Class 11 Biology Chapter 2 Biological Classification, 1st Year
Biological Classification
Q1. Discuss how classification systems have undergone several changes over a period of time?
Answer: With time the classification systems undergoing a number of changes. Aristotle had made the first attempt at classification. He listed herbs, shrubs, and trees as plants. On other hand, animals have been categorized based on the presence or lack of red blood cells. This classification system failed to classify all the known organisms. Therefore, Linnaeus gave a two kingdom classification system. It includes the Plantae kingdom and the Animalia kingdom. This system, however, did not distinguish between unicellular and multicellular organisms and between eukaryotic and prokaryotic. Thus, vast numbers of species were present that could not be categorized under the two kingdoms.
Q2. State two economically important uses of:
a) Heterotrophic bacteria
b) Archaebacteria
Answer: Two economically important uses of:
a) Heterotrophic bacteria:
• Heterotrophic bacteria help in the curd production from milk.
• Many antibiotics are also obtained from these bacteria.
b) Archaebacteria:
• These bacteria help in production of methane gas from the dung of ruminants by the methanogens.
• Methanogens also engaged in biogas production and waste treatment.
Q 3. What is the nature of cell-walls in diatoms?
Answer: In diatoms, cell walls are embedded with silica which keeps them indestructible. They create two thin overlapping shells which fit together like a soap box.
Q4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
Answer: Algal bloom refers to an increase in algae or blue-green algae population in water which result in discoloration of water body.
Red tides are caused by the rapid accumulation of red dinoflagellates. The sea appears red in colour, because of its huge numbers. Toxins which they release can destroy other marine organisms.
Q5. How are viroids different from viruses?
Answer: Viroids have free RNAs without the protein coat, while virus has RNA which is surrounded with a protein coat.
Q6. Describe briefly the four major groups of Protozoa.
Answer: The four major groups of protozoa are:
• Amoeboid protozoans are those organisms which live in fresh water or moist soil. They have pseudopodia through which they can move and capture their prey. Marine forms have shells of silica on their surface. Some are parasites such as Entamoeba.
• Flagellated protozoans are the parasites or free-living which have flagella. Example: Trypanosoma.
• Ciliated protozoa or ciliates are aquatic organisms. They have numerous cilia on the entire surface of the body and the presence of two types of nuclei. Example: Paramoecium.
• Sporozoans include disease causing endoparasites and other pathogens. Their body is covered by a pellicle. They are uninucleate. They do not have cilia or flagella. Example: Plasmodium.
Q7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer: Bladderwort and venus fly trap are insectivorous plants which are heterotrophic.
Q8. What do the terms phycobiont and mycobiont signify?
Answer: In lichens, phycobiont is the name of the region that composed of algae and mycobiont is the name of the region composed of fungi.
Q9. Give a comparative account of the classes of Kingdom Fungi under the following:
i. Mode of nutrition
ii. Mode of reproduction
Answer:
i. Mode of nutrition: They are heterotrophic and they absorb soluble organic matter from dead substrates i.e., they are saprophytres, they lives on living animals and plants i.e., they are parasites.
ii. Mode of reproduction: They can reproduce by vegetative means such as fragmentation, budding, and fission; asexual reproduction by conidia or zoospores or sporangiospores; sexual reproduction by oospore, basidiospores, and ascospores.
Q10. What are the characteristics features of Euglenoids?
Answer: The characteristics features of Euglenoids are
• They are fresh water organisms found in stagnant water.
• They have pellicle which makes their body flexible.
• They are both autotrophic and heterotrophic.
• A small light sensitive eye spot is present.
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 have a protein capsule which contains genetic materials. These genetic materials get activated when they are inside the nucleus of a host cell. Inside the nucleus of the host cell they begin to reproduce themselves and cause disease. Viruses that infect plants have single stranded RNA. Viruses that infect animals have double stranded DNA or RNA. Viruses which infect bacteria have DNA double stranded. Examples of virus diseases are: small pox, AIDS, Influenza etc.
Q12. Organise a discussion in your class on the topic – Are viruses living or non-living?
Answer: Viruses are microscopic organisms which have the characteristics of both living and non-living. They have genetic material either DNA or RNA which shows they are living. Viruses cannot reproduce without using their host cell machinery which indicates that they are non-living.
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