IP Biology Notes: Movement of Substances (Upper Sec 02)
26 Nov 2025, 00:00 Z
Reviewed by
Ezekiel Tan·Academic Advisor (Biology)
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Use this as a free IP Biology notes chapter on movement of substances for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
What you must know
- Diffusion: net movement of particles down concentration gradient; no energy needed; faster with higher temperature/steeper gradient.
- Osmosis: net movement of water across partially permeable membrane from higher to lower water potential (dilute → concentrated).
- Active transport: movement against gradient using energy from respiration and carrier proteins (e.g., mineral ions into root hair, glucose in ileum).
- Osmosis effects: plant cells become turgid in dilute solutions, flaccid/plasmolysed in concentrated; animal cells lyse in very dilute, crenate in concentrated.
Detailed notes
- Diffusion drivers: random molecular movement; faster with higher temperature, steeper gradient, larger surface area, smaller molecules, and shorter distance. Occurs in liquids/gases.
- Osmosis language: water potential (higher → lower) across partially permeable membrane. Plant cells: turgid in hypotonic; flaccid then plasmolysed in hypertonic. Turgor supports non-woody plants.
- Active transport: uses ATP and carrier proteins to move substances against gradient. Root hairs uptake nitrate/minerals; ileum absorbs glucose/amino acids even when lumen concentration is low.
- Surface area:volume: small cells and extensions (root hairs, microvilli) increase SA:V for faster diffusion/absorption relative to volume.
Worked walkthroughs
- Predict plant cell appearance in distilled water vs concentrated sucrose: firm/turgid vs plasmolysed (membrane pulls from wall); note reversibility when returned to dilute solution.
- Root hair uptake: water via osmosis, ions via diffusion then active transport; relate to many mitochondria (ATP) and long protrusion (high SA).
- Small intestine: diffusion/facilitated diffusion/active transport of nutrients; villi/microvilli increase area, blood flow maintains gradient.
Pitfalls and fixes
- Using “water concentration” instead of “water potential.”
- Forgetting membrane in osmosis definition.
- Saying active transport works without energy-state ATP from respiration and carrier proteins.
- Mixing osmosis (water) with diffusion of solutes.
Practice drills
- Explain why amoeba rely on diffusion but humans need transport systems.
