Please refer to Class 12 Biology Sample Paper with solutions provided below. All sample papers for Biology Class 12 have been designed as per the latest paper pattern issued by CBSE for the current academic year. Students should practice these guess papers for Class 12 Biology as it will help them to gain more understanding of the type of questions that are expected to be asked in upcoming Class 12 Biology exams. Please click on the links below to access free CBSE Sample Papers for Class 12 Biology.
Class 12 Biology Sample Paper Term 2 With Solutions Set A
SECTION-A
1. Elaborate on meaning and role of MALT.
Answer : There is lymphoid tissue also located within the lining of the major tracts (respiratory, digestive and urogenital tracts) called mucosal associated lymphoid tissue (MALT). It constitutes about 50 per cent of the lymphoid tissue in human body.
2. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
What are flocs formed during secondary treatment of sewage? What is their fate in the next step of treatment?
Answer : Fertilizers and pesticides are synthetic and may be non-biodegradable in nature. They may cause environmental pollution, biomagnification and eutrophication. To counter these problems associated with the overuse of chemical fertilizers, there is a need to switch to organic farming – to use biocontrol of pests and bio fertilizers.
OR
Flocs are aerobic microbes -bacteria associated with fungal filaments that consume the major part of the organic matter in the effluent which is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment.
Answer : This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of 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.
3. (i) How is the disease in which there is an uncontrolled division of cells detected?
(ii) How do interferons help in controlling the disease?
Answer : (i) The two techniques useful in detecting cancers of internal organs, are CT (Computed Tomography) and MR1
(Magnetic Resonance Imaging).
(ii) As tumour cells are capable of avoiding recognition and destruction by immune system, the cancer patients are given a-interferons which are biological response modifiers. It helps activate the immune system and destroy tumours.
4. Mention the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained. How are these substances useful?
Answer : Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infraction leading to heart attack.
Statins produced by the yeast Monascus purpureus have been commercialized as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.
Cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polysporum.
5. (i) Bear hibernates, whereas some species of zooplanktons enter diapause to avoid stressful external conditions.
How are these two ways different from each other?
(ii) How does our body adapt to low oxygen availability at high altitudes?
Answer : (i) Difference between diapause and hibernation
(ii) Body adaptations at high altitudes are: The physiological condition or responses in order to get acclimatised to high attitudes are:
(a) To compensate low oxygen, the production of red blood cells is increased.
(b) High haemoglobin content and its decreased binding capacity.
(c) Faster breathing rate. [any two]
6. With an example, explain how biotechnology has been applied in each of the following:
(i) In producing more nutritionally balanced milk
(ii) Chemical safety testing
Answer : (i) In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk (2.4 grams per litre). The milk contained the human alpha-lactalbumin and was nutritionally a more balanced product for human babies than natural cow-milk.
(ii) Vaccine safety: Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humAnswer : Transgenic mice are being used to test the safety of the polio vaccine. If successful and found to be reliable, they could replace the use of monkeys to test the safety of batches of the vaccine.
OR
Draw the figure of vector pBR322 and label the following: Origin of replication, Ampicillin resistance site, Tetracycline resistance site, Bam H1 restriction site.
Answer :
SECTION-B
7. (i) Name the Protozoan parasite that causes amoebic dysentery in humans
(ii) Mention two diagnostic symptoms of the disease.
(iii) How is this disease transmitted to others?
Answer : (i) Entamoeba histolytica is a protozoan parasite in the large intestine of human which causes amoebiasis (amoebic dysentery).
(ii) Symptoms of this disease include constipation, abdominal pain and cramps, stools with excess mucous and blood clots.
iii) Houseflies act as mechanical carriers and serve to transmit the parasite from faeces of infected person to food and food products, thereby contaminating them. Drinking water and food contaminated by the faecal matter are the main source of infection.
OR
(i) Why do the symptoms of malaria not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles? Explain.
(ii) Give the scientific name of the malarial parasite that causes malignant malaria in humAnswer :
(iii) Give a flow chart of the part of the life cycle of this parasite passed in this insect.
Answer : (i) Malarial parasite completes its asexual cycle in liver cells and then it attacks the Red Blood Cells (RBCs) resulting in their rupture. The ruptured RBCs release toxic substance called haemozoin that is responsible for the symptoms of malaria like chill and high fever. Thus, no symptoms appear in the infected person between the period, the parasite enters the body and till RBCs release haemozoin,
(ii) Plasmodium falciparum causes malignant malaria. It enters into human body in sporozoites form.
