2.1.5c Osmosis

Question 1

INTRO: 5 ways different substances enter/leave cells

Answer 1

1. Simple diffusion (passive)
2. Facilitated diffusion (passive)
3. Osmosis (passive)
4. Active transport (active)
5. Bulk transport (endocytosis & exocytosis) (active)

Question 2

Definition of Osmosis

Answer 2

The net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane

Question 3

What is water potential

Answer 3

The pressure exerted by water molecules as they collide with a membrane or container
It is the potential (likelihood) of water molecules to diffuse out of or into a solution

Question 4

What is water potential measured in

Answer 4

kPA - Kilopascals

Question 5

What is the symbol for water potential

Answer 5

Greek letter psi - (see slide 2)

Question 6

Is osmosis a passive or active process

Answer 6

Passive - no ATP energy required

Question 7

What is the water potential of pure water

Answer 7

Zero
Pure water has the highest water potential

Question 8

What would the water potential of solutions be

Answer 8

A lower value, eg. -50
All solutions have a lower water potential than pure water

Question 9

Describe a solution with a high water potential

Answer 9

Has a large no. of water molecules that are free to move

Question 10

What is the amount of water that moves into cells dependent on

Answer 10

How much water moves in/out of cells depends on the water potential of the surrounding solution

Animal & plant cells behave differently in diff solutions

Question 11

Movement of water into a cell dependent on water potential of surround solution: Animal cell

Answer 11

• Solution with a higher water potential than the cell (HYPOTONIC SOLUTION) -> Water moves into cell, cell bursts
• Solution with the same water potential as the cell (ISOTONIC SOLUTION) -> Water molecules pas into & out of cell in equal amounts, the cell stays the same
• Solution with a lower water potential than the cell (HYPERTONIC SOLUTION) -> Water moves out of cell, the cell shrinks

Question 12

Movement of water into a cell dependent on water potential of surround solution: Plant cell

Answer 12

• HYPOTONIC SOLUTION - Water moves into cell. Vacuole swells - so cytoplasm & vacuole push against cell wall, cell becomes turgid (swollen)
• ISOTONIC SOLUTION - Water moves into & out of cell in equal amounts - the cell stays the same
• HYPERTONIC SOLUTION - Water moves out of cell. Cell becomes flaccid (limp). Cytoplasm & membrane pull away from the cell wall. This is called plasmolysis

Question 13

see pg58 for dias of animal/plant cell (solutions)

Question 14

Define a Hypotonic solution

Answer 14

A solution with MORE water in it than the solute, compared to another solution
(water moves into cell)

Question 15

Define a Hypertonic solution

Answer 15

A solution with MORE solute in it than the water, compared to another solution
(water moves out of cell)

Question 16

Define an Isotonic solution

Answer 16

Two solutions/cells that have the same water potential

Question 17

What does the movement of water by osmosis change?

Answer 17

The movement of water by osmosis, into or out of a cell changes the hydrostatic pressure of the cell

Question 18

Method for osmosis practical

Answer 18

1. Prepare sucrose solutions of the following concentrations: 0.0dm^-3, 0.2, 0.4, 0.6, 0.8, 1.0
2. Use a cork borer/chip maker to cut potatoes into same sized pieces (1cm in diameter)
3. Divide the chips into groups of 3 & use a mass balance to measure the mass of each group
4. Place one group in each solution
5. Leave chips in solution for set amount of time (at least 20mins)
6. Remove chips & pat dry gently w a paper towel
7. Weigh each group again & record results
8. Calculate % change in mass for each group, plot results on a graph

Question 19

Important to notte about sucrose concentrations in osmosis practical

Answer 19

The higher the sucrose concentration, the lower the water potential