Respiration and Plant Growth and Development
What the exam tests
Plant respiration and growth and development include aerobic and anaerobic respiration, the respiratory quotient, growth phases, plant hormones, photoperiodism, vernalization, and seed dormancy.
Core rules
- Glycolysis occurs in the cytoplasm; the Krebs cycle and electron transport chain occur in mitochondria. Aerobic respiration yields more ATP than fermentation. The respiratory quotient (RQ) = CO2 released / O2 consumed.
- Growth has lag, log, and stationary phases; meristems provide indeterminate growth. Differentiation, dedifferentiation, and redifferentiation allow tissue culture.
- Hormones: auxin promotes apical dominance and rooting; gibberellin promotes stem elongation and seed germination; cytokinin promotes cell division; ABA closes stomata and induces dormancy; ethylene promotes ripening and senescence.
- Photoperiodism controls flowering in short-day and long-day plants; vernalization is cold treatment that promotes flowering.
Worked example
A respiring tissue consumes 6 O2 and releases 6 CO2 per glucose molecule. RQ = 6/6 = 1.0, indicating carbohydrate respiration. If a fat is respired, more O2 is consumed than CO2 released, so RQ is less than 1 (about 0.7). If an organic acid is respired, RQ is greater than 1. Reasoning: RQ reflects the chemical composition of the respiratory substrate, not the rate of respiration.
Traps
Do not state that fermentation produces ATP in the mitochondria; it occurs in the cytoplasm. Auxin does not always promote growth-high concentrations can inhibit. Ethylene is a gas, not a nutrient. Photoperiodism depends on night length, not just day length. Vernalization is not the same as photoperiodism.