second midterm Flashcards
Go back and add flashcards from the last chapter of mineral nutrients and the first part of solute transport
deal. will do
What form is Fe usually found / used? in
Fe3+, iron is largely oxidized and insoluble
What is interveinal chlorosis?
the characteristic symptom of iron deficiency
What is chelation?
the formation of bonds between two or more seperate binding sites within a ligand and a single central atom
- a central metal atom attactched to a ligand in a cyclic structure
What is the tonoplast?
the membrane of the central vacuole
Define chemical potential
The energy (ability) of a substance to perform (move) freely work
- the sum of the concentration, electrical and hydristatic potentials under standard conditions
specific definition of diffusion?
movement of molecules from a region of high concentration or high chemical potential to an area of low concentration or low chemical potential
What is facilitated diffusion?
- involves the movement of specific molecule / ions
- needs specific channels or carrier proteins
- does not use ATP for transport - it is passive transport
Which requires a greater gibbs free energy, simple or facilitated diffusion?
simple diffusion is less efficient because the membrane acts as a barrier and kinda slows it down
- facilitated diffusion is more efficent - has a lower gibbs free energy
When does simple diffusion overtake facilitated diffusion?
facilitated diffusion has a much higher rate of transport at low concentrations - but will plateau at some point when all membrane transporters / membrane proteins are fully saturated at the high concentration. As long as the area or concentration gradient does not change simple diffusion will eventually overtake facilitated diffusion in transport rate
How does diffusion continue once the solute has reached an equilibirum on either side of the membrane?
for example, metabolic consumption of glucose will lower the concentration of glucose on one side of the membrane - then the concentration gradient will be restablished - like that one chem thing of removing a reagent to push the equilibirum forward
- facilitated diffusion will continue
Two examples of passive transporters in plants
Plastid glucose transporter in the chloroplast inner envelope
triose phosphate translocator in the stoma - mediates a passive counter exchange of Pi and triose phosphate
Explain facilitated diffusion of charged species, ex) KCl
If you have K+ and Cl- ions on one side of the membrane, and a K+ transporter, then K+ will move to the other side of the membrane. Diffusion gradient will move K+ across, chemical potential gradient will go across, electrochemical potential gradient will go across, electrical gradient will go back the other way -this system will be in equilibrium even tho the concentrations arent equal
explain the difference between an ATPase, symporter, and anitporter
ATPase - is a proton pumping transporter that uses ATP for power
Symporter - couples with ATPase to transport two different ions in the same direction
Antiporter - couples with ATPase to transport two different ions in different directions
Which three mineral elements are transported by symporters?
NO3-, Pi (PHT1), and K (HAK)
Which directions do proton pumps usually move protons?
usually pump protons outside of the cell
Which side of the plasma membrane is more acidic - based on the gradient generated by proton pumps
outside of the cell is more acidic - because
in the current voltage relationship curve, which values are represented by the axis?
y axis = flux - positive = efflux, negative = influx
x axis = current in mV
What is the relationship between stomatal aperture and the presence of photosynthetically active radiation?
stomatal aperture increases - meaning the stomata open wider - when photosynthetically active light is present
the two are highly correlated and coincides with time of day.
How do guard cells respond to blue light?
blue light causes dramatically increased stomatal opening
- stimulated HATPase
you need to come back and look at these slides plz n thanks
yes forsolute transport 3`
Why is xylem(?) and phloem considered a non circulatory vascular system?
- xylem transports from root to shoot - in one direction
- phloem translocates from source to sink - meaning it will move sugars produced by photosynthesis from a source leaf either up into the vegetative meristem or down to the root meristem
What is the pathway for guard cell opening?
Blue light triggers HATPase - pumps H out of guard cells - causes K and Cl to accumulate - lowers solute potential - lowers water potential - water uptake into cells - guard cell becomes turgid and the stomata opens
- blue light also triggers starch degradation and malate synthesis - increases level of sucrose and malate - accumulates sucrose and malate which also lowers solute potential
What is the pathway for guard cell closing?
