Chapter 13Chapter 13Diffusion and OsmosisDiffusion and Osmosis

Diffusion & Osmosis

Draw a spider diagram about what you know about movement of substances in & out of the cell

Syllabus Syllabus -- Objectives-- Objectives

Define the term: Selectively permeableDefine the term: Selectively permeable Explain the role of selectively permeable Explain the role of selectively permeable

membranes.membranes. Define the terms: osmosis & diffusionDefine the terms: osmosis & diffusion Give examples of diffusion and osmosis.Give examples of diffusion and osmosis. Define the term: turgor.Define the term: turgor. Explain turgidity in plant cells.Explain turgidity in plant cells. Describe the application of high salt or Describe the application of high salt or

sugar concentration in food preservation.sugar concentration in food preservation.

Selective permeability of membranes

All cell membranes (biological membranes) are similar in structure.

The cell membrane (plasma membrane) around a cell works the same as membranes around organelles eg. Mitochondria & nucleus.

Movement in cells takes place Movement in cells takes place through membranesthrough membranes

All the membranes in a cell act in the same All the membranes in a cell act in the same wayway

Mitochondrial membranes

Cell Membranes

Chloroplast membranes

Nuclear membranes

New Vocabulary

Selectively permeable: A selectively permeable membrane allows some but not all substances to pass through. E.g. cell membrane

Permeable: A permeable membrane allows all substances through e.g. cell wall is fully permeable.

Impermeable: An impermeable membrane does not allow substances to pass through.

Biological membranes are semi-permeable. Other membranes e.g. cellophane, visking tubing & dialysis tubing are semi permeable (selectively permeable)

These membranes allow small molecules such as water, oxygen and carbon dioxide to pass through freely.

They do not allow large molecules e.g. protein, sugars and salts to pass through easily.

Cells have specialised mechanisms in their membranes to allow these substances e.g. proteins, sugars & salts through when necessary.

DialysisDialysis is used on patients whose kidneys do not work properly. The dialysis membrane in the machine is used to filter the persons blood and remove substances e.g. salts, water and urea.

MovementMovement

Substances move in and out of cells in 2 waysSubstances move in and out of cells in 2 ways

1. 1. DiffusionDiffusionMovement of molecules from a region of higher concentration to Movement of molecules from a region of higher concentration to a region of lower concentration. This method a region of lower concentration. This method does not require does not require energyenergy..

2. 2. Active TransportActive TransportMovement of molecules from a less crowded to a more crowded Movement of molecules from a less crowded to a more crowded area WITH the use of energy.area WITH the use of energy.

Molecules are “carried" into or out of the cell using some of the Molecules are “carried" into or out of the cell using some of the

cell's energy.cell's energy.

Learning checkLearning check

What type of movement in cells requires What type of movement in cells requires energy?energy?

What type of movement in cells does What type of movement in cells does not require energy?not require energy?

Diffusion is the movement of substances Diffusion is the movement of substances from an area of ....... concentration to an from an area of ....... concentration to an area of ......... concentrationarea of ......... concentration

Name 3 different types of membranesName 3 different types of membranes

PermeabilityPermeabilityMembranes can be:Membranes can be:

PermeablePermeable – let everything in and out – let everything in and out e.g. cell walle.g. cell wall

Semi PermeableSemi Permeable - let some things in and - let some things in and out e.g. cell membraneout e.g. cell membrane

ImpermeableImpermeable – let nothing in and out e.g. – let nothing in and out e.g. wall of cork cells wall of cork cells

Diffusion in everyday lifeDiffusion in everyday life

Smell of perfumeSmell of perfume Bread bakingBread baking Food colouring in waterFood colouring in water Sugar in teaSugar in tea

Diffusion in a LeafIn photosynthesis Carbon dioxide gas diffuses into leaf and

oxygen gas diffuses out

Carbon dioxide

Oxygen

Learning CheckLearning Check

What type of permeability allows free What type of permeability allows free movement of substances?movement of substances?

What type of permeability allows What type of permeability allows some movement of substances?some movement of substances?

What type of permeability allows no What type of permeability allows no movement of substances?movement of substances?

Can you name a few common Can you name a few common examples of diffusion?examples of diffusion?

