Photosynthesis Flashcards
Name structural features of a chloroplast
Thylakoids
Grana
Lamella
Thylakoids are stacked up into grana. The grana are linked by lamella.
Chloroplasts contain photosynthetic pigments. What are they?
Coloured substances that absorb the light energy needed for photosynthesis. They are found in the thylakoid membranes and attached to proteins. (photosystem)
What wavelength does photosystem I absorb the best at?
700nm
What wavelength does photosystem II absorb the best at?
680nm
Name the two stages of photosynthesis
Light dependent reaction
Light independent reaction
What is the light dependent reaction?
Needs light energy and takes place in the thylakoid membranes
What is the energy from photoionisation of chlorophyll used for?
Making ATP from ADP & Pi (photophosphorylation)
Making reduced NADP from NADP
Splitting water into protons, electrons, oxygen (photolysis)
Name the two types of phosphorylation that occurs in the light dependent reaction
Non cyclic
Cyclic
Explain what happens during non-cyclic phosphorylation
- Light energy is absorbed by PSII which excites the electrons in the chlorophyll. The electrons move to a higher energy level. These high energy electrons are released from the chlorophyll and move down the ETC to PSI
- As the excited electrons leave PSII they must be replaced. Light energy splits water into proteins, electrons and oxygen
- The excited electrons lose energy as they move down the ETC. The energy is used to transport protons into the thylakoid meaning it has a higher concentration of protons than the stroma. This forms a proton gradient across thylakoid membrane
- Protons move down their concentration gradient into stroma via ATP synthase. Energy from this movement combines ADP and Pi to form ATP
- Light energy is absorbed by PSI which excites electrons to a higher energy level. Electrons are transferred to NADP along with a proton to form reduced NADP
Explain what happens during cyclic photophosphorylation
Only uses PSI
Electrons from chlorophyll molecules aren’t passed onto NADP but passed back to PSI via electron carriers
Electrons are recycled and repeatedly flow through PSI
Produces small amounts of ATP
What is the light independent reaction?
Doesn’t use light energy (relies on products from LDR)
Takes place in the stroma
Also known as the Calvin Cycle
Explain what happens during the Calvin Cycle
- Oxygen enters leaf through stomata and diffuses into stroma. It combines with RuBP and is catalysed by the enzyme rubisco. This gives an 6C molecule which breaks down into two 3C molecules of glycerate 3-phosphate (GP)
- The hydrolysis of ATP provides energy to turn GP into TP. This reaction also requires proton which come from reduced NADP. Some TP is converted into useful organic compounds and some continues in the cycle
- 5 out 6 molecules of TP produced in the cycle are used to regenerate RuBP. Regeneration uses the rest of the ATP produced by the LDR
What organic substances are TP and GP converted into?
Carbohydrates
Lipids
Amino acids
How many times does the Calvin Cycle need to turn to make one hexose sugar?
6
What are the optimum conditions needed for photosynthesis?
The higher the light intensity the more energy is provided to the LIR
Photosynthesis involves enzymes (temp below 10 the enzymes are inactive and temp above 45 the enzymes are denatured)
High temperatures close stomata resulting in lower levels of carbon dioxide
Increasing carbon dioxide in the atomosphere to 0.4%
