CLASS XI BIOLOGY - Excellup.com

Finish Line & Beyond

CLASS XI BIOLOGY Classification 1. Discuss how classification systems have undergone several changes over a period of time? Answer: Aristotle was the first to use scientific basis for classification. He used morphological characters to differentiate plants and animals. Further, Aristotle classified Plants into trees, shrubs and herbs. He classified animals based on presence or absence of the red blood. Later Linnaeus proposed two kingdoms, viz. Plant Kingdom and Animal Kingdom. This system became very popular because of its simplicity and was used for a long time by scientists. But as the knowledge about finer characteristics of living being increased, scientists started to find that there were some organisms which couldn’t fit either of the kingdoms. A need was being felt to include more number of characteristics like mode of reproduction, evolutionary relationship, etc. to facilitate better categorization. Thus the latest ‘Five Kingdom Classification’ evolved. Five kingdoms are as follows: 1. Monera. 2. Protista. 3. Fungi 4. Plantae. 5. Animalia 2. State two economically important uses of: (a) heterotrophic bacteria (b) archaebacteria Answer: (a) Economically Important Use of Heterotrophic bacteria: (i) Preparation of curd (ii) Production of antibiotics (b) Economically Important Use of Archaebacteria: (i) Methanogens are type of archaebacteria and are present in the gut of ruminating animals. They are responsible for production of methane from ruminating animal’s dung. (ii) Archaebacteria can live in the most harsh environments, like sulphur springs, volcano, etc. They are important as they give us clue how life may have started when the earth was too hot or too cold.

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Finish Line & Beyond 3. What is the nature of cell-walls in diatoms? Answer: The cell walls in diatoms are embedded with silica, which makes them indestructible. They form two thin overlapping shells which fit together as in a soap box. Thus diatoms have left behind large amounts of cell wall deposits in their habitat. 4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify. Answer: Dianoflagellates can be of different colours depending on the type of pigment present. The red dianoflagellate sometimes multiply at a very rapid rate. This is called as algal bloom. This gives a red appearance to the part of affected sea. This is also known as ‘red tide’. Toxins released by them can kill other marine species. 5. How are viroids different from viruses? Answer: Viroids are free RNAs without the protein coat, while virus have a protein coat encapsulating the RNA. 6. Describe briefly the four major groups of Protozoa. Answer: Four major groups of Protozoa is as follows: (a) Amoeboid Protozoa: They are found in fresh water, sea water or moist soil. They have pseudopodia like amoeba, hence the name amoeboid protozoa. (b) Flagellated Protozoans: They have flagella for movement. They are either free living or parasitic. (c) Ciliated Protozoans: They have thousands of cilia present all over the body. The cilia helps in locomotion and steering of food into the gullet. (d) Sporozoans: Many protozoans have an infectious spore-like stage in the life cycle. The spore-like stage helps them get transferred from one host to another host. 7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic? Answer: Certain insectivorous plants, like bladderwort and venus fly trap are partially heterotrophic. 8. What do the terms phycobiont and mycobiont signify? Answer: Lichens are good examples of symbiotic life of algae and fungi. Phycobiont is the name of the part composed of algae and Mycobiont is the name of the part composed of fungi. Fungi provide minerals and support to the alage, while algae provide nutrition to the fungi.



9. Give a comparative account of the classes of Kingdom Fungi under the following: (i) mode of nutrition (ii) mode of reproduction Answer: Fungi Phycomycetes Ascomycetes

Mode of Nutrition Obligate parasite or saprophytes Saprophytic, decomposers, parasitic or coprophilous

Basidiomycetes

Saprophytes parasites

or

Deuteromycetes

Mainly decomposers, some are parasites.

Mode of Reproduction Asexual reproduction by zoospores(motile) or by aplanospores(non-motile) Asexual spores called conidia produced exogenously on the special mycelium called conidiophores. Sexual spores called ascospores are produced endogenously in sac like structure. Vegetative reproduction by fragmentation. Plasmogamy is brought about by fusion of two vegetative cells of different genotyopes Only vegetative phase of reproduction is known.

10. What are the characteristic features of Euglenoids? Answer: Characterisitic Features of Euglenoids: (a) Fresh water organisms found in stagnant water. (b) Instead of cell wall they have a protein rich layer called pellicle whick makes their body flexible. (c) They are autotrophs in the presence of sunlight and heterotrophs in the absence of sunlight. 11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases. Answer: Structure of viruses: Viruses have a protein capsule and genetic materials inside the capsule. These genetic material become active once they are inside the nucleus of a host cell. They start replicating themselves and in turn spreading the disease. Generally viruses that infect plants have single stranded RNA. Viruses infecting animals have double stranded RNA or DNA. Viruses which infect bacteria have double stranded DNA. Four Common Viral Diseases: (a) AIDS (b) Small Pox (c) Herpes (d) Swine Flu


