Unit 2.5 Flashcards
Explain the effect of light intensity and temperature on the rate of photosynthesis.
light: affects the light-dependent stage; at low intensities, insufficient ATP; and insufficient NADPH+H+ produced; this stops the Calvin cycle operating (at maximum rate);
temperature: affects light-independent stage / Calvin cycle; temperature affects enzyme activity; less active at low temperatures / maximum rate at high temperatures; but will then be denatured (as temperature rises further);
Explain how the rate of photosynthesis can be measured.
- CO2 + H2O –> (CH2O)n + O2/ suitable photosynthesis equation
- amount of CO2 absorbed (per unit time) can be measured
- increase in biomass (per unit time) can be measured
- O2 excretion (per unit time) can be measured
- volume of O2 (bubbles) produced per unit time can be measured
- dry mass can be measured
- increase in starch concentration in leaves (as measured by iodine)
- use of pH indicator can monitor CO2 uptake in water
- the rate of photosynthesis measured is relative because some of the CO2 is produced by the plant internally through respiration
- the rate of photosynthesis measured is relative because some of the carbohydrates are used internally by the plan for respiration
Explain the role of water in photosynthesis.
- water is a substrate / reactant / raw material / for photosynthesis / equation for photosynthesis
- water is a source of electrons
- to replace those lost by chlorophyll / photosystem II
- water is a source of H+ needed to produce NADPH + H
- photolysis / splitting / breaking of water
- water for non-cyclic photophosphorylation / ATP production
- water is transparent so photosynthesis can take place underwater / light can penetrate to chloroplasts
Photosynthesis and transpiration occur in leaves. Explain how temperature affects these processes.
- photosynthesis rate increases as temperature rises (up to an optimum temperature);
- (due to) increase in the rate of enzyme catalysed reactions/light independent
- reactions/the Calvin cycle;
- (steep) drop in rate of photosynthesis above the optimum;
- at high temperatures enzymes/Rubisco/RuBP carboxylase denature(s);
- graph with correctly labelled axes showing relationship between temperature and rate
- of photosynthesis;
- transpiration rate increases as temperature rises;
- (energy/heat leads to more) to more evaporation of water (in the leaf);
- faster diffusion of water vapour at higher temperatures;
- relative humidity falls as temperature rises / warmer air can hold more water vapour;
- stomata may close at very high temperatures reducing the transpiration rate;
- some plants open their stomata at very high temperatures to cool by transpiration;
photorespiration
Photorespiration is far less efficient at storing energy than photosynthesis. It produces only one molecule of G3P, along with a toxic phosphoglycolate molecule that the plant must expend energy to convert to a non-toxic substance.
since photorespiration binds oxygen instead. the CO2 is made which is just a waste for same amount of energy. you get only 1 G3P made per 6 cycles?? (1/2 the number of G3P made)
slows down calvin cycle
- higher photorespiration when there is high temp (that means that photorespiration still occurs at lower temperatures)
to test for photosystem II
to test for PSII, text the presence of oxygen in light
thylakoid membrane is punctured
less ATP is made, less sugar made
sun loving vs shady plant
a sun-loving plant will have more co2 uptake per light intensity than a shade loving plant but both graphs will be exponential and plateau out
high temperature
less water: photosynthesis will decrease even if the enzymes don’t denature at that point
- to conserve water, the stomata closes but CO2 doesn’t get in, there is less CO2 than there already is! The 1:4 ratio will shift to photorespiration and the graph will peak and then decrease are photorespiration occurs
light intensity
- the temperature: will plateau as the number of collisions at that temperature stabilizes the rate
- at higher light, other factors become limiting
- CO2: it plateaus since there isn’t enough substrate for the enzyme to bind (CO2 in environment is so low)
- everything limited: the enzyme concentration will limit the rate
- always positive as more light= more photosynthesis
- sometimes, some plants are adapted for different light intensities and can decrease is because
- too much light in chlorophyll can be damaged
photooxidation
damaging of the chlorophyll
other limiting factors
: chlorophyll concentration, water and pollution but water is RARELY limiting
calvin cycle
? light independent
primary electron acceptor
chlorophyll a
pigments
- during photosynthesis, chlorophyll a becomes oxidized and donates an electron to a primary electron acceptor
- carotenoids and chlorophyll b a re referred to as accessory pigments because after light absorption, they transfer this excitation energy to molecules of chlorophyll a
antenna complex
a cluster of light absorbing pigments embedded in the thylakoid membrane able to capture and transfer energy to special chlorophyll a molecules in the reaction center
reaction center
a complex of proteins and pigments that contains the primary electron acceptor
How are the Thylakoids important to photosynthesis?
