c) Predict and explain what would happen to the potato cells if they were placed in a 0.8 mol dm⁻³ sucrose solution. [3]

[Total: 7]

12. Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. An experiment was conducted to measure the volume of oxygen produced over time at different substrate concentrations.

(a) Define the term active site. [2]

(b) Explain why the rate of reaction increases as substrate concentration increases, up to a certain point. [3]

(c) Explain why the rate of reaction levels off (reaches $V_{max}$ ) at high substrate concentrations. [2]

[Total: 7]

13. Competitive and non-competitive inhibitors affect enzyme activity differently.

(a) Complete the table below to compare competitive and non-competitive inhibition. [4]

Feature	Competitive Inhibition	Non-competitive Inhibition
Binding site
Effect on $V_{max}$
Effect of increasing substrate concentration
Structural similarity to substrate

(b) Malonate is a competitive inhibitor of succinate dehydrogenase. Explain how malonate inhibits this enzyme. [2]

[Total: 6]

14. Fig. 14.1 shows the structure of an amino acid.

(a) Identify the group labelled R. [1]

(b) Name the type of bond formed between two amino acids during condensation. [1]

(c) Explain how the sequence of amino acids (primary structure) determines the final 3D shape of a protein. [3]

[Total: 5]

15. Prokaryotic and eukaryotic cells differ in structure.

(a) State two structural features present in eukaryotic cells but absent in prokaryotic cells. [2]

(b) Describe the structure of the bacterial cell wall. [2]

(c) Explain why antibiotics that target cell wall synthesis (e.g., penicillin) do not harm human cells. [2]

[Total: 6]

Section C: Extended Response

Answer the question in this section.

16. Discuss the importance of membrane transport mechanisms in maintaining homeostasis in living organisms. In your answer, refer to:

Simple diffusion and osmosis.
Facilitated diffusion.
Active transport.
Specific examples of substances transported.

[10]

[Total: 10]

17. Proteins perform a wide variety of functions in living organisms.

(a) Describe the levels of protein structure, from primary to quaternary. [6]

(b) Explain how the structure of collagen makes it suitable for its function in connective tissues. [4]

[Total: 10]

18. Enzymes are biological catalysts.

(a) Explain the 'induced fit' model of enzyme action. [4]

(b) Discuss the effects of pH and temperature on enzyme activity, referring to the concept of denaturation. [6]

[Total: 10]

19. Carbohydrates and lipids are both used as energy sources.

(a) Compare the energy yield per gram of carbohydrates and lipids. Explain the chemical basis for this difference. [4]

(b) Describe the formation of a glycosidic bond in maltose. [3]

(c) Explain why starch is a suitable storage molecule in plants. [3]

[Total: 10]

20. The cell membrane acts as a barrier and a gateway.

(a) Describe the structure of the phospholipid bilayer and explain how it forms a barrier to water-soluble substances. [4]

(b) Explain the role of membrane proteins in cell signalling and transport. [6]

[Total: 10]

End of Paper

Answers

TuitionGoWhere Practice Paper - Biology H1 A-Level

Answer Key and Marking Scheme

Subject: Biology H1
Topic: Cells and Biomolecules
Version: 1 of 5

Section A: Structured Questions

1. (a)
A: Phosphate head / Hydrophilic head [1]
B: Fatty acid tails / Hydrophobic tails [1]

(b)
Phospholipids are amphipathic (have hydrophilic heads and hydrophobic tails). [1]
In water, they arrange into a bilayer with hydrophilic heads facing the aqueous environment (outwards) and hydrophobic tails facing inwards (away from water). [1]

(c)
The interior of the bilayer is hydrophobic / non-polar. [1]
(Accept: Non-polar molecules can dissolve in the lipid layer.)

