MODEL PAPER 7 — BIOLOGY STD 12 Science — Question

When Morgan conducted dihybrid cross on Drosophila like Mendel did with pea plants, the F₂ ratio deviated significantly from that of Mendel's F, ratio. Write the explanation Morgan and his group gave to the observations they obtained from their experiment.

Differentiate between T-helper cells and T-killer cells.

Differentiate between an Expanding age pyramid and a Stable age pyramid. Substantiate your answer with diagrams.

Draw and label the enlarged view of microsporangium of an Angiosperm. State the function of its innermost wall layer.

A considerable amount of lactose is added to the growth medium of E.coli. How is the lac operon switched on in the bacteria? Mention the state of the operon when lactose is digested.

Sperms have a tail whereas egg does not, why?

Name the cells that nourish the germ cells in the testes. Where are these cells located in the testes?

Community service department of your school plans a visit to a slum area near the school with an objective to educate the slum dwellers with respect to health and hygiene.

1. Why is there a need to organise such visits?
2. Write the steps you will highlight as a member of this department, in your interactions with them to enable them to lead a healthy life.

Two parents Mr. X and Mrs. X and Mr. Y and Mrs. Y consider the same child as their respective children. Both Mr. and Mrs. A have blood group A, Mr. But the blood group of children is O. Tell whose child it could be and why?