Free Biodiversity and Variety of Life MCQs with Answers

141. Viruses that infect bacteria multiply and cause their lysis, are called

• A. Lysozymes
• B. Lipolytic
• C. Lytic
• D. Lysogenic

Explanation: Viruses that infect bacteria, multiply within them, and ultimately cause the lysis (bursting) of the bacterial host cells are called "Lytic" viruses. These viruses are often referred to as bacteriophages or phages. They are specifically designed to replicate inside bacterial hosts and lyse them, releasing new virus particles to infect other bacteria. Here's the breakdown of the options: Lysozymes: Lysozymes are enzymes found in various organisms, including humans, that can break down bacterial cell walls. They are not viruses. Lipolytic: Lipolytic enzymes are involved in the hydrolysis of lipids (fats), and they are not viruses. Lysogenic: Lysogenic viruses, in contrast to lytic viruses, can integrate their genetic material into the host's genome and replicate along with the host for an extended period without causing immediate lysis. They can switch to the lytic cycle later. So, the correct answer is "Lytic" when referring to viruses that cause bacterial lysis.

142. A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is

• A. Tolypothrix
• B. Chlorella
• C. Nostoc
• D. Anabaena

Explanation: a)Tolypothrix: Tolypothrix is another genus of filamentous cyanobacteria, but it is not typically associated with the water fern Azolla. It does not have the same symbiotic relationship as Anabaena. b)Chlorella: Chlorella is a green alga, not a cyanobacterium. While it can form symbiotic associations with certain organisms, it is not known for its nitrogen-fixing abilities. c)Nostoc: Nostoc is a genus of cyanobacteria, and like Anabaena, it is capable of nitrogen fixation. However, it is not commonly associated with the water fern Azolla. d)The free-living nitrogen-fixing cyanobacterium that can also form a symbiotic association with the water fern Azolla is "Anabaena." Anabaena is known for its ability to fix atmospheric nitrogen and establish symbiotic relationships with certain plants, including Azolla. This symbiotic association can benefit both the cyanobacterium and the host plant through nitrogen fixation and improved nitrogen nutrition. In summary, the correct answer is "Anabaena," as it is a well-known nitrogen-fixing cyanobacterium that can form a symbiotic relationship with Azolla. The other options are not typically associated with this specific symbiosis.

143. During replication of a bacterial chromosome, DNA synthesis starts from a replication origin site and

• A. RNA primers are involved
• B. is facilitated by telomerase
• C. moves in one direction of the site
• D. moves in bidirectional way.

Explanation: During replication of a bacterial chromosome, DNA synthesis starts from a replication origin site and moves in a bidirectional way. This means that replication begins at the origin of replication and proceeds in two directions along the chromosome, creating two replication forks. This bidirectional replication allows for the efficient and rapid duplication of the entire bacterial chromosome. The other options can be explained as follows: RNA primers are involved: In DNA replication, RNA primers are indeed involved. These primers provide a starting point for DNA polymerase to initiate DNA synthesis. However, the direction of replication is not determined by the presence of RNA primers. Is facilitated by telomerase: Telomerase is an enzyme involved in the maintenance of eukaryotic chromosome ends (telomeres) and is not typically found in bacteria. It is not directly related to the initiation or direction of bacterial DNA replication. Moves in one direction of the site: DNA replication in bacteria is bidirectional, meaning that it proceeds in two directions away from the origin site. It does not occur in only one direction. In summary, the correct statement is that DNA synthesis during bacterial chromosome replication starts from a replication origin site and moves bidirectionally.

144. Tobacco mosaic virus is a tubular filament of size

• A. 300 × 10 nm
• B. 300 × 5 nm
• C. 300 × 20 nm
• D. 700 × 30 nm.

Explanation: TMV is rod shaped measuring 300 × 20 nm. It is made of RNA and proteins.

145. Viruses are no more "alive" than isolated chromosomes because

• A. They require both RNA and DNA
• B. They both need food molecules
• C. They both require oxygen for respiration
• D. Both require the environment of a cell to replicate.

