5.6 Flashcards
Granum
Inner part of chloroplasts made of stacks of thylakoids membranes where light-dependant stage of photosynthesis occurs
Photosynthetic pigment
Pigment that absorbs specific wavelengths of light and traps energy associated with light, such pigments include chlorophyll a and b, carotene and xanthophyll
Photosystem
System of photosynthetic pigments found in thylakoids of chloroplasts, each photosystem contains about 300 molecules of chlorophyll that traps photons and pass their energy to a primary pigment reaction centre, a molecule of chlorophyll a, during light dependant stage of photosynthesis
Stroma
Fluid filled matrix of chloroplasts where light independent stage of photosynthesis takes place
Thylakoid
Flattened membrane bound sac found inside chloroplasts, contains photosynthetic pigments/photosystems and is the site of light dependent stage of photosynthesis
What is photosynthesis
A physiological process used by plants, algae and some bacteria to covert light energy from sunlight into chemical energy
What do organisms do with chemical energy converted form light energy
Use chemical energy to synthesise large organic molecules which form building blocks of living cells from simple inorganic molecules like water and CO2 (autotrophic nutrition)
What are organisms that photosynthesise called
Photoautotrophs as they use light as an energy source for autotrophic nutrition, they are described as producers as they’re at the beginning of the food chain and provide energy and organic molecules to other non-photosynthetic organisms
What is photosynthesis equation
6CO2 +6H2O + energy from photons -> C6H12O6 + 6O2
What is a photon
A light particle, each photon contains an amount of energy
What is main product of photosynthesis
Monosaccharide sugar which can be converted to disaccharides for transport and then starch for storage
What is photosynthesis an example of
Carbon fixation
What is carbon fixation
Process by which CO2 is converted into sugars, carbon for synthesising all types of organic molecules is provided by carbon fixation
What reaction is carbon fixation
Endothermic so needs energy, carbon fixation also needs electrons, the addition of electrons is a reduction reaction
What does carbon fixation help
Helps regulate concentration of CO2 in atmosphere and oceans, most forms of life on earth rely directly or indirectly on photosynthesis
What do plants that photosynthesise also do
Respire, during respiration they oxidise organic molecules that they have previously synthesised by photosynthesis and stored releasing chemicals
What are heterotrophs
Non-photosynthetic organisms like fungi, animals, many protoctists and many bacteria, they get energy by digesting complex organic molecules of food to smaller molecules that are used as respiratory substrates, they obtain energy from digestion products by respiration
What happens during respiration
Glucose and other organic compounds are oxidised to produce CO2 and h20, respiration releases chemical energy (exothermic) that can drive organisms metabolism
What is respiration equation
C6H12O6 + 6O2 -> 6H2O + 6CO2 + energy
What are both photosynthesis and aerobic respiration important in
Cycling of CO2 and o2 in atmosphere, products of one process are raw materials for the other process (aerobic respiration removes oxygen from atmosphere and adds CO2 while photosynthesis does opposite
What is the circle of aerobic respiration and photosynthesis
Photosynthesis in photoautotrophs-> carbohydrate + oxygen -> respiration in all living organisms -> carbon dioxide + water -> photosynthesis in photoautotrophs
Plants respire all the time but when does photosynthesis occur
Only during daylight
Why do plants often compete with each other
For light, intensity of light has to be sufficient to allow photosynthesis at a rate that replenishes carbohydrate stores used up in respiration
When photosynthesis and respiration occur at the same rate what is the net gain of plants and what’s this called
No net gain or loss of carbohydrates, the plant is at its compensation point
What is the compensation period
Time takes to reach compensation point
Is compensation period the same of all plants
No it varies depending on the plant species, eg. When exposed to sunlight after darkness shade plants reach compensation point sooner than sun plants which need higher light intensity to reach optimum rate of photosynthesis
What are chloroplasts
Organelles in plants where photosynthesis occurs (algae have chloroplasts but photosynthetic bacteria don’t