ABA accumulation triggers sucrose to starch conversion - also stops HATPase - opens outward K and Cl channels - sucrose and malate levels decrease - solute potential increases (less solute), water potential increases - water leaves via osmosis - the guard cells become flaccid and close
What is source tissue and what is sink tissue?
source tissue - exporting plant tissues or organs that produces photosynthate - sugars - a mature photosynthetically active leaf
sink tissue - non photosynthetic developing organ or an organ that does not produce a significant amount of photosynthate
How are sources and sinks related to tissue maturity?
phloem will move sugars from source to sink, or mature tissue to immature tissue - will move from an older leaf to a younger leaf - some leaves are in the middle and represent a source - sink transition leaf
What are the two strong sinks in a plant>
vegetative meristem and root meristem - both are young immature tissue and are not differentiated
within one leaf - which area is more mature and therefore a source and which area is less mature and therefore a sink?
the leaf tip is more mature / differentiated and therefore is a source - the leaf base is immature and therefore a sink
what is the functional unit of phloem?
sieve tubes - functional units for long distance translocation of plant materials - consists of stacked sieve elementsW
What is the sieve plate?
perforated wall between sieve elements and maybe also companion cells?
What are four key structures contained in a sieve element?
- structural phloem specific P-proteins
- endoplasmic reticulum
- mitochondria
- sieve element plastids
Which phloem structure contains a nucleus, vacuole and chloroplasts?
companion cells
What do P-proteins do in sieve elements?
seals off damaged sieve elements by plugging up sieve plate pores
- is a quick plant response and represents a short term solution
What does callose do in the sieve element?
seals off damaged sieve elements by plugging up sieve pores
- is a slower plant response but represents a long term solution
Two types of sucrose loading models in minor veins?
Symplasmic loading model - sugar moves through plasmodesmata from the mesophyll cells to the phloem
Apoplasmic sucrose loading model - sucrose will move on the outside of plant cells (bundle shealth cell or phloem parenchyma cell) into companion cells - happens via passive transport out of the cell via a permease - and then moves into companion cells by active transport via a sucrose symporter
Can all sugars move through phloem?
no, some “reducing” sugars are too reactive to be transported through the phloem - aldehydes / ketones
glucose, fructose, mannose
Which sugars will be able to move through the phloem?
non reducing - or less reactive sugars can be transported - sucrose
Which sugars cannot move through the phloem and why?
sugars with reactive groups like aldehydes and ketones are too reactive - glucose, mannose, fructose
How do plants get around moving reactive sugars through the phloem?
will bind other sugars to sucrose or as sugar alcohols
transport as sucrose, raffinose, stachyose, and verbascose
What is being loaded and translocated in phloem?
-water
- photosynthate (sugars in specific forms)
- specific amino acids
- ions (K+ and Mg2+
- metabolites
- hormones (auxin, gibberellic acid)
- proteins (signaling and sieve element maintenance)
- RNA (information macromolecules)
Pressure flow mechanism for phloem translocation
- sucrose is transported into companion cells
- sucrose is loaded into sieve tubes from companion cells
- sucrose concentration increases in the sieve tubes
- water moves into sieve tube and causes pressure to build
- this pressure pushes the sucrose laden fluid towards the sink
- at the sink sucrose and water are unloaded and distributed among surrounding cells.
- basically solute concentration is greatest at the source - meaning water will move there and build up pressure as water potential is lowered - pressure will push sugars towards sinks - even though water potential is lower at the source, there is a significant amount of solute in the phloem so pressure is the main acting component. - sink areas have a low turgor pressure bc they are losing water to the xylem as xylem has a higher solute potential
Direction and rate of phloem translocation is likely controlled by ____ _____ _______
controlled by local sink strength - is not an even split between shoot and root meristem sinks - usually more is transported to the shoot
3 reactions of photosynthesis
1- photochemical reaction
2- electron trasnfer reaction coupled with formation of ATP and NADPH
3 - biochemical reaction - incorporation of CO2 into carbohydrates (3C sugar)
Is the product of photosynthesis glucose?
yes, but a better answer is a 3C carbohydrate
Is photosynthesis restricted to plants only?
No - theres photosynthetic bacteria and cyanobacteria
- single celled organisms like chlamydomonas also have a single large chloroplast
What is the light reaction?
The first step of photosynthesis - capture of light energy as ATP and reducing power, NADPH
- starts with the low energy oxidized carbon in CO2
- happens in the thylakoid membranes
What is the carbon fixing reaction in photosynthesis?
