Transport, Transpiration, & Translocation Flashcards
What do you call the pathway or water moving from the soil through the plant to the atmosphere?
Soil-Plant-Atmosphere Continuum
What do you call a complex medium with solid, liquid, and gas phases?
Soil
Soil structures vary in composition, which are different due to their particle size. Arrange sand, clay, silt, and coarse sand in increasing particle size.
Clay < Silt < Sand < Coarse Sand
What are the factors that affect soil structure?
- Porosity
- Water Retention
- Aeration
This refers to the interconnected channels between soil particles.
Porosity
When can you say that the soil is in its water holding capacity?
When air has been displaced and the soil is saturated with water.
When can you say that the soil is in its field capacity?
When what’s left in the capillary pores of soil is gravitational water.
What type of soil must be used to maintain optimal plant growth? Why?
Loam soil, which is a combination of sand (40), silt (40), and clay (20). This type of soil ensures the balance between aeration and water retention.
What type of water is considered to be available and the principal source in the soil? Why?
Capillary water because the attractive forces are not too strong and the roots could absorb water.
This type of water occurs as a thin film on soil surfaces and cannot be absorbed by the plant.
Hygroscopic water
This is tied to the percentage of water remaining in the soil when a plant wilts because the remaining water in the soil is held too strongly for the plants to absorb it.
Permanent Wilting Point
Water potential in plants drives the uptake of water from the soil. This is driven by what type of gradient?
Pressure Gradient
Describe how the root absorbs water from the soil.
It first absorbs capillary water from the macropore since attractive forces are not very powerful here. As water becomes scarce, it recedes to micropores and this causes the surface of the water to have a meniscus. Such meniscus is a result of surface tension and it generates a negative tension that pulls water. Hence, as more water is removed, the radius of the curvature becomes very small. A more acute meniscus means greater tension.
In the root, where does most of the water absorption take place?
In the root hair zone (region of maturation).
What must be the conditions in order for absorption to take place in the roots?
When water potential in roots is more negative in the soil, which is possible when:
> more solutes in root cells
> decrease in turgor pressure
How does the root uptake ions from the soil?
Ions are included in the water the the roots absorb from the soil. It moves through the SYMPLASTIC AND APOPLASTIC PATHWAY but only the FORMER when traveling through the endodermis and the stele because of the presence of the casparian band. This hindrance is important because it allows the ions to accumulate in the xylem so that it would have a negative osmotic potential that could pull water towards the interior root cells.
Does the root push water to the stem or do leaves pull water from the roots to each of the stem?
Water primarily moves because of a pulling force caused by transpiration. Root pressure does not supply sufficient magnitude to push water at a height reached by most trees. Also, root pressure is absent in conifers.
What is guttation?
A condition wherein water absorption > water loss. As a result, water exits through HYDATHODES, and water droplets are observed in leaf surfaces.
What drives the movement of water from the leaf to the atmosphere?
The difference in concentration of water vapor because the atmosphere has a low water vapor content compared to the substomatal chamber. As a result, water vapor would move from a region of high to low water vapor content. This pull is responsible for the absorption of water form the soil since water forms a continuous column due to cohesion and is able to resist gravitational pull of gravity through adhesion. Hence, making the Soil-Plant-Atmosphere Continuum possible
What theory accounts for the quantity and rate of water movement in a vigorously transpiring plant?
Cohesion-Tension Theory
What do you call the process of rapid formation of gas bubbles in the xylem?
Cavitation
Why does the risk of having cavitation increase in freezing temperatures?
This is because gas is less soluble in ice. As a result, bubble formation would occur. This bubble could appear in the thawing phase and has a great possibility of increasing in size due to the negative pulling force. This puts the plant in danger as it inhibits the continuous water flow.
What are some ways that plants do to minimize cavitation?
- Avoid bubble invasion to neighboring tracheary elements (lodging of torus, imperforate end walls)
- Detour by traveling through neighbors
- Increase positive pressure
- Secondary growth replaces old xylem
How does the stomata move?
The stomata is able to close or open depending on the osmotic potential of the guard cells.
What happens when water moves in the guard cells?
The guard cells become turgid and open.
What happens when water moves out of the guard cells?
Flaccid and close
How does the radial arrangement of cellulose microfibrils help in the movement of guard cells?
The restrict the expansion of guard cells in the longitudinal direction, making them open up.
Which part of the guard cell wall is thicker?
Inner wall, adjacent to the stomatal pore.
What are the only epidermal cells that contain chloroplastids?
Guard cells
Describe the process of stomatal opening.
K ions are accumulated in the guard cells through the ATP-powered H pump. Th extrusion of protons leads to hyperpolarization that must be balanced. This happens by the opening of potassium channels. K ions are balanced against proton extrusion through the presence of counterions or organic acids (mostly malate).
How does CO2 concentration affect stomatal movement?
Increase CO2 concentration causes the closure of stomata.
How does light affect stomatal movement?
Blue light opens stomata because plants have a receptor for such light called PHOTOTROPIN. When this is activated, it stimulates the activity of ATP-powered proton pumps that prompts the uptake of K+ ions.
How does water deficit affect stomatal movement?
Water deficit closes the stomata.
What is the difference between hydropassive and hydroactive closure?
Hydropassive: water loss due to direct evaporation
Hydroactive: water loss due to rate of absorption being less than rate of transpiration
What is the overall effect of ABA to stomatal movement?
It closes K in channels and open Cl out channels. As a result, the membrane is depolarized (positive inside) anbd this causes the K out channels to open. As a result, osmotic potential decreases and water moves out.
What are the three types of transpiration?
Stomata (greatest contribution)
Cuticular
Lenticular
What is the two-step process of transpiration?
- Evaporation of water from moist cell walls to substomatal air space
- Substomatal space to atmosphere
How does the humidity of air affect the rate of transpiration?
High humidity —> decreased rates of transpiration because water vapor moves form higher to lower concentration
How does temperature affect transpiration?
+ Temp —> + Molecular Motion —>+ Vapor Pressure —> + Transpiration
How does air in the immediate vicinity of the leaf affect rate of transpiration?
Transpiring leaf becomes saturated with water vapor —> lowered rated of transpiration
How does low speed wind affect rate of transpiration?
Increases rate of Transpiration
How does high speed wind affect rate of transpiration?
Lowers Rate of Transpiration
What do you call a layer of unstirred air next to the leaf surface?
Boundary layer
