Students can access the CBSE Sample Papers for Class 12 Biology with Solutions and marking scheme Term 2 Set 6 will help students in understanding the difficulty level of the exam.
CBSE Sample Papers for Class 12 Biology Standard Term 2 Set 6 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.
HTV (human immunodeficiency virus) is a virus that attacks the body’s immune system. If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). Learning the basics about HIV can keep you healthy and prevent HIV transmission. How does HIV differ from a bacteriophage?
Answer:
HIV or Human Immunodeficiency Virus is a member of group of viruses known as retrovirus; they possess an envelope enclosing the RNA genome. The phage virus has an envelope that encloses the DNA genome.
Question 2.
Write the scientific names of the causative agent and vector of above disease and write its symptoms.
OR
Biogas is produced by anaerobic digestion with methanogens or anaerobic organisms, which digest material inside a closed system, or perform fermentation of biodegradable materials. How does methanogen help in producing biogas?
Answer:
Plasmodium vivax, P. malaria and P. falciparum are causative agents of malaria. Female Anopheles mosquito is the vector of malaria and symptoms include chill and high fever recurring every three to four days.
OR
Some bacteria, such as methanogens, are commonly found in the anaerobic sludge during the sewage treatment. Biogas is a mixture of gases produced during the microbial activities and which is used as fuel. The type of the gas that is produced depends upon the type of microbes and the organic substrates they utilise. Methanogens produce methane, C02, hydrogen gas by anaerobic digestion of cellulosic plant part.
Question 3.
The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called A. Refer to the figure below and identify what is “A”?
Answer:
Antibody
The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies. T-cells do not secrete antibodies but help B-cells to produce them.
Question 4.
The given below diagram is naturally occurring in?
Answer:
Circular duplex DNA
Circular double-standard DNA is double stranded and has no terminal ends and is circular. Such type of DNA is found in bacteria.
Question 5.
When organisms interact with the various environmental factors, be it the abiotic components or the biotic components, there comes a time when adaptations begin to form, for the better survival of the race. Substantiate with the help of one example that in an ecosystem mutualists:
(i) tend to co-evolve and
(ii) are also one of the major causes of biodiversity loss.
Answer:
(i) In case of fig species, it is pollinated only by its partner wasp species. The female wasp uses the fruit
of the fig as a site for egg laying and nourishing its larvae. They tend to co-evolve, e.g., the moth and the yucca plant cannot complete their life cycle without each other. The moth deposits its eggs in the locule of the ovary and the flower in turn gets pollinated by the moth.
(ii) When any of the two species becomes extinct, the other species associated with it in an obligatory way also becomes extinct and leads to biodiversity loss.
Question 6.
Explain the birth rate and death rate in the population with the help of an example. What is age pyramid?
OR
How is diapause different from hibernation?
Answer:
The birth rate is number of births per unit population per unit time whereas death rate is number of deaths per unit population per unit time. Birth rate is called Natality whereas, death rate is called Mortality. Under favourable conditions, the death rate is minimal and the birth rate is high making the population to grow at faster rate. Under stressful conditions, the death rate is high making the population to decrease.
A population at a given time is composed of individuals of different ages. If the age distribution that is the percent individuals of a given age group is plotted for these populations, the resulting structure will be referred as an age pyramid.
OR
Diapause is a stage of suspended development of an organism in order to cope up with the changing environment. Many species including zooplanktons and certain insects exhibit diapause to cope with the adverse climatic stress. On the other hand, hibernation is a state of sleep or resting phase where the organism suspends itself from the adverse climatic conditions. The metabolic activity slows down and the organism experiences near death situation. Certain rodents and bears follow such mechanisms.
Section – B
Question 7.
Cancer is one of the most feared diseases in the world and it affects over 11 lakh people every year in India alone. Worldwide, more than 10 million people succumb to this disease every year.
(i) Name the cancer that starts in the skin or the tissues that line other organs?
(ii) Name the cancer that occurs in bone marrow and creates blood cells?
(iii) The most common types of treatment of cancer are:
OR
Secondary treatment of the sewage is also called Biological treatment. Justify this statement and explain the process.
Answer:
(i) Carcinoma
(ii) Leukemia
(iii) Chemotherapy, Surgery, Radiation therapy
OR
It is called biological treatment because it involves living organisms such as aerobic or anaerobic bacteria and fungi to digest organic waste.
The primary effluent is passed into an aeration tank where vigorous growth of aerobic microbes (floes) takes place as a result of which BOD gets reduced. The effluent is passed to a settling tank where floes sediment to produce activated sludge. The sludge is pumped to an anaerobic sludge digester to digest the bacteria and fungi.
Question 8.
Adolescence is the period of dramatic physical and psychological changes in a person. An adolescent person is at high risk of falling in the trap of drug or alcohol abuse.
(i) Nicotine acts as a stimulant because it mimics the effect of:
(ii) Continuous use of alcohol causes:
(iii) Tobacco inhalation causes:
Answer:
(i) Acetylcholine
(ii) Gastritis, neuritis, swelling of liver.
(iii) Nerve stimulation, heart diseases, decrease in 02 carrying capacity, lung cancer, chronic bronchitis etc.
Question 9.
The bioreactor is a place where an optimum external environment is provided to meet the needs of the biological reaction system so that a high yield of the bio-process is achieved. Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
Answer:
Some of the other advantages that the stirred tank bioreactors have over shake flasks are:
- Small volumes of culture can be taken out from the reactor for sampling or testing.
- It has a foam breaker for regulating the foam.
- It has a control system that regulates the temperature and pH.
Question 10.
A transgenic animal is one whose genome has been altered by the transfer of a gene or genes from another species or breed.
(i) What are the method of transfection for making transgenic animals?