[Total: 5]

2. (a)
The rate of reaction increases as temperature increases. [1]
This is due to increased kinetic energy of molecules, leading to more frequent successful collisions between enzyme and substrate. [1]

(b)
High temperatures break the hydrogen bonds / ionic bonds holding the tertiary structure. [1]
The enzyme loses its specific 3D shape / active site shape changes. [1]
Substrate can no longer bind to the active site (enzyme is denatured). [1]

(c)
At 50°C, some enzyme molecules may begin to denature, reducing the number of available active sites. [1]
Alternatively, the increase in collision frequency is outweighed by the beginning of structural instability. [1]
(Note: Accept reasonable explanation linking to partial denaturation or optimal temperature being near 40°C.)

[Total: 7]

3. (a)
Facilitated diffusion. [1]

(b)
Glucose is a large / polar molecule. [1]
It cannot pass through the hydrophobic fatty acid tails of the phospholipid bilayer. [1]

(c)
Process: Active transport. [1]
Energy Source: ATP (from respiration). [1]

[Total: 5]

4. (a)
Haemoglobin consists of four polypeptide chains (subunits). [1]
These chains are held together by bonds (e.g., hydrogen bonds) to form a specific 3D shape. [1]

(b)
The specific shape creates a binding site for oxygen (heme group). [1]
The quaternary structure allows for cooperative binding (binding of one oxygen facilitates binding of others). [1]

(c)
The primary structure is the sequence of amino acids. [1]
This sequence determines the position of R-groups, which form bonds (H-bonds, disulfide bridges) that fold the protein into its tertiary structure. [1]
A change in one amino acid can disrupt these bonds, altering the 3D shape and function. [1]

[Total: 7]

5. (a)
Glucose. [1]

(b)

Glycogen is branched; Cellulose is unbranched / straight chains. [1]
Glycogen has $\alpha$ -glycosidic bonds; Cellulose has $\beta$ -glycosidic bonds. [1]
(Accept: Glycogen is coiled/helical; Cellulose forms straight chains.)

(c)
Cellulose molecules form straight chains that lie parallel to each other. [1]
Hydrogen bonds form between adjacent chains, creating strong microfibrils with high tensile strength. [1]

[Total: 5]

6. (a)
Golgi apparatus. [1]

(b)
Modifies, packages, and sorts proteins. [1]
Prepares them for secretion or transport to other parts of the cell. [1]

(c)
Mitochondria produce ATP via aerobic respiration. [1]
Liver cells are metabolically active (e.g., protein synthesis, detoxification) and require large amounts of ATP. [1]

[Total: 5]

7. (a)
The amount of energy required to raise the temperature of 1 kg of water by 1°C. [1]

(b)
Water resists rapid temperature changes. [1]
This helps organisms maintain a stable internal body temperature / provides a stable environment for aquatic organisms. [1]

(c)
Metabolic reactions occur in solution / cytoplasm. [1]
Water dissolves ions and polar molecules, allowing them to move and react easily. [1]

[Total: 5]

8. (a)

DNA has deoxyribose sugar; RNA has ribose sugar. [1]
DNA is double-stranded; RNA is single-stranded. [1]
(Accept: DNA has Thymine; RNA has Uracil.)

(b)
mRNA carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm. [1]
It serves as a template for translation (protein synthesis). [1]

(c)
If Adenine = 20%, then Thymine = 20% (A pairs with T). [1]
Total A + T = 40%. Remaining 60% is G + C.
Since G = C, Cytosine = 60% / 2 = 30%. [1]

[Total: 6]

9. (a)
One glycerol molecule bonded to three fatty acid molecules. [1]
Bonds are ester bonds formed by condensation reactions. [1]

(b)
Lipids have a higher ratio of carbon-hydrogen bonds to oxygen atoms. [1]
Therefore, they release more energy per gram upon oxidation than carbohydrates. [1]

(c)
Insulation (thermal) / Protection of organs / Component of cell membranes. [1]

[Total: 5]

10. (a)
Phospholipids and proteins can move laterally within the layer. [1]
The membrane is not static/rigid; it is flexible. [1]