The second step of photosynthesis - transfer of energy and reducing power from ATP and NADPH respectively to CO2
- generates a high energy reduced carbon - sugars
- happens in the chloroplast stroma
Is photosynthesis an endergonic or exergonic reaction?
endergonic - energy in reaction - product is higher energy than the reactants (sugar compared to CO2
Is respiration an endergonic or exergonic reaction?
exergonic - energy out reaction - substrate has a higher energy than the product (sugar compared to CO2)
Is most photosynthesis oxygenic or anoxygenic?
Oxygenic -
- removal of electrons from H2O – release O2
- reduction of CO2 to carbohydrate (3C sugar)
- occurs in plants, algae, and cyanobacteria
What is anoxygenic photosynthesis?
Anoxygenic
- photosynthesis without extracting electrons from water
- Uses H2A instead of H2O
- purple sulfur bacteria use H2S / sulfur
Starting with a proplastid, how do you get chloroplasts and chromoplasts?
Proplastids - undifferentiated, colorless, found in seeds, meristems and reproductive tissue
Etioplast - photosynthetic tissue but no chloroplhyll - occurs when plastid is grown in the dark
Chloroplast
Chromoplast - red and yellow pigment (carotenoids) found in flowers and fruit
Starting with proplastid, what are the three storage plastids you can differentiate into?
First goes to leucoplast then either -
Amyloplast - starch storage
Elaioplast - storage of oils
Proteinoplast - storage of proteins
What does light do to convert etioplast to chloroplast?
Light will separate the prolamellar body of the dark etioplast into primary lamellar layers or single thylakoids - which will fuse to form thylakoids and grana layers
Grana stacks in thylakoids are a specialty of what kind of plants?
land plants
WIll plants move their chloroplasts around?
Yes, high light means they need to crowd chloroplasts on the top and bottom of the leaf to maximize sunlight uptake
- in conditions where light is too strong, plants will move chloroplasts around side of leaf so that they do not get damaged or overheat from overexposure
- at night chloroplasts move to the bottom of the leaf but the reason is still unsure
All chlorophyll based photosynthesis use what kind of chlorophyll?
Chlorophyll A
Light absorption of photosynthetic pigments is affected by (2)
chemical structure of the chlorophyll
noncovalent interactions of chlorophylls with proteins in photosynthetic membranes
Which mineral element is essential to the structure of chlorophyll A?
Mg - magnesium
What are the four accessory pigments?
Chlorophyll B
B carotene
phycoerythrin
phycocyanin
- above 2 are types of phycobilins
Why does chlorophyll make plants green?
Because it absorbs all colours of light that are not green, so only green is reflected towards our eyes
Function of chromoplasts? (3)
- accessory pigments
- protecting photosynthesizing organisms from destructive photooxidation - anti oxidants
- structural roles in assembly of the light harvesting complex
What are phycobilins?
phycocyanin and phycoerythrin (blue and red)
- linear tetrapyrroles - derived from the same biosynthetic pathway as chlorophyll and heme groups
- water soluble
- accessory pigment with no associated metal
What is the only essential pigment?
chlorophyll a
What are the major factors to sustain plant life from an energy generation standpoint?
- Water - solvent for enzymatic activity and formation of biological membranes
- air - basic elements C O N H
- Light - thermonuclear fusion generates ultimate form of energy from the sun which gets passed on to plants
What percent of the total energy radiated from the sun is emitted as visible light?
~43%
What is photosynthetically active/ available radiation?
The portion of light that can be captured by autotrophs and used for photosynthesis
- units of umol/m2/sec
- photons / area / time
What is the photosynthetic action spectrum?
- magnitude of biological response to light (wavelength)
- rate of photosynthesis
- focuses on a single wavelength of light shining on the plant
What is the absorption spectrum
- the amount of absorbed light by a molecule (pigment)
- functional wavelengths of light in photosynthesis
Why do pigments capture the light?
- to get energy from photons
- energy from a photon will excite an electron from the ground state to a higher energy orbital / excited state
4 possible photoexcitation outcomes?
Heat - thermal dissipation, converting excitation energy to heat - chlorophylls return to ground state
Fluorescence - immidiate reemission of energy as a long wavelength
Energy transfer - excited pigment molecule like chlorophyll transfers its energy to another molecule
Photochemistry - energy of the excited state triggers a chemical reaction and becomes and e donor
- linkage of the excited e donor to a proper e acceptor
- transduction of chemical energy
What is the difference between a lower excited state and a higher excited state?
some pigments take in higher energy light like blue wavelengths which will excite an electron to a greater degree than a lower energy wavelengths like red light
- this means that when returning to ground state, an electron in the higher excited state might release heat to return to the lower excited state before returning down to the ground state
Explain the energy transfer during photosynthesis?
