Biology - Structure and Function of the Human Body and Reproduction
This domain covers digestion, circulation, respiration, excretion, nervous control, and reproduction. Niigata questions often ask you to trace a substance through the body or explain a homeostatic response such as heart rate during exercise.
Digestion and absorption
- Mechanical digestion occurs in the mouth and stomach; chemical digestion uses enzymes.
- Salivary amylase: starch → maltose; pepsin: protein → peptides in the acidic stomach; pancreatic enzymes and lipase work in the small intestine.
- Bile from the liver is stored in the gallbladder and emulsifies fat.
- Villi increase surface area; nutrients are absorbed into blood or lymph.
Circulation and respiration
- The right side of the heart sends blood to the lungs; the left side sends blood to the body. Arteries carry blood away; veins carry it toward the heart.
- Capillaries exchange gases and nutrients.
- Breathing: the diaphragm contracts and moves down; ribs move up and out; alveoli exchange O₂ and CO₂ by diffusion.
- Cellular respiration: glucose + oxygen → CO₂ + water + energy.
Excretion and control
- Kidneys filter blood and form urine; the liver detoxifies; skin excretes water and salts.
- Reflex arc: receptor → sensory neuron → CNS → motor neuron → effector.
- Insulin lowers blood glucose; adrenaline raises heart rate and glucose.
Reproduction
- Testes produce sperm and testosterone; ovaries produce eggs and estrogen and progesterone.
- Fertilization occurs in the fallopian tube; implantation in the uterus; the placenta exchanges materials without mixing maternal and fetal blood.
- Gestation is about 38 weeks.
Worked example
A person has stroke volume 70 mL and heart rate 75 beats/min. Cardiac output = 70 × 75 = 5,250 mL/min ≈ 5.3 L/min. During exercise, heart rate and stroke volume rise because muscles need more O₂ and produce more CO₂; the medulla increases sympathetic signals, so output can reach about 20 L/min.
Traps
- Saying the left heart sends blood to the lungs.
- Calling all arteries oxygenated.
- Confusing the digestion site with the absorption site.
- Saying maternal and fetal blood mix in the placenta.
- Reversing the reflex arc.