All Free Biology MCQs with Answers

2541. Black(stem) rust of wheat is caused by:

• A. Alternaria solani
• B. Ustilago nuda
• C. Puccinia graminis triticina
• D. Xanthomonas oryzae

Explanation: Certainly, I can provide explanations for the options you listed in the context of black stem rust of wheat:1. Alternaria solani: Alternaria solani is a fungus that causes early blight in tomatoes and potatoes. It is not the causal agent of black stem rust in wheat.2. Ustilago nuda: Ustilago nuda is a fungus that causes loose smut in barley. It is not responsible for black stem rust in wheat.3. Puccinia triticina: Puccinia triticina, also known as wheat leaf rust, is the primary pathogen responsible for black stem rust in wheat. It's a fungal rust disease that affects the leaves, stems, and grains of wheat plants.4. Xanthomonas oryzae: Xanthomonas oryzae is a bacterial pathogen that causes bacterial leaf blight in rice and does not relate to black stem rust in wheat.In summary, black stem rust of wheat is primarily caused by Puccinia triticina, a fungal pathogen that affects wheat plants. The other options listed do not cause black stem rust in wheat.

2542. Phylogenetic system of classification is based on:

• A. Morphological features
• B. Chemical constituents
• C. Floral characters
• D. Evolutionary relationships

Explanation: Certainly, here's an explanation of each of the options you mentioned in the context of phylogenetic classification:1. **Morphological Features**: This aspect of classification is based on the physical characteristics of organisms, such as their shape, size, structure, and other visible traits. Taxonomists use these features to group organisms that share similar physical characteristics into the same taxonomic category. For example, animals with backbones are classified as vertebrates based on their morphological feature of having a spinal column.2. **Chemical Constituents**: Some organisms have distinct chemical compounds or constituents that are unique to their group. These chemicals can be used for classification. For instance, the presence of specific chemical compounds in the cell walls of bacteria, like peptidoglycan, is a key feature used to differentiate between two major groups of bacteria, the Gram-positive and Gram-negative bacteria.3. **Floral Characters**: Floral characters are specific to plants and refer to the characteristics of their flowers. These characters can include features like petal number, arrangement of floral parts, and other flower-related traits. Botanists use floral characters to classify plants into various taxonomic groups, including families, genera, and species.4. **Evolutionary Relationships**: This is a fundamental concept in phylogenetic classification. Instead of focusing solely on superficial characteristics, phylogenetic classification aims to group organisms based on their evolutionary history. It considers the genetic and ancestral relationships between species. This approach often involves the use of molecular data, such as DNA and RNA sequencing, to construct phylogenetic trees that depict the evolutionary connections between different organisms.Phylogenetic classification is primarily concerned with understanding the evolutionary history and genetic relationships between organisms, making it a more accurate and dynamic system of classification compared to classifications based solely on superficial features.

2543. Thermococcus, Methanococcus and Methanobacterium examplify:

• A. Bacteria whose DNA is relaxed or positively supercoiled but which have a cytoskeleton as well as mitochondria
• B. Bacteria that contain a cytoskeleton and ribosomes
• C. Archaebacteria that contain protein homologous to eukaryotic core histones
• D. Archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is negatively supercoiled.

Explanation: Thermococcus, Methanococcus and Methanobacterium are examples of archaebacteria which are characterized by a unique cell wall that lack peptidoglycan and consist of polysaccharides and protein and closely resemble the eukaryotic cell in the mechanism of protein synthesis, structural protein and RNA compliments of the ribosomes.

2544. Which one of the following is a slime mould?

• A. Physarum
• B. Thiobacillus
• C. Anabaena
• D. Rhizopus

Explanation: All options are explained below:a)Physarum is a genus of slime molds. Slime molds are unique organisms that belong to the group Amoebozoa. They have a complex life cycle that includes both single-celled amoeboid stages and multicellular stages. Physarum is known for its ability to form intricate patterns and make decisions based on environmental cues.b)Thiobacillus is not a slime mold. It is a genus of bacteria belonging to the phylum Proteobacteria. Thiobacillus species are known for their ability to oxidize sulfur compounds, which is important in various biogeochemical cycles.c) Anabaena is not a slime mold either. It is a genus of cyanobacteria, often referred to as blue-green algae. Cyanobacteria are photosynthetic prokaryotes that play a crucial role in the oxygenation of the Earth's atmosphere.d) Rhizopus is not a slime mold. It is a genus of fungi, specifically belonging to the group Zygomycota. Rhizopus species include bread molds and are common in decaying organic matter.Correct Option: PhysarumSummary: Physarum is a type of slime mold, which is an unusual organism with a unique life cycle that includes amoeboid and multicellular stages. It is known for its ability to make complex decisions and form intricate patterns based on environmental conditions. The other options, Thiobacillus, Anabaena, and Rhizopus, represent bacteria, cyanobacteria, and fungi, respectively, and are not classified as slime molds.

