Movement of substances

Question 1

What is diffusion?

Answer 1

it is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient

Question 2

What is a concentration gradient?

Answer 2

concentration gradient is the difference in concentration between 2 regions

Question 3

Simple diffusion v.s. facilitated diffusion

Answer 3

simple diffusion
- molecules move across the membrane without the help of channel/ carrier proteins

facilitated diffusion

• molecules move across the membrane via channel/ carrier proteins
• no energy is being used

Question 4

How does diffusion occur?

Answer 4

• through a permeable membrane that allows both the solvent and the solute to pass through it
• some particles are able to pass through like oxygen and carbon dioxide but not others like proteins

Question 5

What is osmosis?

Answer 5

it is the net movement of water molecules from a solution of higher water potential to a solution of lower water potential
- it has to pass through a partially permeable membrane

Question 6

What is water potential and how is it related to osmosis?

Answer 6

• it is the measure of the tendency of water to move from one place to another
  1. a dilute solution contains more water molecules than a concentrated solution
  2. a concentrated solution has a lower water potential
• when a partially permeable membrane separated 2 solutions of different water potentials a water potential gradient is formed
• water always moves from a solution with higher water potential to a solution with a lower one down a water potential gradient

Question 7

What is a hypotonic solution?

Answer 7

when cells are placed in a solution of higher water potential, the cell has lower water potential than the solution outside the cell

Question 8

What is a hypertonic solution?

Answer 8

when a cell is immersed in a solution with lower water potential, the water potential of its cell is higher than the solution outside the cell

Question 9

What is an isotonic solution?

Answer 9

a cell immersed in a solution with the same water potential as its cytoplasm will not change in its shape and size

Question 10

What is the surface area to volume ratio?

Answer 10

• the greater the area of cell surface membrane per unit volume, the faster the rate of diffusion of a substance for a given concentration gradient
• as the cell becomes bigger the surface area to volume ratio decreases
  the largest cell of the same shape has the smallest surface area to volume ratio

Question 11

Why is surface area to volume ratio important?

Answer 11

• a large cell will have difficulties absorbing useful substances and removing harmful substances at a fast enough rate
• active cells tend to be smaller or have shapes that increase surface area to volume ratio
• larger cells like fat cells or ovums are less active ger cells like fat cell and ovum are less active

Question 12

What is active transport?

Answer 12

• it is the process in which energy is used to move the particles of a substance across a membrane against its concentration gradient from a region of lower concentration to a region of higher concentration
• only occurs in living cells as they respire