Biology:2016:CBSE:[Delhi]:Set-II

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

Sickle-cell anaemia is a genetic disorder which is caused by a single gene mutation.

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

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.

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

OR

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.

1. In a sexual life cycle of an organism, both meiosis and syngamy are the important events.
2. Meiosis leads to the formation of haploid gametes by reductional division, whereas syngamy leads to the fusion of haploid gametes and formation of a diploid zygote.

1. Once the BOD of waste water is significantly reduced, the effluent is passed into a settling tank for sedimentation. This sediment is called activated sludge.
2. A small part of activated sludge is pumped back into the aeration tank to serve as the inoculum.
3. The remaining part of activated sludge is transferred into the large tanks called anaerobic sludge digesters.
4. In anaerobic sludge digesters, anaerobic bacteria digest the organic matter in the sludge and produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas which can be used as a source of energy.

1. Desert plants are adapted to survive in water stress conditions as their cuticle is thick, leaf is reduced to spines and have low rate of transpiration.
2. On the other hand, mangrove plants are adapted to survive in water-logged and anoxic conditions. These plants have prominent leaves and high rate of transpiration.

Since desert plants have different adaptations than mangrove plants, they cannot survive in mangrove.