chapter 3: movement of substances

Question 1

what is a concentration gradient?

Answer 1

• it is the difference in concentration between two regions

Question 2

what is the meaning of diffusion?

Answer 2

diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration

Question 3

what is water potential?

Answer 3

the tendency of water to move from one place to another

Question 4

define osmosis.

Answer 4

• it is the net movement of water molecules from a solution of higher water potential to a solution of lower potential, through a partially permeable membrane

Question 5

what happens to a plant cell in a solution with higher water potential?

Answer 5

• water enters the cell through the partially permeable cell surface membrane via osmosis
• cell expands and becomes turgid
• vacuole increases in size and pushes cytoplasm against the cell wall
• cell wall does not burst: protected by its inelastic cell wall
• pressure exerted by the water in the vacuole on the cell wall is the turgor pressure

Question 6

what is a solution with higher water potential called? and what is a solution with a lower potential called?

Answer 6

hypotonic solution

hypertonic solution

Question 7

what happens to a plant cell in a solution with lower water potential?

Answer 7

• water from vacuole and cytoplasm leaves the cell through the partially permeable cell surface membrane
• cell decreases in size and becomes flaccid or limp
  -vacuole decreases in size, cytoplasm shrinks away from cell wall
  >plasmolysis
  > cell is plasmolysed
• plasmolysed cell can be restored by placing it in a water or a solution with a higher water potential

Question 8

what happens to an animal cell in a solution of lower water potential?

Answer 8

• an animal cell in a hypertonic solution will cause it to lose water
  > cell shrinks and little spikes appear on the cell surface membrane
• become dehydrated and eventually die

Question 9

what is active transport?

Answer 9

• the process in which energy is needed 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

Question 10

when is active transport used and why?

Answer 10

• it only occurs in living cells because they respire
  > during respiration energy is set free
  > part of the energy is used in active transport

Question 11

what are the similarities of diffusion and osmosis?

Answer 11

• they are both passive processes

- movement of substances down a concentration gradient

Question 12

why is turgor important in plants?

Answer 12

• turgor plays an important role is maintaining the shape of soft tissue in plants
• leaves and young stems of herbaceous and non woody plants