NCERT Solutions for Class 11 Biology Chapter 2 Question Answers

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

Answer:

Classification systems have evolved significantly over time. Aristotle first introduced a basic classification system using observable morphological traits, grouping plants into trees, shrubs, and herbs, and animals based on the presence or absence of red blood. Later, Linnaeus proposed a two-kingdom classification, dividing organisms into Plantae and Animalia, but this system lacked the ability to differentiate between eukaryotes and prokaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms. Over time, R.H. Whittaker introduced a more comprehensive five-kingdom classification system (Monera, Protista, Fungi, Plantae, and Animalia) based on cellular structure, body organization, nutrition, reproduction, and phylogeny. Subsequently, a three-domain system emerged, dividing Monera into two domains (Archaea and Bacteria), highlighting evolutionary relationships more effectively.

2. State two economically important uses of:

(a) heterotrophic bacteria

(b) archaebacteria

Answer:

(a) Heterotrophic bacteria

1. Used in the production of antibiotics, vitamins, and dairy products like cheese and curd.
2. Aid in nitrogen fixation and the formation of humus, enriching soil fertility.

(b) Archaebacteria

1. Play a role in biogas production, especially methane.
2. Useful in bioleaching processes in mining to extract metals.

3. What is the nature of cell walls in diatoms?

Answer:

Diatoms have silica-embedded cell walls, giving them unique patterns and making them indestructible. These cell wall deposits accumulate over time to form diatomaceous earth.

4. Find out what the terms ‘algal bloom’ and ‘red tides’ signify.

Answer:

• Algal bloom : An overgrowth of algae, especially blue-green algae, in contaminated water. It leads to oxygen depletion and water pollution.
• Red tides : Caused by rapid multiplication of red-pigmented dinoflagellates (e.g., Gonyaulax), giving the water a red appearance. These algae produce toxins harmful to aquatic life.

5. How are viroids different from viruses?

Answer:

• Viroids consist of single-stranded RNA without a protein coat, while viruses have genetic material (RNA or DNA) encased in a protein coat.
• Viroids are much smaller in size compared to viruses.
• Viroids infect only plants, whereas viruses infect plants, animals, and microorganisms.

6. Describe the four major groups of Protozoa briefly.

Answer:

• Amoeboid Protozoans : Use pseudopodia for movement and capturing prey; found in aquatic environments.
• Flagellated Protozoans : Use flagella for movement; can be free-living or parasitic.
• Ciliated Protozoans : Possess cilia for locomotion and feeding; thrive in aquatic habitats.
• Sporozoans : Produce spores during their life cycle; often parasitic and spread through hosts.

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

Answer:

Some plants, such as Utricularia (bladderwort), Drosera (sundew), and Nepenthes (pitcher plant), are partially heterotrophic. They trap and digest insects to supplement their nitrogen needs.

8. What do the terms phycobiont and mycobiont signify?

Answer:

In lichens, the phycobiont refers to the algal partner that performs photosynthesis to produce food, while the mycobiont is the fungal partner that provides protection and structure.

9. Give a comparative account of the classes of Kingdom Fungi under the following:

Answer:

Feature	Phycomycetes	Ascomycetes	Basidiomycetes	Deuteromycetes
Mode of Nutrition	Saprophytic or parasitic	Decomposers, saprophytic	Saprophytic	Decomposers, saprophytic
Mode of Reproduction	Asexual (zoospores, aplanospores); sexual (zygotes)	Asexual (conidia); sexual (ascospores)	Sexual (basidiospores)	Asexual (conidia)

10. What are the characteristic features of Euglenoids?

Answer:

• Lack a cell wall; have a flexible protein layer called pellicle.
• Possess two flagella of unequal lengths.
• Autotrophic in sunlight but heterotrophic in its absence.

11. Give a brief account of viruses with respect to their structure and genetic material. Name four common viral diseases.

Answer:

Viruses are non-cellular entities with genetic material (RNA or DNA) encased in a protein coat (capsid). Capsids are made of subunits called capsomers. They infect plants, animals, and microorganisms. Common viral diseases include Influenza, AIDS, Herpes, and Rabies.

12. Organise a discussion in your class on the topic ‘Are viruses living or nonliving’?

Answer:

Non-living Characters (i) No cellular structure (ii) They can be stored in bottles like crystals (iii) There will be no energy storage or energy liberation systems (iv) They cannot grow or multiply outside the host Living Characters (i) They are host-specific (ii) The presence of genetic material (iii) The ability to multiply (iv) They have antigenic properties (v) They are obligate parasites (vi) Mutations occur