7.7 Transport of water in the xylem

Question 1

How does water enter a flowering plant?

Answer 1

Water is absorbed by the roots through extensions called root hairs

Question 2

What is the name of the tissue that transports water?

Answer 2

Xylem- hollow and thick walled tubes.

Question 3

What is Transpiration?

Answer 3

evaporation of water from a plant’s leaves.

Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere
(caused by osmosis and evaporation)

Question 4

Where does the energy for transpiration essentially come from?

Answer 4

The energy is supplied by the sun (transpiration) and is therefore passive.. As the evaporation at MESOPHYLL CELLS “pulls” water molecules up due to their cohesive nature.
Remember: the xylem is dead cells

Question 5

what is the cohesion tension theory?

Answer 5

1)When water evaporates from the MESOPHYLL cells in the leaf through the holes called STOMATA…
2)MORE Water is pulled up behind the evaporating water due to the COHESION
3)Therefore: Water is constantly being pulled UP the xylem AS A RESULT OF TRANSPIRATION (evaporation of water through leaves… try picturing it in your head)
4)The Water being pulled (as a RESULT OF TRANSPIRATION) up is called the 5)TRANSPIRATION PULL
This TRANSPIRATION PULL puts the xylem under TENSION (because it’s forcing water up the xylem)

Question 6

What two types of calls surround each stomata

Answer 6

Guard cells

Question 7

What is passed through the stomata when its opened?

Answer 7

Carbon dioxide enters, and lets water and oxygen out.
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Question 8

What happens when the loss of water from the leaves is greater than the uptake of water by the roots?

Answer 8

The plant wilts

Question 9

What happens when the plants wilt?

Answer 9

The cells are not turgid anymore

Question 10

What is Transpiration?

Answer 10

The loss of water vapour by evaporation from a plant to the air surrounding it through its open stomata in the cells.

Question 11

The greater the water potential gradient…

Answer 11

the faster the rate of movement

Question 12

Water molecules diffuse along a water potential gradient towards…

Answer 12

an area with a more negative (lower) water potential value.

Question 13

What 3 factors increase the water potential gradient and hence the rate of transpiration?

Answer 13

1. An increase in temperature
2. a decrease in humidity
3. An increase in wind velocity/ air movement

Question 14

What is the main factor that is responsible for the movement of water up the xylem?

Answer 14

Cohension- tension

Question 15

What evidence is there to support cohesion-tension theory?

Answer 15

Change in diameter of tree trunks according to the rate of transpiration.

Question 16

What effect does transpiration have during the day plants?

Answer 16

The rate of transpiration is at its greatest, there is more tension (more negative pressure) in the xylem. This pulls the walls of the xylem vessels inwards and causes the trunk to shrink in diameter.

Question 17

What effect does transpiration have during the night of plant?

Answer 17

The rate of transpiration is at its lowest- and therefore there is less tension in the xylem and so the diameter of the trunk increases.

Question 18

What happens if a xylem vessel was broken?

Answer 18

Air is drawn in- which is consistent with it being under tension

Question 19

Why can a tree no longer draw up water if a xylem vessel is broken?

Answer 19

Because the continuous column of water is broken and so the water molecules can no longer COHERED TOGETHER.

Question 20

What experiment could you set up in to investigate e the effect of
a named environmental
variable on the rate of
transpiration.

Answer 20

potometer