New Vocabulary

OsmosisOsmosis

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

Solvent: A solvent is a liquid that dissolves other substances e.g. water

Solute: A solute is a substance that has been dissolved e.g. sugar & salt

Solution: The mixture of the solvent and solute is a solution. E.g. salty water

Osmosis is a special type of diffusion Osmosis is a special type of diffusion that does not require energythat does not require energy

Osmosis is Osmosis is passive passive (no energy required)

Experiment to Demonstrate Osmosis

Sucrose Solution

Distilled Water

Turgid (fullness) at start

Turgid (fullness) at end

Mass at start (g)

24.1g 24.0g

Mass at end of Activity (g)

29.5g 24.0g

Results Table T/B pg 134

If pure water is If pure water is separated from salt separated from salt water by a membrane water by a membrane the following occurs:the following occurs:

1.1. The water molecules The water molecules move randomly in both move randomly in both directionsdirections

2.2. The salt molecules The salt molecules cannot move out so cannot move out so more water moves in to more water moves in to the salt solutionthe salt solution

3.3. What you have is water What you have is water moving from where moving from where there is a high there is a high concentration of water concentration of water to where there is a to where there is a lower concentration of lower concentration of water this is water this is osmosisosmosis

Learning CheckLearning Check

What is osmosis?What is osmosis? Does osmosis require energy?Does osmosis require energy?

Osmosis and Animal CellsOsmosis and Animal Cells

Animal cells are only enclosed by a Animal cells are only enclosed by a membranemembrane

If an animal cell is surrounded by a If an animal cell is surrounded by a solution that is the same solution that is the same concentration as the cytoplasm in concentration as the cytoplasm in the cell water will move in and out at the cell water will move in and out at the same rate and the cell will the same rate and the cell will remain intact.remain intact.

Many animals that live in the sea have Many animals that live in the sea have cytoplasm with a similar concentration cytoplasm with a similar concentration to sea water. If this didn’t happen the to sea water. If this didn’t happen the fish would swell up or shrivel up.fish would swell up or shrivel up.

It is the function of our kidneys to It is the function of our kidneys to make sure the fluid in our bodies that make sure the fluid in our bodies that surrounds our cells (plasma) has a surrounds our cells (plasma) has a stable concentration.stable concentration.

Animal cells in a less Animal cells in a less concentrated solutionconcentrated solution

If an animal cell is in a solution that If an animal cell is in a solution that is less concentrated than its is less concentrated than its cytoplasm (i.e. if there is more water cytoplasm (i.e. if there is more water outside than inside the cell) the outside than inside the cell) the water from outside will move into the water from outside will move into the cell and may cause it to burst or die.cell and may cause it to burst or die.

Amoebas (microscopic animal Amoebas (microscopic animal cells)cells)

Amoeba Amoeba Amoeba is a microscopic animalAmoeba is a microscopic animal

that lives in fresh water or sea that lives in fresh water or sea

water.water.

Amoeba has a special organelle Amoeba has a special organelle

called a contractile vacuole called a contractile vacuole

When amoeba absorbs water throughWhen amoeba absorbs water through

its cell membrane it sends it to the its cell membrane it sends it to the contractile vacuole.contractile vacuole.

When the contractile vacuole is full of When the contractile vacuole is full of water it bursts onto the surface of the water it bursts onto the surface of the amoeba like a pimple releasing its amoeba like a pimple releasing its water.water.

If amoeba did not have a contractile If amoeba did not have a contractile vacuole it would not be able to get rid of vacuole it would not be able to get rid of the absorbed water and would swell up the absorbed water and would swell up and burst. and burst.

Animal Cells in a more Animal Cells in a more concentrated solutionconcentrated solution

If animal cells are in a solution that is If animal cells are in a solution that is more concentrated than their more concentrated than their cytoplasm (i.e. if there is more water cytoplasm (i.e. if there is more water in their cytoplasm than in the in their cytoplasm than in the solution outside) then the water may solution outside) then the water may leave the animal cell and the cells leave the animal cell and the cells shrivel up and may die. shrivel up and may die.

Shrivelled Animal CellsShrivelled Animal Cells

Normal cells

Swollen cells

Red blood cells (animal cells)

Learning checkLearning check

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

an animal cell?an animal cell? What will happen to animal cells in a What will happen to animal cells in a

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

very concentrated solution?very concentrated solution?

