Notes 6

Question 1

How do water and minerals enter the plant?

Answer 1

Water and minerals enter the plant through root epidermis, cross root cortex, and pass to the vascular cylinder.
Xylem sap, water and dissolved minerals, transported from roots to veins of each leaf by bulk flow.

Question 2

What is bulk flow?

Answer 2

Bulk Flow is the movement of a fluid due to a difference in pressure between 2 locations.

Question 3

Transpired water is ___ as water travels up from the roots

Answer 3

replaced

Question 4

Sap is mainly ____ from the roots or pulled up by the leaves

Answer 4

pushed up

Question 5

At night do root cells continue to pump into the xylem?

Answer 5

Yes. At night ( no transpiration) root cells continue pumping mineral ions into xylem and water flows in from the root cortex, generating pressure that pushes xylem sap. Positive root pressure is a minor mechanism of xylem bulk flow.

Question 6

T or F: Root pressure can produce too much water into the leaves

Answer 6

True. Root pressure sometimes causes more water to enter leaves than is transpired. Results in guttation, the exudation of water droplets on tips of edges of leaves

Question 7

What is the cohesion-tension hypothesis?

Answer 7

According to cohesion-tension hypothesis, transpiration provides the pull for the ascent of xylem sap and the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots,

Question 8

When water diffuses out of the stomata, what happens?

Answer 8

Water vapor in air spaces of a leaf diffuses out via the stomata because the outside is drier. This water is replaced from water lining surface of mesophyll cells creating surface tension (neg pressure).This tension pulls water from xylem to leaf.

Question 9

How does the generation of transpirational pull work?

Answer 9

First water vapor diffuses outside via stomata. Water vapor is replaced from the water film. Air water interface to retreats. The increased surface tension pulls water from cells and air spaces.Water from the xylem is pulled into cells and air spaces. Negative pressure (tension) at the air-water interface in the leaf is the basis of transpirational pull that draws water out of the xylem.

Question 10

What are the 2 things that facillitate bulk flow?

Answer 10

Adhesion and cohesion.Water molecules are attracted to cellulose in xylem cell walls through adhesion. This adhesion helps offset the force of gravity.
Each water molecule is cohesively bound to the next by hydrogen bonds
Cohesion makes it possible to pull a column of xylem sap water molecules exciting xylem in leaf tug on adjacent water molecules
This pull is relayed molecule by molecule down the entire column of water in xylem.

Question 11

What is credited to preventing vessel elements and tracheids from collapsing under negative pressure?

Answer 11

Thick secondary walls

Question 12

What character of leaves increases photosynthesis but also increases water loss through the stomata?

Answer 12

Its high SA and surface to volume ratio.

Question 13

What is the purpose of the opening and closing of the guard cells?

Answer 13

Opening and closing by guard cells helps balance water conservation with gas exchange for photosynthesis. Each stoma is flanked by a pair of guard cells which control the diameter of the stoma by changing shape.

Question 14

What causes open and closes the stomata?

Answer 14

Changes in turgor pressure open and close the stomata. When turgid guard cells bow outward and the pore between them opens. When flaccid, guard cells become less lowered and the pore closes.

Question 15

What can changes in tugor pressure be a result of?

Answer 15

Changes in turgor pressure result from the reversible uptake and the loss of K+ ions by the guard cells.

Question 16

How does osmotic water loss occur from guard cells?

Answer 16

Active transport of H+ out of guard cells creates a membrane potential that drives K+ into cell through specific membrane channels.
Water enters by osmosis, cells become turgid, and stomata opens.
Stomatal closing results from exit of K+ from guard cells, which leads to an osmotic loss of water.

Question 17

T or F: Generally stomata closed during the day and open at night

Answer 17

False. Generally stomata open during the day and close at night to avoid water loss. Stomatal opening at dawn is triggered by light, CO2 deprivation, and an internal clock in guard cells.

Question 18

What are cycles with intervals of 24 hours called?

Answer 18

Circadian Rhythms

Question 19

What are xerophytes?

Answer 19

Plants that are adapted to arid climates.

Question 20

What is Crassulacean acid metabolism (CAM)?

Answer 20

Specialized photosynthesis in succulents. Leaves taken in CO2 at night and stomata are closed in the day.

Question 21

The products of photosynthesis are transported through phloem by the process of ____.

Answer 21

Translocation.

Question 22

In angiosperms, sieve tube elements are the channels for what?

Answer 22

Translocation

Question 23

What is a phloem sap?

Answer 23

Phloem sap is an aqueous solution that is high in sucrose.
It travels from a sugar source to a sugar sink.

Question 24

What is a sugar source?

Answer 24

A sugar source is an organ that is a net producer of sugar such as mature leaves.

Question 25

What is a sugar sink?

Answer 25

A sugar sink is an organ that is a net consumer or storer of sugar, such as growing roots, buds, stems, and fruits.

Question 26

T or F: A storage organ can be both a sugar sink in summer and a sugar source in the spring.

Answer 26

True. A storage organ( eg tuber or bulb) can be both a sugar sink in summer (stocking carbs) and a sugar source in the spring (starch broken down to sugar carried to growing shoot tips)

Question 27

T or F: Sugar must only move by symplatic pathways to load into sieve tube elements.

Answer 27

False. Depending on the species, sugar may move by symplastic or both symplastic and apoplastic pathways to load into sieve tube elements.

Question 28

What do companion cells do?

Answer 28

Companion cells enhance solute movement between the apoplast and symplast.

Question 29

In many plants, sugar movement into phloem requires what?

Answer 29

In many plants, sugar movement into phloem requires active transport. Sucrose is more concentrated in sieve tube elements and companion cells than mesophyll.

Question 30

What enables cells to accumulate sucrose?

Answer 30

Proton pumping and cotransport of sucrose and H+ enable cells to accumulate sucrose.

Question 31

What is the mechanism of translocation in angiosperms?

Answer 31

Phloem sap moves through a sieve tube by bulk flow driven by positive pressure called pressure flow. At the source sugar is loaded into a sieve tube, water follows by osmosis. Uptake of water generates positive pressure that forces sap to flow along the tube. At sink sugar molecules move by facilitated diffusion from phloem into sink tissues. Build up of pressure at source and reduction of pressure at sink cause sap to flow from source to sink.

Question 32

In leaf to root translocation xylem recycles water from ___ to ___.

Answer 32

sink to source