Short & Long Question Answers with Solution: Biological Classification | Biology Class 11 - NEET PDF Download

Short Answer Type Questions

Q1. Why is Neurospora an important genetic tool? 
Ans:  Neurospora can thrive readily in laboratory settings when supplied with organic salts, carbohydrates, and vitamins. By subjecting Neurospora cells to X-ray treatments, mutations can be effortlessly induced, and the process of meiotic division becomes readily observable. 

Q2. What is diatomaceous earth? Why are diatoms referred to as ‘pearls of the ocean’? 
Ans: For billions of years, there has been a continuous buildup of substantial diatom deposits, creating a silica layer spanning hundreds of meters. Diatoms serve as the primary oceanic producers, generating nourishment not only for themselves but also for various other marine organisms. Their physical structure consists of a siliceous shell referred to as a frustule.

Q3. What is the role of fungi our daily lives? 
Ans: Fungi play various important roles in our everyday lives, including:

• Some fungi, such as Agaricus compestris, are abundant sources of nutrients and serve as food.
• Saprophytic fungi break down and transform complex organic matter into simpler compounds, which plants can then absorb as nutrients.
• Certain fungi, like Mucor and Absidia, have the ability to bind soil particles together, improving soil quality for cultivation.
• Fungi can provide natural resistance against pests in certain contexts.
• Fungi are employed in the production of alcohol and yeast thanks to their fermentation capabilities, exemplified by Saccharomyces.

 
Q4. State important uses of (a) heterotrophic bacteria and (b) archaebacteria. 
Ans: Key applications of Heterotrophic bacteria include their role as decomposers, contributing to the creation of organic manure known as humus. Additionally, they encompass bacteria like Rhizobium, which aids in the nitrogen fixation process in plants, and Lactobacillus, which plays a crucial role in curd formation.

As for Archaebacteria, they find significant utility in mineral bleaching and serve as polymerase enzymes in recombinant DNA technology. A notable example of Archaebacteria is Methanobacterium, which contributes to methane production, a valuable fuel source.

Q5. Please give a brief account of viruses concerning their structure and nature of genetic material. Also, name four common viral diseases. 
Ans: A virus is a contagious entity that becomes active within the host organism. Its genetic material is not fixed; it can be either RNA or DNA but never both simultaneously. These viral particles are enveloped by a protein coat and exhibit a crystalline structure. Plant-infecting viruses typically carry single-stranded RNA as their genetic material, while those infecting animals may contain double-stranded RNA or DNA as their genetic makeup. Common viral diseases include AIDS, Herpes, Rabies, and Influenza. 

Q6. What do you understand by ‘phycobiont’ and ‘mycobiont’?
Ans: The algal part of lichens is referred to as the phycobiont, and the fungal part is known as the mycobiont. These two organisms engage in a mutually beneficial symbiotic relationship. The algae produce nourishment for the fungi, while the fungi, in exchange, offer protection and absorb nutrients from the soil.

Q7. Find out what the terms ‘algal bloom’ and ‘red tides’ signify. 
Ans: An algal bloom refers to the proliferation of algae and other phytoplankton at the surface of water bodies. These blooms hinder the penetration of sunlight into the deeper layers of the water, leading to reduced light availability. The surface algae compete for dissolved oxygen, which can result in the mortality of aquatic organisms. The primary cause of algal blooms is often an increase in the nitrate levels within water bodies.

Red tides, on the other hand, occur when there is a sudden elevation in the levels of photosynthetic accessory pigments. This spike in accessory pigments triggers a rapid expansion of phytoplankton populations, which produce toxins that can be detrimental to the aquatic flora and fauna within the water bodies.

Q8. What are the Insectivorous plants?
Ans: Plants that obtain their nutrients by capturing and consuming insects, arthropods, or protozoans are commonly referred to as insectivorous plants or carnivorous plants. Acidic bogs provide some of the most notable examples of these insectivorous plants.

