Biology Class 11 NCERT Solutions: Chapter 2 Biological Classification Part 1

Download PDF of This Page (Size: 1.5M)

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

Answer:

The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.

Therefore, Linnaeus gave a two-kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.

To solve these problems, a five-kingdom system of classification was proposed by R.H Whittaker in 1969. On the basis of characteristics, such as cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms, Monera, Protista, Fungi, Plantae and Animalia were formed.

Q: 2. State two economically important uses of:

(A Heterotrophic bacteria

(B) Archaebacteria

Answer:

(A) Heterotrophic bacteria

(1) They act as decomposers and help in the formation of humus.

(2) They help in the production of curd from milk.

(3) Many antibiotics are obtained from some species of bacteria.

(4) Many soil bacteria help in fixation of atmospheric nitrogen.

(B) Archaebacteria

(1) Methane gas is produced from the dung of ruminants by the methanogens.

(2) Methanogens are also involved in the formation of biogas and sewage treatment.

Image of the important uses of bacteria

Important Uses of Bacteria

Image of the important uses of bacteria

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

Answer:

The cell walls of diatoms are made of silica. Their cell wall construction is known as frustule. It consists of two thin overlapping shells that fit into each other such as a soap box. When the diatoms die, the silica in their cell walls gets deposited in the form of diatomaceous earth. This diatomaceous earth is very soft and quite inert. It is used in filtration of oils, sugars, and for other industrial purposes.

Image of cell walls in diatoms

Image Shows the Diatoms

Image of cell walls in diatoms

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

Answer:

Algal bloom

Algal bloom refers to an increase in the population of algae or blue-green algae in water, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.

Image shows the Algal bloom

Image Shows the Algal Bloom

Image shows the Algal bloom

Red-tides

Red tides are caused by red dinoflagellates (Gonyaulax) that multiply rapidly. Due to their large numbers, the sea appears red in colour. They release large amounts of toxins in water that can cause death of a large number of fishes.

Image shows the Red-tides

Image Shows the Red-Tides

Image shows the Red-tides

Q: 5. How are viroid’s different from viruses?

Answer:

Viroid’s were discovered in 1917 by T.O. Denier. They cause potato spindle tuber disease. They are smaller in size than viruses. They also lack the protein coat and contain free RNA of low molecular weight.

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

Answer:

Protozoa are microscopic unicellular protists with heterotrophic mode of nutrition. They may be holozoic, saprobic, or parasitic. These are divided into four major groups.

Image of the four major groups of Protozoa

Four Major Groups of Protozoa

Image of the four major groups of Protozoa

(1) Amoeboid protozoa or sarcodines

They are unicellular, jelly-like protozoa found in fresh or sea water and in moist soil. Their body lacks a periplast. Therefore, they may be naked or covered by a calcareous shell. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia. These pseudopodia or false feet help in movement and capturing prey. They include free living forms such as Amoeba or parasitic forms such as Entamoeba.

(2) Flagellated protozoa or zooflagellates

They are free living, non-photosynthetic flagellates without a cell wall. They possess flagella for locomotion and capturing prey. They include parasitic forms such as Trypanosoma, which causes sleeping sickness in human beings.

(3) Ciliated protozoa or ciliates

They are aquatic individuals that form a large group of protozoa. Their characteristic features are the presence of numerous cilia on the entire body surface and the presence of two types of nuclei. All the cilia beat in the same direction to move the water laden food inside a cavity called gullet. They include organisms such as Paramoecium, Vorticella, etc.

(4) Sporozoans

They include disease causing endoparasites and other pathogens. They are uninucleate and their body is covered by a pellicle. They do not possess cilia or flagella. They include the malaria causing parasite Plasmodium.

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

Answer:

Plants have autotrophic mode of nutrition as they contain chlorophyll pigment. Thus, they have the ability to prepare their own food by the process of photosynthesis. However, some insectivorous plants are partially heterotrophic. They have various means of capturing insects so as to supplement their diet with required nutrients derived from insects, causing proliferation of growth. The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.