Bio205 CCS SU26 Microbiology (202620785) Cochise College
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Free Bio205 CCS SU26 Microbiology (202620785) Cochise College Questions
1. In the name Staphylococcus aureus, Staphylococcus is the _____ and aureus is the _____.
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species, genus
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domain, kingdom
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genus, species
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family, class
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kingdom, domain
Explanation
Explanation
Correct Answer: (C) Genus, species
In binomial nomenclature, the naming convention established by Carolus Linnaeus, every organism is given a two-part Latin name. The first word, always capitalized, denotes the genus, and the second word, written in lowercase, denotes the species. Therefore in Staphylococcus aureus, Staphylococcus is the genus and aureus is the species epithet. This system allows for precise, universally recognized identification of organisms.
Why the other options are incorrect:
A. Species, genus — This reverses the correct order. The first name is always genus, not species.
B. Domain, kingdom — Domain and kingdom are broader taxonomic levels far above genus and species. They are not represented in a binomial name.
D. Family, class — These are also higher-level taxonomic classifications and are not components of a binomial scientific name.
E. Kingdom, domain — Like options B and D, these represent upper-level taxonomy and are not part of the two-part binomial naming system.
Correct Answer: (C) Genus, species
In binomial nomenclature, the naming convention established by Carolus Linnaeus, every organism is given a two-part Latin name. The first word, always capitalized, denotes the genus, and the second word, written in lowercase, denotes the species. Therefore in Staphylococcus aureus, Staphylococcus is the genus and aureus is the species epithet. This system allows for precise, universally recognized identification of organisms.
Why the other options are incorrect:
A. Species, genus — This reverses the correct order. The first name is always genus, not species.
B. Domain, kingdom — Domain and kingdom are broader taxonomic levels far above genus and species. They are not represented in a binomial name.
D. Family, class — These are also higher-level taxonomic classifications and are not components of a binomial scientific name.
E. Kingdom, domain — Like options B and D, these represent upper-level taxonomy and are not part of the two-part binomial naming system.
2. Which statement best describes anabolism?
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It occurs only when oxygen is absent.
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It builds complex molecules and requires energy.
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It produces ATP only through fermentation.
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It breaks down molecules and is usually exergonic.
Explanation
Explanation
Correct Answer: (B) It builds complex molecules and requires energy.
Anabolism refers to the constructive metabolic processes by which cells synthesize complex molecules from simpler precursors. Examples include protein synthesis from amino acids, DNA replication, and the synthesis of polysaccharides and lipids. These biosynthetic reactions are endergonic, meaning they require an input of energy, typically in the form of ATP.
Why Other Options are Incorrect:
A. It occurs only when oxygen is absent — Anabolism is not restricted to anaerobic conditions. Biosynthetic reactions occur under both aerobic and anaerobic conditions depending on the organism and cellular environment.
C. It produces ATP only through fermentation — Anabolism consumes ATP rather than producing it. ATP production through fermentation or respiration is a catabolic process, not an anabolic one.
D. It breaks down molecules and is usually exergonic — This describes catabolism, which is the opposite of anabolism. Catabolic reactions break down complex molecules, release energy, and are generally exergonic.
Correct Answer: (B) It builds complex molecules and requires energy.
Anabolism refers to the constructive metabolic processes by which cells synthesize complex molecules from simpler precursors. Examples include protein synthesis from amino acids, DNA replication, and the synthesis of polysaccharides and lipids. These biosynthetic reactions are endergonic, meaning they require an input of energy, typically in the form of ATP.
Why Other Options are Incorrect:
A. It occurs only when oxygen is absent — Anabolism is not restricted to anaerobic conditions. Biosynthetic reactions occur under both aerobic and anaerobic conditions depending on the organism and cellular environment.
C. It produces ATP only through fermentation — Anabolism consumes ATP rather than producing it. ATP production through fermentation or respiration is a catabolic process, not an anabolic one.
D. It breaks down molecules and is usually exergonic — This describes catabolism, which is the opposite of anabolism. Catabolic reactions break down complex molecules, release energy, and are generally exergonic.
