Chapter 13 Diffusion and osmosis

Syllabus Explain the role of selectively permeable membranes. Define the terms: osmosis & diffusion Give examples of diffusion and osmosis. Define the term: turgor. Explain turgidity in plant cells. Describe the application of high salt or sugar concentration in food preservation.

The Cell

Cell membrane is the boundary between inside & outside… separates cell from its environment Can it be an impenetrable boundary? NO! IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT waste ammonia salts CO2 H2O products OUT IN cell needs materials in & products or waste out

Permeability Membranes can be Permeable – let everything in and out Semi Permeable - let some things in and out Impermeable – let nothing in and out

Homeostasis – Maintaining a Balance 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.

Diffusion and Osmosis Animations View movement in the cell membrane, diffusion, osmosis Video on Osmosos & Diffusion

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

Diffusion

Diffusion in everyday life CO2 diffusing into a leaf O2 diffusing out of a leaf O2 diffusing into an animal cell CO2 diffusing out of an animal cell

Learning check Name 3 different types of membranes. Explain the term Homeostasis. How does the membranes play a role in maintaining Homeostasis? Explain the role of selectively permeable membranes. Define Diffusion

Osmosis 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. Occurs until water is balanced on both sides of the membrane.

osmosis movement of water

Learning Check What is osmosis? Does osmosis require energy?

OSMOSIS & Animal cells Animal cells in a solution that is the same concentration as their Cytoplasm - stay the same size less concentrated solution - gain water, swell and may burst more concentrated solution - lose water, shrivel and may die

Osmosis in animal cells

Shrivelled Animal Cells

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

Learning check What surrounds an animal cell? How does water move in and out of an animal cell? What will happen to animal cells in a very dilute (watery) solution? What will happen to animal cells in a very concentrated solution?

OSMOSIS & PLANT cells

Plant cells in a: less concentrated solution than their cytoplasm - gain water and become turgid (swells) and strong.

Turgor pressure 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 Osmosis in the kitchen

Plant cells in a: more concentrated solution - lose water and become plasmolysed (wilts) and weak.

Learning Check What surrounds the membrane of a plant cell? Can this structure control what moves in and out of cells? How does water enter roots of a plant? What is meant by a turgid cell? How could you identify a turgid cell?

Food Preservation 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.

Learning Check What is meant by plasmolysis? What kind of a solution would you put plant cells in to cause them to palsmolyse? How is plasmolysis used to preserve food? Give an example of some types of food preserved in this way?

Annimation showing molecules moving in osmosis

Animation: Membrane How Osmosis work – animation + audio lesson Animation: 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

To show osmosis: 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 swells as water enters due to osmosis.

Osmosis Experiment Fill each of the petri dishes about half full of water and place them on a table or flat surface where they can sit for several hours without being in the way. Use the paper and pen to make a label for each bowl. One label should say "Plain Water", and one should say "Salt" Next you want to add salt to the water in the bowl labeled "Salt." Keep adding salt. CAREFULLY slice the potato down the middle, lengthwise. You want there to me as much of the raw potato exposed as possible. Place one potato half with the flat side down onto one dish, and the other half down on the other dish. Then, you wait.  After 30 minutes, take the potato out of the bowls and examine them. What do you see? 

Video on Pototoe Expt

Instructions on drowning-gummies-aka-gummy-bear-osmosis-experiment Gummy Bear Video