CELL PHYSIOLOGY

Question 1

Simple diffusion

Answer 1

-non polar molecules such as carbon dioxide can pass through the membrane unaided (protein molecules are not involved)
-Net movement of water from where it is in a high concentration to a low concentration

Question 2

Factors affecting diffusion across membranes

Answer 2

-The concentration gradient
-The size of the molecule (smaller molecules diffuse faster than bigger ones)
-The temperature ( diffusion takes place quicker in higher temperatures)
-The thickness of the exchange surface
-The surface area of the membrane (the greater the surface area, the faster the diffusion. in cells where the speed of diffusion is important, the surface area of the membrane is extended by microvilli)

Question 3

Facilitated diffusion

Answer 3

-Diffusion process is facilitated by proteins
-Rate of facilitate difusion depends on the number of carrier or channel proteins in the membrane

Question 4

Active transport

Answer 4

-Against the concentration gradient
-Involves protein carrier molecules
-Metabolic energy in the form of ATP is required
-Cells that carry out a lot of active transport have many mitochrondria to provide ATP

Question 5

Cytosis is important in transporting…

Answer 5

-Large molecules that are too big for the carriers
-The bulk transport of smaller molecules (water)

Question 6

Endocytosis

Answer 6

-Movement of substances into the cell
-The cell surface membrane invaginates around substances entering the cell from the outside to form a membrane-bound sac or a vesicle which then pinches off the inside of our cell surface membrane

Question 7

Two types of endocytosis

Answer 7

-Phagocytosis (transport of solid material into the cell eg phagocytes)
-Pinocytosis (Transport of fluid into the cell)

Question 8

Exocytosis

Answer 8

Movement of substances out of the cell. Secretory vesicles move to and fuse with the cell surface membrane. the contents of the vesicle are then released outside the cell. as with endocytsosis, the creation of the gap in the cell surface membrane is followed by the reforming of the membrane

Question 9

Osmosis

Answer 9

-Net movement of water from a high water concentration to a low concentration across a selectively permeable membrane
-Most water moves through special channel proteins called aquaporins
-The stonger solution is hypertonic and the weaker solution is hypotonic, if they are the same concentration, they are both isotonic

Question 10

Water potential

Answer 10

-It’s tendency to take in water by osmosis from pure water across a selectively permeable membrane
-kPa
-Indication of the free energy of the water molecules. in solutions, some of the water molecules are not free as they form hydration shells around the solutes
-OSMOSIS can be defined as the net movement of water through a selectively permeable membrane from a solution of less negative water potential to a solution of more negative water potential

Question 11

Solute potential

Answer 11

Potential of a solution to take in water, and releates to the solute concntration only

Question 12

Pressure potential

Answer 12

The effect of pressure on the solution, which influences the ability of the cell to take in or lose water by osmosis

Question 13

Water potential of the cell =

Answer 13

Ψw = Ψs + Ψp
solute potential + pressure potential

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