2545. Which one of the following statements about mycoplasma is wrong?

• A. They are pleomorphic.
• B. They are sensitive to penicillin.
• C. They cause diseases in plants.
• D. They are also called PPLO.

Explanation: All options are explained below: a)They are pleomorphic: This statement is correct. Mycoplasma is known for its pleomorphic nature, meaning it can have various shapes and sizes. b) They are sensitive to penicillin: This statement is incorrect. Mycoplasma is typically resistant to antibiotics like penicillin because they lack a cell wall, which is the target of penicillin. Penicillin primarily acts on bacteria with cell walls, making it ineffective against mycoplasma. c) They cause diseases in plants:This statement is correct. Mycoplasma can indeed infect plants and cause diseases, often referred to as "phytoplasmas." These phytoplasmas are plant pathogens that are related to mycoplasma. d) They are also called PPLO (Pleuropneumonia-like organisms):This statement is correct. Mycoplasma was formerly referred to as Pleuropneumonia-like organisms (PPLO). The name was changed to reflect the unique characteristics of these microorganisms. Correct option: B. They are sensitive to penicillin. Summary: The incorrect statement is that mycoplasma is sensitive to penicillin. In reality, mycoplasma is generally resistant to penicillin and other antibiotics that target bacterial cell walls. Mycoplasma is pleomorphic, can infect both animals and plants, and was historically known as PPLO.

2546. Which pair of the following belongs to basidiomycetes?

• A. Puffballs and Claviceps
• B. Peziza and stink horns.
• C. Morchella and mushrooms.
• D. Birds nest fungi and puffballs.

Explanation: All options are explained below: a)Puffballs and Claviceps:Puffballs belong to the Gasteromycetes group, and Claviceps is indeed a member of the Ascomycota group. Neither of these fungi belongs to basidiomycetes. b) Peziza and stinkhorns: Peziza is an ascomycete fungus, while stinkhorns are basidiomycetes. The pair contains one basidiomycete, stinkhorns, so this option is partially correct. c) Morchella and mushrooms: Morchella is a type of ascomycete, and mushrooms, in general, are examples of basidiomycetes. This pair includes one basidiomycete, which is mushrooms, so this option is also partially correct. d)Bird's nest fungi and puffballs: Bird's nest fungi belong to the class Nidulariaceae, which is a subgroup of basidiomycetes (specifically in the Agaricomycetes class). Puffballs are indeed basidiomycetes, but they belong to the Gasteromycetes group, which is a subgroup of basidiomycetes. Therefore, this pair includes two fungi that are both basidiomycetes. Correct Pair: D. Bird's nest fungi and puffballs Summary: The correct pair belonging to basidiomycetes is Bird's nest fungi and puffballs (option D). Both of these fungi are part of the basidiomycetes group. The other pairs include either non-basidiomycetes or a mix of basidiomycetes and non-basidiomycetes.

2547. Curing of tea leaves is brought about by the activity of:

• A. Fungi
• B. Bacteria
• C. Mycorrhiza
• D. Viruses

Explanation: The curing of tea leaves, also known as tea fermentation or oxidation, is a critical step in the post-harvest processing of tea leaves. This process is especially important for certain types of tea, such as black tea and oolong tea, as it significantly influences the flavor, aroma, and overall quality of the final tea product. All options are explained below: a)Fungi: While fungi can play a role in some fermentation processes, such as in the production of certain fermented teas, they are not primarily responsible for the curing of tea leaves. b)Bacteria: Bacteria are the microorganisms that are mainly involved in the fermentation and curing of tea leaves. Specific strains of bacteria are responsible for the chemical changes that occur during the curing process, leading to the development of tea's flavors and aromas. c)Mycorrhiza: Mycorrhiza is a symbiotic association between fungi and plant roots and is not directly related to the curing of tea leaves. d)Viruses: Viruses do not have a role in the curing of tea leaves. They are not involved in the fermentation or processing of tea. Summary: The correct answer is Bacteria. Bacteria are the microorganisms responsible for the fermentation and curing of tea leaves, a critical step in tea processing that influences the flavor and quality of the final tea product. Fungi, mycorrhiza, and viruses are not the primary agents involved in the tea curing process.

