CBSE 12th Term-2 2022 : Biology Most Important 3 Marks Questions with Solution

Given below is the set of important questions which are suggested by the experts to practice for the CBSE Class 12 Biology Term 2 Exam 2022 that is going to be conducted on 30 May. These questions are best for last-minute revision and fine-tune your preparations for the exam.

Q1. The immune system of a person is suppressed. In the Elisa test, he was found positive to a pathogen.

(a) Name the disease the patient is suffering from.
(b) What is the causative organism?
(c) Which cells of body are affected by the pathogen?

Ans : (a) AIDS (Acquired Immuno deficiency Syndrome)

(b) HIV (Human Immuno deficiency Virus)

(c) Helper T-lymphocytes.

Q2. A farmer while working on his farm was bitten by a poisonous snake. The workers in the farm immediately rushed him to the nearby health center. The doctor right away gave him an injection to save his life. What did the doctor inject and why? Explain.

Ans : The doctor injected antitoxin to the farmer bitten by a poisonous snake to save his life. This is because:

• Snake venom contains a deadly poison that can kill a person in a very short time.
• Natural antibodies against poison take a very long time to show their effect which can be fatal to his life.
• Therefore, the doctor injected antitoxin into the farmer immediately. It contains artificially prepared antibodies into the body to neutralize the effect of snake poison.
• The antitoxin injection shows its effect much faster than any vaccine or medication

Q3. (a) It is generally observed that the children who had suffered from chicken pox in their childhood may not cause the same disease in their adulthood. Explain giving reasons the basis of such an immunity in an individual. Name the kind of immunity.

(b) What is interferon? Mention their role.

Ans : (a) The type of immunity is active immunity. When exposed to the pathogen for the first time, the primary immune response casues the release of the relevant antibodies against the pathogen. Some memory cells are created. These help to prevent the second recurrence of the disease in adulthood by eliciting a highly intensified secondary response.

(b) Interferon : These are proteins made and released by viral infected cells which protect other non-infected cells from viral infection.

Role of interferons - They help in preventing viral infection of the adjoining cells. They are also given to cancer patients to destroy tumour as it activates the immune system.

Q4. (a). Why is there a fear amongst the guardians that their adolescent wards may get trapped in drug /alcohol abuse?

(b) Explain addiction and dependence in respect of drug/alcohol abuse in youth.

Ans : (a) Due to the increasing addiction of the growing children and adults towards drugs and alcohol, there is a fear among the minds of the guardians and parents. The consequences of this addiction results in damaging the life of te young minds. The bad involvement with the peer might influence the child to get engaged in these activities.

(b) Addiction is a psychological attachment due to alcohol and drug effects. It consists euphoria and the temporary feeling of well being. It makes the people to have drug or alcohol even when there is no need. Dependence is the ability of the body to menifest the characteristics and unpleasant withdrawl syndrome if regular dose of drug or alcohol is discontinued.

Q5. How does the HIV break down the immune system of the AIDS patients?

Ans : The HIV break down the immune system of the AIDS patients are following :-

• Virus enters in macrophages,
• RNA genome replicates to form viral DNA with help of form viral DNA with help of reverse transcriptase,
• Viral DNA gets incorporated into host cells DNA to produce virus particles,
• HIV enters into helper 'T' lymphocytes and produces progeny virus,
• Which are released in the blood and attack other helpers 'T' lymphocytes,
• This leads to a progressive decrease number of helps 'T' lymphocytes and the persons starts suffering from infections (loss of immunity).

Q6. Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify.

Ans : Organic farmers prefer the biological control of disease and pest over the use of chemicals and pesticides because:

* Biological method do not kill the useful and harmful life forms indiscriminately.

* They are not toxic to human beings.

* It is a non-polluting practice.

* It does not affect the natural predator-prey relationship and food chains.

Q7. (a) How is activated sludge formed during sewage treatment?

(b) This sludge can be used as an inoculum or as a source of biogas. Explain.

Ans : (a) When the BOD of sewage or waste is reduced significantly, the effluent is then passed into a settling tank where the bacterial 'flocs' are allowed to sediment. This sediment is called activated sludge.

