CBSE 12th Term-2 Exam 2022 : Biology Analysis, Review & Question Paper with Answer Key

Students of CBSE Board Class 12 appeared for their Term 2 Bio exam today from 10:30 AM across the country. The students were seen as anxious as this is the last science paper they had to appear for and wanted to perform their best in this exam. They were seen following all the Covid 19 guidelines at the exam centre. Check the first reaction of the students as they exited the exam centres today. our team went to various centres across Delhi- NCR to know the first reaction of students and got to know that the exam was lengthy but easy. Many students had a great paper today. Check the answer key link available below and expert reactions to the CBSE Class 12 Biology Exam Term 2 today.

CBSE Class 12 Biology Term 2 Question Paper 2022 Q.P. Code - 57/4/1 - Set- 1

CBSE Class 12 Biology Term 2 Question Paper 2022 Q.P. Code - 57/5/1 - Set- 1

CBSE Class 12 Biology Term 2 Exam 2022 : Student Reactions

The students of class 12 were seen exiting the exam centre happily. “It was a lengthy but good exam”, said Mayuri Das, a student in class 12 Biology.

“The paper was well balanced and was easy,” said the boys exiting the exam centres in Malviya Nagar Delhi. "It was lengthy but then it was Bio, so we expected to write and write", said the girls outside the same school.

The students were happy as they found the paper to be from their syllabus strictly with nothing out of the premises of the syllabus.

“It was easy and representation of the answers matters, I drew diagrams in most questions and hope to score atleast 90% this time,” said Rohit Singh, from Mayur Vihar.

Overall, the students were satisfied with the question paper and the pattern today. Many said that they expect better marks than CBSE Term 1 Biology exam.

CBSE Class 12 Biology Term 2 Exam 2022 : Expert Opinion

The experts are of the view that it was an easy exam. “It was easier for the students this time as the exam was subjective and they had a habit of writing answers from earlier years,” said Asha Sharma, a teacher from Central School. The paper was completely from the syllabus and so the exam was easy.

Experts are of the opinion that the exam was easy for the students who had studied well and it should be high scoring for the science students. Term 2 exam for CBSE Class 12 Biology can generate more than 90% marks for almost 80-85% of the students this year.

The marking is also direct and easy this time. Thus the students can relax and prepare for the coming exams now and in case CBSE just considers Term 2 exam marks, Bio can be a 90% paper for many.

Class 12 Biology Term 2 Answer Key: Paper Code 57/4/1

Section A

Q.1 Explain, giving two reasons, how immune response by “vaccine” is different from that by “antitoxin” in humans.

Answer:

1. Vaccines can be classified into two broad groups. The first group, live attenuated vaccines, comprises weakened versions of the pathogens; these mimic the kind of protective immunity induced in people who survive live infection.

2. Passive immunity is protection by antibody or antitoxin produced by one animal or human and transferred to another. Passive immunity provides immediate protection against infection, but that protection is temporary. The antibodies will degrade during a period of weeks to months, and the recipient will no longer be protected.

Q.2(a) Mention the common bacterium found in the anaerobic sludge during sewage treatment and also in the rumen of cattle. How is this bacterium commercially useful?

Answer: The group of bacteria found in both the rumen of cattle and sludge of sewage treatment is Methanogen bacteria. Biological methanation occurs naturally in swamps, digestive systems of animals, oil fields and other environments and is already commonly used in sewage water plants and biogas plants.

b) Name the effective biocontrol agents of several plant pathogens belonging to group of viruses. Also, write about the ways they support the environment.

Answer: Promising achievements in terms of biological control have emerged, especially after the successful use of certain antagonistic biocontrol agents (BCAs), in particular Pseudomonas spp., Bacillus spp., Burkholderia spp., and Trichoderma sp. against pathogens causing foliar and soilborne diseases like Agrobacterium radiobacter var radiobacter, Erwinia spp., Fusarium spp., Rhizoctonia solani, Phytophthora spp. and Pythium spp. diseases.

BCAs are applied in the disease management of plant pathogens, where they act via a variety of different modes of action to control plant pathogens. Understanding the mechanisms behind the protective effects of BCAs will facilitate the optimization of control and will allow the use of more efficient strains in the correct environment.

