Moving Molecules Around Flashcards
What is transpiration?
The loss of water via the aerial part of a plant
Transpiration occurs when ________
Two things are needed:
- The stomata are open
- The area surrounding the leaves is drier than the air inside the leaves
Define water potential
The potential energy that water has in a particular environment compared to the potential energy of pure water at room temp and 1 atm
The direction that water moves is determined by ______
- Differences in water potential
- Water always moves from higher water potential to lower water potential
Isotonic solution
- Solute concentration in the cell and surrounding the cell are the same
- No net movement
Solute potential
- 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
Wall pressure
Force exerted by a cell wall
Turgor pressure
-Pressure inside a cell when water moves in
When cells are firm and experience wall pressure they are said to be ______
Turgid
Why is turgor pressure important?
- It counteracts the movement of water due to osmosis
- Rigid cell wall limits the amount of water that can flow in
Pressure potential
- Any kind of physical pressure on water
- Can be positive (compressed) or negative (tensed)
Water potential equation
Water potential = solute potential + pressure potential
How does water move when selectively permeable membranes are present?
From high solute potential to low solute potential
How does water move when no membranes are present?
From high pressure potential to low pressure potential
How does water move in general?
From high water potential to low water potential
Water potential in soil
- Generally high relative to water potential in a plant’s roots.
- Exceptions: salty soils and dry soils
What happens when water potential in soil drops?
- Water is less like to move from soil to plants
- When soil is over-irrigated, it becomes salty and plants cannot absorb water
Plant adaptations to salty soil
- Accumulate solutes in root cells
Three types of water movement
Apoplastic, symplastic, transmembrane
Guttation
Water forces water droplets out of low growing plants
Root pressure
A pressure potential that develops in roots-could drive water up against the force of gravity
The vascular system contains____
xylem and phloem
Water potential gradient
- 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
Epidermis
The “outside skin” A single layer of cells.
Cortex
-Consists of ground tissue that stores carbohydrates
Endodermis
The “inside skin” - a cylindrical layer of cells that forms a boundary between the cortex and vascular tissue
Apoplast
- Movement takes place outside the cell membranes
- Must eventually pass the cytoplasm of endodermal cells before entering xylem
Symplast
-Movement, continuous connections through the cells that exists via the plasmodesmata
Casparian strip
- Narrow band of wax composed of suberin
- Blocks the apoplastic route by preventing water from moveing through the walls of the endodermal cells
Why is the casparian strip important?
- 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
Capillary Action
- Movement of water through a narrow tube
- Occurs in response to: adhesion, cohesion, and surface tension
Adhesion
Molecular attraction among unlike molecules
Cohesion
Molecular attraction among like forces
e.g. hydrogen bonding
Surface tension
Molecules at the surface of a liquid stick together, resulting in tension that minimized surface area
How does capillary action occur?
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
Cohesion-tension theory
States that water is pulled to the tops of trees along a water-potential gradient, via forces generated by transcription at leaf surfaces
True/false Water transport is solar powered
True
How do vasular tissues withstand extremely negative pressures?
The have evolved lignified secondary cell walls (tall trees)
Bulk Flow
The mass movement of molecules along a pressure gradient
Translocation
The movement of sugars by bulk flow through a plant from sources to sink
Source
- Where sugar enters the phloem in a tissue
- High turgor pressure
Sink
- A tissue where sugar exits the phoem
- Low turgor pressure
What cell types make up the phloem?
sieve tube elements and companion cells
What is required for translocation?
Lots of ATP
or
Large difference in turgor pressure
