Life Processes
Life processes covers nutrition, respiration, transport and excretion - mostly process-pathway and labelled-diagram questions.
Nutrition
Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, in chloroplasts, using chlorophyll and sunlight; stomata admit CO₂ and release O₂. Heterotrophs may be saprophytic (fungi), parasitic (Cuscuta) or holozoic (humans). Human digestion: mouth (saliva, amylase) → stomach (HCl, pepsin) → small intestine (bile from the liver, pancreatic and intestinal enzymes), where absorption occurs through villi → large intestine absorbs water.
Respiration
Aerobic respiration releases more energy: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy, in the mitochondria. Anaerobic: in yeast, glucose → ethanol + CO₂; in vigorous exercise our muscles give glucose → lactic acid, causing cramps. Breathing is the mechanical exchange of gases; respiration is a chemical process.
Transport
In plants, xylem carries water and minerals upwards, driven by transpiration pull; phloem carries food. In humans there is double circulation: the right side pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body. Arteries carry blood away from the heart, veins towards it, capillaries exchange materials. Blood contains plasma, RBCs (haemoglobin), WBCs and platelets.
Excretion
Kidneys filter blood: the glomerulus filters, the tubules reabsorb useful substances, and urine passes through the ureters to the bladder. Plants release oxygen and lose wastes in shed leaves.
Worked example
After a sprint your legs ache. Oxygen supply is short, so muscles respire anaerobically, producing lactic acid, which accumulates and causes cramp; later, oxygen breaks it down.
Traps
Writing the photosynthesis equation without the light and chlorophyll condition; confusing transpiration with translocation; saying arteries carry oxygenated blood always (the pulmonary artery does not).