transport across a membrane

Question 1

describe the fluid mosaic model

Answer 1

A phospholipid bilayer containing:
Channel/carrier proteins
Cholesterol
Glycolipid
Glycoprotein

fluid as phospholipids and proteins are constantly moving in their layer.
mosaic as contains multiple types of proteins distributed unevenly in the membrane.

Question 2

Describe the function of cholesterol

Answer 2

cholesterol controls membrane fluidity.
the more cholesterol, the less fluid and permeable the membrane becomes.

Question 3

Describe osmosis

Answer 3

The passive net movement of water molecule, from an area of higher water potential to area of lower water potential (=down a water potential gradient), across a partially permeable membrane.
-Requires an aquaporin in cell membrane

Question 4

Describe the function of glycoproteins/glycolipids

Answer 4

glycoproteins/glycolipids/proteins are involved in cell recognition) and cell signalling due to their specific tertiary structure that is complementary to one molecule/ binding site

Question 5

List the factors that affect the rate of diffusion

Answer 5

1.Surface area
2.oncentration gradient
3. Diffusion distance:
ficks law
rate of diffusion=surface area x concentration gradient /diffusion distance

4. Temperature
5. number of channel/carrier proteins in the phospholipid bilayer.

Question 6

1. Describe Facilitated diffusion

Answer 6

1. The passive net movement of polar/large molecules/ions down a concentration gradient (high->low), across a partially permeable membrane
   Requires: channel or carrier protein with complementary binding site.

Question 7

2. Describe Active transport

Answer 7

2. The active movement of molecules/ions against a concentration gradient (low->high), across a partially permeable membrane.
   Requires: carrier proteins with complementary binding sites and the release of energy from the hydrolysis of ATP -> ADP and P.

Question 8

Describe exocytosis

Answer 8

Vesicles contain large volume of molecules (eg enzymes/ antibodies ect)
Vesicles fuse with cell membrane
Contents of vesicle released into blood/extracellular space.

[Note:
Bulk movement that requires energy released from the hydrolysis of ATP into ADP and P. ]

Question 9

Describe Endocytosis

Answer 9

1.Large concentration/volumes of molecules
outside the cell.
2. Engulfing, by cell membrane pulling inwards, forms a vesicle around molecules.
3. Vesicle remains inside cell cytoplasm.

[Note:
A Bulk movement that requires energy released from the hydrolysis of ATP into ADP and P. ]