Moving Molecules Around

Question 1

What is transpiration?

Answer 1

The loss of water via the aerial part of a plant

Question 2

Transpiration occurs when ________

Answer 2

Two things are needed:

1. The stomata are open
2. The area surrounding the leaves is drier than the air inside the leaves

Question 3

Define water potential

Answer 3

The potential energy that water has in a particular environment compared to the potential energy of pure water at room temp and 1 atm

Question 4

The direction that water moves is determined by ______

Answer 4

• Differences in water potential

- Water always moves from higher water potential to lower water potential

Question 5

Isotonic solution

Answer 5

• Solute concentration in the cell and surrounding the cell are the same
• No net movement

Question 6

Solute potential

Answer 6

• Total solute concentration of a solution relative to pure water
• Always negative
• More solutes = lower solute potential
• Water moves to a region with more solutes

Question 7

Wall pressure

Answer 7

Force exerted by a cell wall

Question 8

Turgor pressure

Answer 8

-Pressure inside a cell when water moves in

Question 9

When cells are firm and experience wall pressure they are said to be ______

Answer 9

Turgid

Question 10

Why is turgor pressure important?

Answer 10

• It counteracts the movement of water due to osmosis

- Rigid cell wall limits the amount of water that can flow in

Question 11

Pressure potential

Answer 11

• Any kind of physical pressure on water

- Can be positive (compressed) or negative (tensed)

Question 12

Water potential equation

Answer 12

Water potential = solute potential + pressure potential

Question 13

How does water move when selectively permeable membranes are present?

Answer 13

From high solute potential to low solute potential

Question 14

How does water move when no membranes are present?

Answer 14

From high pressure potential to low pressure potential

Question 15

How does water move in general?

Answer 15

From high water potential to low water potential

Question 16

Water potential in soil

Answer 16

• Generally high relative to water potential in a plant’s roots.
• Exceptions: salty soils and dry soils

Question 17

What happens when water potential in soil drops?

Answer 17

• Water is less like to move from soil to plants

- When soil is over-irrigated, it becomes salty and plants cannot absorb water

Question 18

Plant adaptations to salty soil

Answer 18

• Accumulate solutes in root cells

Question 19

Three types of water movement

Answer 19

Apoplastic, symplastic, transmembrane

Question 20

Guttation

Answer 20

Water forces water droplets out of low growing plants

Question 21

Root pressure

Answer 21

A pressure potential that develops in roots-could drive water up against the force of gravity

Question 22

The vascular system contains____

Answer 22

xylem and phloem

Question 23

Water potential gradient

Answer 23

• Water potential is high in soil, lower in roots, lower in leaves, and lowest in the atmosphere
• To move up a plant, water moves down the water potential gradient

Question 24

Epidermis

Answer 24

The “outside skin” A single layer of cells.

Question 25

Cortex

Answer 25

-Consists of ground tissue that stores carbohydrates

Question 26

Endodermis

Answer 26

The “inside skin” - a cylindrical layer of cells that forms a boundary between the cortex and vascular tissue

Question 27

Apoplast

Answer 27

• Movement takes place outside the cell membranes

- Must eventually pass the cytoplasm of endodermal cells before entering xylem

Question 28

Symplast

Answer 28

-Movement, continuous connections through the cells that exists via the plasmodesmata

Question 29

Casparian strip

Answer 29

• Narrow band of wax composed of suberin

- Blocks the apoplastic route by preventing water from moveing through the walls of the endodermal cells

Question 30

Why is the casparian strip important?

Answer 30

• It means that for water and solutes to reach vascular tissue, they have to move through the cytoplasm of endodermal cells
• Plants can use specific carrier and channel proteins to control what moves into the shoots

Question 31

Capillary Action

Answer 31

• Movement of water through a narrow tube

- Occurs in response to: adhesion, cohesion, and surface tension

Question 32

Adhesion

Answer 32

Molecular attraction among unlike molecules

Question 33

Cohesion

Answer 33

Molecular attraction among like forces

e.g. hydrogen bonding

Question 34

Surface tension

Answer 34

Molecules at the surface of a liquid stick together, resulting in tension that minimized surface area

Question 35

How does capillary action occur?

Answer 35

It results when:
Adhesion creates an upward pull at the water-container surface
Surface tension creates an upward pull all across the surface
Cohesion transmits both forces to the water below

Question 36

Cohesion-tension theory

Answer 36

States that water is pulled to the tops of trees along a water-potential gradient, via forces generated by transcription at leaf surfaces

Question 37

True/false Water transport is solar powered

Answer 37

True

Question 38

How do vasular tissues withstand extremely negative pressures?

Answer 38

The have evolved lignified secondary cell walls (tall trees)

Question 39

Bulk Flow

Answer 39

The mass movement of molecules along a pressure gradient

Question 40

Translocation

Answer 40

The movement of sugars by bulk flow through a plant from sources to sink

Question 41

Source

Answer 41

• Where sugar enters the phloem in a tissue

- High turgor pressure

Question 42

Sink

Answer 42

• A tissue where sugar exits the phoem

- Low turgor pressure

Question 43

What cell types make up the phloem?

Answer 43

sieve tube elements and companion cells

Question 44

What is required for translocation?

Answer 44

Lots of ATP
or
Large difference in turgor pressure