Animal Structure, Function and Physiology
This domain tests how mammalian and other animal systems exchange materials, transport them and maintain internal stability. Expect digestion, gas exchange, circulation, excretion, nervous and endocrine control, and homeostasis.
Digestion and gas exchange
Digestive enzymes are named by substrate: amylases break down starch, proteases hydrolyse proteins and lipases hydrolyse lipids. Villi in the ileum increase surface area for absorption. Alveoli provide a large, thin, moist surface with a steep diffusion gradient; fish gills use countercurrent exchange, and insects use tracheae.
Circulation and excretion
Mammals have double circulation; arteries carry blood away from the heart and veins return it. The pulmonary artery carries deoxygenated blood. Cardiac output = stroke volume × heart rate. In the nephron, filtration occurs at the glomerulus, selective reabsorption in the proximal tubule, and the loop of Henle creates a medullary osmotic gradient. ADH increases collecting-duct permeability, reducing urine volume.
Homeostasis and control
Negative feedback corrects deviations. Insulin lowers blood glucose and glucagon raises it. Thermoregulation uses vasodilation, sweating and shivering. Neurones transmit impulses; synapses use neurotransmitters.
Worked example
Stroke volume is 70 cm³ and heart rate is 72 beats min⁻¹. Cardiac output = 70 × 72 = 5040 cm³ min⁻¹, about 5.0 dm³ min⁻¹. During exercise both stroke volume and heart rate rise, so output increases several-fold.
Traps
Do not call the pulmonary artery oxygenated. Distinguish afferent from efferent arterioles. ADH reduces urine volume; it does not increase it. Do not confuse reabsorption with secretion in the nephron.