(b) A small part of the activated sludge is pumped back into aeration tanks to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Other kinds oi bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as a source of energy as it is inflammable.

Q8. How are the following microbes useful to us?

a) Trichoderma polysporum
b) Monascus purpureus
c) Penicillium notatum.

Ans : (a) Trichoderma is a genus of fungi in the family Hypocreaceae, that is present in all soils, where they are the most prevalent culturable fungi. Many species in this genus can be characterized as opportunistic avirulent plant symbionts. Several strains of Trichoderma have been developed as biocontrol agents against fungal diseases of plants.

(b) Monascus purpureus is a species of mold that is purplish-red in color. This fungus is most important because of its use, in the form of red yeast rice, in the production of certain fermented foods in China.

(c) Penicillin is a group of antibiotics which include penicillin G, penicillin V, procaine penicillin, and benzathine penicillin. Penicillin antibiotics were among the first medications to be effective against many bacterial infections caused by staphylococci and streptococci.

Q9. With the help of diagrams show the different steps in the formation of recombinant DNA by the action of restriction endonuclease.

Ans :

Q10. How are restriction endonuclease enzymes named? Write examples.

Ans : Naming of Restriction enzymes is done according to the convention which as follows :

1. The first letter of the name is taken from the genus.

2. The next two letters comes from the name of the species of the cell from which they are isolated.

3. The next letter comes from the strain of the organism.

4. The roman number following these four letters indicate the order in which the enzymes was isolated from that strain of the bacterium.

Example : EcoR I is isolated from Escherichia coli. R Y 13 strain and it was the first restriction enzyme isolated from E.coli.

Q11. How are DNA segments separated by gel electrophoresis be visualised and isolated?

Ans : The separated DNA molecules are visualised only after staining DNA with ethidium bromide followed by exposure to UV radiation, as bright orange coloured bands. The separated bands of DNA (on the gel) are cut from the agarose gel and extracted from the gel piece and the process is called elution.

Q12. List 6 recombinant proteins which are used in medical practice? Find where they are used as therapeutics.

Ans : Recombinant proteins are obtained from the recombinant DNA technology. This technology involves the transfer of specific genes from an organism into another organism using vectors and restriction enzymes as molecular tools.

Ten recombinant proteins used in medical practice are −

Recombinant protein		Therapeutic use
1.	Insulin	Treatment for type I diabetes mellitus
2.	Interferon-α	Used for chronic hepatitis C
3.	Interferon -β	Used for herpes and viral enteritis
4.	Coagulation factor VII	Treatment of haemophilia A
5.	Coagulation factor IX	Treatment of haemophilia B
6.	DNAase I	Treatment of cystic fibrosis

Q13. Sketch the two types of bioreactors. What is the utility? Which is the common type of bioreactors?

Ans : Small volume cultures cannot yield appreciable quantities of products. To produce these products in large quantities the development of ‘bioreactors’ was required where large volumes (100-1000 litres) of culture can be processed. Thus bioreactors can be thought of as vessels in which raw materials are biologically converted into specific products, using microbial, plant, animal or human cells or individual enzymes.

Role. A bioreactor provides the optimal conditions for achieving the desired product by providing optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen).

One of the most commonly used bioreactors is of stirring type.

A stirred tank reactor is cylindrical or a container with a curved base which facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor. Alternatively, air can be passed through the reactor. It consists of agitator system, an oxygen delivery system, a foam control system, a temperature control system, pH control system and sampling ports so that small volumes of the culture can be withdrawn periodically.

(a) Simple stirred-tank bioreactor (b) Sparged stirred-tank bioreactor through which sterile air bubbles are sparged

Q14. What are transgenic animals? How was the first transgenic cow found to be more useful than the normal cow, for humans?

Ans : Those animals which go under the DNA manipulation to express an extra gene in them. The first transgenic cow was Rosie, and these were its features:

• produced human protein-enriched milk
• 2.4 gm protein per litre which contained human alpha-lactalbumin
• milk was nutritionally more balanced for human babies than natural cow milk

Q15. How does silencing of specific mRNA in RNA interference prevent parasitic infestation?

