Students can access the CBSE Sample Papers for Class 12 Biology with Solutions and marking scheme Term 2 Set 3 will help students in understanding the difficulty level of the exam.
CBSE Sample Papers for Class 12 Biology Standard Term 2 Set 3 with Solutions
Time Allowed: 2 Hours
Maximum Marks: 40
General Instructions:
- All questions are compulsory.
- The question paper has three sections and 13 questions. All questions are compulsory.
- 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.
- 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.
- Wherever necessary, neat and properly labeled diagrams should be drawn.
Section – A
Question 1.
Person showing the withdrawal symptoms needs medical supervision. Explain.
Answer:
Withdrawal syndrome is the manifestation of unpleasant characteristic when a regular dose of a drug or alcohol is discontinued abruptly. The withdrawal symptoms can be characterised by anxiety, shaking of hands, nausea, vomiting and severe sweating which can be life threatening in some cases. Person may get irreversible mental disturbance for his/her life. In order to reduce the effects of withdrawal symptoms, person may need proper medical supervision.
Question 2.
Infectious diseases are disorders caused by organisms such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They’re normally harmless or even helpful. But under certain conditions, some organisms may cause diseases. What are the various public health measures, which you would suggest as safeguard against infectious diseases?
OR
The diagram depicts the process of making yogurt at home.
Identify X, and the microorganism used in this process:
Answer:
Certain public health measures as safeguard against infection and related diseases are:
- Proper education and awareness about various modes of infection and related disease should be spread within the population.
- The individual that shows the symptoms of infection must be isolated so as to prevent further spread of pathogens.
- So as to avoid infections, the program of vaccination should be conducted.
- Proper sanitary measures should be taken so as to manage the sewage and waste water.
- The vectors that are responsible for transmitting the pathogens should either be sterilised or completely eradicated.
OR
X: Lactic acid
Bacteria (usually Streptococcus thermophilus and Lactobacillus bulgaricus) are used to ferment milk. Lactic ; acid is produced which helps to coagulate the milk.
Question 3.
The given graphs show the amount of different antibodies P and Q in the blood of a person during a pathogenic infection and after complete recovery.
(i) The Bt toxin does not kill the Bacillus because the Bt toxin protein exists as inactive A. Identify A.
(ii) To which cells (marked B) does the activated Bt toxin bind?
Answer:
(i) Graph 1 shows rise of antibodies Q level during pathogenic infection, as its amount was very high ‘V
during infection which reduced significantly after recovery.
(ii) Antibody P is present in small amount consistently in the person’s blood which indicates that they are memory cells and the person is either vaccinated for this pathogen (artificial active immunity) or has contracted the pathogenic disease and recovered from it (natural active immunity).
Question 4.
The figure below shows the mode of action of Bacillus thuringiensis against X larvae. Study the figure
below and answer the following questions:
(i) The Bt toxin does not kill the Bacillus because the Bt toxin protein exists as inactive A. Identify A.
(ii) To which cells (marked B) does the activated Bt toxin bind?
Answer:
(i) Prototoxins: The Bacillus is not killed by its own Bt toxin because this Bt toxin protein exists as
inactive protoxins in it. This toxin converts into an active form in an alkaline pH. This later on form crystals which lead to the death of that insect.
(ii) Epithelial cells: The activated Bt toxin binds to the midgut epithelial cells. These cells line the inner ’
and outer surface of our bodies such as skin, alimentary canal, urinary tract, and organs.
Question 5.
Cattle egret remains close to the cattle. Explain.
Answer:
The cattle egret and grazing animals are in close association with each other. This association is termed
as commensalism. The cattle egret always forge close to where the cattle are grazing because, as the cattle move, they stir and flush out the insects from the vegetation which may be difficult to find out by themselves. Hence closely associated to the cattle egrets remain close to them.
Question 6.
“In a food-chain, a trophic level represents a functional level, not a species.” Explain.
OR
Alien species are highly invasive and are threat to indigenous species. Substantiate this statement with any three examples.
Answer:
Position of a species in any trophic level is determined by the function performed by that mode of
nutrition of species in a particular food chain. A given species may occupy more than one trophic level
in the same ecosystem at a given time. If the function of the mode of nutrition of species changes, its position shall change in the trophic levels. The same species can be at the primary level of consumer in
one food chain and at the secondary consumer level in another food chain in the same ecosystem at a given time.
OR
Alien species invasion is the species that is not of an area and invades rapidly, thereby causing partial or complete extinction of the native, indigenous species. Also they cause an environmental damage by disturbing the ecosystem.
The plant species for example, Lantana camara and Eicchornia crassipes are of such type. Animal species such as African catfish threat to the indigenous catfish are among the type.
Section – B
Question 7.
Antibody, also called immunoglobulin, is a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens in order to remove them from the body. A wide range of substances are regarded by the body as antigens, including disease-causing organisms and toxic materials such as insect venom. Explain antibodies and describe about its structure.Where these antibodies are found in human body?
