plasma membrane- moving in and out of cells

Question 1

what is the plasma membrane

Answer 1

The plasma membrane controls entry and exist in cells.
The fluids inside and outside cells are aqueous solutions, where water is the solvent for the molecules and salts.
Lipids do not dissolve in water, therefore the plasma membrane is a barrier between the solutions inside and outside the cell.

Question 2

what are the two layers that the plasma membrane is built from

Answer 2

The cell membrane is built from two layers of lipids or phospholipids. A phospholipid is a lipid molecule with a ‘phosphate head’ attached to it.
The phosphate head is hydrophilic, meaning it is attracted to water.
The fatty acid tails of the phospholipid molecules are hydrophobic, meaning they are repelled by water.

Question 3

crossing the plasma membrane

The properties of a substance determine whether it can diffuse across the plasma membrane

Answer 3

• Water molecules can move through the spaces in the membrane because they are small and have no charge.
• Small gas molecules like xygen and carbon dioxide can diffuse across the plasma membrane.
• Molecules that dissolve in lipids, such as alcohol can diffuse across the membrane.
• Water-soluble substances, such as sugars and salts, stay in solution inside or outside the cell. They can cross through the membrane through special channels.
• Charged compounds and ions, such as sodium, chloride and potassium also need a channel to cross the membrane.

Question 4

crossing the cell membrane Different processes are involved in moving across cell membranes:

Answer 4

Passive diffusion - where a solute diffuses across the membrane from a region where concentration is high to a region where concentration is lower. It is a passive process as it does not require energy to occur.

Facilitated diffusion - where a channel is present in the membrane to facilitate the movement of a solute across a membrane.

Active transport - when a substance is moved to a region where it is already present at a higher concentration. This process requires energy to move the substance across the membrane.

Question 5

When a molecule cannot diffuse across the plasma membrane

endocytosis

exocytosis

Answer 5

Endocytosis - the process where the cell membrane wraps around a required particle and the cell engulfs it.

Exocytosis - the reverse process of endocytosis allows the cell to release waste.