Class 12 Biology: CBSE Sample Question Paper- Term II (2021-22)- 3 | Sample Papers for Class 12 Medical and Non-Medical PDF Download

Class-XII

Max. Marks: 35

General Instructions :

1. All questions are compulsory.
2. The  question  paper  has  three  sections  and  13  questions.  All  questions  are compulsory.
3. Section–A has 6 questions of 2 marks each; Section–B has 6 questions of 3 marks each; and Section–C has a case-based question of 5 marks.
4. There  is  no  overall  choice.  However,  internal  choices  have  been  provided  in some questions. A student has to attempt only one of the alternatives in such questions.
5. Wherever necessary, neat and properly labelled diagrams should be drawn.

Q.1. Mention a product of human welfare obtained with the help of each one of the following microbes :
(a) LAB
(b) Saccharomyces cerevisiae
(c) Propionibacterium shermanii
(d) Aspergillus niger

(a) Milk to curd
(b) Bread / ethanol / alcoholic drinks / whisky / brandy / beer/ rum
(c) Swiss cheese
(d) Citric acid

Q.2. Large quantities of sewage is generated everyday in cities and towns, which is treated in sewage treatment plants (STPs) to make it less polluted. Given below is the flow diagram of one of the stages of STP.
Observe the given flow diagram and answer the questions accordingly.

(a) Why primary effluent is passed into large aeration tanks?
(b) Write the technical term used for the sediment formed? Mention is significance.

(a) Vigorous growth of useful aerobic microbes into flocs.
(b) Activated sludge - Some of it is pumped back into the aeration tank to serve as the inoculum.

OR

Differences between opioids and cannabinoids are:

Q.3. Which term is used to refer the state experienced by addicts when their regular dose of alcohol/drug is abruptly discontinued. List any two symptoms, it is characterized by.

Withdrawal syndrome.
Anxiety, shakiness, nausea and sweating.

Q.4. Identify the given structure. Name the parts A, B and C shown in the diagram.

The given figure represents the structure of an antibody molecule.
A- Antigen binding site
B- Light chain
C- Heavy chain

Q.5. Define the term age pyramid. Label the three tiers 1, 2, 3 given in the below age pyramid.

Age pyramid is defined as a graphical illustration that shows the distribution of various age groups in a population forming the shape of a pyramid when the population is growing. The three tiers labelled in the diagram are :

• Pre-reproductive phase
• Reproductive phase
• Post-reproductive phase

Q.6. Predators play an important role in the food chain. They also maintain the level of diversity in communities. What other roles you observe in nature that they can play.

A population has more young individuals compared to the older individuals. What would be the status of the population after some years?

(a) Predators act as conduits (channels) for energy transfer across trophic levels.

(b) They keep prey population under control. An efficient predator may cause extinction of prey species.

OR

Variations in number of individuals in a population can be expressed as population density and population size. A population of  younger individual than older individuals will show positive growth in future (after some years), that is, it will increase after some time.

Q.7. (a) List the causative agents of pneumonia and common cold.
(b) State the differences in their symptoms?
(c) List any two symptoms that are common to both.

Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body's ability to fight infection and disease. How does the HIV breakdown the immune system of the AIDS patients? 

(a) Streptococcus pneumoniae
Causative agent of common cold: Rhinoviruses
(b) Symptoms are :

(c) Common symptoms are:
(i) Headache
(ii) Cough

OR

Mechanism of AIDS infection involves :

• Entry of virus in the macrophages.
• RNA genome replicates to form viral DNA with the help of reverse transcriptase. 
• Viral DNA gets incorporated into host's cell DNA to produce virus particles, 
• HIV enters into helper ‘T ’ lymphocytes and produces progeny virus.
• These get released in the blood and attack another helper ‘T’ lymphocytes.
• This leads to progressive decrease in number of helper ‘T’ lymphocytes and the person starts suffering from infections (loss of immunity).

Q.8. The table lists some factors related to innate immunity. Identify A, B, C, D, E, F.

A- Physiological barrier.
B- Acid in Stomach, Saliva in mouth, Tears.
C- Cellular Barrier.
D- Phagocytose/Destroy microbes.
E- Interferons.
F- Protect non-infected cells from virus attack.

Q.9. In an experiment, Sohan amplified a 'gene of interest' using PCR technique. It relies on a thermostable DNA polymerase, Taq polymerase, and requires DNA primers designed specifically for the DNA region of interest. Explain the technique. 

Polymerase Chain Reaction technique can be used to obtain multiple copies of a gene of interest in vitro. The PCR consists of three steps :
(a) Denaturation: The segment of doublestranded DNA of interest is heated to separate the two strands at a high temperature of about 94°C-98°C.
(b) Annealing: A set of primers (chemically synthesised oligonucleotides that are complementary to the regions of DNA) are annealed to both the separated DNA segments. DNA polymerase (Taq polymerase) extends the primer in the 5’ to 3’ direction.
(c) Extension: The separated DNA segments act as templates and primer synthesises new strands along the entire length of DNA strands.
(d) Amplification: The cycle is repeated several times to generate up to one billion identical copies of DNA.

