All Free Biology MCQs with Answers

2591. Tobacco mosaic virus (TMV) genes are:

• A. Single stranded RNA
• B. Double stranded DNA
• C. Proteinaceous
• D. Double stranded RNA

Explanation: Let's explain each option individually:a) Single-stranded RNA:This option is correct. The genes of the Tobacco mosaic virus (TMV) are composed of single-stranded RNA (ribonucleic acid). TMV is a plant virus known for causing the tobacco mosaic disease, which affects various plants, including tobacco, tomatoes, peppers, and other members of the Solanaceae family. The RNA genome of TMV encodes the genetic information necessary for the virus to replicate and produce its proteins during the infection process.b) Double-stranded DNA:Double-stranded DNA (deoxyribonucleic acid) is a genetic material found in most living organisms, including plants, animals, and bacteria. However, TMV is not a DNA virus; it is an RNA virus with a single-stranded RNA genome.c) Proteinaceous:The term "proteinaceous" refers to something that is primarily composed of proteins. While TMV is a virus made up of proteins and RNA, the genes of TMV are specifically composed of single-stranded RNA, not just proteins.d) Double-stranded RNA:This option is not correct. TMV does not have a double-stranded RNA genome. Instead, its genome consists of a single-stranded RNA molecule.In summary, the correct answer is a) Single-stranded RNA. The genes of the Tobacco mosaic virus (TMV) are composed of single-stranded RNA. This RNA genome contains the instructions for the virus to infect host plant cells, replicate, and produce new viral particles, leading to the characteristic mosaic-like patterns and other symptoms observed in infected plants.

2592. Phylogenetic classification is one which is based on:

• A. Overall similarities
• B. Utilitarian system
• C. Habits of plants
• D. Common evolutionary descent

Explanation: Let's explain each option individually: a) Overall similarities: Phylogenetic classification is not solely based on overall similarities between organisms. While similarities are considered in phylogenetics, it is essential to differentiate between homologous traits (traits inherited from a common ancestor) and analogous traits (traits that have evolved independently due to similar environmental pressures). Phylogenetic classification aims to reconstruct evolutionary relationships based on shared, homologous characteristics that reflect common ancestry. b) Utilitarian system: The term "utilitarian system" is not commonly used in the context of biological classification. It does not specifically refer to a method of classification based on evolutionary relationships or common descent. c) Habits of plants: Phylogenetic classification is not solely based on the habits or ecological characteristics of plants or other organisms. While ecological traits and adaptations can provide valuable information about the biology of organisms, they are not the primary focus of phylogenetic classification. Instead, phylogenetics aims to establish evolutionary relationships and construct evolutionary trees that depict the branching patterns of organisms over time. d) Common evolutionary descent: This option is correct. Phylogenetic classification is based on the principle of common evolutionary descent. It seeks to organize organisms into groups based on their evolutionary history and shared ancestry. By analyzing homologous traits (similarities inherited from a common ancestor), scientists can construct phylogenetic trees that represent the evolutionary relationships between different organisms. The tree's branching patterns reflect the divergence of lineages over time, showing the common descent and relatedness among different species or groups of organisms. In summary, the correct answer is d) Common evolutionary descent. Phylogenetic classification is based on reconstructing the evolutionary relationships between organisms by analyzing shared, homologous characteristics, and depicting their common ancestry through the construction of phylogenetic trees.

2593. The protists have:

• A. Only free nucleic acid aggregates
• B. Membrane bound nucleoproteins lying embedded in the cytoplasm
• C. Gene containing nucleoproteins condensed together in loose mass
• D. Nucleoprotein in direct contact with the rest of the cell substance.

Explanation: Let's explain each option individually: a) Only free nucleic acid aggregates: This option is not correct. Protists, like other eukaryotic organisms, have their genetic material (DNA) organized into chromosomes and located within a nucleus. They do not have only free nucleic acid aggregates floating in the cytoplasm. b) Membrane-bound nucleoproteins lying embedded in the cytoplasm: This option is correct. Protists are eukaryotic organisms, meaning their cells have a well-defined nucleus that contains the genetic material (DNA). The DNA is associated with proteins to form nucleoproteins, and these nucleoproteins are contained within the nucleus, which is a membrane-bound organelle. The nucleus is typically embedded within the cytoplasm of the protist cell. c) Gene-containing nucleoproteins condensed together in a loose mass: This option is not correct. In eukaryotic cells, including protists, the DNA is not present as a loose mass but is rather organized into chromosomes within the nucleus. Chromosomes are condensed structures formed by tightly packing the DNA with histone proteins during cell division. However, during interphase, when the cell is actively carrying out its functions, the chromosomes are not as condensed, allowing access to the genetic information for transcription and translation. d) Nucleoprotein in direct contact with the rest of the cell substance: This option is not correct. In eukaryotic cells, the nucleus is separated from the rest of the cytoplasm by a nuclear envelope, which consists of a double membrane with nuclear pores. These nuclear pores regulate the exchange of materials between the nucleus and the cytoplasm. The genetic material in the form of nucleoproteins is contained within the nucleus and is not in direct contact with the rest of the cell substance (cytoplasm) except through the nuclear pores. In summary, the correct answer is b) Membrane-bound nucleoproteins lying embedded in the cytoplasm. Protists, as eukaryotic organisms, have a nucleus with membrane-bound nucleoproteins (DNA and associated proteins) located within the cytoplasm of the cell. The nucleus is enclosed by a nuclear envelope that separates it from the rest of the cell and regulates the exchange of materials between the nucleus and the cytoplasm.