(b)
Proteins are embedded in the bilayer in a scattered pattern. [1]
Like tiles in a mosaic. [1]

(c)
Regulates membrane fluidity / Stabilizes the membrane at high temperatures / Prevents packing at low temperatures. [1]

[Total: 5]

Section B: Data Interpretation and Application

11. (a)
0.3 mol dm⁻³ (or value where line crosses x-axis/zero change). [1]

(b)
Water potential of distilled water (0.0 mol dm⁻³) is higher than in potato cells. [1]
Water enters cells by osmosis. [1]
Down a water potential gradient, through a partially permeable membrane. [1]
Cells become turgid, increasing mass. [1] (Max 3 marks)

(c)
Water potential of 0.8 mol dm⁻³ solution is lower than in potato cells. [1]
Water leaves cells by osmosis. [1]
Cells become plasmolysed / flaccid, decreasing mass. [1]

[Total: 7]

12. (a)
A region on the enzyme surface. [1]
With a specific shape complementary to the substrate. [1]

(b)
More substrate molecules collide with active sites. [1]
More enzyme-substrate complexes form per unit time. [1]
Rate increases. [1]

(c)
All active sites are occupied/saturated. [1]
Substrate molecules must wait for an active site to become free. [1]
Adding more substrate cannot increase the rate further. [1] (Max 2 marks)

[Total: 7]

13. (a)

Feature	Competitive Inhibition	Non-competitive Inhibition
Binding site	Active site [1]	Allosteric site [1]
Effect on $V_{max}$	Unchanged [1]	Decreased [1]
Effect of increasing substrate concentration	Inhibition can be overcome [1]	Inhibition cannot be overcome [1]
Structural similarity to substrate	Similar [1]	Not similar [1]

(Award 1 mark for each correct row, max 4 marks.)

(b)
Malonate has a similar shape to succinate (the substrate). [1]
It competes with succinate for the active site of succinate dehydrogenase. [1]

[Total: 6]

14. (a)
Variable group / Side chain. [1]

(b)
Peptide bond. [1]

(c)
The sequence determines the interactions between R-groups. [1]
These interactions (H-bonds, ionic bonds, etc.) cause folding into secondary and tertiary structures. [1]
The final 3D shape determines the protein's function. [1]

[Total: 5]

15. (a)

Nucleus / Nuclear envelope. [1]
Membrane-bound organelles (e.g., mitochondria, Golgi). [1]

(b)
Made of murein / peptidoglycan. [1]
Provides structural support and prevents bursting due to osmotic pressure. [1]

(c)
Human cells do not have cell walls. [1]
Therefore, antibiotics targeting cell wall synthesis have no target in human cells. [1]

[Total: 6]

Section C: Extended Response

16. Membrane Transport and Homeostasis [10]

Introduction: Homeostasis is the maintenance of a stable internal environment. Membrane transport regulates the composition of cells and body fluids. [1]
Simple Diffusion/Osmosis:
- Oxygen and Carbon Dioxide move by simple diffusion down concentration gradients. [1]
- Essential for gas exchange in lungs/gills. [1]
- Osmosis regulates water balance. Example: Kidney tubules reabsorb water to maintain blood water potential. [1]
Facilitated Diffusion:
- Allows polar/charged molecules (e.g., glucose, ions) to enter cells down gradients via channel/carrier proteins. [1]
- Example: Glucose uptake in red blood cells. [1]
- Ensures cells get nutrients without expending energy when gradients allow. [1]
Active Transport:
- Moves substances against concentration gradients using ATP. [1]
- Example: Sodium-Potassium pump in nerve cells maintains resting potential. [1]
- Example: Root hair cells absorbing minerals from soil. [1]
- Crucial for maintaining ion balances and electrochemical gradients essential for nerve impulse transmission and nutrient uptake. [1]
Conclusion: Different transport mechanisms work together to ensure cells receive nutrients, remove waste, and maintain optimal conditions for enzyme activity. [1]

(Marking Note: Award marks for clear explanations, correct terminology, and relevant examples. Max 10 marks.)

