Chapter 3 - 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.

Question 2

Define osmosis.

Answer 2

Osmosis is 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

Define plasmolysis.

Answer 3

Plasmolysis is the shrinkage of the cytoplasm and cell surface membrane away from the cell wall. (cell decreases in size and become flaccid)

Question 4

What happens to a cell when placed in a solution of lower water potential?

Answer 4

Water leaves the cell by osmosis. Cell decreases in size and becomes flaccid. (because less turgor pressure exerted on cell wall by water in vacuole/cytoplasm) Animal cells may shrink and become crenated (e.g RBC has little spikes appearing on cell surface membrane)
Plant cells may be plasmolysed (shrinkage of cytoplasm and cell membrane away from the cell wall)

Question 5

What happens to a cell when placed in a solution of higher water potential?

Answer 5

Water enters the cell by osmosis. Cell increases in size and becomes more turgid. (because more turgor pressure exerted on cell wall by water in vacuole/cytoplasm) Animal cells may swell and burst since there is lack of structural support due to absence of cell wall.

Question 6

Importance of turgor in plants.

Answer 6

Plants remain firm and erect.
Movement of certain parts of the plant are controlled by turgor. (e.g turgor of guard cells control opening and closing of stomata)

Question 7

Define active transport.

Answer 7

Active transport is an energy-consuming process by which particles of a substance are transported across a membrane against a concentration gradient. (lower to higher concentration)

Question 8

Cases of active transport.

Answer 8

Ion uptake by root hair cells.

Glucose absorption in the villi of small intestine.