1.3.3: Active transport
Not started yet — this one needs some love.
Active transport: movement of substances against the concentration gradient (from a low to a high concentration).
Requires energy from respiration (glucose broken down in the mitochondria) and carrier proteins in the cell membrane.
Examples:
root hair cells absorb mineral ions from a dilute soil solution (soil concentration < cell concentration)
the small intestine absorbs glucose into the blood, even when the blood already has a higher concentration
Comparison of the three transport processes:
Diffusion: high → low concentration; passive (no energy); any particles, in gases or liquids
Osmosis: high → low water concentration; passive; water only, through a partially permeable membrane
Active transport: low → high concentration; needs energy from respiration; specific molecules/ions via carrier proteins
Common exam mistakes
Active transport requires energy from respiration — NEVER say energy is 'produced', 'created' or 'made'. Energy is released/transferred by respiration.
Active transport moves substances against the concentration gradient — opposite direction to diffusion.
Do not confuse: diffusion (passive, down gradient), osmosis (passive, water only, through partially permeable membrane), active transport (requires energy, against gradient).
In root hair cells, mineral ions are absorbed by active transport; water is absorbed by osmosis — do not confuse the two mechanisms.