Lecture 6 Flashcards
In any region, water energy is the SUM of the:
Solute (osmotic) potential energy (0 or negative)
Pressure potential energy (any value, negative, positive or 0)
process of: Water evaporates from moist cells (like how clothing dries on clothes line outside, will dry down to level of atmosphere) in leaf stomatal
transpiration
Water potential is lowered (because water is being pulled out like a rope) at air-water interface; causing negative pressure in xylem
tension
Hydrogen bonds hold water molecules together
cohension
Xylem under tension gradient: pressure potential _____at top, _____ as you go down the plant
negative, getting more positive as you go down the plant
Water and minerals enter roots by osmosis because….
there is higher solute concentration inside plant than in soil
special cells that open and close to allow for the exchange of gases
guard cells
Gas exchange couldn’t happen through the cell wall of land plants because of _________
the waxy cuticle
type of cell?
Have microfibrils oriented transversally
When cell swells (turchid; filled with water) it causes opening
Create an opening, the inside (the stomata)
guard cell
How does the plant open and close the guard cells?
Pumping potassium ions
How To open guard cells
The plant pumps K ions into cell Solute potential, osmotic potential, goes down Water enters spontaneously Guard cells swell Stoma is open
what is conducted by abscisic acid
the closing of guard cells
the process of closing guard cells
Conducted by abscisic acid
Abscisic acid tells K ions to leave guard cells
Water leaves guard cells once solute is out of guard cells
Guard cells close
No access to stoma
cues for plant to open stomata at dawn?
Light
CO2 depletion
Circadian rhythms
what does the plant do in dry conditions to avoid water loss? How do they do this?
Abscisic acid (hormone)
Causes K positive to leave guard cells
Stimulates stomata closure
phloem transport, passive or active?
active
method of phloem transport?
bulk flow
: extra cells, parts of the phloem; type of parenchyma cells; actively pump sugar water
companion cells
companion cell that is where water starts
source cell
companion cell where water ends up
sink cell
what does Sucrose being pumped by source cell goes into sieve tube do to the osmotic potential?
osmotic potential goes down; more negative
What happens to the top of the tube if the osmotic potential is down due to sucrose having been just pumped into it?
water rushes in to balance out the sucrose molecules; water flows into the sieve tube
where does the water that rushes into the sieve tube when osmotic potential is down come from?
xylem tube next to it
what happens to the pressure of the sieve tube in the top area where water and sucrose was just pumped into?
the pressure goes up
The pressure going up in the top of the sieve tube causes what?
water and sucrose to flow down to the lower pressured end
What is the sink cell’s role in bulk flow?
The sink cell at the lower pressure end actively takes sugar out
when the sink cell takes out sucrose molecules, what happens to the osmotic pressure and the water?
the osmotic pressure goes up so the water flows back into the xylem tube beside the sieve tube
what type of cells are the sink and source cell?
companion cells
why does the water not follow the sugar into the companion cells?
the pressure in companion cell is higher than pressure in phloem; water wants to flow into lowest pressured spot
location of source and sink cells in fall? why?
source in leaves sink in roots - Leaves make glucose Turn it into sucrose The plant moves sucrose through phloem tissue down to the roots
location of sink and source in winter? why?
nothing happens in winter
- the sucrose is stored in the roots as starch
- plant loses its leaves
location of sink and source in spring? why?
source is root
sink is leaves
- Plant needs to make leaves so it can photosynthesize again
- Plant takes starch from roots, turns back into sucrose
- Moves sucrose through stem from roots to the buds
- Makes new leaves and starts photosynthesising
what are the sources of oxygen in the atmosphere? percentages?
50% terrestrial plants
50% phytoplankton and macroalgae
what is the carbohydrate ratio
1C: 2H: 1O
most basic sugar most other sugars are made from
C6H12O6
glucose
What are the two stages of photosynthesis?
light reactions dark reactions (Calvin cycle)
Organelle that makes plants green
chloroplast
organelle that used to be cyanobacterium
Has two membranes
has own genome
chloroplast
light reactions happen in _____
thylakoids
Calvin cycle occurs in
stroma
step 1 of light reaction
Light hits chlorophyll molecule (chlorophyll is a pigment, it absorbs wavelengths when light hits it)
step 2 of light reaction; what happens when light hits chlorophyll
When chlorophyll absorbs light, electrons increase in energy, some increase then go back down but some increase so much in energy that they bounce off the chlorophyll molecule
step 3 of light reaction: what does chlorophyll do after it loses some electrons
Chlorophyll steals electrons from H2O to compensate for its lost electrons
what happens to water after chlorophyll steals its electrons in the light reactions?
photolysis: falls apart
what does photolysis create?
oxygen
what creates the oxygen we breath all the time?
photolysis: the falling apart of WATER
how is NADPH created
NADP+ + 2e- + H+ = NADPH
takes electrons that other molecules have lost and and takes a proton/H from the photolysis of water
Photophosphorylation reaction?
