Term 1 Lesson 4: Osmosis

Question 1

Osmosis

Answer 1

The movement of water across a partially permeable membrane from a high concentration to a low concentration.

Question 2

Selectively preamble membrane

Answer 2

A membrane that allows certain materials to pass through it and not others.

Question 3

Factors that affect the rate (speed) of osmosis

Answer 3

• temperature
  -distance
  -concentration gradient
  -membrane permeability
• surface area (to volume ratio).

Question 4

Can you give other examples of osmosis?

Answer 4

• storing blood

Question 5

Blood is stored in special solution. What will happen if there is too much water in the solution?

Answer 5

The blood cell would burst.

Question 6

Blood is stored in special solution. What will happen if there is too little water in the solution?

Answer 6

The blood cell would shrivel up.

Question 7

Why does osmosis happen?

Answer 7

because particles move. They have kinetic energy.

Question 8

What kind of process is osmosis? Passive or active?

Answer 8

passive as it doesn’t require energy for it to be added.

Question 9

What part of the body ensures that our blood plasma as enough water in it?

Answer 9

Kidneys

Question 10

Describe a practical where you can see osmosis happen?

Answer 10

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

Question 11

Why can only very small molecules like oxygen, water and glucose diffuse through the cell membrane?

Answer 11

Big molecules like starch and proteins can’t fit through the membrane

Question 12

The bigger the concentration gradient…

Answer 12

the faster the diffusion rate

Question 13

The larger the surface area of a cell membrane…

Answer 13

the faster the diffusion rate, because more particles can pass through at once

Question 14

What is the concentration gradient?

Answer 14

The difference in the concentration of a substance between two areas

Question 15

What is a solution?

Answer 15

A solution issomething dissolved in
something else (normally water).

Question 16

Osmosis can be described as water potential. What is water potential?

Answer 16

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.

Question 17

Give a definaition of water potential

Answer 17

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.

Question 18

You can emonstrate osmosis in a practical using a visking tube. How does the visking tube represent this?

Answer 18

Visking tubing is an artificial partially permeable membrane made into a sausage shape. It imitates the cell membrane so is used to demonstrate osmosis.

Question 19

Explain how you would do a practical demonstrating osmosis using a visking tube?

Answer 19

• 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.

Question 20

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?

Answer 20

Change in percentage mass = (end mass - start mass/start mass) x 100