Osmosis

Question 1

what is the definition of osmosis?

Answer 1

-the passage of water from a region where it has a high water potential to a region where it has a low water potential through a selectively permeable membrane

Question 2

What is a solute?

Answer 2

• any substance that is dissolved in a solvent

- a solute + a solvent form a solution

Question 3

what is water potential?

Answer 3

• water potential is represented by psi and is measured in units of pressure (kPa)
• water pressure is created by water molecules
• water potential is lowered as more solute is added
• the highest value of water potential (pure water) is zero so all other values are negative

Question 4

How does water potential affect osmosis?

Answer 4

-water will move by osmosis from a region of higher water potential to one of lower water potential

Question 5

how do you find water potential of cells or tissues?

Answer 5

• place them in a series of solutions of different water potentials
• when there is no net gain or loss of water from the cells or tissues the water potential inside the cells or tissues must be the same as that of the external solution

Question 6

How does a selectively permeable plasma membrane separate two solutions?

Answer 6

• on one side there is a low concentration of solute molecules while on the other there is a high concentration of solute molecules
• both solute and water molecules are in random motion due to their kinetic energy
• the selectively permeable membrane only allows water molecules across it and not solute molecules
• the water molecules diffuse from the side with high water potential to the side with the lower water potential
• at the point where the water potentials on either side of the plasma membrane are equal a dynamic equilibrium is reached and there is no net movement of water

Question 7

how does osmosis work in red blood cells?

Answer 7

• if red blood cells are placed in pure water it will absorb water by osmosis since it has a lower water potential
• red blood cells are surrounded by blood plasma which has the same water potential as red blood cells so osmosis wont occur

Question 8

How does osmosis work in animal cells?

Answer 8

• cell surface membranes are very thin and flexible but cant stretch much
• the cell surface membrane will break bursting the cell and releasing its contents
• to prevent this happening animal cells normally live in a liquid which has the same water potential as the cells

Question 9

What does selectively permeable mean?

Answer 9

-cell surface membranes and other plasma membranes are selectively permeable as they are permeable to water molecules and a few other smaller molecules but not to larger molecule