(ii) DNA microinjection into the egg has been used to produce which of the transgenic animals?
(iii) Transgenic goats produce a variant of human tissue type plasminogen activator protein in:
Answer:
(i) Transfer of whole nuclei. Transfer of whole individual chromosomes or fragment. Transfer of DNA.
(ii) Mice, chicken, pigs
(iii) milk
Question 11.
(i) The given graph represents the environment in the graph. Which from the graph would you expect
to have experienced the greatest amount of change?
(ii) Give various methodologies for conserving biodiversity.
Answer:
(i) Environment C
Environment A is stable or uniform, environment B follows cyclic pattern, environment C shows an irregular fall and rise in the rate of speciation.
(ii) In order to conserve and protect biodiversity of a region, we can adopt certain desirable approaches as given below:
(a) In-situ conservation: The conservation strategies when implemented on the same place where
the species is habituated, such conservation strategies are referred as in-situ conservation ‘ strategies. For example, conserving endemic species that are confined to the biological hotspots which have very high species richness. The establishments such as National parks, wild life reserves, sanctuaries etc. can be grouped under this method.
(b) Ex-situ conservation: In this type of conservation strategy, the species is shifted to an artificial environment so as to preserve and to conserve. For example, zoological parks, seed and gene banks, botanical gardens can be grouped under this type of strategies. Conservation of marine \ sea turtles by shifting the eggs nested by female to an artificial hatchery and further release of them into the sea is another such example of ex-situ type of conservation. The only disadvantage of this method is the detachment of the species from its natural habitat.
Question 12.
(i) In gene therapy for the ADA deficient patients the type of vector “A” is used here to incorporate ”B” into ”C” type of cells. Identify A ,B and C.
(ii) Mention the cause and the body system affected by ADA deficiency in humans. Name the vectors used for transferring ADA-DNA into the recipient cell in humans. Name the recipient cell.
Answer:
(i) A : Retrovirus, B : DNA, C : Lymphocytes ‘
Retrovirus is used as a vector that helps in incorporation of C-DNA which is functional and thus can produce adenosine deaminase enzyme. This C-DNA is transferred in the cultured lymphocytes which are then subsequently returned to the patient.
(ii) Gene therapy is an advanced technique for correcting a defective gene with the help of gene manipulation. It involves the delivery of a normal gene into the individual to replace the defective gene. Introduction of gene for Adenosine Deaminase (ADA) in ADA deficient individual is an example. The Adenosine Deaminase enzyme plays a vital role in maintaining the normal functioning of the immune system. The individual suffering from this disorder can be cured by transplantation of bone marrow cells. The initial step involves the extraction of lymphocyte from the patient’s bone marrow. Then, a functional gene for ADA is introduced into lymphocytes with the help of retrovirus. These treated lymphocytes containing ADA gene are then introduced into the patient’s bone marrow. Thus, the gene gets activated producing functional T-lymphocytes thereby activating the patient’s immune system.
Section – C
Question 13.
The biological wealth of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities. The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds. The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
Tn-situ’ conservation can help endangered or threatened species. Justify the statement.
What are the causes of biodiversity loss?
OR
(i) What is the reason for the difference in population size between time 2 and time 3? The population size of a species over time is show in the graph.
(ii) What is the growth pattern demonstrated by population at time 1 of population size of a species over time is shown in the graph.
(iii) Explain in brief logistic growth model using universal equation.
Answer:
In “In-situ” conservation, the threatened organisms are conserved in their natural habitat or ecosystem. Such habitats are legally protected as hotspots, biosphere reserves, national parks, sanctuaries, sacred groves or Ramsar sites.
Causes of biodiversity loss are:
(i) Habitat loss or fragmentation: The Amazon rain forest is being cut out and cleared for raising cattle, or conversion to grasslands or cultivating soyabeans. The large habitats are broken up into small fragments due to human activities. Mammals and birds which require large territories are badly affected leading to decline in population.
(ii) Over-exploitation: When “need” turns to “greed”, it leads to over-exploitation of natural resources.
E.g., stellar7s sea cow, passenger pigeon, marine fish population were overexploited.
(iii) Alien species invasions: When alien species are introduced deliberately, some of them turn invasive and cause decline in indigenous species e.g., Carrot grass, African catfish (Clarias gariepinus) poses a threat to the indigenous cat fishes.
OR
(i) Decline in available food resources
As the population size decreases between 2 and 3 time there is decline in available food which results in decline in size of population between 2 and 3 time.
(ii) Exponential
The population in above graph increase exponentially at time = 1 as this type of graph is shown when resources available to population are unlimited.
Represented by, \(\frac{\mathrm{dN}}{\mathrm{dt}}\) = rN.
(iii) Growth of population of one species can either harm or can be useful for the related species. The growth of the population mainly depends upon the resources available over the habitat where the population has developed. Similarly, there is a constant competition between the species residing over the area for food, shelter, reproduction and protection. These factors govern the population growth. In order to study this growth of population density of a specific geographical unit over a period of time, several growth models have been developed that are:
(a) Exponential Growth Model
(b) Logistic Growth Model
Logistic Growth Model states that there is no such population of any species in the nature that ideally grows without any hindrance. Two important factors that govern population growth is food availability and disease outbreak. Initially, the growth of population shows the lag phase. Further the lag phase is followed by phases of acceleration and deceleration and finally an asymptote till the population density reaches the carrying capacity.
If the values are plotted on the curve, it results in sigmoid curve. This type of population growth is called Verhulst – Pearl logistic growth. The equation can be given as:
Where, \(\frac{\mathrm{dN}}{\mathrm{dt}}\) = rN \(\frac{\mathrm{k}-\mathrm{N}}{\mathrm{k}}\)
N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity.