Photosynthesis - Finished Flashcards
What is Photosynthesis?
The process (occuring in plants and some other organisms) by which carbohydrates are synthesis from carbon dioxide using light energy as an energy source.
What is the equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
Where is the main site of photosynthesis?
The chloroplasts in the Palisade Mesophyll cells/tissue
What are the 4 main photosynthetic pigments?
- Chlorophyll A
- Chlorophyll B
- Carotene
- Xanthophyll
Where are the photosynthetic pigments located?
in the Thylakoid membranes
What is the fuction of the photosynthetic pigments?
To absorb light energy
What was Engelmann’s experiment?
He reflected a rainbow of light onto a strip of algae and saw that the motile bacteria that fed off the algae clustered towards the algae under the red and blue light. This shows that the red and blue light wavelengths resulted in increased photosynthesis whiched produced more oxygen that attracted the bacteria which need oxygen for respiration.
What is an absorbtion spectrum?
A graph that shows how much light is absorbed at different wavelengths.
What is an action spectrum?
A graph that shows the rate of photosynthesis at different wavelengths.
What is the relationship between the action and absorbtion spectrum?
The graphs have a similar shape. This suggests that it is the absorbance of light that allows photosynthesis to occur.
What is the advantage to a plant of having more than 1 photosynthetic pigments?
Each pigment absorbs light from a limited part of the spectrum .
Additional pigments allow a range of different wavelengths of light to be absorbed.
This enables an increased rate of photosynthesis so more carbohydrates are made.
What is a photosystem made up of?
- Antenna Complex - A cluster of photosynthetic pigments in the thylakoid membrane.
- Reaction centre - where the light is funnelled to.
How many photosystems are there?
Photosystem 2 = Also called P680 as its chlorophyll A molecule has an absorption peak at 680nm
Photosystem 1 = Also called P700 as its chlorophyll A molecule has an absorption peak at 700nm
What are Photosystems for?
For Light Harvesting and Donating Protons
Where would you find a photosystem?
In the light dependant stage of photosynthesis
Where does the light dependent stage happen in a plant?
Thylakoids
What is the light dependant stage also known as?
The Z scheme
What is the light dependant stage made up of?
2 photosystems and an electron transport chain.
What happens in the light dependant stage of photosynthesis?
- When light energy reaches the reaction centre of the photosystem 2. Chlorophyll A emits 2 electrons and leaves the chlorophyll oxidised.
- These electrons are raised up to a higher energy level and are picked up by electron accepters
- The electrons pass along a chain of electron carriers and proton pumps resulting in the generation of ATP from ADP (By a process called photophosphorylation)
What happens to the electrons that are emmitted from photosystem 1?
They either re-enter the electron transport chain to be used in cyclic photoposphorylation
or they are used with 2H+ to reduce NADP
How does the Chlorophyll A in photosystem 2 replenish its electron number?
a molecule of H2O breaks down by photolysis and donates 2e- to photosystem 2 and a 2H+ to reduce NADP
What are the 4 main things the light dependant stage consists of?
- Electron transfer through the z scheme
- reduction of NADP
- photolysis of water
- Synthesis of ATP by photophosphorylation (cyclic/non-cyclic)
THESE PROCESSES ARE INTERLINKED
Where is the source of electrons for cyclic and non-cyclic photophosphorylation?
Cyclic = Derived from photosystem 1 - pass along the first ETC and return to PS1
Non Cyclic = Derived from water. They pass through the z scheme untill they end up in reduced NADP
what photosystems are used in cyclic and non cyclic ?
Non Cyclic: PSI PSII
Cyclic: PSI
Is NADP reduced in cyclic and non cyclic?
Non Cyclic : Yes
Cyclic : No
What are the products of non cyclic photophosphorylation?
ATP, reduced NADP, O2
What are the products of cyclic photophosphorylation?
ATP
WHat are the uses of H+ and e- in photophosphorylation?
- Electrons from photolysis of H20 are used to replace these lost from PSII
- H+ ions produced contribute to a raised H+ ion concentration inside the thylakoid.
- Some of the Hydrogen ions produced from the photolysis of water are used to reduced NADP in the stoma.
Where does the production of reduced NADP take place?
Stroma
What is phosphorylation?
The process of generating ATP from ADP and phosphate
What is Photophosphorylation?
Phosphorylation which occurs in the chloroplast during the light dependant reactions
what is Non Cyclic Photophosphorylation?
The electrons from photosystems I & II are non recycled back into the original photosystems
What is cyclic photophosphorylation?
The electrons from photosystem 1 are recycled back into the cycle
How is NAPD reduced?
ELectrons from PSI may combine with H+ ions and NADP to form reduced NADP
NADP + 2H++2E-= reduced NADP
Takes place in the stroma and as a result helps maintain a low concentration of hydrogen ions in the stroma.
Where do the H ions used in the reduction of NADP come from?
Photolysis of water Splitting of a water molecule. Light s thought to be directly responsible for this. H20 -> 2H+ +1/2O2 + 2e- Occurs in the thylakoid space.
What is the Chemiosmotic theory?
Proposes that the energy for ATP synthesis comes from the electrochemical gradient of H+ ions(protons) across the membrane.
How is ATP synthesised in the chloroplast?
There is a higher concentration of H+ ions inside the thylakoid than in the stoma.
As a result, H+ ions flow out of the thylakoid through channel proteins down a gradient into the stroma.
This flow provides the energy for the formation of ATP by ATP synthetase.
How is the H+ ion gradient generated?
Photolysis of water produces H+ ions inside the thylakoid lumen
Transfer of electrons through a chain of electron carriers provides the energy for the pumping pf H+ ions from the thylakoid lumen into the stroma.
REduction of NADP lowers the concentration of H+ ions in the stroma.
The products of the light dependant stage are:
ATP and reduced NADP (used in the light independant stage)
O2
What is the light independant stage also known as?
The Calvin cycle
Where does the light independant stage take place?
In the stroma
What happens in the light independant stage?
- CO2 combines with a 5C acceptor molecule called Ribulose Bisphosphate (RuBP) - this reaction is catalysed by an enzyme known as Rubisco
- Produces an unstable 6C compound which immediately splits into 2 molecules of a 3C compound called Glycerate-3-phosphate (GP) CO2 has now been fixed into an organic molecule.
- Both GP molecules are phosphorylated by ATP then reduced by NADP - This produces 2 molecules of a carbohydrate called Triose Phosphate (TP)
- SOME of the Triose Phosphate canbe used to make: Carbohydrates (Glucose). Fatty Acids and Glycerol. Amino Acids.
- MOST of the molecules of Triose Phosphate (TP) (5/6) are used to regenerate RuBP via a series of reactions involving more ATP
RuBP MUST BE REGENERATED SO THAT THE CYCLE CAN CONTINUE
Where did the ATP and NADP for the Calvin cycle come from?
From the light independant stage.
What are inorganic nutrients?
Plants can obtain a variety of inorganic nutrients from the soil. These can be “limiting factors to metabolism” if in short supply
Give 3 examples of inorganic nutrients?
Nitrates
Magnesium
Phosphates (Phosphorus)
How are nitrates used in plants?
Source of Nitrogen
Needed for the synthesis of amino acids (and therefore proteins)
Also needed for the synthesis of nucleotides in combination with phosphates.
Nitrogen deficiency will hinder cell division and cause stunted growth.
How is magnesium used in plants?
Synthesis of chlorophyll molecule
Deficiency leads to yellowing (Chlorosis) of leaves and death.
How are phosphates used in plants?
Synthesis of phospholipids
Synthesis of nucleotides (Nitrates and phosphates are needed to synthesise these)
