EXERCISES

Q1. Discuss how classification systems have undergone several changes over a period of time?
Answer: Classification systems have changed over time as scientists learned more about living organisms.

1. Early Classification (Aristotle): He grouped plants into trees, shrubs, and herbs, and animals into those with or without red blood.
2. Two Kingdom System (Linnaeus): Divided all organisms into Plantae and Animalia, but it didn’t separate unicellular from multicellular or prokaryotes from eukaryotes.
3. Five Kingdom System (R.H. Whittaker, 1969): Introduced Monera, Protista, Fungi, Plantae, and Animalia — based on cell structure, nutrition, and organization.
4. Modern View: Scientists now use genetic and evolutionary studies, leading to systems like the three-domain model (dividing Monera into Archaea and Bacteria).

Q2. State two economically important uses of:
(a) Heterotrophic bacteria
Answer: Heterotrophic bacteria are useful because:

1. They help make curd from milk.
2. They are used in producing antibiotics.

(b) Archaebacteria
Answer: Archaebacteria like methanogens produce methane gas (biogas) in the guts of cattle and from animal dung.

Q3. What is the nature of cell-walls in diatoms?
Answer: In diatoms, the cell wall has two thin overlapping shells like a soap box. These walls contain silica, making them hard and indestructible. Over time, their remains form ‘diatomaceous earth’.

Q4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
Answer:

• Algal Bloom: When blue-green algae (cyanobacteria) grow rapidly in polluted water, forming a thick green layer.
• Red Tides: When red dinoflagellates like Gonyaulax multiply rapidly, turning the sea red and releasing toxins harmful to fish and other marine life.

Q5. How are viroids different from viruses?
Answer: Viroids and viruses differ mainly in structure:

• Viroids: Made only of RNA, no protein coat, and smaller in size.
• Viruses: Have either DNA or RNA covered by a protein coat (capsid) and are larger than viroids.

Q6. Describe briefly the four major groups of Protozoa.
Answer: The four major groups of protozoa are Amoeboid, Flagellated, Ciliated, and Sporozoans.

1. Amoeboid Protozoans: Live in water or soil; move using pseudopodia. Example – Amoeba.
2. Flagellated Protozoans: Move using flagella; some cause diseases. Example – Trypanosoma.
3. Ciliated Protozoans: Use cilia for movement and food capture. Example – Paramecium.
4. Sporozoans: Do not move; many are parasites. Example – Plasmodium (causes malaria).

Q7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer: Yes! Some plants make their own food but also get nutrients from other sources.

• Insectivorous plants: Catch insects for nitrogen. Example – Venus flytrap, Bladderwort.
• Parasitic plants: Take food from host plants. Example – Cuscuta (dodder).

Q8. What do the terms phycobiont and mycobiont signify?
Answer: In lichens, two organisms live together –

1. Phycobiont: The algal part; makes food using photosynthesis.
2. Mycobiont: The fungal part; provides water and minerals and protects the alga.

Q9. Give a comparative account of the classes of Kingdom Fungi under the following:
(i) Mode of Nutrition
(ii) mode of reproduction 
Answer: Mode of Nutrition in Fungi are-

• Phycomycetes: Grow on decaying wood or as plant parasites.
• Ascomycetes: Can be saprophytes, decomposers, or parasites.
• Basidiomycetes: Live on soil, logs, or as plant parasites (rusts and smuts).
• Deuteromycetes: Mostly decomposers that help recycle minerals.

(ii) Mode of Reproduction
Answer: Mode of Reproduction in Fungi are-

• Phycomycetes: Asexual spores (zoospores/aplanospores); sexual by zygospore formation.
• Ascomycetes: Asexual by conidia; sexual by ascospores in asci.
• Basidiomycetes: Asexual spores rare; sexual by basidiospores on basidium.
• Deuteromycetes: Only asexual reproduction by conidia; sexual phase unknown.

Q10. What are the characteristic features of Euglenoids?
Answer: Euglenoids are single-celled, freshwater organisms with unique features:

1. Pellicle: A flexible, protein layer instead of a cell wall.
2. Flagella: Two flagella — one long and one short.
3. Nutrition: Photosynthetic in light, heterotrophic in dark (mixotrophic).
4. Pigments: Similar to those of plants.
   Example – Euglena.

Q11. 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 non-cellular and can live only inside a host cell.

Structure: Made of genetic material (DNA or RNA) covered by a protein coat (capsid).

Nature of Genetic Material:

• Plant viruses – single-stranded RNA
• Animal viruses – RNA or DNA
• Bacteriophages – double-stranded DNA

Examples of Viral Diseases: Mumps, Smallpox, Herpes, Influenza (Flu).

Q12. Organise a discussion in your class on the topic Are viruses living or non-living?
Answer: Here’s how you can discuss:

Arguments for Non-living:

• No cell structure.
• Inactive crystals outside the host.

Arguments for Living:

• Contain genetic material (DNA/RNA).
• Reproduce inside host cells.
• Can evolve and mutate.

Conclusion: Viruses show both living and non-living traits, so they are best described as organisms at the border of life and non-life — active only inside a host.