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1. Explain the role of selectively permeable membranes.

2. Define the terms: osmosis & diffusion3. Give examples of diffusion and osmosis.4. Define the term: turgor.5. Explain turgidity in plant cells.6. Describe the application of high salt or

sugar concentration in food preservation.

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INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUTwasteammoniasaltsCO2

H2O products

cell needs materials in & products or waste out

IN OUT

Can it be an impenetrable boundary? NO!

Cell membrane is the boundary between inside & outside…separates cell from its environment

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Membranes can be1.Permeable – let everything in and

out2.Semi Permeable - let some things

in and out3.Impermeable – let nothing in and

out

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Cells must keep the proper concentration of nutrients and water and eliminate wastes.

The plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things.

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Diffusion and Osmosis Animations

View movement in the cell membrane, diffusion, osmosis

Video on Osmosos & Diffusion

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Lipid bilayer – two sheets of lipids (phospholipids). Found around the cell, the nucleus,

vacuoles, mitochondria, and chloroplasts.

Embedded with proteins that determine what particles can pass through the membrane.

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movement of molecules from an area of high concentration to an area of low concentration. Passive transport / no external energy

needed.

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Diffusion

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CO2 diffusing into a leaf O2 diffusing out of a leaf O2 diffusing into an animal cell CO2 diffusing out of an animal cell

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1. Name 3 different types of membranes.2. Explain the term Homeostasis.3. How does the membranes play a role in

maintaining Homeostasis?4. Explain the role of selectively

permeable membranes.5. Define Diffusion

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is the movement of water from a region of high water concentration to a region of low water concentration across a semi-permeable membrane

Passive transport / no external energy needed.

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movement of water

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1. What is osmosis?2. Does osmosis require energy?

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Animal cells in a solution that is the1.same concentration as their Cytoplasm - stay the same size2.less concentrated solution - gain water, swell and may burst3.more concentrated solution - lose water, shrivel and may die

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Osmosis in animal cells

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1. What surrounds an animal cell?2. How does water move in and out of an

animal cell?3. What will happen to animal cells in a

very dilute (watery) solution?4. What will happen to animal cells in a

very concentrated solution?

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1. less concentrated solution than their cytoplasm - gain water and become turgid (swells) and strong.

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This turgor pressure gives plants their strength

If plants did not have this they would wilt

Plants that don’t have wood such as lettuce and house plants rely on turgor pressure for strength

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2. more concentrated solution - lose water and become plasmolysed (wilts).

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1. What surrounds the membrane of a plant cell?

2. Can this structure control what moves in and out of cells?

3. How does water enter roots of a plant?4. What is meant by a turgid cell?5. How could you identify a turgid cell?

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Amoeba survives in a less concentrated (freshwater) environment due to its contractile vacuole, which eliminates water.

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Bacteria and Fungi are the most common causes of food spoilage

If a food is placed in a high sugary or salty solution then any bacteria or fungi present, will lose the water in their cells by osmosis, shrivel and die.

E.g. Salting fish or high sugar concentration in jam.

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1. What is meant by plasmolysis?2. What kind of a solution would you put

plant cells in to cause them to palsmolyse?

3. How is plasmolysis used to preserve food?

4. Give an example of some types of food preserved in this way?

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Annimation showing molecules moving in osmosis

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How Osmosis work – animation + audio lessonAnimation: How Osmosis Works

Check out this Shockwave video of simple diffusion, facilitated diffusion, and osmosis. This is a great overview of these terms

Animation: Membrane

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Place bags of visking tubing half-filled with(a) distilled water, (b) 80% sucrose solution, in distilled water.

Bag (a) stays the same mass and size.Bag (b) increases in mass and swellsas water enters due to osmosis.

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