Human Health and Disease — BIOLOGY STD 12 Science — Question

Why should biological control of pests and pathogens be preferred to the conventional use of chemical pesticides? Explain how the following microbes act as biocontrol agents:

1. Bacillus thuringiensis.
2. Nucleopoly hedrovirus.

Explain how xerarch succession progresses from serie to mesic condition and forms a stable climax community. You may use a flow chart.

Replication was allowed to take place in the presence of radioactive deoxynucleotides precursors in E.coli that was a mutant for DNA ligase. Newly synthesised radioactive DNA was purified and strands were separated by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result?

Draw only well labelled diagram of 8-nucleate angiospermic embryosac.

Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)

Differentiate between the following:

1. Polygenic inheritance and Pleiotropy.
2. Dominance, Codominance and Incomplete dominance.

Answer the following questions:
Give a schematic representation of spermatogenesis in humans.

The graph given below shows the variation in the levels of ovarian hormones during various phases of menstrual cycle:

Compare the role of A and B.

1. List the three different allelic forms of gene ‘I’ in humans. Explain the different phenotypic expressions, controlled by these three forms.
2.  A woman with blood group'A'marries a man with blood group 'O'. Discuss the possibilities of the inheritance of the blood groups in the following, starting with 'yes' or 'no' for each:

1. They produce children with blood group ‘A’ only.
2. They produce children, some with 'O' blood group and some with 'A' blood group.

How do ecologists estimate the total number of species present in the world?