Plant and Animal Structure and Function
Plant and Animal Structure and Function
This domain tests how multicellular organisms maintain homeostasis through specialized tissues, organs, and systems. Expect questions on plant transport, transpiration, hormones, and on animal circulation, respiration, digestion, excretion, nervous control, endocrine signaling, immunity, and reproduction. You must predict physiological responses to environmental change.
Core rules and concepts
- Xylem transports water and minerals upward; phloem transports sugars. Cohesion-tension, root pressure, and transpiration pull water through xylem.
- Stomata open for CO2 uptake but lose water; abscisic acid closes stomata under drought stress.
- Animal systems use negative feedback to stabilize internal conditions. Examples include insulin lowering blood glucose and osmoreceptors triggering ADH release.
- Mammalian circulation is a double circuit; arteries carry blood away from the heart, veins return it, and capillaries exchange materials.
- The nephron filters blood, reabsorbs useful solutes and water, and secretes wastes.
- Plant hormones include auxin, gibberellin, cytokinin, ethylene, and abscisic acid.
Worked example
On a hot, dry day, a plant wilts because transpiration from leaves exceeds water uptake by roots. Water loss lowers turgor pressure in leaf cells. The plant responds by producing abscisic acid, which closes stomata and reduces further water loss, though it also limits CO2 entry and photosynthesis. If water uptake resumes, turgor returns and the plant recovers. The reasoning links an environmental variable to a hormonal response and then to a whole-plant water balance, not just to one tissue.
Traps that cost marks
- Reversing xylem and phloem functions.
- Confusing arteries and veins with oxygenated and deoxygenated blood; the pulmonary artery carries deoxygenated blood.
- Treating positive feedback as the main mechanism of homeostasis.
- Ignoring that stomatal closure reduces both water loss and carbon gain.