Free Biodiversity and Variety of Life MCQs with Answers

2421. In chlorophyceae, the mode of sexual reproduction is

• A. Isogamy
• B. Anisogamy
• C. Oogamy
• D. All of these

Explanation: d. In Chlorophyceae, the mode of sexual reproduction can be all of these-Isogamy, Anisogamy, and Oogamy. The specific reproductive mode may vary among different species within this group, and they can exhibit various reproductive strategies depending on the species and environmental conditions. Isogamy involves the fusion of gametes that are similar in size and structure, anisogamy involves the fusion of gametes that are dissimilar in size, and oogamy involves the fusion of a large, non-motile egg cell with a smaller, motile sperm cell. These modes offer flexibility in reproduction and adaptability to different ecological niches.Other options are explained below:a. Isogamy: In isogamy, the gametes (reproductive cells) are similar in size and structure. Both the male and female gametes are morphologically alike. The fusion of isogametes results in the formation of a zygote.b. Anisogamy: Anisogamy involves the production of gametes that differ in size or structure between the male and female. One type of gamete is typically smaller (male), and the other is larger (female). The fusion of these dissimilar gametes leads to the formation of a zygote.c. Oogamy: Oogamy is a more specialized form of sexual reproduction where one gamete (usually the egg or ovum) is large and non-motile, while the other gamete (sperm) is small and motile. Oogamy is common in many green algae, including Chlorophyceae.

2422. The sexual reproduction is absent in

• A. Spirogyra
• B. Nostoc
• C. Ulothrix
• D. Volvox

Explanation: b. Nostoc belongs to Cyanophyceae. In this entire class sexual reproduction is completely absent. It reproduces by colony formation, hormogonia, akinetes, heterocysts, and endospores. However genetic recombination has been observed. It may be probably through transformation or conjugation. The other three algae­ Spirogyra, Ulothrix andVolvox belong to Chlorophyceae. The members of this class show isogamous, anisogamous, and oogamous types of sexual reproduction. Explain other options too: a. Spirogyra: Spirogyra reproduces both sexually and asexually. It undergoes a process called conjugation for sexual reproduction, where two filaments come into contact, and a conjugation tube forms between them. However, it doesn't involve the formation of specialized reproductive structures like gametes. c. Ulothrix: Ulothrix is a filamentous green alga. It reproduces both sexually and asexually. Asexual reproduction involves the formation of zoospores, and sexual reproduction involves the formation of isogametes (similar-sized gametes). d. Volvox: Volvox is a colonial green alga. It also reproduces both sexually and asexually. Asexual reproduction occurs through the formation of daughter colonies, while sexual reproduction involves the formation of specialized reproductive cells, including eggs and sperm.

2423. Auxospores and hormogonia are formed, respectively, by

• A. Some diatoms and several cyanobacteria
• B. Some cyanobacteria and many diatoms
• C. Everal cyanobacteria and several diatoms
• D. Several diatoms and a few cyanobacteria.

Explanation: d. Until 1907, auxospore formation was regarded as asexual process but now it is considered as an act of sexual process. The auxospores may be autogamous, isogamous, anisogamous or oogamous. Their pattern of formation differs in pennate and centric diatoms. Formation of hormogonia is the common method of reproduction in Nostoc which are produced by accidental breaking of trichome into several pieces. It may also be formed by death and decay of ordinary intercalary cells. Soon, the hormogonium escapes from mucilage and grows into a new filament and then into a new colony. Auxospores are formed by several diatoms, and hormogonia are produced by a few cyanobacteria. a. Some diatoms and several cyanobacteria: This option is incorrect. Auxospores are formed by diatoms, but hormogonia are not associated with cyanobacteria. b. Some cyanobacteria and many diatoms: This option is also incorrect. Auxospores are typically formed by diatoms, while hormogonia are mainly a feature of cyanobacteria. c.Several cyanobacteria and several diatoms: This option is incorrect as well. While diatoms do produce auxospores, the term "hormogonia" is more commonly associated with cyanobacteria. Summary: Auxospores are primarily produced by diatoms, while hormogonia are a feature of a select group of cyanobacteria. Option 4 correctly identifies the organisms associated with the formation of these structures.

2424. How many organisms in the list given below are autotrophs? Lactobacillus, Nostoc, Chara, Nitrosomonas, Nitrobacter, Streptomyces, Saccharomyces, Trypanosoma, Porphyra, Wolffia.

