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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: ______ / 68
Duration: 1 hour 30 minutes

Instructions: Answer all questions in the spaces provided. Where a figure is referenced, a description is provided; base your answer on standard biological knowledge and, where applicable, on the concepts described.

Describe the arrangement of phospholipid molecules in a cell membrane. [2]
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Organelle A is a double-membraned structure with inner membranes folded into cristae. Organelle B is a network of flattened membrane sacs studded with ribosomes.
(a) Name organelle A and organelle B. [2]
Organelle A: ……………………
Organelle B: ……………………
(b) State the main function of each organelle in a mammalian liver cell. [2]
A: ………………………………………………………………………………
B: ………………………………………………………………………………
Radioactive thymidine is added to a culture of dividing mammalian cells. After a short period, radioactivity is detected in the nuclei.
(a) With reference to the cell cycle, identify the phase during which radioactive thymidine is first incorporated into the nuclear DNA. [1]
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(b) Explain why radioactivity appears in the nuclei during this phase. [2]
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Isolated mitochondria were incubated with either pyruvate or glucose. When pyruvate was supplied, carbon dioxide was produced; when glucose was supplied, no carbon dioxide was produced.
(a) Explain why carbon dioxide is produced when mitochondria are incubated with pyruvate. [2]
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(b) Explain why no carbon dioxide is produced when mitochondria are incubated with glucose. [1]
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Fig. 5.1 shows part of a cell membrane containing aquaporins.
Describe how water molecules move across this membrane. [2]
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Table 6.1 below shows the activity of enzyme X at different temperatures.

Temperature (°C) Relative activity (%)
10 25
20 40
30 65
37 100
45 75
60 10

(a) Explain why enzyme X is most active at 37°C. [1]
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(b) Account for the sharp decrease in activity at 60°C. [2]
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Amylose is a polysaccharide that serves as an energy storage molecule in plants.
Describe the structure of amylose and explain how this structure relates to its function. [4]
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Compare the structure and functions of a triglyceride and a phospholipid. [4]
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When a protein is heated to 80°C, it loses its biological activity.
Explain this observation in terms of the levels of protein structure. [3]
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Fig. 10.1 illustrates a short segment of a DNA double helix, with three components of a nucleotide labelled X, Y and Z.
(a) Identify X, Y and Z. [2]
X: ……………………… Y: ……………………… Z: ………………………
(b) State the type of chemical bond that links adjacent nucleotides in a polynucleotide strand. [1]
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Describe the fluid mosaic model of membrane structure. [4]
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Compare active transport and facilitated diffusion, giving one example of each process in a typical animal cell. [4]
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Water has a high specific heat capacity and exhibits cohesion.
Explain the importance of each of these properties to living organisms. [4]
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Compare the structure and function of glycogen and cellulose. [5]
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Distinguish between competitive and non-competitive inhibition of an enzyme. [4]
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Describe how a cell takes in large particles by endocytosis and how it releases proteins by exocytosis. [4]
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State the functions of the nucleus and the nucleolus in a eukaryotic cell. [3]
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Compare the cell walls of a typical prokaryotic cell and a plant cell. [3]
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A plant cell is placed in a hypertonic solution.
Describe the changes that occur and explain the reason for these changes. [3]
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State three structural or chemical differences between DNA and RNA. [3]
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Temperature (°C)	Relative activity (%)
10	25
20	40
30	65
37	100
45	75
60	10