2548. Which of the following environmental conditions are essential for the optimum growth of Mucor on a piece of bread? A. Temperature of about 25° C B. Temperature of about 5° C C. Relative humidity of about 5% D. Relative humidity of about 95% E. A shady place F. A brightly illuminated place Choose the answer from the following options.

• A. B, C and F only
• B. A, C and E only
• C. A, D and E only
• D. B, D and E only

Explanation: The environmental conditions essential for the optimum growth of Mucor on a piece of bread typically include: A. Temperature of about 25°C: Mucor tends to grow well at moderate temperatures. D. Relative humidity of about 95%: Mucor thrives in humid conditions. E. A shady place: Mucor prefers dark or shaded environments. Therefore, the correct answer is: A, D, and E only: These conditions are conducive to the growth of Mucor on bread. Options B and C are not typically favorable for the growth of Mucor. A low temperature (5°C) and low relative humidity (5%) are not ideal for its growth. Option F, a brightly illuminated place, is also not conducive to Mucor growth, as it prefers darkness or shade.

2549. All of the following statements concerning the actinomycetous filamentous soil bacterium Frankia are correct except that Frankia

• A. Can induce root nodules on many plant species
• B. Can fix nitrogen in the freeliving state
• C. Cannot fix specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids
• D. Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex.

Explanation: a)Can induce root nodules on many plant species: This statement is correct. Frankia is known for its ability to induce root nodules on a wide range of plant species, particularly actinorhizal plants. These nodules provide a symbiotic environment for Frankia to fix nitrogen. b)Can fix nitrogen in the free-living state: is the incorrect statement. Frankia, like many nitrogen-fixing bacteria, cannot fix nitrogen in the free-living state, unlike some other nitrogen-fixing bacteria, such as free-living diazotrophs. Frankia typically forms symbiotic relationships with host plants and fixes nitrogen within root nodules. c)Cannot fix specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids: is the correct statement. Frankia can fix nitrogen within specialized vesicles, and triterpene hopanoids are involved in maintaining low oxygen levels in these vesicles. d)Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex : This statement is correct. Similar to Rhizobium, Frankia often initiates the infection of its host plant by inducing deformation of root hairs. It also stimulates the proliferation of plant cells in the root cortex, leading to the formation of nodules where the bacterium resides and performs nitrogen fixation. Summary: The correct statements are A and D, which describe Frankia's ability to induce root nodules on various plant species and its infection process through root hair deformation and cortex cell proliferation, similar to Rhizobium. Option B is the incorrect statement, as Frankia cannot fix nitrogen in the free-living state, and it relies on symbiotic associations for nitrogen fixation. Option C is also incorrect as Frankia does indeed form specialized vesicles and employs mechanisms like triterpene hopanoids to protect nitrogenase from oxygen during nitrogen fixation.

2550. For retting of jute the fermenting microbe used is

• A. methanophilic bacteria
• B. butyric acid bacteria
• C. Helicobactor pylori
• D. Streptococcus lactis

Explanation: The fermenting microbe used for retting jute is not methanophilic bacteria, Helicobacter pylori, or Streptococcus lactis. The correct microbe used in the retting process is butyric acid bacteria. Here's an explanation of all the options and a summary: Methanophilic bacteria: Methanophilic bacteria are not used in the retting of jute. They are specialized bacteria that produce methane and are typically found in anaerobic environments, such as certain wetlands and the digestive systems of animals. Helicobacter pylori: Helicobacter pylori is a bacterium associated with stomach ulcers and gastritis in humans. It has no role in the retting of jute. Streptococcus lactis: Streptococcus lactis is a lactic acid bacteria used in the fermentation of dairy products, but it is not used in the retting of jute. Summary: Butyric acid bacteria are the fermenting microbes used in the retting process of jute. They help break down the pectin substances in jute fibers, facilitating the separation of the fibers from the plant's woody core. Methanophilic bacteria, Helicobacter pylori, and Streptococcus lactis are not involved in this specific industrial process.