CBSE Class 11 Biology Exemplar Chapter 2: Biological Classification NCERT Solutions

Protista is a diverse group comprising unicellular eukaryotic organisms. These organisms can be autotrophic (photosynthetic), heterotrophic, or parasitic. In contrast, Monera includes prokaryotic organisms like bacteria. Fungi are eukaryotic but are predominantly multicellular, with yeast being a notable unicellular exception. Therefore, all unicellular eukaryotes fall under the kingdom Protista.

In 1969, the American taxonomist R.H. Whittaker proposed a five-kingdom classification system to establish a more phylogenetic basis for organizing life. The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia. Carl Linnaeus, on the other hand, developed the earlier two-kingdom classification system, dividing organisms into Plantae and Animalia. Virchow is associated with cell theory, not the five-kingdom classification.

Halophiles are microorganisms that thrive in environments with high salt concentrations. The term 'halophile' originates from Greek words meaning 'salt-loving'. Methanogens are bacteria that produce methane under anaerobic conditions. Heliophytes are plants that grow best in direct sunlight. Thermoacidophiles are extremophilic archaea that live in hot, acidic environments.

Slime molds are saprophytic protists that exhibit characteristics such as naked cytoplasm (protoplasm not enclosed by a cell wall), multinucleated structure (forming a plasmodium), and a saprophytic mode of nutrition, feeding on decaying organic matter. Monerans are prokaryotes. Protists are eukaryotic but typically have a cell membrane around their cytoplasm. Fungi possess cell walls made of chitin and do not typically have naked cytoplasm.

Mycorrhiza refers to the symbiotic association between the fungi and the roots of higher plants, such as gymnosperms and angiosperms. In this relationship, the fungus benefits from the plant by obtaining carbohydrates and shelter, while the plant benefits from the fungus through enhanced absorption of water and mineral nutrients from the soil. Lichens are a symbiotic association between algae and fungi. Ferns are vascular plants belonging to pteridophytes, and BGA stands for blue-green algae, which are prokaryotic cyanobacteria.

A dikaryon is a stage in the life cycle of certain fungi where two haploid cells fuse, but their nuclei do not immediately fuse. This results in a cell containing two distinct haploid nuclei, referred to as a dikaryotic cell (n+n). Meiosis is a process of cell division that reduces chromosome number and does not directly lead to dikaryon formation. Cytoplasmic fusion (plasmogamy) precedes nuclear fusion (karyogamy) in many fungal life cycles, leading to the dikaryotic stage.

M.W. Beijerinck, a Dutch microbiologist, proposed the concept of 'contagium vivum fluidum', which translates to 'contagious living fluid'. He used this term to describe the infectious agent of tobacco mosaic disease, recognizing it as something smaller than a bacterium and capable of passing through filters. D.J. Ivanowsky is credited with discovering viruses and their filterable nature. Stanley Miller is known for his experiments on the origin of life, and Robert Hooke was the first to observe and describe cells.