Science (English Medium) Class 12 - CBSE Important Questions

How are 'sticky ends' formed on a DNA strand? Why are they so called? 

State the role of “biolistic gun” in biotechnology experiments.

Name and explain the technique used for separating DNA fragments and making them available for biotechnology experiments.

Write the role of ‘restriction sites’ in the cloning vector pBR322.

Answer the following question:
Describe the formation of recombinant DNA by the action of EcoRI.

Answer the following question.
"The size of a population for any species is not a static parameter." Justify the statement with specific reference to fluctuations in the population density of a region in a given period of time.

A Tight one-to-one relationship between many species of fig tree and certain wasps is an example of ______.

Important attributes belonging to a population but not to an individual are:

1. Birth rate and death rate
2. Male and female
3. Birth and death
4. Sex-ratio

Select the correct option from the given options:

"Cattle and goats do not browse the Calotropis plant." Justify the statement giving reasons.

What is primary productivity?

Define decomposition.

Why does primary productivity vary in different types of ecosystems?

State the relation between gross and net primary productivity.

The following graph shows the species-area relationship. Answer the following questions as directed.

(a) Name the naturalist who studied the kind of relationship shown in the graph. Write the observations made by him.

(b) Write the situations as discovered by the ecologists when the value of ‘Z’
(Slope of the line) lies between:

1. 0.1 and 0.2
2. 0.6 and 1.2

What does ‘Z’ stand for?

(c) When would the slope of the line ‘b’ become steeper?

Answer the following question:
Substantiate with the help of one example that in an ecosystem mutualists
(i) tend to co-evolve and
(ii) are also one of the major causes of biodiversity loss.

Given below is an equation describing the Species-Area relationship between species richness and area for a wide variety of taxa as angiosperm plants, birds, bats etc. S = CA^z

1. Give a graphical representation of the given equation showing Species-Area relationship.
2. What does 'S' represent in the given equation?
3. What is the value of 'Z' (regression coefficient) for frugivorous birds and mammals in the tropical forests of different continents?

Given below is a 'pie chart' representing the global biodiversity:

Proportionate number of species of major taxa.

1. Identify (X) and (Y) in the given 'pie chart'.
2. "Extinction of species across taxa are not random." Which group amongst the vertebrates is more vulnerable to extinction?
3. Give one example of each of the recent extinctions of species in Russia, Mauritius and Australia.

Write the inference drawn by Alexander von Humboldt after his extensive explorations of South American jungle.

Study the graph given below:

As per Alexander von Humboldt, what do the symbols S, A, Z and C in the graph stand for, in respect of a species and area relationship?

"Biodiversity plays a major role in many ecosystem services that nature provides."

Describe any two broadly utilitarian arguments to justify the given statement.