Osmoregulation in Plants

Question 1

Osmoregulation

Answer 1

Regulation of solute concentrations and water balance by a cell or organism

Question 2

Solute

Answer 2

A substance that is dissolved in a solution

Question 3

Osmosis

Answer 3

The diffusion of (free) water across a selectively permeable membrane, in this case, the plasma membrane

Question 4

Water potential equation

Answer 4

solute potential + pressure potential

Question 5

Water potential

Answer 5

Water always moves away from the system with a higher water potential to the system with a lower water potential

Question 6

Solute potential and concentration

Answer 6

Solute potential decreases with increasing solute concentration

A decrease in solute potential causes a decrease in the total water potential

Question 7

Can water move directly through the membrane

Answer 7

yes

Question 8

Can solutes move directly through the membrane

Answer 8

most cannot

Na+ and K+ need their own channels to move through membranes

Question 9

Turgor pressure

Answer 9

pressure exerted by the protoplast (everything in the cell except the cell wall) against the plant cell wall

Question 10

Where does water cross the membrane

Answer 10

through the aquaporins

Question 11

Aquaporin

Answer 11

Integral membrane proteins that form water-selective channels across membrane

Accounts for observed higher rates of water movement than diffusion alone

Question 12

Advantages of aquatic life

Answer 12

• Buoyancy
• Abundant water
• moderate temperatures
• Filtered light

Question 13

Obstacles of transition to land

Answer 13

• No buoyancy
• Scarce water
• Extreme temperatures
• Excess light including UV

Question 14

How did plants respond to water deficit

Answer 14

• increase root growth
• decrease shoot growth
• decrease in transpiration
• decrease in photosynthesis

Question 15

Osmotic adjustment

Answer 15

A biochemical mechanism that helps plants acclimate to dry or saline/salty soil

While some plants are highly sensitive to water stress and will dehydrate (wilt), others can endure dry or saline conditions without loss of turgor pressure

Question 16

Extracting water from the soil

Answer 16

A plant root must establish a water potential gradient so that water flows towards the cells of the root from the soil

Water potential must be lower in the rot than in the surrounding soil

Question 17

Solute potential

Answer 17

• A solution is directly proportional to its molarity
• Aka osmotic potential
• 0 for pure water
• Decreases with addition of solutes

Question 18

Pressure potential

Answer 18

Physical pressure on a solution

Question 19

Drought tolerant plants and osmotic adjustment

Answer 19

They regulate their solute potential to compensate for temporary or extended periods of water stress

Results from a net increase in the number of solute particles in the plant cell

Question 20

By adding solutes to the cell and decreasing plants solute potential…

Answer 20

…osmotic adjustment can drive root water potential to values lower than soil water potential, thereby allowing water to move from soil to plant down a potential gradient

Question 21

How does the accumulation of solutes affect flow of water

Answer 21

As the cell actively accumulates solutes, water potential drops, promoting the flow of water into the cell

Question 22

Using osmosis to control stomatal openin

Answer 22

Changes in turgor pressure inflate or deflate guard cells, changing stomata size

Question 23

What is guard cell turgor pressure controlled by

Answer 23

Controlled by regulation of K+ movement

Question 24

If isolated plant cells with a water potential averaging -.05 MPa inside the cells are placed into a solution with a water potential of -0.3 MPa, which of the following would be the most likely outcome?

Answer 24

Water would move into the cells

Question 25

Halophytes

Answer 25

Salt-tolerant plants that are genetically adapted to saline conditions

Question 26

Glycophytes

Answer 26

Less salt-tolerant plants that are not adapted to saline conditions

Question 27

Non-saline conditions

Answer 27

The cytosol of plant cells contains about 100 mM K+ and <10 mM Na+

Enzymes function optimally

Question 28

Saline environments

Answer 28

Cytosolic Na+ may increase to >100 mM and these ions can become toxic

Proteins denature and membranes destabilize

Question 29

How do halophytes deal with high levels of salinity

Answer 29

• Reduction of the Na+ influx
• Compartmentalization of Na+ in vacuoles
• Excretion of Na+ through salt glands