3. Fermentation is the other form of carbohydrate catabolism, and it uses ______ as the final electron acceptor. It synthesizes ATP via ______ phosphorylation. The 2 steps of fermentation are 1. ______ and 2. ______.
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an organic molecule / substrate-level / glycolysis / reduction of pyruvic acid
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oxygen / oxidative / glycolysis / Kreb's cycle
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NADH / photo / reduction of oxygen / electron transport chain
-
an inorganic molecule / substrate-level / glycolysis / reduction of oxygen
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an organic molecule / oxidative / Kreb's cycle / reduction of pyruvic acid
Explanation
Explanation
Correct Answer Is:
(A) An organic molecule / substrate-level / glycolysis / reduction of pyruvic acid
Fermentation is an anaerobic process that uses an organic molecule, typically pyruvate or one of its derivatives, as the final electron acceptor rather than oxygen or an inorganic molecule. ATP is produced exclusively through substrate-level phosphorylation, meaning phosphate is transferred directly from a phosphorylated intermediate to ADP without involvement of the electron transport chain. The two steps of fermentation are glycolysis, in which glucose is broken down to pyruvate generating 2 net ATP and 2 NADH, followed by the reduction of pyruvic acid, in which pyruvate accepts electrons from NADH to regenerate NAD⁺ and produce fermentation end products such as lactic acid or ethanol and CO₂.
Why the other options are incorrect:
B. Oxygen / oxidative / glycolysis / Kreb's cycle — Oxygen as a final electron acceptor and oxidative phosphorylation define aerobic respiration, not fermentation. The Krebs cycle is also not a step in fermentation.
C. NADH / photo / reduction of oxygen / electron transport chain — NADH is an electron carrier produced during fermentation, not the final electron acceptor. Photophosphorylation is associated with photosynthesis. Fermentation does not involve oxygen reduction or an electron transport chain.
D. An inorganic molecule / substrate-level / glycolysis / reduction of oxygen — Using an inorganic molecule other than oxygen as the final electron acceptor defines anaerobic respiration, not fermentation. Fermentation uses an organic molecule and does not reduce oxygen.
E. An organic molecule / oxidative / Kreb's cycle / reduction of pyruvic acid — While the electron acceptor and final step are partially correct, fermentation uses substrate-level phosphorylation, not oxidative phosphorylation. The Krebs cycle is not a step in fermentation; it is part of aerobic respiration.
Correct Answer Is:
(A) An organic molecule / substrate-level / glycolysis / reduction of pyruvic acid
Fermentation is an anaerobic process that uses an organic molecule, typically pyruvate or one of its derivatives, as the final electron acceptor rather than oxygen or an inorganic molecule. ATP is produced exclusively through substrate-level phosphorylation, meaning phosphate is transferred directly from a phosphorylated intermediate to ADP without involvement of the electron transport chain. The two steps of fermentation are glycolysis, in which glucose is broken down to pyruvate generating 2 net ATP and 2 NADH, followed by the reduction of pyruvic acid, in which pyruvate accepts electrons from NADH to regenerate NAD⁺ and produce fermentation end products such as lactic acid or ethanol and CO₂.
Why the other options are incorrect:
B. Oxygen / oxidative / glycolysis / Kreb's cycle — Oxygen as a final electron acceptor and oxidative phosphorylation define aerobic respiration, not fermentation. The Krebs cycle is also not a step in fermentation.
C. NADH / photo / reduction of oxygen / electron transport chain — NADH is an electron carrier produced during fermentation, not the final electron acceptor. Photophosphorylation is associated with photosynthesis. Fermentation does not involve oxygen reduction or an electron transport chain.
D. An inorganic molecule / substrate-level / glycolysis / reduction of oxygen — Using an inorganic molecule other than oxygen as the final electron acceptor defines anaerobic respiration, not fermentation. Fermentation uses an organic molecule and does not reduce oxygen.