Answers

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

Phospholipid arrangement [2]
- Phospholipids form a bilayer; [1]
- Hydrophilic phosphate heads face outward towards the aqueous environment (cytoplasm/extracellular fluid); hydrophobic fatty acid tails face inward, away from water. [1]
(a) Organelles [2]
- A: mitochondrion; B: rough endoplasmic reticulum (rough ER).
  (b) Functions in a liver cell [2]
- Mitochondrion: site of aerobic respiration / synthesis of ATP.
- Rough ER: synthesis of proteins / transport of proteins.
(a) Phase [1] – S phase (synthesis phase).
(b) Explanation [2]
- During S phase, DNA replication occurs;
- radioactive thymidine is incorporated as a precursor of thymine into newly synthesised DNA, so radioactivity concentrates in the nuclei.
(a) CO₂ from pyruvate [2]
- Pyruvate enters the mitochondrial matrix and is converted to acetyl‑CoA, which enters the Krebs cycle;
- CO₂ is released during the Krebs cycle.
  (b) No CO₂ from glucose [1]
- Glucose cannot enter the Krebs cycle directly; glycolysis (before CO₂ production) occurs in the cytoplasm, and isolated mitochondria lack the necessary glycolytic enzymes.
Water movement [2]
- Water moves by osmosis / facilitated diffusion through aquaporins;
- moves down the water potential gradient / from higher water potential to lower water potential.
(a) Optimum activity [1]
- 37°C is the optimum temperature; kinetic energy and molecular collisions are maximal while the enzyme’s tertiary structure is maintained.
  (b) Decrease at 60°C [2]
- High temperature disrupts hydrogen bonds, ionic bonds and hydrophobic interactions that maintain the enzyme’s specific three‑dimensional shape;
- the active site denatures, substrate can no longer bind, and activity falls to low levels.
Amylose structure–function [4]
- Amylose is a linear polymer of α‑glucose units linked by α‑1,4 glycosidic bonds;
- it coils into a helical shape;
- its compact helical shape allows it to pack tightly, storing large amounts of glucose in a small volume;
- it is insoluble so does not affect water potential;
- it can be readily hydrolysed to release glucose for respiration.
  (Any four points)
Triglyceride vs phospholipid [4]
- Triglyceride: one glycerol + three fatty acids; function: long‑term energy storage, insulation, protection.
- Phospholipid: one glycerol + two fatty acids + a phosphate group; amphipathic; function: major component of cell membranes, forming the bilayer.
  (2 marks structure, 2 marks function, credit comparison)
Protein denaturation [3]
- The protein’s tertiary structure is maintained by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges;
- heating provides kinetic energy that breaks these weak bonds, causing the protein to lose its precise conformation (denaturation);
- the active site or binding site is altered, so the protein can no longer function. (Primary structure remains intact.)
(a) Identifications [2]
- X: deoxyribose sugar; Y: phosphate group; Z: nitrogenous base (any specific base acceptable).
  (b) Bond [1] – Phosphodiester bond.
Fluid mosaic model [4]
- Membrane is composed of a phospholipid bilayer;
- proteins are scattered throughout, embedded (integral) or on the surface (peripheral);
- membrane is fluid because phospholipids and some proteins can move laterally;
- cholesterol stabilises fluidity;
- carbohydrate chains attach to proteins/lipids on the outer surface (glycocalyx) involved in cell recognition.
  (Any four features)
Active transport vs facilitated diffusion [4]
- Active transport requires metabolic energy (ATP) to move substances against their concentration gradient; e.g., Na⁺/K⁺ pump.
- Facilitated diffusion moves substances down their concentration gradient through protein channels/carriers without energy; e.g., glucose uptake via GLUT proteins.
Water properties [4]
- High specific heat capacity: water absorbs/releases large amounts of heat with minimal temperature change → stable thermal environment for aquatic organisms, helps maintain constant internal temperature.
- Cohesion: water molecules stick together via hydrogen bonds → enables water transport in plants (transpiration stream) and surface tension for some organisms.
Glycogen vs cellulose [5]
- Glycogen: branched polymer of α‑glucose with α‑1,4 and α‑1,6 glycosidic bonds; compact; stored in liver/muscle; easily hydrolysed for energy.
- Cellulose: linear polymer of β‑glucose linked by β‑1,4 glycosidic bonds; parallel chains form microfibrils via hydrogen bonds; main component of plant cell walls; provides structural support; indigestible by most animals.
  (Structure 2, function 2, comparison 1)
Competitive vs non‑competitive inhibition [4]
- Competitive inhibitor: structurally similar to substrate; binds to the active site, preventing substrate binding; effect can be overcome by increasing substrate concentration.
- Non‑competitive inhibitor: binds to an allosteric site (not active site); alters shape of active site so substrate cannot bind; cannot be overcome by increasing substrate concentration.
Endocytosis and exocytosis [4]
- Endocytosis: cell membrane invaginates, forming a vesicle around large particles (phagocytosis) or fluid (pinocytosis); vesicle pinches off into cytoplasm.
- Exocytosis: vesicles containing proteins (e.g., secretory vesicles from Golgi) move to and fuse with the cell membrane, releasing contents outside; requires ATP.
Nucleus and nucleolus [3]
- Nucleus: contains most genetic material (DNA), controls cellular activities via gene expression; site of DNA replication and transcription. (2 marks)
- Nucleolus: synthesises rRNA and assembles ribosomal subunits. (1 mark)
Prokaryotic vs plant cell wall [3]
- Prokaryotic cell wall: composed of peptidoglycan (murein); provides shape and protection.
- Plant cell wall: composed mainly of cellulose; provides structural support, may contain lignin.
- Both are external to the cell membrane.
Plant cell in hypertonic solution [3]
- Water moves out of the cell by osmosis (from higher water potential to lower water potential);
- the vacuole shrinks, the plasma membrane pulls away from the cell wall (plasmolysis);
- the cell becomes flaccid and loses turgor pressure.
DNA vs RNA differences [3]
- DNA: deoxyribose sugar; RNA: ribose sugar.
- DNA bases: A, T, C, G; RNA bases: A, U, C, G.
- DNA is double‑stranded; RNA is usually single‑stranded.
  (Any three clear differences accepted)