The thylakoids are the site of the light dependent reactions of photosynthesis. The thylakoids themselves contain the chlorophyll, but the thylakoid membrane is where the light reactions take place. These reactions include light driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the Photosystems and cytochrome complex and ATP synthesis by the ATP synthase utilising the generated proton gradient.
adaptations for photosynthesis
- the top layer epidermis is so much compared to other plants so water doesn’t evaporate
- sunken stomates, thicker waxy cuticle, trichomes in the stomatal crypt
- there is also a very thick waxy cuticle on the surface of the leaf
- lower epidermis is collapsed in sunken pits. the guard cells care found inside the pits. when water evaporates out, it evaporates into the sunken pits. since wind increases the transpiration rate, the moist air is trapped which prevents further evaporation from taking place. the little hairs (tricones) prevent the wind from getting inside
- this won’t be able to survive as well in cold environment as the thick skin may stop the light from getting through as efficiently
what happens to a plant during dehydration:
- a decrease on chlorophyll causes lowered rate of light dependent reactions/less absorption of light energy
- decrease in CO2 take up causes lowered rate of light independent reactions/less CO2 fixation/Calvin cycle
- both stages reduced due to wilting/less surface of leaf/closure of stomata
c3 plants are best in
cool, wet environments where stomata can remain open and no adaptations for weather
c4 plants are best in
hot, sunny environments where there is separation of co2 between mesophyll and bundle sheath cells, stomata open during day
CAM plants are best in
very hot and dry environments. stomata remain open at night and there is a separation between day and night
light dependent reactions
- h20 splits to make o2
- h+ is a good source of electrons
- NADPH + H+ carries these h+ to the calvin cycle
z scheme
- there are two photosystems in the thylakoid membrane (PSII and PSI)
- first one is photosystem II since bacteria only have one photosystem the photosystems will be stimulated by slightly different wavelengths of red light but slightly different version of the reaction center chlorophylls and the ETC they are associated with
- reaction center contains actually two chlorophylls which is why two electrons are boosted to a higher energy level
locations of calvin cycle
stroma
where does light absorption take place
thylakoid disk
understand functions of parts of the leaf
- grana are staggered, any angle of light will eventually collide with the stack of light to make sure that it is all photosynthized
- cuticle: made of wax. keeps water trapped in leaf.
- epidermis: has no nuclei and are transparent to let light through
- spongy mesophyll: has spaces in between to allow air to go through
cyclic photophosphorylation
i. Photosystem absorbs light energy and the energy is transferred to the reaction center chlorophyll. The reaction center chlorophyll loses an electron to the primary electron acceptor.
ii. Reaction centre chlorophyll is oxidized and must be reduced to work again
iii. Electrons are passed from electron acceptor to ETC and drive chemiosmosis to make ATP
iv. Low energy electrons reduce chlorophyll
* happens in bacteria
Non-cyclic
i. Photosystem I passes excited electrons to ferredoxin and they are used to reduce NADP to NADPH
ii. Photosystem II passes excited electrons to plastoquinone which delivers them to ETC yielding ATP by chemiosmosis – called photophosphorylation
iii. Electrons from PSII reduce chlorophyll in PS I.
