Active transport and the sodium-potassium pump
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Question
What is active transport?
Answer
The movement of a substance **against** its concentration gradient, using energy from **ATP**.
Question
How is active transport different from diffusion?
Answer
Active transport moves particles **against** the gradient and **uses ATP**; diffusion is passive — **down** the gradient with **no ATP**.
Question
Which protein uses ATP to move particles against a concentration gradient?
Answer
A **pump protein** (the protein responsible for active transport).
Question
What two words tell you a process is active transport?
Answer
**'Against' the gradient** and **'uses ATP'** — either one signals active transport.
Question
What does the sodium-potassium pump do per ATP?
Answer
Pumps **3 sodium ions (Na⁺) out** of the cell and **2 potassium ions (K⁺) in**, both against their gradients.
Question
Which way does the Na⁺/K⁺ pump move each ion?
Answer
**Sodium (Na⁺) OUT**, **potassium (K⁺) IN**.
Question
Why must the sodium-potassium pump run continuously?
Answer
Because ions constantly **leak back** down their gradients; the pump keeps replacing them to **maintain** the gradients.
Question
How does a cell maintain a high internal K⁺ and low internal Na⁺?
Answer
By **active transport** — the Na⁺/K⁺ pump uses **ATP** to keep moving ions against their gradients.
Question
What happens to ion gradients if the cell runs out of ATP?
Answer
The pump stops, ions keep leaking back, and the gradients gradually **even out**.
Question
Is active transport passive or does it need energy?
Answer
It **needs energy** — it always uses **ATP**.
Question
Name the three ways molecules cross the bilayer.
Answer
**Simple diffusion**, **facilitated diffusion** (both passive) and **active transport** (active, uses ATP).
Question
Give one example of active transport other than the Na⁺/K⁺ pump.
Answer
Uptake of **mineral ions by plant root cells** against their concentration gradient.
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Membranes and membrane transport
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