1.4 : Membrane Transport

Question 1

what is diffusion & what type of energy does this require?

Answer 1

• free passage of molecules from a region of their high concentration to a region of low concentration .
• energy source : kinetic energy of their molecules.

Question 2

what is facilitated diffusion & an example of this?

Answer 2

• a substance that is otherwise unable to diffuse across a plasma membrane , does so as a result of its effect on particular molecules present in the membrane.
• in the presence of a substrate –> membrane molecules mad of globular proteins form into pores, large enough to allow diffusion.

Question 3

what is osmosis? what force holds water molecules together?

Answer 3

• net movement of water molecules from a region of high concentration to a region of low concentration, across a selectively permeable membrane.
• held by hydrogen bonds

Question 4

what is solute potential and what generates this?

Answer 4

• generated by dissolved solutes

- the force generated by dissolved solutes present in the cytoplasm and vacuoles of cells = osmotic pressure?

Question 5

what is a hypotonic solution? what occurs in this case?

Answer 5

• when the external solution is less concentrated than the cell solution
• net inflow of water into the cell by osmosis (goes where the concentration is higher) –> cell contents press against cell wall –> cell becomes turgid –> increased pressure developed (prevents further water uptake) –> cell becomes turgid.

Question 6

what is a hypertonic solution? what occurs in this case?

Answer 6

• when the external solution is more concentrated than the cell solution.
• net outflow of water (higher concentration outside) –> volume of cell decreases –> cytoplasm pulls away from parts of cell –> cell becomes flaccid = plasmolysed .

Question 7

what are medical applications of osmosis & diffusion?

Answer 7

• osmosis : human organs donated –> have to be maintained in saline solution (isotonic with cell tissues and organs) –> prevent damage by unbalanced water uptake/loss.
• diffusion : in kidney failure, urea and sodium accumulate in the blood –> blood is circulated through partially permeable membrane –> urea & toxic substances are removed = hemodialysis.

Question 8

what is active transport? what energy source is required?

Answer 8

• movement of dissolved substances into or out of cells through the cell membrane, from a region of low concentration to high concentration, against a concentration gradient.
• energy source : metabolic energy produced by cell (ATP)

Question 9

how is active transport different from diffusion?

Answer 9

• occurs against a concentration gradient (low to high –> cytoplasm holds reserves of valuable molecules –> they don’t escape = retained by cell membrane until more are available for uptake = all absorbed even if concentration outside is lower)
• active uptake is highly selective (only absorbs what is required)
• involves pump molecules (pick up molecules & ions & transport to other side, globular proteins = carrier proteins–> require reaction with ATP)

Question 10

what is bulk transport? what are the specific names for the uptake and export? what is the energy required?

Answer 10

• movement of vesicles of matter across the plasma membrane by cytosis (transport mechanism for movement of large quantities of molecules in and out of cells)
• uptake : endocytosis
• export : exocytosis
• energy from metabolism (ATP) required

Question 11

what is an example that shows how bulk transport works?

Answer 11

phagocytosis (engulfing solid matter) –> part of plasma membrane is pulled inwards –> surrounding cytoplasm & plasma membrane bulge out –> matter becomes enclosed within a small vesicle.

Question 12

what are macrophages?

Answer 12

Phagocytic cells in the human body that engulf the debris of damaged or dying cells and dispose of it.