Class 12 Biology: CBSE Sample Question Paper- Term II (2021-22)- 2 | 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. Humans have innate immunity for protection against pathogens that may enter the gut along with the food. What are the two barriers that protect the body from such pathogens?

Barriers that protects the body from microbial pathogens entering the gut of humans along with food are:

• Physical  barriers:  Mucous  coating  of  the  epithelium  lining  the gastrointestinal tract helps in trapping the microbes entering our body.
• Physiological barriers: Acid in the stomach, saliva in the mouth prevents microbial growth.

Q.2. A  patient  admitted  in  ICU  was  diagnosed  to  have  suffered  from myocardial infarction. The condition of coronary artery is depicted in the image below.
Name two bio-active agents and their mode of action that can improve this condition.

Substantiate by giving two reasons as to why a holistic understanding of the flora and fauna of the cropland is required before introducing an appropriate biocontrol method.

Streptokinase (produced by the bacterium Streptococcus) is used as a ‘clot buster’ for removing clots from the blood vessels of the patients who have undergone myocardial infarction.  
Statins (produced by the yeast Monascus purpureus) act as blood- cholesterol lowering agents.    

OR

Eradication of pests will disrupt predator-prey relationships, where beneficial predatory and parasitic insects which depend upon flora and fauna as food or hosts, may not be able to survive.
Holistic approach ensures that various life forms that inhabit the field, their life cycles, patterns of feeding and the habitats that they prefer are extensively studied and considered. 

Q.3. Identify the compound : Chemical structure is shown below. State any three of its physical properties.

It is Morphine.
Physically it appears as a white, odourless, crystalline compound extracted from the latex of Poppy plant.

Q.4. Water samples were collected at points A, B and C in a segment of a river near a sugar factory and tested for BOD level. The BOD levels of samples A, B and C were 400 mg/L, 480 mg/L and 8 mg/L respectively.
What is this indicative of? Explain why the BOD level gets reduced considerably at the collection point C?

At collection points A and B, the BOD level is high due to high organic pollution caused by sugar factory and sewage discharge.
At the collection point C, the water was released after secondary treatment/ biological treatment (where vigorous growth of useful aerobic microbes into flocs consume the major part of the organic matter present in the river water or effluent due to sugar factory and sewage discharge).  

Q.5. An ecologist study an area with population A, thriving on unlimited resources and showing exponential growth, introduced population B and C to the same area. What will be the effect on the growth pattern of the population A, B and C when living together in the same habitat?

This interaction will lead to competition between the individuals of population A, B and C for resources. Eventually, the ‘fittest’ individuals will survive and reproduce. The resources for growth will become finite and limiting, and population growth will become realistic. 

Q.6. With the decline in the population of fig species, it was noticed that the population  of  wasp  species  also  started  to  decline.  What  is  the relationship between the two and what could be the possible reason for decline of wasps?

With the increase in the global temperature, the inhabitants of Antarctica are facing fluctuations in the temperature. Out of the regulators and the conformers, which of the two will have better chances of survival?
Give two adaptations that support them to survive in the ambient environment? Give one suitable example. 

The relationship between the plant and pollinator is called mutualism. Fig depends on wasp for pollination, and wasp depends on fig for food and shelter.
With the decline in population of figs, wasp loses its source of food and shelter.

OR

Regulators;
Thermoregulation, osmoregulation
Birds/mammals.  

Q.7. (a) Which organ of the human body is initially affected when bitten by an infected female Anopheles? Name the stage of the parasite that infects this organ.
(b) Explain the events that are responsible for chill and high fever in the patient.

OR

Define vector. Name two diseases whose spread can be controlled by the eradication of Aedes mosquitoes.

(a) Liver cells, sporozoites.
(b) Parasites reproduce asexually in RBC / multiply, Rupture of RBCs is associated with release of toxic substance called as hemozoin.

Detailed Answer :

The infected female Anopheles is the carrier of malarial parasite called Plasmodium. When bitten by this carrier, the liver is initially affected. The infective stage of Plasmodium is sporozoite which is injected into the blood by female anopheles. From blood, the sporozoites reach the liver cells where they multiply in liver cells. The liver cells rupture and liberate the parasite in blood where they attack RBCs, multiply and cause their rupture. Rupture of RBCs is associated with the release of a toxin called as hemozoin, which causes chill and high fever recurring every 3-4 days.

OR

Vector is an organism, typically a biting insect or tick, that transmits a disease or parasite from one animal to another.
Dengue, Chikungunya/Yellow Fever / Eastern Equine Encephalitis / West Nile Fever / Zika / Zika Viral Disease.

Q.8. Prior to a sports events, blood and urine samples of sportspersons are collected for drug tests.
(a) Why is there a need to conduct such tests ?
(b) Name the drugs the authorities usually look for.
(c)  Write the generic names of two plants from which these drugs are obtained.

(a) To detect drug abuse / use of banned drugs / use of cannabinoids / anabolic steroids / narcotic analgesics/ diuretics / hormones / drugs used to accelerate performance / increase muscle strength / bulk / promote aggressiveness / to ensure fair game.
(b) Cannabinoids / cocaine / coca alkaloid / coke / crack / hashish / charas / ganja / hemp plant extract.
(c) Cannabis / Atropa / Erythroxylum / Datura.

