Active transport question

Compare the roles of active transport and diffusion across a cell membrane. (6)

CarrierProtein Channel protein ComplementaryCharged/largeATP – ADP + P EnergyFasterConcentration gradient.

Osmosis How does water move through

plasma membranes?

Starter: What can you remember from GCSE? 1) Definition?2) is it passive/active?3) Direction of movement4) What moves?5) The difference between a solute, solvent & solution6) The difference between concentrated & dilute solutions in terms of FREE water molecules

Success criteria

• Explain what is meant by osmosis in terms of water potential (no calculations)

• Recognise and explain the effects that solutions of different water potentials could have upon plant and animal cells.

At AS, you must call it water potential (not concentration!)

Osmosis Water Potential• Diffusion of water

molecules that are free to move from an area of high water potential to a low water potential through a partially permeable membrane

• Measured in Kilopascals (kPa).

• Pure water has a water potential (WP or Y) of 0 kPa.

• Whenever something is a solution in water, it will have a negative Y

• The more solute is dissolved in water, the more negative it is.

• (less water = more negative)

Osmosis - definition

•Osmosis is the movement of water across a partially permeable membrane from a region of higher to a region of lower water potential.

High Y lower Yosmosis

Which beaker contains more “free” water molecules?

A beaker with exactly 150 ml pure water.

A beaker with exactly 150 ml pure water and 50g sugar dissolved in it.

What happens? Draw what happens in your book.

Why does osmosis occur?

partially permeable membrane

High Low

At high water molecules have more energy because they are less restricted by presence of solutes.

At low water molecules have less energy because they are more restricted by presence of solutes.

Why does osmosis occur?

partially permeable membrane

High Low

More water molecules can diffuse from left to right (high to low ) than from right to left.

There is a net movement from high to low

more water

less water

Water potential

•The higher the water potential the greater the energy of water molecules and the more likely they are to move by osmosis.•At standard temperature and pressure the of pure water is ZERO.•So, the addition of solutes lowers , and so makes the more negative.

In which direction will net osmosis take place?

Ysolution

= -230 kPa

cell

= -150 kPa

net osmosis Osmosis is the movement of water across a partially permeable membrane from a higher to a lower water potential.

In which directions will net osmosis take place?

Cell A = -100 kPa

Cell C = -150 kPa

Cell B = -200 kPa

net osmosisnet osmosis

net o

smos

is

What happens to cells in pure water?

• Animal cell will eventually burst-HAEMOLYSED

• Plant cells-swelling cytoplasm & vacuole will push against the cell wall which will stop the cell getting any larger-TURGID

What happens to cells in concentrated sugar solution?

• Animal cell: cell contents shrink & membrane wrinkles-FLACCID

• Plant cell-cytoplasm & vacuole shrink and PM pulls away from cell wall-PLASMOLYSIS

Quick Quiz

1) What is the water potential of pure water?2) Which has more free water, -167 Y kPa or Y

-302 kPa ?3) What is the definition of osmosis? 4) Which has a higher water potential, a

concentrated sugar solution or a weak sugar solution?

8 mark question

• Describe how the processes of diffusion and active transport can move molecules including water, across membranes.

• Marks will be given for correct use of terminology. You can use diagrams to support your answer.

Draw the table below & fill with annotated diagrams to explain what is happening…

Hypotonic solution (high conc of water)

Hypertonic solution(low conc of water)

Animal cells

Plant cells

Keywords to include: TurgidFlaccidPlasmolysisWater potentialkPaSoluteFree water Haemolysed

Complete the venn diagram