[ Biology , Class - 9 ]
Chapter :- The fundamental unit of life
Assertion and reasoning Question
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Answers
19 : b
Viruses are non cellular structures. They possess the genetic material enclosed in a protein coat. They do not show characteristics of life until they enter a living body. These can be crystallized. Once inside the living organisms they use host's cell machinery to reproduce virus, therefore they are also called living chemicals.
20 : a
Mitochondria are membrane bound cell organelles essential for aerobic respiration of eukaryotic cells. They are popularly called power house of the cell and are associated with generation of ATP.
21 : c
Plant cell possesses rigid cell wall that counteract turgor pressure developed on account of endosmosis thereby prevents it from bursting.
22 : a
The cell wall is the non living rigid part of the cell due to which it can protect and support the cell from the attack of pathogens and mechanical injuries. It provide definite shape to cell.
23 : b
Pinocytes is the non specific intake of a tiny droplet of extracellular fluids by a cell through the cell membrane which cannot otherwise pass through it.
24 : d
All cells contain genetic material in the form of either DNA or RNA which contains genes. Genes are self replicating units and are located in chromosomes.
25 : c
When a cell divided by meiosis it produces four new cells. The new cells only have half of the number of chromosomes than that of mother cells.
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Answer:
19. (b)
20. (a)
21. (c)
22. (b)
23. (b)
24. (c)
25. (c)
Explanation:
19. Crystallization of virus particles is its transformation into solid particles. Viruses have no metabolic processes outside the host cell. Viruses use host machinery for reproduction via lytic or lysogenic phases.
20. Yes, mitochondria are the powerhouse of the cell. It generates energy in the form of ATP and NADPH via an electron transport system.
21. Plant cells do not burst in the hypotonic solution. Endosmosis occurs and results in the swelling of plant cells but bursting does not occur due to the presence of cell walls in plant cells. It provides turgor pressure.
22. Cell wall is the outermost covering of the cell and it is non-living. It is made up of cellulose, chitin, etc in different organisms. Yes, it provides protection and shape to the cell. It also helps in the transport of materials.
23. Pinocytosis is “cell drinking”. In this process, the cell membrane invaginates to take up the material by forming small pockets to capture the fluid.
24. Yes, the genetic material in every cell is DNA. Genes are located on the DNA that is condensed to form chromosomes. Chromosomes are capable of self-replication before cell division.
25. Mitosis occurs in all somatic cells, it helps in the growth and repairing of tissues in living organisms. It is an equational division as the number of chromosomes in the daughter cells is the same. However, meiosis is a reductional division in which the number of chromosomes is reduced to half.
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