Cells in sugary water
Water leaves by osmosis. Wall or no wall decides what you see.
Onion peel in sugar water
Put a thin onion peel in very concentrated sugar solution. Outside the cells there is less water and more sugar than inside.
Which way will water mostly move?
What this lesson covers
The idea
In a concentrated sugar solution cells lose water by osmosis: a plant cell keeps its shape because of its rigid wall while its membrane and contents pull away from the wall, but an animal cell, lacking a wall, shrinks.
Onion peel in sugar water
Put a thin onion peel in very concentrated sugar solution. Outside the cells there is less water and more sugar than inside.
Which way will water mostly move?
- Out of the cells
- Into the cells
- It will not move
Add the sugar
Put both cells in the solution and let time pass.
Wall or no wall
In a concentrated sugar solution cells lose water by osmosis. A plant cell keeps its shape because of its rigid wall, but its membrane and contents pull away from the wall. An animal cell, with no wall, shrinks.
This is how the Rhoeo leaf or onion peel experiment shows that the wall keeps plant cells firm.
- Plant cell | Animal cell
- Cell wall | yes | no
- Outer shape | stays the same | shrinks
- Contents | pull away from the wall | shrink with the cell
Notes
In a concentrated solution cells lose water by osmosis: a plant cell keeps its shape (the wall) while its contents pull away; an animal cell shrinks.
Check yourself
In concentrated sugar solution, water moves…
A plant cell in concentrated solution…
An animal cell (cheek cell) in concentrated sugar solution…
What does the experiment show about the cell wall?
- out of the cells, by osmosis — correct. Yes.
- into the cells. Water moves toward the more concentrated solution.
- nowhere. Osmosis moves it.
- keeps its outer shape, but its contents pull away from the wall — correct. Yes.
- shrinks completely like an animal cell. The wall stops the outer shape from shrinking.
- swells and bursts. It is losing water, not gaining.
- shrinks — correct. Yes. With no wall, it loses water and shrinks.
- keeps its shape exactly. That needs a rigid wall.
- grows bigger. It is losing water.
- The wall helps plant cells stay firm in their original shape — correct. Yes.
- The wall makes water move faster. It does not.
- The wall stops osmosis. Water still leaves; the shape just stays.