Root pressure & Guttation

Question 1

Describe the relative humidity and transpiration rate of plants at night

Answer 1

At night, when relative humidity is high, approaching 100%, transpiration rate is low, or 0

Question 2

How do mineral ions accumulate in the vascular cylinder?

Answer 2

Root cells continuously pump water and mineral ions into xylem.

The endodermis prevents ions from leaking back into cortex and soil

More mineral ions accumulate in the vascular cylinder, and reduce the water potential

Question 3

What is the result of more mineral ions accumulating in the vascular cylinder?

Answer 3

water potential reduces

Question 4

What is guttation?

Answer 4

Due to root pressure, more water enters the leaf than is lost by transpiration

This results in the removal of water droplets from leaf tips or leaf of some herbaceous plants, which is guttation

Question 4

How does guttation differ from dew?

Answer 4

Dew is condensed moisture of the atmosphere

Question 5

Why is no guttation seen at daytime?

Answer 5

Because xylem sap isn’t then pushed, but pulled by transpiration

Root pressure isn’t sufficient to push water up a distance over meters

Question 5

What are hydrathodes?

Answer 5

Guttation takes place thorough hydrothodes, which are formed by special cell groups located near the ends of small veins

Question 6

How are hydrothodes formed?

Answer 6

by special cell groups located near the ends of small veins

Question 7

Give examples for plants which perform guttation

Answer 7

Alocasia
Colocasia

Question 8

Describe guttation in depth

Answer 8

At night, when relative humidity is high, approaching 100%, transpiration rate is very low or 0.

Root cells continuously pump water and mineral ions into xylem tissue,

Endodermis prevents ions from leaking back into cortex and soil.

Therefore, more mineral ions accumulate in the vascular cylinder, reducing water potential

Water moves from the cortex.

It generates a root pressure and upward push of xylem sap

Due to root pressure, more water enters the leaves than lost by transpiration

This results in removal of water droplets from leaves of some herbaceous plants, called guttation.

Guttation differs from dew, as dew is condensed moisture of the atmosphere

Many plants don’t generate root pressure and no guttation occurs.

Even in plants which display guttation, root pressure can’t match water loss by transpiration by sunrise

So no guttation can be seen at daytime, because then xylem isn’t pushed but pulled by transpiration

Root pressure is never sufficient push water up a distance of meters.

Guttation takes place through hydathode, which are formed by special groups of cells located near the ends of small veins, and doesn’t take place through stomata.

Ex: Alocasia, Colocasia