Topic Summary: Cell Transport

Key Terms

• Diffusion — high → low concentration, passive, any particle
• Osmosis — water only, through partially permeable membrane, passive
• Active transport — low → high (against gradient), needs ATP
• Concentration gradient — difference in concentration between two areas
• Turgid — plant cell full of water (firm)
• Flaccid — plant cell partially dehydrated (limp)
• Plasmolysed — cell membrane pulled away from cell wall (severe dehydration)
• Partially permeable membrane — allows water through, not large solutes

Must-Know Facts

• Diffusion and osmosis = passive (no energy needed)
• Active transport = requires ATP from mitochondria
• Only water moves by osmosis; osmosis requires a partially permeable membrane
• Active transport goes AGAINST the concentration gradient
• Cells doing lots of active transport have many mitochondria
• Percentage change in mass = (Final − Initial) ÷ Initial × 100
• Hypertonic = water moves OUT of cell; Hypotonic = water moves INTO cell
• Alveoli, villi, root hair cells — all adapted to maximise transport rate

Quick Reference: Three Transports

Process	Direction	Energy
Diffusion	High → Low	No
Osmosis	Dilute → Concentrated (water)	No
Active transport	Low → High (against)	Yes (ATP)

% change in mass:

(Final − Initial) ÷ Initial × 100

Common Exam Mistakes

• "Osmosis is movement of any particles" — WRONG: water only
• "Active transport goes down the gradient" — WRONG: against the gradient
• Forgetting "partially permeable membrane" in osmosis definition
• Not including ATP/mitochondria when explaining active transport
• Using change in mass instead of percentage change (makes comparison unfair)
• Saying water moves from concentrated to dilute — WRONG: it moves from dilute to concentrated