14.3 Plant Vascular Tissue Flashcards
Describe two adaptations that increase the
surface area available for plant roots to absorb water and minerals from the soil.
Root hairs:
-one way that plants increase the absorption of water and minerals
-root hairs are the tiny outgrowths of the root’s epidermal cells
-they increase the root’s surface area,
growing into the spaces between soil particles and greatly increasing absorption
Epidermal cells have waxy cell walls that prevent water and minerals from leaking back out of the xylem and are well suited to absorb water and dissolved minerals from the soil
Explain the role of the following in the ascent of xylem sap within a plant.
(a) cohesion and adhesion
Cohesion is the tendency of molecules of the same kind to stick to one another.
-in water, hydrogen bonds make the water
molecules stick to one another.
-the water molecules in the xylem tubes
form continuous chains, extending all the
way from the leaves down to the roots
Adhesion is the attraction between unlike molecules.
-water molecules adhere, or stick to, cellulose molecules in the xylem walls
-this assists the upward movement of xylem sap by counteracting the downward pull of gravity
Explain the role of the following in the ascent of xylem sap within a plant.
(b) tracheids and vessel elements
Both tracheids and vessel elements
are stacked, forming hollow tubes that carry water through a plant horizontally or vertically
Describe how the guard cells around each stoma change shape to open the stomata.
Daytime→most stomata open→allows C02 to enter (photosynthesis) → sun+low levels of CO2 →guard cells collect potassium ions from cells→osmosis→ water goes with potassium ions into guard cells→water goes in, guard cells swell→ buckle away from centres →gap called stoma opens between them
Describe how the guard cells around each stoma change shape to close the stomata.
Stomata close at night (water isn’t being lost as much) or they close when the rate of water loss is higher than getting water from soil
Potassium ions leave guard cells→water follows (osmosis)→guard cells sag together as water pressure is lost→stoma closes
Explain how the pressure-flow mechanism
drives the flow of phloem sap from sugar
source to sugar sink
Sugar made in source (mature leaf) →ATP energy moves materials from cell membrane into sieve-tube member of phloem→creates high concentration of sugar at source end of phloem→water goes with sugar into phloem (osmosis) → creates higher water pressure at source end than at sink end of the phloem.
Explain how the pressure-flow mechanism
drives the flow of phloem sap from sugar sink to sugar source
Sugars leave sieve-tube members & water goes too→pressure is reduced.
Water goes from high pressure to low pressure →pressure-flow mechanism → water is returned to source by xylem
Compare and contrast the effects of root pressure and the pressure-flow mechanism.
root pressure
-helps push water up xylem and mainly functions at night
-cells in root’s epidermis and ground tissue take energy from ATP + use it to get certain minerals
-minerals then move from cell to cell through specific channels+enter xylem
-epidermal cells have waxy cell walls that prevent water and minerals from leaking back out of the xylem.
-as minerals build up in xylem, water follows by osmosis.
- osmotic movement of water accumulates a positive root pressure
- this pressure forces water + minerals up xylem, pushing XYLEM sap upward
pressure flow mechanism
-describes how sap moves through PHLOEM from areas of high to low sugar concentration and water pressure from source to sink
-sugar made in source (mature leaf) →ATP energy moves materials from cell membrane into sieve-tube member of phloem→creates high concentration of sugar at source end of phloem→water goes with sugar into phloem (osmosis) → creates higher water pressure at source end than at sink end of the phloem.
Explain why each of the following statements is incomplete or incorrect.
(a) Plants absorb proteins from the soil.
plant roots absorb water and mineral nutrients from the soil
-use these to form proteins
Explain why each of the following statements is incomplete or incorrect.
(b) Mycorrhizae are parasitic fungal
growths on plant roots.
Roots of most vascular plants form a symbiotic association with fungi called mycorrhizae
-association increases ability of the root to absorb water and inorganic ions, especially
phosphate
Explain why each of the following statements is incomplete or incorrect.
(c) Transpiration prevents a plant from
wilting.
Transpiration causes tremendous loss of water from the plant.
as long as water moves up from the soil fast enough to replace water lost, this amount of transpiration presents no problem
if transpiration exceeds the rate of water delivery to the leaves, the leaves will wilt (too much water)
relationship between transpiration rate and temperature
As the temperature increases, transpiration will increase due to a higher concentration in sunlight and warm air. However, if temperatures remain high for long periods of time eventually leading to drought, transpiration may go down to conserve water in the plant.
What kinds of sap do you expect to find in
the veins of a leaf?
phloem sap
Water loss by transpiration has been called a “necessary evil.”
(a) How does transpiration benefit a
plant?
(b) How can it harm a plant?
benefits:
-provides evaporative cooling, forming a major component of the leaf energy balance
-provides the driving force for transport of water and nutrients from roots to shoots
harmful:
-results in water scarcity that can damage the plants due to no water
-causes wilting of the leaves and results in stunted growth of the plants
If a plant root is deprived of oxygen, will root pressure cease?
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