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A Level H1 Biology Cells Biomolecules Quiz

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Questions

A-Level Biology H1 Quiz - Cells Biomolecules

Name: __________________________
Class: __________________________
Date: __________________________
Score: ______ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

Answer all questions.
Write your answers in the spaces provided.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a calculator.

Section A: Multiple Choice (Questions 1–5)

Choose the correct answer for each question. Each question carries 1 mark.

1. Which of the following statements correctly describes the structure of a phospholipid molecule? A. It has a hydrophobic phosphate head and two hydrophilic fatty acid tails. B. It has a hydrophilic phosphate head and two hydrophobic fatty acid tails. C. It has a hydrophilic glycerol backbone and three hydrophobic fatty acid tails. D. It has a hydrophobic glycerol backbone and three hydrophilic phosphate heads.

[1]

2. A student observes a cell under an electron microscope. The cell contains ribosomes, a cell wall made of peptidoglycan, and no membrane-bound organelles. This cell is most likely: A. A prokaryotic cell. B. A plant cell. C. An animal cell. D. A fungal cell.

[1]

3. Which bond is responsible for maintaining the primary structure of a protein? A. Hydrogen bonds B. Ionic bonds C. Peptide bonds D. Disulfide bridges

[1]

4. Why is water described as a universal solvent in biological systems? A. It has a high specific heat capacity. B. It is a polar molecule, allowing it to dissolve ions and polar substances. C. It has strong cohesive forces due to hydrogen bonding. D. It has a high latent heat of vaporisation.

[1]

5. Which of the following molecules is a component of DNA but not RNA? A. Ribose B. Uracil C. Thymine D. Phosphate group

[1]

Section B: Structured Response (Questions 6–15)

Answer the questions in the spaces provided.

6. Fig. 6.1 shows a diagram of a cell membrane.

(Imagine Fig 6.1 showing a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins.)

(a) Identify the structure labelled X in Fig. 6.1 and state its function in the membrane. Structure: _______________________________________________________ [1] Function: ________________________________________________________ [1]

(b) Explain how the arrangement of phospholipids in the bilayer contributes to the membrane’s ability to act as a barrier to water-soluble substances. _________________________________________________________________________ [2]

7. A student investigated the effect of temperature on the activity of the enzyme amylase. The results are shown in Table 7.1.

Table 7.1

Temperature (°C)	Rate of Reaction (arbitrary units)
10	2.0
20	4.5
30	8.0
40	12.0
50	6.0
60	1.0
70	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 70°C. _________________________________________________________________________ [2]

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

(a) Name the process that occurs in the mitochondrial matrix which produces carbon dioxide. _________________________________________________________________________ [1]

(b) Explain why isolated mitochondria can produce ATP when supplied with pyruvate, but not when supplied with glucose. _________________________________________________________________________ [3]

9. Fig. 9.1 shows the structure of a triglyceride.

(Imagine Fig 9.1 showing 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) State one structural difference between a triglyceride and a phospholipid. _________________________________________________________________________ [1]

(c) Explain why triglycerides are suitable for long-term energy storage in animals. _________________________________________________________________________ [2]

10. Describe the role of the Golgi apparatus in a secretory cell, such as a pancreatic cell producing insulin. _________________________________________________________________________ [3]

11. Water has several properties that make it essential for life.

(a) Explain how the high latent heat of vaporisation of water helps mammals regulate their body temperature. _________________________________________________________________________ [2]

(b) Explain how the cohesion of water molecules supports transport in plants. _________________________________________________________________________ [2]

12. Compare and contrast the structure of glycogen and cellulose. _________________________________________________________________________ [4]

13. Fig. 13.1 shows the results of an experiment where red blood cells were placed in solutions of different water potentials.

(Imagine Fig 13.1 showing three cells: one swollen/burst, one normal, one shrivelled.)

(a) Identify which cell was placed in a solution with a lower water potential than the cytoplasm. Cell: ______________________________________________________________ [1]

(b) Explain the appearance of this cell. _________________________________________________________________________ [2]

14. DNA and RNA are both nucleic acids.

(a) State two differences in the chemical structure of DNA and RNA.

__________________________________________________________________ [1]
__________________________________________________________________ [1]

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

15. Active transport is a mechanism for moving substances across cell membranes.

(a) Define active transport. _________________________________________________________________________ [2]

(b) State one example of active transport in human physiology. _________________________________________________________________________ [1]

Section C: Data Interpretation and Extended Response (Questions 16–20)

Answer the questions in the spaces provided.

