Transport Mechanisms

Question 1

What are the factors that determine whether a molecule can pass through the cell membrane?

Answer 1

• Size of molecule
• Shape of the molecule
• Charge of the molecule

Question 2

What are the two methods of transport?

Answer 2

• Passive processes
• Active processes

Question 3

What are the ways molecules pass through cell membrane?

Answer 3

• Directly through the cell membrane via Diffusion (O2 and CO2, small uncharged molecules)
• Membrane channels: proteins that extend from one side of cell membrane to the other
• Carrier molecules: bind to molecules, transport them across the cell membrane, and drop them off in the cell.

Question 4

What are the ways molecules move in passive processes called?

Answer 4

• Simple diffusion
• Facilitated diffusion
• Osmosis

Question 5

Define facilitated diffusion.

Answer 5

• When the passage of a solute requires the presence of a CHANNEL or CARRIER PROTEIN

Question 6

What are the features of passive processes?

Answer 6

• Direction of movement of molecules is along the concentration gradient (High to low concentration)
• Does not require energy

Question 7

Define Osmosis.

Answer 7

• Movement of water molecules across the cell membrane from an area of higher water concentration to an area of lower concentration.

Question 8

What are the three types of tonicity?

Answer 8

• Isotonic
• Hypotonic
• Hypertonic

Question 9

Define the three types of tonicity

Answer 9

• Isotonic, When the solute and water concentration are the same inside and outside the cell.
• Water goes in and out of the cell at an equal rate (No net movement)
• Hypotonic, When the solute concentration in the cell is greater inside the cell and the water concentration is greater outside the cell.
• Cell could burst/rupture from water pressure. (Net inflow of water molecules, water molecules from outside of the cell move into the cell)
• Hypertonic, When the solute concentration is greater outside the cell and the water concentration is greater inside the cell.
• Cell shrinks (Net outflow, water molecules from the cell move out of the cell into the surrounding)

Question 10

What are the two forms of Active Processes?

Answer 10

• Active transport
• Vesicle-mediated transport (Endocytosis, Exocytosis)

Question 11

What are the features of Active Processes?

Answer 11

• Requires Adenosine Triphosphate (ATP) to push substances against concentration gradient
• Direction of movement of molecules is against the concentration gradient (From low to high concentration gradient)

Question 12

An example of active transport?

Answer 12

Sodium-potassium pump.
- Proteins transport sodium ions out of cells and potassium ions into the cell. (Both against steep concentration gradients)

Question 13

Features of Endocytosis?

Answer 13

• Extracellular substances are engulfed by being enclosed in a membranous vesicle
• Types of endocytosis:
  Phagocytosis (Cell Eating)
  Pinocytosis (Cell drinking)
  Receptor-mediated endocytosis
• A portion of the cell membrane is internalized and pinched off forming a endosome. (Membrane-bound vesicle)

Question 14

What happens during Exocytosis?

Answer 14

• Movement of materials out of the cell (Exocytosis)
• Material carried in a membranous vesicle
• Vesicle migrate to cell membrane and combines with cell membrane
• Material is emptied outside of cell