movement of substances

Question 1

define diffusion

Answer 1

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

Question 2

diffusion across a membrane

Answer 2

through a permeable membrane, the permeable membrane allows solutes and solvents to go pass through it. as a result, dissolved particles of substance A will diffuse across the membrane to the left side of the beaker. dissolved particles of substance B will diffuse across the membrane to the right side of the beaker. eventually there will be an equal concentration of all particles on both sides of the membrane

Question 3

state 3 factors affecting rate of diffusion

Answer 3

concentration gradient, diffusion distance and surface area-to-volume ratio

Question 3

diffusion distance

Answer 3

time taken for a substance to move from one point to another depending on the distance between the two points.

the shorter the diffusion distance, the lesser the time is needed for the substance to travel hence rate of diffusion is higher

Question 4

surface area-to-volume ratio

Answer 4

cells need more oxygen, nutrients and waste materials across their cell membrane fast enough to stay alive

rate of movement of a substance across a cell membrane depends on how large the cell membrane is

Question 5

define osmosis

Answer 5

osmosis is the net movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane

Question 6

what happens to a plant cell in solution of higher water potential

Answer 6

the cell sap has a lower water potential than the solution outside the cell. by osmosis, water molecules enter the cell through the partially permeable membrane.
as water molecules enter the cell, the vacuole increases in size pushing the cytoplasm against the cell wall. the cell swells/expands and is said to be turgid

Question 7

what happens to a plant cell in solution of lower water potential

Answer 7

the cell sap has a higher water potential than the solution outside the cell. by osmosis, water molecules from the cytoplasm and vacuole enter the cell through the partially permeable membrane.
as the cell loses water, the vacuole decreases in size. the shrinkage of cell membrane and cytoplasm away from the cell wall. cell becomes plasmolysed. the cell decreases in size and becomes flaccid

Question 8

what happens to an animal cell in solution of higher water potential

Answer 8

the cytoplasm has a lower water potential than the solution outside the cell. water molecules move into the cell by osmosis.
an animal cell will swell and may even burst in a solution of higher water potential than the cytoplasm. unlike plants, it doesn’t have a cell wall to protect it

Question 9

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

Answer 9

the cytoplasm has a higher water potential than the solution outside the cell. water molecules move out of the cell by osmosis.
the cell shrinks and spikes appear on the cell surface, this is called crenation. an animal cell becomes dehydrated and eventually dies when placed in a solution of lower water potential than its cytoplasm

Question 10

what happens to a cell in solution of the same water potential

Answer 10

cell’s cytoplasm doesn’t change in shape or size. the movement of water molecules is the same in both directions. hence there is no net movement of water molecules in and out of the cell