Ans : In the process of silencing of mRNA, a eukaryotic cell produces a strand of RNA which is complimentary to the mRNA of the parasite, thus making it's RNA double stranded. This inhibits the parasite to translate it's RNA to any kind of protein and thus it prevents infection.

Q16. What is the cause of Adenosine deaminase deficiency?

Ans : Adenosine deaminase deficiency is caused by mutations in the ADA gene. This gene provides instructions for producing the enzyme adenosine deaminase. This enzyme is found throughout the body but is most active in specialized white blood cells called lymphocytes. These cells protect the body against potentially harmful invaders, such as bacteria and viruses, by making immune proteins called antibodies or by directly attacking infected cells. Lymphocytes are produced in specialized lymphoid tissues including the thymus, which is a gland located behind the breastbone, and lymph nodes, which are found throughout the body. Lymphocytes in the blood and in lymphoid tissues make up the immune system.

Q17. List any four ways by which GMOs have been useful for enhanced crop output.

Ans : Four ways by which GMOs have been useful for enhanced crop output are following :-

1. GMO's have genetic modifications outcomes of these genetic modifications include increased food production.
2. Genetically modified crops are stress tolerant to extreme conditions like cold, heat, drought, etc.
3. Some crops are made pest resistant by genetic modification which cuts down the use of pesticides and hence becomes economically and ecologically beneficial.
4. Helps in increasing the efficiency of mineral usage by plants which maintains the mineral content of the soil and keeps it fertile for longer duration.

Q18. Suggest any two possible treatments that can be given to a patient exhibiting adenosine deaminase deficiency.

Ans : i. Enzymes replacement therapy (in which functional ADA is injected)

ii. Bone marrow transplantation

iii. Gene therapy/Culturing the lymphocytes followed by introduction of functional ADA cDNA into it and returning it into the patient’s body.

Q19. (a) Explain any two defence mechanisms plants have evolved against their predators.

(b) How does predation differ from parasitism ?

Ans : Plants develop 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)

S.No.	Parasitism	Predation
1.	Lives and feed on the host	Only feeds on prey.
2.	host specific	prudent / not prey specific.
3.	Co-evolve with the host.	Control / check prey population.

Q20. On a visit to a Hill station, one of your friend suddenly became unwell and felt uneasy.

(a) List two symptoms you would look for to term it to be due to allergy.

(b) Explain the response of the body to an allergen.

(c) Name two drugs that can be recommended for immediate relief

Ans : (a) Sneezing, watery eyes, running nose, difficulty in breathing

(b) Body releases antibodies, IgE type and chemicals like histamine and serotonin from mast cells which produce symptoms of allergy.

(c) Antihistamine, adrenalin, steroids

Q21. (a) ‘‘Organisms may be conformers or regulators.’’ Explain this statement and give one example of each.

(b) Why are there more conformers than regulators in the animal world?

Ans : (a) "Regulators" : - The organism is able to maintain homeostasis by physiological and behavioural means. All birds and mammals and few lower vertebrates and invertebrates species maintain homeostasis by thermoregulation and osmoregulation. For eg : - Birds & Mammals. "Conformers" : - Majority (99%) of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature is not constant. They are simply conformers. Eg; - Fishes, Frogs etc.

(b) Because they lack the capability maintain a constant internal environment or homeostasis.

Q22. Different animals respond to changes in their surroundings in different ways. Taking one example each, explain ‘‘some animals undergo aestivation while some others hibernation’’. How do fungi respond to adverse climatic conditions.

Ans : Aestivation is known as summer sleep. Some animals like land crabs suffer from low metabolic rate as a response to high temperature and arid conditions so they aestivate. While on the other hand hibernation is known as winter sleep which is characterised by low body temperature, slow breathing and heart rate, and low metabolic rate as a response to low temperature. This is mainly shown by cold-blooded animals.

Fungi produces resistant spores under unfavourable conditions which further enters the reproductive cycle when it receives favourable conditions.

Q23. (a) Compare, giving reasons, the J-shaped and S-shaped models of population growth of a species.

