module 3 Flashcards
What is photosynthesis
The process whereby light energy from the sun is transformed into chemical energy and used to synthesise large organic molecules from inorganic substances
Why is photosynthesis nearly the most important biochemical process
Cz nearly all life depends on it
Why do consumers and decomposers depend on photosynthesis
Because it transforms light energy into chemical potential energy
Why do strobes depend on photosynthesis for their respiration
Cz it releases oxygen from water into the atmosphere
What are autotrophs
Organisms that use light energy or chemical energy and inorganic molecules to synthesise complex organic molecules
2 Examples of an autotroph
Plants
Nitrifying bacteria
Examples of inorganic molecules
CO2
H2O
What are heterotrophs
Organism that ingest and digest complex organic molecules releasing the chemical potential energy stored in them
Examples of complex organic molecules
Lipids Carbohydrates Proteins Nucleic acids Vitamins
What are chemo autotrophs
Prokaryotic that synthesise complex organic molecules using energy derived from exergonic chemical reactions
Role of Nitrifying bacteria
Recycle nitrogen
How do Nitrifying bacteria obtain their energy
By oxidising ammonia to nitrite or oxidising nitrite to nitrate
What are photo photo autotrophs
What is their source of energy and the raw materials
Organism that Photosynthesise
Light energy and inorganic molecules
Examples of heterotrophs
Bacteria some
Fungi
Animals
What is respiration in terms of chemical energy organic and inorganic molecules etc
Releasing chemical potential energy ok complex organic molecules such as glucose
Who can respire autotrophs or heterotrophs
Both
Products of photosynthesis
Glucose and oxygen
Products of aerobic respiration
CO2 and water and energy
How can you use and what for would you use radioactive isotopes in terms of importance of oxygen
Use water containing radioactive isotopes of oxygen they found that the oxygen produces during photosynthesis was radioactive. When they gave the plant CO2 containing radioactive oxygen, the oxygen produced wasn’t radioactive this suggests the oxygen is released from water
6 structures of the chloroplasts
Disc shaped
2-10 micrometersA double membrane called an envelope
Inter membrane space between inner and outer membrane
Outer membrane permeable to smaller ions
Inner membrane less permeable and has transport proteins embedded in it. Folded into lamellae. Each stack of lamellae is called a gramum
What are the stacks of flattened membrane compartments
Thylakoids
2 regions in chloroplast seen under a light microscope
Stroma
Grana
What happens in the stroma
The reaction of the light independent stage happen here
What is found in the stoma
Necessary enzyme for light independent stage
Starch grains
Oil droplets
Ribosomes
What happens in the grana
The light dependent stage if photosynthesis
How can thylakoids be seen
EM only
7 ways chloroplasts are adapted for their role
Inner membrane with it transport proteins can control entry and exit of substance between the cytoplasm and the stroma
Many grana increase surface area for photosynthetic pigments, electron carriers and ATP syntheses enzymes involved in light dependent stage
Arrangement of photosynthetic pigment into photo systems allows maximum absorption of light energy
Proteins embedded in grana hold photo systems in place
Stroma contains enzyme s needed to catalyse reactions of the light independent stage
Grana surrounded by stroma so products og the light dependent stage can readily pass into the stroma for the light independent stage
Chloroplast can make some of the proteins they need for photosynthesis using chloroplast dna and ribosomes
What are photosynthetic pigments
Molecules that absorb light energy
Each pigment absorbs a range of wavelengths of light and has its own distinct peak of absorption. Other wavelengths are reflected
Why do different pigments act together
To absorb as much light as possible
Where are photosynthetic pigments found
In thylakoid membranes
What are photosynthetic pigments arranged in
Photisystems
What are photosynthetic pigments held in place by
Proteins
What is chlorophyll
A mixture of pigments
What structure do chlorophyll share in common
A hydrocarbon chain (phytol) and a porphyrin group
What does the porphyrin group in chlorophyll contain
A magnesium atom
What is the porphyrin group similar to
Haem group
What happens when light hits chlorophyll
Light hitting chlorophyll causes a pair of electrons associated with magnesium to become excited
What are the 2 types of chlorophyll a
Their colours?