Q.10. (a) Define 'Alien species invasion'.
(b) Illustrate its effects on the biodiversity of a given area by giving two examples.

(a) Alien species invasion is the accidental, intentional introduction  of foreign species to a particular area.
(b) Introduction of alien species causes decline or extinction of indigenous species due to tough competition for utilization of resources.
Examples : Introduction of Nile perch in Lake Victoria led to extinction of more than 200 species of Cichlid fish / Introduction of African catfish (Clarias gariepinus) for aquaculture poses threat to indigenous catfish/ Threat posed to native species by invasive exotic weeds like carrot grass (Parthenium) / Lantana and water hyacinth (Eichhornia) /Extinction of Abingdon tortoise by introduction of goat on the island because goats have greater browsing efficiency than tortoise.

Q.11. (a) List differences between in situ and ex situ approaches for conserving biodiversity.
(b) Give example for each.

(a) In situ conservation: Threatened / endangered plants and animals are provided with urgent measures to save from extinction within their natural habitat and they are protected and allowed to grow naturally.
Ex situ conservation: Threatened animals and plants are taken out of their natural habitat and placed in a setting where they can be protected and given special attention and care.
(b) Example of in-situ conservation: Wildlife sanctuaries/ national parks / biosphere reserves/ sacred groves.
Example of ex-situ conservation: Botanical gardens/ zoological gardens/ seed/pollen/ gene banks.

Q.12. Study the diagram given below representing the observations that were made for separating DNA fragments by Gel electrophoresis technique and answer the questions that follow.

(a) The DNA fragments are seen to be moving in the direction A → B. Why?
(b) Name the medium used to separate DNA fragments here.
(c) Explain how the separated DNA fragments can be visualized for further technical use.

(a) The DNA fragments more from A → B because, B is the anode end. DNA fragments are negatively charged, thereby moving towards anode which is a positive rod, under the influence of an electric field during gel electrophoresis.

(b) Most commonly used matrix is agarose. Agarose is a natural polymer extracted from seaweeds.
(c) Ethidium bromide is used as a stain for DNA, which on exposure to UV-light appear as orange coloured bands.

Q.13. Some restriction enzymes break a phosphodiester bond on both the DNA strands, such that only one end of each molecule is cut and these ends have regions of single stranded DNA. BamHI is one such restriction enzyme which binds at the recognition sequence, 5’-GGATCC- 3’and cleaves these sequences just after the 5’- guanine on each strand.
(a) What is the objective of this action?
(b) Explain how the gene of interest is introduced into a vector.
(c) You are given the DNA sequence shown below.

If this DNA was cut with BamHI, how many DNA fragments would you expect? Write the sequence of these double-stranded DNA fragments with their respective polarity.
(d) A  gene  M  was  introduced  into  E.coli  cloning  vector  pBR322  at BamHI site. What will be its impact on the recombinant plasmids? Give   a   possible   way   by   which   you   could   differentiate   non-recombinant to recombinant plasmids.

GM crops especially Bt crops are known to have higher resistance to pest attacks. To substantiate this, an experimental study was conducted in 4 different farmlands growing Bt and non Bt-Cotton crops. The farm lands had the same dimensions, fertility and were under similar climatic conditions. The histogram below shows the usage of pesticides on Bt crops and non-Bt crops in these farm lands.

(a) Which of the above 4 farm lands has successfully applied the concepts of Biotechnology to show better management practices and use of agrochemicals? If you had to cultivate, which crop would you prefer (Bt or Non- Bt) and why?
(b) Cotton Bollworms were introduced in another experimental study on the above farm lands wherein no pesticide was used. Explain what effect would a Bt and Non Bt crop have on the pest.

(a) The two different DNA molecules will have compatible ends to recombine.
(b) Restriction enzyme cuts the DNA of the vector and then ligates the gene of interest into the DNA of the vector.
(c) 2 fragments

(d) BamHI  site  will  affect  tetracycline  antibiotic  resistance  gene, hence the recombinant plasmids will lose tetracycline resistance due to inactivation of the resistance gene.
Recombinants can be differentiated from non recombinants by plating into a medium containing tetracycline, as the recombinants will not grow in the medium because the tetracycline resistance gene is cut.

OR

(a) Farm Land III.
Bt crop.    
Because the use of pesticides is highly reduced for Bt crop. And fertility of soil can be maintained by reduced use of pesticide.
(b) In Bt cotton, a cry gene has been introduced from bacterium Bacillus thuringiensis(Bt) which causes synthesis of a toxic protein.  This  protein  becomes  active  in  the  alkaline  gut  of bollworm  feeding  on  cotton,  punching  holes  in  the  gut lining causing death of the insect.  
However; a  non  Bt  crop  will  have  no  effect  on  the  cotton bollworm/  the  yield  of  cotton  will decrease /  non  Bt  will succumb to pest attack.