Model Paper 3 — BIOLOGY STD 12 Science — Question

Explain Gause's Competitive Exclusion Principle with the help of a suitable example.

Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?

Explain the development of embryo after fusion in dicot plants. Development of endosperm is advanced in comparison of development of embryo. Explain.

Name the stage ofthe Plasmodium thall is trrnsmitted to human body by the vector. Describe the life cycle of the plrasite in humans.

OR

Trace the life cycle of Plasmodium in humans from the stage of entry, until it is picked up by the female Anopheles.

A and B are two different cloning vectors in two different bacterial colonies cultured in chromogenic substrate. Bacterial colonies with cloning vector A were colourless, whereas those with B were blue coloured. Explain by giving reasons the cause of difference in colour that appeared.

Name the term used for metamorphosis of spermatids?

Name the pest that destroys the cotton bolls. Explain the role of Bacillus thuringiensis in protecting the cotton crop against the pest to increase the yield.

During a school trip to 'Rohtang Pass', one of your classmate suddenly developed 'altitude sickness'. But, he/she recovered after some time.

1. Mention one symptom to diagnose the sickness.
2. What caused the sickness?

A plant with red flowers was crossed with another plant with yellow flowers. If F₁ showed all flowers orange in colour, explain the inheritance.