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The O2 produced by plants during photosynthesis is glucose. Glucose is a simple sugar that serves as the primary source of energy for the plant and is also used as a building block for other organic molecules.
During photosynthesis, plants use sunlight, carbon dioxide, and water to produce glucose and oxygen. The chemical equation for photosynthesis is:
6CO2 + 6H2O + light energy → C6H12O6 + 6O2
This process occurs in the chloroplasts of plant cells, where the pigment chlorophyll absorbs light energy and converts it into chemical energy. This energy is used to convert carbon dioxide and water into glucose and oxygen.
The production of glucose only occurs during daylight hours because it requires light energy. Without sunlight, the chlorophyll cannot absorb the necessary energy to drive the photosynthetic reactions. As a result, plants only produce glucose and oxygen when they are exposed to light. During the night, plants rely on stored glucose for energy and other metabolic processes.
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The conversion of 3-phosphoglycerate int...View Answer
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A) chlorophyll a
B) carotene
C) pheophytin a
D) lutein
E) both chlorophyll a and carotene
G) B) and E)
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A) dihydroxyacetone phosphate
B) fructose 2,6-bisphosphate
C) glucose 1-phosphate
D) 6-phosphogluconate
E) xylulose 5-phosphate
G) B) and D)
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A) glucose and fructose.
B) UDP-glucose and fructose 6-phosphate.
C) UDP-fructose and glucose 6-phosphate.
D) UDP-glucose and fructose.
E) UDP-glucose and UDP-fructose.
G) A) and B)
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A) erythrose 4-phosphate
B) glyceraldehyde 3-phosphate
C) mannose 6-phosphate
D) ribulose 5-phosphate
E) sedoheptulose 7-phosphate
G) A) and E)
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C
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Sucrose is synthesized from glucose 6-ph...View Answer
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A) It can be uncoupled from electron flow by agents that dissipate the proton gradient.
B) The difference in pH between the luminal and stromal side of the thylakoid membrane is 3 pH units.
C) The luminal side of the thylakoid membrane has a higher pH than the stromal side.
D) The number of ATPs formed per oxygen molecule is about three.
E) The reaction centers, electron carriers, and ATP-forming enzymes are located in the thylakoid membrane.
G) B) and E)
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A) fructose-6-phosphate
B) glucose-6-phosphate
C) UDP-glucose
D) sucrose-6-phosphate
E) glucose-1-phosphate
G) B) and C)
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The Calvin cycle is a series of biochemi...View Answer
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A) increased stromal pH.
B) light-driven entry of Mg2+ into the stroma.
C) phosphorylation by cAMP-dependent protein kinase.
D) phosphorylation of phosphoenolpyruvate carboxylase.
E) reduction of a disulfide bridge by thioredoxin.
G) A) and D)
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Plants primarily produce glucose through the process of photosynthesis. However, glucose is not the main form in which they transport sugars from the leaves (where photosynthesis occurs) to other parts of the plant. Instead, plants convert glucose into sucrose for transport, and there are several reasons why sucrose is the preferred molecule for this purpose:
1. Energy Efficiency: Sucrose is a disaccharide composed of one molecule of glucose and one molecule of fructose. This configuration allows plants to transport twice the amount of carbon per molecule compared to glucose alone, making it a more energy-efficient transport form.
2. Reduced Osmotic Pressure: Sucrose is less reactive and less osmotically active than glucose. If glucose were transported in high concentrations, it would cause water to enter the phloem (the plant's vascular tissue for transporting nutrients) by osmosis, potentially leading to issues with water balance. Sucrose allows for the transport of a high concentration of carbon without significantly affecting the osmotic balance.
3. Stability: Sucrose is a non-reducing sugar, which means it does not readily participate in reduction-oxidation reactions that can break down sugars. This stability is beneficial during transport as it reduces the risk of the sugar being metabolized or degraded before it reaches its destination.
4. Storage and Mobilization: Sucrose can be easily converted back into glucose and fructose, or into other forms like starch for storage. This flexibility allows plants to efficiently move carbon around to where it is needed, whether for immediate energy, growth, or storage for later use.
5. Phloem Loading and Unloading: The process of moving sucrose into and out of the phloem (phloem loading and unloading) is well-regulated by the plant. Sucrose can be actively transported against its concentration gradient into the phloem, and then later removed at the site where it is needed. This targeted delivery system is crucial for the plant's overall resource management.
6. Reduced Risk of Pathogen Attraction: Simple sugars like glucose can be signals for pathogens, attracting them to the site of sugar availability. By transporting sucrose instead of glucose, plants may reduce the risk of pathogen attack during the transport process.
In summary, the use of sucrose as the transport form of carbon in plants is a result of its energy efficiency, reduced osmotic effects, stability, ease of conversion for storage or use, efficient phloem loading and unloading, and potentially reduced attraction of pathogens. These advantages make sucrose an ideal carbohydrate for long-distance transport within the plant's vascular system.
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A) involve addition of a sugar residue at the reducing end of the growing polymer.
B) take place in liver and muscle of mammals.
C) use a sugar nucleotide as substrate.
D) use glucose 1-phosphate as the only substrate.
E) use glucose-6-phosphate as substrate.
G) A) and B)
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A) only QA is an isoprenoid.
B) QA is a prosthetic group for photosystem II, while QB is a cosubstrate.
C) QA will only accept single electrons, while QB will accept two electrons.
D) only QA is an isoprenoid, and QA is a prosthetic group for photosystem II, while QB is a cosubstrate.
E) QA is a prosthetic group for photosystem II, while QB is a cosubstrate, and QA will only accept single electrons, while QB will accept two electrons.
G) A) and C)
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A) aldolase
B) glyceraldehyde 3-phosphate dehydrogenase
C) phosphofructokinase-1
D) ribulose-5-phosphate kinase
E) transketolase
G) C) and D)
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An action spectrum is a graphical repres...View Answer
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Plants and some microorganisms have the ...View Answer
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A) chloroplast.
B) endoplasmic reticulum.
C) mitochondrion.
D) cell membrane.
E) peroxisome.
G) C) and D)
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A) It is driven by light.
B) It oxidizes substrates to CO2.
C) It produces O2.
D) It results from a lack of specificity of the enzyme rubisco.
E) It results in no fixation of carbon.
G) B) and D)
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A) integral membrane proteins.
B) found on the lumen side of thylakoid membranes.
C) proteins that interact with photosystem I.
D) All of the answers are correct.
E) None of the answers is correct.
G) A) and D)
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