Worksheet with Solutions : Biological Classification | Biology Class 11 - NEET PDF Download

Ans: Diatoms

Ans: Basidiomycetes

Ans: R.H. Whittaker

Ans: Archaebacteria

Ans: Lichens

Ans:

Ans: B) Nostoc
Nostoc, a cyanobacterium (eubacteria), can fix atmospheric nitrogen in specialized cells called heterocysts. Mycoplasma lack cell walls, methanogens produce methane, and thermoacidophiles thrive in hot, acidic environments.

Ans: ​B) Presence of a dikaryotic stage
Basidiomycetes undergo a dikaryotic stage (n + n) during sexual reproduction, where two nuclei coexist in a cell before fusing to form a diploid nucleus in the basidium.

Ans: A) Both A and R are true, and R is the correct explanation of A.
The content states that Phycomycetes are found in aquatic habitats, on decaying wood in moist places, or as obligate parasites on plants (e.g., Albugo on mustard). Their mycelium is aseptate and coenocytic (lacking cross walls and having multinucleated cytoplasm), which supports their growth in moist or aquatic environments. The reason explains why they thrive in such habitats, making option A correct. 

Ans: A) Both A and R are true, and R is the correct explanation of A.
The content states that viruses are non-cellular and have an inert crystalline structure outside living cells, making them non-living until they infect a host. W.M. Stanley’s work (1935) demonstrated that viruses could be crystallized, as mentioned in the MCQ, supporting their inert nature. The reason explains why viruses are non-living outside hosts, making option A correct.

Ans: Archaebacteria, such as halophiles, thrive in extreme salty areas.

Ans:  Euglena, a euglenoid, is photosynthetic in sunlight but can behave as a heterotroph by preying on smaller organisms when light is absent.

Ans: Slime moulds form a multinucleated aggregation called a plasmodium, which can spread over several feet.

Ans: Ascomycetes are called sac-fungi because they produce ascospores endogenously in sac-like structures called asci.

Ans: Deuteromycetes are known as imperfect fungi because only their asexual or vegetative phases are known.

Ans: Kingdom Plantae exhibits alternation of generations between diploid sporophytic and haploid gametophytic phases.

Ans: Cuscuta is a parasitic plant that depends on host plants for nutrition.

Ans: Animals in Kingdom Animalia have a holozoic mode of nutrition, involving ingestion and internal digestion of food.

Ans: Viroids, discovered by T.O. Diener in 1971, are free RNA molecules without a protein coat, causing diseases like potato spindle tuber disease.

Ans: Prions are infectious agents made of abnormally folded proteins, causing⠀diseases like bovine spongiform encephalopathy (mad cow disease).

Ans: Classification systems for living organisms have evolved significantly, reflecting advancements in scientific understanding. Initially, a two-kingdom system divided organisms into Plantae and Animalia, based on simple morphological characters. This system was inadequate as it did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms, or photosynthetic and non-photosynthetic organisms, failing to account for diverse life forms like bacteria and fungi.

To address these limitations, R.H. Whittaker proposed the five-kingdom classification in 1969, comprising:

• Monera: Prokaryotic organisms, including bacteria.

• Protista: Unicellular eukaryotic organisms, such as protozoans and algae.

• Fungi: Heterotrophic organisms, like mushrooms and yeast, that are saprophytic or parasitic.

• Plantae: Multicellular, photosynthetic organisms, including algae and plants.

• Animalia: Multicellular, heterotrophic organisms with holozoic nutrition.

This system categorized organisms based on cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships, better accommodating the diversity of life.

The three-domain system emerged later, dividing life into three domains: Bacteria, Archaea, and Eukarya. Bacteria include prokaryotic organisms, Archaea encompass prokaryotes living in extreme environments, and Eukarya cover eukaryotic organisms, including plants, animals, fungi, and protists. This system reflects a deeper understanding of evolutionary relationships, distinguishing Archaea from Bacteria and grouping all eukaryotes together.

Ans: Protozoans are unicellular, eukaryotic organisms classified into four major groups based on their modes of movement and nutrition, all heterotrophic and living as predators or parasites:

• Amoeboid Protozoans: These organisms move and capture prey using pseudopodia, extensions of their cytoplasm. They inhabit freshwater, seawater, or moist soil, with some being parasitic. Their heterotrophic nutrition involves engulfing food. Examples include Amoeba and Entamoeba, the latter causing diseases.

• Flagellated Protozoans: Characterized by flagella for movement, these protozoans are free-living or parasitic. They feed heterotrophically by preying on smaller organisms or as parasites. Trypanosoma, which causes sleeping sickness, is a key example.

