The cell In It’s Environment• Function of the cell membrane?

– To regulate what enters and leaves the cell.

• Structure of the cell membrane – Double layer of lipids with carbohydrates and proteins

scattered throughout.

The Cell in Its Environment• The cell membrane is selectively permeable:

– means some substances can pass through it while others cannot.

Balloon

The Cell in Its Environment• Three ways substances can move in

and out of the cell

1. Diffusion - no energy required2. Osmosis – no energy required3. Active Transport – energy required

Diffusion• Diffusion:

• The movement of molecules from an area

of higher concentration to an area of lower

concentration.

– Caused by molecules in motion.

– Collisions cause molecules to spread out.

http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf

Air freshenerFood dye in water

Diffusion• Concentration gradient - Created when

different concentrations are in contact with one

anotherHigh Low

Diffusion• Substances naturally move with the gradient

High to low concentration is like going

down hill – with the gradient.

Diffusion

– Example in living organisms – movement of oxygen

from water into cells.

Osmosis – A special type of diffusion• Osmosis is the diffusion of water

molecules across a selectively permeable membrane

– Water moves from high to low concentration

What are three ways substances can pass across

the cell membrane?Diffusion

Osmosis

Active transport

Movement Across the Cell Membrane

• Passive Transport

Moving materials across a cell membrane

WITHOUT using energy

• Two examples of passive transport:

• Diffusion

• Osmosis

Movement Across the Cell Membrane

• Active Transport

Movement of materials across a cell

membrane which requires energy

Active Transport• Sometimes molecules must move against the

concentration gradient (from low to high or uphill) and this requires energy.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

Methods of Active Transport• Two ways that the cell moves things by active

transport.

1. Transport proteins

2. Engulfing

Transport Proteins – Active Transport

Transport proteins in the cell membrane act as

channels through the membrane

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

http://www.youtube.com/watch?v=STzOiRqzzL4

Engulfing – Active Transport

Engulfing: cell membrane surrounds and then engulfs

a particle (amoeba and white blood cells).

http://www.youtube.com/watch?

v=STzOiRqzzL4&feature=related http://www.youtube.com/watch?

v=s0p1ztrbXPY&feature=related

http://www.youtube.com/watch?v=W6rnhiMxtKU

Cell Size• Why are cells so small?

– Small size makes it easier to move materials

into and out of the center of the cell.

– Makes all cell processes more efficient.

Cell Size• How do cells maintain their small size?

When a cell reaches a certain size it

divides.

We call this cell division MITOSIS.

Let’s Review Explain the difference between osmosis

and diffusion?• Diffusion refers to the movement of

molecules from high concentration to low concentration.

• Osmosis is diffusion of WATER across a selectively permeable membrane. Also from high concentration to low concentration.

Let’s Review Do osmosis and diffusion require

energy?• No because they both are a form of Passive

transport.• Molecules or water (osmosis) move with the

concentration gradient (downhill).

Let’s Review Why does active transport require

energy?• Because the cell is trying to move molecules

against the concentration gradient – from low to high concentration

Why are cells so small?• To allow materials to move in and out

quickly making the cell more efficient.

Let’s Review What happens to a cell when it reaches a

certain size?• It divides to maintain its small efficient size

What do we call this cell division?• Mitosis

Diffusion

http://www.youtube.com/watch?v=ULR79TiUj80

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf

http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf

Osmosis and salt