Transport of water

Question 1

Buliform Cells

Answer 1

in monocot leaves, control the folding of leaves

Question 2

Motor cells

Answer 2

control rapid movements of Mimosa leaves. Although similar in principle,

Question 3

are motor or buliform cells faster

Answer 3

motor cells mechanism is much faster than in buliform cells.
That is possible because of the rapid movement of ions, followed by water exiting the cells via aquaporins.

Question 4

what do sieve tubes consist of
describe

Answer 4

sieve elements, elongated cells that are connected to eachother via sieve plates forms

Question 5

seive elements characteristics

Answer 5

they don’t have nucleus and vacuoles. Importantly though, they maintain their semi-permeable plasma membrane.

Question 6

Companion cells

Answer 6

derive from the same mother cell and maintain close connection w the sieve element.
Companion cells contain all organelles typical for a plant cell, including nucleus, vacuoles, and chloroplasts.

Question 7

Sieve plates

Answer 7

are end walls containing large pores to provide a connection
between adjacent sieve elements.

Question 8

Sieve elements

Answer 8

have aquaporins in their plasma membrane. This may control the flow of water into, and out of the sieve tubes.

Question 9

Xylem and phloem exchange

Answer 9

Some of the water in a plant cycles between phloem and
xylem.

Question 10

Munch pressure flow hypothesis

Answer 10

-Pressure flow hypothesis (Münch, 1930): states that phloem sap (water + sugar) is moved by a pressure gradient
-Maintained by loading at source and unloading at sink.
-phloem

Question 11

how does loading and unloading work in munch pressure flow hypothesis

Answer 11

-Phloem loading creates a high sugar concentration at the source. Water enters the phloem by osmosis. This creates very high pressure (like turgor pressure)
-At the sink, sugars are unloaded, and water exits as well.

Question 12

what does the pressure difference do in munch pressure flow hypothesis

Answer 12

So, there is a pressure difference between the source and sink. The phloem sap moves via bulk flow from high to low pressure in the sieve tubes.
* Creating this pressure difference requires energy.
* Phloem sap is under very high pressure.

Question 13

2 different types of phloem loading

Answer 13

apoplastic and symplastic loading

Question 14

Apoplasmic loading

Answer 14

Active transport of sugars from apoplast (cell wall) into companion cell
* Sugars can’t leak back to bundle sheath (no plasmodesmata there)
* Most herbs do this

Question 15

Symplasmic loading

Answer 15

• Sugar follows a downhill concentration gradient from bundle sheath into the phloem
• All cells are well connected via plasmodesmata
• Most trees do this
• Much of the water comes from the xylem

Question 16

Callose

Answer 16

used to seal off seal plates in response to injury

Question 17

what are used to collect sap?

Answer 17

aphids

Question 18

what does phloem sap contain?

Answer 18

phloem sap contains sugar (mostly sucrose, ~20% of the total sap), amino acids, RNA, viruses, hormones, and many
other types of molecules

Question 19

why is transpiration significant in xylem transport

Answer 19

-creates a pulling force
-Water is pulled up into the leaves against gravity and friction. This is possible due to strong cohesion and adhesion.
-Both the atmosphere and the soil are pulling on the water column. The atmosphere pulls much harder (is much drier than the soil), so water moves
up.

Question 20

xylem sap easily changes states to gas, what is the word for this?

Answer 20

Metastable

Question 21

water in the xylem is under great

Answer 21

tension

Question 22

air filled vessels

Answer 22

xylem embolism

Question 23

what is xylem transport driven by ULTIMATELY, and what does that make it

Answer 23

the energy of the sun that causes transpiration, a passive transport,

Question 24

Xylem water is under tension =

Answer 24

negative pressure

Question 25

how are airbubbles formed and how do they form embolized vessels

Answer 25

-Transport under tension usually works quite well, but drought and frost can create air bubbles in a vessel.
- If the sap around the bubble is under tension, the bubble may expand and the vessel will embolize (fill with air).
- Embolized vessels cannot transport water anymore, unless they are refilled via root pressure

Question 26

Drought-induced xylem embolism can cause

Answer 26

dieback and mortality

Question 27

water drops on leaf tips

Answer 27

guttation

Question 28

what causes guttation

Answer 28

The drops are created by water being pushed out of the xylem through root pressure.

Question 29

when does guttation happen?

Answer 29

at night or in the morning during times of little transpiration

Question 30

when does root pressure occur in grapevine and trees?

Answer 30

before the leaves emerge in the spring.