Lecture 6 Flashcards
Two main tissues for transport
Xylem: transports sap, upward only, tracheids and vessel elements
Phloem: transports sugar water, all directions, sieve tube elements
Transpiration Tension Cohesion Hypothesis
1) Water is being pulled out of moist cells in leaf by the atmosphere. Atmosphere has really low water potential
2) As water is being pulled out of cells, causes water to be pulled out of adjacent tissues, causing tension in the xylem
3) Water sticks together via hydrogen bonds (cohesion)
4) Tension in xylem creates negative pressure. Pressure potential at top of plant is lower (more negative) than at bottom
5) Water flows up the plant via tracheids and vessel elements
6) Water enters roots via osmosis
Facts about Transpiration Tension Cohesion Hypothesis
-Passive process, doesn’t require energy because tracheids and vessel elements are dead
highest to lowest in water potential
Stomates
where gas exchange occurs
-flanked by guard cells
Guard cells
- open and close the stomate
- turgid/ filled with fluid, stomate open
- flaccid/ no fluid, stomate is closed
How to open stomate
Guard cells to pump K+ ions into cell. Increases osmotic potential, water flows inside cell and stomate open
Cues to open stomates
- light
- CO2 depletion
- circadian rhythm
Close stomate
Abscisic acid (hormone) pumps K+ out of cell, closes stomate
Phloem flow: Pressure-flow hypothesis
- from source to sink
1) Companion cell has sucrose, sucrose enters phloem. Phloem increases in solute potential, water enters phloem from nearby xylem.
2) Water entering creates positive pressure, sugar water flows down to sink where pressure is lower
3) Sucrose goes out of phloem into companion cell at the sink
4) Sink is decreasing in osmotic potential, water spontaneously flows to xylem where water potential is the lowest
5) Water moves up xylem due to negative pressure
Source and sink depend on the time of year
summer and fall right hand side, spring left hand side
aphids
eat phloem fluid
Photosynthesis
Source of oxygen in atmosphere
50% terrestrial plants
50% marine phytoplankton and macroalgae
First step in moving energy into the living world, the source of all energy in ecosystems
Photosynthesis equation to make one glucose
6CO2 + 12H2O —-> C6H12O6 + 6O2 +6H2O
CO2
electron accepter/gets reduced
H2O
electron doner/ gets oxidized
2 Stages of photosynthesis
1) Light reactions: occur in thylakoid, need light
2) Calvin cycle: occur in stoma, don’t need light
Light reaction steps
1- Light hits chlorophyll
2- electrons bounce to higher energy level and off of chlorophyll
3- Chl steals electrons from H2O, causing photolysis: splitting water to release O2
4- NADP+ + 2e +H+ reacts to produce NADPH
5- ADP + Pi yields ATP
Overview of light reactions
Converts light into:
- NADPH
- ATP via photophosphorylation
- O2 from photolysis of water
Light reaction equation
Light + H2O + ADP + P + NADP+ + 2E + H+ —> ATP + NADPH + O2
NADP+ AND NAD+
-oxidizing agents
-gain electrons
NADP+ + 2E +H+ —> NADPH
NADPH and NADH
- reducing agents
- lose electrons
Why is chlorophyll green
doesn’t absorb green wavelengths, reflects green wavelength
chl a: all photosynthetic organism
chl b: accessory pigment, extends wavelengths
Dark Reactions/ Calvin cycle
- doesnt require light
- occur in stroma
- produce sugar
- supply light rxns with NADP+ AND ADP +P
Calvin cycle steps
CO2 comes in, rubisco takes C off and puts in on RuBP (ribulose bi-phosphate) making it a 6 carbon sugar.
RuBP breaks into two three carbon sugars called 3-Phosphoglyerate, C3 photosynthesis.
3-Phosphoglyerate + NADPH + ATP–> G3P glyceraldehyde-3-phosphate
makes 6 G3P, one gets shunted off
5 G3P turn into 5 glucose
5 glucose turn into 3 RuBP
Produces ADP + P and NADP+ to give to light reactions cycle
Dark reactions equation
CO2 + ATP + NADPH —> sugar + ADP + P + NADP+
Rubisco
-most abundant and important protein
-dual nature
-Ribulose 1, 5-biphosphate carboxylase oxygenase
grabs co2 makes o2
A plant experiencing dry conditions
-Not enough water to supply
