Maintenance of Life

Osmosis in red blood cells.

If a red blood cell is placed in water, water enters the cell by osmosis. Because the membrane is quite weak the cell will burst as the volume and therefore the pressure in the cell increases. Red blood cells shrink when placed in concentrated solutions of sugar as water moves out of them by osmosis. This makes the cells appear wrinkled when viewed through a microscope.

This does not happen inside the body because the kidneys make sure the concentration of the blood stays about the same as the concentration of the solution inside the red blood cell.

Osmosis in plant cells

Plant cells have a strong rigid cell wall on the outside of the cell membrane. This stops the cell bursting when it absorbs water by osmosis. The increase in pressure makes the cell rigid. This is useful as plants do not have a skeleton. Instead the leaves and shoots can be supported by the pressure of water in their cells. If plant cells lose too much water by osmosis they become less rigid and eventually the cell membrane shrinks away from the cell wall.

A plant cell that looks slightly bloated

Water entering the cell by osmosis inflates the cell and makes it rigid

a plant cell with walls that curve in slightly

Loss of water makes the cell limp and shrinks the cell membrane away from the cell wall.

  • Lysis – bursting an animal cell by osmosis
  • Crenation – shrinking an animal cell by osmosis
  • Turgid – a plant cell fu
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  • Created by: night
  • Created on: 08-05-14 19:31

Plant Cells and Osmosis

Plants and water.

 The absorbed water is transported through the roots to the rest of the plant where it's used for different purposes:

  • It's a reactant used in photosynthesis
  • It supports leaves and shoots by keeping the cells rigid
  • It cools the leaves by evaporation
  • It transports dissolved minerals around the plant


Leaves are adapted for photosynthesis by having a large surface area, and contain stomata (openings) to allow carbon dioxide into the leaf. These design features can result in the leaf losing a lot of water. The cells inside the leaf have water on their surface. Some of this water evaporates, and the water vapour can then escape from inside the leaf by diffusionTo reduce loss the leaf is coated in a wax cuticle to stop the water vapour escaping through the epidermis.

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Plant Cells and Osmosis

Reducing water loss - higher tier


Plants growing in drier conditions tend to have small numbers of tiny stomata and only on their lower leaf surface, to save water loss. Most plants regulate the size of stomata with guard cells. Each stoma is surrounded by a pair of sausage-shaped guard cells. In low light the guard cells lose water and become flaccid, causing the stomata to close. 


Most plant cells are turgid at all times. This supports the weight of the plant, which is especially important where there is no woody tissue, such as leaves, shoot and root tip. If the plant loses water faster than it can be absorbed the cells lose turgor pressure and become flaccid. This causes the plant to wilt.

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