Transport in plants and humans
Transport
This domain tests water and mineral uptake, transpiration, xylem and phloem, blood, the heart and blood vessels.
Core rules
- Root hair cells increase surface area for osmosis and active transport of minerals. Water enters by osmosis; minerals such as nitrate are taken up by active transport.
- Transpiration is water loss as vapour from leaves, mainly through stomata. It is driven by evaporation and pulls water up the xylem. Light, temperature, wind and humidity affect the rate.
- Xylem transports water and dissolved minerals upward; phloem transports sucrose and amino acids to growing and storage organs.
- Blood: plasma transports dissolved substances; red blood cells carry oxygen using haemoglobin; white blood cells defend; platelets clot.
- Heart: right side to lungs, left side to body. Arteries carry blood away at high pressure; veins return blood at low pressure and have valves; capillaries are one cell thick for exchange.
Worked example
A potometer shows the water meniscus moving 60 mm in 5 minutes in a tube of cross-sectional area 1 mm². Volume = area × length = 1 × 60 = 60 mm³ = 0.060 cm³. Rate = 0.060 / 5 = 0.012 cm³/min. Reasoning: the potometer measures water uptake, which is used as an estimate of transpiration; it does not measure water lost from the whole plant directly. Units must be consistent.
Traps
- Saying xylem carries sugars.
- Confusing transpiration with translocation.
- Saying arteries always carry oxygenated blood.
- Forgetting valves in veins.
- Using potometer distance as volume without multiplying by tube area.