9.1 (Plant Biology) Flashcards
Define transpiration.
the loss of water vapor from the stems and leaves of plants
Outline gas exchange that occurs through leaf stomata.
transpiration rates will be higher when stomatal pores are open than when they are closed
The exchange of oxygen and carbon dioxide in the leaf (as well as the loss of water vapor in transpiration) occurs through pores called stomata
Outline structures and mechanisms involved in the flow of water from roots to leaves.
1) Water enters the roots through osmosis.
2) Water is transported through the xylem.
3) Cohesion and adhesion maintain a chain of water in the xylem from roots to leaves.
4) Water evaporates from the leaves through the stomata.
5) The rate of water loss depends on abiotic factors.
Describe structure of xylem.
Dead cells (composes the tube. Their hollowness allows water to move freely)
- tracheids (They are tapered cells which exchange water by pits that allow water to slow down when moving)
- vessel elements (allows the end walls to become fused in a continuous tube so water can travel faster)
Define cohesion.
Cohesion is when water molecules stick to each other.
-water molecules are polar, can form intermolecular association w/ hydrogen bond and causes water molecules to be dragged up xylem towards leaves in continuous stream
Explain the decrease in pressure and transpiration-pull that results from evaporation of water from the leaf.
Water is lost from leaves of the plant when its converted to water vapor and diffuses from stomata
- Vapor diffuses out of leaf via stomata, creating negative pressure gradient w/in leaf
- Negative pressure creates tension due to adhesive attraction between water and leaf cell walls
Explain why roots are hypertonic relative to the soil.
There are more mineral particles in the soil which means there is less water in the soil. There is more water in the root cells.
Roots are hypertonic to the soil with about 100x the concentration of ions such as Ca2+, Mg2+, K+, Na2+. Roots are hypertonic because they actively transport ions into them.
Describe how water enters roots from the soil.
Water will follow the mineral ions into root via osmosis (moving towards the region w/ higher solute concentration
1-Water is passively transported into the roots and then into the xylem.
2-The forces of cohesion and adhesion cause the water molecules to form a column in the xylem.
3- Water moves from the xylem into the mesophyll cells, evaporates from their surfaces and leaves the plant by diffusion through the stomata.
Compare the symplastic and apoplastic pathways of water transport through the root.
Once water is at the roots, it moves through two paths.
Apoplast pathway: water moves from root hairs to xylem between cells, the cell walls. The water doesn’t go into a plant.
Symplast pathway: water moves from roots hairs to xylem within cells. Cytoplasm through channels between cells called plasmodesmata.
Define xerophyte and halophytic.
plants that can tolerate dry conditions
plants that can tolerate salty conditions
Outline how xylem is able to maintain rigidity even under low pressure or mechanical disturbance.
Walls of the xylem tube are thickened by a polymer called LIGNIN, provide extra rigidity and support so they can withstand very low pressures without collapsing.
State that transpiration is a passive process.
Xylem is DEAD.
• Cytoplasm a membrane gone.
• Cellulose cell wall skeleton remains (unable to do active transport! Water transport in the xylem is PASSIVE
Outline the role of active transport in maintaining root tonicity.
Roots are hypertonic to the soil with about 100x the concentration of ion such as Ca2+, Mg2+, K+, Na2+. Roots are hypertonic because they activity transport ions into them.
Water then moves from hypotonic (soil) to the hypertonic (roots) passively by osmosis.
_Roots has cellular extensions which further increases surface area
Outline strategies used by xerophytes and halophytes to reduce water loss
- Xerophytes= high rates of transpiration due to high temperatures and low humidity of desert environments
- Halophytes= lose water as the high intake of salt from surrounding soils draws water from plant tissue via osmosis