ADP + Pi = ATP
is an accessory pigment that extends the wavelengths that can be used by chlorophyll a, takes its energy and passes it to chlorophyll a
chlorophyll b
Makes sugar (precursor) Supply light reactions with NADP+ and ADP
dark reactions: calvin reaction
Occurs in stroma of chloroplast
Does not require light
Rubisco takes inorganic carbon from CO2 and adds it to organic carbon RuBP (5 carbon sugar)
dark reactions; calvin reaction
Very special protein Most abundant protein Most important protein Dual nature Grabs CO2 Grabs oxygen
rubisco
step one of calvin cycle
Rubisco adds CO2 to RuBP creating unstable 6-carbon compound
step 2 of calvin
6-carbon compound breaks into two 3-carbon compounds (3-phosphoglycerate)
step 3 of calvin
ATP and NADPH is used- don’t worry about the details
Two-faced jekyll and hyde enzyme (CO2 and O2); dual nature exposed when oxygen is too plentiful
rubsico
step 4 of calvin
Finally G3P (Glyceraldehyde-3-phosphate; sugar) is produced
step 5 of calvin? what leaves the cycle?
1 G3P LEAVES calvin cycle, 5 G3P stay (six total)
step 6 of calvin: what happens to product of calvin?
The G3P that leaves becomes the 6-carbon glucose
step 7 of calvin: what happens to remaining items in calvin cycle?
The 5 G3P that stayed turn into 3 RuBP
why is the calvin cycle a “true cycle”?
Start with RuBP and end RuBP
: first stable organic molecule in calvin cycle
3-phosphoglycerate
: photosynthesis using 3-phosphoglycerate because it has three carbons. Occurs in 85% plant species
C3 photosynthesis
enzyme that is used in 15% of plant species; particularly of plant species in dry regions (like desert plants)
PEP carboxylase (PEPC)
Used by two kinds of photosynthetic mechanisms C4 photosynthesis (common in tropical grasses) CAM photosynthesis
PEP C
Photosynthetic mechanism that uses the enzyme PEPC
Commonly used by tropical grasses like corn or sugar cane
Air comes into the mesophyll cell (they are open to atmosphere) on the outside of the leaf
The bundle sheath cell of C4 plants surrounds the vascular tissue
Allows plant to keep rubisco from atmosphere
C4 photosynthesis
step 1 in C4 pathway
1) CO2 comes in, from atmosphere mesophyll cell is exposed to, and is attached by the PEPC to PEP which creates acids (like oxaloacetate and malate)
step 2 in C4 pathway
2) The acids are pushed into the bundle sheath cell, which is shielded from outside world, The malate is broken down to CO2 which then enters the calvin cycle as CO2 usually does
step 3 in C4 pathway
3)Rubisco is used in calvin cycle in bundle sheath cell, which is not exposed to atmosphere air
step 4 in C4 pathway
4) The calvin cycle gives off a G3P, which is eventually turned into glucose, and goes to the vascular tissue
Why is it called C4 photosynthesis?
Called C4 photosynthesis because first stable carbon molecule has 4 carbons
PEPC doesn’t grab to Oxygen/ It doesn’t have the problem Rubisco has
Crassulacean Acid Metabolism
Occurs in 10% of species
Occurs in plants of crassulaceae family
Photosynthesis of all succulent plants (jade plant, pineapple, agave)
CAM photosynthesis
CAM photosynthesis during night
photosynthesizing using PEPC
CAM photosynthesis during the day
close stomata, break down products made with PEPC (malate acid), turn it into CO2 and then the CO2 enters carbon cycle in the day
fun fact: taste difference in CAM plant night vs morning?
if you taste CAM plant in early morning it is much sourer than later on in the day because during the day the calvin cycle is making sugar from the PEPC products made at night
Why does the CAm photosynthesis cycle work from keep Rubisco from Oxygen?
This works from keeping Rubisco from attaching to O2 because the stomata are open during the night
plant physical defences?
Thorns
Trichomes
plant chemical defences?
Distasteful compounds
Toxic compounds
Ex: caffeine, cocaine, codeine
: organic substance made in one place and transported to another place, where it affects growth and other processes
hormone
hormone action step 1
Hormone binds to specific protein receptor, either in membrane or cytoplasm
hormone action step 2
Receptor protein goes through conformational change
hormone action step 3
Stimulates production of “relay molecules” in cytoplasm
hormone action step 4
Relay molecules trigger various responses to the original signal
what is responsible for plants bending towards light?
auxins
where are auxins primarily found?
Primarily in…
Young leaves
Shoot apical meristems
phototropism
: stem elongation towards light (low concentrations only)
what is auxins effect on roots? how does it get to the roots?
Auxins are made in the shoots and travel down the vascular tissue to the roots and in the roots they promotes root branching
what is auxins affect on the stem/ internode region?
Enhances apical dominance/ suppresses lateral branch formation (opposite of roots)
In shoots they inhibit side branches
So they promote central stem being dominant stem
when is phototropism easy to see? what side is what?
when one side of the plant is darker than the other
elongate greater on dark side
how does the plant stem bend?
The cells elongate more greatly on the dark side, the shaded side
how does auxin promote elongation?
Promotes cell elongation by:
Loosening cell walls → loosening the “glue” (like pectin)
what is the acid growth hypothesis?
Auxin increases in proton activity/ pumping
Increased H concentration increases acidity
So.. increase in proton pumping causes cell wall to become more acidic
Once more acidic, a number of reactions occur…
1) Auxin increases activity of proton pumps (H pumps)
2) Acidity increases in wall. Ion uptake increases
3) Expansins (enzymes), activated by a low pH, separate microfibrils from cross linking polysaccharides (remember from cell wall lecture)
4) The polysaccharides are now more accessible to further enzymes that loosen cell wall
