The essential processes that keep living things alive
Life processes are the basic functions that maintain living organisms: nutrition, respiration, transport and excretion. In autotrophic nutrition, green plants make food by photosynthesis, using carbon dioxide, water and sunlight, with chlorophyll in chloroplasts; oxygen is released through stomata. In heterotrophic nutrition, animals depend on other organisms; in humans, food is digested along the alimentary canal with enzymes and absorbed in the small intestine.
Respiration releases energy from glucose. Aerobic respiration uses oxygen and gives carbon dioxide, water and plenty of energy, while anaerobic respiration happens without oxygen, producing ethanol in yeast or lactic acid in muscles, which causes cramps. In humans, blood carries oxygen, food and waste through a double circulation powered by a four-chambered heart. In plants, xylem transports water and minerals upward, helped by transpiration, and phloem carries food in translocation. Excretion removes waste: in humans, nephrons in the kidneys filter blood to form urine, while plants lose waste through falling leaves and resins.
Why it matters
Understanding life processes explains why exercise makes you breathe faster, how athletes get muscle cramps, why kidneys failing need dialysis and why plants wilt without water. Photosynthesis is the source of almost all food and oxygen on Earth. This chapter is the base for human physiology and plant physiology in Classes 11 and 12.
Key terms
- Photosynthesis
- The process by which green plants make glucose from carbon dioxide and water using sunlight.
- Aerobic respiration
- Breaking down glucose with oxygen to release energy, carbon dioxide and water.
- Translocation
- The transport of food from leaves to other parts of a plant through phloem.
- Excretion
- The removal of harmful metabolic wastes from the body.