iv. Enzyme associated with PS II splits water on inside of thylakoid membrane, using electrons to reduce chlorophyll in PS II, releasing H+ and O2
c4 photosynthesis
- in the mesophyll near the stomata, there is an enzyme that can only bind CO2 called PEP carboxylase
- this fixes the carbon onto a 3 carbon molecule called PEP to produce 4 carbon acid called oxaloacetate
- then it becomes malate and transfers to the bundle sheath cells and breaks back down into PEP and carbon dioxide through the plasmodesmata
- this produces an environment that is spacially separated from oxygen and then the calvin cycle occurs
- the breakdown product that releases CO2 can go back and make more PEP and fix more CO2
CAM plants photosynthesis
- a subset of C4 plants but they keep there stomata open at night and closed during the day to prevent water loss
- it uses PEP in the mesophyll to fix carbon and produce malate but malate then gets stored in the vacuole of the plant during the night
- then the malate goes to the stroma of the chloroplast and breaks down into CO2 (+ PEP)
photolysis:
water splitting in the ETC of the light dependent reactions
most protons are found in the
in the thylakoid lumen
ways to limit photorespiration
- limit water loss
- the guard cells will hold the stomata open longer
- increase the concentration of CO2 somehow, even when you are using it up so much
- take CO2 and turn it into a weak organic acid. this keeps the carbon fixed so the molecule can be broken down to release CO2
- can also have a waterproofing
leaf adaptations
- waxy cuticle keeps water trapped
- epidermis is transparent and nuclei-less to let light in
- thin leaf allows shorter diffusion distance for gases
- ## pores on lower epidermis of lead allow co2 to directly access the mesophyll membrane
chlorophyll a and b
have lightly different absorption spectrums t o absorb the most amount of light
light dependent reactions step 1
photons from the sun hit a photosystem located in the thylakoid disk. excited electrons pass on the energy
photosystem II: a pair of chlorophylls in the reaction centre absorb 2 photons of light. this excited two electrons to raise the energy of the reaction centre. these 2 electrons from the reaction centre produces an oxidation potential capable of oxidizing water.
B6-f complex: electrons pass through this complex which uses the energy released to pump protons across the thylakoid membrane. the proton gradient is used to produces atP by chemiosmosis
light dependent step 2
- electrons get oxidized at the reaction centre which then gets reduced at PQ. B6-f receives the reduced electrons and oxidizes them. The energy is then used to pump hydrogen into the thylakoid lumen. PC then reduces the electrons
photosystem I: a pair of chlorophyll a molecules in the reaction centre absorb 2 photons. this excites 2 electrons that are passed to NADP+, reducing it to NADPH. electron transport from photosystem 2 replaces these electrons. since photosystem I receives photons as well, it needs electrons to excite to transfer energy, this is why e- arriving are excited to even higher e- levels
light dependent step 3
NADP reductase: e- then go to ferredoxin to NADP reductase with reduces NADP from NADH + H+. the water’s electrons end up here and the H+ that are being pumped. this can be used to make ATP using ATP synthase. this process is called photophosphorylation
*water can only be split using light which is photolysis in photosystem II
light independent reactions
just like krebs, RuBP is used to continue the cycle by using condensation to fix with a CO2 called carbon fixation done by Rubisco enzyme which can accommodate both o2 and co2
- co2 enters one at a time (each cycle happens 3 times for 1 g3p)
- yeah….
fructose
monomer
glucose
monomer
maltose
disaccaride
role of pigment molecules
is to absorb light energy and convert it to chemical energy using transfer of electron excitation to funnel energy to the reaction centre chlorophyll
end products of cyclic
ATp
end products of noncyclic
o2, atp and nadph
draw out locations of each thingy
check A
draw out the z scheme
check b
draw out the etc
check c
draw out the calvin cycle
rip check d
draw out c4
check e
draw out c4
check f
season change
leaves stop making chlorophyll which shows the other pigments and the light they reflect
spongey mesophyll function
permits the rapid diffusion of gases in the leaf
oxygen released from photosynthesis comes from
the splitting of water
flow of electrons doing photosynthesis
h20 to nadph to calvin cycle
how many turns are required on calvin cycle to make 1 glucose
6
major product of the calvin cycle is
g3p
what can you make after photosynthesis
starch, sucrose, glucose
pumping H+ location
from stroma to thylakoid lumen
why is measuring co2 bad in photosynthesis
photorespiration occurs in a 1-4 ratio which is also a photosynthetic activity but it is wasteful since co2 is not always taken during photosyntehsis
review graphs and test
ahh
when co2 is given off
that means reparation is occurring as there is too little _light intensity__ for light dependent reactions to feed light independent reactions for co2 uptake
photolysis occurs in the
occurs in the lumen
