Lecture 24: Plant Transport II

Question 1

transpiration

Answer 1

• evaporation of water from a plant’s surface
• 95% of H2O is lost thru transpiration

Question 2

how is water replaced in the xylem?

Answer 2

it’s replaced by bulk flow of water & minerals called** xylem sap**, from the steles of roots to the stems & leaves

Question 3

at night transpiration is ____, which leads to

Answer 3

very low; root cells continue pumping mineral ions into the xylem of the vascular cylinder, lowering water (osmotic) potential

Question 4

water flows in from the _____, and generates

Answer 4

root cortex; root pressure

Question 5

positive root pressure is _____ ? and a _____ ? of xylem bulk flow

Answer 5

relatively weak; minor mechanism

Question 6

what is gutttation

Answer 6

drops on edge of leaf as the result of root pressure pushing water up when transpiration is off/low; a weak force

Question 7

explain the transpiration-cohesion-tension mechanism

Answer 7

• water is pulled upward by negative pressure in the xylem
• water vapor in the airspaces moves down its potential gradient and exits the leaf via stomata; lowers psi in the mesophyll

Question 8

transpiration produces what type of pressure in the leaf, and it exerts what type of force

Answer 8

negative pressure; pulling force on water in the xylem, pulling water into the leaf

Question 9

How is the transpiration pull on xylem sap transmitted

Answer 9

from the leaves to the root tips; even into the soil solution

Question 10

transpiration pull is facilitated by ____ of water molecules to each other & ____ of water molecules to cell walls

Answer 10

cohesion; adhesion

Question 11

water molecules are attracted to

Answer 11

cellulose in xylem cell walls through adhesion which helps offset the force of gravity

Question 12

the thick walls of the tracheid & vessels do what

Answer 12

they withstand pressure & prevent collapse

Question 13

cavitation

Answer 13

water expands when frozen & breaks tracheids/vessels, making ain air bubble leading to cavitation

Question 14

How much of the water a plant loses escapes through stomata

Answer 14

95%

Question 15

a stoma is flanked by a pair of what, which control the diameter of what by changing shape

Answer 15

guard cells; stoma

Question 16

What force open and closes stomata, and what uptake occurs

Answer 16

changes in turgor pressure; uptake and loss of K+ ions by the guard cells

Question 17

When do stomata open and close during the day

Answer 17

open during the day, close at night

Question 18

What triggers stomatal opening

Answer 18

light, CO2 depletion, internal clock in guard cells

Question 19

all eukaryotic organisms have internal clocks called

Answer 19

circadian rhythms

Question 20

What can cause stomata to close during the day time

Answer 20

drought, high temperature, and wind

Question 21

What hormone is produced in response to water deficiency & causes the closure of stomata

Answer 21

abscisic acid

Question 22

If the lost water isn’t replaced by sufficient transport of water then what happens

Answer 22

the plant will lose water & wilt; turgor is lost throughout the plant

Question 23

Another thing that transpiration also results in is

Answer 23

evaporative cooling, which can lower the temperature of a leaf and prevent denaturation of enzymes

Question 24

Xerophytes

Answer 24

• plants adapted to arid climates
• some complete life cycle during rainy season
• others have leaf modifications reducing transpiration rate

Question 25

some plants used a specialized form of photosynthesis called

Answer 25

crassulacean acid metabolism where stomatal gas exchange occurs at night

Question 26

the products of photosynthesis are transported through ____ by the process of

Answer 26

phloem; translaction

Question 27

phloem sap and it’s path of travel

Answer 27

• aqueous solution high in sucrose
• travels from sugar source to sugar sink
• sugar source: net producer of sugar
• sugar sink: net consumer or storer of sugar

Question 28

A storage organ can be both

Answer 28

a sugar sink in summer & sugar source in winter

Question 29

sugar can move through which pathways

Answer 29

• symplastic
• both symplastic & apoplastic pathways

Question 30

transfer cells

Answer 30

• modified companion cells that enhance solute movement between the apoplast & symplast

Question 31

in many plants, phloem loading requires what method

Answer 31

active transport

Question 32

what enables the cells to accumulate sucrose

Answer 32

proton pumping & cotransport of sucrose and H+

Question 33

what occurs at the sugar sink in phloem loading

Answer 33

sugar molecules diffuse from phloem to sink tissues & are followed by water