Detailed Answer :

(a) The blood test is conducted to check the level of certain drugs in the blood which are banned by sports authorities.
(b) Authorities look for certain drugs like narcotic analgesics, anabolic steroids, diuretics and certain hormones.
(c) The generic name of the plants from which drugs are obtained are Cannabis sativa and Papaver somniferum.

Q.9. Given below is the diagram representing the observations made for separating DNA fragments by Gel electrophoresis technique. Observe the illustration and answer the questions that follow.

(a) Why are the DNA fragments seen to be moving in the direction A → B?
(b) Write the medium used on which DNA fragments separate.
(c) Mention how the separated DNA fragments can be visualised for further technical use.

(a) B is the anode end. DNA fragments are negatively charged thereby moving towards anode which is a positive rod, through sieving effect provided by agarose 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 appears as orange coloured bands.

Q.10. "The population of a metro city experiences fluctuations in it's population density over a period of time."
(a) When does the population in a metro city tend to increase?
(b) When does the population in metro city tend to decline?
(c) If 'N' is the population density at the time 't', write the population density at the time 't + 1'. 

(a) Population in a metro city will tend to increase when natality and immigration will be higher.
(b) Population in metro city will tend to decline when mortality and emigration will be higher.
(c) The equation N_t+1 = N_t + [(B + I) – (D + E)] represents the population density at time t + 1.
Here,
N_t+1 = Population density at time t+1.
N_t = Population density at time t.
B = Natality
I = Immigration
D = Mortality
E = Emigration

Q.11. The picture shown below shows defence mechanisms in a plant.

(a) Explain any two defence mechanisms plants have evolved against their predators.
(b) How does predation differ from parasitism ?

Plants have developed following defence mechanisms :
(a) (i) Thorns are (morphological) means of defence.
(ii) Plants may produce / store chemicals such as nicotine, strychnine etc, for defence which inhibit digestion / disrupts reproduction / kill the predator / Calotropis produces highly poisonous cardiac glycosides / plants may produce chemicals such as nicotine/ caffeine/ quinine/ strychnine/ opium are produced as defence.
(b)

Q.12. Identify and explain the steps 'A', 'B' and 'C' in the given diagram representing the Polymerase Chain Reaction (PCR). 

Polymerase chain reaction is a technique that is used to reproduce (amplify) selected sections of DNA or RNA for analysis.
In PCR, each cycle has three steps:
(a) The step 'A' in the given diagram is Denaturation of DNA : This step involves unwinding of two strands of DNA by heating the sample at 94oC–98oC.
(b) The step 'B' is Primer annealing : In this, primer gets positioned on the exposed nucleotides, according to the base-pairing rules.
(c) The step 'C' is Extension of primers : DNA polymerase recognises primers as 'start' tags and begins to extend the primers using the free nucleotides provided in the reaction and the genomic DNA as template.
The DNA doubles with each round of reactions.

Q.13. A schematic representation of Polymerase Chain Reaction (PCR) up to the extension stage is given below. 

(a) (i) Name and explain the process ‘a’.
(ii) Identify ‘b’.
(b) Mention the applications of PCR in the field of
(i) Biotechnology
(ii) Diagnostics

A large number of transgenic animals have been produced for scientific purposes. They are created deliberately inserting a gene into the genome of an animal. The first transgenic sheep developed was Tracy. It’s genome was changed and it carried genes from other species. The reason behind producing the transgenic animals was for specific economic trait.
(a) What are transgenic animals? How they are helpful to humans?
(b) Name the transgenic animal having the largest number amongst all the existing transgenic animals.
(c) Name the first transgenic cow developed and state the improvement in the quality of the product produced by it.
(d) Mention any two purposes for which these animals are produced.

 (a) (i) "a" represents denaturation process. During the process, the double stranded DNA molecules are heated to a high temperature (94˚C–98˚C), so that the two strands separate into a single-stranded DNA molecule. Each strand acts as a template for DNA synthesis.
(ii) "b" represents the primer annealing.
(b) Applications of PCR in the field of:
(i) Biotechnology : It is used to amplify a single or a few copies of a piece of DNA. The amplified fragment can be used to ligate with a vector for further cloning. This results in recombinant DNA (rDNA).
(ii) Diagnostics : PCR is used to detect HIV in suspected AIDS patients. It is also used to detect mutations in genes in suspected cancer patients. It is a powerful technique to identify many other genetic disorders.

OR

(a) Transgenic animals are those animals whose genome has been altered by the introduction of an extra gene through manipulation, e.g, transgenic rats, rabbits, sheep, etc.
They are helpful to humans is many ways:
(i) Transgenic animals are produced to study how genes are regulated and how they effect the normal functions and development of the animal body.
(ii) Medicines are produced from transgenic animals, e.g., alpha-1-antitrypsin.
(iii) Transgenic animals are used to test vaccine safely before using them on humans.
(iv) They are designed to increase our understanding of how genes contribute to the development of diseases.
(b) Mice
(c) Rosie, it produced human protein-enriched milk (2.4 grams per litre).
(d) Transgenic animals are produced to:
(i) Study the disease in animals.
(ii) Ensure vaccine safety and chemical safety testing.