Photosynthesis Flashcards
1
Q
What is the definition of photosynthesis?
A
process that converts solar energy to chemical energy.
2
Q
In what organisms does photosynthesis occur?
A
Plants, algae, some protists (euglena), some prokaryotes (cyanobacteria)
3
Q
What are heterotrophs?
A
Organisms that obtain their organic material from other organisms
These are the CONSUMERS
4
Q
What do almost all heterotrophs depend on for O2 and food?
A
photoautotrophs.
5
Q
What is a chloroplast likely to have evolved from?
A
A photosynthetic bateria
These are where photosynthesis occurs
6
Q
What are the major locations of photosynthesis in a plant?
A
Leaves
7
Q
Where do plants get their green color?
A
Chlorophyll
8
Q
What is chlorophyll?
A
the pigment that absorbs different wavelengths of light, green color comes from green light that is reflected and not absorbed by the pigment.
9
Q
Where does CO2 and O2 enter and exit the leaf?
A
The stomata
10
Q
What structure of what organ are the chloroplasts primarily found in a plant?
A
mesophyll (interior tissue of the leaf
11
Q
How many chloroplasts does one mesophyll cell have?
A
30-40
12
Q
Where is chlorophyll located in the chloroplast?
A
in the membrane of the thylakoids.
13
Q
What is a thylakoid? Granum? Stroma?
A
Thylakoid - the single “coin” membrane that separates stroma from thylakoid space
Granum - a stack of thylakoids
Stroma - Space between inner membrane and thylakoid membrane
14
Q
Does a chloroplast have a two membrane or a three membrane system?
A
3
15
Q
What is the equation for photosynthesis?
A
6CO2 + 12H2O + light energy -> C6H12O6 + 6O2 + 6H20
if only considering net consumption of water:
6CO2 + 6H2O + light energy -> C6H12O6 + 6O2
above equation divided by 6:
CO2 + H2O -> CH2O (sugar precursor that does not exist in nature) + O2
16
Q
How do chloroplasts produce the oxygen we breath?
A
split it into hydrogen and oxygen, incorporating their hydrogen electrons into sugar molecules. and leaving oxygen
17
Q
What type of reaction is photosynthesis?
A
Redox - H2O is oxidized and CO2 is reduced.
18
Q
Where did we think the oxygen we breath resulted from in the past? How did we prove this wrong?
A
CO2
A scientist found H2S used in a sulfabacterium for photosynthesis was split and Sulfur was released into the atmosphere and hydrogen was used to reduce CO2.
19
Q
What are the two stages of photosynthesis and where do they occur?
A
- light reactions (in thylakoids)
2. calvin cycle (in stroma)
20
Q
What occurs during the light reactions?
A
Light is absorbed
Water is split
O2 released
NADP+ reduced to NADPH
ATP generated from ADP by PHOTOPHOSPHORYLATION
21
Q
What occurs during the calvin cycle?
A
sugar is formed from CO2 using ATP and NADPH
22
Q
What does the calvin cycle begin with?
A
Carbon fixation - the incorporation of CO2 into organic molecules.
23
Q
What are the 3 products of the light reactions?
A
O2
NADPH
ATP
24
Q
What are the inputs of the light reactions?
A
Light
H2O
ADP
NADP+
25
What are the inputs for the calvin cycle?
ATP
NADPH
CO2
26
What are the products of the clavin cycle?
CH2O (G3P)
Byproducts:
NADP+
ADP
27
What is light a form of?
Electromagnetic energy, or electromagnetic radiation
28
How does electromagnetic energy travel?
In rhythmic waves
29
What is wavelength?
the distance between the crest of waves.
30
How is wavelength related to energy?
Wavelength is INVERSELY related to energy
SO...
higher wavelengths = lower energy
31
Is visible light (wavelengths that produce light we can see) the only light found in the electromagnetic spectrum?
HELL TO THE NO NO
32
What are the discrete particles that light consists of?
Photons
33
IS visible light the only light that can power photosynthesis?
