Osmosis

Question 1

All cells are surrounded by a cell membrane which is partially permeable
Water can move in and out of cells by osmosis

Osmosis is the ……..

Answer 1

Osmosis is the net movement of water molecules through a semi-permeable membrane, from a region of high water potential to a region of low water potential. Also passive process

In doing this, water is moving down its concentration gradient

The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)

Question 2

what is water potential

Answer 2

Water potential is pressure exerted by water molecules on a membrane, and this pressure is measured in kilopascals (kPascals).

The greater the concentration of water in a membrane, the more kinetic energy the system has, and therefore the greater the water potential.

Water potential describes the tendency of water to move out of a solution. This term is used to avoid confusion between water concentration and concentration of a solution

Question 3

What is high water potential

Answer 3

water molecules collide with membrane and create pressure

the area with more water molecules will apply more pressure

So high water potential area has lots of water molecules(concentrated) and creates more pressure

Question 4

low water potential

Answer 4

water molecules collide with membrane and create pressure

the area with less water molecules will create less pressure

So less water potential area has less of water molecules(dilute) and creates less pressure

Question 5

The water potential of pure water (without any solutes) at atmospheric pressure is

Answer 5

0kPa, therefore any solution that has solutes will have a water potential lower than 0kPa (it will be a negative value)

equilibrium

Question 6

Exam Tip

Water can pass through the phospholipid bilayer because water molecules are small molecules that can pass between phospholipids in the cell membrane. Although water molecules are polar, they can still pass through the bilayer because of their small size.

When interpreting questions on water potential, remember – the more negative the water potential, the lower the water potential (the further it is away from pure water which has a water potential of 0 kPa).