Respiration and Transport in Living Organisms
This domain asks how organisms release energy from food and how materials are moved to and from cells. The exam tests the stages of respiration with their sites, breathing mechanics in humans, the pathway of water in plants, and blood, heart and circulation facts.
Respiration
- Glycolysis in the cytoplasm converts glucose to pyruvate with a small ATP yield. The Krebs cycle occurs in the mitochondrial matrix and the electron transport chain on the inner membrane, where most ATP is made.
- Anaerobic: in muscle, glucose gives lactic acid; in yeast, ethanol and carbon dioxide. Anaerobic release is far less than aerobic.
- Breathing is the exchange of gases; respiration is the release of energy inside cells.
Gas exchange and transport in humans
- Alveoli are thin-walled, moist and surrounded by capillaries for diffusion.
- Inhalation: diaphragm contracts and flattens, ribs move up and out, thoracic volume increases, pressure falls.
- Blood: plasma, red cells with haemoglobin for oxygen, white cells for defence, platelets for clotting.
- Heart: four chambers; right side carries deoxygenated blood, left side oxygenated; double circulation; the SA node sets the pace; arteries carry blood away from the heart and veins towards it.
Transport in plants
- Root hairs absorb water by osmosis; the transpiration pull, cohesion of water molecules and root pressure raise water through xylem.
- Transpiration occurs mainly through stomata and cools the leaf; phloem translocates food in either direction by pressure flow and needs energy.
Worked example
On a hot windy day a potted plant wilts faster. High temperature and wind increase the water vapour gradient, so transpiration speeds up. Water loss exceeds uptake, cells lose turgor and the leaves droop; on a humid day the same plant stays upright because the gradient is small.
Traps that cost marks
- The pulmonary artery carries deoxygenated blood - arteries are defined by direction, not oxygen content.
- Phloem transport is not only upward; it moves to roots and growing tips.
- Transpiration is not respiration; it is water loss.