osmosis

Question 1

give the definition of osmosis ?

Answer 1

the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential (i.e. higher concentration of water molecules) to an area of lower water potential (i.e. lower concentration of water molecules).

Question 2

what is water potential ?

Answer 2

the potential (likelihood) of water molecules to diffuse out of or into a solution.

Question 3

what is the water potential of pure water ?

Answer 3

0

Question 4

what does adding solutes do to water ?

Answer 4

lowers it potential

Question 5

what is the water potential of a solution ?

Answer 5

negative

Question 6

the more negative the water potential …..

Answer 6

the stronger the concentration of solutes in the solution.

Question 7

what does it mean if two soloutions are called isotonic?

Answer 7

they have the same water potential

Question 8

what happens to cells in an isotonic soloution ?

Answer 8

Cells in an isotonic solution won’t lose or gain any water — there’s no net movement of water

Question 9

what happens to cells when placed in a higher water potential ?

Answer 9

they will swell as the water rushed into the cells by osmosis

Question 10

what happens if a cell is placed in a lower water potential?

Answer 10

it will shrink as water rushes out by osmosis

Question 11

Solutions with a higher water potential compared with the inside of the cell are called ….

Answer 11

hypotonic

Question 12

Solutions with a lower water potential than the cell are called….

Answer 12

hypertonic

Question 13

what are the factors affecting the rate of osmosis

Answer 13

the water potential gradient
the thickness of exchange surfaces
the surface area of exchange surfaces

Question 14

how is the water potential gradient a factor affecting osmosis ?

Answer 14

the higher the water potential gradient, the faster the rate of osmosis. As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time. ƒ

Question 15

how is the thickness of exchange surfaces a factor affecting osmosis?

Answer 15

the thinner the exchange surface, the faster the rate of osmosis.

Question 16

how is the surface area of exchange surfaces a factor affecting osmosis ?

Answer 16

the larger the surface area, the faster the rate of osmosis.

Question 17

how do you investigate water potential (1st step) using sucrose solutions ?

Answer 17

A.make serial dilutions
1. Line up five test tubes in a rack.
2. Add 10 cm3 of the initial 2 M sucrose solution to the first test tube and 5 cm3 of distilled water to the other four test tubes .
3. Then, using a pipette, draw 5 cm3 of the solution from the first test tube, add it to the distilled water in the second test tube and mix the solution thoroughly. You now have 10 cm3 of solution that’s half as
concentrated as the solution in the first test tube (it’s 1 M).
4. Repeat this process three more times to create
solutions of 0.5 M, 0.25 M and 0.125 M

Question 18

how do you find the scale factor to make solutions ?

Answer 18

1. Start with a solution of a known concentration
   2.Find the scale factor by dividing the concentration of this solution by the concentration of the solution you want to make.
   3.use that amount less of the solution
   4.Top up the test tube with distilled water to get the volume you want to make.

Question 19

how do you investigate water potential (2nd step) using sucrose solutions?

Answer 19

Measuring change in mass
1. Use a cork borer to cut potatoes into identically sized chips, about 1 cm in diameter. Divide the chips into groups of three and measure the mass of each group using a mass balance.

2. Place one group into each of your sucrose solutions and leave the chips in the solutions for at least 20 minutes (making sure that they all get the same amount of time).
3. Remove the chips and pat dry gently with a paper towel. Weigh each group again and record your results. Calculate the percentage change in mass for each group. The potato chips will gain water (and therefore mass) in solutions with a higher water potential than the chips, and
   lose water in solutions with a lower water potential.

Question 20

how do you investigate water potential (3rd step) using sucrose solutions?

Answer 20

produce a calibration curb
plot percentage change in mass against the concentration of sucrose solution. The point at which your calibration curve crosses the x-axis (where the percentage change in mass is 0) is the point at which the water potential of the sucrose solution is the same as the water potential of the potato cells . Find the concentration at this point, then look up the water potential for that concentration of sucrose .solution