Year 12 - Transport across the membrane

Question 1

Describe the fluid mosaic model

Answer 1

A phospholipid bilayer containing channel/carrier proteins, cholesterol, glycoprotein and glycolipid.
Fluid as the 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 named partially permeable membrane. ​

-Requires an aquaporin in cell membrane

Question 4

How do you make a calibration ​curve for a reducing sugar and use it to find an unknown concentration?

Answer 4

Make several known concentrations of named reducing sugar​

Carry out benedict’s test on each sample. ​

Use colorimeter to measure absorbance of light in each sample. ​

Plot calibration curve with concentration on X axis and absorbance on Y axis. ​

Find the concentration of unknown using the calibration curve.

Question 5

Describe the function of glycoproteins/glycolipids

Answer 5

Glycoproteins/glycolipids/proteins are antigens (cell recognition) and receptors (cell signaling) due to their specific tertiary structure that is complementary to one molecule/ binding site

Question 6

List the factors that affect the rate of diffusion

Answer 6

Surface area
Concentration gradient
Diffusion distance
Temperature
Number of channel/carrier proteins in the phospholipid bilayer

Question 7

Describe Facilitated diffusion

Answer 7

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 8

Describe Active transport

Answer 8

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 9

Describe exocytosis

Answer 9

Vesicles contain large volume of molecules (eg enzymes/ antibodies ect) ​

Vesicles fuse with cell membrane ​

Contents of vesicle released into blood/extracellular space.

(Requires energy from ATP)

Question 10

Describe Endocytosis

Answer 10

Large concentration/volumes of molecules ​outside the cell. ​

Engulfing, by cell membrane pulling inwards, forms a vesicle around molecules. ​

Vesicle remains inside cell cytoplasm.

(Requires energy from ATP)