2594. Organisms, which fix atmospheric nitrogen in the soil, fall under the category of

• A. Bacteria
• B. Green algae
• C. Soil fungi mosses.
• D. Mosses

Explanation: Let's explain each option individually: a) Bacteria: This option is correct. Organisms that fix atmospheric nitrogen in the soil primarily belong to the category of bacteria. Specifically, certain bacteria are capable of converting atmospheric nitrogen gas (N2) into a biologically usable form called ammonia (NH3) through a process called nitrogen fixation. Some of the most well-known nitrogen-fixing bacteria include species from the genera Rhizobium, Azotobacter, and Bradyrhizobium, among others. These bacteria form symbiotic associations with certain plants, like legumes, or can live freely in the soil, contributing to the nitrogen cycle and making nitrogen available to plants and other organisms. b) Green algae: Green algae are photosynthetic organisms that typically inhabit aquatic environments. While some algae can fix nitrogen, they are not the primary category of organisms responsible for nitrogen fixation in the soil. Nitrogen-fixing algae mostly occur in marine environments, where they play a role in nitrogen cycling in marine ecosystems. c) Soil fungi: While some soil fungi form beneficial associations with plants, such as mycorrhizal associations, they are not known for nitrogen fixation. Mycorrhizal fungi aid in the uptake of nutrients, including nitrogen, by forming symbiotic relationships with plant roots. However, they do not fix atmospheric nitrogen into a usable form in the soil. d) Mosses: Mosses are non-vascular plants that play a role in the ecosystem by contributing to soil formation and moisture retention. However, mosses are not capable of nitrogen fixation. They do not have the ability to convert atmospheric nitrogen gas into a biologically available form. In summary, the correct answer is a) Bacteria. Organisms that fix atmospheric nitrogen in the soil belong to the category of bacteria, specifically nitrogen-fixing bacteria, which play a crucial role in the nitrogen cycle by converting nitrogen gas into a form that can be used by plants and other organisms.

2595. Transduction in bacteria is mediated by

• A. Plasmid vectors
• B. Phage vectors
• C. Cosmids
• D. F-factors

Explanation: Let's explain each option individually: a) Plasmid vectors: Plasmid vectors are small, circular DNA molecules that can be used to carry foreign DNA and introduce it into bacterial cells during genetic engineering experiments. However, plasmids are not involved in transduction in bacteria. b) Phage vectors: This option is correct. Transduction in bacteria is mediated by phage vectors. Bacterial transduction is a process in which bacteriophages (viruses that infect bacteria) transfer bacterial DNA from one bacterium to another. During the lytic cycle of bacteriophage infection, the phage can accidentally package a fragment of bacterial DNA from the host cell into its viral capsid. When this bacteriophage subsequently infects another bacterium, it can inject the bacterial DNA fragment into the new host cell. This results in the transfer of bacterial genes from one bacterium to another, effectively mediating horizontal gene transfer in bacteria. c) Cosmids: Cosmids are hybrid plasmids that combine the features of plasmids and bacteriophage lambda vectors. They are used in molecular biology for cloning large fragments of DNA. While cosmids can be used for cloning, they are not directly involved in transduction in bacteria. d) F-factors: F-factors, also known as fertility factors or sex factors, are plasmids found in certain bacteria, such as Escherichia coli (E. coli). They play a role in bacterial conjugation, a form of direct DNA transfer between bacterial cells. F-factors are not directly involved in transduction, which is a process mediated by bacteriophages (phages). In summary, the correct answer is b) Phage vectors. Transduction in bacteria is mediated by bacteriophages (phages) that transfer bacterial DNA from one bacterium to another during the process of viral infection. This horizontal gene transfer mechanism can lead to the exchange of genetic material and contribute to the genetic diversity of bacterial populations.

