Lab 4 Diffusion and Osmosis

Osmosis

Low to high

hypo

low (outside), water goes into the cell, burst

Which tube had the stiff potato strip? (water gain)

tube 1, hypotonic, The potato will swell and become stiff because there is a greater concentration of water outside its cells (=hypotonic solution). Thus water will enter the potato's cells by osmosis. turgor pressure.

Which poptato had the limp/floppy strip (water loss)

tube 2, hypertonic, plasmolysis makes it limp no pressure.

Hypertonic

when comparing two solutions, the solution with the greater concentration of solutes

Hypotonic

when comparing two solutions, the solution with the lesser concentration of solutes

Isotonic

when the concentration of two solutions is the same

Tonicity - diffusion

-ability of a solution to change the shape or tone of cells by altering the cells internal water volume. * Isotonic solution has same osmolarity as inside the cell, so volume remains unchanged. * hypertonic solution has higher osmolarity than inside so, so water flows out of cell, resulting in cell shrinking. Shrinking is referred to as crenation. * hypotonic solution has lower osmolarity than inside cell, so water flows into cell, resulting in cell swelling. Can lead to cell bursting, referred to as lysing.

Hypotonic blood cell

Burst= Hemolysis (animal cells)

if RBCs have 0.9% NaCl inside and the solution they are placed in had a 2% NaCl concentration, which direction will water move?

Cell will shrivel, water will move out

Plasmolysis

Collapse of a walled cell's cytoplasm due to a lack of water

Osmosis

Diffusion of water through a selectively permeable membrane. Hypo to hyper.

Calculate Diffusion rate

Dividing (mm) by your total time (h)

How can you tell that hemolysis occurred

Hemolysis: The destruction of red blood cells which leads to the release of hemoglobin from within the red blood cells into the blood plasma. Etymology: The word "hemolysis" is made up of "hemo-", blood + "lysis", the disintegration of cells.

Understand tonicity in red blood cells

If placed in a hypotonic solution, a red blood cell will bloat up and may explode, while in a hypertonic solution, it will shrivel—making the cytoplasm dense and its contents concentrated—and may die.

Why couldn't the scratch leave the bag

It is too large to cross the membrane

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

important

On the other hand, plant cells become turgid in a hypotonic solution. In a hypertonic solution, animal cells shrink dramatically while plant cells become plasmolysed which happens because the cell wall does not change shape but the cell membrane shrinks inside the cell.

Why do blood cells rupture with too much water and why plant cells do not

Plant cells are enclosed by a rigid cell wall. When the plant cell is placed in a hypotonic solution, it takes up water by osmosis and starts to swell, but the cell wall prevents it from bursting. The plant cell is said to have become "turgid" i.e. swollen and hard. The pressure inside the cell rises until this internal pressure is equal to the pressure outside. This liquid or hydrostatic pressure called the turgor pressure prevents further net intake of water. Turgidity is very important to plants as it helps in the maintenance of rigidity and stability of plant tissue and as each cell exerts a turgor pressure on its neighbor adding up to plant tissue tension which allows the green parts of the plant to "stand up" into the sunlight. Animal cells do not have cell walls. In hypotonic solutions, animal cells swell up and explode as they cannot become turgid because there is no cell wall to prevent the cell from bursting.

Hypertonic blood cell

Shrivel = Crenation (animal cells)

hypertonic plant cell

Shrivel = plasmolysis (plant cell)

Cell membranes are semi-permeable

Some molecules can cross, others will not be able to Small uncharged molecules undergo simple diffusion across the membrane Large molecules are too big to cross

hypotonic plant cell

Swell= turgid or turgor pressure (plant cell)

Turgor pressure

The pressure that water molecules exert against the cell wall

Crenation

This happens when a cell shrinks and shrivels; can result in cell death if severe.

Plasmolysis

This happens when a cell shrinks inside its cell wall while the cell wall remains intact.

important

When an animal cell is in a hypotonic solution, it usually swells up and since there is no cell wall to keep it from swelling too much it can burst.

What happened to the plant cells when you added NaCl solution? (remember this is called plasmolysis) How can you tell when you are looking at them under the microscope?

When the plant cells are placed in the salt solution, there is a higher concentration of water molecules in the cell and a lower concentration of water in the salt solution and thus a concentration gradient has been set up. ... The cell membrane is now pressed up against the cell wall and the cell is said to be turgid.

Turgor pressure can

be observed when everything is pushed up against the cell wall

Be able to explain how and why the water moved in each situation

by osmosis

plasmolysis is when the

cell contents shrink and shrivel toward the center and away from the wall (think white space around the wall)

hyper in blood

cell intact (shriveled), cloudy solution

iso in blood

cell intact, cloudy solution, light is refracted

hypo in blood

cell ruptured, clear solution, print is visible

hemolysis

destruction of red blood cells

Hyper

high (outside), water leaves the cell, shrivel.

Diffusion

high to low

Understand that the movement of water will always be to the area of

higher concentration

TUbe 2

potato + salt solution

Potato strip: Tube 1

potato + water

iso

same

Turgid (plant)

swollen

If cells are intact then

the blood solution will be cloudy