Please refer to Class 12 Biology Sample Paper Term 2 Set B with solutions below. The following CBSE Sample Paper for Class 12 Biology has been prepared as per the latest pattern and examination guidelines issued by CBSE. By practicing the Biology Sample Paper for Class 12 students will be able to improve their understanding of the subject and get more marks.
CBSE Class 12 Biology Sample Paper for Term 2
1. Direction Read the following passage and answer the questions that follows.
During the unfortunate corona virus lockdown, Kavita started cursing the existence of microbes on earth.
On hearing this, Deepak told Kavita that not all the microbes are harmful for us. Many microbes are useful in producing medicines, bioactive molecules and household products.
(i) Microbes responsible for large holes in cheese belong to genes
(ii) The microbes through which ‘wonder drug’ was derived was
(a) Aspergillus fumigatus
(b) Penicillium notatum
(c) Penicillium chrysogenum
(d) Monascus purpureus
(iii) Beside making curd, which of the following is the correct function of the same bacteria?
(a) Fermentation of fish
(b) Inhancing the taste and texture of cheese
(c) Increase vitamin-B12 content
(d) Production of biogas
(iv) Nucleopolyhedrovirus do not show
(a) host specificity
(b) narrow spectrum application
(c) effect on non-targeted pathogen
(d) utility in IPM programme
(v) Identify the correct source and function of cyclosporin-A.
(a) Monascus purpureus – Suppresses immune system
(b) Trichoderma polysporum – Activate immune system
(c) Monascus purpureus – Activate immune system
(d) Trichoderma polysporum – Suppresses immune system
2. (i) Cancer is one of the most dreaded disease. Explain ‘contact inhibition’ and ‘metastasis’ with respect to the disease.
(ii)Why are cancer patients often given a-interferon as part of the treatment?
Answer : (i)’Contact inhibition’ is the property exhibited by normal cells. It prevents their uncontrolled proliferation when they are in contact with other neighboring cells. But cancerous cells seem to have lost this property and continue to divide despite being in contact with other cells, which leads to masses of cells called tumors.’ Metastasis’ is the property exhibited by malignant tumors which grow rapidly, invades, neighboring tissues and are capable of reaching distant sites through blood and lymph thus, spreading malignant tumors to other organs or parts of the body.
(iv) As tumor cells are capable of avoiding recognition and destruction by the immune system, the cancer patients are given α-interferons which are biological response modifiers. It helps activate the immune system and destroy tumors.
An organic farmer relies on natural predation for controlling plant pests and diseases.
Justify giving reasons why this is considered to be a holistic approach.
Answer : Organic farming is holistic approach for controlling plant pest because it seeks to develop an understanding of the interactions amongst the organisms in the ecosystem. Organic farmers do not try to completely eradicate the pest but keep them at manageable levels. A complete eradication of the pest is not beneficial and also not desirable because many beneficial predatory and paralytic insects can not survive without them.
3. (i) Identify A and B illustrations in the following.
(ii)Write the term given to A and C and why?
(iii)Mention one importance of biotechnology.
Answer : (a) A represents – Sticky end.
B represents – Foreign DNA insert.
(b) The term used for A is Sticky ends, it is called so because they form hydrogen bonds with their complementary cut counterparts. Their stickiness of the ends facilitates the action of the enzyme DNA ligase.
C are called the palindromic nucleotide sequence. These are named so because the sequence of base pairs reads same on the two strands when orientation of reading is kept the same.(c) PCR stands for Polymerase Chain Reaction. PCR is a technique used to synthesize multiple copies of the gene (or DNA) of interest in vitro using two sets of primers (small chemically synthesized oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. It is extensively used in the process of gene manipulation.
With respect to understanding diseases, discuss the importance of transgenic animal models.
Answer : Transgenic animals can serve as models to understand progression of various diseases in human. Transgenic models exist for many human diseases like cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer’s. These animals can be observed to understand the causative gene for a particular disease.
4. What is addiction? State any four reasons of drug addiction.
Answer : Addiction can be defined as the psychological and physical inability to stop consuming a chemical, drug or substance even though it is causing psychological and physical harm to the consumer.
Four major reasons for drug addiction are:
2. Family History/Genetics
3. Prescription Drugs
5. Peer Pressure
5. Explain briefly
(i) Restriction enzymes and DNA
Answer : (i) Restriction enzymes recognize specific sequences, mostly 4-6 bp, in the DNA and cut it into fragments by breaking the phosphodiester linkage between two successive nucleotides of DNA. DNA is polymer of deoxyribonucleotides and serves as genetic material
(ii) Chitinases are class of enzymes that can digest chitin; the major component of fungal cell wall.
