Lesson 41- Osmosis

Question 1

Osmosis definition

Answer 1

The passive movement (diffusion) of water from a region of higher water potential to a region of lower water potential, through a selectively permeable membrane.

Question 2

How much water potential in pure water?

Answer 2

0kPa

Question 3

4 cells have the following water potentials:
Cell A = -200kPa
Cell B = -250kPa
Cell C = -100kPa
Cell D = -150kPa
Determine the order in which the cells have to be placed for water to pass from one cell to the next if they are arranged in a line

Answer 3

CDAB

Question 4

What’s the difference between putting an animal cell into a hypertonic, hypotonic and isotonic solution?

Answer 4

hypertonic solution - net movement of water out of the cell, which shrivels (crenation)
hypotonic solution - net movement of water into cell, which may burst (lyses)
isotonic solution - no net movement of water

Question 5

What’s the difference between putting a plant cell into a hypertonic, hypotonic and isotonic solution?

Answer 5

hypertonic solution - vacuoles lose water, the cytoplasm shrinks (plasmolysis), and chloroplasts are seen in the centre of the cell
hypotonic solution - vacuoles fill with water, turgor pressure develops, and chloroplasts are seen next to the cell wall
isotonic solution - no net movement of water, incipient plasmolysis

Question 6

What is the water potential equation?

Answer 6

Water potential = Pressure potential + Solute potential

Question 7

How would you make 15cm3 of 0.4 M sucrose solution?

Answer 7

1. Start with a solution of a known conc. - 1M
2. Find the scale factor by dividing the conc. of this solution by the conc. of the solution you want to make. Scale factor = 1 M/0.4 M = 2.5
3. The solution you want to make is 2.5 times weaker than the one you have. So use 2.5 times less of it, i.e. 15cm3 / 2.5cm3 = 6cm3
4. Pour this into a clean test tube. Top up the test tube with distilled water to get the volume you want. 15 - 6 = 9cm3 of distilled water.