Plant Biology Flashcards
Transpiration
inevitable consequence of gas exchange in a leaf. Exchange of two gases for photosynthesis
Waxy cuticle
low permeability so stoma is used for gas exchange and guard cells used to minimize water loss (open and close)
Xylem structures and Cohesive properties of water
Withstand low pressure and allows transport under tension.
Xylem - the long continuous tube which is thickened and has lignin for strength/rigidity to prevent collapse. Flow is passive and pressure inside the xylem is lower than ATP
Water - Can be pulled up through xylem in a cohesive stream due to cohesion and adhesion
How is xylem formed
plasma membrane breaks down so mature xylem are not living.
water properties
cohesion
adhesion
Cohesion
water is polar so negative oxygen will attract positive hydrogen
Adhesion
H2O is attracted to hydrophilic parts of the xylem
Tension in cell leaf wall maintains the transpiration stream
water properties and evaporation will generate tension forces in the walls.
When water evaporates from leaf wall, adhesion will cause the closest source of water to replace the water lost. This nearest supply is in the xylem vessel
Why is pressure low is xylem
adhesion between water and cell walls is strong enough to suck water out of the xylem. Further reducing pressure
generates pulling force to H2O from stem to root. This is called transpiration pull (H2O upwards).
Cavitation
pressure is too low and it results in the breakage of the column of liquid which disrupts the transportation pull.
Active transport of mineral ions
active uptake of mineral ions also will result in more absorption of water (osmosis).
Requires protein pumps in the membrane of the root cell. Or happen through mass flow as water carries ions.
What do ions move through soil slowly how it relates to fungi
Ion binds to the surface of soil plants, so the relationship with fungi is important.
Fungus hyphae grow out of soil and absorb mineral ions on the surface. Allows plants to grow in nutrient deficient sol (mutualistic relationship)
Replacing loss of transpiration
water travels into the leaf replacing the loss of water from transpiration.
Water in the xylem climbs the stem through transpiration pull with cohesion and adhesion. Once water is in the root travels through the xylem through the cell wall (apoplastic pathway) and through the cytoplasm (symplastic pathway)
What is transpiration pull a result of
Low pressure generates fulling force from stem to root upwards
diffusion space
small diffusion space leads to the fast rate of diffusion and H2o driven out by distance and gradient
How does heat increase transpiration
heat turns water into gas leading to more evaporation and faster leaving of leaf
xerophytes
adapted to dry habitats. Therefore increases H2o uptake and reduces H2o loss. short life cycle and go dormant
cacti how its adapted
small leaves
water storage tissue (pleats swell after rainfall)
stoma spaced widely
thick waxy cuticle
open at night
Marram how its adapted
rolled leaf creates a localized environment. Prevent H2o loss
Hair reduced air movement
Sunken stoma
halophytes adaptations
reduced leaves
Leaves shed when h2o is scarce
sunken stoma
long root more water uptake
structure removes salt buildup
Translocation
Occurs in the phloem from source to sink
what are sieve tubes
phloem is composed of them. Columns of specialized cells are separated by perforated walls called sieve plated. Associated with companion cell.
- Reduced cytoplasm and no nucleus
- depends on membrane to maintain concentrations of organic molecules
Phloem
transports organic material throughout the plant. Transport organic solute. Links to parts of plant that need amino acids, sugars etc…
Phloem loading
How plants bring sugar into the phloem
- Active transport is used to load organic compounds into sieve tubes at source.
Phloem loading of sucrose
Most prevalent solute in phloem sap
- Not easily metabolized therefore food for carbohydrate transport. Doesn’t change easily
- Travels through cell walls - from mesophyll cells to cell wall to companion cell and sometimes sieve tubes.
- Sucrose transports protein and then actively transports sugar through the apoplast route
Companion cell and sucrose
Active transport develops a concentration gradient of sucrose.
- H+ ions transported out of companion cell using ATP
- Buildup of H+ ions flows down the concentration gradient through co-transport protein.
- Energy released is used to carry sucrose into companion cell-sieve tube complex
Plasmodesmata
Symplastic route. When sucrose reaches companion cell convert to oligosaccaride to maintain sucrose concentration gradient
How water potential impacts translocation
- Water cannot be compressed creating a hydrostatic pressure gradient. The buildup of carbohydrates draws water into companion cells by osmosis.
- Allows for high pressure so is able to flow from high-pressure areas to low
- Then solute is used therefore will be drawn back into the transpiration stream
What is sucrose used for at the sink
used as an energy source for either growth or turned to starch to be stored.
Companion cell
- has more mitochondria for active transport of sucrose
- unfolding to increase loading capacity through the apoplastic route
Importance of perforated walls and reduced cytoplasm
less resistance to flow of phloem sap
Photoperiods
switch to flowering is due to length of light and dark periods.
Pigment in photoperiods
Phytochrome red - in light converted to Pfr conversion is fast
phytochrome far-red - In dark concerted to Pr is slow. Not as stable
used to determine the length of dark periods
