Chapter 2 : Biological Classification

Class 11 Biology Chapter 2 Biological Classification Exercise Questions and Answers :

1. Discuss how classification systems have undergone several changes over a period of time?

Answer : Classification systems for living organisms have seen substantial transformations throughout history. Early categorizations were pragmatic, driven by the utilitarian purposes of food, shelter, and clothing. Aristotle laid the groundwork for a more scientific approach, using basic morphological traits to distinguish between plants and animals. Linnaeus introduced the Two Kingdom system, grouping organisms into Plantae and Animalia, which proved inadequate as it didn't account for the diversity of life.

Recognizing these limitations, subsequent classification systems integrated a broader range of characteristics such as cell structure, nutritional modes, habitat, reproductive methods, and evolutionary relationships. Over time, different scientists proposed alternative systems. R.H. Whittaker, in 1969, introduced the Five Kingdom Classification, including Monera, Protista, Fungi, Plantae, and Animalia, based on various criteria.

Further developments led to the three-domain system, separating the Kingdom Monera into two domains, ultimately resulting in a six-kingdom classification. These changes reflect the evolving understanding of biological diversity and the need for more comprehensive and accurate categorization.

2. State two economically important uses of :
(a) heterotrophic bacteria
(b) archaebacteria

Answer : (a) Heterotrophic Bacteria:

(i) Heterotrophic bacteria are employed in bioremediation to clean up oil spills, contaminated soil, and wastewater by breaking down harmful pollutants.

(ii) Certain heterotrophic bacteria like lactic acid bacteria are used in food fermentation processes, preserving and enhancing the flavor of products like yogurt, cheese, and sauerkraut.

(b) Archaebacteria:

(i) Archaebacteria, particularly extremophiles, offer enzymes and metabolic pathways valuable in biotechnological applications, such as PCR and bioleaching for mining.

(ii) Methanogenic archaea help in producing methane-rich biogas from organic waste materials, serving as a renewable energy source for electricity and heating
3. What is the nature of cell-walls in diatoms?

Answer : The cell walls of diatoms are composed of two thin overlapping shells embedded with silica, making them practically indestructible. Over billions of years, diatoms have left behind extensive deposits of these walls in their habitat, known as 'diatomaceous earth.' This gritty soil is used in various industrial applications, including polishing and filtration of oils and syrups, thanks to its durability and abrasive properties.
4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Answer :  Algal Bloom : An algal bloom is the rapid proliferation of algae in aquatic environments, often caused by factors like increased nutrients, warm water, and sunlight. While not always harmful, excessive algal growth can block sunlight, reduce oxygen, and impact aquatic ecosystems.

Red Tide : A red tide is a type of harmful algal bloom, characterized by specific algae species producing red or brown pigments. These blooms can release toxins that harm marine life and humans, leading to fish kills, shellfish contamination, and respiratory issues, impacting both ecosystems and economies in affected areas
5. How are viroids different from viruses?

Answer :

Characteristic	Viroids	Viruses
Genetic Material	Single-stranded circular RNA	DNA or RNA, often double-stranded
Protein Coat (Capsid)	Absent	Present (protein coat)
Host Range	Mainly plants	Various hosts, including plants, animals, and bacteria
Replication	Autonomous within host cell	Require host cell for replication
Size	Smaller, a few hundred nucleotides	Larger, can vary in size with more complex structures
Diseases	Mainly in plants, interference with growth and metabolism	Diverse diseases in a wide range of organisms, often by disrupting cellular functions

6. Describe briefly the four major groups of Protozoa.

Answer :  The four major groups of Protozoa are :

Amoeboid protozoans: These organisms live in fresh water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine forms have silica shells on their surface. Some of them such as Entamoeba are parasites.

Flagellated protozoans: The members of this group are either free-living or parasitic. They have flagella. The parasitic forms cause diaseases such as sleeping sickness. Example: Trypanosoma.

Ciliated protozoans: These are aquatic, actively moving organisms because of the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet. Example: Paramoecium .

Sporozoans: This includes diverse organisms that have an infectious spore-like stage in their life cycle. The most notorious is Plasmodium (malarial parasite) which causes malaria, a disease which has a staggering effect on human population.

