5.2 Passive transport

Chapter 5 Biology 1230

What can pass through the phospholipid bilayer?

• Gases

• Hydrophobic/nonpolar molecules (large hydrocarbons)

• Small polar molecules

What cannot pass through phospholipid bilayer?

• Large polar molecules

• Ions/electrically charged molecules

Passive transport…

requires no energy

Active transport…

Requires energy in the form of ATP or a coupled electrochemical gradient

What is diffusion?

Is a type of passive transport and it occurs when a substance moves from a high concentration to a low concentration until it’s equal across a space

How does concentration gradients affect diffusion rates?

Greater difference, faster diffusion. The closer it gets to equilibrium the slower the diffusion rate

How does the mass of molecules affect diffusion rates?

Smaller molecules diffuse more quickly while heavier molecules move more slowly

Temperature affects diffusion rate because?

Molecules move faster when temperatures are higher

How does surface area affect diffusion rates?

Increased surface area speeds up diffusion rates

How does pressure affect diffusion rates?

In some cells blood pressure forces solutions through membranes speeding up diffusion rates

What is facilitated transport or facilitated diffusion?

Diffuses ions and smaller polars by moving substances down their concentration gradients through transmembrane, integral membrane proteins.

What are channel proteins?

• Is a type of facilitated transport protein

• The top, bottom and inner core which are composed of hydrophilic amino acids.

  • Attracts ions or polar molecules

• Some are open others are gated (opens when receiving a signal)

What are carrier proteins?

• A type of facilitated transport protein

• Are specific to a single substance, which they bind to and change shape and carry it to the other side

• Allows movement in any direction as the concentration gradient changes

Osmosis…

Is the diffusion of water across a membrane. Water always moves from higher concentration to lower water concentration

What is tonicity?

Describes how an extracellular solution can change the volume of a cell by affecting osmosis. Usually correlates with the solutions osmolarity

A hypertonic extracellular fluid…

Has higher osmolarity than the cytosol, water is leaving the cell

A isotonic extracellular fluid…

Has the same osmolarity as the cytosol, water moves equally in both directions (no net movement)

A hypotonic extracellular fluid…

Has lower osmolarity and lower solute concentration than the cytosol, water enters the cell

Plasmolysis…

Is when the plasma membrane detaches from the cell wall

What is tugor pressure?

Pressure exterted by the plasma membrane against the cell wall

Selectively permeable means…

Some molecules can pass through but not others

What gases can pass through the phospholipid bilayer?

N_2, O₂, and CO₂

What are some small polar molecules that can pass through the phospholipid bilayer?

H₂O, glycerol, and urea

What large polar molecules cannot pass through the phospholipid bilayer?

Glucose, uncharged monosaccharides and disaccharides

What is osmolarity?

The solutions total solute concentration

What causes plasmolysis?

Hypertonic solutions

Animal cells functio best when extracellular fluids are…

Isotonic