2596. A non-photosynthetic, aerobic, nitrogen fixing soil bacterium is

• A. Rhizobium
• B. Clostridium
• C. Azotobacter
• D. Klebsiella

Explanation: Let's explain each option individually: a) Rhizobium: Rhizobium is a genus of soil bacteria that are known for their ability to form a symbiotic relationship with leguminous plants. They are aerobic and can fix atmospheric nitrogen into ammonia within specialized structures called nodules on the roots of legume plants. This nitrogen fixation benefits both the bacteria and the plants in a mutualistic association. b) Clostridium: Clostridium is a genus of bacteria that includes various species, some of which are involved in nitrogen fixation. However, the nitrogen-fixing species within the Clostridium genus are anaerobic, meaning they carry out their activities in the absence of oxygen. Clostridium species are well-known for their diverse metabolic capabilities, including the production of spores and their role in various biological processes. c) Azotobacter: This option is correct. Azotobacter is a genus of non-photosynthetic, free-living aerobic nitrogen-fixing bacteria. These bacteria are commonly found in soil environments and can fix atmospheric nitrogen into ammonia, making it available for plants and other organisms. Azotobacter plays a significant role in the nitrogen cycle, contributing to soil fertility. d) Klebsiella: Klebsiella is a genus of bacteria that includes both nitrogen-fixing and non-nitrogen-fixing species. Some species of Klebsiella are capable of nitrogen fixation, while others are not involved in this process. Like Azotobacter, some nitrogen-fixing Klebsiella species are also free-living aerobic bacteria that contribute to nitrogen availability in the soil. In summary, the correct answer is c) Azotobacter. Azotobacter is a non-photosynthetic, free-living, aerobic soil bacterium that can fix atmospheric nitrogen into ammonia, playing an essential role in nitrogen cycling and soil fertility. The other options (Rhizobium, Clostridium, and Klebsiella) are also relevant to nitrogen fixation but differ in their specific characteristics and associations with plants or other organisms.

2597. Mycorrhiza exhibits the phenomenon of:

• A. Parasitism
• B. Symbiosis
• C. Antagonism
• D. Endemism

Explanation: Let's explain each option individually: a) Parasitism: Parasitism is a symbiotic relationship between two organisms where one organism (the parasite) benefits at the expense of the other organism (the host). The parasite derives nutrients or resources from the host, often causing harm or negative effects on the host's health. This relationship is not exhibited by mycorrhiza. b) Symbiosis: This option is correct. Mycorrhiza exhibits symbiosis. Symbiosis is a close and long-term interaction between two different species, where at least one of the species benefits from the relationship. In the case of mycorrhiza, it is a mutualistic symbiosis between certain fungi and the roots of most higher plants (vascular plants). The fungal partner (mycorrhizal fungus) benefits from receiving carbohydrates and other nutrients from the plant, while the plant benefits from enhanced nutrient uptake, particularly in accessing phosphorus and other minerals from the soil. c) Antagonism: Antagonism refers to an interaction between two organisms that is harmful or detrimental to at least one of the organisms involved. In this type of relationship, both organisms compete for resources or produce substances that inhibit the growth or survival of the other. Mycorrhiza does not exhibit antagonism; instead, it shows mutualistic symbiosis. d) Endemism: Endemism refers to the ecological state of being unique to a particular geographic region or location. It describes species or organisms that are restricted to a specific area and are not found elsewhere. Mycorrhiza is not related to endemism. It is a widespread phenomenon found in various ecosystems around the world where mycorrhizal fungi associate with plants. In summary, the correct answer is b) Symbiosis. Mycorrhiza exhibits symbiosis, specifically mutualistic symbiosis, between certain fungi and the roots of most higher plants, benefiting both partners in the relationship.

2598. Schizont stage of Plasmodium occurs in human cells

• A. Erythrocytes
• B. Liver cells
• C. Erythrocytes and liver cells
• D. Erythrocytes, liver cells and spleen cells.

Explanation: Let's explain each option individually: a) Erythrocytes: The erythrocyte stage of Plasmodium occurs during the asexual reproduction phase of the parasite within the human host. Plasmodium species, which are responsible for causing malaria, go through a schizont stage in the erythrocytes (red blood cells) during their life cycle. b) Liver cells: The liver cell stage of Plasmodium also occurs during the asexual reproduction phase, but this happens before the parasite enters the erythrocytes. When an infected mosquito bites a human, it injects sporozoites (the infective stage of the parasite) into the bloodstream. These sporozoites travel to the liver, where they infect liver cells and undergo a schizont stage, multiplying and forming merozoites. c) Erythrocytes and liver cells: This option is correct. The schizont stage of Plasmodium occurs in both erythrocytes and liver cells. As mentioned above, the initial phase of the parasite's life cycle involves infecting liver cells and undergoing schizogony, forming merozoites. These merozoites are then released into the bloodstream and infect erythrocytes, where they undergo further schizogony, leading to the destruction of red blood cells and the release of more merozoites, which can infect new erythrocytes. d) Erythrocytes, liver cells, and spleen cells: This option is not correct. While the schizont stage of Plasmodium occurs in erythrocytes and liver cells, it does not occur in spleen cells. The spleen is an essential organ involved in filtering and removing damaged or infected red blood cells, but it is not a site for the schizont stage of Plasmodium. In summary, the correct answer is c) Erythrocytes and liver cells. The schizont stage of Plasmodium occurs both in liver cells and later in erythrocytes during its life cycle within the human host. The liver cell stage precedes the erythrocyte stage in the Plasmodium life cycle.