Q.3 Some of the microbes used as biofertilizers are prokaryotes. Name the taxonomic group they come under. With the help of an example, mention how they act as biofertilizers.

Answer: The following microorganisms are used as biofertilizers:

Rhizobium: They form root nodules in leguminous plants and fix the atmospheric nitrogen into an organic form. Rhizobium also has no negative effect on soil quality and improves the quality, nutrient content, and growth of the plant.

Azotobacter: These are free-living nitrogen fixers found in all types of upland crops. These not only fix nitrogen but also provide certain antibiotics and growth substances to the plant.

Azospirillum: Unlike Azotobacter, these can be used in wetland areas. They are found inside the roots of the plant (non-free-living) where they fix the atmospheric nitrogen.

Blue-green algae: These are free-living nitrogen-fixing Cyanobacteria that are present only in wet and marshy lands. However, they do not survive in acidic soil.

Mycorrhiza: It is a symbiotic association between the fungi and the roots of a plant. The mycorrhizal fungi play an important role in binding the soil together and improves the activity of the microbes. The fungi draw water and nutrients from the soil thereby increasing the plant productivity. It also helps the plant to survive under various environmental stresses.

Q.4 Different species belonging to the genus Trichoderma are useful to humans as well as to plants. Justify their roles by giving one instance of each.

Answer: In biological control, genus Trichoderma serves as one of the best bioagents, which is found to be effective against a wide range of soil and foliar pathogens. Genus Trichoderma is a soil inhabiting green filamentous fungus, which belongs to the pision Ascomycota. The efficacy of Trichoderma depends on many abiotic parameters such as soil pH, water retention, temperature and presence of heavy metals.

The use of microorganisms as bioagents is a less hazardous method for controlling plant pathogens. Almost 20 species of the genus Trichoderma act as bioagents against many soil-borne as well as foliar plant pathogens T. harzianum, T. pseudokoningii, T. atroviride, T. koningii, T. viride, T. atroviride, T. longibrachiatum, T. hamatum, T. polysporum and T. reesei are the most important species, which act as potential antagonists.

Section B

Q. 7(b) How did Dr. David Tilman relate experimentally, the stability of community and its species richness? Explain.

Answer: David Tilman used outdoor plot in his experiments. In his experiment, he found plots with more species but with fewer variations in total biomass from previous years. He also concluded that increasing persity contributed to higher productivity. Thus, David Tilman shows that ” stability of a community depends on its species richness”.

Q.8 What are the consequences of loss of biopersity in a region? Explain.

Answer:

1. Decline in plant production/Decline in number of animal species.

2. Lowered resistance to environmental perturbations such as drought.

3. Increased variability in certain ecosystem processes such as plant productivity/ water use/pest & disease cycles.

4. Species may become endangered/increased rate of species extinction.

Q. 9 Bacillus thuringiensis plays an important role in Integrated Pest Management strategy. Explain how. Name any two crops that are protected efficiently from pests.

Answer: Bacillus thuringiensis (Bt) crops are plants genetically engineered (modified) to contain the endospore (or crystal) toxins of the bacterium, Bt to be resistant to certain insect pests. In 1995, the Environmental Protection Agency (EPA) in USA approved the commercial production and distribution of the Bt crops: corn, cotton, potato, and tobacco. Currently, the most common Bt crops are corn and cotton. The crystal, referred to as Cry toxins, is proteins formed during sporulation of some Bt strains and aggregate to form crystals. Such Cry toxins are toxic to specific species of insects belongs to orders: Lepidoptera, Coleoptera, Hymenoptera, Diptera, and Nematoda.

Bt crops are plants genetically engineered (modified) to contain the endospore (or crystal) Bt toxin to be resistant to certain insect pests. The most widely used Bt vegetable crop is sweet corn. Shelton compared sweet corn varieties grown in the USA where the primary insect pest was Heliothis zea and demonstrated that non-sprayed Bt varieties produced more clean marketable ears than corn varieties sprayed with chemical insecticides up to 8 times.

Q.10 With the help of a storyboard or a flowchart only, explain all the stages of how human insulin is produced through r-DNA technology.