What does ‘Hind’ and ‘III’ refer to in the enzyme Hind III?
Answer : In the enzyme Hind III; ‘H in’ refers to Haemophilus influenzae, D refers to the strain of H. influenzae and III refers to the sequence In which this enzyme was discovered.
6. How does the human body protect itself from infections?
Answer : Natural barriers and the immune system defend the body against organisms that can cause infection.
Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and stomach acid. Also, the normal flow of urine washes out microorganisms that enter the urinary tract.
The immune system uses white blood cells and antibodies to identify and eliminate organisms that get through the body’s natural barriers.
7. Describe the consumptive use value of biodiversity as food, drugs and medicines, fuel and fibre with suitable examples.
Answer : Consumptive Use Value: Many natural products are consumed at local level by human beings. But we neither sell nor buy these products. These products do not make direct contribution to the nation’s economy. The value of these products is called consumptive use value of biodiversity.
(a) We pay for almost all the food we consume but we do not pay for the soil, water and air which play Important role in food production.
(b) Many naturally occurring herbs are used for their medicinal use by indigenous people. In most of the cases, people do not need to pay for using such plants. This also shows consumptive use value.
(c) Firewood is used by about 2.4 million people all over the world for cooking and heating. People who use firewood do not need to pay for that. Had they been using some other fuel they would have paid some money for that. This shows consumptive use value of firewood.
(d) In rural area, people often use naturally growing fibre plants for making ropes and other useful Items. They don’t pay for the fibre. This shows consumptive use value of fibre.
How can you as an individual, prevent the loss of biodiversity?
Answer : Prevent felling of trees especially native plants or trees in a particular area.
Reduce, recycle and reuse resources. Especially, reduce pollution and use of plastic bags and other materials that are potential threats for the environment.
Use environment friendly products, segregate and dispose garbage correctly.
8. What is genetic engineering? List the steps involved in rDNA technology.
Answer : Genetic engineering: It is manipulation of genetic material which can be added or detected through their bases or parts of DNA to introduce these into host organisms and thereby change the phenotype of the host organism.
(i) Isolation of DNA.
(ii) Fragmentation of DNA by restriction endonuclease.
(iii) Isolation of the desired DNA fragments.
(iv) Amplification of the gene of interest.
(v) Ligation of the DNA fragment into a vector using DNA Ligase.
(vi) Transfer of recombinant DNA into the host organism.
(vii) Culturing the host cell on a suitable medium on a large scale.
(viii) Extraction of the desired product.
(ix) Downstream processing of the products as finished products ready for marketing.
Compare and contrast the advantages and disadvantages of the production of genetically modified crops.
Answer : The advantages of GM crops are:
(i) More tolerance to biotic and abiotic stresses (hormones, nutrition and cold, drought, salt, heat).
(ii) Resistance to pests, thereby less relayed on chemical pesticides (pest-resistant crops).
(iii) Increases fertility of soil with the efficiency of mineral usage prevents early exhaustion of fertility of the soil.
(iv) Enhanced nutritional value of food, e.g., vitamin-A enriched rice (Golden rice), protein enriched vegetables like spinach, brocolli etc.
In addition to these uses, GM has been used to create special plants to supply alternative resources to industries, in the form of starches, fuels and pharmaceuticals.
The disadvantage of GM crops are:
(a) Transgenic genes in GM crops endanger native species.
(b) They cause damage to natural environment by reducing biodiversity.
(c) They may cause human health problems by altered genes
(d) Development of new strains of bacteria with are antibiotic resistance or other drug resistance.
9. ‘Analysis of age pyramids for human population can provide important inputs for long-term planning strategies’.Explain.
Answer : The reproductive status of population and growth of population is determined by the different age group of the population. There are three types of age pyramid:
Thus, the analysis of age pyramids for the human population can provide important inputs for long term planning strategies.
(i) Compare giving reasons, the J-shaped and S-shaped models of population growth of a species.
(ii) Explain ‘fitness of a species’, as mentioned by Darwin.
Answer : (a) Comparision between the J-shaped and S-shaped models of population growth is shown below:
Resources are unlimited
Growth is exponential.
As resources are unlimited reproduce.
Resources are limited.
The fittest individuals will
all individuals survive and survive and reproduce.
Fig: J-shaped growth curve (red) and S- shaped growth curve (blue).
(b) According to Darwin, ‘fitness of a species” means reproductive fitness in which organisms evolve towards the most efficient reproductive strategy. When resources are limited, competition occurs between individuals. The fittest will survive and reproduces to leave more progeny.