8

Question 1

Xylem not only pushes water but also acts as a?

Answer 1

Filter

Question 2

Pits in xylem is essentially a membrane with a pore. What is it for?

Answer 2

A membrane to filter water, primarily bacteria.

Question 3

What controls the pressure in the xylem which also controls the pulling force?

Answer 3

The stomata on whether its open or closed.

Question 4

three stages of plant filtration?

Answer 4

•Passive exclusion: root hair
•Active exclusion: antiporter after being stopped by casparian strip
•Pits: in xylem

Question 5

Capillarity involve 3 forces?

Answer 5

•Adhesion: attraction between water molecules and the tube walls (constant)
•Cohesion: Attraction between molecules of water (constant)
•Weight of the water column: variable

Question 6

Average radius of xylem tube?

Answer 6

0.25mm

Question 7

If capillary radius increases, then water height?

Answer 7

Lowers

Question 8

Why does a larger xylem tube radius makes it harder for water to flow up?

Answer 8

Because of less adhesion forces.

Question 9

How does xylem prevent vascular collapse?

Answer 9

By having a thick cell wall exterior

Question 10

The push of water up is only from?

Answer 10

Root pressure.

Question 11

Which type of pressure can occur when the stomata is closed?

Answer 11

Root pressure

Question 12

Large plants will benefit with water uptake primary by? 2•

Answer 12

•transpiration and •capillary

Question 13

Capillary will only pull water up by how many meters?

Answer 13

2 meters

Question 14

Petiole?

Answer 14

The stem that connects the leaf and the stem of the plant.

Question 15

When we talk about root pressure on water uptake throughout the plant, what is important about root pressure?

Answer 15

How it pushes water up to the xylem, and since water is getting pushed, pressure is positive.

Question 16

Root pressure occurs when solute potential is?

Answer 16

Very very negative

Question 17

The maximum height that water can climb in respect to capillary action is proportional to?

Answer 17

Radius of the tube.

Question 18

Water rises in xylem since?

Answer 18

Adhesive forces is higher than the weight of the water column.

Question 19

What capillary force causes negative pressure (tension) in the xylem?

Answer 19

Cohesive forces generated by the h-bonds between water molecules.

Question 20

Phloem is made out of two cells? 2•

Answer 20

•Companion cells
•Sieve cell

Question 21

Sieve cell (conducting tube), and what does it lack?

Answer 21

Sugar conducting cell and lacks nucleus and major organelles.

Question 22

Companion cell?

Answer 22

Sugar loading/unloading cell and has nucleus and major organelles. It is metabolically active.

Question 23

Source tissue?

Answer 23

A tissue that can provide sugars

Question 24

Sink tissue?

Answer 24

Any tissue that needs sugars

Question 25

Sugars in the plant always move from?

Answer 25

Source to sink.

Question 26

Translocation?

Answer 26

The direction in which sugars move in a plant.

Question 27

The strength of translation depends on?

Answer 27

Developmental stage and season.

Question 28

Water and sugar transport in the phloem has what pressure?

Answer 28

Positive pressure, therefore, it is pushed.

Question 29

Water movement between xylem and phloem is driven by?

Answer 29

Osmotic flow driven by water potential.

Question 30

Steps for sucrose secretion?

Answer 30

1. Active transport moves sucrose from source cells (leaves) into companion cells since the companion cell establishes a proton pump to pump sucrose via symporter. This is because the sucrose concentration is higher in the companion cell than the source since the source is trying to get rid of sucrose.
2. Once sucrose is in companion cell, sucrose builds up in sieve tube member cells via concentration gradient, therefore diffusion.
3. The high sugar concentration in sieve cells generate very negative solute potential. Water flows from adjacent xylem increasing the pressure potential in the phloem.

Question 31

Phloem Loading in metabolically active sinks?

Answer 31

•Sucrose flows into the companion cell, and then into the flower cell (active sink) through passive transport. Passive transport is kept since the active sink always ensures that it uses the sucrose. Sucrose accumulates inside the vacuole through an antiporter as a storage mechanism.

Question 32

!!!!!!!Pressure in sink vs source?

Question 33

Phloem unloading?

Answer 33

When sugars are exported to cells by facilitated diffusion or active transport. The decrease in sucrose concentrations in sieve tube elements decrease the solute potential, phloem pressure is reduced, and water potential increases. Water moves out of the phloem and into the xylem tissue since the water potential inside the xylem tissue is lower.

Question 34

Pressure throughout phloem?

Answer 34

High pressure is maintained in the phloem at the source since water potential in the xylem is relatively high. Low pressure is maintained in the phloem at the sink since low water potential is present at the xylem. Because of the high pressure at the source, it can push sucrose into the low pressure environment of the sink (since positive flow).

Question 35

What is the main contributor to water flow between xylem and phloem?

Answer 35

Water potential.

Question 36

!!!!!Sign of turgor potential?

Answer 36

Always positive (P >= 0)

Question 37

!!!!!!What causes the push in root pressure?

Answer 37

Root pressure pressurizes the xylem as water and ions concentrates. REVIEW root pressures slide