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Page 1: JDH Diffusion and Osmosissd67.bc.ca/teachers/jheinrich/Sci 10 pdf/Biology/Diffusion and... · Diffusion and Osmosis. ... Diffusion and the Cell Movement of molecules by diffusion

Diffusion and

Osmosis

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The Cell Membrane

� The cell membrane is:

�Selectively permeable

� Permeable = Pass through (Latin)

� Cell membrane = Gate-Keeper that determines what can and can’t enter the cell.

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The Gate Keeper: The Cell

Membrane

� Who comes in for the

party?

� Small molecules like

water, carbon dioxide,

or oxygen can easily

pass through the

pores of the

membrane.

� Who gets bounced?

� Large molecules like

glucose

� Charged molecules

like salts.

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Molecule Movement

� Recall cells are small because they need to

obtain sufficient nutrients and dispose of their

wastes.

� This is done by the cell membrane by three

means:

1. Diffusion

2. Osmosis

3. Active Transport (Senior Science)

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Definitions.

� Solution = A homogenous, liquid mixture of two or more substances.

� Solvent = The dissolving agent of a solution. Water is the most versatile solvent known.

� Solute = Substance that is dissolved in a solution.

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Diffusion

� The process by which molecules tend to move

from an area of higher concentration to an area

of lower concentration.

� Concentration= amount of substance in a given

volume.

� Think of the perfume example (high� low)

� Think of the food-dye example (high� low)

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Why Diffusion?

� Kinetic molecular theory.

� Molecules are always moving

� Collisions occur between molecules, which causes the molecules to move away from one another.

� If there is space these molecules want to spread out evenly.

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What direction will the molecules move?

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Diffusion and the Cell

� Movement of molecules by diffusion is how the cell fulfills its needs.

� Nutrients: Low concentration in the cells, high concentration outside of the cells.

� What direction will the nutrients diffuse?

� From outside the cell to inside the cell.

� High to Low Concentration!!

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Diffusion and the Cell

� Wastes: High concentration in the cell, low outside of the cell.

� What direction will the wastes move?

� From inside the cell to outside the cell.

� High to Low concentration

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A special case of diffusion:

Osmosis

� Water moves through the pores of the cell

membrane like other molecules.

� The movement of water from a high

concentration to a low concentration (thru a

semi-permeable membrane) is called: Osmosis

� Osmosis = movement of water (the solvent)

� Diffusion = movement of dissolved materials

(the solutes)

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Osmosis is the movement of water (red dots) through a semipermeable membrane to a higher concentration of

solutes (blue dots).

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Activity — Predicting

Movement of Water� This “U” tube has a

selectively permeable membrane separating side A and B.

� Side A has a 40% solution of sugar and side B has a 60% solution of sugar.

� Which side has more water?

� Which way will the water move?

Selectively Permeable Membrane

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Osmosis – a cure for the flu?

� Who here has taken penicillin to combat sickness?

� Penicillin weakens bacterial cell walls

� Water is at higher conc. outside the cell…which way will water move?

� With a weak cell wall, the bacterial cell swells and…POP!

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**Summary**

� Both osmosis and diffusion involve the movement of molecules from an area of high concentrations to a area of low concentrations.

� Osmosis = movement of water (the solvent)

� Diffusion = movement of dissolved materials (the solutes)

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Water Balance

� The cell membrane doesn’t actually control the movement of water.

� The environment around the cell determines the direction of water movement.

� For example, a cell is placed in a salt water tide pool. The sun evaporates some water.

� The concentration of water inside the cell is higher than outside.

� What happens?

� Water leaves the cell. � Possible shrinking of the cell.

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Water Balance

� On the contrary imagine it rains.

� A higher concentration of water outside the cell is the result.

� What happens?

� Water moves into the cell

� Possible swelling of the cell.

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Water Regulation

� Without other mechanisms the cell would burst or shrivel.

� Plant vacuoles store water even when the environment is dry.

� The cell wall is rigid to prevent bursting or shriveling.

� Animals can increase or decrease their amount of water intake and outtake (Urine concentration/amount of water that is drank)

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Hypertonic Solution – More water inside cell than outside

Plasmolysis

Plasmolysis

Cells shrink

and die

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Iso-osmotic Solution – same concentration of water inside and outside cell

Animal cell

Plant cell

No net gain or

loss of water

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Hypotonic Solution – more water

outside cell than inside

Cytolysis –

cell swells and

bursts

Builds up turgor

pressure – cell

becomes stiff,

keeping plant

upright

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� What would happen to a cell placed in pure water?

90% water

10% solute100% water

Cell’s are about 90% water.

Human Red Blood Cell Before: After

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� What would happen to a cell

placed in a 20% salt solution?

90% water

10% solute

Cell’s are about 90% water.

80% water

Human Red Blood Cell Before: After

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Potatoes and Corn Starch…..

� Finish your Experiments…

� Remember Unit Test on Friday

� Microscopes & Cells

� Structures/Functions

� Cellular Respiration/Photosynthesis

� Cell Size

� Osmosis/Diffusion

� Single Celled Organisms.

� Similar to Quiz Yesterday


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