Osmosis Learning Objective To know osmosis is the diffusion of water from a dilute sugar solution to a more concentrated sugar solution through a partially permeable membrane. To be able to work in a group to produce primary data from experimental work To be able to analyse the data and produce a line of best fit graph. To be able to draw conclusions from your analysis of the data To be able to evaluate the experiment.

Success Criteria All can carry out the practical work to obtain primary data. All can describe the movement of water across a partially permeable membrane by osmosis. Most can analyse the data and draw a line of best fit graph. Most can draw valid conclusions based on the data and knowledge of osmosis. Some can evaluate the experiment. Some can explain in detail how water moves down a concentration gradient from a high concetration of water to a low concentration of water.

What is osmosis? Osmosis is the diffusion of water molecules from a low sugar concentration solution to high sugar concentration solution, across a partially-permeable membrane.

Osmosis is passive and requires no energy. It is the NET movement of water molecules across a partially permeable membrane

Dilute vs. concentrated During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions. Dilute solutions have a high concentration of water molecules. Concentrated solutions have a low concentration of water molecules. pure water dilute solution concentrated solution

Predicting osmosis Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of osmosis.

Osmosis in action Teacher notes This activity could be used as a starter exercise to work on osmosis.

Osmosis and cells Plant and animal cells are surrounded by a partially-permeable plasma membrane. This allows water and other small molecules to diffuse across. Plant cells additionally have a strong cell wall surrounding the membrane which offers support and protection. plasma membrane cell wall red blood cell plant cell

Osmosis and plant cells Teacher notes This activity could be used to check students’ understanding of the effects of osmosis on plant cells.

Osmosis and animal cells Animal cells do not have a cell wall. This means they respond differently to plant cells to the gain and loss of water. In dilute solutions, osmosis can cause animals cells, such as red blood cells, to swell up and burst. This is called lysis. In concentrated solutions, water loss causes the cells to shrink. When this happens to red blood cells, it is called crenation.

Osmosis and animal cells Teacher notes This activity could be used to check students’ understanding of the effects of osmosis on red blood cells.

Osmosis and animal cells In order to remain healthy, animal cells need to maintain an isotonic water balance. This means that the water concentration both inside and outside the cell are equal. hypothalamus The concentration of water and salt in the blood are controlled by the kidneys. The kidneys are controlled by the portion of the brain called the hypothalamus. Teacher notes See the ‘Homeostasis’ presentation for more information on osmoregulation.

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