Bio lecture 7

What is selective permeability?

The membrane allows some substances to cross more easily than others

What is homeostasis?

Keeping the cell's internal environment stable

The middle of the phospholipid bilayer is

hydrophobic

-meaning it does not mix well with water

Which molecules cross easily?

Small, nonpolar molecules such as oxygen and carbon dioxide

Why do ions need transport proteins?

They are charged and cannot easily cross the hydrophobic membrane interior.

concentration gradient means

there is more of a substance in one place than another.

Simple diffusion

Small, nonpolar molecules move directly through

• High → low

• NO energy or protein needed

Osmosis

Water moves according to water potential

• NO energy or protein needed

Facilitated diffusion

substances move from high to low concentration with help from a membrane protein

• High → low

• protein NEEDED, energy NO

Active transport

transport protein moves a substance against its concentration gradient

• Low → high'

• protein YES energy YES

an example of an active transport is

the sodium-potassium pump

Channel protein

creates a passage through the membrane

Carrier protein

binds a substance and changes shape to move it across

• Carriers can work in facilitated diffusion or active transport

Hypotonic solution

solution outside has LESS solute than inside the cell

• Water moves INTO the cell

Hypertonic solution

solution outside has more solute than inside the cell.

• Water moves OUT of the cell

Isotonic solution

Both sides have EQUAL solute concentration.

• Water moves IN and OUT at equal rates.

• There is NO net water movement.

What does the sodium-potassium pump do?

Moves 3 Na⁺ OUT and 2 K⁺ IN per cycle

Membrane potential

a difference in electrical charge across the cell membrane

ATP is used to create

electrochemical gradients