E. An organic molecule / oxidative / Kreb's cycle / reduction of pyruvic acid — While the electron acceptor and final step are partially correct, fermentation uses substrate-level phosphorylation, not oxidative phosphorylation. The Krebs cycle is not a step in fermentation; it is part of aerobic respiration.
4. Match the scientists to their contribution to microbiology.
Alexander Fleming — ?
Edward Jenner — ?
Robert Hooke — ?
Louis Pasteur — ?
Carolus Linnaeus — ?
Ignaz Semmelweis — ?
Rudolf Virchow — ?
Anton van Leeuwenhoek — ?
- Alexander Fleming — Discovered the first antibiotic
- Edward Jenner — Vaccinations
- Robert Hooke — First to observe cells
- Louis Pasteur — Theory of biogenesis / silkworm disease was caused by microbes
- Carolus Linnaeus — Formal system for classifying and naming organisms
- Ignaz Semmelweis — Handwashing to prevent disease
- Rudolf Virchow — Theory of biogenesis / fermentation
- Anton van Leeuwenhoek — First to observe microorganisms
Explanation
Explanation
Correct Answers:
Alexander Fleming — Discovered the first antibiotic Fleming discovered penicillin in 1928 after observing that the mold Penicillium notatum inhibited bacterial growth on a culture plate, revolutionizing the treatment of bacterial infections.
Edward Jenner — Vaccinations Jenner developed the first vaccine in 1796 using cowpox material to protect against smallpox, laying the foundation for the entire field of immunization.
Robert Hooke — First to observe cells Hooke first described and named cells in 1665 after observing cork tissue under a compound microscope in his publication Micrographia.
Louis Pasteur — Theory of biogenesis / silkworm disease was caused by microbes Pasteur disproved spontaneous generation and established that life arises from pre-existing life (biogenesis). He also demonstrated that silkworm disease was caused by microbes and developed the process of pasteurization.
Carolus Linnaeus — Formal system for classifying and naming organisms Linnaeus developed binomial nomenclature, the standardized two-part Latin naming system for all living organisms that remains the foundation of modern taxonomy.
Ignaz Semmelweis — Handwashing to prevent disease Semmelweis demonstrated in the 1840s that handwashing by physicians dramatically reduced puerperal fever and maternal mortality, pioneering antiseptic practice in medicine.
Rudolf Virchow — Theory of biogenesis / fermentation Virchow advanced cell theory by establishing that all cells arise from pre-existing cells, contributing to the broader theory of biogenesis.
Anton van Leeuwenhoek — First to observe microorganisms Leeuwenhoek was the first to observe and describe living microorganisms using his hand-crafted microscopes in the 1670s, earning him the title Father of Microbiology.
Correct Answers:
Alexander Fleming — Discovered the first antibiotic Fleming discovered penicillin in 1928 after observing that the mold Penicillium notatum inhibited bacterial growth on a culture plate, revolutionizing the treatment of bacterial infections.
Edward Jenner — Vaccinations Jenner developed the first vaccine in 1796 using cowpox material to protect against smallpox, laying the foundation for the entire field of immunization.
Robert Hooke — First to observe cells Hooke first described and named cells in 1665 after observing cork tissue under a compound microscope in his publication Micrographia.
Louis Pasteur — Theory of biogenesis / silkworm disease was caused by microbes Pasteur disproved spontaneous generation and established that life arises from pre-existing life (biogenesis). He also demonstrated that silkworm disease was caused by microbes and developed the process of pasteurization.
Carolus Linnaeus — Formal system for classifying and naming organisms Linnaeus developed binomial nomenclature, the standardized two-part Latin naming system for all living organisms that remains the foundation of modern taxonomy.
Ignaz Semmelweis — Handwashing to prevent disease Semmelweis demonstrated in the 1840s that handwashing by physicians dramatically reduced puerperal fever and maternal mortality, pioneering antiseptic practice in medicine.
Rudolf Virchow — Theory of biogenesis / fermentation Virchow advanced cell theory by establishing that all cells arise from pre-existing cells, contributing to the broader theory of biogenesis.
