diffusion

Question 1

diffusion (def.)

Answer 1

net movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient, using kinetic energy from the continuous random movement of molecules

*continuous random movements of all molecules ensures complete mixing and even distribution of molecules

Question 2

diffusion (energy source)

Answer 2

kinetic energy of molecules

Question 3

osmosis (def.)

Answer 3

the net movement of water molecules from a region of higher water potential to a region of lower potential, through a partially permeable membrane, down a water potential gradient

Question 4

water potential

Answer 4

tendency of water molecules to move about, measure of free kinetic energy of the water molecules

Question 5

equilibrium

Answer 5

reached when the water potential is the same in both regions = no net movement of water molecules, but random movements continue

Question 6

solution

Answer 6

solute + solvent

Question 7

osmosis in plants

Answer 7

• if plants become short of water for a prolonged period, the plant wilts, ultimately, a wilted plant will die if it does not receive water
• when external solution is diluted and has a higher water potential, there is a net flow of water into the cell, the cell solution becomes diluted, and the volume of the cell is expanded by water uptake
  → cytoplasm press hard against cell wall 【turgid】 = net uptake of water stops

*cell wall has protected the delicate cell contents from damage due to osmosis

• when external solution is concentrated and has a lower water potential, there is a net flow of water out of the cell, the cell solution becomes more concentrated, and the volume of the cell solution decreases
  → cytoplasm starts to pull away from parts of cell wall 【plasmolysed】 = net uptake of water stops

Question 8

osmosis in animals

Answer 8

osmotic concentration of body fluids is very precisely regulated

Question 9

osmoregulation

Answer 9

water potential is regulated both inside and outside body cells

Question 10

active transport

Answer 10

involves movement of molecules from a region of lower concentration to a region of higher concentration, against a concentration gradient, using metabolic energy in the form of adenosine triphosphate produced by the cell

Question 11

active transport (e.g.)

Answer 11

ion uptake by root hairs

uptake of glucose by cells in villi

Question 12

importance as an energy-consuming process by which substances are transported against a concentration gradient

Answer 12

the cell holds some reserves valuable in metabolism e.g. ions and glucose, these useful molecules and ions do not escape and the cell surface membrane retains them inside the cell, when more useful molecules/ions become available, they are actively absorbed into the cells