All Free Biology MCQs with Answers

3121. Major cells that are infected by HIV?

• A. Red blood cells
• B. Platelets
• C. T-Helper cells
• D. Neutrophils

Explanation: The major cells infected by HIV are CD4+ T lymphocytes, as the virus binds to CD4 receptors to gain entry and replicate. Red blood cells, platelets, and neutrophils are not directly infected because they either lack nuclei or do not express the necessary receptors.

3122. In HIV, reverse transcriptase converts single-stranded RNA into double-stranded viral DNA. This process is called

• A. Transcription
• B. Translation
• C. Replication
• D. Reverse transcription

Explanation: In HIV, the enzyme reverse transcriptase is essential for converting single-stranded viral RNA into double-stranded DNA, a process known as reverse transcription. This newly formed DNA can then integrate into the host genome, allowing the virus to replicate. The other options are incorrect: transcription involves making RNA from DNA, translation refers to protein synthesis from mRNA, and replication is the process of duplicating DNA. Therefore, reverse transcription is the only option that accurately describes the action of reverse transcriptase in HIV.

3123. The artificial system of classification was first used by

• A. Linnaeus
• B. Whittaker
• C. Theophrastus
• D. Aristotle

Explanation: The artificial system of classification was first introduced by Theophrastus, often called the Father of Botany. He grouped plants on the basis of superficial characters such as form, habit, and utility, dividing them into categories like herbs, shrubs, and trees. This was the earliest attempt to classify living organisms, but it was limited because it did not consider natural relationships. Aristotle, though he classified animals into those with red blood and without red blood, did not propose the first artificial system. Carolus Linnaeus later developed a more natural system along with the binomial nomenclature, which improved upon Theophrastus's work. R.H. Whittaker, much later, proposed the five-kingdom classification in 1969, which was far more advanced and based on natural and evolutionary relationships. Thus, the correct answer is Theophrastus, while the other options represent later or different contributions to classification.

3124. The common cold is not cured by antibiotics because it is:

• A. Caused by a virus
• B. Caused by a Gram positive bacterium
• C. Caused by a Gram negative bacterium
• D. Not an infectious disease

Explanation: The common cold is caused by some 100 types of rhinoviruses. It is one of the most common infectious diseases in humans. Antibiotics are substances that destroy or inhibit the growth of microorganisms, particularly disease-producing bacteria and fungi. Antibiotics are obtained from microorganisms (especially molds) or synthesised. Many antibiotics interfere with the pathogen's protein synthesis. Some (e.g., penicillin) prevent cross-linking of the glycan chains of peptidoglycan molecules in bacterial cell walls. Since the viruses do not possess cell walls or their own protein-synthesizing apparatus, antibiotics do not attack them.

3125. Study the four statements (A-D) given below and select the two correct ones out of them. A. The definition of biological species was given by Ernst Mayr. B. Photoperiod does not affect reproduction in plants.C. The binomial nomenclature system was given by R.H. Whittaker. D. In unicellular organisms, reproduction is synonymous with growth.

• A. B and C
• B. C and D
• C. A and D
• D. A and B

Explanation: Among the given statements, A is correct because Ernst Mayr proposed the widely accepted biological species concept, which defines a species as a group of interbreeding organisms that are reproductively isolated from others. B is incorrect since photoperiod, or the duration of light and dark, plays a crucial role in regulating flowering and reproduction in plants, with many species classified as short-day, long-day, or day-neutral. C is also incorrect because the system of binomial nomenclature was not given by R.H. Whittaker but by Carl Linnaeus. At the same time, Whittaker is known for the five-kingdom system of classification. D is correct, as in unicellular organisms like amoeba and bacteria, growth and reproduction are synonymous processes; cell growth directly leads to cell division and multiplication. Therefore, the two correct statements are A and D, while B and C are contrary to the rules and concepts of biology.

3126. Nomenclature is governed by certain universal rules. Which one of the following statements is correct according to these rules?

• A. Both the genus name and species name begin with capital letters.
• B. The generic name always starts with a capital letter, while the species name starts with a small letter.
• C. The author's name should always be written in full (never abbreviated) after the scientific name.

Explanation: The correct option is C because the genus name begins with a capital letter and the species name with a lowercase letter. Options A, B, and D are contrary to the rules of nomenclature.

3127. Which of the following is less general in character as compared to the genus?

• A. Species
• B. Order
• C. Class
• D. Family

Explanation: Among the given options, species is the correct answer because it is less general in character than genus. A species represents the most specific unit of classification, describing a group of organisms that share close similarities and can interbreed, whereas a genus is broader, as it includes one or more species. In contrast, family, order, and class are higher taxonomic categories that are progressively more general in nature, since each of them groups together multiple genera, families, or orders, respectively. Thus, compared to genus, species stands out as the most specific and least general category, making it the right choice.

3128. Species are considered:

• A. Species are the basic units of classification.
• B. Species are the highest units of classification.
• C. Species are imaginary units of classification.
• D. Species are optional units of classification.

Explanation: Species are a natural population or group of natural populations of individuals that are genetically distinct and reproductively isolated with similar essential morphological traits. A species is also a genetically closed system because its members do not interbreed with members of other species. Species are the lowest or basic taxonomic category, e.g., mango (Mangifera indica), potato (Solanum tuberosum), and lion (Panthera leo). Hereindica, tuberosum, and Leo are species of the genera Mangifera, Solanum, and Pantera, respectively. All other taxonomic categories are defined and described in relation to species. For example, a genus is a group of species, and a subspecies or a variety is a part of a species. New species originate from already existing species. A species is considered a basic unit of taxonomy since, in the greater majority of cases, we do not have intraspecific names.

3129. The sequence of taxonomic categories is:

• A. Kingdom-Class-Phylum-Order-Family-Genus-Species
• B. Kingdom-Division-Class-Family-Order-Genus-Species
• C. Kingdom-Division-Class-Order-Family-Genus-Species
• D. Kingdom-Phylum-Order-Class-Family-Species-Genus

Explanation: According to biosystematics, to construct the hierarchy of classification, one or more species are grouped into a genus, one or more genera into a family, families are clubbed into an order, orders into a class, classes into a phylum, and various phyla into a kingdom.

3130. Linnaeus developed a system of nomenclature called

• A. Mononomial
• B. Trinomial
• C. Binomial
• D. Polynomial

Explanation: Binomial nomenclature of scientific naming was first given by C. Linnaeus (1735) in his book Systema Naturae and later in "Species Plantarum" (1753). He used two Latin words for any organism, the first being a generic name and the second being a specific name. The generic name begins with a capital letter and the species name with a small letter.