What is the structure of most chloroplasts
Disc shaped and around 2-10um long, surrounded by a double membrane, the envelope with intermembrane space of 10-20nm between inner and outer membrane
How permeable is chloroplasts outer membrane
Highly permeable
What are the 2 distinct regions of chloroplasts on electronmicrographs
Inside chloroplasts are fluid filled matrix (stroma) and stacks of thylakoid membranes (grana)
What is the chain between each stroma called
Intergranal lamellae
What is the difference between grana and thylakoid
Thylakoid are individual discs and grana is the whole stack
Where does first stage of photosynthesis, light dependant stage occur
Grana
What 3 membranes do chloroplasts have
Outer, inner and thylakoid
What does chloroplasts having 3 membranes mean
It gives 3 separate internal compartments (intermembrane space, stroma and thylakoid space)
What may thylakoids with a granum be connected to another thylakoids with a granum with
Intergranal lamellae
What is the structure of thylakoid membrane of each chloroplast
It’s less permeable and is folded into flattened disc-like sacs called thylakoids that form stacks (each stack of thylakoid called a granum), one granum can contain up to 100 thylakoids
What does chloroplasts having many grana mean
Many grana in every chloroplasts and many chloroplasts on each photosynthetic cell there is high SA for distribution of photosystems that contain photosynthetic pigments that trap sunlight energy, electron carriers and ATP synthase enzymes needed to covert that light energy to ATP
What is the role of proteins embedded in thylakoid membranes
Hold photosystems in place
What are grana surrounded by and why
Stroma, so products of light dependant stage can easily pass to stroma to be used in light independent stage
What is the stroma
Fluid filled matrix, it contains enzymes needed to catalyse reactions of light independent stage of photosynthesis, as well as starch grains, oil droplets, small ribosomes like those in prokaryote cells and DNA
What is the loop of DNA in stroma needed for
Contains genes that code for some proteins needed for photosynthesis, these proteins assembled at chloroplasts ribosomes
What are within thylakoid membranes of each chloroplast
Funnel shaped structures called photosystems which contain photosynthetic pigment
What does each pigment in photosystems do
Absorbs light of a certain wavelength and reflects other wavelengths of light, each pigment appears to our eyes and brain the colour of the wavelength of light it’s reflecting
What happens to energy associated with wavelengths of light in photosystems
It’s captured and funnelled down to primary pigment reaction centre, consisting of a type of chlorophyll, at the base of the photosystem
What are chlorophylls
A mixture of pigments, they all have a similar molecular structure consisting of a porphyrin group, in which is a magnesium atom and a long hydrocarbon chain
How many forms of chlorophyll a are there
2 and both appear blue-green and both situated at centre of photosystem
What colour light does chlorophyll a absorb and what’s the difference between the 2 forms of chlorophyll a
Both absorb red light but they have different absorption peaks
Where is P680 found and what is it’s peak of absorption
It’s a type of chlorophyll a found in photosystem II and it’s peak of absorption is light of wavelength 680nm
Where is P700 found and what is it’s peak of absorption
Type of chlorophyll a and found in photosystem I and it’s peak of absorption is light of wavelength 700nm
What other colour light does chlorophyll a absorb and what’s its wavelength
Also absorbs some blue light of wavelength 440nm
What light does chlorophyll b absorb
Light of wavelength 400-500nm and wavelength 640nm too, it appears yellow green
What are 2 types of accessory pigments
Carotenoids and xanthophylls
What do carotenoids absorb and reflect and at what wavelength
Absorb blue light of wavelength 400-500nm, they reflect orange and yellow light
What do xanthophylls absorb and reflect and at what wavelength
Absorb blue and green light of wavelength 375-550nm, they reflect yellow light
Where does Light dependant stage occur and what does it involve
Occurs in grana and involves photosystems, involves direct use of light energy
What does the light dependant stage consist of
1.light harvesting at photosystems 2.photolysis of water 3.phosphorylation (production of ATP in light presence) 4. Formation of reduced NADP, oxygen, the byproduct of photosynthesis also produced in light dependant stage
