Osmosis — final check

1. predict

Solution X (5 % sugar) and solution Y (20 % sugar) are separated by a membrane that lets water through but not sugar. What happens?

Circle one answer.

• Sugar moves from Y into X
• Water moves from Y into X
• Nothing happens, because both are sugar solutions
• There is a net movement of water from X into Y

2. predict / explain

A bag of dialysis tubing holding 10 % sugar solution is weighed and placed in a beaker of 30 % sugar solution for 30 minutes. (a) Predict the change in mass of the bag. (b) Explain your prediction. (c) Name one variable to keep the same if the experiment is repeated.

(a) Prediction

(b) Explanation

(c) Variable to keep the same

3. describe

Water is a solvent in organisms. For each process, name one substance that is dissolved in water and say what happens to it: (a) digestion, (b) excretion, (c) transport in the blood.

(a) Digestion

(b) Excretion

(c) Transport in the blood

4. estimate

Carrot cylinders were soaked for 30 minutes. Mean percentage changes in mass: water +9.5 %; 0.2 mol/dm³ +2.1 %; 0.4 mol/dm³ −4.9 %; 0.6 mol/dm³ −10.2 %. Estimate the sucrose concentration at which there would be no net movement of water into or out of the carrot cells. Give your answer to two decimal places.

Concentration with no net movement of water: ______________ unit ________

5. identify / explain

Pieces of the same leaf skin were left for 20 minutes in three sucrose solutions, A, B and C, then looked at under a microscope. In A the cell contents press on the cell walls. In B the contents touch the walls but no longer press on them. In C the cytoplasm and cell membrane have pulled away from the walls. (a) Name the state of the cells in A, B and C. (b) Put the solutions in order from most dilute to most concentrated. (c) Explain what happened to the cells in C.

(a) States in A, B and C

(b) Order of the solutions

(c) What happened in C

6. predict / explain

The cell sap of a plant’s root hair cells has the same water potential as a 0.4 mol/dm³ sucrose solution. The plant is grown in two soils. Soil X: the soil water is like a 0.05 mol/dm³ solution. Soil Y: the soil water is like a 0.6 mol/dm³ solution. For each soil, state the direction of the net movement of water between the soil and the root hair cells, and the effect on the plant.

Soil X

Soil Y

7. identify / explain

Three tubes each contain a few drops of blood in a different liquid. After 10 minutes, under a microscope: in tube 1 the red blood cells are normal discs; in tube 2 there are almost no cells, only pale torn membranes; in tube 3 the cells are small with crinkled edges. (a) Which tube held pure water, which a strong salt solution, and which a salt solution with the same water potential as plasma? (b) Explain what happened in tube 2.

(a) Which liquid in each tube

(b) What happened in tube 2