P680
P700
Yell/green
What wavelength do the chlorophyll types absorb light
P680
680 nm
P700
700nm
What light do they absorb both P680 and P700?
Red light at different wave lengths
Where are P680 and P700 found and what are they known as
At the centre of photo systems
Aka the primary pigment reaction centre
Which photo system is P680 found in
Photisystem 2
Which photo system is P700 found in
Photo system 1
What else other than red light does chlorophyll a absorb
At what wavelength
Blue
450nm
What wavelength does chlorophyll b absorb light
What colour is chlorophyll b
500 & 680 nm
Blue-green
Accessory pigments:
Give 2 examples of accessory pigments
Carotenoid
Chlorophyll b
What light colour do carotenoid reflect and absorb
Reflect yellow and orange
Absorb
Blue
What do carotenoids not include and are they involved in the light dependent reaction?
Porphyrin group
Not directly
They absorb light wavelengths that are not well absorbed by chlorophyll and pass the energy associated with that light to the chlorophyll a at the base of the photo system
Just a reminder
What are the main carotenoids pigments
Carotene(orange)
Xanthophyll (yellow)
What is chemical energy from light dependent stage
ATP and reduced NADP
Where does the light dependent stage take place
Thylakoid membranes of the chloroplasts
Grana
Where are photo systems with the photosynthetic pigments found
Embedded in the thylakoid membrane
Where does photisystem 1 mainly occur
Intergranal lamellae
Where does photosystem 2 mainly occur
Granal lamellae
Why do the pigments trap light energy
To convert it to chemical energy in the form of ATP
What allows photisystem 2 to split water into protons electrons and oxygen
It’s enzyme
What is the splitting of water called
Photolysis
What happens to the oxygen produced by photolysis
Used in aerobic respiration or leaves through the stomata
Water in the light dependent stage is a source of what
Hydrogen ions
Electeons
What are hydrogen ions from water used for
They’re used in chemiosmosis to produce ATP
These protons are then accepted by a coenzyme nadp which becomes reduced nadp
It would be used during the light independent stage to reduce CO2 and produce organic molecules
What are the electrons from water used for?
To replace those lost by the oxidised chlorophyll
Other reasons why water is important in photosynthesis
Keeps plant cells turgid enabling then to function
Where does oxygen from photosynthesis cone from
Water
What is photophosphorylation
9
Is the making of ATP from ADP and Pi in the presence of light
Describe the stages of photophosphorylation
Light can be thought of as travelling as photons rather than waves
When a photon hits a chlorophyll molecule the energy from the photon is transferred to 2 electrons that become excited
These electrons are captured by electron acceptors and passed along a series of electron carries in the membrane of thylakoid
Energy is released as electrons pass along the chain of electron carriers
This pumps proton across the thylakoid membranes into the thylakoid space where they accumulate
A proton gradient is formed across the thylakoid membrane, the protons flow town their gradient through channels associated with ATP synthase enzymes
This flow of protons is called chemiosmosis
It produces a force that join ADP and Pi to make ATP
The kinetic energy in the proton flow is converted to chemical energy in the ATP molecules, which is used in the light independent stage of photosynthesis
What is the making of ATP using light energy called
Photophosphorylation
What 2 types of photophosphorylation are there
Cyclic
Non cyclic
Talk about cyclic photophosphorylation
Only uses photosystem 1 (p700)
The excited electrons pass to an electron acceptor and back to the chlorophyll molecule from which they were lost
No photolysis of water
No generation of reduced nadp, but small amounts of ATP are made
This may be used in light independent stage or it may be used in guard cells to bring in potassium ions lowering the WP and causing water to follow by osmosis. This causes the guard cells to swell and opens the stomata.
