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All 14 Flashcards — Osmosis in cells without a wall
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Question
Define osmosis.
Answer
The net movement of **water** across a partially permeable membrane, from a **more dilute** solution to a **more concentrated** one.
Question
Why are animal cells especially affected by tonicity?
Answer
They have **no cell wall** — only a flexible plasma membrane — so they can **burst** or **shrivel** as water moves in or out.
Question
Define a hypotonic solution.
Answer
A solution that is **more dilute** than the inside of the cell (lower solute concentration); water moves **into** the cell.
Question
Define an isotonic solution.
Answer
A solution with the **same** solute concentration as the cell; there is **no net movement** of water.
Question
Define a hypertonic solution.
Answer
A solution that is **more concentrated** than the inside of the cell (higher solute concentration); water moves **out** of the cell.
Question
What happens to an animal cell in a hypotonic solution?
Answer
Water enters by osmosis, so the cell **swells and may burst** — this bursting is called **lysis** (haemolysis in red blood cells).
Question
What happens to an animal cell in an isotonic solution?
Answer
**No net movement** of water, so the cell **stays the same** shape and size.
Question
What happens to an animal cell in a hypertonic solution?
Answer
Water leaves by osmosis, so the cell **shrinks and wrinkles** — this is called **crenation**.
Question
What is lysis?
Answer
The **bursting** of a cell when too much water enters it by osmosis (haemolysis if it is a red blood cell).
Question
What is crenation?
Answer
The **shrivelling / wrinkling** of an animal cell when water leaves it in a hypertonic solution.
Question
Why do cells placed in distilled water burst?
Answer
Distilled (pure) water is strongly **hypotonic**, so water rushes in by osmosis and the cell **swells and bursts (lyses)**.
Question
How can you deduce the tonicity of a solution from a cell's appearance?
Answer
**Burst/swollen = hypotonic; unchanged = isotonic; shrunken/crenated = hypertonic** — read the cell's shape backwards.
Question
What is osmoregulation?
Answer
The **control of water balance** in a cell or organism — keeping the internal water content steady.
Question
How does a Paramecium avoid bursting in fresh water?
Answer
A **contractile vacuole** collects the excess water that enters by osmosis and **pumps it back out** of the cell.
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Topic 4.6 hub
Water potential
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