cells need such things as food and oxygen, and need to get rid of wastes. what structure surrounds...

• Cells need such things as food and oxygen, and need to get rid of wastes. What structure surrounds all cells?

• Cell Membrane

• Substances must go through the cell membrane in order to get in or out of a cell.

Some things to consider before we start

• Cell membranes are selectively permeable, which means that they allow some substances to pass through but not others.

• Selective means “choosy” and • Permeable means “to go through”

• Molecules in solids, liquids, and gases are always moving. In which state of matter are molecules moving the fastest?

• Gas• Slowest?• Solid• Molecules will always move from

an area where they are more concentrated to an area where they are less concentrated.

What does concentrated mean?

• How many particles are packed in an area

• This process of molecules moving from where they are more concentrated to an area where they are less concentrated is called diffusion.

• Diffusion continues until the molecules of a substance are evenly distributed in an area.

• This state of “evenly spread” is called equilibrium.

• Do molecules stop moving once equilibrium is reached?

• NOhttp://www.wisc-online.com/objects/index_tj.asp?objid=AP1903

• Diffusion

Osmosis is a special kind of diffusion that is very important to living things.

•Osmosis is the diffusion of water through a selectively permeable membrane.

• This is the manner in which water gets into and out of cells.

http://www.wisc-online.com/objects/index_tj.asp?objid=AP11003

• Water molecules will naturally flow from an area in which the water molecules are in greater numbers to an area where they are in fewer numbers.

http://www.biologycorner.com/bio1/diffusion.html

• Which way are water molecules moving when a plant begins to wilt?

• Out of the cells

Passive transport requires no energy. Diffusion and osmosis are examples of passive transport.

• The cell does not have to use energy to move substances into or out of the cell.

facilitated transport also does not require energy

• Molecules in the cell membrane called transport proteins help to move larger molecules into or out of the cell. This still does not require energy. Think of this as being like taking a ferry ride without having to pay.

facilitated transport

• Active transport requires energy and uses transport proteins in the cell membrane.

Used when: Cells need to move substances from areas of lower concentration to an area of higher concentration.

• This is the opposite of diffusion and requires energy.

• Think of this as being like taking a ferry ride BUT having to pay!

Other types of active transport

Endocytosis occurs when very large things need to move into a cell.

• A white blood cell “eating” a bacterial cell would be an example of endocytosis.

• What does “endo” mean?• “IN”

Exocytosis occurs when very large molecules need to move out of a cell.

It is also a type of active transport. • An example of exocytosis is

proteins packaged by the Golgi Golgi BodiesBodies moving out of a cell.

• What does “exo” mean?• “OUT”

Let’s get some practice:Label each of the following as diffusion, osmosis, facilitated transport, active transport, endocytosis, or exocytosis.

• Large waste molecules stored in vacuoles need to be moved out of a cell:

• exocytosis

Water concentration outside a cell is 85%. Water concentration inside the cell is 70%. Water flows into the cell:

• Osmosis

• You can smell the cookies baking in the oven even before you enter the kitchen:

• Diffusion

The concentration of Na ions outside the cell is 10%. The concentration of Na ions inside the cell is 25%. Na ions move into the cell.

• Active Transport

A one-celled organism “eats” another one-celled organism:

• Endocytosis

• Glucose molecules are helped to move into the cell by transport proteins in the cell membrane, but no energy is used to do this:

• Facilitated transport