Diffusion and Diffusion and OsmosisOsmosis

Importance of WaterImportance of Water

Living things are Living things are composed of more composed of more than 50 percent than 50 percent water and depend water and depend on water to survive.on water to survive.

You can live for You can live for weeks without food weeks without food but only a few days but only a few days without water.without water.

Why is water so Why is water so important?important?1.1. All the All the chemical reactionschemical reactions in living things in living things

take place in water solutions.take place in water solutions.

2.2. Organisms use water to Organisms use water to transport transport materialsmaterials through their bodies. through their bodies.

PlantsPlants use water to use water to move minerals and move minerals and sugarssugars between roots and leaves. between roots and leaves.

3. The large percentage of water in living 3. The large percentage of water in living things things acts like an insulatoracts like an insulator..

The water in a cell helps The water in a cell helps keep its keep its temperature constanttemperature constant, which allows life-, which allows life-sustaining chemical reactions to take place.sustaining chemical reactions to take place.

Cell MembraneCell Membrane

Cells take in food, Cells take in food, and oxygen, from and oxygen, from their environment their environment and release waste and release waste material.material.

A cell has a A cell has a membrane around membrane around it that works like a it that works like a window screen.window screen.

Selectively PermeableSelectively PermeableA cell’s membrane is A cell’s membrane is selectively permeableselectively permeable. .

-Allows some things to enter or -Allows some things to enter or leaveleave the cell the cell while while keepingkeeping other things outside or inside other things outside or inside the cell. the cell. – Cell membranes Cell membranes will allow small moleculeswill allow small molecules

like O2, H20 and , CO2, to pass through. like O2, H20 and , CO2, to pass through. – Cell membranes Cell membranes will not allow larger will not allow larger

moleculesmolecules like Sucrose, and Starch. to pass like Sucrose, and Starch. to pass through.through.

Passive TransportPassive Transport

How things move through a cell How things move through a cell membrane depends on the size of membrane depends on the size of the particles, the path taken the particles, the path taken through the membrane, and through the membrane, and whether or not energy is used.whether or not energy is used.

The movement of substances The movement of substances through the cell membrane through the cell membrane without the input of energywithout the input of energy is is called called passive transportpassive transport..

3 Types of Passive 3 Types of Passive TransportTransport

1.1. DiffusionDiffusion

2.2. Osmosis Osmosis

3.3. Facilitated diffusionFacilitated diffusion

1. Diffusion1. Diffusion

Molecules in solids, Molecules in solids, liquids, and gases move liquids, and gases move constantly.constantly.

This random This random movement movement of moleculesof molecules from from one one areaarea where there are where there are moremore of them of them into into another areaanother area where where there are there are fewer fewer of them of them is called is called diffusiondiffusion. .

Example: Food Coloring Example: Food Coloring and Waterand Water

EquilibriumEquilibrium

Molecules of a substance will Molecules of a substance will continue to move from area into continue to move from area into another until the relative number another until the relative number of these molecules is equal in the of these molecules is equal in the two areas.two areas.

When this occurs, When this occurs, equilibriumequilibrium is is reached and diffusion stops.reached and diffusion stops.

2. Osmosis2. Osmosis

Water molecules Water molecules move move by diffusionby diffusion into and into and out of cells. out of cells.

Osmosis is the Osmosis is the passage passage of water of water from a region from a region of high water of high water concentration concentration through through a semi-permeable a semi-permeable membranemembrane to a region to a region of low water of low water concentration.concentration.

OsmosisOsmosis If the area If the area surrounding the surrounding the

cell has acell has a lower lower concentration of water concentration of water moleculesmolecules than inside the than inside the cell, the cell will cell, the cell will loselose water water by osmosis.by osmosis.

If the area If the area surrounding the surrounding the cell has a higher cell has a higher concentration of water concentration of water moleculesmolecules than inside the than inside the cell, the cell will cell, the cell will gaingain water water by osmosis.by osmosis.

Example:CarrotsExample:Carrots

Why do carrots in salt Why do carrots in salt water become limp?water become limp?

When there is a When there is a lowerlower concentration of water concentration of water molecules surroundingmolecules surrounding the carrot cells, water is the carrot cells, water is lost from inside the lost from inside the cells. The cell cells. The cell membrane comes membrane comes away from its cell wall.away from its cell wall.

The loss of water The loss of water reduces pressure reduces pressure against the cell wall, against the cell wall, and carrot cell becomes and carrot cell becomes limp.limp.

Why do carrots stay Why do carrots stay crisp in pure water?crisp in pure water? When there is a When there is a higherhigher

concentration of water concentration of water surrounding surrounding the carrot the carrot cells than inside the cell, cells than inside the cell, water moves into the water moves into the cells. cells.

The cells would fill with The cells would fill with water. water.

Their cell membranes Their cell membranes press against their cell press against their cell walls.walls.

Pressure increases and Pressure increases and the cells become firm.the cells become firm.

3rd Type of Passive Transport:

Facilitated Diffusion

• Some substances pass easily through the cell membrane by diffusion.

• Other substances are so large that they can enter and leave the cell only with the help of molecules in the cell membrane called transport proteins. Glucose, Calcium, Potassium

• This process, a type of passive transport, is known as facilitated diffusion.

Facilitated Diffusion

is a process of is a process of passive transport in which in which molecules diffuse across membranes, with the help of transport diffuse across membranes, with the help of transport proteins.proteins.

Re-CapRe-CapPassive Transport: Passive Transport: The movement of The movement of

substances through the cell membrane substances through the cell membrane without the input of energywithout the input of energy

Types of Passive Transport:Types of Passive Transport:1.1. DiffusionDiffusion is the process by which molecules is the process by which molecules

move from an area of higher concentration to move from an area of higher concentration to an area of lower concentration. O2 and CO2an area of lower concentration. O2 and CO2

2.2. OsmosisOsmosis is the is the diffusion of water diffusion of water from a from a region of high water concentration region of high water concentration through a through a semi-permeable membranesemi-permeable membrane to a region of to a region of low water concentration.low water concentration.

3.3. Facilitated Diffusion is the transport of Facilitated Diffusion is the transport of substances through the cell membrane with substances through the cell membrane with the help of proteinsthe help of proteins

Active Transport• Sometimes a substance is

needed inside the cell even though the amount of that substance inside the cell is already greater than the amount outside the cell.

• Active transport is the movement of materials through a cell membrane using cellular energy.

Two Types of Active TransportTwo Types of Active Transport1.1. EndocytosisEndocytosis

2.2. ExocytosisExocytosis

1. Endocytosis

• Large protein molecules and bacteria, can be transported into a cell when they are surrounded by the cell membrane.

• This process of taking substances into a cell by surrounding it with the cell membrane is called endocytosis

Endocytosis

• Some one-celled organisms take in food this way.

• The cell membrane surrounds and engulfs a particle wraps around the particle and forms vesticle. (storage and transport structures)

2. Exocytosis

• The contents of a vesicle can be released by a cell using the process called exocytosis.

• Exocytosis occurs in the opposite way that endocytosis does.

• Exocytosis occurs when a vesicle’s membrane fuses with a cell’s membrane, and the contents are released.