Biotechnology and its Applications — BIOLOGY STD 12 Science — Question

Why both the strands of DNA are not copied during transcription? Explain.

Differentiate between two different types of pyramids of biomass with the help of one example of each.

Name any two natural cloning vectors. Give reasons that make them act as cloning vectors. Write the two characteristics the engineered vectors are made to possess.

Describe the development of endosperm after double fertilization in an angiosperm. Why does endosperm development precedes that of zygote?

Draw a labelled schematic sketch of replication fork of DNA. Explain the role of the enzymes involved in DNA replication.

Answer the following questions:
Write the characteristic features of anther, pollen and stigma of wind pollinated flowers.

Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

How are assisted reproductive technologies helpful to humans? How are ZIFT and GIFT different from intrauterine transfers? Explain.

What changes are seen in human male and females by onsetting of puberty.

During reproduction, the chromosome number (2n) reduces to half (n) in the gametes and again resume the original number (2n) in the offspring, what are the processes through which these events take place?