Biology - Membrane Transport

Factors affecting molecule transport across the plasma membrane

1. Size

2. Polarity

Polar and Nonpolar

Polar molecules have an uneven distribution of electron charge while nonpolar have an even distribution.

Passive and Active transport

Passive transport is when a molecule moves from high to low concentration, therefore not using ATP.

Active transport is when a molecule moves from low to high concentration, therefore using ATP.

• Carrier proteins for active transport DO use ATP and changes the shape of the molecule.

Bulk Transport

A kind of active transport, therefore uses ATP. It transports big molecules.

• ENDOCYTOSIS (molecule ENTERS)

  • “Cell eating” or Phagocytosis = for molecules

  • “cell drinking” or Pinocytosis = for solutes

• EXOCYTOSIS (molecule EXITS)

  • materials inside are discharged form the plasma membrane

  • transported OUT through secretory vesicles.

  • EX. hormones

Simple Diffusion

For non-polar molecules that can pass through the plasma membrane without external help. Uses passive transport.

EX. carbon dioxide, ethanol, oxygen.

Facilitated Diffusion

Polar molecules that need to be aided by a channel protein or a carrier protein to pass through the plasma membrane. Uses passive transport.

• Channel protein acts like a tunnel through the plasma membrane

• Carrier proteins in Facilitated diffusion DOES NOT use ATP; it’s when the molecule binds a molecule to a protein, moves it across the plasma membrane, then unbinds.

Osmosis

Movement of water across the plasma membrane to where the concentrate of solute is HIGHER. Has three types of osmosis.

Hypertonic

When the solute level OUTSIDE of the cell is HIGHER, meaning the water moves OUTSIDE of the cell; the cell shrinks.

Hypotonic

The solute level INSIDE the cell is HIGHER, meaning the water moves INSIDE of the cell; the cell expands.

Isotonic

The solute level both inside and outside of the cell is EQUAL; there is no movement and no size change.

APPLICATION OF MEMBRANE TRANSPORT

Breathing = simple diffusion (only uses O2 and CO2)

• Oxygen entering the blood from the alveoli is a SIMPLE DIFFUSION so it doesn’t use ATP or protein.