Find the CBSE Class 11 Biology NCERT Solution for the Chapter- 2, Biological Classifications. It has been framed keeping the Students’ perspective in mind. This will help the Students with easy and simple understanding of the concept and technique employed in solving as per the CBSE Marking Scheme.
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Few Sample Question from this Chapter are given below:
Q. Discuss how classification systems have undergone several changes over a period of time?
Ans. Many scientists used different criteria to classify the organisms during their respective time periods. First of all a Greek scientist, Aristotle made an attempt to classify the organisms on the basis of their morphological characters. He classified the living beings into plants and animals. Then he further classified plants as herbs, shrubs, and trees. Animals were classified on the basis of the presence or absence of red blood cells. This system of classification failed to classify all the known organisms.
Then to resolve the problem, Carolus Linnaeus proposed a two kingdom system of classification. It consists of kingdom Planate and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms, eukaryotes and prokaryotes and photosynthetic (green algae) and non- photosynthetic (fungi) organisms. Therefore, this system was found to be an inadequate system f classification.
Hence, to improve this system, a five kingdom system of classification was proposed by R.H Whittaker in 1969. This system included Monera, Protista, Fungi, Plantae, and Animalia. This type of classification system was based on characteristics like cell structure, mode of nutrition, presence of cell wall, etc.
But, Whittaker did not describe viruses lichens. Then, Stanley described viruses, viroids, lichens, etc.
Q. What is the nature of cell-walls in diatoms?
Ans. In case of diatoms, the cell wall forms two thin overlapping shells that fit into each other as the two parts of a soap box. The cell wall is made of silica. Due to the siliceous nature of the cell wall, it is known as diatomaceous earth. This diatomaceous earth is a whitish, soft, chemically inert, highly absorbant and fire proof substance. It is used in filtration of oils, sugars, and for other industrial purposes.
Q. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
Ans. Algal bloom: A rapid increase in the population of green algae in a water body, imparting a green colour to the water body, is termed as algal bloom. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.
Red-tides: Red tides are caused by the red dinoflagellates (Gonyaulax) that multiply rapidly in sea and impart it a red colour. They release large amounts of toxins in water that can cause death of a large number of aquatic animals.
Q. How are viroids different from viruses?
Ans. Viroids are different from viruses as:
- Viroids are smaller in size than viruses.
- In viruses, protein coat is present and they contain both RNA as well as DNA whereas the viroids lack the protein coat and contain only free RNA.
- Virus causes diseases like mumps and aids. On the other hand, viroid causes plant diseases like potao-spindle tuber disease.
Q. What do the terms phycobiont and mycobiont signify?
Ans. The algal component of the lichens which is capable of carrying out the process of photosynthesis and hence produces food, is known as phycobion , whereas the fungal component which provides shelter to algae and absorbs water and nutrients from the soil is called mycobiont.
[Source:- Jagranjosh]