Non cyclic photophosphorylation
8
Involves both photo systems
7 steps
1 list strokes photosystem 2 exciting a pair of electrons that leave the chlorophyll molecule from the primary pigment reaction centre
2 the electrons pass along a chain of electron carriers and the energy released is used to synthesise ATP
3 light also strokes photosystem 1 and a pair of electrons has been lost
4 these electrons along with protons (produces by photolysis of water at photosystem 1) join nadp which become reduced nadp
5 electrons front he oxidised photosystem 3-2 replace the electrons list from ps1
6 electrons from photolysed water replace those lost by the oxidised chlorophyll in ps2
7 protons from photolysed water tale part I’m chemiosmosis to make ATP and are then captured by nadp, in the stroma. They’ll be used in the light independent stage.
What are electron carriers
Are molecules that transfer electrons
What are electron acceptors
Are chemicals that accept electrons from another compound. They are reduced while acting as oxidising agents
Where does the light independent stage take place
In the stroma of chloroplasts
What happens to light independent stage if light isn’t available
It ceases cz it depends on the products of the light dependent stage
Role of CO2 what is it the soul race of
Carbon and oxygen fir the production of all large organic molecules
Which act as structures, energy store res or sources for all life forms on this planet
What is the 1st step of the Calvin cycle (light independent stage)
CO2 diffuses into lead through open stomata
Then diffuses throughout air spaces in spongy mesophyll layer and reaches palisade mesophyll layer
It then diffuses through the thin cellulose wall, the surface men bra be, the cytoplasm, and the chloroplast envelope, then into the stroma
What is the 2nd stage of the Calvin cycle
In stroma CO2 combines with ribulose bisphospate (a CO2 acceptir) (5C)
Reaction catalysed by ribulose bisphosphate carboxylase-oxygenase (rubisco)
RuBP becomes carboxylated
Talk about 3rd step of Calvin cycle
Product of 2nd step reaction is 2× glycerate 3-phosphate (gp) (3C)
CO2 is now fixed
Talk about 4th step of Calvin cycle
Gp is reduced and phosphorylated to triode phosphate (tp)
ATP and reduced nadp from light dependent reaction are used in this process
Talk about step 5 of Calvin cycle
Five out of every 6 molecules of TP (3C) are recycled by phosphorylation, using ATP from the light dependent reaction, to 3 molecules of RuBP
How the products of the Calvin cycle can be used
6 ways
Some GP can be used to make amino acids and fatty acids
Pairs of TP molecules combine to make Hexose Sugars such as glucose
Some glucose molecules can be isomerised to form another Hexose sugar, fructose glucose and fructose molecules may be combines to form sucrose
Hexose Sugars can be polymerised into other carbohydrates (polysaccharide) such as cellulose and starch
TP can be converted to glycerol and this may be combined with fatty acids formed from GP to make lipids
What are 4 limiting factors of photosynthesis
Chlorophyll
Light
CO2
H2O
What is a limiting factor
A factor that is present at the lowest or least favourable level
What did blackman find about a constant temp
That photosynthesis varies with light intensity. At zero light intensity rate of photosynthesis is 0
What did blackman find about low light intensities
As light intensity increases, photosynthesis rate increases therefore light intensity in this case is limiting factor
What did blackman find about higher light intensities
Rate plateaus. Light intensity is no longer the limiting factor cz changing light intensity doesn’t alter the rate
So a duff factor must now be limiting rate
What did blackman find about increasing CO2 concentration
Increases rate but not indefinitely. Rate will plateau again as temp is now the limiting factor
What did blackman find about increasing temp
Increases rate but rate will still reach plateau where a duff factor is limiting the process. Too high temp denatured the enzyme in Calvin cycle, which decreases the rate of photosynthesis
Talk about the effect of CO2 concentration on rate of photosynthesis
When fossils are made CO2 levels decrease. When fossils are burnt CO2 levels increase
Oceans act as carbon sinks, they absorb 1/3 of the CO2 on earth
