Cell Membranes and Transport

Question 1

What is the fluid mosaic model?

Answer 1

Fluid - Phospholipid molecules within the layer can move relative to each other
Mosaic - The proteins within the bilayer are of different sizes and shapes and form different patterns

Question 2

What are intrinsic proteins?

Answer 2

Proteins found within the bilayer, includes channel and carrier proteins

Question 3

What are extrinsic proteins?

Answer 3

Proteins found at the edges of the phospholipid bilayer

Question 4

Name factors that affect permeability

Answer 4

• Temperature
• Organic Solvents
• pH

Question 5

How does temperature affect permeability of the plasma membrane?

Answer 5

As temperature increases, the phospholipids have more kinetic energy and move more, increasing fluidity and permeability of the membrane

Question 6

What happens to the membrane if the temperature becomes too high?

Answer 6

Channel and carrier proteins will become denatured
Cell will eventually break down completely

Question 7

How do organic solvents affect permeability of the plasma membrane?

Answer 7

Organic solvents dissolve membranes, disrupting the cell. Increasing the permeability

Question 8

Define diffusion

Answer 8

The passive movement of small non-polar molecules from an area of high concentration to an area of low concentration

Question 9

State the factors that affect the rate of diffusion

Answer 9

-temperature
- Steepness of concentration gradient
- Size of molecule
- Diffusion distance

Question 10

Define osmosis

Answer 10

Movement of water molecules from a region of high water potential to a region of lower water potential through a selectively permeable membrane

Question 11

What is water potential ?

Answer 11

Negative value , fresh water = 0
A measure of the tendency of water molecules to move from one area to another

Question 12

What is incipient plasmolysis?

Answer 12

Where the water potential = the solvent potential
- effect produced when plant cells are placed in isotonic solution
- Causes cell membrane to pull away from the cell wall in some areas
- Cell is neither plasmolysed nor turigd

Question 13

What is facilitated diffusion?

Answer 13

Net movement of substances through a transport protein without the use of energy

Question 14

Define active transport

Answer 14

The movement of substances from a low concentration to a high concentration, use of energy in the form of ATP

Question 15

How does cyanide affect active transport?

Answer 15

Cyanide inhibits respiration and the formation of ATP, preventing active transport

Question 16

What are two mechanisms of bulk transport?

Answer 16

Endocytosis
Exocytosis

Question 17

Phospholipid Heads

Answer 17

-Hydrophilic
Allow the movement of lipid soluble molecules , but not water molecules as they are polar

Question 18

Fatty acid tails

Answer 18

-Hydrophobic
- Point towards each other in the centre of the bilayer

Question 19

Channel Protein

Answer 19

• Pores lined with polar molecules (hydrophillic)
• Allowing charged ions through
  -Each protein is specific to one type of ion, open and close depending on the needs of the cell.

Question 20

Carrier Protein

Answer 20

• Allows larger molecules through e.g. amino acid, water
  -Molecules attach to protein at its binding site and causes protein to change shape or rotate within membrane. Releasing the molecule the other side

Question 21

Explain co-transport and give an example

Answer 21

Type of facilitated diffusion that brings molecules and ions into the cell together on the same protein transport e.g. sodium-glucose co transport

Question 22

Cholesterol

Answer 22

Presents between phospholipids in animal cells, maintains the fluidity of the cell. Too much and the cell becomes turgid, too little and the cell will break apart

Question 23

What happens to animal and plant cells in hypotonic solution

Answer 23

Higher water solution to the cell
Animal - Cell swells and may lyse
(burst)
Plant - The cytoplasm and the vacuole swell and push against the cell wall; cell becomes turgid.

Question 24

What happens to animal and plant cells in hypertonic solution?

Answer 24

• Water potential is higher in cell, solution has a lower water potential
  Animal - The cell shrinks
  Plant - The cytoplasm and vacuole shrink causing the cell membrane to pull away from the cell wall. This process is called plasmolysis and cell are said to be plasmolysed.

Question 25

What happens to animal and plant cells in isotonic solution?

Answer 25

Animal - animal cells optimal bathing medium, water potential of cell is equal to the water potential of the external medium at this point.
Plant - Cells become flaccid, this is the point of incipient plasmolysis

Question 26

What are the 2 types of endocytosis?

Answer 26

Pinocytosis and phegocytosis

Question 27

What is endocytosis?

Answer 27

The bulk intake of material by a cell by the formation of vesicle

Question 28

Pressure Potential

Answer 28

Always a positive value
Pressure exerted by the cell contents on the cell wall as water enters the vacuole

Question 29

What do channel and carrier proteins do to the rate of diffusion?

Answer 29

Increase it
- Initial increase due to concentration gradient becoming steeper, carrier & channel proteins facilitate the process.
- Rate of diffusion then levels off at a higher concentration gradient due to proteins being occupied

Question 30

Describe how bulk transport occurs in large particles entering the cell

Answer 30

Via endocytosis
1) the plasma membrane folds inwards
2) Plasma membrane continues to fold engulfing the material
3) Plasma membrane fuses to enclose the material

Question 31

Functions of the cell membrane

Answer 31

• Separate the living cell from its non-living surroundings
• control which substances pass into and out of the cell
• cell recognition