Cellular Transport

Or- How do I get in and

out of here?

Cells need to:

• Move nutrients into the cell• Remove waste products

from the cell• Export products made for

other parts of the organism (hormones, enzymes, neurotransmitters, etc.)

• Control the concentration of materials inside the cell.

The Cell Membrane:

Controls what enters and leaves the cell

Is Semi permeable – allows some molecules to move freely through, but keeps others out

Three Ways to Move In/Out of a Cell:

• Passive Transport

• Active Transport

• Bulk Transport

Passive Transport

• The cell does not need to use any energy

• Movement of materials is from an area of

high concentration to an area of low concentration (molecules spread out)

• Molecules move with the concentration gradient

High

Low

Passive Transport - DiffusionMovement :• Occurs until equilibrium is achieved

• Caused by random motion of molecules

Diffusion is Affected by:•Temperature

Faster at higher temperatures•Molecular weight

Lighter molecules move faster•Concentration gradient

Faster when gradient is high

Can diffusion happen through the cell membrane?

YES, as long as the particles are small enough and not charged

Small, non charged molecules and water can move between the phospholipid molecules of the membrane.

This includes: carbon dioxide, oxygen, alcohol, glycerol

Passive Transport: Facilitated

Diffusion• Substances helped

into the cell by channel proteins– Polar molecules such

as glucose – Ionic molecules such

as amino acids

• Still does not use any cellular energy.

Transport Protein

Diffusion vs. Facilitate Diffusion

What happens when the particles are too big to cross the membrane and there are no protein channels?

Large Molecules

Large Molecules

Water Moves

osmosis

Passive Transport: Osmosis

• The movement of WATER across a differentially permeable membrane – Solutes can not move across membrane

but water can– Water moves from an area of high water

concentration to low water concentration– Water diffuses towards the higher

concentration of solute.

Three Concentration Situations:

Isotonic: a solution that has an equal solute concentration to a neighboring solution.

Hypertonic: a solution that has a relatively higher solute concentration.

Hypotonic: a solution that has a relative lower solute concentration.

Water moves towards the higher solute concentration:

What does this mean to a cell?

The water content of the cell will be affected by the

concentration of solutes around and

in the cell.

HypertonicIsotonic Hypotonic

Plasmolysis occurs – cell shrinks as

water leaves

Water enters the cell. If too much water enters the

cell will burst

No net movement of water in or out of cell

Plants have a cell wall to protect from bursting.

Vegetables are crisp when they hold a lot of water and wilt when they lose it.

Active Transport

Active Transport: Energy Required

Transport protein uses energy (ATP) to

change shape

Transport protein able to move

molecule in or out of cell

Molecule is moved to increase the

concentration gradient

Transports against the concentration gradient (low to high)

Active Transport: Nerve Cells

Bulk Transport

• Macromolecules are too large to move with membrane proteins and must be transported across membranes in vesicles.

• The transport of macromolecules out of a cell in a vesicle is called exocytosis.

• The transport of macromolecules into a cell in a vesicle is called endocytosis.

Exocytosis – molecules leave the cell when the vesicle fuses with the membrane

Endocytosis – molecules brought into the cell by infolding the membrane and forming a vesicle

Bulk Transport• If the material taken up by

endocytosis is a large particle it is called phagocytosis.

• If the material taken up by endocytosis is a liquid or small particle it is called pinocytosis.

• Receptor-mediated endocytosis is a selective, highly efficient form of endocytosis.

Bulk Transport: Receptor Mediated

Receptor attaches to a specific molecule and moves it into the cell