Anton van Leeuwenhoek — First to observe microorganisms Leeuwenhoek was the first to observe and describe living microorganisms using his hand-crafted microscopes in the 1670s, earning him the title Father of Microbiology.
5. In noncyclic photophosphorylation, O₂ is produced from ______.
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CO₂
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H₂O
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C₆H₁₂O₆
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Sunlight
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Chlorophyll
Explanation
Explanation
Correct Answer: (B) H₂O
In noncyclic photophosphorylation, which occurs in oxygenic photosynthesis, water molecules are split in a process called photolysis during the light-dependent reactions. This splitting of water releases electrons to replace those lost by chlorophyll, produces hydrogen ions that contribute to the proton gradient for ATP synthesis, and releases molecular oxygen as a byproduct. The oxygen we breathe is entirely derived from the photolysis of water during this process.
Why Other Options are Incorrect:
A. CO₂ — Carbon dioxide is fixed during the Calvin cycle in the light-independent reactions to produce glucose. It is not the source of oxygen produced in noncyclic photophosphorylation.
C. C₆H₁₂O₆ — Glucose is a product of photosynthesis, not a reactant in the light reactions. It is not the source of oxygen production.
D. Sunlight — Sunlight provides the energy that drives photophosphorylation and activates chlorophyll, but light itself is not the molecular source of oxygen. Water is the molecule that is split to release O₂.
E. Chlorophyll — Chlorophyll is the pigment that absorbs light energy and becomes excited, initiating the electron transport process. It is not the source of molecular oxygen released during the reaction.
Correct Answer: (B) H₂O
In noncyclic photophosphorylation, which occurs in oxygenic photosynthesis, water molecules are split in a process called photolysis during the light-dependent reactions. This splitting of water releases electrons to replace those lost by chlorophyll, produces hydrogen ions that contribute to the proton gradient for ATP synthesis, and releases molecular oxygen as a byproduct. The oxygen we breathe is entirely derived from the photolysis of water during this process.
Why Other Options are Incorrect:
A. CO₂ — Carbon dioxide is fixed during the Calvin cycle in the light-independent reactions to produce glucose. It is not the source of oxygen produced in noncyclic photophosphorylation.
C. C₆H₁₂O₆ — Glucose is a product of photosynthesis, not a reactant in the light reactions. It is not the source of oxygen production.
D. Sunlight — Sunlight provides the energy that drives photophosphorylation and activates chlorophyll, but light itself is not the molecular source of oxygen. Water is the molecule that is split to release O₂.
E. Chlorophyll — Chlorophyll is the pigment that absorbs light energy and becomes excited, initiating the electron transport process. It is not the source of molecular oxygen released during the reaction.
6. Treatment of disease with chemicals is called ______.
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chemo
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medication
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antimicrobial therapy
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chemotherapy
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All of these
Explanation
Explanation
Correct Answer Is:
D
In its broadest scientific definition, chemotherapy refers to the treatment of disease using chemical agents. While the term is commonly associated in clinical practice with cancer treatment, its original and technical meaning encompasses any use of chemical substances to treat disease, including antibiotics, antifungals, and antivirals. This broader definition originates from Paul Ehrlich's work in the early twentieth century developing chemical treatments for infectious diseases.
Why the other options are incorrect:
A. Chemo — Chemo is an informal abbreviation used colloquially to refer specifically to cancer chemotherapy. It is not the precise scientific term for chemical treatment of disease broadly.
B. Medication — Medication is a general term for any substance used to treat, cure, or prevent disease and is not specific to chemical-based disease treatment in the scientific sense.
C. Antimicrobial therapy — Antimicrobial therapy refers specifically to treatment targeting microorganisms such as bacteria, fungi, and viruses. It is a subcategory of chemotherapy, not a synonym for the broader concept.
E. All of these — While there is overlap among these terms in everyday usage, chemotherapy is the single most precise and scientifically accurate term for treatment of disease with chemicals as defined in microbiology and pharmacology.
