Photosynthesis Flashcards
1
Q
Where does photosynthesis occurs?
A
- photosynthesis occurs in the chloroplast
- the stroma is the site of the light independent stage whereas the light dependent stage occurs in the thylakoid
2
Q
What is the structure of the thylakoid membranes
A
- Thylakoids are flattened fluid sacs that stack into structures called grana
- these grana are held together by bits of thylakoid membrane called lamellae which ensure they are held together but also distanced which increases the SA of grana so it can absorb more light
- thylakoid membranes also contain photosynthetic pigments which absorb the light needed for photosynthesis.
- There are two photosystems used for this, PSI which absorbs light best at 700nm and PSII which absorbs light best at 680nm
- The stroma also contains enzymes used for photosynthesis
3
Q
What is the equation for photosynthesis?
A
6CO2 + 6H20 = C6H1206 + 602
4
Q
What are the three main stages of photosynthesis?
A
- capturing light energy
- Light dependent reaction
- Light - independent reaction
5
Q
What are the two purposes of the light - dependent reaction
A
- to add an inorganic phosphate molecule to ADP therefore making ATP
- To split water into H+ ions and OH- ions, this known as photolysis
- Making reduced NADP from NADP
6
Q
Define oxidation and reduction
A
- Oxidation = when a substance gains oxygen or looses electrons
- Reduction = when a substance looses oxygen or gains electrons
7
Q
Describe the electron transfer chain and the photoionisation of chloroplasts
A
- When a chlorophyll molecule absorbs light energy (PS11) , it boosts the energy of a pair of electrons within the chlorophyll molecule, raising them to a higher energy level
- The electrons are said to be in a excited stage
- The electrons are said to be so excited that they leave the chlorophyll pigment all together
- As a result the chlorophyll molecule becomes ionised
- So this process is called photoionisation
- The electrons that leave the chlorophyll are taken up by an electron carrier
- This means the chlorophyll molecule (PS11) has been oxidised and the electron carrier has been reduced
- The electrons are now passed along a number of electron carriers in a series of oxidation - reduction reactions
- These electron carriers form a electron transfer chain in the membranes of the thylakoids
- Each electron carrier has a lower energy level than the previous stage so energy is lost at each stage
- some of this energy is used to combine an inorganic phosphate molecule with an ADP molecule to form ATP (through the chemiosmotic theory)
8
Q
what is the chemiosmotic theory?
A
- The process of electrons flowing down the electron transport chain and creating a protein gradient across the membrane to drive ATP synthesis
9
Q
Describe the chemiosmotic theory
A
- each thylakoid is an enclosed chamber in which H+ protons are pumped from the stroma into the thylakoid membrane through protein carriers called proton pumps
- The energy used to drive this process comes from electrons released when water molecules are split by light (photolysis of water)
- The photolysis of water also produces protons which further increases the concentration inside the thylakoid space
- This maintains a high concentration of H+ ions in the thylakoid membrane compared to the stroma
- The protons then move down the concentration gradient through ATP synthase channel protein
- this catalyses the reaction of ADP and Pi to form ATP
10
Q
What is the purpose of the photolysis of water and what is it
A
- the loss of electrons when light strikes a chlorophyll molecule means it is oxidised. In order for the chlorophyll pigment to keep absorbing light energy, these must be replaced
- these electrons are providied by splitting water molecules using light energy
2H20 = 4H+ + e- + 02 - the protons increase the conc of protons in the thylakoid membrane
- the oxygen is used for respiration
11
Q
How is reduced NADP formed
A
- After the protons pass through the thylakoid space through ATP synthase channels, they are taken up by an electron carrier called NADP
- reduced NADP is the main product of the light dependent stage and it enters the light independent reaction
12
Q
What is cyclic photophosphorylation
A
- cyclic photophosphorylation produces ATP and only uses PSI
- it is cyclic because the electrons from the chlorophyll molecule are not used to reduce NADP but are passed back to PSI via electron carriers . This means that they are recycled and only reduce a small amount of ATP
13
Q
How are chloroplasts adapted to capturing light
A
-the thylakoid membranes provide a large SA for the attachment of chlorophyll, electron carriers and enzymes which carry out the light dependent reaction
- granal membranes contain ATP synthase channels which are selectively permeable to protons to generate to H+ concentration gradient
14
Q
Describe the light independent stage of photosynthesis
A
- In the second stage of photosynthesis, ATP and reduced NADP are used to reduce glycerate 3 - phosphate
- light is not directly required
- the light independent reaction takes place in the stroma of the chloroplast
15
Q
Draw the calvin cycle
A