Q9. Plants are autotrophic. Can you think of some heterotrophic plants? 
Ans: Plants can be categorized into two primary types based on their nutritional mode: autotrophic and heterotrophic. Autotrophic plants are capable of producing their own food and energy, while heterotrophic plants rely on insects and other plants as a source of nourishment and energy. Examples like Drosera and Nepenthes fall into the category of heterotrophic plants because they consume insects to obtain nitrogen, which is subsequently utilized in the process of photosynthesis.

Q10. Name a few plants that are partially heterotrophic.
Ans: A few members are partially heterotrophic such as the insectivorous plants or parasites. Bladderwort and Venus fly trap are examples of insectivorous plants and Cuscuta is a parasite

Long Answer Type Questions

Q1. Discuss how the classification system has undergone several changes over a period of  time. 
Ans:  Aristotle initially categorized plants into herbs, shrubs, and trees, while he also attempted to classify animals into two groups based on the presence or absence of red blood cells. However, this classification proved inadequate.

Subsequently, Carolus Linnaeus introduced a two-kingdom classification system, comprising Plantae for plants and Animalia for animals. This system, however, lacked differentiation between eukaryotes, prokaryotes, single-celled, and multicellular organisms, rendering it insufficient.

R.H. Whittaker later developed a more comprehensive classification system of five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. These kingdoms were categorized based on criteria such as reproductive methods, nutritional modes, cell structure, and overall body organization.

Q2. Give a detailed account of the classes of Kingdom Fungi under the following: 
(i) Mode of nutrition
(ii) Mode of reproduction
Ans: 
(i) Nutritional Method – This pertains to the manner in which organisms obtain their sustenance and is primarily categorized into autotrophic and heterotrophic modes. In the fungal kingdom, four main classes exist. Phycomycetes are obligatory parasites that thrive on decaying organic matter. Ascomycetes are sporophytic and also play a role in decomposition. Basidiomycetes grow on logs or tree stumps and are responsible for diseases like plant rust. Deuteromycetes encompass a group of fungi that include sporophytic species and parasites.
(ii) Reproductive Mechanisms – Reproduction involves the processes by which organisms propagate and proliferate. In the case of Phycomycetes fungi, reproduction occurs via zoospores produced within sporangia. Ascomycetes utilize ascospores located within sac-like structures known as ascocarps for reproduction. Basidiomycetes employ fragmentation as their reproductive method, while Deuteromycetes rely on asexual spores referred to as conidia for reproduction.

Q3.

• What are heterocysts?
• Write a note on dikaryophase.
• Differentiate the Protista and Fungi in terms of their nutrition. 

Ans: Heterocysts are colorless cells that belong to the cyanobacteria group. These specialized cells are responsible for nitrogen fixation and house the enzyme nitrogenase. For example, Nostoc and Anabaena are known for this feature.

The term "dikaryophase" is also referred to as the "dikaryotic phase." Cells in this phase do not have a diploid configuration but instead contain two nuclei. This phase is observed in fungi groups like Basidiomycetes and Ascomycetes, serving as an intermediate stage in the fungal life cycle.

Protists are unicellular eukaryotic organisms that reproduce sexually through gametes. The primary divisions within the Protista kingdom include algae, molds, and protozoans. Many protists are autotrophic, meaning they can produce their own food, while some are heterotrophic. Conversely, fungi possess chitin cell walls and are heterotrophic, relying on other organisms for their survival.

Q4. Explain sexual reproduction in bacteria. 
Ans: There are three main steps for bacterial reproduction. The steps are as follows – 

• Conjugation was originally discovered by Lederberg and Tatum. In this process, the male cell, also known as the donor cell, transfers its DNA to the recipient cell.
• Transformation, as elucidated by Griffith, involves the death of the donor cell, releasing its DNA content into the surrounding environment. This released DNA is then incorporated into active cells. The new cell that takes up the donor cell's DNA is termed the recipient cell, which inherits all the characteristics of the donor cell. The recipient cell is also referred to as a recombinant cell.
• Transduction, discovered by Zinder and Lederberg, entails the transfer of donor genes into the recipient cell facilitated by a virus.

Q5. How many types of bacteria are there?
Ans:  Bacteria can be found in pairs, chains, clusters, or as single cells. They exhibit various shapes and are categorized according to their morphology, Gram stain characteristics, and oxygen requirements.