Correct Answer Is:
D
In its broadest scientific definition, chemotherapy refers to the treatment of disease using chemical agents. While the term is commonly associated in clinical practice with cancer treatment, its original and technical meaning encompasses any use of chemical substances to treat disease, including antibiotics, antifungals, and antivirals. This broader definition originates from Paul Ehrlich's work in the early twentieth century developing chemical treatments for infectious diseases.
Why the other options are incorrect:
A. Chemo — Chemo is an informal abbreviation used colloquially to refer specifically to cancer chemotherapy. It is not the precise scientific term for chemical treatment of disease broadly.
B. Medication — Medication is a general term for any substance used to treat, cure, or prevent disease and is not specific to chemical-based disease treatment in the scientific sense.
C. Antimicrobial therapy — Antimicrobial therapy refers specifically to treatment targeting microorganisms such as bacteria, fungi, and viruses. It is a subcategory of chemotherapy, not a synonym for the broader concept.
E. All of these — While there is overlap among these terms in everyday usage, chemotherapy is the single most precise and scientifically accurate term for treatment of disease with chemicals as defined in microbiology and pharmacology.
7. Which of the illustrations in Figure 1.1 has an axial filament?
-
a
-
b
-
c
-
d
-
e
Explanation
Explanation
Figure 1.1 illustration a shows a spirochete, which is a helically coiled bacterium. Spirochetes possess a unique internal motility structure called an axial filament, also known as periplasmic flagella. These flagella are located between the inner and outer membranes of the cell envelope and wrap around the cell body, causing the characteristic corkscrew-like rotation that propels the organism through viscous environments. Examples of spirochetes with axial filaments include Treponema pallidum and Borrelia burgdorferi.
Why the other options are incorrect:
B. b — Illustration b appears to show cocci, which are spherical bacteria. Cocci do not possess axial filaments and are non-motile in most cases.
C. c — Illustration c appears to show a chain of cocci such as streptococci. These organisms do not have axial filaments.
D. d — Illustration d appears to show a different bacterial morphology without the defining spirochete structure needed for axial filament presence.
E. e — Illustration e appears to show a bacterium with external flagella, which are standard external appendages distinct from the internal axial filament found in spirochetes.
Figure 1.1 illustration a shows a spirochete, which is a helically coiled bacterium. Spirochetes possess a unique internal motility structure called an axial filament, also known as periplasmic flagella. These flagella are located between the inner and outer membranes of the cell envelope and wrap around the cell body, causing the characteristic corkscrew-like rotation that propels the organism through viscous environments. Examples of spirochetes with axial filaments include Treponema pallidum and Borrelia burgdorferi.
Why the other options are incorrect:
B. b — Illustration b appears to show cocci, which are spherical bacteria. Cocci do not possess axial filaments and are non-motile in most cases.
C. c — Illustration c appears to show a chain of cocci such as streptococci. These organisms do not have axial filaments.
D. d — Illustration d appears to show a different bacterial morphology without the defining spirochete structure needed for axial filament presence.
E. e — Illustration e appears to show a bacterium with external flagella, which are standard external appendages distinct from the internal axial filament found in spirochetes.
8. The second step of respiration is ______, which is the oxidation of the coenzyme ______, and it happens twice. This yields a net gain of ______ ATP, ______ NADH, and ______ FADH₂.
-
The Kreb's cycle / pyruvic acids / 2 / 8 / 2
-
Glycolysis / glucose / 4 / 2 / 0
-
The electron transport chain / NADH / 1 / 4 / 2
-
The Kreb's cycle / pyruvic acids / 2 / 6 / 2
-
Fermentation / glucose / 2 / 2 / 0
Explanation
Explanation
Correct Answer: (A) The Kreb's cycle / pyruvic acids / 2 / 8 / 2
The second stage of aerobic respiration is the Krebs cycle (also called the citric acid cycle), which takes place in the mitochondrial matrix in eukaryotes or the cytoplasm in prokaryotes. Before entering the Krebs cycle, each pyruvic acid molecule is oxidized and converted to acetyl-CoA in the pyruvate oxidation step. The Krebs cycle itself runs twice per glucose molecule (once for each pyruvate). Per complete cycle for one glucose molecule, the Krebs cycle yields a net gain of 2 ATP (1 per turn via substrate-level phosphorylation), 8 NADH (including those from pyruvate oxidation), and 2 FADH₂. These electron carriers then deliver their electrons to the electron transport chain for the majority of ATP production.