16. A student tested three unknown solutions (A, B, and C) using Benedict’s reagent and Biuret reagent. The results are shown below.

Table 16.1

Solution	Benedict’s Test (after heating)	Biuret Test
A	Blue	Purple
B	Brick-red precipitate	Blue
C	Blue	Blue

(a) Identify the type of biomolecule present in Solution A. _________________________________________________________________________ [1]

(b) Identify the type of biomolecule present in Solution B. _________________________________________________________________________ [1]

(c) Solution C gave negative results for both tests. Suggest one further test the student could perform to identify if Solution C contains lipids, and describe the positive result. Test: ________________________________________________________________ [1] Positive Result: _______________________________________________________ [1]

17. Fig. 17.1 shows the fluid mosaic model of a cell membrane.

(Imagine Fig 17.1 depicting the standard fluid mosaic model.)

(a) Explain why the membrane is described as "fluid". _________________________________________________________________________ [2]

(b) Explain why the membrane is described as a "mosaic". _________________________________________________________________________ [2]

18. Enzymes are biological catalysts.

(a) Describe the "lock and key" hypothesis of enzyme action. _________________________________________________________________________ [3]

(b) Explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction. _________________________________________________________________________ [3]

19. The cell cycle consists of interphase and mitosis.

(a) Describe the events that occur during the S phase of interphase. _________________________________________________________________________ [2]

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

20. Extended Response: Discuss the importance of the specific properties of water to living organisms. In your answer, refer to at least three properties of water and explain their biological significance. ...... [6]

[END OF QUIZ]

Answers

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

Total Marks: 40

Section A: Multiple Choice

1. B

Marking Note: Phosphate head is hydrophilic (water-loving), fatty acid tails are hydrophobic (water-fearing).

2. A

Marking Note: Peptidoglycan cell wall and lack of membrane-bound organelles are key features of prokaryotes (bacteria).

3. C

Marking Note: Primary structure is the sequence of amino acids held together by peptide bonds.

4. B

Marking Note: Polarity allows water to form hydration shells around ions and polar molecules, dissolving them.

5. C

Marking Note: Thymine is found in DNA; Uracil is found in RNA. Both have phosphate and pentose sugars (deoxyribose vs ribose).

Section B: Structured Response

6. (a)

Structure: Cholesterol [1]
Function: Regulates membrane fluidity / stabilises the membrane / prevents packing of phospholipids at low temps or excessive movement at high temps. [1]

(b)

The hydrophobic fatty acid tails face inwards, away from the aqueous environment. [1]
This creates a non-polar interior that repels water-soluble (polar/charged) substances, preventing them from passing freely. [1]

7. (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, increasing the rate of reaction. [1]

(b)

At 70°C, the high temperature breaks the hydrogen bonds and other bonds maintaining the tertiary structure of the enzyme. [1]
The enzyme is denatured; the active site changes shape and is no longer complementary to the substrate, so no complexes can form. [1]

8. (a)

Krebs cycle (or Citric Acid Cycle / Link Reaction). [1]

(b)

Glucose must first be broken down into pyruvate via glycolysis. [1]
Glycolysis occurs in the cytoplasm, not in the mitochondria. [1]
Isolated mitochondria lack the enzymes for glycolysis, so they cannot process glucose, but can process pyruvate directly in the Krebs cycle. [1]

9. (a)

Condensation (or Esterification). [1]

(b)

A triglyceride has three fatty acids attached to glycerol, whereas a phospholipid has two fatty acids and one phosphate group attached to glycerol. [1]
Alternative: Phospholipids have a hydrophilic head and hydrophobic tails; triglycerides are entirely hydrophobic.

(c)

Triglycerides are insoluble in water, so they do not affect the water potential of cells/osmotic balance. [1]
They have a high energy-to-mass ratio (more C-H bonds than carbohydrates), storing more energy per gram. [1]

10.

Receives proteins (from RER) in transport vesicles. [1]
Modifies proteins (e.g., adding carbohydrate groups to form glycoproteins, folding, or packaging). [1]
Packages proteins into secretory vesicles for transport to the cell membrane for exocytosis. [1]

11. (a)

High latent heat of vaporisation means a large amount of heat energy is required to evaporate water. [1]
When sweat evaporates from the skin, it removes a large amount of body heat, cooling the organism without significant loss of water volume. [1]

(b)

Cohesion allows water molecules to stick together via hydrogen bonds. [1]
This creates a continuous column of water in the xylem, allowing it to be pulled up the plant under tension (transpiration pull). [1]

12.

