Ch 6 covers the fundamental life processes — nutrition, respiration, transportation, and excretion — in both plants and animals, explaining how organisms maintain and sustain themselves.
Autotrophic: plants make food by photosynthesis (CO₂ + water + sunlight → glucose + O₂ in chloroplasts). Heterotrophic: animals eat other organisms. Human digestion: mouth (saliva, amylase) → stomach (HCl, pepsin) → small intestine (bile, pancreatic juice, absorption via villi) → large intestine (water absorption) → excretion.
Respiration: breakdown of glucose for energy. Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (in mitochondria). Anaerobic: without O₂ → ethanol + CO₂ (yeast) or lactic acid (muscles). Transportation in humans: double circulation — heart pumps blood through lungs (pulmonary) and body (systemic). Plants: xylem (water upward) and phloem (food — translocation).
Removal of metabolic waste. In humans: kidneys filter blood → nephron (glomerulus → Bowman's capsule → tubule) → urine. Each kidney has ~1 million nephrons. Plants: store waste in vacuoles, old leaves; excrete O₂ and CO₂ through stomata.
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The small intestine (~6.5 m) needs to be long to allow maximum absorption of digested food. Its inner wall has finger-like projections (villi) that greatly increase the surface area for absorption. Each villus has a network of blood capillaries for efficient transfer of nutrients into the blood.
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