Transport, Respiration and Gaseous Exchange
What this domain tests
This domain links three systems: transport in plants (xylem, transpiration, phloem), transport in humans (heart, blood vessels, blood) and gas exchange with respiration (lungs, gills, stomata, aerobic and anaerobic pathways).
Core rules
- Mammals have a double circulation: pulmonary (heart–lungs–heart) and systemic (heart–body–heart). Arteries carry blood away from the heart; veins return it.
- The left ventricle has the thickest muscle because it pumps blood around the whole body.
- Transpiration is water loss as vapour through stomata; the transpiration pull moves water up the xylem. Phloem carries sucrose and amino acids, and translocation needs living cells.
- Gas exchange surfaces are thin, moist, have a large area and a steep diffusion gradient.
- Aerobic respiration releases much more energy per glucose molecule than anaerobic respiration; in human muscle anaerobic respiration produces lactate.
Worked example
A resting student has a stroke volume of 70 mL and a heart rate of 75 beats per minute. Cardiac output = 70 × 75 = 5250 mL min⁻¹ = 5.25 dm³ min⁻¹. State the formula, substitute, then convert to dm³ by dividing by 1000.
Traps that cost marks
- Assuming all arteries carry oxygenated blood - the pulmonary artery does not.
- Confusing transpiration with translocation.
- Writing that anaerobic respiration “produces no energy” - it produces less, not none.
- Describing inhalation without saying the diaphragm contracts and flattens and the intercostal muscles raise the ribs.