Active transport question Compare the roles of active transport and diffusion across a cell membrane. (6) CarrierProtein Channel protein Complementary Charged/large ATP ADP + P Energy Faster Concentration 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 movement 4) What moves? 5) The difference between a solute, solvent & solution 6) 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 osmosis lower Y 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? High Y Low Y At high Y water molecules have more energy because they are less restricted by presence of solutes.
At low Y water molecules have less energy because they are more partially permeable membrane restricted by presence of solutes. Why does osmosis occur? more water less water High Y Low Y More water molecules can diffuse from left to right
(high to low Y) than from right to left. partially permeable membrane There is a net movement from high to low Y Water potential Y 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 Y of pure water is ZERO.
So, the addition of solutes lowers Y, and so makes the Y more negative. In which direction will net osmosis take place? Ysolution Y cell = -230 kPa = -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 Y = -100 kPa os
m os m os is os is net osmosis ne t
ne t Cell B Y = -200 kPa Cell C Y = -150 kPa 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 wallPLASMOLYSIS Quick Quiz 1) What is the water potential of pure water? 2) Which has more free water, Y -167 -167 -167 kPa or
Y -167 -302 -167 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) Animal cells Plant cells Hypertonic solution (low conc of water)
Keywords to include: Turgid Flaccid Plasmolysis Water potential kPa Solute Free water Haemolysed Complete the venn diagram
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