Osmosis and Plant CellsOsmosis and Plant Cells Plant cells have a membrane Plant cells have a membrane

which is surrounded by a cell wallwhich is surrounded by a cell wall Cell walls are fully permeable and Cell walls are fully permeable and

will allow all substances in and out will allow all substances in and out of the cellof the cell

If a plant cell is surrounded by a If a plant cell is surrounded by a less concentrated solution then less concentrated solution then water from outside will move into water from outside will move into the cytoplasm and vacuole of the cytoplasm and vacuole of plant cellsplant cells

This is how roots absorb water by This is how roots absorb water by osmosisosmosis

Water entering roots by Water entering roots by osmosisosmosis

The water outside is The water outside is less concentrated less concentrated than the water in the than the water in the cytoplasmcytoplasm

TurgorTurgor

When the outside water enters the When the outside water enters the plant cell the vacuole becomes plant cell the vacuole becomes bigger and the cytoplasm swellsbigger and the cytoplasm swells

This causes the membrane to be This causes the membrane to be pushed out towards the cell wallpushed out towards the cell wall

When cells are fully “swelled” like When cells are fully “swelled” like this with the membranes pushing this with the membranes pushing against the cell wall they are against the cell wall they are described as described as Turgid.Turgid.

Turgid CellsTurgid Cells

Plant Cells in solutions of different concentration

Turgor pressureTurgor pressure

This turgor pressure gives plants This turgor pressure gives plants their strengththeir strength

If plants did not have this they would If plants did not have this they would be wilted (dead)be wilted (dead)

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

Plant cells

Plant cells in a more Plant cells in a more concentrated solutionconcentrated solution

If plant cells are surrounded by a If plant cells are surrounded by a more concentrated solution (for more concentrated solution (for example if plant cells were example if plant cells were surrounded by salt water) the water surrounded by salt water) the water inside the cell would move out to the inside the cell would move out to the more concentrated solution outside more concentrated solution outside and the cell will shrivel up (flacid cell)and the cell will shrivel up (flacid cell)

Turgid plant cell & flacid plant Turgid plant cell & flacid plant cellcell

a) Wilted Plant, b) normal plant,

c) plant with too much water

Learning CheckLearning Check

What surrounds the membrane of a What surrounds the membrane of a plant cell?plant cell?

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

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

PlasmolysisPlasmolysis

When this happens the cell wall stays When this happens the cell wall stays intact but the membrane shrivels up intact but the membrane shrivels up away from itaway from it

This is called This is called PlasmolysisPlasmolysis Cells in this condition are called Cells in this condition are called

plasmolysed cellsplasmolysed cells we can look at we can look at this easily by placing a layer of red this easily by placing a layer of red onion cells in salt wateronion cells in salt water

Normal plant cell and plasmolysed plant cell

Plasmolysed Plant CellsPond weed (Elodea)

Plasmolysed red onion cellsPlasmolysed red onion cells

Food Preservation

Why might you need to preserve foods?

Can you name any food preservation methods?

Osmosis and Food Osmosis and Food PreservationPreservation

Bacteria and Fungi are the most Bacteria and Fungi are the most common causes of food spoilagecommon causes of food spoilage

Both these cells are enclosed by a Both these cells are enclosed by a membranemembrane

If a food is placed in a sugary or salty If a food is placed in a sugary or salty solution then any bacteria or fungi solution then any bacteria or fungi present will lose the water in their present will lose the water in their cells to the more concentrated cells to the more concentrated solution outsidesolution outside

When this happens the cells will When this happens the cells will shrivel and die and the food will not shrivel and die and the food will not become contaminated with loads of become contaminated with loads of bacteria and fungi.bacteria and fungi.

These types of preservation can keep These types of preservation can keep food fresh for long periods of time. food fresh for long periods of time.

Prevents and delay microbial decomposition and damage from mechanical causes, insects and rodents

Ensures more interesting and nutritionally adequate family meals

Ensure a safer food intake

Food Preservation

Commonly used in meat and fish and less in fruits and vegetables

In some foods, salting is combined with other methods like smoking, fermenting, drying, freezing

Examples: ham, bacon, salted eggs, sausage, tocino

Salting

Sodium Chloride (NaCl) preserves food by removing water content through osmosis

Salt as a preservative

When food is salted, its water content is drawn out, freeing the food or reducing the moisture content which makes the food less susceptible to microorganisms

Draws out water through osmosis Examples of foods preserved by adding

sugar are jams and fruit

Sugar as a preservative

ExamplesExamples

Fish and Meat (bacon) may be stored Fish and Meat (bacon) may be stored in a salty solution in a salty solution

Jams, marmalades and tinned fruits Jams, marmalades and tinned fruits are stored in a sugary solutionare stored in a sugary solution

Learning CheckLearning Check

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

plant cells in to cause them to plant cells in to cause them to palsmolyse?palsmolyse?

How is plasmolysis used to preserve How is plasmolysis used to preserve food?food?

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

Exam questions Exam questions 2005 Ordinary level Q72005 Ordinary level Q7

2008 Higher level Q14C2008 Higher level Q14C