Life Processes and Control and Coordination
Life Processes and Control and Coordination covers nutrition, respiration, transport, excretion, and how nervous and endocrine systems coordinate responses. Expect diagram-based reasoning and function comparisons.
Core ideas
- Autotrophic nutrition uses photosynthesis: carbon dioxide + water -> glucose + oxygen in the presence of chlorophyll and light.
- Aerobic respiration releases more energy than anaerobic respiration. Anaerobic respiration in muscles produces lactic acid; in yeast it produces ethanol and carbon dioxide.
- Transport: xylem carries water and minerals upward; phloem carries food. In humans, arteries carry blood away from the heart and veins carry it back; capillaries allow exchange.
- Excretion removes wastes: kidneys filter blood and form urine; nephrons are the filtering units.
- Nervous coordination uses neurons and electrical impulses; a reflex action is a fast, automatic response through a reflex arc.
- Endocrine coordination uses hormones such as insulin, which lowers blood glucose, and thyroxine, which controls metabolic rate.
Worked example
A person touches a hot pan and withdraws the hand before feeling pain. Trace the reflex arc: heat receptors in the skin -> sensory neuron -> spinal cord -> motor neuron -> arm muscle contracts. Reasoning: the spinal cord coordinates the reflex quickly; the brain receives the signal and registers pain slightly later.
Traps that cost marks
Arteries are not always oxygen-rich: the pulmonary artery carries deoxygenated blood. Photosynthesis and respiration are not opposites in timing; respiration occurs all the time. Do not say xylem carries food. Reflexes are not decided by conscious thought.