Ch 3 · Active Transport · IGCSE Biology 0610
Topic 3 of 3 in Movement into and out of Cells — IGCSE Biology 0610 — 53 lessons.
Introduction
Diffusion and osmosis can only move substances down a concentration gradient. Yet a root hair cell absorbs nitrate ions from soil water that contains far fewer ions than the cell already holds. This needs active transport, which uses energy from respiration to pump particles the "wrong" way. This lesson defines it, explains where it matters and ends with the comparison table examiners like to set.
Key ideas — What active transport is
Active transport is the movement of particles through a cell membrane from a region of their lower concentration to a region of their higher concentration, against a concentration gradient, using energy from respiration.
🧑🏫 Teacher's explanation
Imagine you are trying to move a heavy boulder up a steep hill. Gravity wants to pull it down (the concentration gradient), so you have to exert physical effort to push it up. In a cell, molecules like glucose or ions often want to move from where there is a lot of them to where there is very little (diffusion). To move them the 'wrong' way—from low to high concentration—the cell must spend energy.
📖 Definitions
🔍 Worked example — Easy
A plant root hair cell uses active transport to absorb nitrates from the soil. The concentration of nitrates in the soil is 0.01 mol/dm^3, while the concentration inside the cell is 0.05 mol/dm^3. State the direction of movement and the requirement for this process.
🔍 Worked example — Standard
Explain why a decrease in temperature would reduce the rate of active transport in the epithelial cells of the small intestine.
🔍 Worked example — Exam-style
Calculate the percentage increase in glucose concentration in a kidney tubule cell if the concentration increases from 2 mmol/dm^3 to 10 mmol/dm^3 via active transport.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Why active transport matters
🧑🏫 Teacher's explanation
Imagine you are trying to move a crowd of people from a sparse hallway into a very crowded room. If you just let them drift naturally, they will spread out evenly. But if you want to pack more people into that crowded room, you have to physically push them in, which requires effort and energy. This is exactly what cells do with molecules.
📖 Definitions
🔍 Worked example — Easy
A root hair cell has a concentration of nitrate ions of 0.05 mol/dm^3. The concentration of nitrate ions in the surrounding soil water is 0.01 mol/dm^3. Describe the method the cell uses to increase the internal concentration of nitrate ions.
🔍 Worked example — Standard
Compare the movement of glucose into the epithelial cells of the villi during the initial stages of digestion versus the final stages of absorption.
🔍 Worked example — Exam-style
A patient's urine test shows a high concentration of glucose. Explain why this indicates a failure in the kidney tubules.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Explain why the plant must use active transport to absorb magnesium ions into its root hair cells. [2] (b) State the source of energy used for this process. [1] [3 marks]
Key ideas — How active transport works
🧑🏫 Teacher's explanation
Imagine you are trying to move a heavy box up a flight of stairs. If you are just walking down, gravity does the work for you (this is like diffusion). But to move the box up, you have to exert effort and use your muscles to fight against gravity. In a cell, 'gravity' is the concentration gradient. Molecules naturally want to spread out from where there are many to where there are few. Active transport is the cell's way of 'climbing the stairs' to pull more of what it needs into the cell, even when it is already crowded inside.
📖 Definitions
🔍 Worked example — Easy
A plant root hair cell uses active transport to absorb mineral ions from the soil. If the concentration of ions in the soil is 0.01 mol/dm^3 and the concentration inside the cell is 0.05 mol/dm^3, describe the direction of movement and the requirement for energy.
🔍 Worked example — Standard
Compare active transport and diffusion in terms of concentration gradient and energy requirement.
🔍 Worked example — Exam-style
Explain why a cell might use active transport to absorb glucose even if the glucose concentration is already high inside the cytoplasm.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Key ideas — Comparing the three processes
Diffusion and osmosis are passive and continue in dead tissue; active transport stops when the cell stops respiring. Raising the temperature speeds up all three, but only active transport is affected by oxygen concentration or respiratory poisons.
🧑🏫 Teacher's explanation
Imagine you are at a crowded music festival. Diffusion is like people naturally spreading out from the mosh pit into the empty spaces around them because it's easier to move where there is more room. Osmosis is like water flowing into a sponge to balance out the dryness. Active transport, however, is like a security guard physically pushing people through a narrow gate into an already packed VIP area. It requires effort and energy to force things where they don't 'want' to go naturally.
📖 Definitions
🔍 Worked example — Easy
A plant root hair cell uses active transport to absorb nitrates from the soil. If the concentration of nitrates in the soil is 0.01 mol/dm^3 and the concentration inside the root hair cell is 0.05 mol/dm^3, describe the direction of movement and the energy requirement.
🔍 Worked example — Standard
Calculate the percentage increase in the concentration of glucose in an epithelial cell if the concentration increases from 2 mmol/L to 10 mmol/L via active transport.
🔍 Worked example — Exam-style
Compare the processes of osmosis and active transport in terms of membrane requirements and energy usage.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
Worked example — Question
A student measured the uptake of nitrate ions by barley roots kept in aerated and in non-aerated nutrient solutions. After 3 hours the roots in aerated solution had absorbed 4.2 units of nitrate; the roots in non-aerated solution had absorbed 0.9 units.
🔍 Worked example — Easy
Calculate the percentage increase in nitrate uptake when moving from non-aerated to aerated solution. Initial: 0.9 units. Final: 4.2 units.
🔍 Worked example — Standard
A plant cell requires 5.0 × 10^-6 mol of ions per second. If the concentration gradient requires the use of 2.5 × 10^-7 Joules of energy per ion, calculate the total energy required per second.
🔍 Worked example — Exam-style
Compare the movement of glucose into epithelial cells in the villi using diffusion versus active transport.
⚠️ Common errors
Worked example — Model answer
(a) Movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration [B1], against a concentration gradient [B1], using energy from respiration [B1].
🔍 Worked example — Easy
Identify the three essential components required for active transport to occur in a plant root cell.
🔍 Worked example — Standard
A plant root hair cell is placed in a solution where the concentration of nitrate ions is 0.01 mol/dm^3 outside the cell and 0.05 mol/dm^3 inside the cell. Explain why the cell must use active transport to increase nitrate uptake.
🔍 Worked example — Exam-style
An experiment measures the rate of nitrate uptake by root hair cells in two different environments: (A) Aerated water and (B) Deoxygenated water. Predict and explain the difference in nitrate uptake between (A) and (B).
⚠️ Common errors
Common mistakes
Practice
Answers