11 Biology

Biological Classification

NCERT Solution

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

Answer: Scientific classification of living beings was first done by Aristotle. He used morphological characters as the basis of classification. He classified the living beings into plants and animals. He further classified the plant into trees, shrubs and herbs. He further classified the animals on the basis of presence of absence of red blood.

After that, Linnaeus proposed two kingdoms, i.e. Plant Kingdom and Animal Kingdom.

But there were certain organisms which could be kept in both of the kingdoms or could not be kept in either of the kingdoms. Hence, a need was felt for a better system of classification. At present, the Five Kingdom Classification is the most accepted one. This was proposed by Robert Whittaker in 1969. Whittaker used phylogenetic relationship to classify the living beings.

Question 2: State two economically important uses of:

(a) Heterotrophic bacteria

Answer: Curd and antibiotic are made by using heterotrophic bacteria.

(b) Archaebacteria

Answer: Methanogens are responsible for production of biogas which can be used as fuel. The archaebacteria which live in extreme conditions give us a clue about the beginning of life on earth.

Question 3: What is the nature of cell-walls in diatoms?

Answer: The cell walls in diatoms form two thin overlapping shells; which fit together as the two parts of a soapbox. The cell walls are embedded with silica and hence are indestructible.

Question 4: Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Answer: A rapid increase in the population of microscopic algae in an aquatic habitat is called algal bloom. The algal bloom involving the dianoflagellates is called the ‘red tide’ because of its red hue. Red tide can be harmful for other aquatic life forms.

Question 5: How are viroids different from viruses?

Answer: The free RNAs without the protein coat are called viroids, while virus have a protein coat to protect the genetic material.

Question 6: Describe briefly the four major groups of Protozoa.

Answer: Four major groups of Protozoa is as follows:

Amoeboid protozoans: The amoeboid protozoans live in freshwater, sea water or in moist soil. They produce pseudopodia for locomotion and for capturing food. The marine forms have silica shells on their surface. Some of them are parasites, e.g. Entamoeba histolytica.

Flagellated protozoans: They are either free-living or parasitic. Flagella is present for locomotion. Many of them are parasites, e.g. Trypanosoma.

Ciliated protozoans: They are aquatic. Cilia are present for locomotion. A cavity (gullet) is present which opens to the outside of the cell surface. The coordinated movement of cilia facilitates the entry of food-laden water into the gullet. Example: Paramoecium.

Sporozoans: The sporozoans have an infectious spore-like stage in their life cycle. Example: Plasmodium.

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

Answer: Pitcher plant, Venus fly trap and bladderwort are examples of partially heterotrophic plants.

Question 8: What do the terms phycobiont and mycobiont signify?

Answer: Lichens are the symbiotic association of fungi and algae. The algal part of lichen is called phycobiont and the fungal part is called mycobiont. The mycobiont part provides minerals and support, while the phycobiont part provides nutrition.

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

(a) Mode of nutrition

Answer: Phycomycetes are obligate parasites or saprophytes.
Ascomycetes are saprophytes or parasites or coprophilous.
Basidiomycetes are saprophytes or parasites.
Deuteromycetes are manly saprophytes, some are parasites.

(b) Mode of reproduction

Answer: In phycomycetes, asexual reproduction is by zoospores (motile) or by aplanospores.
In ascomycetes, asexual spores (conidia) and sexual spores (ascospores) are produced.
In basidiomycetes, vegetative reproduction takes place by fragmentation. Plsamogamy is also seen.
In deuteromycetes, only vegetative reproduction is seen.

Question 10: What are the characteristic features of Euglenoids?

Answer: Most of them live in freshwater habitat in stagnant water. Cell wall is absent in them and instead there is a protein rich layer; called pellicle. The pellicle makes their body flexible. Two flagella; one short and another long; are present. They are photosynthetic; but behave as heterotrophs in the absence of sunlight.

Question 11: Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Answer: Virus contains genetic material surrounded by a protein capsule. The protein coat on the virus is called capsid. It is made up of small subunits called capsomeres. The capsid protects the nucleic acid. The capsomeres are arranged in helical or polyhedral geometric forms.

The genetic material can be either RNA or DNA. Both RNA and DNA cannot be present in the same virus. Plant infecting viruses usually have single-stranded RNA and animal infecting viruses usually have double-stranded RNA or double-stranded DNA. Bacteriophages (bacterial viruses) usually have double-stranded DNA.

Four common viral diseases are: Common cold, mumps, jaundice and influenza.