All Free Biology MCQs with Answers

2551. There exists a close association between the alga and the fungus within a lichen. The fungus

• A. Provides protection, anchorage and absorption for the algae
• B. Provides food for the alga
• C. Fixes the atmospheric nitrogen for the alga
• D. Releases oxygen for the alga.

Explanation: In a lichen, the association between the alga and the fungus is a mutualistic one, where both partners benefit: The fungus provides protection, anchorage, and absorption for the algae: The fungal partner forms a protective structure around the algal cells, which helps shield them from harsh environmental conditions and provides a stable substrate to grow on. The fungal partner also aids in the absorption of water and nutrients from the environment. The alga provides food for the fungus: The algal partner, through photosynthesis, produces organic compounds (such as sugars) using sunlight and carbon dioxide. These compounds serve as a source of nutrition for the fungal partner. The association typically does not involve nitrogen fixation: Nitrogen fixation is not a primary role of the fungus in the lichen symbiosis. The association does not involve the release of oxygen: While photosynthesis by the algal partner generates oxygen, the primary benefit to the fungus is the food produced by the alga. So, the correct statement is that the fungus provides protection, anchorage, and absorption for the algae, and the algae provide food for the fungus.

2552. Which of the following statements is not true for retroviruses?

• A. DNA is not present at any stage in the life cycle of retroviruses.
• B. Retroviruses carry gene for RNA dependent DNA polymerase.
• C. The genetic material in mature retroviruses is RNA.
• D. Retroviruses are causative agents for ertain kinds of cancer in man.

Explanation: a) "DNA is not present at any stage in the life cycle of retroviruses" - This statement is not true. Retroviruses have a unique life cycle that involves the conversion of their RNA genome into DNA. They carry the gene for reverse transcriptase, an enzyme that allows them to synthesize a DNA copy of their RNA genome once they infect a host cell. This DNA form is integrated into the host cell's genome.b) "Retroviruses carry the gene for RNA-dependent DNA polymerase" - This statement is true. Retroviruses carry the gene for reverse transcriptase, which is also known as RNA-dependent DNA polymerase. This enzyme is responsible for transcribing the viral RNA into DNA.c) "The genetic material in mature retroviruses is RNA" - This statement is true. Retroviruses store their genetic information as RNA. However, during the replication process, they reverse transcribe this RNA into DNA, which becomes integrated into the host cell's genome.d) "Retroviruses are causative agents for certain kinds of cancer in man" - This statement is true. Some retroviruses are known to be oncogenic, meaning they can cause cancer in humans. For example, the human T-cell lymphotropic virus type 1 (HTLV-1) is associated with the development of adult T-cell leukemia (a form of cancer).Summary: The correct answer is option A. Retroviruses do have DNA at some stages in their life cycle, specifically in the form of a DNA copy of their RNA genome, which is integrated into the host cell's genome. This process is mediated by reverse transcriptase (RNA-dependent DNA polymerase). Retroviruses are indeed linked to certain types of cancer in humans.

2553. 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.

2554. 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.

2555. 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.

2556. 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.

2557. 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.

2558. 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

2559. 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.

2560. 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.