Why the other options are incorrect:
B. Glycolysis / glucose / 4 / 2 / 0 — Glycolysis is the first stage of respiration, not the second. It does not involve FADH₂ and produces only 2 net ATP and 2 NADH.
C. The electron transport chain / NADH / 1 / 4 / 2 — The electron transport chain is the third and final stage of aerobic respiration, not the second. It uses NADH and FADH₂ as inputs rather than oxidizing pyruvic acids directly.
D. The Kreb's cycle / pyruvic acids / 2 / 6 / 2 — The stage and ATP and FADH₂ counts are correct, but the NADH count of 6 is incorrect. When including NADH generated during pyruvate oxidation (2 NADH) plus the Krebs cycle itself (6 NADH), the total NADH per glucose is 8.
E. Fermentation / glucose / 2 / 2 / 0 — Fermentation is not a stage of aerobic respiration. It is an alternative anaerobic pathway that bypasses the Krebs cycle and electron transport chain entirely and produces no FADH₂.
Correct Answer: (A) The Kreb's cycle / pyruvic acids / 2 / 8 / 2
The second stage of aerobic respiration is the Krebs cycle (also called the citric acid cycle), which takes place in the mitochondrial matrix in eukaryotes or the cytoplasm in prokaryotes. Before entering the Krebs cycle, each pyruvic acid molecule is oxidized and converted to acetyl-CoA in the pyruvate oxidation step. The Krebs cycle itself runs twice per glucose molecule (once for each pyruvate). Per complete cycle for one glucose molecule, the Krebs cycle yields a net gain of 2 ATP (1 per turn via substrate-level phosphorylation), 8 NADH (including those from pyruvate oxidation), and 2 FADH₂. These electron carriers then deliver their electrons to the electron transport chain for the majority of ATP production.
Why the other options are incorrect:
B. Glycolysis / glucose / 4 / 2 / 0 — Glycolysis is the first stage of respiration, not the second. It does not involve FADH₂ and produces only 2 net ATP and 2 NADH.
C. The electron transport chain / NADH / 1 / 4 / 2 — The electron transport chain is the third and final stage of aerobic respiration, not the second. It uses NADH and FADH₂ as inputs rather than oxidizing pyruvic acids directly.
D. The Kreb's cycle / pyruvic acids / 2 / 6 / 2 — The stage and ATP and FADH₂ counts are correct, but the NADH count of 6 is incorrect. When including NADH generated during pyruvate oxidation (2 NADH) plus the Krebs cycle itself (6 NADH), the total NADH per glucose is 8.
E. Fermentation / glucose / 2 / 2 / 0 — Fermentation is not a stage of aerobic respiration. It is an alternative anaerobic pathway that bypasses the Krebs cycle and electron transport chain entirely and produces no FADH₂.
9. Which statement best distinguishes oxidation from reduction?
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Oxidation occurs only in photosynthesis, while reduction occurs only in fermentation.
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Oxidation loses electrons, while reduction gains electrons.
-
Both oxidation and reduction involve only ATP production.
-
Oxidation gains electrons, while reduction loses electrons.
Explanation
Explanation
Correct Answer: (B) Oxidation loses electrons, while reduction gains electrons.
Oxidation and reduction always occur together as coupled redox reactions. Oxidation is defined as the loss of electrons from a molecule, while reduction is the gain of electrons. A useful mnemonic is OIL RIG: Oxidation Is Loss, Reduction Is Gain. These processes are fundamental to cellular respiration, photosynthesis, and many metabolic reactions in which electron transfer drives energy production.
