3.3.3 movement of water through plants

Question 1

plasmodesmata

Answer 1

gaps in cell wall containing cytoplasm connecting 2 cells

Question 2

cellulose cell walls in plants are…

Answer 2

fully permeable to water

Question 3

what are many plant cells joined by

Answer 3

special cytoplasmic bridges (plasmodesmata)
= cell junctions where the cytoplasm of 1 cell is connected to that of another via a gap in their cell walls

Question 4

name the 3 possible pathways taken by water through a plant

Answer 4

1. apoplast
2. symplast
3. vacuolar

Question 5

describe the apoplast pathway

Answer 5

• water passes through spaces in cell walls & between cells
• doesn’t pass through any plasma membranes
• water moves by mass flow
• dissolved mineral ions/salts can be carried by water

Question 6

describe the symplast pathway

Answer 6

• water enters cell cytoplasm via plasma membrane
• can then pass through plasmodesmata from 1 cell to next

Question 7

describe the vacuolar pathway

Answer 7

(similar to symplast but water isn’t confined to cytoplasm)
- water able to enter/pass through vacuoles

Question 8

draw apoplast, symplast & vacuolar pathways

Answer 8

pg. 212 in textbook

Question 9

water potential

Answer 9

measure of tendency of water molecules to move from region of higher water potential to region of lower water potential

Question 10

water potential of pure water

Answer 10

0

Question 11

why is the water potential of plants always negative

Answer 11

• cytoplasm contains mineral ions & sugars (solutes) = reduce water potential
• fewer ‘free’ water molecules available

Question 12

describe the water uptake of a plant cell (in pure water)

Answer 12

• take up water molecules by osmosis (as water potential in cell is more negative)
• water molecules move down water potential gradient into cell
• strong cellulose walls stops it bursting when turgid
• water inside cell exerts pressure on cell wall = pressure potential
• as pressure potential builds up = reduces influx of water

Question 13

describe the water loss of a plant cell (in salt solution)

Answer 13

• salt solution = very negative water potential
• lose water via osmosis
• water potential of cell is higher = water moves down water potential gradient out of cell
• as water loss continues = cytoplasm & vacuole shrink
• when cytoplasm no longer pushes against cell wall (cell isn’t turgid)
• water continues to leave cell = plasma membrane will lose contact with cell wall (plasmolysis) & tissue is now flaccid

Question 14

describe movement of water between cells

Answer 14

• if plant cells touching, water molecules can pass from 1 to the other
• move from higher water potential to cell with lower water potential via osmosis