Component 1: Photosynthesis Flashcards
What is the general formula for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
What are the 2 stages of photosynthesis?
- Light dependent reaction (light energy converted to chemical energy)
- Light independent reaction (ATP and NADPH reduce CO2 and produce glucose)
Where does photosynthesis occur?
- in chloroplasts
- chloroplast found in any part that is exposed to light
- chlorophyll is contained in the thylakoids (green pigment)
What are the adaptations of leaves for photosynthesis?
- AIR SPACES between spongy mesophyll allows CO2 to diffuse to photosynthesising cells
- LARGE SA to capture as much light as possible
- THIN to let light penetrate all the way through
- STOMATAL PORES to allow CO2 diffusion
What are the adaptations of chloroplasts for photosynthesis?
- More chloroplasts is palisade than spongy mesophyll cells allows for them to be exposed to more light
- Large SA allows more maximum CO2 and light absorption
- Thylakoid stacking maximises light catchment
- Single pigment layher in thylakoid membrane allows for pigments to maximise light absorption
- Chloroplasts can move within palisade cells allows for maximum absorption of light and protection from bleaching
Name all photosynthetic pigments
- Chlorophyll a
- Chlorophyll b
- Carotenes (carotenoid)
- Xanthophylls (carotenoid)
Why is there more than one photosynthetic pigments?
- Different pigments absorb photons at different wavelengths of light
- Function is to absorb light energy and start conversion into storable chemical energy
- More than one pigment allows for a large range of wavelengths to be absorbed
What is the role of the stroma in the chloroplast?
- site of the light independent reaction (requires enzymes)
- CO2 is fixed to produce sugar
- ATP and NADPH is required
- Contains starch grains that store the products of pss
What is the role of thylakoids in the chloroplast?
- site of the light dependent reactions
- chlorophyll absorbs light energy
- ATP, NADPH and O2 produced
What is the role of the granum/grana in the chloroplast?
provides surface area of the absorption of light energy
What is the role of the starch grain in the chloroplast?
- excess carbs stored as a starch grain
- starch doesn’t affect water potential
What is the role of the double membrane in the chloroplast?
Controls movement of substances in and out of the chloroplasts
Why are plants green?
reflect green wavelengths on the leaf
What is an absorption spectra?
A graph showing how much light is absorbed at different wavelengths (degree of light absorption by a pigment)
What is an action spectrum?
A graph showing the rate of of photosynthesis at different wavelengths
What is the relationship between an absorption spectra and an action spectrum?
Together they can suggest that the pigments responsible for absorbing a specific wavelength of light are used in photosynthesis
What happened in the engelmann’s experiment?
- As the spiral chloroplast of Spirogyra photosynthesises oxygen gas is produced as a waste product
- The mobile aerobic bacteria move towards the parts of the chloroplasts exposed to red and blue parts of the spectrum
What is an overview statement of photosynthesis?
The process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
Describe the structure of photosystems?
- located in the thylakoid membranes
- antenna complex are the groups/clusters of photosynthetic pigments, held together by protein molecules
- reaction centre contains 2 molecules of chlorophyll a
What are the 2 types of photosystems?
- Photosystem 1 (PS1) is arranged around a chlorophyll a molecule with a maximum absorption at a wavelength of 700nm (P700). Mostly found on intergranal lamellae
- Photosystem 2 (PS2) is arranged around a chlorophyll a molecules with and absorption peak of 680nm (P680), found on the granal lamellae
What is a photosystem?
Each photosystem is a collection of accessory pigments which absorb light at various wavelengths and transmit the energy to a reaction centre
What stage of photosynthesis is non-cyclic and cyclic photophosphorylation apart of and where does it happen?
Light dependent stage (first stage)
thylakoid membrane
What happens in the first part of cyclic-photophosphorylation?
- photon hits PSI and is absorbed by accessory pigments in the antenna complex
- they transfer energy to the primary pigment and this excites an electron (higher energy level)
- the excited electron moves down the electron transfer chain (ETC)
- as it moves down the ETC is loses energy and at the end of the ETC returns to the primary pigment in PSI
What happens in the second part of cyclic-photophosphorylation?
- energy released by the electron is used by the proton pumps to pump protons from the stroma into the thylakoid space
- this creates a proton gradient (pH and electrochemical gradient also)
- to back down the gradient protons move through ATPsynthase
- energy released is used to make ATP from ADP and Pi
- this process is called chemiosmosis
What is the definition of cyclic photophosphorylation?