Growing Forests absorb CO2 from atmosphere.mature ones produce just as much as they absorb
In greenhouses levels of CO2 are very low cz of close proximity of plants to each other even with ventilation, so growers gave to introduce CO2 by burning methane
An increase in CO2 increases rate of photosynthesis (if no other factor is limiting)
What is the effect of light intensity on photosynthesis
Increase in light intensity leads to an increase in rate (if no other factors are involved)
Light has 3 main effecfs:
Causes stomata to open which means more CO2 enters leaf
It’s trapped by chlorophyll where it can excite electrons
Then splits water molecules to produce protons
The electrons and protons are involved in photophosphorylation, producing ATP for the fixation of CO2
But rate if photosynthesis varies throughout the day due to varied light intensity
Effects of temp on rate of photosynthesis
Enzymes are involved in the Calvin cycle so enzyme controlled reaction are influenced by the temp
Btw 0-25 degrees Celsius the rate of photosynthesis doubles for every 10 degree Celsius rise in temp
25+ leads to the rate leveling off and falling
This is cz the enzymes have been denatured or at least work less efficiently
It’s is also because oxygen more successfully competes against CO2 for the active site if rubisco
This also causes more water loss from the stomata leading them to close which limits the availability of CO2
What does light intensity measure
How much energy is associated with the light
How does an increase in light intensity effects light dependent stage
It alters the rate of the light dep reaction
Why does increasing light intensity alter rate of light dep reaction
More light energy is available to excite more electrons
Electrons take part in photophosphorylatio. To sum u, increased light intensity means more ATP and reduced nadp are produced
ATP and reduced nadp are both used in the light independent stage (Calvin cycle) as sources of hydrogen and energy to reduce glycerate phosphate to triose phosphate.
ATP is also used to phosphorylate 5 out of every 6 molecules of TP to regenerate RuBP
Why would the light independent stage cease if there’s no light even though it doesn’t depend on it
Cz it uses the products of the light dep stage, without light the light dep stage ceases
Explain why the light independent stage will stop if there’s no light
GP can’t be changed to TP, so GP will accumulate & levels of TP will fall
This in turn will lower the amount of RuBP cz there’s not enough TP to be recycled. This in turn reduces the fixation of CO2 and the formation of gp
Effects of increasing CO2 concentration on CO2 fixation
Increases it if light intensity isn’t a limiting factor
Tall about carbon dioxide concentration in terms of limiting factors and Calvin cycle
3
An increase in CO2 fixation means that more gp is formed (some are converted to fatty/amino acids) and hence more molecules of TP. It also means there are more regeneration of RuBP cz of more tp.
If water uptake from soil by plant can’t exceed it’s water loss by transpiration the plant will wilt which lead to a stress response where plant growth regulator hormones are released which leads to stomata closing - this decreases chances of it wilting cz when they’re close transpiration rate is decreased cz of less gaseous exchanges
This will reduce CO2 uptake and reduce the rate of photosynthesi
If CO2 concentratio is reduced below 0.01%, then RuBP (a CO2 acceptor) will accumulate which means level of gp and subsequently tp will fall
Talk about temp in terms of limiting factors and the Calvin cycle
Increasing temp won’t greatly affect rate of light dependent reaction as, apart from photolysis, it’s not dependent upon enzymes. But it will affect light independent stage cz it involved enzyme controlled reactions
But once temp goes over 25 the oxygenate activity of rubisco increases more than its carboxylase-oxygenase activity
This means that photo respiration exceeds photosynthesis
Due to this, ATP and reduced nadp from the light dependent stage are dissipated and wasted
This reduces the overall rate of photosynthesis cz they need these
V Hugh temps can also damage the proteins involved on photosynthesis
Increase in temp increases water loss from leaves by transpiration which leads to closure of stomata and subsequent reduction in the rate of photosynthesis
