11. Photosynthesis Flashcards
(52 cards)
1
Q
What is the site of photosynthesis
A
- leaf (organ)
- chloroplast (organelle)
2
Q
What 3 substances is the leaf adapted for
A
- CO2
- water
- light
3
Q
List adaptations of the leaf
A
- large SA (for light)
- thin (most light absorbed within first few micrometers, keeps diffusion distance shirt)
- long narrow upper mesophyll packed with chloroplasts that collects sunlight
- numerous stomata so all mesophyll cells are a short diffusion from one
- air spaces in lower mesophyll layer
4
Q
Write the overall equation for photosynthesis
A
6CO2 + 6H2O ——> C6H12O6 + 6O2
5
Q
Name the three main stages of photosynthesis
A
- capturing of light energy
- light dependent reaction
- light independent reaction
6
Q
What is light captured by
A
Chloroplast pigment such as chlorophyll
7
Q
What occurs in the light dependent reaction
A
- in which some of the light energy is absorbed and conserved in chemical bonds
- electron flow is created by photolysis of water into protons, electrons and oxygen
- products are NADPH ATP and oxygen
8
Q
What occurs in the light independent reaction
A
-protons (hydrogen ions) are used to produce sugars and other organic molecules
9
Q
Where does the light dependent reaction take place
A
The grana on structures called thylakoids
10
Q
Where does the light independent reaction take place
A
The stroma
11
Q
What is the grana
A
- stacks of thylakoids
- where LDR takes place
- thylakoids contain chlorophyll
- some have inter-granal lamellae that are tubular extensions that join up with thylakoids in adjacent grana
12
Q
What is the stroma
A
- fluid filled matrix
- light independent stage of photosynthesis takes place
- in stroma there are another series of structures such as starch grains
13
Q
What two purposes does the capture of light energy have un the LDR
A
- to add an inorganic phosphate (Pi) molecule to ADP, producing ATP
- to split water into H+ ions (protons) and OH- ions (photolysis)
14
Q
What is the biological definition of oxidation
A
- when a substance
- gains oxygen
- loses hydrogen
15
Q
What is the biological definition of reduction
A
- when a substance
- loses oxygen
- gains hydrogen
16
Q
Describe photoionisation
A
- the ionisation of the chlorophyll molecule
- as a result of the electrons moving to an excited state
- caused by the light energy absorbed by the chlorophyll
- two electrons lost from Mg prosthetic group
17
Q
If chlorophyll loses a pair of electrons it is said to be…
A
oxidised
18
Q
What are the two electrons from photoionisation energy taken up by
A
electron carrier
19
Q
What is the mechanism by which ATP is produced explained by
A
The chemiosmotic theory
20
Q
Describe the steps in the LDR (up to chemiosmotic theory)
A
- chlorophyll absorbs light energy, causing the electrons to be promoted to an excited state, ionising the chlorophyll molecule. This is photoionisation.
- the electrons that leave the chlorophyll are taken up by an electron carrier
- the electrons pass down along a number of electron carriers in a series of oxidation reduction reactions that happens in the membranes of the thylakoids
- each new carrier is a slightly lower energy level than the previous so the electrons lose energy at each stage
- some of the energy released is conserved in the production of ATP (and indirectly NADPH)
- the replacement of electrons from the chlorophyll molecule is provided by the photolysis of water
- this can be explained by the chemiosmotic theory
21
Q
Describe the steps in the LDR (after the chemiosmotic theory)
A
- each thylakoid is an enclosed chamber in which protons are pumped (active transport) from the stroma to the thylakoid space using protein carriers in the thylakoid membrane
- the energy of this comes from the photoionization of chlorophyll and the electrons through the electron transport chain
- photolysis of water also produces protons (further increasing amount of protons in the thylakoid space)
- this maintains a concentration gradient for the protons meaning the protons from the water crosses the thylakoid membrane through ATP synthase channel proteins
- the rest of the membrane is impermeable to protons
- as protons pass through the ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination if ADP with Pi to form ATP
- these protons are taken up by NADP producing NADPH
22
Q
What are electrons that leave the chlorophyll taken up by
A
Electron carrier proteins in the thylakoid membrane
23
Q
How do electrons lose energy moving down the electron carrier chain
A
Each new carrier level is a slightly lower energy than the previous
24
Q
What is some of the energy conserved from the electron transport chain used in
A
The production of ATP (and indirectly NADPH)
25
How are the electrons replaced in the chlorophyll molecule
By the electrons released in the photolysis of water
26
What supplies the energy for the active transport of H+ through electron carrier proteins
Photoionisation of chlorophyll causing electrons to flow through these electron carrier proteins.