- purely physical phenomenon
- no chemical changes
- done by resonance energy transfer - energy is transferred from pigment to pigment by resonance untll it reaches the reaction center pigment
go back and add cards for electron transport and energy transfer lectures (missed two classes)
4 outcomes of photoexcitation?
- Heat
- thermal dissipation - converting excitation energy to heat
- return to ground state - Fluorescence
- immediate reemission of energy as a long wavelength - Energy transfer
- excited pigment molecule transfers its energy to another molecule - Photochemistry
- energy of the excited state triggers a reaction and becomes an e- donor
- linkage of e donor to proper e acceptor
- transduction of chemical energy
What is non photochemical quenching? 3 types
- how plants deal with excess light energy - heat outcome of photoexcitation
- losing energy as heat
- energy dependent quenching - the xanthophyll cyclce - qE - major form of quenching
- state transition - conformational changes in light harvesting complex 2 - qT
- photoinhibition - light induced reaction in quantum yeild as a consequence of damage - qI
What is the dominant form of non photochemical quenching and how does it work?
- energy dependent quenching
- lumen acidification activates VDE
- zeaxanthin leads to energy dissipation by rearrangement of LCHII and reaction center II - decrease of energy transfer to RCII
- the structural changes result in dissipation of light enrgy as heat
explain the state transition quenching pathway
high light intensity will cause accumulation of PQH2
- will activate LHCII kinase - will phosphorylate substrate
- phosphorylated LHCII prevents energy transfer to PSII
explain the photoinhibiton quenching pathway
D1 protein of PSII is succeptible to photodamage - photosynthesis is inhibited
- OEC is inactivated - followed by reaction center
- will dissolve and digest D1 protein before reforming it and reactivating PSII
All forms of quenching target ____________ to some degree to regulate electron transport?
photosystem II
How do herbicides work?
DCMU - targets plastoquinone so it cannot transport electrons from PSII to PSI
Paraquat - prevents reduction of NADP+ by accepting electrons in PSI
What is needed to fix carbon in the calvin cycle?
3 CO2, 3 ATP, 2 NADPH
- Rubisco enzyme
Explain the steps of the calvin cycle
Carboxylation - 3X RuBP and 3xCO2 to make 6 3-PGA via RUBISCO
Reduction - 6ATP and 6 NADPH to reduce 3-PGA to make 6 G3P - 1 G3P leaves for energy - 5 G3P regenerate RuBP
How does RUBISCO act as a carboxylase and an oxygenase
- carboxylase - takes CO2 and RuBP to make 2 3 PGA
- oxygenase - takes O2 and RuBP to make 1 3 PGA and 2PG
Can rubisco discriminate between CO2 and O2
Not well - catalytic domains are too similar
What is the usual form of RUBSICO in plants?
Form 1 in most plants - hexadecameric form
- 8 large subunits and 8 small subunits
- found in some other forms in algae and bacteria
Is RUBISCO efficient? How does this affect plants
RUBISCO is very slow and inefficient as it will often bind O2 instead of CO2
- to make up for this, plants will make lots of it - up to 50%
How is RUBISCO regulated at the transcription, assembly and inhibition levels?
- transcription of rbcS in nuclear genome, but rbcL gene is transcribed in plastid - chloroplast- genome
- several chaperone proteins are required to assemble
- activity is inhibited by a sugar phosphate inhibitor, rubisco activase removes the inhibitor
What amino acid is required in the active site of RUBISCO that must be carbamylated for proper activity?
A lysine is carbamylated in the active site of rubisco
What 4 things are needed to make active rubisco?
Carbamylated lysine
- Mg
- CABP
- CA1P - sugar phosphate inhibitor
you missed alot of lectures :/
yup
How do carboxylases compare between C4 and CAM plants
C4 - carboxylases are spatially seperated - mesophyll and bundle sheath cells
CAM - carboxylases are temporally seperated - day and night
do C4 and CAM plants use Rubisco enzyme for the first carboxylation?
No, they uses PEPC, C3 plants use Rubisco
Three factors that influence photosynthesis rate?
