A Level H1 Biology Cells Biomolecules Quiz

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

Section A

1. Phospholipid Arrangement: Phospholipids form a bilayer [1]. Hydrophilic heads face the aqueous environment (extracellular/cytoplasm) and hydrophobic tails face inward, away from water [1].
2. Golgi Apparatus: Modification of proteins (e.g., glycosylation) [1] and packaging them into secretory vesicles for transport to the cell surface/exocytosis [1].
3. Organelle: Smooth Endoplasmic Reticulum (SER). [1]
4. Fluid Mosaic Model: "Fluid" refers to the ability of phospholipids and proteins to move laterally within the layer [1]. "Mosaic" refers to the diverse proteins embedded in or attached to the bilayer [1].
5. Nucleolus: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly. [1]
6. Bond: Peptide bond. [1]
7. Protein: Aquaporin. [1]
8. Genetic Storage: Prokaryotes have circular DNA located in the nucleoid region/cytoplasm (no membrane) [1]; Eukaryotes have linear DNA enclosed within a membrane-bound nucleus [1].

Section B

9. (a) S phase. [1] (b) Thymidine is a nucleotide analogue [1]. During S phase, DNA replication occurs, and thymidine is incorporated into the newly synthesized DNA strands [1].
10. G1 to S: DNA amount doubles as replication occurs [1]. S to G2: DNA amount remains constant [1]. M phase: DNA amount is halved as sister chromatids separate into two daughter nuclei [1].
11. Glucose moves via facilitated diffusion [1]. It binds to a specific carrier protein [1], which changes shape to move the glucose down its concentration gradient [1].
12. Glucose is a large, polar molecule [1]. It is repelled by the hydrophobic core of the phospholipid bilayer [1].
13. (a) Pyruvate can enter the mitochondrial matrix to be converted to Acetyl-CoA and enter the Krebs cycle [1]. Glucose requires glycolysis to be converted to pyruvate [1], but the enzymes for glycolysis are located in the cytoplasm, not the mitochondria [1]. (b) Mitochondrial matrix. [1]
14. RER: Studded with ribosomes [1], synthesizes proteins for secretion or membrane insertion [1]. SER: Lacks ribosomes [1], synthesizes lipids/steroids and detoxifies toxins [1].
15. Phospholipid is amphipathic [1]. Hydrophilic head attracts water [1], while hydrophobic tail repels water, forcing the molecules to align tails-to-tails to minimize contact with water [1].
16. Increasing temperature increases kinetic energy of molecules [1]. This increases the frequency of successful collisions between enzyme active site and substrate [1]. Rate increases until the optimum temperature is reached [1].

Section C

17. Membrane Transport & Photosynthesis:
    • CO₂ entry: Diffuses from high concentration (air) to low concentration (leaf) across stomata and cell membranes [1].
    • Water uptake: Osmosis across root cell membranes is essential for photolysis in PSII [1].
    • Ion transport: Active transport of Mg²⁺ (central atom of chlorophyll) and K⁺ (stomata regulation) [1].
    • Product export: Glucose/sucrose transported out of chloroplasts/cells via transport proteins [1].
    • Regulation: Membrane permeability controls the rate of raw material entry, thus limiting the photosynthetic rate [1].
    • Integration: Without selective permeability, the chloroplast could not maintain the proton gradient necessary for ATP synthesis [1].
18. DNA Structure & Storage:
    • Double helix structure with antiparallel strands [1].
    • Sugar-phosphate backbone held by phosphodiester bonds [1].
    • Nitrogenous bases (A, T, C, G) paired by hydrogen bonds (A-T, C-G) [1].
    • Sequence of bases constitutes the genetic code [1].
    • Complementary nature allows for accurate replication and transcription [1].
19. Protein Structure:
    • Primary: Linear sequence of amino acids [1].
    • Secondary: Folding into alpha-helices or beta-pleated sheets via hydrogen bonds [1].
    • Tertiary: Overall 3D folding due to R-group interactions (disulfide bridges, ionic, hydrophobic) [1].
    • Change in primary structure (mutation) changes the R-groups present [1].
    • This alters the folding/tertiary structure [1].
    • The active site or binding site is deformed, leading to loss of function [1].
20. Active Transport vs. Facilitated Diffusion:
    • Similarities: Both use transmembrane proteins (carriers/channels) [1]. Both move substances that cannot cross the bilayer alone [1].
    • Differences (Direction): Facilitated diffusion is passive (down gradient) [1]; Active transport is against the gradient [1].
    • Differences (Energy): Facilitated diffusion requires no ATP [1]; Active transport requires ATP hydrolysis [1].
    • Differences (Protein): Facilitated diffusion can use channels or carriers [1]; Active transport uses specific pump proteins [1].