A Level H1 Biology Cells Biomolecules Quiz

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

Section A: Cell Structure and Organelles

1. Answer: Prokaryotic genetic material is circular and "naked" (not associated with histones), whereas eukaryotic genetic material is linear and associated with histone proteins. [1]
2. (a) Answer: Secretory cell (e.g., pancreatic cell producing enzymes). [1] (b) Answer: Proteins are synthesized on the ribosomes of the RER (1); they are then transported via vesicles to the Golgi apparatus for modification, sorting, and packaging into secretory vesicles (1). [2]
3. Answer: Smooth Endoplasmic Reticulum (SER). [1]
4. Answer: Structure: Dense region of RNA and proteins within the nucleus (1). Function: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly (1). [2]
5. Answer: Mitochondria have an inner membrane folded into cristae to increase surface area for the ETC/ATP synthase (1). Chloroplasts have an internal system of thylakoids stacked into grana (1), providing a large surface area for light-harvesting pigments (1). [3]
6. Answer: To increase the surface area of the inner membrane (1), allowing for more electron transport chains and ATP synthase complexes to be embedded, thereby increasing ATP production (1). [2]
7. Answer: Lysosome (1). In autophagy, the lysosome fuses with a vacuole containing damaged organelles, and its hydrolytic enzymes break down the organelle components for recycling (1). [2]

Section B: Biological Molecules

8. Answer: A condensation reaction occurs (1) between the hydroxyl (-OH) groups of two $\alpha$-glucose molecules, releasing a molecule of water (1). [2]
9. Answer: Amylose is an unbranched chain of $\alpha$-glucose linked by 1,4-glycosidic bonds (1), forming a helix (1). Amylopectin is branched due to the presence of 1,6-glycosidic bonds (1). [3]
10. Answer: Triglycerides are highly reduced/contain more C-H bonds per unit mass than glycogen (1), providing more energy upon oxidation (1). They are hydrophobic and stored without water, making them more compact/less heavy than hydrated glycogen (1). [3]
11. Answer: Primary structure is the specific sequence of amino acids in a polypeptide chain (1). The R-groups of these amino acids interact (via H-bonds, ionic bonds, hydrophobic interactions, etc.) (1) to fold the protein into a specific 3D shape (1). [3]
12. Answer: In $\alpha$-helix, H-bonds form between the C=O and N-H groups of the same polypeptide chain every 4th amino acid (1). In $\beta$-pleated sheets, H-bonds form between parallel or anti-parallel segments of the polypeptide chain (1). [2]
13. Answer: Strong covalent bonds form between the sulfur atoms of two cysteine residues (1), locking the tertiary structure in place and providing stability (1). [2]
14. Answer: Cohesion is the attraction between water molecules due to hydrogen bonding (1). In tall plants, this allows water to be pulled up the xylem as a continuous column (transpiration pull) (1), ensuring water reaches the leaves from the roots (1). [3]

Section C: Membrane Structure and Transport

15. Answer: Phospholipids form a bilayer with hydrophilic heads facing the aqueous environments (inside/outside) (1) and hydrophobic tails facing inward (1). This is spontaneous because it minimizes the contact of hydrophobic tails with water, reaching a lower energy state (1). [3]
16. Answer: "Fluid" refers to the ability of phospholipids and proteins to move laterally within the membrane (1). "Mosaic" refers to the varied proteins (integral/peripheral) embedded in or attached to the phospholipid bilayer (1), creating a patchy appearance (1). [3]
17. (a) Answer: Facilitated diffusion. [1] (b) Answer: The substance moves down its concentration gradient (1), meaning the process is passive and driven by kinetic energy/entropy rather than metabolic energy (1). [2]
18. Answer: Uses carrier proteins to move ions against a concentration gradient (1). ATP is hydrolyzed to provide energy (1). For the Na+/K+ pump: 3 Na+ ions are pumped out and 2 K+ ions are pumped in (1), maintaining electrochemical gradients (1). [4]
19. Answer: Endocytosis is the engulfing of materials into the cell via vesicle formation (1) (e.g., phagocytosis of bacteria by macrophages). Exocytosis is the fusion of a vesicle with the plasma membrane to release contents outside (1) (e.g., release of insulin from beta cells). [4]
20. Answer: At high temperatures, cholesterol restricts the movement of phospholipids, preventing the membrane from becoming too fluid/leaky (1). At low temperatures, it prevents phospholipids from packing too tightly, preventing the membrane from freezing/becoming too rigid (1). This maintains optimal membrane fluidity (1), ensuring proteins can function and the membrane remains a selective barrier (1). This is crucial for maintaining homeostasis in mammals (1). [5]