Photosynthesis Flashcards
Label the structure of chloroplast
See notes include
- granum
- lamella
- ribosomes
- stoma
- outer membrane
-inner membrane
- starch grain
- thylakoid
- lipid droplet
What photosynthetic pigments do plants contain
Chlorophyll ( a & b)
Carotenoid (b-carotene & xanthophyll)
explain why plant benefits from having pigments that absorb different wavelengths
E,g what does chlorophyll absorb
Each pigment absorbs slightly different wavelengths so having different pigments plants maximise the wavelengths of light they can absorb energy from
E.g chlorophyll absorbs blue and red wavelengths of visible light
Absorption spectrum shows…
% light of different wavelengths absorbed by isolated pigments
What type of light does chlorophyll absorb
Blue and red wavelengths
Action spectrum shows..
Rate of photosynthesis of plants exposed to different wavelengths of light
E.g. highest rates of photosynthesis stimulated by blue and red wavelengths of light
Def of photosystem
Light- harvesting cluster of pigment molecules in the thylakoid membrane
What is photosystem I and photosystem II?
Photosystem I
Reaction centre (cluster of pigment molecules) = chlorophyll A with peak absorption 700nm
Photosystem II
Reaction centre (cluster of pigment molecules) = chlorophyll A with peak absorption 680nm
Role of accessory pigments in photosystem
(Examples of pigments)
Accessory pigments (Chlorophyll A & B and carotenoids) pass energy from light to the chlorophyll A at the reaction centre for start of photosynthesis
Def of Photophosphorylation
The synthesis of ATP using energy harvested from light
The process of cyclic photophosphorylation (photosystem I)
(5 steps)
1) light energy excites electron from chlorophyll A in photosystem I
2) electron passes down electron transport chain (ETC) in the thylakoid membrane
3) energy lost from electron used to pump protons across membrane into thylakoid lumen
4) protons diffuse through ATP synthase & energy is used to synthesis ATP
5) electron returns to chlorophyll molecule
Compare photophosphorylation & oxidative phosphorylation
1) organelle
2) location of ETC
3) Location of high [H+]
4) source of high energy electrons
organelle
Photo) Chloroplast
OP) mitochondrion
location of electron transport chain
Photo) thylakoid membrane
OP) inner mitochondrion membrane
location of high H+ concentration
Photo) thylakoid lumen
OP) inter mitochondrion membrane
source of high energy electrons
Photo) chlorophyll A
OP) glucose
What does the light- dependent reaction of photosynthesis (non-cyclic phototphosphorylation) involve?
-both photo systems 1 & 2
- synthesis of ATP and reduced NADP
- the splitting of water (photolysis)
Process of photolysis
1) energy from light used to split water into
H2O —> 2H+. + 2e- + 1/2 O2
2) electrons from water replace electrons lost from chlorophyll a and PS2
Explain the differences between cyclic and non-cyclic photophosphorylation
Cyclic
- only photosystem 1 used
- exited electrons return to photosystem 1 to go through cycle again
- no photolysis
- only ATP produced
- produces steady supply of ATP in presence of sunlight
Non-cyclic
- photosystems 1 & 2 used
- exited electrons enter photosystem 1 to be picked up by NADP —> reduced NADP
- photolysis of water replenishes electrons lost to photosystem 1
- produces both NADPH and ATP
- allows for synthesis’s of organic molecules for long term energy
Summaries non-cyclic photophosphorylation into a diagram
- light absorbed by photosystem 2, exited electron enters into an electron transport chain to produce ATP
- photoactivation of photosystem 1 results in the release of electron which reduce NADP+ ( to from reduced NADP)
- the photolysis of water releases electrons which replace those lost by photosystem 2
Step by step of non-cyclic photophosphorylation
- Photons are absorbed by PSII
- An e- is exited and reduces and e- accpetor
- The e- passed onto ETC
- At the of ETC from PSII an electron replaces that lost at PSI
- ETC drives H+ into thylakoid lumen
- Protons pass through ATP synthase due to the concentration gradient (chemiosmosis) generating ATP from ADP + Pi
- Protons diffused through ATP synthase are available to reduce NADP
- Photons also absorbed y PSI
- E- exited and reduces e- acceptor
- The ETC (in PSI) transfers e- to NADP forming reduced NADP
- Photolysis of water provides e- to replace those lost from PSII, proton contributes to chemiosmosis, O2 is waste
Where does Calvin cycle take place
The stroma of the chloroplast