27
How is the reaction for ATP catalysed in the LDR
Protons move through the ATP synthase channels
28
How is the reaction for ATP catalysed in the LDR
Protons move through the ATP synthase channel it changes to the structure of the enzyme which then catalyses the combination if ADP with Pi to form ATP
29
Why is it important that NADP accepts protons
- NADPH is needed in the LIR
| - H + will cause the pH to decrease harming the cell (e.g denature enzymes)
30
What are chloroplasts adapted for ie. what is their function
Capturing sunlight and carrying out LDR
31
How are chloroplasts adapted for their function
- thylakoids provide large surface area for attachment of chlorophyll electron carrier and enzymes that carry out LDR
- network of proteins in grana hold chlorophyll in very precise manner that allows maximum absorption of light
- granal membrane have ATP synthase channels which catalyse production of ATP
- chloroplasts contain DNA and ribosmomes so they can quickly and easily manufacture some of the proteins involved in the light dependent reaction
32
Why must the LDR take place before the LIR
LDR produces ATP and NADPH which is necessary in LIR
33
What is the cycle called that takes place in the LIR
Calvin cycle
34
Describe the calvin cycle
- CO2 from the atmosphere diffuses into the leaf though stomata and through the cell-surface, cytoplasm and chloroplast membrane of a mesophyll cell into the stroma of the chloroplast
- CO2 reacts with the 5C compounds RuBP catalysed by rubisco
- this produces two molecules of 3C GP
- NADPH from LDR is used to reduce GP to TP using ATP supplied by ATP
- NADP is reformed and goes back to LDR
- some TP molecules are converted into organic substances that the plant requires eg. starch
- most TP are used to regenerated RuBP using ATP from the LDR
35
How does CO2 enter the stroma
CO2 from the atmosphere diffuses into the leaf though stomata and through the cell-surface, cytoplasm and chloroplast membrane of a mesophyll cell into the stroma of the chloroplast
36
What does RuBP stand for
Ribulose bisphosphate
37
What does GP stand for
glycerate 3-phosphate
38
What does TP stand for
triose phosphate
39
How many carbons is RuBP
5
40
What does Rubisco catalyse
The reaction of CO2 with RuBP
41
What are organic molecules required by the plant
- starch
- cellulose
- lipids
- glucose
- amino acids
- nucleotides
42
What fraction of carbon is used to make an orgnaic molecule in the LIR
1/6
43
What is 5/6 of the carbons used to do in the LIR
Used to regenerate RuBP molecules using ATP
44
What is the order of carbons
1C + 5C ---- 2x 3C ---- 2 x 3C ----- 1 + 5C
45
Write the three reactions in the LIR
```
RuBP (5C) + CO2 (1C) ---> 2 GP (3C)
2 GP (3C) + NADPH + ATP ---> 2 TP (3C) + NADP
2 TP (3C) + ATP ---> RuBP (5C) + organic molecule (1C)
```
46
What does CO2 react with in the calvin cycle and what is produced
RuBP. 2 GP is produced
47
What does NADPH react with in the calvin cycle and what is produced
ATP and 2 GP. 2 TP is produced
48
What does 2TP react with and produce
ATP. RuBP is regenerated and 1C organic molecule
49
Why can the calvin cycle not take place without light if light is not required?
NADPH and ATP are vital in the Calvin cycle and are produced in the LDR which is dependent on light
50
Why is the Calvin cycle temperature dependent
LIR is an enzyme controlled reaction and realises on Rubisco so if temperature too low/high enzymes cant function
51
How is the chloroplast adapted to carry out the light-independent reaction
- stroma contains all enzymes needed to carry out LIR
- stromal fluid is membrane bound so a high concentration of enzymes and substrates can be maintained within it
- stroma fluid surrounds grana so the products of LIR can readily diffuse into stroma
- contains DNA and ribosomes so it can quickly and easily manufactures proteins involved in LIR
52
Name 3 factors than could limit rate of photosynthesis
- light intensity
- CO2 concentration
- temperature