2599. If all ponds and puddles are destroyed, the organism likely to be destroyed is

• A. Leishmania
• B. Trypanosoma
• C. Ascaris
• D. Plasmodium

Explanation: The correct option is d) Plasmodium. Let's explain each option individually: a) Leishmania: Leishmania is a parasitic protozoan that causes the disease known as leishmaniasis. The life cycle of Leishmania involves two main stages: one in the sandfly vector and another in the vertebrate host (including humans). While ponds and puddles are not the primary habitat for Leishmania, their destruction would not necessarily lead to the organism's complete destruction, as the parasite can also be present in other environments where the sandfly vector and vertebrate hosts are found. b) Trypanosoma: Trypanosoma is a genus of parasitic protozoa that includes species causing diseases such as African trypanosomiasis (sleeping sickness) and Chagas disease. The parasites are transmitted by tsetse flies (in the case of African trypanosomiasis) and triatomine bugs (in the case of Chagas disease). While ponds and puddles are not the primary habitat for Trypanosoma, their destruction would not necessarily lead to the organism's complete destruction, as these parasites have other transmission routes and can also be present in other environments where their insect vectors and mammalian hosts are found. c) Ascaris: Ascaris lumbricoides is a parasitic roundworm that infects the intestines of humans. It is an intestinal parasite and primarily spreads through the ingestion of Ascaris eggs present in contaminated soil or water. While ponds and puddles can potentially be a source of contamination with Ascaris eggs, their destruction would not lead to the complete destruction of the organism, as it can also be transmitted through other routes and persist in the environment. d) Plasmodium: This option is correct. Plasmodium is the protozoan parasite responsible for causing malaria. Its life cycle involves two hosts: mosquitoes (as the vector) and humans (as the vertebrate host). Ponds and puddles are critical breeding sites for mosquitoes, and the destruction of these water bodies would significantly reduce mosquito breeding grounds. Without suitable water bodies, the mosquito population, particularly those that transmit Plasmodium, would decline, leading to a reduced transmission of malaria. Therefore, the organism likely to be most affected and reduced in numbers by the destruction of ponds and puddles is Plasmodium, the malaria parasite. In summary, the correct answer is d) Plasmodium. The destruction of ponds and puddles would have the most significant impact on the malaria parasite, Plasmodium, as it would reduce mosquito breeding sites and subsequently lower malaria transmission rates.

2600. Genophore/bacterial genome or nucleoid is made up of

• A. Histones and nonhistones
• B. RNA and histones
• C. A single double stranded DNA
• D. A single stranded DNA

Explanation: Let's explain each option individually: a) Histones and nonhistones: In eukaryotic cells, histones are proteins associated with DNA, and nonhistones are other proteins involved in DNA packaging and regulation. However, in prokaryotic cells like bacteria, histones are generally absent, and the bacterial genome is not organized in the same way as eukaryotic chromatin. Bacterial DNA is not associated with histones or nonhistones. b) RNA and histones: This option is not correct. While RNA plays a role in various cellular processes, it is not a major component of the bacterial genome or nucleoid. As mentioned earlier, histones are generally absent in prokaryotes like bacteria. c) A single double-stranded DNA: This option is correct. The genophore, also known as the bacterial genome or nucleoid, is made up of a single double-stranded DNA molecule. Bacterial DNA is usually a circular, double-stranded molecule that contains the genetic information necessary for the bacterium to function and reproduce. Unlike eukaryotic cells, bacteria do not have a true nucleus, so their DNA is found in a region called the nucleoid, which lacks a membrane. d) A single-stranded DNA: This option is not correct. The bacterial genome is not a single-stranded DNA molecule. Instead, it is a double-stranded DNA molecule, which means that each DNA strand is paired with another complementary strand. The double-stranded DNA structure is essential for DNA replication and accurate transmission of genetic information during cell division. In summary, the correct answer is c) A single double-stranded DNA. The bacterial genome, also known as the genophore or nucleoid, is composed of a single circular double-stranded DNA molecule, which contains the genetic instructions necessary for the functioning and reproduction of the bacterium.