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All 12 Flashcards — Osmosis and water potential
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Question
Define osmosis.
Answer
The **net movement of water** across a **partially permeable membrane**, from a **higher** water potential to a **lower** water potential.
Question
Define water potential.
Answer
A measure of **how freely water can move out** of a solution. **Pure water** has the highest water potential; adding solute lowers it.
Question
What is solvation?
Answer
The process in which **water molecules surround and separate** each dissolved **solute** particle, holding it in solution.
Question
What is a partially permeable membrane?
Answer
A membrane that lets **water** through but blocks (most of) the dissolved **solute** particles.
Question
Which way does water move in osmosis?
Answer
From a **higher** water potential (dilute) to a **lower** water potential (concentrated).
Question
What does adding solute do to water potential?
Answer
It **lowers** the water potential — the more concentrated the solution, the lower its water potential.
Question
Which solution has the higher water potential — dilute or concentrated?
Answer
The **dilute** solution — it has fewer solutes and more free water, so a higher water potential.
Question
What two conditions are required for osmosis across a membrane?
Answer
A **partially permeable membrane** AND a **difference in water potential** (a solute-concentration gradient).
Question
Is osmosis active or passive?
Answer
**Passive** — it needs no energy (no ATP); water moves down its own gradient.
Question
What happens when both sides of a membrane have equal water potential?
Answer
There is **no net movement** of water — water still crosses both ways, but in equal amounts (isotonic).
Question
Why does a concentrated solution have fewer 'free' water molecules?
Answer
Because **solvation** ties up water molecules around the solute particles, leaving fewer free to move.
Question
How do you predict the direction of osmosis from two solute concentrations?
Answer
The **more concentrated** side has the **lower** water potential, so water moves **into** it from the more dilute side.
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Topic 4.6 hub
Water potential
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