(b) Explain ‘‘fitness of a species’’ as mentioned by Darwin.

Ans : (a) S-shaped pattern of population growth form shows an initial gradual increase, followed by an exponential increase and then a gradual decline to a near constant level. It is different from J-shaped curve because J-shaped pattern shows exponential population growth and its abrupt crash after attaining the peak value.

A-When resources are not limiting the growth, plot is exponential

B-When resources are limiting the growth, plot is logistic, K is the carrying capacity.

(b) As mentioned by Darwin, “fitness of a species” was best explained in the theory of evolution by natural selection. This theory states that the organisms having a stable reproductive capacity and the ones that can produce healthy offspring are more fit and thus have more chances of survival. Thus, the fitness of a species is the capability of a species to survive.

Q24. State how does ex-situ conservation help in protecting biodiversity.

Ans : Ex-situ conservation is the protection of elements of biological diversity outside their natural environments. In this method, the genetic information of cultivated and wild plant species is preserved in the form of in vitro cultures and seeds, which are stored as gene banks for long-term use. This type of preservation is valuable in the case where the certain species going to eradicated shortly and if the species present in the very limited amount.

Q25. Mention the kind of biodiversity of more than a thousand varieties of mangoes in India represent. How is it possible?

Ans : Genetic diversity/single species show high diversity at genetic level.Single species show high diversity at genetic level over its distributional range/different varieties grow in different geographical areas/climatic conditions/breeding/mutations.Detailed Answer :More than a thousand varieties of mangoes in India represent the genetic diversity because i a single species show high diversity at genetic level over its distributional range. ii different varieties grow in different geographical regions and climatic condition. This is also possible because of breeding and mutations.

Q26. Co-extinction and introduction of alien species too are responsible for the loss of biodiversity. Explain, how.

Ans : i. Alien (exotic) species invasions

• Some alien (exotic) species when introduced unintentionally or deliberately, become invasive and cause harmful impact, resulting in extinction of the indigenous species.

• Nile perch, a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of Cichlid fish in the lake.

ii. Co-extinctions

• When a species becomes extinct, the plant and animal species associated with it in an obligatory manner, also become extinct.

• For example, if the host fish species becomes extinct, all those parasites exclusively dependent on it, will also become extinct; in plant–pollinator mutualism also, extinction of one results in the extinction of the other.

Q27. Name and describe any three causes of biodiversity losses.

Ans : Three causes of biodiversity losses are :

1. Habitat destruction: It is considered as the primary cause of biodiversity loss. It is generally caused by deforestation, fire and over-use and urbanization. It leads to the extinction or decrease in the number of animals living in that particular habitat.

2. Alien species invasion: Sometimes the alien species introduced in a geographical area unintentionally or deliberately may turn invasive and can cause decline or extinction of the indigenous species.

3. Over-exploitation of natural resources: Over-exploitation of resources has been one of the major contributors of diversity loss. Due to increasing human population, resource demands have increased which has resulted into exploitation of already present resources and development of various forms of energy resources. Development of these energy sources modifies natural habitat and accelerate loss of biodiversity.

Q28. Narrowly utilitarian arguments are put forth in support of biodiversity conservation. Explain the other two arguments that are put forth in support of the same cause.

Ans : Broadly utilitarian arguments :

Biodiversity plays an important role in maintaining sustaining supply of good & ecological services.

The different ecosystem services provided are : purify air, cycling of nutrients, habitat for wildlife, pollinating crops,aesthetic pleasure.

Ethical reasons :

It is our philosophical/spiritual & moral duty to ensure well being of all living brings for utilization of future generations.

CBSE Class 12 Term 2 Study Material

CBSE Class 12 Term 2 Study Material
CBSE Class 12 Reduced Syllabus for Term 2 Exam 2022	CBSE Class 12 Sample Paper for Term 2 Exam 2022
CBSE Class 12 Previous Year Question Paper with Solutions	CBSE Class 12 Term 2 Full Study Material 2022
CBSE Revision Notes For Class 12	CBSE Class 12 Topper Answer Sheet