Module 5- Photosynthesis Flashcards
(25 cards)
What structures does chloroplast contain?
-thylakoid membrane-folded membranes which contain photosynthetic proteins (chlorophyll) and electron carrier proteins are embedded within these membranes which are both involved in LDR
-stroma-fluid centre which contains enzymes involved in the LIR
-inner and outer membrane-control what can enter and leave the organelle
Where is chlorophyll located?
-in the photosystems on the thylakoid membrane and in a mix of coloured proteins that can absorb light
What are the 4 key types of pigments?
-chlorophyll A-blue/green (found in all plants)
-chlorophyll B-yellow/green
-carotenoids-orange
-xanthophylls-yellow
What gives leaves slightly different colours?
The different proportion of each pigment in leaves
What froms the light harvesting system?
Chlorophyll B, xanthophylls, cartenoids that are all embedded in the thylakoid membrane and are known as accessory pigments
What does the light harvesting system do?
-where light energy of different wavelengths is absorbed and this energy is then transferred to the reaction centre
What makes up the photosystem?
Light harvesting system and reaction centre
What does chromatography do?
Isolate the pigments in chloroplast
How to carry out chromatography?
-pigments added to TLC plate which is placed in a solvent
-the solvent dissolves the pigments and the more soluble the pigments, the further they move op the TLC plate
-this can be converted to an rf value
What is the purpose of the light dependent stage?
To harvest light energy to split water and create ATP and reduced NADP which are both used in the light independent stage
What are the 4 stages of the light dependent stage in order
-non cyclic photophosphorylation
-cyclic photophosphorylation
-photolysis
-chemiosmosis
Describe process of non cyclic photophosphorylation
-ps11 absorbs light with a wavelength of 680nm
-ps1 is then used and absorbs light with a wavelength of 700nm
-the light energy that is absorbed causes electrons within the reaction centres to become excited and released
-the electrons released from PS11 are replaced from water molecules broken down using energy from the sun
-the electrons released from PS1 are passed to another ETC and ATP is again produced by osmosis. The electrons leaving the etc following PS1 are accepted, along with a hydrogen ion by the coenzyme NADP
Describe the process of cyclic photophosphorylation
-some of the electrons released from PS1 are not picked up by NADP and instead are recycled back into PS1
-the transport of electrons still results in ATP production by chemiosmosis
-High-energy electrons are released from the chlorophyll and transferred to an electron carrier.
-The electrons are transferred along a chain of electron carriers in the electron transport chain (ETC).
-Unlike in non-cyclic photophosphorylation, the electrons are not transferred from PSII to PSI.
-Instead the electrons cycle continuously through the electron carriers to PSI.
Describe the photolysis of water
-light energy is absorbed by chlorophyll and splits water into oxygen, H+ and e-
-the h+ is picked up by NADP to form NADPH and is used in the LIR
-the electron is passed along a chain of electron carrier proteins
-the O2 is either used for respiration or diffuses out of the leaf through the stomata
Describe the process of chemiosmosis
-the electrons that gained energy and left the chlorophyll move alongside a series of proteins embedded within the thylakoid membrane
-as they move alongside a series the proteins they release energy and some of the energy from electrons is used to pump the proteins across chloroplast membranes
-an electrochemical gradient is created
-the protons pass through the enzyme ATP synthase which results in the production of ATP
-the protons combine with the coenzyme NADP to become reduced NADP because protons move from a high to low concentration (chemiosmosis)
What is the light independent reaction also known as?
Calvin cycle
Where does the Calvin cycle occur?
In the stromatolites
Why is the Calvin cycle temperature sensitive?
As it involves enzymes
Describe the process of the Calvin cycle
-CO2 diffuses into the laves of the stomata and reacts with ribulose bisphosphate RuBP to form 2 molecules of glycerate triphosphate which is a 3 carbon compound. This reaction is catalysed by RuBisCO and is called carbon fixation
-glycerate triphosphate is reduced to triose phosphate using energy from 2 ATP and by accepting a H from 2 reduced NADP
-some of the carbon from triose phosphate leaves the cycle each turn to be converted into useful organic substances
-the rest of the molecule is used to regenerate RuBP with the energy from 1 ATP which is then recycled in the light dependent reaction
-whilst glucose is the product, this monosaccharide can join to form disaccharides such as sucrose and polysaccharides such as cellulose. It can also be converted into glycerol and therefore combines with fatty acids to make lipids for the plant
Define limiting factor
-any factor that reduces the rate of photosynthesis
How is CO2 a limiting factor in photosynthesis?
-if low there will be less carbon fixation, so levels of RuBP build up. Less carbon fixation will prevent glycerate triphosphate and triose phosphate from being made so their levels will decrease
How is water stress a limiting factor in photosynthesis?
-will cause abscisic acid to move to the guard cells, closing the stomata so there will be less carbon fixation so levels of RuBP build up. Also prevents GP and TP being made
How is temperature a limiting factor in photosynthesis?
-affects the enzyme controlled reactions e.g fixation of CO2 by RuBisCO so RuBP will build up and less GP and TP
How is light intensity a limiting factor in photosynthesis?
-needed for production of ATP and reduced NADP in the light independent stage
-less ATP and NADPH stops GP being converted to TP so GP levels increase
-TP and RuBP levels will decrease as they can’t be made and regenerated
