Human Health and Diseases — BIOLOGY STD 12 Science — Question

What is a cistron? Why is the structural gene in a transcription unit of eukaryotes called monocistronic and that in prokaryotes/bacteria called polycistronic? Give reasons.

What does secondary productivity in an ecosystem indicate? List any two factors by which productivity is limited in an aquatic ecosystem.

Alien species invasion is one of the causes of biodiversity loss. Explain with the help of an example.

OR

Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples.

What will be happen if the decomposers are removed from the food chain?

What is sewage? In which way can sewage be harmful to us?

A student on a school trip started sneezing and wheezing soon after reaching the hill station for no explained reasons. But on return to the plains, the symptoms disappeared. What is such a esponsecalled? How does the body produce it? 

Name the following:

1. The vector of dengue fever.
2. A vaccine produced by recombinant DNA technology.
3. The type of immunity that is present at the time of birth.
4. A fish that helps in eradication of mosquito larvae.

Suggest two practices giving one example of each, that help protect rare or threatened species.

(a) Name the organism in which the vector shown in inserted to get the copies of the desired gene.
(b) Mention the area labelled in the vector responsible for controlling the copy number of the inserted gene.
(c) Name and explain the role of selectable marker in the vector shown.

How does tobacco smoking lead to oxygen deficiency in human body?