OR
Tumours are groups of abnormal cells that form lumps or growths. They can start in any one of the trillions of cells in our bodies. Tumours grow and behave differently, depending on whether they are cancerous (malignant), non-cancerous (benign) or precancerous. There are several types of tumours that get converted into cancer in later stage. Enlist any three causes of cancer that get induced in the human body.
Answer:
Antibodies, also known as immunoglobulins are a type of protein molecule produced by B-lymphocytes
in response to pathogens. Each antibody consists of four polypeptides – two heavy chains (H) and two
light chains (L) joined to form a “Y” shaped molecule.
Variable region is the amino acid sequence in the tips of the ” Y” varies greatly among different antibodies.
This is composed of 110-130 amino acids and give the antibody its specificity for binding antigen. An antibody is represented as H2L2 molecule. Antibodies are divided into five major classes, IgM, IgG, IgA,
IgD, and IgE, based on their constant region structure and immune function. Response via antibodies is also called as humoral immune response. These antibodies are found in blood.
OR
Cancer is one of the most deadly diseases of human beings. The major causes behind cancerous growth are:
- Over consumption of any cancer inducing carcinogenic or oncogenic agent. For example Lathyrus (Kesar).
- Over smoking and alcoholism along with dietary factors.
- Chemical and environmental factors.
Question 8.
The exaggerated response of the immune system to certain antigens present in the environment is called allergy. The substances to which such an immune response is produced are called allergens. The antibodies produced to these are of IgE type. Common examples of allergens are mites in dust, pollens, animal dander, etc. Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing.
How is an allergic reaction caused by an allergen? Name a drug that can reduce the symptom of allergy.
Answer:
Allergy is because of release of certain chemicals like Histamine and Serotonin from the mast cells. ‘ Common examples of allergens are pollens, mites in dusts and animal dander. The drugs that can reduce
the symptoms are anti-histamine, steroids and adrenaline.
Question 9.
β-galactosidase enzyme is considered a better selectable marker. Justify the statement.
Answer:
The non-recombinants can be differentiated from recombinants on the basis of colour change when β-galactosidase is used as a selectable marker. When grown on a chromogenic substrate the nonrecombinants show a colour change from colourless to blue whereas the recombinants are not able to show any colour change due to insertional activation. Moreover, the procedure involving β-galactosidase is single step, easy and non-cumbersome.
Question 10.
A corn farmer has perennial problem of corn-borer infestation in his crop. Being environmentally conscious he does want to spray insecticides. Suggest solution based on your knowledge of biotechnology. Write the steps to be carried out to achieve it.
Answer:
With the advent of genetic engineering, genes for insect resistance now can be moved into plants with more resistance and deliberately. Bt technology is only one example of ways genetic engineering may be used to develop insect resistant crops now and in the future. Bt proteins are lethal to insects and transfer the gene into crop plants.
Steps Involved are:
- Identification of a strain of Bt that kills the targeted insect.
- Isolation of gene that produces the lethal protein.
- Gene is removed from the Bt bacterium and a gene conferring resistance to a chemical usually antibiotic or herbicide is attached.
Question 11.
Analyse the graph given below and answer the questions based on it?
(i) What does the graph represent?
(ii) In the given graph what are A and B?
(iii) In the whole equation and related graph, K is quoted. What is K?
Answer:
(i) The graph represents a population growth curve.
(ii) A is the situation where responses are not limiting the growth showing exponential growth. B is the situation where responses are limiting the growth showing logistic growth.
(iii) K is the value of carrying capacity. It is the upper limit of environment to bear the growth of population.
Question 12.
Study the diagram given below and answer the questions asked in relation with it?
(i) What role does the acid-base inlet play?
(ii) Name another type of bioreactor used commercially?
Answer:
(i) The acid-base inlet enables to control the pH of the mixture in the bioreactor vessel.
(ii) Another such type of bioreactor is sparged stirred-tank bioreactor through which the sterile air bubbling is done.
Section – C
Question 13.
Analyse the graph given below and answer the questions based upon it:
(i) In what reference is the graph given above?
(ii) What do ‘a’ and ‘b’ represent in the graph?
(iii) What are the two regulatory mechanisms that are followed by the organisms to maintain homeostasis?
(iv) Why tiny organisms are not found in the Polar Regions?
OR
There are many animals that have become extinct in the wild but continue to maintain in zoological parks.
(i) What type of biodiversity conservation is observed in this case?
(ii) Explain any two ways which help in this type of conservation.
Answer:
(i) It is the response given by the organism to the abiotic factors. When plotted on the graph they can
be represented as above.
(ii) ‘a’ denotes the conformer organisms whereas ‘b’ denotes regulator organisms.
(iii) Organisms either thermoregulate (Regulation of temperatures) or osmoregulate (Regulation of osmotic pressure) to maintain homeostasis.
(iv) Tiny organisms expose maximum surface area through which large amount of heat produced in the body is given out. So in order to generate the energy again, they have to expand much more energy. Therefore, they are not found in the polar region.
OR
(i) It is Ex-situ conservation approach.
(ii) The approaches which will help in this type of conservation are botanical gardens, wildlife sanctuaries, seed and gene banks etc.