Life Processes

How living things get food, release energy, transport materials and remove wastes: nutrition, respiration, transportation and excretion.

Key ideas

Plants make food by photosynthesis, using sunlight, chlorophyll, carbon dioxide and water; gases pass through stomata.
In humans, digestion starts in the mouth (salivary amylase), continues in the stomach (HCl and pepsin) and finishes in the small intestine, where villi absorb the food.
Aerobic respiration in the mitochondria breaks glucose into carbon dioxide and water and releases much energy (ATP).
Without oxygen, yeast makes ethanol and carbon dioxide, and tired muscles make lactic acid.
The human heart has four chambers and blood passes through it twice in each circuit (double circulation).
Arteries carry blood away from the heart; veins carry it back. In plants, xylem carries water and phloem carries food.
The kidneys filter the blood in nephrons and make urine; useful substances are taken back.

Remember

Photosynthesis	6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (sunlight, chlorophyll)
Aerobic respiration	glucose + oxygen → carbon dioxide + water + energy
Anaerobic (yeast)	glucose → ethanol + carbon dioxide + energy

Watch out

Saying all arteries carry oxygen-rich blood: the pulmonary artery carries blood low in oxygen to the lungs.
Mixing up xylem (water) and phloem (food).
Thinking plants only photosynthesise and never respire (they respire all the time).

Worked example

Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in sunlight, with chlorophyll). A plant takes in 211.2 g of carbon dioxide. Find the mass of glucose made and the mass of oxygen given out. (Atomic masses: H = 1 u, C = 12 u, O = 16 u)

Working: C₆H₁₂O₆ = 180 u; 6 × CO₂ = 264 u give 180 u of glucose and 192 u of oxygen

Answer: Glucose 144 g; oxygen 153.6 g