[Total: 10]

17. Protein Structure and Function [10]

(a) Levels of Structure: [6]

Primary: Sequence of amino acids linked by peptide bonds. Determines all higher levels. [1.5]
Secondary: Local folding into $\alpha$ -helix or $\beta$ -pleated sheet, stabilized by hydrogen bonds between backbone atoms. [1.5]
Tertiary: Overall 3D shape of a single polypeptide, stabilized by interactions between R-groups (H-bonds, ionic bonds, disulfide bridges, hydrophobic interactions). [1.5]
Quaternary: Association of two or more polypeptide subunits (e.g., haemoglobin). [1.5]

(b) Collagen Structure/Function: [4]

Collagen is a fibrous protein. [1]
Three polypeptide chains twisted into a triple helix. [1]
Cross-links between chains provide high tensile strength. [1]
Suitable for tendons/ligaments/bone matrix where strength is needed to withstand pulling forces. [1]

[Total: 10]

18. Enzymes as Catalysts [10]

(a) Induced Fit Model: [4]

Active site is not perfectly complementary to substrate initially. [1]
Substrate binds to active site. [1]
Active site changes shape slightly to fit substrate more closely (moulds around it). [1]
This puts strain on substrate bonds, lowering activation energy. [1]

(b) pH and Temperature Effects: [6]

Temperature:
- Increase in T increases kinetic energy and collision rate, increasing rate. [1]
- Optimum temperature gives maximum rate. [1]
- Beyond optimum, heat breaks bonds holding tertiary structure. [1]
- Enzyme denatures, active site lost, rate drops to zero. [1]
pH:
- Each enzyme has an optimum pH. [1]
- Changes in pH alter charges on R-groups, disrupting ionic/H-bonds. [1]
- This changes tertiary structure/active site shape. [1]
- Extreme pH causes denaturation. [1] (Note: Candidates should link both factors to the integrity of the active site.)

[Total: 10]

19. Carbohydrates and Lipids [10]

(a) Energy Yield: [4]

Lipids yield more energy per gram (~38 kJ/g) than carbohydrates (~17 kJ/g). [1]
Lipids have more C-H bonds and fewer C-O bonds. [1]
More hydrogen atoms are available for oxidation in the electron transport chain. [1]
This produces more ATP per molecule. [1]

(b) Glycosidic Bond Formation: [3]

Condensation reaction between two $\alpha$ -glucose molecules. [1]
Hydroxyl (-OH) groups on C1 and C4 react. [1]
Water is removed, forming an $\alpha$ -1,4-glycosidic bond. [1]

(c) Starch as Storage: [3]

Insoluble in water, so does not affect water potential of cells. [1]
Compact/coiled structure allows large amounts to be stored in small space. [1]
Branched (amylopectin) allows for rapid hydrolysis/release of glucose when needed. [1]

[Total: 10]

20. Cell Membrane Structure and Function [10]

(a) Phospholipid Bilayer Barrier: [4]

Composed of two layers of phospholipids. [1]
Hydrophilic heads face outwards; hydrophobic tails face inwards. [1]
The hydrophobic core repels charged/polar ions and large polar molecules. [1]
This prevents free passage of water-soluble substances, maintaining distinct internal/external environments. [1]

(b) Role of Membrane Proteins: [6]

Transport: Channel proteins allow facilitated diffusion of ions; Carrier proteins allow active transport or facilitated diffusion of larger molecules (e.g., glucose). [2]
Signalling: Receptor proteins bind specific signalling molecules (hormones/neurotransmitters). [1]
This binding triggers a conformational change or cascade inside the cell. [1]
Allows cell communication and response to environment. [1]
Example: Insulin receptor binding insulin to trigger glucose uptake. [1]

[Total: 10]