Why Other Options are Incorrect:
A. Oxidation occurs only in photosynthesis, while reduction occurs only in fermentation — Both oxidation and reduction occur in virtually all metabolic pathways including respiration, photosynthesis, and fermentation. They are not confined to specific pathways.
C. Both oxidation and reduction involve only ATP production — ATP production is one outcome of redox reactions in cellular respiration, but oxidation and reduction are electron transfer processes that occur across many reactions not directly linked to ATP synthesis.
D. Oxidation gains electrons, while reduction loses electrons — This reverses the correct definitions. Oxidation involves electron loss and reduction involves electron gain.
Correct Answer: (B) Oxidation loses electrons, while reduction gains electrons.
Oxidation and reduction always occur together as coupled redox reactions. Oxidation is defined as the loss of electrons from a molecule, while reduction is the gain of electrons. A useful mnemonic is OIL RIG: Oxidation Is Loss, Reduction Is Gain. These processes are fundamental to cellular respiration, photosynthesis, and many metabolic reactions in which electron transfer drives energy production.
Why Other Options are Incorrect:
A. Oxidation occurs only in photosynthesis, while reduction occurs only in fermentation — Both oxidation and reduction occur in virtually all metabolic pathways including respiration, photosynthesis, and fermentation. They are not confined to specific pathways.
C. Both oxidation and reduction involve only ATP production — ATP production is one outcome of redox reactions in cellular respiration, but oxidation and reduction are electron transfer processes that occur across many reactions not directly linked to ATP synthesis.
D. Oxidation gains electrons, while reduction loses electrons — This reverses the correct definitions. Oxidation involves electron loss and reduction involves electron gain.
10. Viruses are not technically considered living organisms because they ______.
-
are structurally very simple.
-
can only be visualized using an electron microscope.
-
are ubiquitous in nature.
-
cannot reproduce by themselves.
-
are typically associated with disease.
Explanation
Explanation
Correct Answer: (D) Cannot reproduce by themselves.
One of the fundamental criteria for life is the ability to independently reproduce. Viruses lack the cellular machinery, including ribosomes, enzymes, and energy-producing organelles, necessary for self-replication. They can only reproduce by infecting a living host cell and hijacking its metabolic processes. Because they are entirely dependent on a host for replication and cannot carry out any metabolic activity independently, viruses do not meet the scientific criteria to be classified as living organisms.
Why the other options are incorrect:
A. Are structurally very simple — Structural simplicity alone does not exclude an entity from being classified as living. Many living organisms such as bacteria and archaea are structurally simple but are still considered alive.
B. Can only be visualized using an electron microscope — Size and visibility have no bearing on whether something is classified as living. Many living microorganisms also require microscopy for visualization.
C. Are ubiquitous in nature — Being widespread in nature is a characteristic shared by many living organisms and is not a criterion that determines whether something is classified as living or non-living.
E. Are typically associated with disease — Many living organisms including bacteria, fungi, and parasites cause disease. Disease association is irrelevant to the classification of something as living or non-living.
Correct Answer: (D) Cannot reproduce by themselves.
One of the fundamental criteria for life is the ability to independently reproduce. Viruses lack the cellular machinery, including ribosomes, enzymes, and energy-producing organelles, necessary for self-replication. They can only reproduce by infecting a living host cell and hijacking its metabolic processes. Because they are entirely dependent on a host for replication and cannot carry out any metabolic activity independently, viruses do not meet the scientific criteria to be classified as living organisms.
Why the other options are incorrect:
A. Are structurally very simple — Structural simplicity alone does not exclude an entity from being classified as living. Many living organisms such as bacteria and archaea are structurally simple but are still considered alive.
B. Can only be visualized using an electron microscope — Size and visibility have no bearing on whether something is classified as living. Many living microorganisms also require microscopy for visualization.
C. Are ubiquitous in nature — Being widespread in nature is a characteristic shared by many living organisms and is not a criterion that determines whether something is classified as living or non-living.
E. Are typically associated with disease — Many living organisms including bacteria, fungi, and parasites cause disease. Disease association is irrelevant to the classification of something as living or non-living.
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