ATP can be produced by electrons that take a cyclical pathway and are recycled back into the chlorophyll a is PSI
What is the first part of non-cyclic photophosphorylation?
- photon hits PSII and the energy excites an electron in chlorophyll a
- electron travels down the ETC, releasing energy as it goes and travels to the chlorophyll a in PSI
- energy from the electron is used by the proton pump to pump H+ from the stroma to the thylakoid space
- proton gradient is used by ATP synthase to make ATP by chemiosmosis
What is the second part of non-cyclic photophosphorylation? (final electron acceptor)
- light energy hits PSI and excites an electron from chlorophyll a and travels down the ETC
- at the end it joins to the final electron acceptor NADP (nucleotide)
NADP + e- + H+ -> NADPH
What is the third part of non-cyclic photophosphorylation? (photolysis)
- for PSII to replace the lost electron it splits water in photolysis (2H2O -> 4H+ + 4e- + O2)
- the electrons replace those lost is PSII in chlorophyll a and the protons add to the proton gradient
- the O2 diffuses away as a waste product
What are the three things contributing to the proton gradient in the light dependent stage?
photolysis
proton pump
NADP removing H+ from stroma
What is the definition of non-cyclic photophosphorylation?
ATP can be produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which they reduce
What is the definition of photolysis?
the splitting of water molecules by light producing hydrogen ions, electrons and oxygen
What does the electrochemical gradient produce?
- the electrochemical gradient produced by protons becomes a source of potential energy
- when H+ diffuses back it makes available derived from light
Draw the calvin cycle
Ribulose Bisphosphate (5C)
CO2 + RUBISCO enzyme
Unstable 6C compound
(splits)
2 x Glycerate-3-Phosphate (3C0
ATP -> ADP + Pi (energy released), NADPH -> NADP
2 x Triose Phosphate (3C)
1/6 of TP = manufactures glucose -> lipids -> amino acids with the addition of nitrogen obtained from nitrates
5/6 of TP = Ribulose Phosphate (5C)
ATP -> ADP (inorganic phosphate group added)
RuBP (start of cycle)
What stage of photosynthesis is the calvin cycle?
The light-independent stage
What is chromatography?
a separation technique to separate pigments in plant leaves
What does an Rf value show?
shows how far a component has travelled compared with the solvent front
- a ration of distance solvent moved to solvent front
What are the limiting factors for plant metabolism?
inorganic nutrients: nitrogen and magnesium
What happens when nitrogen is in short supply?
- limits metabolism
- nitrogen is required to synthesise proteins and nucleic acids
- usually transported as nitrates in the xylem and as a.a. in the phloem
- a lack of N = stunted growth of all organs, hindered cell division and chlorosis (inadequate chlorophyll production)
What happens to plants when magnesium is in short supply?
- limits metabolism
- transported as Mg2+ in the xylem
- Magnesium is required to make chlorophyll and for the activation of ATPase
- lack of Mg2+ leads to chlorosis (inability to photosynthesise)
What are the 3 limiting factors of photosynthesis?
Light intensity, carbon dioxide concentration and temperature
- if one of these factors is restricted the rate of photosynthesis will be blow the maximum possible rate, restricted factor is the limiting factor
What happens to the rate of photosynthesis as light intensity is increased?
- as the amount of light increases so does pss rate, light is therefore the limiting factor
- eventually the rate will plateau no matter how much the light intensity is increasing, light intensity is no longer the limiting factor
What happens to the rate of photosynthesis as carbon dioxide concentration increases?
- initially as the amount of CO2 increases, so does the pss rate, CO2 is therefore the limiting factor
- eventually increasing CO2 conc has no effect on the rate, CO2 conc is no longer the LF
What happens to the rate of photosynthesis as temperature is increased?
- initially as temp increases so does the rate of photosynthesis because photosynthetic enzymes work best in the warmth (temp is LF)
- most plant enzymes are destroyed at about 45 degrees, rate stops and falls to 0, temp is still the LF
What is a compensation point?
Where the rate of photosynthesis and the rate of respiration ar equal
- the net carbon uptake is 0 at compensation poi
Why would the compensation point never be reached at night?
The light dependent reaction of photosynthesis can’t take place while respiration will occur through the night
Why can water also act as a limiting factor?
- photolysis can’t happen in severely short water supply
- stomata will close, less gas exchange and pss is limited
What happens in photosystems?
-photons of light that hit the PS excite pigments in the antenna complex, transfer light energy until it reaches the primary pigment (chlorophyll a in the reaction centre) and an electron is excited and raised to a higher energy level