YES
34
What are pigments?
substances that absorb light
35
Why have multiple pigments?
having multiple pigments allows for more wavelengths of light to be absorbed.
36
What happens to the wavelengths of light that aren't absorbed by a pigment? Use chlorophyll as an example, why is it green?
It is reflected and transmitted
Chlorophyll absorbs violet-blue, and red light, it doesnt absorb green light and therefore is reflected and transmitted to give a green color
37
Where are the pigments located in the chloroplast?
the thylakoid membrane
38
What is a spectrophotometer? How does it work?
this is a machine that measures a pigments ability to absorb various wavelengths of light.
It sends light through pigments and measures the fraction of light that is transmitted (not absorbed) at each wavelength.
39
What type of light would be used to be able to send the entire visible spectrum of light ONE WAVELENGTH AT A TIME to a pigment? In other words, what light contains the entire visible spectrum of light?
White light.
40
What is the difference between an absorption spectrum and an action spectrum?
Absorption spectrum - plots a pigments light absorption versus wavelength (each pigment has its own line)
Action spectrum - profiles the effectiveness of different wavelengths at driving a process (all pigments included in the one line)
41
How was an action spectrum created in the late 1800s?
A filamentous photosynthetic alga was exposed to light passed through a prism (separates wavelengths and exposes different segments to different wavelengths)
Then,
An aerobic bacteria was placed near the entire filament and allowed time to grow, the bacteria grew the most in the areas of the filament where the wavelegnth of light allowed for the most photosynthesis (allowing for the most O2 to be produced and used by the aerobic bacteria)
42
What is the main photosynthetic pigment? What are the accessory pigments?
Chlorophyll A
Chlorophyll B and carotenoids
43
What is the main purpose of chlorophyll B?
To broaden the spectrum of light used for photosynthesis
44
What are two main functions of carotenoids?
to absorb excessive light that would be harmful to the chlorophyll
also broaden photosynthetic spectrum
45
What is the only difference between a chlorophyl A and chlorophyl B molecularly?
CH3 (methyl group) in chlorophyll a
CHO (carbonyl group) in chlorophyll b
46
What happens when a pigment absorbs light?
It comes to an unstable, excited state
excited electrons will eventually fall back to a ground state and will give off photons, this is called FLUORESCENCE
fluorescence gives off light and heat
47
Will an isolated solution of chlorophyll fluoresce if illuminated?
YES
48
What does a photosystem consist of?
reaction center complex (protein complex) surrounded by light-harvesting complexes
49
What is the purpose of the light-harvesting complexes?
to direct the energy of the photons to the reaction center of the photosystem
50
Where is the primary electron acceptor in the photosystem?
The reaction-center complex
51
What is linear electron flow?
This is the primary pathway of electron flow used within the light reactions that uses both photosystem complexes and produces ATP AND NADPH using light energy.
52
Why are photosystem I and photosystem II named such even though photosystem II comes first within the light reactions?
They are named by their order of discovery.
53
Describe the process of how an electron is transferred from H2O to the final electron acceptor in PSII (steps 1-3 of light reactions).
1. Photon of light excites a pigment located in light-harvesting complexes causing its electron to boost to a higher energy level, as the pigments fall to ground state energy is transferred pigment to pigment as they go from excited to ground state until they reach the P680 pigment in the reaction-center complex (chlorophyll a pigment pair that absorbs light best at 680).
2. The P680 will become excited and an electron from it which will be picked up by the primary electron acceptor. This makes P680+ which is the strongest oxidizing agent known at this time, IT MUST BE REDUCED.
3. Simultaneously, a water molecule is split and its electrons will be transferred to the P680 pigment (reduction) in the reaction-center complex. (this leads to the O2 that we breath as by-product)
54
So the oxygen from the split water used for P680+ reduction will come to be the O2 that we breath, the fate of the electrons is to be accepted by the P680+, what happens to the protons of the hydrogen atoms of the split water?