Explanation: a)They require both RNA and DNA: This statement is not accurate. Viruses can have either RNA or DNA as their genetic material, not both. They do not require both types of nucleic acids for their replication.b)They both need food molecules: Viruses do not need food molecules like living organisms do. They lack metabolic processes and do not engage in activities related to obtaining and utilizing nutrients for energy or growth. They rely on host cells for replication.c)They require oxygen for respiration: Viruses do not respire, and they do not require oxygen for metabolic processes because they do not perform respiration. They do not have the necessary cellular machinery for respiration.d)Viruses are no more "alive" than isolated chromosomes because they both require the environment of a cell to replicate. Viruses lack the cellular machinery and metabolic processes necessary to carry out the functions of living organisms on their own. Instead, they rely on infecting a host cell and hijacking its machinery to replicate and propagate.The correct answer is that both isolated chromosomes and viruses require the environment of a host cell to replicate because viruses, like isolated chromosomes, cannot replicate or carry out their life cycle independently and rely on a host cell to do so.

146. In which kingdom would you classify the archaea and nitrogen fixing organisms, if the five kingdom system of classification is used ?

• A. Plantae
• B. Fungi
• C. Protista
• D. Monera

Explanation: a)Plantae: The Plantae kingdom includes all plants. These are multicellular, eukaryotic organisms that perform photosynthesis and have cell walls primarily composed of cellulose. Plants are typically not associated with archaea or nitrogen-fixing organisms.b)Fungi:The Fungi kingdom includes various fungi, such as mushrooms, yeasts, and molds. These are eukaryotic, heterotrophic organisms that obtain nutrients through absorption. Fungi are not typically associated with archaea or nitrogen fixation.c)Protista: The Protista kingdom is a diverse group that includes various eukaryotic microorganisms, such as protozoa, algae, and certain microscopic organisms. While this kingdom encompasses a wide range of organisms, it doesn't typically include archaea or nitrogen-fixing organisms.d)Monera:Archaea are often considered a separate domain within the Monera kingdom due to their distinct genetic and biochemical characteristics. They are distinct from bacteria and are known for their ability to thrive in extreme environments.Nitrogen-fixing organisms: MoneraMany nitrogen-fixing organisms, such as certain bacteria like Rhizobium and cyanobacteria, fall within the Monera kingdom. They are prokaryotes responsible for converting atmospheric nitrogen into forms that plants can use.So, the correct answer is "Monera" for both archaea and nitrogen-fixing organisms in the five-kingdom classification system. Please note that modern classification systems have evolved beyond the five-kingdom model, and archaea are often recognized as a separate domain in a three-domain system along with Bacteria and Eukarya.In summary, archaea and nitrogen-fixing organisms, according to the five-kingdom system of classification, are primarily classified under the Monera kingdom due to their prokaryotic nature and unique characteristics

147. Which statement is correct for bacterial transduction?

• A. Transfer of some genes from one bacteria to another bacteria through virus.
• B. Transfer of genes from one bacteria to another bacteria by conjugation.
• C. Bacteria obtained its DNA directly from mother cell.
• D. Bacteria obtained DNA from other external source.

Explanation: a)Transfer of some genes from one bacteria to another bacteria through a virus (Correct): Bacterial transduction is a process where genes are transferred from one bacterium to another by a bacteriophage (a type of virus that infects bacteria). During this process, a bacteriophage may carry genetic material from one bacterium to another, leading to genetic recombination. b)Transfer of genes from one bacteria to another bacteria by conjugation: Conjugation is a different mechanism of gene transfer in bacteria. It involves direct cell-to-cell contact, typically through a sex pilus, where genetic material is transferred from a donor bacterium to a recipient bacterium. c)Bacteria obtained its DNA directly from the mother cell: This statement does not describe the process of bacterial transduction. Bacterial transduction involves the transfer of genes through a viral vector, not directly from a mother cell. d)Bacteria obtained DNA from other external sources: This option is too broad and doesn't specifically describe the process of bacterial transduction. While bacteria can acquire DNA from external sources, the context of transduction involves viral-mediated gene transfer. So, the correct answer is Option 1, which accurately describes bacterial transduction as the transfer of genes between bacteria through a virus.

