Animal Structure and Physiology
Animal Structure and Physiology
This domain tests digestion, gas exchange, circulation, excretion, nervous coordination, hormones and homeostasis. Questions often ask you to follow a substance through the body or explain how a variable is regulated.
Core rules
- Villi increase surface area for absorption. Enzymes hydrolyse carbohydrates to monosaccharides, proteins to amino acids, and lipids to fatty acids and glycerol.
- Mammals have double circulation. Arteries carry blood away from the heart; veins carry it back; capillaries allow exchange. The pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein returns oxygenated blood.
- Nephrons form urine by filtration, selective reabsorption and secretion. The loop of Henle helps create a salt gradient for water reabsorption.
- A reflex arc passes from receptor to sensory neurone, relay neurone and motor neurone to effector.
Worked example
Heart rate is 70 beats per minute and stroke volume is 70 mL. Cardiac output = heart rate × stroke volume = 70 × 70 = 4900 mL per minute, about 4.9 L/min. Reasoning: cardiac output is the volume pumped by one ventricle each minute.
Traps
Not all arteries carry oxygenated blood. The pulmonary vein is oxygenated. Most reabsorption occurs in the proximal convoluted tubule, not the collecting duct. A reflex can be coordinated by the spinal cord without conscious brain input. Hormones travel in blood but act only on target cells with receptors.