They remain within the thylakoid space to help with the proton gradient for ATP production using ATP synthase
55
Describe the travel of the electron through the electron transport chain between PSII and PSI (steps 4 & 5 of light reactions).
4. The electron travels down an electron transport chain to get from the primary electron acceptor in PSII to PSI (P700). Each time the electron is passed to a more electronegative molecule in the electron transport chain energy is release and is used to pump hydrogen ions into the thylakoid space.
5. The proton gradient created between the thylakoid space and the stroma is used to make ATP using ATP synthase (chemiosmosis).
56
Describe what happens to the electron after it has been accepted by P700 of PSI after traveling down the 1st ETC in the light reaction (steps 6-8).
6. Light photon will then excite the pigments in the light-harvesting complex of PSI, similar to how it is done is PSII which will eventually lead to the excitement and elevation of the electron that was accepted by P700 which will go to the primary electron acceptor, P700+ will then become reduced by another electron in the ETC from PSII.
7. The electron will travel down a second ETC, this ETC does not create a proton gradient so it is not a part of ATP production. ending up at NADP+ reductase on the outer portion of the thylakoid membrane in the stroma.
8. NADP+ reductase will catalyze the transfer of these electrons to NADP+, reducing it to NADPH. This process also reduces the amount of H+ from the stroma.
57
What are the three products of the light reactions?
1. O2
2. ATP
3. NADPH
58
Where does cyclic electron flow occur?
PSI ONLY
59
What is the product of cyclic electron flow?
ATP
60
What is the basic process of cyclic electron flow? Why is it used?
1. P700 donates electron to primary electron acceptor, electron travels backwards to ferrodoxin, down to cytochrome complex, and eventually right back to P700+ where it began. Energy is released as the elctron is transferred between molecules and is used to create proton gradient used to generate ATP.
This process is used to create a surplus of ATP to satisfy a high demand of ATP for the calvin cycle.
61
What do we assume about the evolution of the different electron flows for the light reactions?
Some organisms only have a PSI
Makes us believe that cyclic electron flow evolved before linear
62
How would cyclic electron flow help with protection from damaging amounts of light?
It would absorb more light energy and convert it to ATP, reducing the harm to the plant.
63
For oxidative phosphorylation and photosynthesis, where do the electrons come from that are used in each process?
Oxidative phosphorylation - food that we eat
Photosynthesis - Water
64
Describe the diference between the spatial organization of protons used in chemiosmosis in a chloroplast and a mitochondria.
Mitochondiria - double membrane - protons pumped from intermembrane space (equivalent to thylakoid space) to mitochondrial matrix (equivalent to stroma)
Chloroplast - triple membrane - protons pumped from thylakoid space (equivalent to cristae or intermembrane space) into the stroma (equivalent to mitochondrial matrix)
BOTH HAVE ETC AND ATP SYNTHASE MOLECULES
65
Where do the ATP and NADPH that are products of the light reactions end up? why is this important?
the STROMA
they will be used in the calvin cycle
66
Where does the calvin cycle take place?
the stroma
67
What is the basic function of the calvin cycle?
to build sugar from smaller molecules by usind ATP and reducing powers of NADPH
68
What is the main input of the calvin cycle that will be converted to a sugar?
CO2
69
What is the product of THREE turn of the clavin cycle? How many CO2 will this take?
G3P
3CO2 will be used.
70
What are the three phases of the calvin cycle?
carbon fixation (catalyzed by rubisco)
Reduction of fixated carbon to G3P
regeneration of acceptor of CO2 (RuBP)
71
Describe the carbon fixation stage of the calvin cycle.
The CO2 will fix itself to RuBP, being catalyzed by rubisco, to create a 6 carbon molecule. this is done 3 times (18 carbons total). each of the fixated molecules are unstable and will break down to two, 3 carbon molecules called 3-phosphoglycerate, there will be a total of 6 of these molecules.
72
Describe the reduction phase of the calvin cycle.