• Ciliated Protozoans: These aquatic organisms use thousands of cilia for active movement and to steer food-laden water into a gullet, a cavity opening to the cell surface. They are heterotrophic, relying on ingested food. Paramoecium is a common example.

• Sporozoans: These non-motile protozoans have an infectious spore-like stage in their life cycle. As parasites, they absorb nutrients from hosts. Plasmodium, causing malaria, is a notable example.

Ans: Viroids and viruses are infectious agents with distinct structures and infection mechanisms:

• Structure: Viroids are smaller than viruses, consisting solely of low-molecular-weight, free RNA without a protein coat. Viruses are nucleoproteins with genetic material—either RNA or DNA, never both—encased in a protein coat called a capsid, made of capsomeres arranged in helical or polyhedral forms.

• Nature: Viroids lack the complex structure of viruses, being non-cellular and simpler. Viruses are non-cellular, inert outside hosts, and replicate only within host cells, often killing the host.

Viroid Structure and Infection: Viroids are composed of free, single-stranded RNA. They infect plants, replicating in the host cell’s nucleus or chloroplast, disrupting growth and development. Infection occurs through wounds or vectors like insects.

Diseases Caused by Viroids: Viroids cause plant diseases, such as potato spindle tuber disease, leading to malformed and stunted tubers.

Ans: Fungi are classified into four classes based on mycelium morphology, spore formation, and fruiting bodies, with variations in nutrition and reproduction:

• Phycomycetes:

  • Mode of Nutrition: Saprophytic, parasitic, or symbiotic, absorbing nutrients from decaying matter or living hosts.

  • Mode of Reproduction: Asexual reproduction occurs via zoospores (motile) or aplanospores (non-motile) produced in sporangia. Sexual reproduction involves zygospore formation through fusion of similar (isogamous) or dissimilar (anisogamous or oogamous) gametes.

  • Examples: Mucor, Rhizopus (bread mould), Albugo (parasitic on mustard).

• Ascomycetes:

  • Mode of Nutrition: Mostly saprophytic, some parasitic or coprophilous (growing on dung), absorbing organic matter.

  • Mode of Reproduction: Asexual reproduction is by conidia, produced exogenously on conidiophores. Sexual reproduction produces ascospores endogenously in sac-like asci within ascocarps, involving a dikaryotic stage.

  • Examples: Penicillium, Aspergillus, Saccharomyces (yeast), Neurospora.

• Basidiomycetes:

  • Mode of Nutrition: Saprophytic or parasitic, decomposing organic matter or infecting plants.

  • Mode of Reproduction: Asexual spores are generally absent; vegetative reproduction occurs by fragmentation. Sexual reproduction involves basidiospores, formed exogenously on basidia in basidiocarps, following a dikaryotic stage.

  • Examples: Agaricus (mushroom), Puccinia (rust fungus), Ustilago (smut).

• Deuteromycetes:

  • Mode of Nutrition: Saprophytic or parasitic, primarily decomposing organic matter.

  • Mode of Reproduction: Only asexual reproduction via conidia is observed, as sexual stages are unknown, earning them the name imperfect fungi.

  • Examples: Alternaria, Colletotrichum, Trichoderma.

Ans: Structure and Nature of Genetic Material in Viruses: Viruses are non-cellular, consisting of a nucleic acid core—either RNA or DNA, never both—surrounded by a protein coat called a capsid, made of capsomeres arranged in helical or polyhedral forms. The capsid protects the genetic material, which is infectious and directs replication within a host cell. Viruses are obligate parasites, inert outside hosts, and replicate by hijacking host machinery, often killing the host.

Classification Based on Genetic Material: Viruses are classified by their nucleic acid type:

• Plant Viruses: Typically have single-stranded RNA.

• Animal Viruses: May have single- or double-stranded RNA or double-stranded DNA.

• Bacteriophages: Usually have double-stranded DNA.

Common Viral Diseases and Impact:

• Mumps: Caused by a virus, it leads to swelling of salivary glands, fever, and discomfort, significantly affecting children and requiring vaccination to control spread.

• Smallpox: A viral disease causing severe skin lesions and high mortality, now eradicated through global vaccination, demonstrating effective public health intervention.

• Herpes: Caused by a virus, it results in recurrent skin and mucous membrane infections, impacting quality of life due to chronic outbreaks.

• Influenza: Caused by a virus, it triggers respiratory illness, leading to seasonal epidemics with widespread morbidity and occasional severe pandemics.