Chapter 36

Question 1

Which direction is negative pressure and what goes in that direction?

Answer 1

Water and minerals are pulled up the plant

Question 2

Which direction is positive pressure and what goes in that direction?

Answer 2

Sugars are pushed both ways

Question 3

What was the purpose of the evolution of xylem and phloem?

Answer 3

Made long-distance transport of water, minerals, and products of photosynthesis possible

Question 4

Apoplast

Answer 4

Major transport pathway ; consists of everything external to the plasma ; includes cell walls, extracellular space, interior of dead cells

Question 5

Symplast

Answer 5

Major transport pathway ; consists of the entire cytosol of all living cells in a plant ; plasmodesmata

Question 6

Short distance active transport

Answer 6

Transport from root hairs to the xylem

Question 7

How can water cross the cortex?

Answer 7

Via the symplast or apoplast or through the transmembrane route

Question 8

Aquaporins

Answer 8

Transport proteins in the cell membrane that facilitate the passage of water

Question 9

What is the last checkpoint for the selective passage of minerals from the cortex to the vascular tissue

Answer 9

Endodermis surrounding the vascular cylinder

Question 10

What does the waxy casparian strip of the endodermal wall do?

Answer 10

It blocks apoplastic transfer of water and minerals from the cortex of the vascular cylinder

Question 11

What is bulk flow?

Answer 11

Long-distance transport ; the movement of a fluid driven by a pressure gradient

Question 12

How do water and solutes move together?

Answer 12

They move through Tracheids and vessel elements of the xylem and the sieve-tube elements of the phloem

Question 13

What do the branching veins in leaves do?

Answer 13

They ensure that all cells are within a few cells of the vascular tissue

Question 14

How does bulk flow move?

Answer 14

Goes from areas of high pressure to areas of low pressure independently of the difference in solute potential

Question 15

What is transpiration?

Answer 15

The movement of xylem sap (water and minerals) against gravity, from the soils to the leaves, without using any energy

Question 16

What does transpiration depend on?

Answer 16

The evaporation of H2O from the leaves pulls water upwards from the roots(tension) ; Physical properties of water(cohesion and adhesion)

Question 17

Cohesion-tension hypothesis

Answer 17

Transpiration provides the pull for the ascent of xylem sap and water cohesion transmits this pull along the entire length of the xylem from shoots to roots

Question 18

What kind of pressure is xylem pressure normally under?

Answer 18

Negative pressure or tension

Question 19

What do guard cells do?

Answer 19

Balance water conservation with the need for gas exchange by opening and closing stomata

Question 20

Characteristics of leaves and what it does

Answer 20

Large surface area and high surface-to-volume ratio ; increases rates of both photosynthesis and water loss

Question 21

How do guard cells change the diameter of the stoma?

Answer 21

By changing shape ; when turgid they bow outward and the pore between them opens ; when flaccid they become less bowed and the pore closes

Question 22

Where does the majority of the water a plant loses escape from?

Answer 22

The stomata ; water loss is limited elsewhere on leaf by waxy cuticle ; amount of water lost per leaf depends largely on stomata density and average stoma size

Question 23

Stomata opening is triggered at dawn by

Answer 23

Light ; co2 depletion ; an internal “clock” in guard cells

Question 24

Circadian rhythms

Answer 24

Internal clock ; 24-hour cycle

Question 25

What causes a change in turgor pressure?

Answer 25

The absorption and loss of potassium ions (K+) by the guard cells

Question 26

Water potential

Answer 26

Tendency of water to move from one area to another

Question 27

How does free water move?

Answer 27

From regions of higher water potential to regions of lower water potential if there is no barrier

Question 28

Water potential equation

Answer 28

Ψ= Ψs (solute potential) + Ψp (pressure potential)

Question 29

Process of cohesion-tension theory

Answer 29

Water vapor diffuses out of leaf, water evaporates inside leaf, water is pulled out of xylem, water is pulled up xylem, water is pulled out of root cortex, water moves from soil into root

Question 30

How is bulk flow driven?

Answer 30

Driven by water potential different at opposite ends of xylem tissue ; doesn’t need energy

Question 31

Translocation

Answer 31

Process by which products of photosynthesis are transported through the phloem

Question 32

What is phloem sap and how does it travel?

Answer 32

It is an aqueous solution high is sucrose ; travels from sugar source to sugar sink through sieve tube elements

Question 33

Sugar source

Answer 33

Organ that is a net producer of sugar (ex: mature leaves)

Question 34

Sugar sink

Answer 34

An organ that is a net consumer or depository of sugar (ex: roots, buds, fruits)

Question 35

What kind of pressure if bulk flow?

Answer 35

Bulk flow by positive pressure is the mechanism of translocation in angiosperms

Question 36

What are the different ways a sugar can travel?

Answer 36

May move by symplastic or both symplastic and apoplastic pathways

Question 37

What do companion cells do?

Answer 37

Enhance solute movement between the apoplast and symplast

Question 38

Pressure flow hypothesis

Answer 38

Predicts that phloem sap near sugar sources should have higher sugar content than phloem sap near sinks

Question 39

What is sugar transport based on?

Answer 39

Turgor pressure near sink tissues to generate the necessary force (not based on transpiration)