IT’S A GREEN WORLD WATER, WATER EVERYWHERE

Starter Raise your hand when you can smell the perfume………………… Why is perfume put on the warm places of the body such as the neck and wrists?

Water, water everywhere Learning objectives  Describe osmosis  Describe the effects of the uptake and loss of water on plant and animal cells.  Explain the key terms: flaccid, plasmolysed, turgid, crenation and lysis Success criteria  Know the definition of osmosis  Be able to understand and describe the effects of different concentrations of sugar solutions on plant cells  Be able to understand and therefore use the key terms correctly

Recap of diffusion

Diffusion and concentration Why can the student smell the sock from a distance? The sock can be smelt because sweat and other molecules are moving away from it and spreading out in the air. This is called diffusion. Where is the smell strongest? The smell is strongest at the sock. The smell becomes weaker further away from the sock.

Changing concentrations The rate of diffusion depends on several factors, such as the distance the particles have to travel and the difference in concentration. Molecules diffuse until they are evenly spaced apart and equilibrium is reached. During diffusion molecules move from an area of high concentration to an area of low concentration. They are said to move down a concentration gradient. Diffusion is a passive process which means that no energy is needed. high concentration low concentration

What is osmosis? water glucose partially- permeable membrane (visking tubing) Osmosis is the diffusion of water molecules from a low concentration solution to high concentration solution, across a partially-permeable membrane. A partially-permeable membrane has holes in it that permit water molecules through but are too small to allow larger molecules through. Osmosis can be demonstrated using visking tubing filled with a solution and placed in a beaker of pure water.

Osmosis demo Before After Before After

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

Support in plant cells Water can move in and out of a plant cell through its  Cell wall - permeable  Cell membrane – partially permeable The presence of water in a plant cell gives it  Shape  Support The cell wall also provides support

Support in plant cells What happens when water uptake and water loss are not balanced a plant? The plant will wilt.

Movement of water in plant cells Read p58-59 of the text book and answer questions 1-5.

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 cell red blood cell cell wall Plant cells additionally have a strong cell wall surrounding the membrane which offers support and protection. plasma membrane

HD only - More on osmosis HD only - More on osmosis When a potato chip is in salt water the chips become flaccid (soft and floppy). WHY? There is a higher concentration of water molecules inside the potato cells than outside. Water leaves the cells by osmosis and the cells become plasmolysed.

Osmosis and 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 concentrated solutions, water loss causes the cells to shrink. When this happens to red blood cells, it is called crenation. In dilute solutions, osmosis can cause animals cells, such as red blood cells, to swell up and burst. This is called lysis.

Osmosis and animal cells

Osmosis in onion cells  Follow instructions on w/s B4b5 – osmosis in onion cells

Osmosis Weak solution Concentrated solution crenated NormalTurgid Normal Plasmolysed Lysed

Plenary - Predicting osmosis

Water, water everywhere Learning objectives  Describe osmosis  Describe the effects of the uptake and loss of water on plant and animal cells.  Explain the key terms: flaccid, plasmolysed, turgid, crenation and lysis Success criteria  Know the definition of osmosis  Be able to understand and describe the effects of different concentrations of sugar solutions on plant cells  Be able to understand and therefore use the key terms correctly