Transport in plants and transpiration

Question 1

What is the stele?

Answer 1

Vascular cylinder containing xylem and phloem (vascular tissue)

Question 2

What does xylem transport?

Answer 2

Water and mineral salts

Question 3

What does phloem transport?

Answer 3

Sugars e.g. sucrose

Question 4

What are some characteristics of xylem vessels?

Answer 4

Highly specialised for transport of water and minerals
No end walls
No cell contents
Are dead
Secondary walls are thickened with lignin

Question 5

What is the purpose of pits?

Answer 5

Allows movement of water between adjacent vessels and surrounding cells

Question 6

What are 2 important properties of lignin?

Answer 6

Strength - prevents vessels from collapsing under the pressure of transpiration
Waterproof - prevents leakage of water

Question 7

What is the definition of transpiration?

Answer 7

Evaporation of water from the mesophyll surface and subsequent diffusion of H2o vapour through the stomata and into the atmosphere.

Question 8

What are the 3 main stages of transpiration?

Answer 8

Into and across the root
Up the root and stem into the xylem
Through the leaf and evaporation of water from the leaf

Question 9

Explain the movement of water through roots:

Answer 9

Vast majority plants are terrestrial
Need to conserve water - waxy cuticle
Cannot absorb water over general surface

Question 10

What helps root absorb water?

Answer 10

Root hairs

Question 11

What does a root hair look like?

Answer 11

Long
thin
extension of a root epidermal cell

Question 12

How long will a root hair be functional?

Answer 12

A few weeks

Question 13

What is the main function of root hair cells?

Answer 13

Exchange surfaces in plants responsible for absorption of mineral ions and water

Question 14

Why are root hairs efficient exchange surfaces?

Answer 14

A large surface area - occur in thousands of each root branch
Thin surface layer - substances can move easily

Question 15

Does the soil have a low or high water potential and why?

Answer 15

High - soil solution is mostly water

Question 16

Do root hair cells have a low or high water potential and why?

Answer 16

Low water potential - contain solutes such as sugars, amino acids and mineral ions

Question 17

What direction will the water move in relation to root hair cells?

Answer 17

From the soil solution into root hair cells -

from high water potential to low water potential

Question 18

What are the two pathways water moves once it has entered the root hair cells?

Answer 18

Apoplastic pathway

Symplastic pathway

Question 19

Where does water move in the apoplastic pathway?

Answer 19

Along the cellulose microfibrils of the cell wall

Question 20

What is special about microfibrils and what does this mean for the movement of water?

Answer 20

They are parallel

Water moves between the layers rather than through them

Question 21

What is the movement of water within the apoplastic pathway?

Answer 21

cell wall - cell wall

Question 22

What is meant by cohesive?

Answer 22

The water molecules stick to each other

Question 23

When water is drawn into the endodermal cells what happens?

Answer 23

More water is pulled along behind it

Question 24

How does water move in the Symplastic pathway?

Answer 24

From cytoplasm to cytoplasm

Question 25

Where does the water pass through?

Answer 25

Through tiny openings in the cell wall

Question 26

What are these tiny openings called?

Answer 26

Plasmodesmata

Question 27

What does each plasmodesmata contain?

Answer 27

filled with a thin strand of cytoplasm

Question 28

What does water entering by osmosis do within the symplastic pathway?

Answer 28

Increases the water potential in the root hair cell

Question 29

What does this therefore mean?

Answer 29

Has a higher water potential than the first cell in cortex

Question 30

In what way does water move in the symplastic pathway?

Answer 30

Water moves from root hair cell to first cell in cortex by osmosis

Question 31

What way will water move by osmosis?

Answer 31

Moves from cell to cell by osmosis along water potential gradient

Question 32

How do ions enter root hair cells?

Answer 32

By facilitated diffusion/ active transport | Either along or against the concentration gradient

Question 33

What is the first step of water moving into xylem?

Answer 33

When water reaches the endodermis by the apoplastic pathway - waterproof casparin strip prevents it from progressing along the cell wall

Question 34

Where is water forced during the symplastic pathway?

Answer 34

Into the living protoplast where it travels along the symplastic pathway

Question 35

What does the endodermal cells transport?

Answer 35

Actively transports salt in the xylem

Question 36

What does this process require?

Answer 36

Energy

Question 37

Where is the only place this process can occur?

Answer 37

In living tissue

Question 38

What must water enter first to get into the xylem?

Answer 38

Must enter the cytoplasm of endodermal cells