movement of substances

Question 1

define diffusion

Answer 1

the movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient

Question 2

define osmosis

Answer 2

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

Question 3

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

Answer 3

1. in a solution of higher water potential, the cell sap of the plant cell has lower water potential than the solution outside the living cell
2. water enters the cell through the partially permeable cell surface membrane by osmosis
3. the cell EXPANDS and becomes TURGID
4. the vacuole increases in size and pushes the cytoplasm against the cell wall. The cell wall does not burst because it is protected by the inelastic cell wall

Question 4

what is the pressure exerted by the water on the cell wall called?

Answer 4

turgor pressure

Question 5

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

Answer 5

an animal cell will swell and may even burst as unlike plant cells, an animal cell does not have a cell wall to protect it

Question 6

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

Answer 6

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

Question 7

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

Answer 7

1.the water potential of the cell sap is higher than that of the solution outside the cell

2. water from the vacuole and cytoplasm leaves the cell through the partially permeable cell surface membrane by osmosis
3. the cell decreases in size and becomes FLACCID
4. the cytoplasm shrinks away from the cell wall and becomes plasmolysed

Question 8

can a plasmolysed cell be restored to its original state? how?

Answer 8

yes! a plasmolysed cell can be restored to its original state by placing it in water or in a solution with higher water potential

Question 9

what is plasmolysis?

Answer 9

the shrinkage of cytoplasm and cell membrane away from the cell wall

Question 10

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

Answer 10

1. the cytoplasm of the animal cell has higher water potential than the solution
2. water molecules leave the cell through the partially permeable cell surface membrane by osmosis
3. cell shrinks and becomes crenated

Question 11

why is osmosis important to plants?

Answer 11

osmosis is important to plants as it allows leaves and young stems to remain firm and stand erect due to the TURGOR PRESSURE in the respective cells

Question 12

what happens to plants that lose excessive amounts of water from evaporation?

Answer 12

the leaves and young stems lose their firmness and wilt due to the loss of turgor pressure in the cells

Question 13

how does the surface area of a cell affect the rate of diffusion of a substance for a given concentration gradient?

Answer 13

the greater the surface area of cell surface membrane to volume ratio, the faster the rate of diffusion of a substance for a given concentration gradient

extra*: this is why cells are so small as it needs to move nutrients and waste materials across their cell surface membrane fast enough to stay alive!