Similarity: Both are polymers of glucose / both contain glycosidic bonds. [1]
Difference 1: Glycogen contains alpha-glucose; Cellulose contains beta-glucose. [1]
Difference 2: Glycogen is branched and coiled (compact for storage); Cellulose is unbranched and forms straight chains held by hydrogen bonds (for strength). [1]
Difference 3: Glycogen has 1,6-glycosidic bonds (branching); Cellulose only has 1,4-glycosidic bonds. [1]
Award max 4 marks.

13. (a)

The shrivelled (crenated) cell. [1]

(b)

The solution had a lower water potential than the cell cytoplasm. [1]
Water left the cell by osmosis, causing the cell to shrink/shrivel. [1]

14. (a)

DNA contains deoxyribose sugar; RNA contains ribose sugar. [1]
DNA contains Thymine; RNA contains Uracil. [1]
Alternative: DNA is double-stranded; RNA is usually single-stranded.

(b)

Complementary base pairing ensures accurate replication of DNA. [1]
Each strand serves as a template for the synthesis of a new complementary strand, preserving the genetic code. [1]

15. (a)

The movement of molecules/ions [1]
From a region of lower concentration to higher concentration (against the concentration gradient), using energy (ATP) and carrier proteins. [1]

(b)

Absorption of glucose/amino acids in the small intestine. [1]
Alternative: Reabsorption of glucose in the kidney nephron.
Alternative: Sodium-Potassium pump in nerve cells.

Section C: Data Interpretation and Extended Response

16. (a)

Protein. [1] (Biuret turns purple in presence of protein; Benedict's remains blue indicating no reducing sugar).

(b)

Reducing Sugar. [1] (Benedict's turns brick-red; Biuret remains blue indicating no protein).

(c)

Test: Emulsion test (Ethanol test). [1]
Positive Result: Formation of a cloudy white emulsion. [1]

17. (a)

The phospholipids and proteins are not static; they can move laterally within the layer. [1]
This movement gives the membrane flexibility and allows for processes like endocytosis/exocytosis. [1]

(b)

The membrane contains a variety of different proteins (channel, carrier, receptor, enzymatic) scattered throughout the lipid bilayer. [1]
These proteins create a "mosaic" pattern when viewed from above. [1]

18. (a)

The enzyme has an active site with a specific shape. [1]
The substrate has a complementary shape to the active site. [1]
The substrate fits into the active site like a key into a lock, forming an enzyme-substrate complex. [1]

(b)

A non-competitive inhibitor binds to an allosteric site (a site other than the active site) on the enzyme. [1]
This binding changes the shape of the enzyme, including the active site. [1]
The active site is no longer complementary to the substrate, so the substrate cannot bind, reducing the rate of reaction. [1]

19. (a)

DNA replication occurs. [1]
The amount of DNA in the cell doubles (from 2n to 4n content, though chromosome number remains 2n until division). [1]

(b)

Semi-conservative replication means each new DNA molecule contains one original (parental) strand and one new strand. [1]
This ensures that the genetic information is conserved and passed on accurately to daughter cells, maintaining genetic stability. [1]

20. Marking Guide for Extended Response (6 Marks):

Level 3 (5-6 marks): Detailed explanation of at least three properties with clear biological examples. Logical structure.
Level 2 (3-4 marks): Explanation of two or three properties, but examples may be generic or less detailed.
Level 1 (1-2 marks): Mentions properties but lacks explanation or biological context.

Indicative Content:

Solvent Property:
- Water is polar, dissolving ions and polar molecules (e.g., glucose, amino acids, salts).
- Significance: Allows metabolic reactions to occur in solution; transports nutrients and waste in blood/plasma.
High Specific Heat Capacity:
- Water requires a lot of energy to change temperature due to hydrogen bonding.
- Significance: Buffers temperature changes in organisms and aquatic environments, maintaining stable conditions for enzyme activity.
High Latent Heat of Vaporisation:
- Much energy is needed to break hydrogen bonds to turn water into gas.
- Significance: Effective cooling mechanism via sweating/panting in mammals; transpiration cooling in plants.
Cohesion/Adhesion:
- Water molecules stick to each other (cohesion) and to other surfaces (adhesion).
- Significance: Enables transpiration stream in plants (water column in xylem); surface tension supports small organisms (e.g., water striders).
Metabolite:
- Water is a reactant in hydrolysis and photosynthesis.
- Significance: Essential for digestion of macromolecules and production of glucose in plants.

Award 1 mark for each property identified and explained with biological significance, up to a maximum of 6 marks.