Answer: The steps in the production of human insulin by genetic engineering method includes:

1. Human insulin is extracted from pancreas cells and an insulin-producing gene is isolated.

2. A plasmid DNA is extracted from a bacterium and cut with restriction enzyme, forming plasmid vector.

3. Insert human insulin-producing gene into the bacterial plasmid vector to form the recombinant DNA of human insulin-producing gene.

4. Introduce this recombinant DNA into a bacterial cell to form the recombinant bacterium.

5. The recombinant bacteria multiply in a fermentation tank and produce human insulin.

6. Insulin is extracted, purified and bottled. It is then ready to be injected into diabetic patients.

Q.11(a) Explain the roles of (i) primary, and (ii) secondary lymphoid organs that are responsible for developing defence to combat the action of pathogen/foreign antigens which enter our body.

Answer: Primary lymphoid organs are those organs in which the production of the cells of the immune system takes place. For example, bone marrow is a primary organ and contains a pluripotent stem cell which serves as the precursor to red blood cells (i.e., erythrocytes) and myeloid progenitors (which ultimately differentiate into granulocytes, mast cells, monocytes, and platelets), in addition to lymphoid progenitors (which ultimately differentiate into the various types of lymphocytes). Hematopoiesis is a general term used to refer to the production of the cells of the blood, and it can be subpided into erythropoiesis, myelopoiesis, and lymphopoiesis, respectively, based on the cell lineages described previously. Lymphoid progenitors will emerge from the bone marrow and travel to other primary lymphoid organs where the final stages of lymphocyte maturation take place. As described later, mature lymphocytes play a major role in discriminating between self and nonself because they are endowed with surface receptors characterized by tremendous specificity. Lymphoid progenitors which receive their final education in the thymus are called thymus-derived lymphocytes or T cells. The other major subtype of lymphocyte is the B cell, so named because it was originally characterized in the chicken as a lymphoid progenitor which receives its final education in a primary lymphoid organ called the Bursa of Fabricious, an outpocket of the gastrointestinal epithelium. Although there is no Bursa in mammals, fetal liver, spleen, and adult bone marrow are considered the ‘bursal equivalents’ and function as the primary lymphoid organs for the production of B cells. The process of lymphopoiesis takes place within specific regions of the thymus and bursal equivalents called microenvironments and is regulated by specialized cells (bone marrow stromal cells and thymic epithelial cells) and their soluble factors (including the interleukins IL-3, IL-7, IL-9, and IL-12; see Table 1), which comprise the microenvironments. The stages of lymphopoiesis are generally believed to be antigen independent, where antigen is defined as any substance which can stimulate a specific immunological reaction. The surface receptors of lymphocytes, mentioned previously, are directed toward ‘antigen’. Although lymphopoiesis is neither antigen dependent nor antigen driven, a role for antigen cannot be excluded because factors secreted during an antigen-specific reaction in the periphery can promote various forms of hematopoiesis in the bone marrow.

There are about 2 × 10¹² lymphocytes in the human body, making the immune system comparable in cell mass to the liver or brain. Despite their abundance, their central role in adaptive immunity was not demonstrated until the late 1950s. The crucial experiments were performed in mice and rats that were heavily irradiated to kill most of their white blood cells, including lymphocytes. This treatment makes the animals unable to mount adaptive immune responses. Then, by transferring various types of cells into the animals it was possible to determine which cells reversed the deficiency. Only lymphocytes restored the adaptive immune responses of irradiated animals, indicating that lymphocytes are required for these responses.

Q.11(b) Doctors generally advise not to undergo surgery of tonsils. Why?

Answer: Inflammation of the palatine tonsils can lead to a sore throat and difficulty swallowing. If the inflammation is caused by bacteria, it is often treated with antibiotics at first. If the tonsils keep on becoming inflamed, doctors may suggest having them (partially) removed instead. It’s important to carefully consider this option before making a decision: On the one hand, there’s the hope that surgery will reduce the number of throat infections or make them go away completely. On the other, the surgery carries risks and there’s no guarantee that it will help in the long term.

Surgery is only considered if

the person has bacterial tonsillitis at least three to five times a year,
they have taken antibiotics for it several times, and
the symptoms greatly affect their everyday life.

If possible, it is also important to rule out that the infections are being caused by a virus. It’s not always easy to tell the difference between bacterial and viral tonsillitis. Bacteria can be detected using a throat swab.

The typical symptoms of bacterial tonsillitis are: