Biology:2016:CBSE':[Delhi]:Set-I

According to de-Vries, the single step large mutation which further leads to the formation of a new species and brings a major change is known as saltation.

Excessive nutrients in a fresh water body cause fish mortality as:

• The release of nutrient-rich sewage and industrial effluents leads to growth of algae which results in deprivation of dissolved oxygen that is necessary for aquatic life.
• Other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved  oxygen content.

Out-crossing is the best breeding method for animals that are below average in productivity in milk production.

Gel electrophoresis is a technique that can be used to separate DNA fragments of different sizes.

Meiocytes are the diploid cells that undergo meiosis in order to produce haploid gametes. Thus, meiocytes help to restore diploidy through zygote formation or syngamy and also restore the chromosome number of an organism.

The thousand varieties of mangoes in India represent genetic diversity, which is defined as the diversity shown by a single species at genetic level. A single species of mango shows high diversity at the genetic level over its distributional range. For example, a particular variety of mango might be able to easily tolerate the natural calamities in its environment, while the other variety carrying different genes might not be able to tolerate the same and gets destroyed. This is known as natural selection and it results in the loss of genetic diversity.

(a) The effluent from the primary settling tank (primary effluent) is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it.

(b) This permits the vigorous growth of useful aerobic microbes into flocs (masses of bacteria which are associated with fungal filaments and lead to the formation of mesh-like structures), which consume a major portion of organic matter present in the effluent while growing. This reduces the Biological Oxygen Demand or BOD of the effluent. Once the BOD of sewage gets reduced, it is passed into the settling tank for further treatment.

During replication, the synthesis of one new strand of DNA on the DNA template with polarity 3’ to 5’is continuous. However, the synthesis of other new strand of DNA on the DNA template with polarity 5’ to 3’ is discontinuous i.e., in the form of small DNA fragments. These discontinuous DNA segments are called okazaki fragments. These fragments are later joined by the enzyme DNA ligase to form continuous strand called lagging strand.

The causative organism of amoebiasis is Entamoeba histolytica.

The symptoms of amoebiasis are:

i. Constipation

ii. Abdominal pain and cramps

iii. Stool with excessive mucous and blood clots

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