Movement across cell membrane

Question 1

two ways for substances to enter / leave a cell

Answer 1

• passive transport
  - diffusion
  - facilitated diffusion
  - osmosis
• active transport

passive transport doesn’t require ATP
molecules, but ATP is needed for active transport as the movement is against the concentration gradient.

Question 2

Diffusion

Answer 2

movement of molecules or particles from a high concentration to a low concentration against the concentration gradient, until equilibrium is reached

Question 3

facilitated diffusion

Answer 3

the movement of polar substances across the membrane with the use of protein molecules

Question 4

facilitated diffusion - carrier protein

Answer 4

Carrier protein :
- has a binding site for a specific
chemical
- chemical binding changes the
structure of the carrier protein
- change in shape brings the
chemical across where it’s
released

Question 5

facilitated diffusion - channell

Answer 5

Channel protein :
- has a central pore that’s lined
with hydrophilic acid
- allows hydrophilic substances
to pass through the channel
- selective for the chemical that
can pass through
- open and close depending on
the need of the cell

Question 6

Active transport

Answer 6

• movement of ions and molecules across a membrane against the concentration gradient.
• requires ATP
• molecule or ion combines with a specific carrier protein outside a membrane
• ATP transfers a phosphate group to the carrier protein
• carrier protein changes shape and mover the molecule or ion inside the cell
• molecule or ion is released into the cytoplasm
• the carrier protein releases the phosphate group and returns to it’s normal shape
  - combines with ADP to form ATP

Question 7

Co-transport

Answer 7

• type of facilitated diffusion
• brings molecules and ions into cells
  together on the same transport
  molecule

Question 8

Co-transport - sodium-glucose

Answer 8

• glucose and two sodium ions bind to a
  carrier protein in the cell membrane
• carrier protein changes shape and
  moves the glucose molecules and
  sodium ions through the cell
  membrane
  - facilitated diffusion
• glucose and sodium separately diffuse through
  the cytoplasm
• glucose passes into the blood through
  facilitated diffusion
• sodium ions are moved out through active
  transport.
  - the same carrier protein moves
  potassium ions in
• sodium ion concentration remains low inside
  the cell
  - so sodium ions move in through
  facilitated diffusion and brings glucose
  molecules with it