IB DP Biology- D1.1 DNA replication - IB Style Questions For SL Paper 2 - FA 2025

(a)
Roles of progesterone in the menstrual cycle:
1. Produced by the corpus luteum in the ovaries after ovulation, stimulated by LH.
2. Inhibits FSH and LH secretion via negative feedback.
3. Prevents follicle development and maturation by inhibiting FSH.
4. Prevents ovulation by inhibiting LH.
5. Maintains and increases the thickness of the endometrium (uterus lining).
6. Levels fall if egg is not fertilized, causing corpus luteum degeneration and menstruation.
✅ Answer: Four key points required for full marks.

(b)
Polymerase Chain Reaction (PCR) process:
1. Amplifies DNA/makes many copies of a specific DNA sequence.
2. Heated to high temperature to denature DNA/separate strands/break hydrogen bonds.
3. Cooled to allow primers to bind to complementary sequences on DNA strands.
4. Heat-stable Taq polymerase extends primers by adding nucleotides.
5. Taq polymerase joins nucleotides forming new DNA strands.
6. Cycle repeated multiple times to exponentially amplify DNA.
✅ Answer: Four key points required for full marks.

(c)
Carbon recycling in terrestrial ecosystems:
1. Plants/autotrophs use CO₂ in photosynthesis to produce organic compounds.
2. Carbon converted to glucose/starch/cellulose/fats/proteins in plants.
3. Carbon transferred to consumers through feeding/food chains.
4. CO₂ released by respiration from plants, animals, and decomposers.
5. Dead organic matter from plants and animals accumulates.
6. Saprotrophs/decomposers digest dead matter and release CO₂ through respiration.
7. Fossilization/incomplete decomposition produces fossil fuels (coal, oil, gas).
8. Combustion of fossil fuels/biomass releases CO₂ back to atmosphere.
9. Anaerobic decomposition can produce methane from ruminants or wetlands.
✅ Answer: Seven key points required for full marks.