In terms of their shapes, bacteria are grouped into five categories:

• Bacilli, which are rod-shaped bacteria.
• Spirilla, characterized by their spiral shape.
• Vibrios, which are comma-shaped bacteria.
• Cocci, displaying a spherical shape.
• Spirochaetes, with a corkscrew-like appearance.

Regarding their cell wall composition, bacteria fall into two main groups:

• Gram-positive bacteria.
• Gram-negative bacteria.

Bacteria can also be classified based on their respiration mode or oxygen demands into two categories:

• Aerobic bacteria or aerobes.
• Anaerobic bacteria or anaerobes.

Lastly, bacteria can be categorized by their nutritional mode into two groups:

• Autotrophic bacteria.
• Heterotrophic bacteria.

Q6. What are the characteristic features of euglenoids?
Ans: The characteristic features of euglenoids are:

• They are unicellular protists, commonly found in freshwater.
• The cell membrane is rich in proteins and is known as a pellicle.
• Two flagella are present on the anterior end of the body.
• They possess a small light-sensitive eyespot.
• They are autotrophic because of the presence of photosynthetic pigment chlorophyll. However, in the absence of light, they behave as heterotrophs.
• They are known as the connecting-link between plants and animals because they possess features common to both plants and animals.

Q 7: Discuss the unique characteristics of viruses and how they differ from cellular organisms in their method of reproduction and structural composition.

Ans: Viruses are unique in the biological world due to their simplistic, acellular structure and method of reproduction. 

•  Unlike cellular organisms, viruses do not possess a cell structure and are considered non-living when outside a host cell. 
•  This acellular nature is characterized by an inert crystalline structure that becomes active only within the confines of a host. 
•  A virus typically consists of genetic material, either RNA or DNA, but never both, which is encased in a protein coat known as a capsid. 
•  This capsid is composed of protein subunits called capsomeres, which may be arranged in either helical or polyhedral geometric forms. 
•  The reproductive process of viruses distinctly sets them apart from cellular organisms. 
• Viruses are obligate parasites, meaning they must infect a host cell to replicate. 
•  Once a virus infects a host cell, it hijacks the host's cellular machinery to synthesize its components: nucleic acids are replicated, and protein coats are produced. 
•  The host cell often dies due to this takeover, leading to the release of new virus particles. 
•  This method of reproduction via host manipulation underlines why viruses did not find a place in traditional biological classification systems, as their life processes are dependent entirely on invading living cells, challenging the typical definitions of what it means to be 'alive'. 

Q8: Compare and contrast the characteristics and impacts of viroids and prions, particularly focusing on the diseases they cause and their biological composition.

Ans: 

• Viroids and prions are two types of infectious agents that, despite their simplicity, cause significant diseases in plants and animals, respectively.
• Viroids, discovered by T.O. Diener in 1971, are notably smaller than viruses and consist solely of a short strand of circular, single-stranded RNA without a protective protein coat.
• This lack of a protein coat differentiates viroids from viruses and contributes to their unique mode of infection.
• The RNA of viroids is of low molecular weight and is capable of interfering with the host cell's genetic regulation, causing diseases such as potato spindle tuber disease in plants.
• Viroids do not encode proteins and rely on the host’s cellular machinery to replicate.
• Prions, on the other hand, represent a different kind of infectious agent, primarily affecting neurological systems in animals and humans.
• Unlike viroids, prions do not contain nucleic acids but are composed of abnormally folded proteins that induce other normal proteins in the host to also misfold.
• These misfolded proteins accumulate in the brain, leading to tissue damage and characteristic spongiform changes.
• Prions are responsible for causing devastating diseases such as bovine spongiform encephalopathy (BSE), commonly known as mad cow disease in cattle, and Creutzfeldt-Jakob disease (CJD) in humans.
• Both viroids and prions are similar in their subviral size and lack of certain components typical of more complex pathogens, such as DNA in prions and a protein coat in viroids.
• However, their modes of infection, the diseases they cause, and their biological impacts vary greatly, highlighting the diversity of mechanisms that infectious agents can employ to affect their hosts.