4.4.2 - Transpiration

Question 1

How are xylem vessels arranged in a dicot root?

Answer 1

In a cross shape

Question 2

How are xylem vessels arranged in a monocot root?

Answer 2

Arranged as tubes that surround the pith

Question 3

Hoe does water vapour diffuse out of the leaf?

Answer 3

Less water in air than in the leaf so there is a water potential gradient.
Leaves have higher water potential

Question 4

What happens when water is evaporated out of the leaf?

Answer 4

Replaced by water in xylem.
water can either move through the cytoplasm or cell wall of mesophyll cells.
Due to water potential gradient.

Question 5

What are the 2 ways water is taken upwards by the xylem?

Answer 5

Cohesion tension
Root pressure

Question 6

How does cohesion tension pull up water?

Answer 6

Water molecules form hydrogen bonds between each other.
A column of water is pulled up through the xylem, this is called transpiration pull

Question 7

Evidence for cohesion tension?

Answer 7

During the day, the diameter of tree trunks is smaller.
Xylem vessels are narrower as they are pulling water upwards.

Question 8

How does an osmotic potential arise in the roots?

Answer 8

Dissolved substances build up in epidermal cells by diffusion.
Gives roots a lower water potential than the soil.

Question 9

What is the role of endodermal cells?

Answer 9

Actively transport solutes into the xylem to create a concentration gradient large enough to pull water up the xylem.

Question 10

What are the 3 routes water can take when going from root hair cells into endodermis?

Answer 10

Apoplast route
Symplast route
Vacuolar route

Question 11

How does water travel from root hair cells to the endodermis in the apoplast route?

Answer 11

Through the cellulose cell walls

Question 12

How does water travel from root hair cells to the endodermis in the Symplast route?

Answer 12

Water diffuses along a water concentration gradient through the cytoplasm of cells

Question 13

How does water travel from root hair cells to the endodermis in the vacuolar route?

Answer 13

Water moves along a water potential gradient but through vacuoles as well as cytoplasm.

Question 14

Describe the differences between the apoplastic and the symplastic pathways

Answer 14

Apolplastic is non-living whereas symplastic is living.
Apoplastic uses cell walls/ intercellular spaces
Apolplastic is faster and less resistance.
Apoplastic occurs via diffusion sympastic by osmosis

Question 15

Compare and contrast the mass potometer with the bubble potometer as methods of
measuring the rate of transpiration.

Answer 15

Both measure water uptake.
Both use a seal to prevent evaporation.
Bubble potometer is quicker to get results.
Bubble potometer uses shoot whereas mass potometer uses plants with roots.