Subject

Biology

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

1.

List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. 


After the primary treatment, the primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it.This leads to the vigorous growth of useful aerobic microbes (Flocs of bacteria and fungi). The microbes consume a major portion of the organic matter of the effluent and thus reduce the BOD significantly.

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2.

State a difference between gene and an allele.


Gene Allele
Gene is a unit of inheritance that is transferred from the parent to the offspring. Allele is the alternative form of a single gene that lie on the same locus in the homologous chromosomes.  
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3.

Explain the significance of meiocytes in a diploid organism.


Meiocytes are specialised cells present in sexually reproductive organisms. They undergo meiotic division to produce male and female gametes that carry only one set of chromosomes and thus help in maintaining the chromosomal number of the organism. 

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4.

According to de-Vries what is saltation?


According to De Vries, Saltation is a single step large mutation which leads to speciation.

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5.

Discuss the role the enzyme DNA ligase plays during DNA replication.


The DNA ligase helps to join or seal the Okazakki fragment or discontinuos DNA strands present on the lagging strands. 

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6.

Name the causative organism of the disease amoebiasis. List three symptoms of the disease.


The Causative agent of amoebiasis is Entamoeba histolytica. 

The symptoms of the disease amoebiasis are :
i. Constipation
ii. Abdominal pain and cramps.
iii. Stools with excess mucous and blood clots.

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7.

Suggest the breeding method most suitable for animals that are below average in milk productivity.


The breeding method of Out-crossing is Most suitable for animals that are below average in milk productivity. In this method, the animal of the same breed but having no common ancestors on either side of their pedigree for up to 4-6 generations are mated.

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8.

Mention the kind of biodiversity of more than a thousand varieties of mangoes in India represent. How is it possible?


Genetic diversity is represented by a large variety of mangoes in India. Genetic diversity is seen due to the difference in the soil of different areas, different agricultural practices and use of different horticulture techniques like grafting and breeding in different areas.

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9.

Excessive nutrients in a fresh water body cause fish mortality. Give two reasons


The presence of large amounts of nutrients in the water bodies lead to excessive growth of algae and cause Algal bloom. The algal blood leads to deterioration of the quality of water, reduces dissolved oxygen and the hence leads to fish mortality.

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10.

Sugggest a technique to a researcher who needs to separate fragments of DNA.


The researcher can use the method Electrophoresis (Gel electrophoresis to separate the fragments of the DNA. In this method, the DNA fragments are loaded into the well made in the gel and separated according to their size under the influence of an electric current.

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