Class 12 Biology: CBSE Sample Question Paper- Term II (2021-22)- 5 | 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. Rahul suffered from amoebiasis. Write the symptoms that confirm this infection. Also, identify the causative pathogen.

Constipation, abdominal pain, stools with mucous, blood clot.
Causative pathogen: Entamoeba histolytica.

Q.2. A bioactive molecule "X" is given to an organ transplant patient. Identify its source organism and the purpose for which it is given to organ transplant patients.

Meenal's father, who is a farmer, wants to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
(a) Recommend two microbes that can enrich the soil with nitrogen.
(b) "The leguminous crops do not require such enrichment of the soil". Give a reason.

Bioactive molecule "X" is: Cyclosporin-A
Source organism – Trichoderma polysporum. Purpose – Immunosuppressive agent.

OR

(a) Azospirillum/ Azotobacter/ Anabaena/ Nostoc / Oscillatoria /Frankia (Any two correct names of microbes).
(b) Leguminous crops can fix atmospheric nitrogen, due to presence of Rhizobium (N2 fixing bacteria) in their root nodules. 

Q.3. Identify the given chemical compound and its effect on human body.

It is the chemical structure of heroin.
Heroin depresses breathing and slows down body functions.

Q.4. A locality marked the growth of plenty of algal bloom. What do you think has caused this bloom and how will it affect the quality of water? Suggest a preventive measure.

(a) Presence of large amount of nutrients in water causes excessive growth of planktonic (free- floating) algae, called as algal bloom. Algal blooms cause deterioration of water quality and fish mortality. Some bloom forming algae are extremely toxic to human beings and animals.
(b) Treatment of wastewater before reaching pond by integrated water treatment method is the preventive measure.

Q.5. A population pyramid is a way to visualize two variables: age and sex. They are used by demographers, who study populations. With the help of neat labelled diagrams, illustrate stable and declining age pyramids of human population.

Q.6. Name the interaction that exists between:
(a) Cuscuta and shoe-flower plant
(b) Fig and wasp

Cryopreservation or cryo conservation is a process where organelles, cells, tissues, extracellular matrix, organs, or any other biological structures are preserved by cooling to very low temperatures, i.e., 196°C in liquid nitrogen. Mention, how it is used in the conversation of biodiversity.

(a) The interaction that exists between Cuscuta and shoe-flower plant is parasitism.
(b) The type of interaction seen between fig and wasps is mutualism.

OR

Cryopreservation is an ex-situ method of conservation of biodiversity. By this method, the gametes of threatened species are preserved in viable and fertile conditions for long period of time. These gametes can be used further when required.

Q.7. Explain with the help of sketch the action of HIV in the body.

"Prevention is better than cure". Comment. 

Action of HIV in the human body :

• After entering the human body, the HIV virus attacks and enters the macrophages. Inside the macrophages, the RNA of the virus replicates with the help of enzyme reverse transcriptase and give rise to viral DNA.
• Then, this viral DNA incorporates into the host DNA and directs the synthesis of virus particles.  

• At the same time, HIV enters the helper T-lymphocytes. It replicates and produces viral progeny here. These newly formed progeny viruses get released into the blood, attacking healthier helper T-lymphocytes in the body.
• As a result, the number of T-lymphocytes in the body of an infected person decreases progressively, thereby decreasing the immunity of the body.

OR

Prevention is always better than cure because some diseases cause extensive damage to the body tissues or organs. They also have a:
(a) negative effect on their capacity to function.
(b) permanent or long-term debilitating effect.
(c) negative mental and psychological effect.
(d) financial burden.
Prevention, therefore is easier and effective, than cure of a disease.

Q.8. Why tobacco smoking is associated with rise in blood pressure and low oxygen efficiency?

Addiction of tobacco is due to the presence of nicotine. Nicotine, which is present in tobacco stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation, both of which raises blood pressure and increases the heart rate. Smoking increases carbon monoxide (CO) content in blood and reduces the concentration of haem bound oxygen. This causes oxygen deficiency in the body.

Q.9. A host cell should be competent enough to take the DNA molecule for the transformation. There are various means by which a competent host is formed for recombinant DNA technology. Why and how bacteria can be made competent ? 

Bacteria can be made ‘competent’ by :
(a) Using divalent cations: Bacteria are treated with Ca²⁺, etc., so that DNA enters the bacterium through pores in its cell wall.
(b) Heat shock: Cells can be incubated on ice and then at 42°C for a heat shock and then again kept on ice.
(c) Microinjection: Recombinant DNA is directly injected into the nucleus of an animal cell.

