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Photosynthesis Mechanisms and Impacts
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Photosynthesis Mechanisms and Impacts
Photosynthesis Mechanisms and Impacts
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1
Question
What is the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis?
Answer
The absorption spectrum for chlorophyll a is represented by a solid line, while the action spectrum for photosynthesis is represented by a dashed line. They differ because the peaks and valleys are not a perfect match, which involves the role of accessory pigments in the light harvesting complexes (LHCs).
2
Question
What are the two types of sea lettuce mentioned, and how do their pigment compositions relate to their habitats?
Answer
Sea lettuce (Ulva) and Nori (Porphyra) have different combinations of pigments and absorb light maximally at different wavelengths. Sea lettuce is typically found in shallow coastal waters, while Nori is found in deeper waters. This distribution may be influenced by available light, their action spectra due to pigments, nutrient requirements, light intensity, and presence of grazers.
3
Question
Design an experiment to test the effect of grazers on Nori's distribution in water depths.
Answer
The experiment should include a control for grazers and involve comparing Nori's presence in different water depths. Consider factors such as light, nutrients, and grazing pressure, and ensure the inclusion of variables, controls, and replicates as discussed in class.
4
Question
What is the main role of the antenna LHC pigment molecules in thylakoid membranes?
Answer
The main role of the antenna LHC pigment molecules in the thylakoid membranes is to capture light energy and transfer it to the reaction center for photosynthesis.
5
Question
What are the possible fates of an electron of a pigment once it has been excited?
Answer
Once an electron of a pigment has been excited, it can either return to the ground state, be transferred to an electron acceptor, or participate in photochemical reactions leading to ATP and NADPH synthesis.
6
Question
What is a reaction center in a photosystem made of?
Answer
A reaction center in any photosystem is made of proteins and chlorophyll molecules that play a critical role in converting light energy into chemical energy.
7
Question
When does the first chemical reaction occur in a given photosystem?
Answer
In a given photosystem, the first chemical reaction occurs upon the excitation of chlorophyll when light is absorbed, leading to electron transfer.
8
Question
List the steps in the photochemical reactions that help establish a proton gradient across the thylakoid membrane.
Answer
The steps include: 1) Light absorption by photosystems, 2) Water splitting releasing protons (H+) into the lumen, 3) Electron transport through the cytochrome b6-f complex pumping protons into the lumen.
9
Question
How do the energy of photons absorbed by pigments lead to the synthesis of O2, ATP, and NADPH?
Answer
The energy of photons absorbed by pigments excites electrons, which are transferred through the electron transport chain, ultimately leading to the splitting of water (producing O2) and the synthesis of ATP and NADPH.
10
Question
Fill in the blank: Following the splitting of water, the resulting protons are released into the ______ contributing to the proton gradient across the membrane.
Answer
lumen.
11
Question
What provides the direct source of energy for making ATP in the thylakoids?
Answer
The direct source of energy for making ATP in the thylakoids is the proton gradient established across the thylakoid membrane.
12
Question
In linear electron transport in the thylakoids, what oxidizes PC? What reduces PC? What oxidizes Fd? What reduces Fd?
Answer
In linear electron transport, PC (plastocyanin) is oxidized by the cytochrome complex and reduced by electrons from PSII; Fd (ferredoxin) is oxidized by NADP+ and reduced by electrons from PSI.
13
Question
What happens when compound X competes with NADP in the Electron Transport Chain?
Answer
When compound X competes with NADP to accept electrons from Fd through the enzyme FNR, it changes from X to X- (an unbalanced negative charge) as it does not combine with a proton.
14
Question
What cannot happen in photosynthetic organisms that lack photosystem II?
Answer
These organisms cannot release O2 through photosynthesis, fix CO2 through photosynthesis, or absorb light at 680 nm.
15
Question
What question was asked in the Jagendorf experiment?
Answer
The question being asked was related to understanding the mechanism of ATP synthesis in thylakoids.
16
Question
In cyclic electron flow in the thylakoid membranes, what is the role of electrons from ferredoxin (Fd)?
Answer
In cyclic electron flow, electrons from ferredoxin (Fd) move to plastoquinone (PQ) and participate in the establishment of a proton gradient.
17
Question
Explain why cyclic electron transport leads to fewer ATP molecules than linear electron transport.
Answer
Cyclic electron transport does not involve water splitting or NADPH synthesis, leading to fewer protons being pumped into the lumen compared to linear transport.
18
Question
What happens if QB is inhibited from oxidizing QA?
Answer
An inhibitor that prevents QB from oxidizing QA will not stop electron transport, as electron transport can still occur through cyclic pathways.
19
Question
Where does the PCR (Calvin-Benson-Basham) cycle take place?
Answer
The PCR cycle takes place in the stroma of the chloroplasts.
20
Question
How was radioactive C used to decipher the steps of the PCR cycle?
Answer
Radioactive C was used to trace carbon atoms through the cycle, allowing researchers to identify the sequence of reactions in the PCR cycle.
21
Question
What are the three major phases in the PCR cycle?
Answer
The three major phases in the PCR cycle are carbon fixation, reduction, and regeneration of RuBP.
22
Question
What happens to RuBP during carboxylation?
Answer
During carboxylation, RuBP (Ribulose-1,5-bisphosphate) reacts with CO2, leading to the formation of 3-phosphoglycerate (3-PGA).
23
Question
What are the consequences of adding glycoaldehyde to chloroplasts?
Answer
Adding glycoaldehyde inhibits phosphoribulokinase, leading to a decrease in RuBP regeneration and a halt in the PCR cycle, impacting the photochemical light-dependent reactions.
24
Question
What happens to the PCR Calvin cycle when stomata close due to drought?
Answer
When stomata close, the availability of CO2 decreases, negatively affecting the carboxylation phase of the PCR cycle and reducing photosynthesis.
25
Question
Why is oxygen a problem in photosynthesis?
Answer
Oxygen can lead to photorespiration, which decreases the efficiency of photosynthesis by consuming energy and releasing CO2.
26
Question
What is one hypothesis as to why Rubisco carries out both oxygenation and carboxylation reactions?
Answer
One hypothesis is that Rubisco evolved to optimize carbon fixation under varying environmental conditions, balancing its dual function.
27
Question
Why is oxygen a bigger problem under hot and dry conditions?
Answer
Under hot and dry conditions, stomata close to conserve water, decreasing CO2 concentration and increasing the likelihood of photorespiration.
28
Question
What are the costs and benefits of the PCO cycle?
Answer
The costs include energy expenditure and potential loss of carbon, while benefits include efficient carbon fixation and maximizing ATP production.
29
Question
Does the PCO cycle cost a plant an NADH?
Answer
Yes, the PCO cycle can be seen as costing a plant an NADH, as it involves redox reactions that utilize reducing power.
30
Question
How might a rise in CO2 concentration affect the carboxylation/oxygenation ratio in C3 plants?
Answer
A rise in CO2 concentration may increase the carboxylation rate, potentially leading to a higher carboxylation/oxygenation ratio.