3.2.3.3 - Osmosis

Question 1

The passive movement of water from an area of high water potential to an area of low water potential through a selectively permeable membrane is…

Answer 1

OSMOSIS

Question 2

Osmosis involves the movement of

Answer 2

water ONLY

Question 3

By adding more solute the a solution how does this affect the water potential

Answer 3

it lowers the WP - becomes more negative

Question 4

Why does pure water have a higher water potential than a solution of sugar

Answer 4

there are more ‘free’ water particles in pure water

Question 5

A potato has a WP of -200kPa was placed in pure water WP 0kPa, what happens?

Answer 5

Water ENTERS the potato by osmosis (water moved from a high WP to a lower WP)

Question 6

water potential is represented by

Answer 6

psi (greek letter)

Question 7

water potential is measured in units of pressure which are

Answer 7

kPa

Question 8

Pure water has a WP of

Answer 8

0kPa

Question 9

How can you determine the the WP of a potato

Answer 9

place potato in a series of solutions of different WP. Where there is no net gain of water by the potato is the WP of the potato.

Question 10

What happens if a red blood cell is placed in pure water

Answer 10

it swells and bursts - water enters the cell

Question 11

What happens if a red blood cell is placed in strong sugar solution

Answer 11

It shrinks - water leaves the cell

Question 12

What happens if a plant cell is placed in pure water

Answer 12

It swells - water enters the cell - it becomes turgid

Question 13

What happens if a plant cell is placed in strong salt solution

Answer 13

water leaves the cell - it shrinks - it plasmolysed

Question 14

What is meant by selectively permeable

Answer 14

Membrane only allows certain molecules through; it is only permeable to water and other small molecules `

Question 15

During an osmosis practical, how and why do you dry the potato chips?

Answer 15

with a paper towel. To remove surface water - This would add to the mass - which we do not want

Question 16

You must control the temperature during your osmosis practical - HOW?

Answer 16

Using a water bath and check the temperature at regular intervals using a thermometer

Question 17

give 2 similarities in the movement of substances by diffusion and osmosis

Answer 17

1. down a gradient (High to Low)

2. passive not active (does not use energy)

Question 18

when preparing cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. this did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of chromsomes when observed with an optical microscope.

suggest how this procedure moved the chromosomes apart?

Answer 18

• water moves into cells by osmosis

- cell gets bigger

Question 19

osmosis potato practical method?

Answer 19

• cut potato cubes to same size
• put potato cubes in solution
• make sure all potato cubes exposed to solution by shaking tube or stirring it
• take cubes out
• blot dry with paper towel