Transport across cell membranes

Question 1

What is a plasma membrane?

Answer 1

All membranes in and around cells and membrane bound organelles.

Question 2

What is the structure and function of the plasma membrane?

Answer 2

Phospholipid bi layer, cholesterol, proteins, glycolipids, glycoproteins.
Separates cell contents from external environment. Controls what enters and exits the cell. Identifies cell as self. Site of chemical reactions.

Question 3

What is the cell surface membrane?

Answer 3

Specifically a plasma membrane that surrounds cells and forms the boundary between the cytoplasm and the environment.

Question 4

What is the role of the phospholipid bilayer in the plasma membrane?

Answer 4

Lipid soluble material is able to move into and out of the cell.
Water soluble material is unable to move in or out of the cell.
The membrane is flexible and self-healing.

Question 5

How are proteins embedded in the plasma membrane?

Answer 5

Occur on the surface only or completely span the bilayer from one side to the other

Question 6

What is the role of proteins which are embedded on the surface of a plasma membrane?

Answer 6

Mechanical support, or as cell receptors

Question 7

What is the role of proteins which span the width of the plasma membrane?

Answer 7

Protein channels- water filled tubes allowing water soluble ions to diffuse across.
Carrier proteins- Bind to molecules and change shape to move them across

Question 8

What are the overall roles of proteins in the membrane?

Answer 8

1 Structural support
2 Channels for water soluble substances
3 Allow active transport
4 Cell surface receptors for identifying cells
5 Cell adhesion

Question 9

How does cholesterol interact with water

Answer 9

Hydrophobic

Question 10

What does cholesterol do to other molecules in the membrane?

Answer 10

Hold phospholipids tightly. Prevent water loss

Question 11

What is the role of cholesterol in the membrane?

Answer 11

Reduce lateral movement of other molecules.
Make the membrane less fluid at high temperatures.
Prevent leakage of water

Question 12

How can the movement of particles be described?

Answer 12

Random
Constant due to kinetic energy
Constantly bouncing of each other

Question 13

Definition of diffusion

Answer 13

Net movement of molecules/ ions from a region where they are highly concentrated to one where their concentration is lower until evenly distributed

Question 14

What kind of molecules can diffuse through the cell surface membrane?

Answer 14

Small, non-polar molecules e.g. oxygen and CO2

Question 15

What does polar mean?

Answer 15

Molecule has a positive charge on one side and a negative charge on the other

Question 16

Which molecules do not diffuse easily across the plasma membranes. Why?

Answer 16

Charged ions and polar molecules.
Due to hydrophobic nature of the fatty acid tails.

Question 17

Define the term facilitated diffusion

Answer 17

Movement of molecules from a high concentration to a low concentration across a partially permeable membrane, via specific channel or carrier proteins. It is passive

Question 18

What is a channel protein?

Answer 18

Creates water filled hydrophilic channel through the cell membrane through which specific ions can pass

Question 19

What is a carrier protein?

Answer 19

Changes shape to allow larger molecules to pass through the membrane.

Question 20

3 factors that affect the rate of diffusion

Answer 20

• Surface area
• number of channel and carrier proteins
• Concentration gradient

Question 21

What is the definition of osmosis?

Answer 21

Movement of water from a region where there is a higher water potential to an area where there is a low water potential through a selectively permeable membrane