What is pigment at photosystem I (PS1)
Pigment at primary reaction is a type of chlorophyll a which has a peak absorption of red light of wavelength 700nm (P700)
What is pigment in photosystem II (PSII)
Pigment at primary reaction centre is also type of chlorophyll a, but peak absorption of red light is wavelength 680nm (P680)
What happens in PSII
There’s an enzyme that in presence of light, splits water molecules to protons (H+), electrons and oxygen, splitting of water like this called photolysis (2H2O -> 4H+ + 4e- + O2
What is some oxygen produced in photolysis used for
By pant cell for aerobic respiration but during high light intensity rate of photosynthesis is greater than respiration rate in plant so lots of oxygen bi-product will diffuse out of leaves through stomata into atmosphere
What is water the source of in photo phosphorylation
Water is the source of protons used in photo phosphorylation, it donates electrons to chlorophyll to replace those lost when light strikes chlorophyll, it’s a source of the bi-product oxygen and it keeps plant cells turgid so they can function
What is photophosphorylation
The generation of ATP form ADP and inorganic phosphate in the presence of light
What are the 2 types of photophosphorylation
Non-cyclic photo phosphorylation and cyclic
What is non-cyclic photophosphorylation
Involves PSI and PSII, it produces ATP, oxygen and reduced NADP
What is cyclic photophosphorylation
Involves only PSI, it produces ATP but in smaller quantities than non-cyclic
What do both photophosphorylations involve
Iron containing proteins embedded in thylakoid membranes that accept and donate electrons and form electron transport systems
What is the first 3 steps of non-cyclic photophosphorylation
1.when photon of light strikes PSII (P680) its energy is channeled to primary pigment reaction centre 2.light energy exited a pair of electrons inside chlorophyll molecule 3.energised electrons escape from chlorophyll molecule and captured by an electron carrier which is a protein with iron at its centre, embedded in thylakoid membrane
What is steps 4,5,6 of non-cyclic photophosphorylation
- These electrons replaced by electrons derived from photolysis 5.when this iron ion combines with an electron it becomes reduced (Fe2+), it can donate the electron becoming reoxidised (Fe3+), to next electron Carrier in the chain 6. As electron passed along a chain of electron carriers embedded in thylakoid membrane, at each step some energy associated with the electron is released
What is steps 7,8,9 of non-cyclic photophosphorylation
7.this energy used used to pump protons across thylakoid membrane into thylakoid space 8.eventually electrons captured by another molecule of chlorophyll a in PSI, these electrons replace those lost form PSI due to excitation by light energy 9. A protein-iron-sulfur complex called ferredoxin accepts electrons from PSI and passes them to NADP in stroma
What is steps 10,11,12 of non-cyclic photophosphorylation
10.as protons accumulate in thylakoid space a proton gradient forms across the membrane 11.protons diffuse down their concentration gradient through special channels in membrane associated with ATP synthase enzymes and as they do so flow of protons causes ADP and inorganic phosphate to join forming ATP 12. As protons pass through channel they are accepted with electrons by NADP which becomes reduced, reduction of NADP catalysed by enzyme NADP reductase
What has happened by the end of non-cyclic photophosphorylation
Light energy has been converted to chemical energy in form of ATP by photophosphorylation, ATP and reduced NADP now in stroma ready for light independent stage of photosynthesis
What does cyclic photophosphorylation use
Uses only PSI (P700)
What happens in cyclic photophosphorylation as light strikes PSI
A pair of electrons in chlorophyll molecule at reaction centre gains energy and becomes excited, they escape from chlorophyll and pass to an electron carrier system and then pass back to PSI
What happens during passage of electrons along electron carriers in cyclic photophosphorylation
During passage of electrons along electron carriers a small amount of ATP generated but no photolysis of water so no protons or oxygen are produced so no reduced NADP generated
What is different about chloroplasts in guard cells and what does this mean
They only contain PSI they produce only ATP which actively brings potassium ions into cell, lowering water potential so water flows by osmosis which causes guard cells to swell and opens the stoma
