Science (English Medium) Class 12 - CBSE Question Bank Solutions for Biology

How do scientists extrapolate the total number of species on Earth?

(a) List two advantages of using bacteria for such biotechnological studies?

(b) For amplification of the gene of interest PCR was carried out. The PCR was run with the help of polymerase which was functional only at a very low temperature. How will this impact the efficiency of the PCR? Justify.

(c) If such bacteria are sprayed on water bodies with oil spills, how will this have a positive or negative effect on the environment? Discuss.

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.

Cloning of genes, play a very significant role in genetic engineering, helping the transfer of desirable foreign genes into different hosts. The scientists, to make this process easier and effective are creating engineered vectors in such a way that they help easy linking of foreign DNA and selection of recombinants from non-recombinants. 'pBR322' is one such engineered vectors developed by scientists. A diagram of an engineered vector pBR322 is given below:

1. Name the host for this cloning vector.
2. Identify 'Rop' and 'Ori' in the diagram from 'U', 'V', 'W', 'X', 'Y' and 'Z'. Write their functions.
3. Draw the fragments that will be formed by the action of 'Z' (marked in the diagram) on the specific site of the DNA segment given below:
   5' --- GTACGAATCCTGA --- 3'
   3' --- CATGCTTAGGACT --- 3'

Describe the dihybrid cross upto F₂ generation as conducted by Gregor Mendel using pure lines of Garden Pea for characters-seed shape and seed colour.

A short piece of DNA, having 20 base pairs, was analyzed to find the number of nucleotide bases in each of the polynucleotide strands. Some of the results are shown in the table.

How many nucleotides containing Adenine were present in strand 2?

What is the smallest part of a DNA molecule that can be changed by a point mutation?

Give three reasons as to why the prokaryotes are not given any figures for their diversity by ecologists.

The structure below shows pUC18, which is similar to pBR322 in its function. However, they differ in some of their restriction sites and the number of ori. The ori number for pBR322 is approximately 20.

1. How are puc18 and pBR322 used in biotechnological studies?
   OR
   What will be the impact if the ori in the above structure gets damaged?
2. The lac z gene has many recognition sites. Study the segment of DNA given below and answer the questions.
   5’... ATC GTA AAG CTT CAT…3’
   3’... TAG CAT TTC GAA GTA…5’
   i) Applying your knowledge of palindrome sequences identify and mark the possible region where the restriction enzyme X will act.
   ii) Restriction enzyme Y was used to extract a gene of interest from a plant. This gene needs to be inserted in the given DNA segment which has been treated with restriction enzyme X. Will there be a successful recombination? Explain with a reason.
3. Which one of the two (pUC18 and pBR322) would you prefer for biotechnological studies? Justify.

(a) Name the two growth models that represent population growth and draw the respective growth curves they represent.

(b) State the basics for the difference in the shape of these curves

(c) Which one of the curves represents the human population growth at present? Do you think such a curve is sustainable? Give reason in support of your answer.

Explain with the help of a suitable example the naming of a restriction endonuclease.

Construct an age pyramid which reflects a stable growth status of human population.

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

Study the graph given below and answer the questions that follow :

(i) Write the status of food and space in the curves (a) and (b).
(ii) In the absence of predators, which one of the two curves would appropriately depict the prey population?
(iii) Time has been shown on X-axis and there is a parallel dotted line above it. Give the significance of this dotted line

Why is the enzyme cellulase needed for isolating genetic material from plant cells and not form the animal cells?

Mention the difference in the mode of action of exonuclease and endonuclease.

Why are the fruit juices bought from market clearer as compared to those made at home?

Name the source of streptokinase. How does this bioreactor molecule function in our body?

Suggest a technique to a researcher who needs to separate fragments of DNA.

How are the following formed and involved in DNA packaging in a nucleus of a cell?