Biology - Human Body Systems, Plants, Ecosystems and the Environment
This domain tests how organ systems maintain the body, how plants transport and make food, and how energy and matter move through ecosystems. Expect questions linking structure to function and interpreting food webs and pyramids.
Human body systems
Digestion breaks food into absorbable nutrients; villi in the small intestine increase absorption. Alveoli provide thin, moist surfaces for gas exchange. The heart pumps blood: arteries carry blood away from the heart, veins return it, and capillaries allow exchange. The kidneys filter blood and regulate water and salts. Nervous and hormonal signals coordinate responses.
Plants
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, using light and chlorophyll. Respiration occurs day and night. Xylem transports water and minerals upward; phloem transports sugars. Transpiration pulls water through the plant and cools leaves; stomata regulate gas exchange and water loss.
Ecosystems
Producers make food; consumers eat other organisms; decomposers break down dead matter and recycle nutrients. Energy flows through food chains and is lost as heat at each step, roughly 90% per level. Matter cycles through carbon, nitrogen, and water cycles. Biodiversity supports ecosystem stability.
Worked example
A grassland has 10,000 J of energy in producers. With about 10% transfer, primary consumers receive 1,000 J, secondary consumers 100 J, and tertiary consumers 10 J. This explains why top predators are few and why food chains are short.
Traps
Plants respire all the time, not only at night. Xylem carries water upward; phloem carries sugars. Arteries carry blood away from the heart, but pulmonary arteries carry deoxygenated blood. Decomposers recycle nutrients, not energy. Arrows in food chains show energy flow, not “who eats whom” in reverse.