Plant Science: Anatomy, Physiology, Growth and Development
What this domain covers
This domain tests plant tissues and organs, water and food transport, photosynthesis and respiration, and the hormonal control of growth, flowering and maturity.
Core rules and concepts
- Meristematic tissues (apical, lateral, intercalary) produce new cells; permanent tissues are simple (parenchyma, collenchyma, sclerenchyma) or complex (xylem, phloem).
- Xylem carries water and minerals upward and is mostly dead tissue (tracheids, vessels). Phloem carries food and is living (sieve tubes with companion cells).
- Root absorbs water and minerals and anchors the plant; stem supports and conducts; leaf performs photosynthesis and transpiration through stomata.
- Photosynthesis: 6CO2 + 6H2O gives C6H12O6 + 6O2, light reaction in thylakoids and Calvin cycle in the stroma. C3 and C4 plants differ in their first carbon product.
- Growth has three phases: cell division, cell elongation and cell differentiation. Flowering is influenced by photoperiod and temperature.
- Hormones: auxin (rooting, apical dominance), gibberellin (stem elongation, bolting), cytokinin (cell division), abscisic acid (stomatal closure, dormancy) and ethylene (ripening, abscission).
Worked example
A crop shows interveinal chlorosis on the youngest leaves while older leaves remain green. Because the young leaves are affected first, the deficient nutrient is immobile in the plant, so the plant cannot move it from old tissue; iron is the likely cause. If instead the older leaves yellow first, the nutrient is mobile (nitrogen or magnesium) and is being shifted to growing points. This reasoning uses mobility, not leaf colour alone.
Traps that cost marks
- Reversing the direction of xylem and phloem transport.
- Assuming stomata occur only on the lower surface; in many monocots they occur on both surfaces.
- Confusing ethylene (ripening) with gibberellin (elongation).
- Confusing immobile-nutrient symptoms on young leaves with mobile-nutrient symptoms on old leaves.