Lesson 37 - Transport across membranes

Question 1

Explain the basis of diffusion

Answer 1

• All particles are constantly in motion due to the KE they possess
• This motion is random (no set way for particles to move around)
• Particles are constantly bouncing off one another

Question 2

What affects the rate of diffusion?

Answer 2

*Temperature
*Concentration gradient
*Surface area
*Diffusion distance
*Size of molecule
*Stirring/moving molecules

Question 3

What are the 2 tyupes of transport across membranes?

Answer 3

• Passive transport - does not require any external energy
• Active transport - requires energy in the form of the energy molecule ATP (an immediate energy source for cells)

Question 4

What is the definition of diffusion?

Answer 4

The net movement of particles from a region of high concentration to a region of lower concentration until evenly distributed (DOWN a concentration gradient)

Question 5

What are the 2 types of diffusion?

Answer 5

• simple
• facilitated

Question 6

What molecules can be transported by simple diffusion directly across phospholipid bilayer?

Answer 6

• Small, lipid-soluble, uncharged molecules
• E.g. Oxygen, carbon dioxide

Question 7

What molecules can be transported by Facilitated diffusion using channel proteins?

Answer 7

• Small, water-soluble molecules (mainly ions or polar)
• E.g. Na+ ions, H+ ions

Question 8

What molecules can be transported by Facilitated diffusion using carrier proteins?

Answer 8

• Larger, water-soluble molecules
• E.g. glucose, amino acids

Question 9

What does a graph for simple diffusion look like with transport rate against substrate concentration?

Answer 9

Straight line rising upwards, directly proportional

Question 10

What does a graph for facilitated diffusion look like with transport rate against substrate concentration?

Answer 10

Curved line rising up, until the facilitated diffusion saturated level, then it levels off

Question 11

What is the definition of active transport?

Answer 11

The movement of particles into or out of a cell from a region of lower concentration to a region of higher concentration (AGAINST its concentration gradient) using ATP and carrier proteins.

Question 12

What is the step by step process of active transport?

Answer 12

1. The molecule or ion to be transported across the membrane binds to specific carrier proteins on one side of the membrane (at binding site)
2. On the inside of the membrane, ATP binds to the carrier protein, causing it to hydrolyse (bond breaks) into ADP + Pi (releasing the ADP).
3. This causes the carrier protein to change shape and open to the opposite side of the membrane (releasing the molecule or ion to the opposite side).
4. The inorganic phosphate is released from the carrier protein causing it to revert back to its original shape
5. The process can then be repeated