Each of the 6 posphoglycerate molecules are phosphorylated by ATP, using 6 ATP total. These phosphorylated molecules are then each reduced by an NADPH (6 used total) to make 6 G3P.
ONE of these G3P can be used as output to make carbohydrates or other organic compounds (3 carbons that were fixated from 3 CO2 molecules)
73
Describe the regeneration of CO2 acceptor phase of the calvin cycle (RuBP regeneration).
After one molecule of G3P is taken for use in other organic processes the remaining 5 G3P (15 carbons total) are rearranged back into RuBP (5 carbon molecule x3) using 3 ATP.
74
In total, how many turns of the calvin cycle, ATP, NADPH, and CO2 are used in producing 1 G3P?
How many G3P are required to make one glucose molecule?
3 turns of calvin cycle
9 ATP
6 NADPH
3 CO2
2 G3P per glucose molecule
75
If it takes 2 G3P to make up one glucose molecule, how many turns of the calvin cycle, ATP and NADPH would be needed to make glucose?
18 ATP
12 NADPH
6 turns of cycle
76
What is the problem with stomata and photosynthesis?
The stomata must be open to allow CO2 into the leaf to perform photosynthesis.
On hot days to prevent water loss the stomata close, not allowing CO2 to enter.
77
Can Rubisco (RuBP) differentiate btween O2 and CO2?
NO
78
If CO2 levels are low and oxygen levels are high, what will RuBP do in the calvin cycle since it can't differentiate between CO2 and O2?
What is this called?
It will pick up O2
PHOTORESPIRATION
79
What are the products of photorespiration?
Consumes O2 and releases CO2 without making ATP of sugar
Also uses ATP in the process
WASTE OF ATP AND CARBON RESOURCES
80
Why would photorespiration be beneficial?
Reducing oxygen buildup in plant when stomata is closed.
81
What are the two classes of plants that have evolved in order to combat photorespiration?
C4 and CAM plants
82
What do C4 plants do in their mesophyll cells as an extra step before the calvin cycle?
Incorporate CO2 into four carbon (C4) compounds like Oxaloacetate.
83
Describe the C4 pathway up until the calvin cycle starting with pyruvate.
pyruvate (3C molecule) is converted to PEP (uses an ATP)
PEP carboxylase (enzyme) helps add CO2 to PEP to create oxaloacetate (4C)
Oxaloacetate is converted to malate and the molecule is transported from the mesophyl cell to the bundle-sheath cell where its CO2 will be removed to be used in the calvin cycle. Malate that has CO2 removed is converted to pyruvate. NOTE THIS IS A CYCLIC PROCESS.
84
Does PEP carboxylase distinguish between CO2 and O2?
YES
85
What is the benefit of the C4 process? What is a small drawback?
THE STOMATA CAN BE CLOSED AND PHOTOSYNTHESIS CAN STILL OCCUR
O2 will not compete
It requires additional ATP
86
How would the extra ATP be generated for the C4 process?
by PSI with cyclic electron flow
87
What does CAM stand for?
Crassulacean acid metabolism
88
When do CAM plants open their stomata? What about during the day?
Why?
Open at night to incorporate CO2 into organic acids
Closed during the day to conserve H2O while being able to release stored CO2 from organic acids to use in the Calvin cycle.
89
What is the difference between CAM and C4 plants? Main similarity?
CAM - All processes occur in same cell, stomata open at night and produce organic acids at night. and stomata closed during the day and will use CO2 from organic acids during the day.
C4 - organic acid production occurs in mesophyll cell and moved to the bundle-sheath cell. whole process takes place during the day.
BOTH FIX CO2 TO ORGANIC ACIDS
90
What are some examples of the importance of photosynthesis (4)?
1. Sunlight gets converted to chemical energy which is stored in organic compounds.
2. Sugars supply many organisms with chemical energy and carbon skeletons to synthesize molecules of cells.
3. Plants can store excess sugars as starch such as in tubers, seeds, and fruits.
4. Not only is food produced, but O2 is also produced.
