The net movement of particles from an area of high concentration to an area of low concentration Due to the random movement of particles A passivepassive process which means that no energyno energy is needed

HIGH concentration

LOW concentration

A difference in concentration between 2 areas is called a

CONCENTRATION GRADIENT.

What effect might the gradient have on speed of diffusion?

Dissolved substances have to pass through the partially permeable cell membrane to get into or out of a cell. Diffusion is one of the processes that

allows this to happen..

What substances are we talking

about?

All living cells rely on diffusion to live.

They use it for:

Getting raw materials for

respiration (dissolved

substances and gases)

Removing waste products (eg. from respiration)

Plants use of photosynthesis (raw materials

in, waste products out)

Examples…

Oxygen in inhaled air diffuses through the lungs and into the bloodstream. The oxygen is then transported throughout the body.

Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from body tissues into the bloodstream and is exhaled via the lungs.

blood vessels

capillary network

Villi

small intestine

The villi and microvilli result in a LARGE SURFACE AREA, for maximum absorption.

Movement of glucose from small intestine lumen into blood capillaried of villi

A synapse is a junction between two neurones across which electrical signals must pass.

Neurotransmitter molecules diffuse from vesicles towards the neurotransmitter receptors, moving from an area of high concentration to low concentration.

•The placenta is an organ that develops in the uterus during pregnancy.

•The umbilical cord connects the placenta to the foetus.

•It enables nutrients and oxygen to pass from the mother to the foetus by diffusion, and waste substances to diffuse from the foetus back to the mother.

•The placenta can stop certain molecules and bacteria from diffusing through

•It is unable to stop many harmful substances such as alcohol, chemicals and some types of virus from diffusing through, reaching the foetus.

How does the placenta work?

umbilical

cord

umbilical

artery

umbilicalvein

Carbon dioxide diffuses in through the stomata Oxygen and water diffuse

out of the stomata

carbon dioxide + water oxygen + glucose

During photosynthesis, the level of CO2 is low inside the leaf This creates a big concentration gradient so CO2 diffuses into the cell

a specialized case of diffusion in which the microscopic holes of membranes were so small that they allow the passage of water molecules but not the sugar molecules.

movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

movement of water molecules across a selectively permeable membrane from a region of lesser solute concentration to a region of higher solute concentration.

If the area outside the cell has more salt

– then water will be sucked out of the

cell

Osmosis demonstration

DIFFUSIONBoth water and solute

particles can moveMolecules tend to

“spread out”

OSMOSIS Only water moves

"ISO" means the same

Cell may burst, or

organelles called

“contractile vacuoles”

remove excess water

Cell will shrink or die,

plants wilt

Why is it dangerous

to drink sea water?

Why does pouring

salt on a slug kill it?

Hypotonic –"HYPO" means less, less solute, Dilute, higher water potential

Hypertonic – "HYPER" means more,more solute, concentrated, low water potential

Isotonic - "ISO" means the same when both solutions have the same water potential (‘iso’: same as; ‘tonicity’: strength of solution).

most plant cell live in_________environment.

There is low concentration of solutes in extracellular fluids than in cells. As a reault, water tend to move first inside cell and then inside vacuole. When vacuole increases in size, cytoplasm presses against the interior of cell wall, which expand a little. Due to strong cell wall plant cell does not repture but instead become rigid or turgid.

There is low concentration of solutes in extracellular fluids than in cells. As a reault, water tend to move first inside cell and then inside vacuole. When vacuole increases in size, cytoplasm presses against the interior of cell wall, which expand a little. Due to strong cell wall plant cell does not repture but instead become rigid or turgid.

This is why it is dangerous to This is why it is dangerous to drink sea water - its a myth drink sea water - its a myth that drinking sea water will that drinking sea water will cause you to go insane, but cause you to go insane, but people marooned at sea will people marooned at sea will speed up dehydration (and speed up dehydration (and death) by drinking sea water.death) by drinking sea water.This is also why "salting This is also why "salting fields" was a common tactic fields" was a common tactic during war, it would kill the during war, it would kill the crops in the field, thus crops in the field, thus causing food shortages.causing food shortages.

Fresh water

sea water /ocean

Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in ahypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. 

Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. 

Isotonic Solutions: contain the same concentration of solute as an another solution (e.g. the cell's cytoplasm). When a cell is placed in anisotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.

Water enter plant (root) cells by______, because the water potential of soil is usually higher than the water potential of a plant‘s cell sap.

The solution in the roots of the plants is

hypertonic, drawing in water from the

surrounding hypotonic soil. Roots are

designed as selectively permeable membranes,

admitting not only water, but some useful

solutes. 

The solution in the roots of the plants is

hypertonic, drawing in water from the

surrounding hypotonic soil. Roots are

designed as selectively permeable membranes,

admitting not only water, but some useful

solutes. 

Xylem tissue: Water and ions travel upwards

Phloem tissue: Sucrose and other assimilates travel upwards and downwards

Movement of water in the xylem and phloem is by mass flow. Everything travels in the same direction within each of column of xylem or phloem

Note that neither plant transport system carries O2 or CO2

Xylem tissue vessel element

tracheids Start as living cells

(nucleus, cell wall) Then differentiated

into specialised structures and died

No living material Just empty shells

sometimes fatal medical condition known as water intoxication occurs when people drink a large amount of water very rapidly, causing a dilution of the water which flows freely through their bodies. This diluted solution is capable of pushing through the cell membranes, thanks to osmosis, and it can cause cells to explode as they expand to accommodate the water.

Conversely, when people become dehydrateddehydrated, cells shrivel and die as the free-flowing water in the body becomes highly concentrated with solutes, causing water to flow out of the cells in an attempt to reach an isotonic state.

A 5% urea solution is hypotonic to a 10% urea solution.yes

no

Reverse osmosis is a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side, meaning it allows the passage of solvent but not of solute. In reverse osmosis, the idea is to use the membrane to act like an extremely fine filter to create drinkable water from salty water.

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs.