All Free Biology MCQs with Answers

2501. Give the correct matching of causative agent/germ and disease.

• A. Anopheles - Malaria
• B. Leishmania - Sleeping sickness
• C. Glossina - Kala-azar
• D. Wuchereria - Filariasis

Explanation: Wuchereria bancrofti is a parasitic filarial nematode worm transmitted by a mosquito vector. It is one of the three parasites that cause lymphatic filariasis. If left untreated, it can lead to elephantiasis. Treatment options are limited, and no vaccines have been developed.Malaria is caused by protozoan parasites of the genus Plasmodium and is transmitted by female Anopheles mosquitoes.Sleeping sickness, also known as African trypanosomiasis, is a parasitic disease affecting both people and animals. It is caused by protozoa of the genus Trypanosoma and transmitted by the tsetse fly.Kala-azar, caused by the protozoan Leishmania, is transmitted by sandflies.

2502. Which of the following are found in extreme saline conditions?

• A. Eubacteria
• B. Cyanobacteria
• C. Mycobacteria
• D. Archaebacteria

Explanation: Halophiles, a type of archaea, typically thrive in extreme saline environments such as salt pans, salt beds, and salt marshes.

2503. Viroids differ from viruses in having:

• A. DNA molecules without protein coat.
• B. RNA molecules with protein coat.
• C. RNA molecules without protein coat.
• D. DNA molecules with protein coat.

Explanation: RNA molecules without a protein coat: This is the correct description of viroids. Viroids are small, circular RNA molecules that lack a protein coat. They are unique infectious agents that can cause disease in plants.

2504. Which among the following are the smallest living cells, known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen?

• A. Pseudomonas
• B. Mycoplasma
• C. Nostoc
• D. Bacillus

Explanation: Mycoplasma is the smallest living cells known without a definite cell wall, pathogenic to both plants and animals, and capable of surviving without oxygen. Here's an explanation of each option:Mycoplasma is the smallest living cells known without a definite cell wall, pathogenic to both plants and animals, and capable of surviving without oxygen. Here's an explanation of each option:Mycoplasma is the smallest living cells known without a definite cell wall, pathogenic to both plants and animals, and capable of surviving without oxygen. Here's an explanation of each option:1. Pseudomonas: Pseudomonas is a type of bacteria that possesses a cell wall and cannot be considered the smallest living cell without a definite cell wall. It is not pathogenic to animals and is aerobic, requiring oxygen for survival.2. Mycoplasma: Mycoplasma is a genus of bacteria that lacks a rigid cell wall and is known to be one of the smallest living cells. Some species of Mycoplasma are pathogenic to both plants and animals. They are also facultative anaerobes, meaning they can survive with or without oxygen.3. Nostoc: Nostoc is a genus of cyanobacteria (blue-green algae) that have a definite cell wall and do not fit the description of the smallest living cells without a cell wall. They are photosynthetic and can fix nitrogen.4. Bacillus: Bacillus is a genus of bacteria that possess a cell wall, and they are not the smallest living cells without a cell wall. They are aerobic bacteria and are not typically pathogenic to both plants and animals.So, Mycoplasma meets all the criteria mentioned in your question.

2505. Which of the following components provides sticky character to the bacterial cell?

• A. Nuclear membrane
• B. Plasma membrane
• C. Glycocalyx
• D. Cell wall

Explanation: The component that provides the sticky character to the bacterial cell is the Glycocalyx. Here's an explanation of each option:1. Nuclear membrane: The nuclear membrane, also known as the nuclear envelope, is found in eukaryotic cells and surrounds the nucleus. Bacterial cells are prokaryotic and do not have a defined nucleus or nuclear membrane.2. Plasma membrane: The plasma membrane, also known as the cell membrane, is present in both eukaryotic and prokaryotic cells, including bacterial cells. It plays a crucial role in controlling the passage of substances into and out of the cell but is not primarily responsible for the sticky character of the cell.3. Glycocalyx: The Glycocalyx is a gel-like layer of carbohydrates that surrounds the cell membrane of many bacterial cells. It is responsible for the sticky character of the cell and plays a significant role in adhesion, protection, and biofilm formation.4. Cell wall: The cell wall in bacterial cells provides structural support and protection but is not primarily responsible for conferring a sticky character to the cell.So, in this context, the Glycocalyx is the component that provides the sticky character to the bacterial cell.

2506. Methanogens belong to:

• A. Eubacteria
• B. Archaebacteria
• C. Dinoflagellates
• D. Slime moulds

Explanation: Methanogens belong to the archaebacteria group. Here's an explanation for each of the options:1. Eubacteria: Methanogens are not part of the eubacteria group. Eubacteria are the typical bacteria that are commonly found in various environments.2. Archaebacteria: Methanogens fall under the archaebacteria group. Archaebacteria are a distinct domain of microorganisms that are known for their ability to thrive in extreme environments, and methanogens are a subgroup of these archaebacteria that produce methane as a metabolic byproduct.3. Dinoflagellates: Dinoflagellates are a type of unicellular protist, not bacteria, so they are not related to methanogens.4. Slime molds: Slime molds are also not related to methanogens. Slime molds are part of the kingdom Protista and have a different biological classification compared to methanogens.

2507. The primitive prokaryotes responsible for the production of biogas from the dung of ruminant animals, include the

• A. Methanogens
• B. Sulphate reducing bacteria
• C. Halophiles
• D. Thermoacidophiles

Explanation: Sure, I can explain each of these options:1. **Methanogens**: Methanogens are a type of archaea, which are primitive prokaryotic microorganisms. They are responsible for the production of biogas from the dung of ruminant animals. Methanogens are unique in that they produce methane (CH4) as a metabolic byproduct. They are often found in the digestive systems of ruminant animals like cows, where they help break down cellulose and other organic matter, producing methane in the process.2. **Sulfate-Reducing Bacteria (Sulfate-Reducing Prokaryotes)**: Sulfate-reducing bacteria (SRB) are a group of bacteria responsible for the production of hydrogen sulfide gas (H2S) as part of their metabolism. While they play a role in biogas production, they are not as directly involved as methanogens. SRB can compete with methanogens in anaerobic environments and can influence the composition of biogas.3. **Halophiles**: Halophiles are prokaryotes that thrive in high-salinity environments, such as salt flats or saline lakes. They are not directly involved in biogas production from ruminant dung but have unique adaptations to saline conditions.4. **Thermoacidophiles**: Thermoacidophiles are prokaryotes that can thrive in extremely high-temperature and acidic environments, such as hot springs or volcanic areas. They are not typically associated with biogas production from ruminant dung but have adapted to harsh conditions.To summarize, methanogens are the primary prokaryotes responsible for producing biogas (methane) from the dung of ruminant animals due to their ability to digest organic matter and produce methane gas during their metabolic processes. Other prokaryotes, like sulfate-reducing bacteria, may also play a role in biogas production but are not as directly involved as methanogens. Halophiles and thermoacidophiles have specific environmental preferences and are not typically associated with biogas production.

2508. Which one of the following statements is wrong?

• A. Eubacteria are also called false bacteria.
• B. Phycomycetes are also called algal fungi.
• C. Cyanobacteria are also called bluegreen algae.
• D. Golden algae are also called desmids.

Explanation: The statement "Eubacteria are also called false bacteria" is incorrect. Eubacteria are commonly referred to as "true bacteria" or "common bacteria," not "false bacteria."Here are explanations for each option:1. Eubacteria are indeed called "true bacteria" or "common bacteria" because they represent the vast majority of known bacteria and are not "false bacteria."2. Phycomycetes are also called "algal fungi" because they share characteristics with both algae and fungi, so this statement is correct.3. Cyanobacteria are indeed called "blue-green algae" because they resemble algae, even though they are actually a type of bacteria, so this statement is accurate.4. Golden algae are also known as "desmids." Desmids are a specific type of unicellular green algae, so this statement is correct.Therefore, the incorrect statement is the first one about Eubacteria.

2509. Which of the following statements is wrong for viroids?

• A. They cause infections.
• B. Their RNA is of high molecular weight.
• C. They lack a protein coat.
• D. They are smaller than viruses.

Explanation: RNA of viroid has low molecular weight. The statement "Their RNA is of high molecular weight" is wrong for viroids.Here are explanations for each option:1. "They cause infections": This statement is correct. Viroids are small, infectious RNA molecules that can cause disease in plants. They do not infect animals or humans, but they can have a significant impact on agriculture by causing diseases in crops.2. "Their RNA is of high molecular weight": This statement is incorrect. Viroids have RNA that is of very low molecular weight. In fact, one of the distinguishing features of viroids is their small size, as they consist of a single-stranded RNA molecule with a low molecular weight. This sets them apart from viruses, which typically have larger and more complex genomes.3. "They lack a protein coat": This statement is correct. Viroids do not have a protein coat, which is another characteristic that distinguishes them from viruses. Viruses usually have a protein coat called a capsid that surrounds their genetic material, while viroids consist solely of the RNA molecule itself.4. "They are smaller than viruses": This statement is correct. Viroids are indeed smaller than viruses. They are among the smallest infectious agents known and consist of a single circular RNA molecule, typically around a few hundred nucleotides in length, whereas viruses can be much larger and more complex in structure.

2510. One of the major components of cell wall of most fungi is:

• A. Cellulose
• B. Hemicellulose
• C. Chitin
• D. Peptidoglycan

Explanation: Certainly! The major component of the cell wall of most fungi is chitin. Here's an explanation of each of the options:1. Cellulose: - Cellulose is a structural polysaccharide found in the cell walls of plants and some algae, but it is not a major component of fungal cell walls. Fungi have chitin in their cell walls, which is different from cellulose.2. Hemicellulose: - Hemicellulose is another complex carbohydrate found in plant cell walls, but it is not a primary component of fungal cell walls. Fungal cell walls primarily consist of chitin.3. Chitin: - Chitin is the primary structural component of fungal cell walls. It is a complex carbohydrate made up of long chains of N-acetylglucosamine (GlcNAc) molecules. Chitin provides strength and rigidity to the fungal cell wall, similar to how cellulose functions in plant cell walls.4. Peptidoglycan: - Peptidoglycan is a structural component of bacterial cell walls, not fungal cell walls. Fungi and bacteria have distinct cell wall compositions, with fungi having chitin in their cell walls and bacteria having peptidoglycan.So, in summary, chitin is the major component of the cell wall of most fungi, while the other options (cellulose, hemicellulose, and peptidoglycan) are not typically found in fungal cell walls.