7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Answer : Yes, some plants are partially heterotrophic. Examples include Drosera (sundews), Nepenthes (tropical pitcher plants), and Utricularia (bladderworts). They capture and digest insects or small organisms to obtain nutrients in nutrient-poor environments while still conducting photosynthesis for energy.
8. What do the terms phycobiont and mycobiont signify?

Answer : The phycobiont is the photosynthetic partner, which can be a green alga or cyanobacterium. The phycobiont performs photosynthesis, providing energy to the lichen.

The mycobiont is the fungal partner in the lichen symbiosis. It forms the structure of the lichen, protects the phycobiont, and absorbs water and nutrients from the environment.

Together, the phycobiont and mycobiont create a unique, mutualistic organism known as a lichen, allowing it to survive in various ecological niches.

9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition
(ii) mode of reproduction

Answer :  Given a comparative account of the classes within the Kingdom Fungi based on mode of nutrition and mode of reproduction:

(i) Mode of Nutrition:

Zygomycetes:

(i) Mostly saprophytic, obtaining nutrients from decaying organic matter.

(ii) Some are mycorrhizal, forming symbiotic relationships with plant roots.

Ascomycetes:

(i) Diverse modes of nutrition, including saprophytic, parasitic, and mutualistic.

(ii) Some form lichens with green algae or cyanobacteria.

Basidiomycetes:

(i) Primarily saprophytic, decomposing wood and plant material.

(ii) Some are mycorrhizal, forming associations with plant roots.

Deuteromycetes (Fungi Imperfecti):

(i) Varied nutrition, including saprophytic, parasitic, and some mutualistic associations.

(ii) Many fungi in this group lack a known sexual reproductive stage.

(ii) Mode of Reproduction:

Zygomycetes:

(i) Reproduce asexually through the formation of sporangia.

(ii) Sexually reproduce by the formation of zygosporangia after the fusion of specialized sexual structures.

Ascomycetes:

(i) Reproduce asexually by producing conidia.

(ii) Sexual reproduction involves the formation of asci containing ascospores.

Basidiomycetes:

(i) Asexual reproduction often involves the production of conidia or other structures.

(ii) Sexual reproduction occurs through the formation of basidia bearing basidiospores.

Deuteromycetes (Fungi Imperfecti):

(i) Primarily reproduce asexually by producing conidia or other asexual spores.

(ii) Lack a known sexual reproductive stage in many cases.

10. What are the characteristic features of Euglenoids?
11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Answer :  Viruses are unique infectious agents characterized by their structure and the nature of their genetic material are :

(i) Viruses contain genetic material, which can be either RNA or DNA, but not both. Plant-infecting viruses typically have single-stranded RNA, while viruses that infect animals can have either single-stranded or double-stranded RNA or double-stranded DNA. Bacterial viruses (bacteriophages) are usually double-stranded DNA viruses.

(ii) Viruses have a protective protein coat called a capsid, composed of small subunits known as capsomeres. This capsid shields the viral genetic material.

(iii) Capsomeres are arranged in various geometric forms, such as helical or polyhedral shapes.

Four common viral diseases are :

Mumps: Caused by the mumps virus, it leads to swelling of the salivary glands, fever, and muscle pain.

Smallpox: Although smallpox has been eradicated due to vaccination efforts, it was caused by the variola virus and resulted in severe skin rashes, high fever, and often death.

Herpes: Herpes viruses, including herpes simplex virus (HSV), cause oral or genital herpes, leading to painful sores in affected areas.

Influenza: Caused by various influenza viruses, it results in respiratory symptoms like fever, cough, and body aches.

12. Organise a discussion in your class on the topic – Are viruses living or non-living?

Answer : The classification of viruses as living or non-living is a subject of scientific debate, and perspectives on this issue vary:

Living Viruses:

(i) Some scientists argue that viruses exhibit life-like characteristics.

(ii) They can replicate within host cells, evolve through mutation, and adapt to changing environments.

(iii) This replication and adaptation suggest a level of agency and life-like behavior.

(iv) Viruses can carry genetic material and pass it on to the next generation, similar to living organisms.

Non-Living Viruses:

(i) Other scientists consider viruses non-living entities.

(ii) They lack cellular structure and are incapable of independent metabolism.

(iii) Viruses are entirely dependent on host cells for replication and energy.

(iv) They do not exhibit essential characteristics associated with life, such as growth, homeostasis, or response to stimuli.

The debate continues, and the classification of viruses as living or non-living remains an open question in the world of microbiology and biology.