• A. Four
• B. Five
• C. Six
• D. Three

Explanation: The autotrophs in the list given are: Nostoc Chara Porphyra Wolffia Autotrophs are organisms that can synthesize their own organic compounds using inorganic substances, such as carbon dioxide and sunlight or other forms of energy. They are capable of producing their own food through photosynthesis or chemosynthesis. The remaining organisms in the list are not autotrophs: Lactobacillus: Lactobacillus is a bacteria that is typically heterotrophic, meaning it obtains its energy from organic compounds produced by other organisms. Nitrosomonas and Nitrobacter: These are bacteria that are involved in the nitrogen cycle and are chemoautotrophs. They derive their energy from the oxidation of inorganic compounds, but they are not capable of photosynthesis. Streptomyces: Streptomyces is a genus of bacteria that is primarily decomposers and obtain their energy from breaking down organic matter. Saccharomyces: Saccharomyces is a yeast that is heterotrophic and obtains its energy from organic compounds. Trypanosoma: Trypanosoma is a parasitic protozoan that is heterotrophic and obtains its energy from consuming organic matter. Therefore, out of the organisms listed, four are autotrophs, and the remaining six are heterotrophs.

2425. It occupies position near center of cell:

• A. Chromosome
• B. Plasmid
• C. Nucleoid
• D. Mitochondria

Explanation: The correct answer is the nucleoid. In prokaryotic cells, the nucleoid is the region where the cell's chromosomal DNA is concentrated. It is centrally located within the cell and is not enclosed by a membrane, unlike a nucleus in eukaryotic cells. This makes it unique to prokaryotes.Option A, Chromosome, refers to the DNA structure found within the nucleoid, not a separate entity. Option B, Plasmid, is a smaller DNA molecule that exists separately in the cytoplasm and is not centrally located. Option D, Mitochondria, are organelles found only in eukaryotic cells and thus not present in prokaryotes.

2426. Cyanobacteria are_in nature.

• A. Autotroph
• B. Heterotroph
• C. Decomposer
• D. None

Explanation: The correct answer is: a) Autotroph.Cyanobacteria are classified as autotrophs because they have the capability to produce their own food through photosynthesis. They utilize sunlight to convert carbon dioxide and water into glucose and oxygen, acting as primary producers in their ecosystems. This distinguishes them from heterotrophs, which depend on other organisms for organic material, and decomposers, which break down dead organic matter. Option D is incorrect because cyanobacteria indeed have a defined mode of nutrition as autotrophs.

2427. The several arrangements of cocci are based on their:

• A. Long chain of cells
• B. Types of division
• C. Shape
• D. All of the above

Explanation: The arrangements of cocci are determined by how they divide and remain connected. These arrangements include diplococcus (pairs), streptococcus (chains), staphylococcus (clusters), tetrads (groups of four), and sarcina (groups of eight). Each arrangement results from specific types of division and how the cells remain connected post-division. Therefore, the correct answer is that the arrangements are based on all these factors: long chains (as in Streptococcus), types of division, and their spherical shape. Options A, B, and C each describe only part of the picture, while Option D correctly encompasses all aspects.

2428. Division of cocci in three planes results in formation of:

• A. Sacrinae
• B. Tetrad
• C. Staphylococcus
• D. All of the above

Explanation: The correct answer is Sacrinae because when cocci undergo division in three planes, they form a cubic arrangement of 8 cells. This is distinct from the other options: Tetrad occurs with division in two planes, creating a square of 4 cocci; Staphylococcus arises from random divisions resulting in irregular clusters; and All of the above is incorrect because not all arrangements are produced by division in three planes.

2429. Comma shaped bacteria is:

• A. E. coli
• B. Vibrio
• C. Mycoplasma
• D. Bacillus

Explanation: The correct answer is Vibrio, which refers to bacteria that are characteristically comma-shaped. E. coli is rod-shaped, Mycoplasma can be spherical or pleomorphic due to its lack of a cell wall, and Bacillus is straight and rod-shaped. Thus, only Vibrio fits the description of being comma-shaped.

2430. Which is a spiral shape bacteria?

• A. Spirochete
• B. E. coli
• C. Pseudomonas
• D. Streptococcus

Explanation: The correct answer is Spirochete because they are spiral-shaped bacteria. The spiral shape allows them to move in unique ways compared to other bacterial shapes. E. coli and Pseudomonas are both rod-shaped bacteria, while Streptococcus is spherical, forming chains, thus none of these match the spiral shape described in the question.