Where does light independent stage of photosynthesis occur
In stroma of chloroplasts
What is the light independent stage
It doesn’t directly use light energy but uses products of light dependant stage, if plant not illuminated light independent stage ceases as ATP and hydrogen not available to reduce CO2 and synthesise large complex organic molecules
What is the role of CO2 in light independent stage
It’s the source of carbon for production of all organic molecules found in carbon-based life forms on earth, these organic molecules may be used as structures (eg. Cell membranes, antigens, enzymes, muscle proteins, cellulose cell wall) or act as energy stores (starch and glycogen)
Where does CO2 in air enter plant and what happens next
CO2 in air enters leaves through stomata and diffuses through spongy mesophyll layer to palisade layer and through palisade layers thin cellulose cell wall to chloroplasts envelope and into stroma
What does the fixation of carbon dioxide in the stroma maintain
Maintains concentration gradient that aids diffusion, CO2 that is a bi-product of respiration in plant cells may also be used for this stage of photosynthesis
What is the Calvin cycle
A series of reactions whereby CO2 is converted to organic molecules
What is step 1 of Calvin cycle
CO2 combines with a CO2 acceptor, a 5C compound ribulose bisphosphate (RuBP), catalysed by enzyme RuBisCO
What is step 2 of Calvin cycle
RuBP by accepting carboxyl (coo-) group becomes carboxylated forming an unstable 6C compound that breaks down immediately
What is step 3 of Calvin cycle
Product of breakdown is 2 molecules of 3C compound, GP (glycerate-3-phosphate) and CO2 has now been fixed
What is step 4 of Calvin cycle
GP then reduced using hydrogens from reduced NADP made in light dependant stage to triose phosphate (TP). Energy from ATP also made in light dependant stage is used at this stage at a rate of 2 ATP molecules for every CO2 molecule fixed during stage 3
What is step 5 of Calvin cycle
In 10 of every 12 TP molecules, atoms are rearranged to regenerate 5 molecules of RuBP, this process requires phosphate groups, chloroplasts contain low levels of RuBP as continuously converted to GP but also constantly regenerated, remaining 2 molecules of the 12 are the product (lipids, hexose sugar etc)
How many turns of Calvin cycle needed to make 1 molecule of glucose
6 turns needed to form 2 TP molecules to make 1 glucose molecule
Why does Calvin cycle only occur in the daylight
Products of light dependant stage, ATP and reduced NADP are continuously needed to run Calvin cycle, during light dependant stage hydrogen ions pumped from stroma to thylakoid spaces so concentration of free protons in stroma falls, raising pH to around 8 which is optimum for enzyme RuBisCo, RuBisCO also activated by extra ATP in stroma
In daylight what happens to concentration of magnesium and what does this cause
Magnesium ion concentration increases in the stroma, these ions attach to active site of RuBisCO acting as a cofactor to activate it, ferredoxin that’s reduced by electrons from PSI activated enzymes involved in reactions of Calvin cycle
What are the different ways Triose phosphate (TP) is used for
Some TP molecules used to synthesise organic compounds like some glucose is converted to sucrose, some to starch and some to cellulose, some TP used to synthesise amino acids, fatty acids and glycerol, rest of TP recycled to regenerate supply of RuBP, 5 molecules of the 3C compound TP interact to form 3 molecules of 5C compound RuBP
What factors effect rate of complex processes of photosynthesis
Raw materials like CO2 and water and the energy source (light intensity) and chlorophyll availability, electron carriers and relevant enzymes, as well as temp and cell turgidity
Do factors that affect rate of complex processes of photosynthesis operate at different times
No they operate simultaneously
What is a limiting factor
At any given moment, rate of metabolic process that depends on a number of factors is limited by a factor that is present at its least favourable (lowest) level
What does light provide in photosynthesis
Energy to power stage 1 of photosynthesis and produce ATP and reduced NADP needed for the next stage, light also causes stomata to open so gaseous exchange occurs
What happens when stomata are open
Transpiration occurs and this leads to water uptake and delivery to leaves
At a constant temp and suitable CO2 concentration what is the limiting factor of photosynthesis
Light intensity
What happens when light intensity is low
