Cell Membranes and Transport

Question 1

What the two functions of ORGANELLE membranes?

Answer 1

• isolate organelles from cytoplasm, allowing cellular processes to occur separately
• site of biochemical reactions

Question 2

How does the plasma membrane appear under an electron microscope?

Answer 2

A double line 7-8nm wide

Question 3

What three things are cell membranes mainly composed of? (Use PPC)

Answer 3

Phospholipids
Proteins
Cholesterol (animal cells)

Question 4

How did Singer and Nicholson describe a cell membrane’s structure in 1972 and why?

Answer 4

‘Fluid mosaic model’

Proteins scattered like a mosaic throughout phospholipids and membrane components can move (fluid)

Question 5

What are the main component of membranes?

Answer 5

Phospholipids

Question 6

What mass on average do proteins make up of a cell membrane?

Answer 6

45%

Question 7

What are the two surfaces of a membrane?

Answer 7

Extracellular (facing outside)

Cytosolic (facing inside)

Question 8

What three proteins can be found in the membrane?

Answer 8

Intrinsic
Extrinsic
Glycoproteins

Question 9

What are the 5 functions of CELL SURFACE membranes?

Answer 9

• allow take up of selected nutrients
• allows secretion of chemicals
• enables cell recognition
• allows cell to change shape
• keep cellular components inside cell

Question 10

Incipient plasmolysis:-

Answer 10

The point at which the protoplast is just about to pull away from the cell wall

Question 11

Hypertonic:-

Answer 11

Higher water potential in cell, water flows out down a water potential gradient

Question 12

Isotonic:-

Answer 12

Water potential equal inside and outside the cell

Question 13

Hypotonic:-

Answer 13

Lower water potential inside the cell= water flowing in by osmosis down a water potential gradient

Question 14

What does cholesterol do in membranes?

Answer 14

Maintain fluidity, increasing stabilty

Question 15

Highest water potential (pure water)?

Answer 15

0kPa

Question 16

What is water potential measured in?

Answer 16

kPa (kilopascals)

Question 17

Solute potential:-

Answer 17

Conc of dissolved substances inside the cell. Always negative. “Measure of the reduction in water pot due to the presence of solute molecules.”

Question 18

Pressure pot:-

Answer 18

Pressure exerted on the cell contents by the cell wall and cell membrane.

Question 19

Haemolysis:-

Answer 19

Red blood cells have a low water pot. In water, water flows in down water pot grad. No cell wall to stop cell expansion so continues until it bursts (haemolysis).

Question 20

Red blood cells in hypertonic solution:-

Answer 20

Water will flow out, cells will be crinkled (crenated).

Question 21

Exocytosis:-

Answer 21

Secretory vesicles carry their contents to the cell surface membrane, merge with it and the secretion is released.

Question 22

Two types of endocytosis:-

Answer 22

Phagocytosis and pinocytosis

Question 23

Phagoxytosis:-

Answer 23

Solid material taken into cell in a vesicle. Lysosomes fuse w/ vesicle and empty their enzymes into it. Enzymes digest material and producta are absorbed into cytoplasm.

Question 24

Pinocytosis;-

Answer 24

Similar to phago but with liquid material. Vesicles formed can be very small.