How can we smell our dinner How can we smell our dinner being made in the room next being made in the room next

door?door?•diffusion

DiffusionDiffusion• Diffusion is the movement of particles from a Diffusion is the movement of particles from a

region where they are concentrated to a region where they are concentrated to a region where they are less concentratedregion where they are less concentrated

• No energy is needed for Diffusion to take No energy is needed for Diffusion to take place. It is a Passive process.place. It is a Passive process.

• It is important in the movement of substances It is important in the movement of substances between cells and inside cells (occurs only over between cells and inside cells (occurs only over short distances, no more than 1mm)short distances, no more than 1mm)

• Hence, larger organisms will require Transport Hence, larger organisms will require Transport systems as well i.e. circulatory system in systems as well i.e. circulatory system in humanshumans

OsmosisOsmosis• Osmosis is the movement of water Osmosis is the movement of water

molecules across a semi-permeable molecules across a semi-permeable membrane, from an area of high membrane, from an area of high concentration of water molecules to an concentration of water molecules to an area of low concentration of water area of low concentration of water molecules.molecules.

Cell Membrane & OsmosisCell Membrane & Osmosis• The cell membrane controls movement The cell membrane controls movement

of substances into and out of the cellof substances into and out of the cell

• It is semi-permeable i.e. it allows small It is semi-permeable i.e. it allows small molecules like water, carbon dioxide and molecules like water, carbon dioxide and oxygen through by diffusion but stops oxygen through by diffusion but stops larger ones.larger ones.

• Where energy is required to move Where energy is required to move molecules in and out of cells is called molecules in and out of cells is called Active transportActive transport

OsmoreregulationOsmoreregulation• Our cells contain sugar and salt at certain Our cells contain sugar and salt at certain

concentrations.concentrations.

• If these concentrations change, action is If these concentrations change, action is taken by cells to counteract the changes and taken by cells to counteract the changes and return to the normal balanced state.return to the normal balanced state.

• This balancing action is called This balancing action is called Osmoregulation. Osmoregulation.

Osmosis in Animal CellsOsmosis in Animal CellsAnimal Cells in Pure waterAnimal Cells in Pure water

• Red blood cells have 1% Red blood cells have 1% salt concentration in them.salt concentration in them.

• What would happen if a red What would happen if a red cell is placed in pure water?cell is placed in pure water?

• The Cytoplasm swells up The Cytoplasm swells up with water and eventually with water and eventually the cell may burst and die.the cell may burst and die.

Animal cells in Salt waterAnimal cells in Salt water

• What would happen if a What would happen if a red cell is placed in a red cell is placed in a very salty solution?very salty solution?

• Experiences a loss of Experiences a loss of water which causes the water which causes the cell to shrivel up.cell to shrivel up.

Osmosis in Plant CellsOsmosis in Plant CellsPlant Cells in Pure WaterPlant Cells in Pure Water

• Onion cells have Salt and Onion cells have Salt and Sugar in their cytoplasm.Sugar in their cytoplasm.

• What happens if an onion What happens if an onion cell is placed in pure cell is placed in pure water?water?

• The cytoplasm & vacuole The cytoplasm & vacuole fill up with water, which fill up with water, which stretches the cell.stretches the cell.

• The cell wall prevents the The cell wall prevents the cell from bursting and the cell from bursting and the cell is said to be Turgid.cell is said to be Turgid.

Plant Cells in Salt SolutionPlant Cells in Salt Solution

• What happens if an onion What happens if an onion cell is placed in a very cell is placed in a very salty solution?salty solution?

• The cytoplasm & vacuole The cytoplasm & vacuole lose water.lose water.

• The cell membrane comes The cell membrane comes away from the cell wall, away from the cell wall, the cell is said to be the cell is said to be Plasmolysed.Plasmolysed.

Turgid describes a plant cell in which the cell wall Turgid describes a plant cell in which the cell wall is rigid, due to the cytoplasm pushing out against it is rigid, due to the cytoplasm pushing out against it as it fills with water.as it fills with water.Osmotic pressure is the main cause of support in Osmotic pressure is the main cause of support in plant leavesplant leaves

(Without water the cell walls are not strong enough (Without water the cell walls are not strong enough to support the weight of the plant, and so it Wilts)to support the weight of the plant, and so it Wilts)

Osmosis in Food PreparationOsmosis in Food Preparation• Naturally occurring chemicals like salt, sugar Naturally occurring chemicals like salt, sugar

and fruit juice will preserve foods by osmosis. and fruit juice will preserve foods by osmosis. • Salt is the oldest and most common method Salt is the oldest and most common method

of preserving fish and meats.of preserving fish and meats.• Water moves, by osmosis, from the cells into Water moves, by osmosis, from the cells into

the salt solution, causing the tissues to the salt solution, causing the tissues to become dehydrated, which destroys become dehydrated, which destroys bacteria.bacteria.

• Sugars are used to preserve fruits Sugars are used to preserve fruits (jams/tinned fruit)(jams/tinned fruit)

Active TransportActive Transport• In order for Large molecules to move across the cell In order for Large molecules to move across the cell

membrane they must do so at certain ‘gates’ and themembrane they must do so at certain ‘gates’ and thecell has to use energy to do this.cell has to use energy to do this.

• These ‘gates’ are proteins within the cellThese ‘gates’ are proteins within the cellmembrane, which pump the molecules across, membrane, which pump the molecules across, often against the concentration gradientoften against the concentration gradient(from where there is less to where there (from where there is less to where there is more of the substance)is more of the substance)

• Active Transport is the movement of substances across Active Transport is the movement of substances across a cell membrane against a concentration gradient, a cell membrane against a concentration gradient, using energy from respiration.using energy from respiration.

SOLUTE CONCENTRATION GRADIENT

Fewer solute

molecules

More solute

molecules

Active transport o

f

solute molecules