148. The growth curve of bacterial population in lab is plotted against time. What will be the shape of graph?

• A. Sigmoid
• B. Hyperbolic
• C. Ascending straight line
• D. Descending straight line

Explanation: a)Sigmoid (Correct): In a controlled laboratory environment, bacterial populations often exhibit a sigmoid growth curve. Initially, there is a lag phase where bacteria adapt to the environment. This is followed by an exponential or logarithmic growth phase, where the population rapidly increases. Eventually, growth levels off, reaching a stationary phase, and can even decline in a death phase. The overall shape of this curve resembles an "S." b)Hyperbolic: A hyperbolic growth curve generally represents unlimited growth. It's not commonly observed for bacterial populations in laboratory settings, as resources are usually limited, leading to the sigmoidal curve instead. c)Ascending straight line: An ascending straight line would suggest continuous exponential growth without reaching a stationary phase or encountering limiting factors. This is rarely seen in laboratory cultures of bacteria. d)Descending straight line: A descending straight line would indicate a population decline or death phase. While this phase might occur eventually in a bacterial culture, it typically follows the stationary phase in a sigmoidal curve. Therefore, the most common shape for the bacterial growth curve in a lab is sigmoid, making Option 1 the correct choice.

149. Some bacteria are able to grow in streptomycin containing medium due to

• A. Natural selection
• B. Induced mutation
• C. Reproductive isolation
• D. Genetic drift.

Explanation: a)Natural Selection (Correct Answer): Bacteria can develop resistance to antibiotics through natural selection. In a population of bacteria, there can be variations in the presence of certain genetic mutations. When exposed to an antibiotic like streptomycin, the bacteria without the mutations are susceptible and die, while those with mutations that confer resistance survive. Over time, the resistant bacteria reproduce, passing on their resistance genes to the next generation. This process represents natural selection favoring antibiotic-resistant bacteria. b)Induced Mutation:Induced mutations occur when external factors, such as exposure to mutagenic agents (chemicals, radiation, etc.), lead to changes in the DNA of an organism. While mutations can create genetic diversity, allowing for the potential development of antibiotic resistance, the specific resistance to streptomycin in bacteria primarily results from natural selection. c)Reproductive Isolation:Reproductive isolation refers to mechanisms that prevent different species from interbreeding. It is not directly related to the development of antibiotic resistance in bacteria. Antibiotic resistance is primarily a genetic adaptation within a single bacterial species. d)Genetic Drift:Genetic drift is a mechanism that can cause changes in the frequency of particular genetic variants in a small population due to chance events. While it can lead to genetic changes over time, the development of antibiotic resistance is more directly related to natural selection in response to antibiotic exposure. In summary, natural selection is the most relevant and widely observed mechanism by which bacteria can develop antibiotic resistance when exposed to antibiotics like streptomycin. Other mechanisms, such as induced mutation, reproductive isolation, and genetic drift, may play roles in evolutionary processes but are less directly related to antibiotic resistance.

150. In bacteria, plasmid is

• A. Extra chromosomal material
• B. Main DNA
• C. Non functional DNA
• D. Repetitive gene.

Explanation: a)Extra-Chromosomal Material: Plasmids are small, circular pieces of DNA that exist independently of the bacterial chromosome. They are considered extra-chromosomal because they are separate from the main bacterial chromosome. b)Main DNA:The main DNA of bacteria is typically found in the bacterial chromosome, which is distinct from plasmids. Plasmids are not considered part of the primary or "main" DNA of the bacterium. c)Non-Functional DNA:Plasmids can contain functional genetic information, such as genes that provide antibiotic resistance or the ability to metabolize specific compounds. While some plasmids may carry non-functional or non-essential genes, many plasmids serve essential roles in bacterial survival and adaptation. d)Repetitive Gene: Plasmids can carry specific genes, and some plasmids may carry multiple copies of the same gene. However, not all plasmids contain repetitive genes. The presence of repetitive genes on a plasmid depends on the specific plasmid's genetic content. In summary, plasmids are indeed extra-chromosomal material in bacteria, separate from the primary bacterial chromosome. They can carry various functional genes and are not limited to non-functional DNA. While some plasmids may contain repetitive genes, this is not a defining characteristic of all plasmids.