Cell water relations

Question 1

water 5 function for plants

Answer 1

1) Provides structural Support

2) Drives growth of cells and tissues

3) Is medium in which nutrients are transported in xylem and in which sugars are transported in phloem

4) Photosynthesis: electron donor

5) “the fluid that lubricates” DNA, enzymes, membranes lose structure w/o water

Question 2

Water properties- polarity

Answer 2

○ Because water is polar, it can form Hydrogen bonds
○ Good solvant
○ Adheres to hydrophillic surfaces, like cell walls

Question 3

Water properties- hydrogen bonds

Answer 3

○ Hydrogen binds to oxygen

○ At surface of water, there are fewer hydrogen bonds; this is why water minimizes surface area

○ Water Strider uses the surface tension created by these to walk on water

Question 4

Water properties- density

Answer 4

• Water is most dense at 4C, ice less dense because hydrogen bond orientation causes molecules to push further apart

○ The freezing of lakes from top provides insulation underneath, allowing life

Question 5

Water properties- Metastable

Answer 5

○ Water in xylem is stretched(metastable), it should be in vapor phase under tension, but is not

○ Means not being in stable equilibrium state
○ If triggered, water will rapidly transition into equilibrium state
Supercooled water:
○ Stretched water:
○ Glassy water:

Question 6

Supercooled water

Answer 6

remains liquid even below 0C

Question 7

Glassy water

Answer 7

Below freezing, has diff molecular arrangement than ice

Question 8

Stretched water

Answer 8

Liquid under tension

Question 9

Diffusion

Answer 9

• Follows concentration gradient
• Effective over short distances
  ie in a cell

Question 10

Osmosis

Answer 10

• When there is a semipermeable membrane
• Flow depends on concentration difference
• Water moves into compartment containing salt-creating pressure

Question 11

what does osmosis generate

Answer 11

• Generates Turgor pressure which provides structural support

Question 12

Osmosis in cells

Answer 12

• Osmosis drives the movement of water in and out of cells
• Cells have higher solute conc so water wants to move in, animal cells would burst, water cell walls prevent from bursting
• Salt water has higher solute conc so water flows out

Question 13

Bulk flow

Answer 13

• Movement of water + solutes together
• Driven by pressure difference
• Water pressure can be positive or negative

Question 14

Aquaporins

Answer 14

• Are channel proteins that facilitate transport of water across membranes
• Water can flow in either direction
• NOT PUMPS
• Facilitate movement ie sensitive plants

Question 15

where are aquaporins located in plants?

Answer 15

• Xylem aquaporins not nessesary
  
  • Involved in leaves: across leaf bundle sheath
  • Involved in roots: Across root endodermis