What is required for the Calvin cycle to occur
CO2
ATP
Reduced NADP
RUBISCO enzyme
Steps of the Calvin cycle
- Enzyme RUBISCO catalyses the reaction combining CO2 and RuBP
This forms 2x GP (3 carbon glycerate 3- phosphate) - The hydrolysis of ATP provides energy to reduce 2x GP to 2x TP (3 carbon triose Phosphate)
This reaction requires H+ ion from reduced NADP which recycles back to NADP - Some of the TP is then converted into useful organic compounds like glucose and some continues in the. Calvin cycle to regenerate RuBP
- 5/6 molecules of TP produced in the cycle are used to regenerate RuBP (5x carbon)
Regenerating RuBP uses energy released from ATP
4 main stages in Calvin cycle
- Carbon fixation
- Reduction of GP
- Formation of glucose
- Regeneration of RuBP
How is CO2 used in the Calvin cycle
CO2 is used as a reactant that combines with RuBP. This reaction is catalysed by RUBISCO. To from 2 molecules of 3 carbon GP
Where is ATP used in the Calvin cycle
ATP is used in 2 places in the Calvin cycle
1) ATP is used to redcue GP into TP
2) ATP is used in the reaction to regenerate RuBP from TP
If the light dependent reactions were inhibited why would this also stoop the light-independent reaction
The light dependent reactions (non-cyclic) produces ATP molecules and reduced NADP which are both used in the Calvin cycle to allow it to occur.
ATP is hydrolysed to provide energy for GP to be reduced by reduced NADP into TP
Without these this stage could not occur preventing the Calvin cycle continuing
ATP is also used in the regeneration of RuBP
Without RuBP not GP can be produced again preventing the Calvin cycle continuing
How are hexose sugars like glucose formed during the Calvin cycle
The Calvin cycle needs 6 x turns to make 1 hexose sugar
this is due to 2 molecules of TP are produced from every 1 CO2 used. 5/6 of the TP molecules are used to regenerate RuBP. This means that for 3 cycle turns only 1 TP used to make Glucose and TP is a 3 carbon so 2 are needed
What is needed in the calvin cycle (how many of each molecule) to allow 1 glucose to be formed
18 ATP
12 reduced NADP
6 Carbon dioxide
How are other organic molecules like lipids and proteins formed from molecules produced in the Calvin cycle
lipids
- made using glycerol, synthesised from Triose phosphate (TP) , and fatty acids, synthesised from glycerate 3- phosphate (GP)
amino acids
- some amino acids are made from glycerate 3-phosphate (GP)
What are limiting factors of photosynthesis?
- light intensity
- carbon dioxide concnetration
- temperature
(Water)
Why is light intensity a limiting factor of photosynthesis
Pigments absorb light to produce high energy electrons which are needed to synthesise ATP and reduced NADP, both of which are required to use CO2 in Calvin cycle to produce sugar.
So in low light intensities rate of photosynthesis is low, an increase in light intensity causes an increase in photosynthesis.
Why is carbon dioxide concentration a limiting factor for photosynthesis
CO2 is reactant which sugars are made from in the Calvin cycle, lower CO2 concentrations means lower rate of reaction
Why is temperature a limiting factor to photosynthesis
The reaction of Calvin cycle are catalysed by enzyme. Enzyme activity is dependent on temperature, reading the temperature means reduced rate of reaction. Increase temperature too high, proteins denature so rate of reaction decreases.
Explain what the most ideal conditions for plants in the UK
High light intensity of a certain wavelength
- different pigments absorb different wavelengths so more wavelengths absorbed by chloroplast A & B and carotene the more photosynthesis
Temperature around 25oC
- if below 10oC photosynthesis enzymes can become inactive, but more than 45oC they denature. Also increased temperature too high = water loss so plants close stomata decrease availability of CO2
CO2 at 0.4%
- rate of photosynthesis is at maximum rate here, any higher concentration stomata dose so rate decreases
How can farmers manage limiting factors of photosynthesis
Light intensity
- farmers use glasshouses to prevent this being limited as light can get through the glass, lamps can also provide light at night time
Temperature
- glasshouses trap heat energy from the sun which warms the air. Heaters and cooling systems can also be used to keep a constant optimum temperature
Carbon dioxide concentration
- Carbon dioxide is added to the air, e.g. by burning a small amount of propane in a CO2 generator