Light
- less photosynthesis in less light
- no effect on the rate of photosynthesis above the optimum condition
CO2 concentration
- decrease of photosynthesis rate in low CO2 concentration
- no effect on the rate of photosynthesis above the optimum
Temperature
- lower photosynthesis above or below the optimum temperature
Why is there a difference between sun leaves and shade leaves?
Chloroplast movement
- will move to surface in shade leaves, will move to edges in sun leaves
How are sun and shade leaves different?
Sun
- high rate of photosynthesis
- thick leaves
- high stomatal density
- long pallisade cells
- low ratio of chlorophyll to soluble protein
Shade
- low rate of photosynthesis
- thin leaves
- low stomatal density
- short pallisade cells, more spongy mesophyll cells
- high ratio of chlorophyll / soluble proteins
In the light response curve, why does the rate of photosynthesis stop at high light intensities?
At the light saturation point, photosynthetic reaction rate is determined by light independant reactions - such as carbon fixation
In the light response curve, at low light intensities, the relationship between net photosynthesis and light intensity is linear, why?
At low light intensities light is limiting for photosynthesis
What is the light compensation point on the light response curve?
The point where photosynthetic CO2 assimilation = amount of CO2 generated by respiration
What is quantum yield in this context? what does it determine?
Is the moles CO2 fixed per moles photons
- determines the efficiency of photosynthesis
How do you calculate quantum yeild?
Slope in the graph when using an initial straight line
number of photochemical products/ number of quanta absorbed.
How does the light response curve change with moderate and high excess light?
Moderate excess light = dynamic photoinhibition
- short term reversible and regulatory process
- slight decrease in rate but max photosynthetic rate stays the same
High excess light = chronic photoinhibition
- long term process
- photodamage - associated with damage and replacement of D1 protein in PSII
- significant photosynthetic rate decreases - plateaus early
What isthe CO2 reponse curve?
CO2 assimilation over Internal CO2 concentration
How does the CO2 response curve differ between C3 and C4 plants?
C4 plants have a lower compensation point than C3 plants (where rate of CO2 produced by respiration = the rate of CO3 used in photosynthesis) - photorespiration is suppressed by the CO2 concentrating mechanism in C4 plants
- ## C3 plant has higher overall CO2 assimilation rate
What are some boundaries to CO2 diffusion?
In air of high humidity, the diffusion gradient of water vapor for driving water loss is about 50 times larger than the gradient of CO2 uptake - the difference is much greater in dry air
- decrease in stomatal resistance (opening the stomata) increases CO2 uptake but also is accompanied by substantial water loss.
Difference between C4 and C3 plants in terms of environmental CO2 concentrations
C4 plants CO2 concentration mechanism saturates at lower ambient CO2 levels, so it works at maximum capacity sooner
C3 plants - carbon asimilation increases with increasing CO2 concentration
- C3 plants are expected to benefit mroe from elevated CO2 levels - although the actual evidence is less than expected
What is the overall affect of increased heat and drought conditions on plant growth?
Drought - stomata are closed to maintain water - decreases of CO2 uptake - lowering internal CO2 concentration - decrease of carbon assimilation
Heat - results in rubisco deactivation at high temperature
-combination of drought and heat stress cause severe inhibition of photosynthesis
What is the relationship between temperature on the rate of photosynthesis?
photosynthesis increases as a normal increase with temperature - caused by an increase in enzyme activity
- to a point then the enzyme stops working / denatures and individuals start dying
Are all glyceraldehyde 3 phosphate created in the calvin cycle used for regeneration of RuBP?
No, 5/6 of them are used for regeneration, one of them is used to fix CO2
One of the products from the calvin cycle is a triose phosphate, glyceraldehyde 3 phosphate, if it remains in the chloroplast, what happens? What about when it leaves the chloroplast?
Within the chloroplast it can be converted into long starch chains of glucose molecules
If it leaves the chloroplast then it can be converted into sucrose for transport in the phloem
If it leaves the chloroplast it can also be used in glycolysis
what two metabolistic pathways are in the mitochondrion?
Krebs cycle and oxidative phosphorylation.
during oxidative phosphorylation, which complrx does not contribute to the proton gradient?
Complex II but is important for electron transport
What is proton movitve force?
energy of the proton concentration gradient
How is proton motive force calculated?
= deltaP (mv) = delta E - 59mv/pH (deltapH)
