Term 1 Lesson 4: Osmosis Flashcards
Osmosis
The movement of water across a partially permeable membrane from a high concentration to a low concentration.
Selectively preamble membrane
A membrane that allows certain materials to pass through it and not others.
Factors that affect the rate (speed) of osmosis
- temperature
-distance
-concentration gradient
-membrane permeability - surface area (to volume ratio).
Can you give other examples of osmosis?
- storing blood
Blood is stored in special solution. What will happen if there is too much water in the solution?
The blood cell would burst.
Blood is stored in special solution. What will happen if there is too little water in the solution?
The blood cell would shrivel up.
Why does osmosis happen?
because particles move. They have kinetic energy.
What kind of process is osmosis? Passive or active?
passive as it doesn’t require energy for it to be added.
What part of the body ensures that our blood plasma as enough water in it?
Kidneys
Describe a practical where you can see osmosis happen?
Investigate the effect of a range of concentrations of salt/sugar solutions on the mass of plant tissue
- Peel a potato and use a cork borer to produce 3 cylinders of potato
- Use scalpel to trim cylinders to same length (4cm)
- Measure mass of each cylinder using balance and record mass
- Using 3 beakers add 10cm^3 of 0.25mol sugar solution, 0.5 mol sugar solution and distilled water
- Leave potato cylinders for 24 hrs
- Gently take them out and dry them with paper towel
- Measure masses again
Why can only very small molecules like oxygen, water and glucose diffuse through the cell membrane?
Big molecules like starch and proteins can’t fit through the membrane
The bigger the concentration gradient…
the faster the diffusion rate
The larger the surface area of a cell membrane…
the faster the diffusion rate, because more particles can pass through at once
What is the concentration gradient?
The difference in the concentration of a substance between two areas
What is a solution?
A solution issomething dissolved in
something else (normally water).
Osmosis can be described as water potential. What is water potential?
Water potential is a measure of how free water molecules are to move
Pure water has the highest water potential. The more stuff you add to it (the more concentrated the solution) the harder it is for the water molecules to move. Therefore, the lower the water potential.
Give a definaition of water potential
the net diffusion of water across a partially permeable membrane, from a solution with a higher water potential to
one with a lower water potential.
You can emonstrate osmosis in a practical using a visking tube. How does the visking tube represent this?
Visking tubing is an artificial partially permeable membrane made into a sausage shape. It imitates the cell membrane so is used to demonstrate osmosis.
Explain how you would do a practical demonstrating osmosis using a visking tube?
- Fill the visking tubing with sugar solution and place in a beaker of distilled water.
- The water concentration will be higher in the beaker than the tube so water will move into the tube by osmosis.
- The level in the capillary tube will rise.
- This works because the sugar is too large to fit through the tubing.
In osmosis we may want to work out what percentage the potato for example as grown in mass. What is the equation for working out the percentage change?
Change in percentage mass = (end mass - start mass/start mass) x 100