Q.10. (a) Give the scientific term for a parasite living on other parasite.
(b) Name a species which is both a prey and a predator.
(c) Name an ecto and an endoparasite.

(a) Hyperparasite
(b) Frog
(c) Lice and Taenia respectively

Q.11. The map below shows the biodiversity hotspots in India.

(a) Explain the importance of biodiversity hotspots and sacred groves.
(b) Name the type of biodiversity represented by the following:
(i) 50,000 different strains of rice in India.
(ii) Estuaries and alpine meadows in India.

(a) Hotspots—region with high level of species richness, high degree of endemism.
(b) Sacred groves—tracts of forest containing tree/wild life were venerated and given total protection//to protect last refuses for a large number of rare, and threatened plants.

Q.12. Study the diagram and answer the following questions:

(a) Name the enzyme (a) and write its functions.
(b) Identify the process (b) and name the enzyme used in the process.
(c) Identify the step (c)

(a) The name of the enzyme (a) is Restriction endonuclease. Restriction enzymes serve as chemical knives also called molecular scissors to cut genes (= DNA) at specific sites into defined fragments. These may then be used to determine the order of genes on chromosomes and to analyze the chemical structure of genes and regions of DNA which regulate the functions of gene.
(b) The process (b) is known as ligation. Ligation is an enzymatic action that joins two biomolecules with a covalent bond. When, the same restriction enzyme cuts the DNA molecules, the resultant DNA fragments have the same kind of "stickyends", and these can be joined together using DNA ligases enzyme.
(c) The step (c) shows the activity of E.coli, introduction of rDNA into Escherichia coli cell. E.coli is preferred as host for gene cloning due to the high efficiency of introduction of DNA molecules into cells.

Q.13. Crown gall is a neoplastic disease of most dicotyledonous plants and is caused by the soil bacterium Agrobacterium tumefaciens. A large chromosomal plasmid in these bacteria was found to be responsible for this disease. The plasmid is known as Ti plasmid. Bacteria free crown gall cells can be cultured in the absence of phytohormones. Ti plasmid is widely used in genetic engineering to deliver the desirable genes. The part of Ti plasmid transferred into plant cell DNA is called T-DNA. T-DNA with desired DNA segment is inserted into the chromosome of the host plant where it produces copies of itself. 
(a) What is the full form of T-DNA?
(b) Ti plasmid cannot infect and develop crown gall disease in which living organisms?
(c) What happens when T-DNA is inserted into the host cell, while making transgenic plant
(d) What are the advantages of Agrobacterium mediated gene transfer in plants?

Plants having foreign genes in their genome inserted through genetic engineering are called transgenic plants. Genes can be incorporated either through a vector or through direct introduction of DNA. Bt cotton is a genetically modified organism which is pest resistant. It contains gene cry I Ac and cry II Ab of Bacillus thuringiensis. It is used to control lepidopterans, coleopterans and dipterans. Bt cotton can resist cotton bollworm and produce higher yields. Cry gene produces cry protein or Bt toxin. It is an endotoxin which remains as protoxin in plants and gets converted to active toxin after getting ingested by the insects. Alkaline pH of the insect gut solubilizes the protein crystals. The activated toxin creates pores in the midgut of the insects which in turn leads to their death. 
(a) Why does the toxin produced by B. Thuringiensis not kill the Bacillus?
(b) How man has exploited Bt toxin genes for his benefit? What type of changes occur in the gut of insects on consuming this protein?

(a) T-DNA stands for transfer DNA.
(b) Ti plasmid cannot infect and develop crown gall disease in humans.
(c) While making transgenic plant, T-DNA is inserted into the host cell, and is then integrated into the target host genome.
(d) Advantages of Agrobacterium mediated gene transfer in plants are:
(i) It allows transfer of relatively large segment of DNA.
(ii) It transfers DNA with defined ends and minimal rearrangement.

OR

(a) The toxin produced is in inactive form as protoxin. It does not kill the bacteria and attacks only its target pest because protoxin is activated in the optimum pH medium of the gut of insect pest.
(b) Specific Bt toxin genes are isolated from Bacillus thuringiensis and is incorporated into several crop plants such as cotton and corn, which become pest resistant against certain insects.
Prototoxin becomes active toxin in alkaline pH of gut of insects. Toxins bind to surface of midgut and cause perforation, swelling, lysis of cells ultimately leading to death.