OSMOSIS
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Is osmosis a type of ACTIVE or PASSIVE transport ? What is meant by this?
Osmosis is a type of PASSIVE transport PASSIVE = No energy required / Down the concentration gradient e.g. Diffusion, Osmosis ACTIVE= Energy required / Against the concentration gradient e.g. Active Transport
DEFINE: osmosis (SKIP , better one later down!)
Osmosis is the diffusion of water from a dilute solution to a more concentrated solution (low concentration of water) through a partially permeable membrane that allows the passage of water molecules but not soluble molecules dilute solution = high concentration of water concentrated solution = low concentration of water
Define : OSMOSIS (better using water potential)
Osmosis is the NET movement of water through a partially permeable membrane from an area of HIGHER water potential to an area of LOWER water potential , DOWN a water potential gradient
Osmosis goes ………… the concentration gradient
Osmosis goes DOWN the concentration gradient
What is the difference between diffusion and osmosis? (ignore , better later down this deck!)
-Osmosis is a special type of diffusion -diffusion is the movement of particles from a high to low concentration -osmosis is the movement of water molecules across a partially permeable membrane from an area of high to low water potential
Osmosis is the movement of water molecules from a region of …… water concentration to a region of …….. concentration across a ……………….. membrane
Osmosis is the movement of water molecules from a region of HIGHER water concentration to a region of LOWER concentration across a SEMIPERMIABLE membrane (better to use partially permeable membrane)
DEFINE: Water potential
the measure of relative tendency of water to move from one area to another NOTE : Water concentration = How much water is in a solution Water potential = how likely water is to move by osmosis.
A bag made from semi permeable membrane is tied to a glass tube and filled with a strong sugar solution , the bag is placed in a beaker of weak sugar solution. What will happen to the water molecules? How long will this occur?
The molecules will move across the semipermeable membrane from the weak sugar solution (high water potential) to the strong sugar solution (low water potential) by osmosis This continues until the concentration is the SAME on both sides of the membrane
PLANT CELLS: what will happen if the surroundings are a more concentrated solution than the cell contents (lower water concentration outside)? note: better to say e.g. surrounding have a lower water potential
If a cell is placed into a more concentrated solution: -it loses water by osmosis -the turgor pressure falls -the cell becomes FLACID (soft) and eventually the cell contents collapse away from the cell wall , this is called a plasmolysed cell
PLANT CELLS: what will happen if the surroundings are a less concentrated solution than the cell contents (higher water concentration outside)?
If a cell is placed into a dilute solution: -it takes up water by osmosis -the turgor pressure increases -the cell becomes firm / TURGID
PLANT CELLS: what will happen if the surroundings have the same concentration as cell contents?
If a cell is placed into a solution with the same concentration as its contents: -there is no NET movement of water -the cell remains the same
What makes osmosis different to diffusion? (2)
Osmosis is the movement of water molecules from a region of higher water potential to lower water potential across a semipermeable membrane whereas diffusion is the movement of ANY particles from an area of higher concentration to an area of lower concentration and does not require a semipermeable membrane (for the osmosis one, I would define osmosis instead)
What is meant by a ‘partially permeable membrane’ ?
a membrane with small pores that allows some substances to pass through but not others
What structure causes the DIFFERENCE in the way plant and animal cells respond to osmosis in or out of cells?
(rigid ) cell wall Plant cells have a limit because of the wall. Animal cells don’t — so they can overfill.
ANIMAL CELLS: what will happen if the surroundings are a more concentrated solution than the cell contents (lower water concentration outside)?
If a cell is placed into a more concentrated solution: -it loses water by osmosis -the cell becomes CRENATED (it crinkles)
ANIMAL CELLS: what will happen if the surroundings are a less concentrated solution than the cell contents (higher water concentration outside)?
If a cell is placed into a more dilute solution than its contents: -it takes up water ( by osmosis ) ,swells and may burst -This is called LYSIS NOTE: Lysis = the bursting of a cell
ANIMAL CELLS: what will happen if the surroundings have the same concentration as cell contents ?
If a cell is placed into a solution with the same concentration as its contents: • there is no NET movement of water -the cell remains the same
What is a flaccid plant cell? (2)
• plant cells lose water by osmosis ( as its surroundings are more concentrated ) and the turgor pressure falls -the cell becomes soft /flaccid (JUST USE THE DESCRIPTIONN EARLIER)
Describe plasmolysis in plant cells (2)
the cell contents collapse away from the cell wall due to the loss of excess water from osmosis (just memorise what was said on previous slides )