Rate of photosynthesis low and as light intensity increases so does photosynthesis as it is still the limiting factor
When light intensity increases why may photosynthesis not increase
Other factors have become the limiting factor
What happens in the Calvin cycle is there is little/no light
1.GP can’t be reduced to TP 2.TP levels fall and GP accumulates 3. If TP levels fall, RuBP not regenerated
Why is CO2 not usually a limiting factor to photosynthesis
Levels of CO2 in atmosphere and aquatic habitats usually high enough that CO2 not usually a limiting factor
What is the effect of changing CO2 on the Calvin cycle
If CO2 concentration falls below 0.01% 1.RuBP can’t accept it and accumulates 2.GP can’t be made 3.TP can’t be made
Why is the Calvin cycle temperature sensitive
As it involves many enzyme catalysed reactions
What are the effects of low temp change to 20-30degreesC on the Calvin cycle
I plants have enough water and CO2 and sufficient light intensity, rate of photosynthesis increases as temp increases
What are the effects of temp change to over 30degreesC on the Calvin cycle
For most plants, growth rates may reduce due to photorespiration, oxygen competes with CO2 for enzyme RuBisCOs active site which reduces amount of CO2 accepted by RuBP and reduces quantity of GP and then TP being made and initially causing build up of RuBP but then due to lack of TP, RuBP not regenerated
What are the effects of temp change to over 45degreesC on the Calvin cycle
Enzymes involved in photosynthesis may denature and this would reduce concentration of GP and TP and eventually RuBP as it can’t be regenerated by TP
What happens if plant has access to sufficient water in the soil
Then transpiration stream has cooling effect on the plant , water passing up xylem to leaves jeeps plant cells turgid so they can function, turgid guard cells keep stomata open for gaseous exchange
What happens if not enough water is available to the plant (water stress)
1.roots unable to take up enough water to replace that lost via transpiration 2.cells lose water and become plasmolysed 3.plant roots produce abscisic acid that when translocated to leaves causes stomata to close reducing gaseous exchange 4.tissues become flaccid and leaves wilt 5.rate of photosynthesis greatly reduces
What are different ways to measure rate of photosynthesis
Rate of uptake of raw materials like CO2, or rate of production of bi-product, oxygen. But for both cases we need to calculate quantity taken up or produced per unit time
In school labs how is rate of photosynthesis often found but what are the limitations to this method
By measuring volume of oxygen produced per minute by an aquatic plant. Limitation are some of oxygen produced by plant used in respiration and may be some dissolved nitrogen in gas collected
What is another name for a photosynthometer
Audus microburette
How is a photosynthometer set up
Set up so it’s air tight and there are no air bubbles in the capillary tubing, gas given off by the plant over a known period of time collects in the flared end of the capillary tube. As the experimenter manipulates syringe, gas bubbles can be moved into the part of capillary tube against the scale and it’s length measured. If radius of capillary tube known then length can be converted to volume
What is the equation for turning length into volume of gas collected
Volume= length of bubble x pi r2
How would you investigate light intensity on rate of photosynthesis
Set up the photosynthometer. 1.put a section of Elodea in sodium hydrocarbonate solution and put light on this 2. Leave it 7mins then measure the bubble and work out the volume as well as the distance the light was to find the light intensity. Then repeat with the light further away
How can you manipulate a photosynthometer to measure other factors instead of light intensity like wavelength of light, temp and CO2 concentration
Before investigating, make a prediction, state iv and dv, state variables you must control, why they need to be controlled and how, write a plan and ask someone to check it
What is alternate method to investigate factors affecting rate of photosynthesis
1.add leaf discs from spinach in a syringe with sodium hydrocarbonate solution 3.put finger over hole and pull plunger to pull air out of spongy mesophyll and replace it with sodium hydrocarbonate, once discs sunk to bottom put light on it and measure time taken for leaves to rise (5-10mins), then repeat but move the light further away and see the effects of light intensity on photosynthesis
