IB HL Biology Key Things to Remember

Personally for Connor Jung in preparation for May 2025

Steps of Photosynthesis

• light-independent reactions in stroma of chloroplast

• using energy/ATP from light-dependent reactions

• Calvin cycle carries out light-independent reactions

• Cycle begins with a 5C compound (ribulose bisphosphate/RuBP)

• CO2 from atmosphere is fixed to RuBP

• catalyzed by Rubisco

• Two 3C compounds (aka glycerate-3-phosphate or G3P

• G3P is reduced

• Using electrons/hydrogen (atoms) from NADPH

• 2 triose phosphate (molecules) used to form a glucose

• Some triose phosphate molecules used to make more/regenerate RuBPand continue the cycle.

Steps of Cellular Respiration

• Glycolysis (occurs in the cytoplasm)

  • Glucose (6C) is phosphorylated using 2 ATP.

  • Converted into two 3C molecules of triose phosphate.

  • Triose phosphate is oxidized; 2 NAD⁺ are reduced to 2 NADH.

  • Produces 4 ATP (net gain of 2 ATP) via substrate-level phosphorylation.

  • Ends with two molecules of pyruvate (3C).

• Link Reaction (occurs in the mitochondrial matrix)

  • Pyruvate (3C) is decarboxylated (removal of CO₂).

  • Oxidized to form acetate; NAD⁺ is reduced to NADH.

  • Acetate combines with Coenzyme A to form acetyl-CoA (2C).

• Krebs Cycle (Citric Acid Cycle) (mitochondrial matrix)

  • Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C).

  • Citrate undergoes decarboxylation (releasing 2 CO₂) and oxidation.

  • Produces 3 NADH, 1 FADH₂, and 1 ATP (per acetyl-CoA).

  • Regenerates oxaloacetate for the cycle to continue.

• Electron Transport Chain (ETC) and Oxidative Phosphorylation (inner mitochondrial membrane)

  • NADH and FADH₂ donate electrons to the ETC.

  • Electrons pass through carriers, releasing energy to pump H⁺ into intermembrane space (creating a proton gradient).

  • Oxygen is the final electron acceptor, forming water (O₂ + 4e⁻ + 4H⁺ → 2H₂O).

  • H⁺ diffuses back into the matrix via ATP synthase (chemiosmosis), driving ATP production.

  • ~34 ATP generated from oxidative phosphorylation.

Entire Menstrual Cycle process

• follicle stimulating hormone (FSH) is secreted from the anterior pituitary and stimulates growth of ovarian follicles

• The dominant follicle produces estrogen, which inhibits FSH secretion via negative feedback to prevent other follicles growing

• idway through the cycle (~ day 12), estrogen concentrations reach a critical threshold which stimulates the anterior pituitary to release a large surge of luteinizing hormone (LH) and a lesser surge of FSH

• LH causes the dominant follicle to rupture and release an egg (secondary oocyte) – this is called ovulation

• The ruptured follicle develops into a corpus luteum that secretes high levels of progesterone, as well as lower levels of estrogen

• Estrogen and progesterone inhibit the further secretion of FSH and LH, preventing other follicles from developing while the corpus luteum is active

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