(iii) Female Anopheies mosquito takes up gametocyte
↓
Fertilisation and development occur in mosquito intestine
↓
Mature sporozoites released from intestine and migrate to the salivary glands of mosquito
↓
Released into the host’s body while sucking blood, along with saliva.
8. Study the diagram showing replication of HIV in humans and answer the following questions accordingly.
(i) Write the chemical nature of the coat.
(ii) Name the enzyme B acting on X to produce molecule C. Name C.
(iii) Mention the name of the host cell D the HIV attacks first when it enters into the human body.
(iv) Name the two different cells the new viruses E subsequently attack.
(v) Name the widely used diagnostic test when a person gets this disease.
Answer : (i) A – Protein coat
(ii) B – Reverse transcriptase C – It is viral DNA
(iii) Macrophage (animal or human cell)
(iv) Macrophages and helper T-cells
(v) A widely used diagnostic test for AIDS is enzyme linked immuno-sorbent assay (ELISA).
9. (i) Given below is a single stranded DNA molecule. Frame and label its sense and antisense RNA molecule. 5’ ATGGGGCTC 3’ sense
(ii) How the RNA molecules made from above DNA strand help in silencing of the specific RNA molecules?
Answer : (i) Template DNA strand = antisense DNA strand
3’ TACCCCGAG 5’
5’ AUGGGGCUC 3’ sense RNA = mRNA
3’ UACCCCGAG 5’ a ntisense RNA
These two RNA’s being complementary to each other formed a double stranded (dsRNA).
If the introduction of a gene of a pathogen/pest [DNA] is such that it produced both sense and anti-sense RNA in the host cells.
The two RNA’s being complementary to each other formed a double stranded (dsRNA). This initiates RNAi.
(ii) RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing).
10. The following graph represents the organismic response to certain environmental condition (e.g. salinity)
(i) Which one of these depicts conformers?
(ii) What does the other line of graphs depict?
(iii) How do B and C organisms differ from each other with reference to homeostasis?
(iv) Mention the category to which human belong with respect to temperature.
(v) What are partial regulators?
Answer : (i) C depicts conformers.
(ii) The other line B depicts regulators while A are partial regulators.
(iii) Differences given:
| Conformer | Regulator |
| These cannot maintain a constant internal environment and change according to the ambient atmospheric conditions. | These organisms maintain a constant internal environment despite changes in the environment |
| They show a narrow range of distribution. | They show a much wider range of distribution. |
(iv) Humans are thermoregulators.
(v) Partial regulators are those organism that try to maintain a constant level of internal environment first but conform later.
11. Recombinant DNA-technology is of great importance in the field of medicine. With the help of a flow chart, show how this technology has been used in preparing genetically engineered human insulin.
Answer : Insulin consists of two polypeptide chains A and B → they are linked by disulphide bonds → Eli Lilly company introduced the human genes of both A and B chains into plasmids of E. coli separately → these genes expressed in E. coli in the form of A and B chains → the chains were extracted and mature insulin was produced by formation of disulphide bonds.
12. A policeman finds a very small piece of body tissue from the site of a crime and takes it to the forensic department.
(i) By which technique will they amplify the DNA collected from the tissue sample?
(ii) Mention in a sequence, the 3 steps involved in each cycle of this technique;
(iii) What is the role of thermostable DNA polymerase in this technique?
Answer : (i) Amplification of Gene of Interest using PCR :PCR stands for Polymerase Chain Reaction.
(ii) In this reaction, multiple copies of the gene (or DNA) of interest is synthesized in vitro using two sets of primers (small chemically synthesized oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.
(iii) If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA. The amplified fragment if desired can now be used to ligate with a vector for further cloning.
SECTION-C
Read the paragraph and answer the questions that follow.
13. The way the world has changed in recent years, it’s no surprise that some wild species are finding themselves at risk for extinction as they can’t adapt to these changes fast enough or find food sources readily available without herbicides and pesticides interfering with their natural habitats.
Researchers from the University of Queensland recently concluded that animal species who live in habitats containing greater diversity are able to survive better than those residing among fewer varieties, and further research should be conducted on how our environment is affecting this phenomenon. There are many ways that the loss of biodiversity can harm plants. Scientists have found that in a wide range of species, loss of diversity in biotic community has led to an increase in vulnerability to climate change-related stresses such as drought and heatwaves. The loss of biodiversity is a significant issue for agriculture. Without diverse habitats, we will lose many species!
(i) What features make a community stable?
(ii) What are the major cause for loss of biodiversity amongst the four main causes of loss of biodiversity?
(iii) In the past, which factor would have caused a mass extinction of species?
Answer : (i) Rich biodiversity and hence good productivity.
(ii) Habitat loss and fragmentation, alien species invasion, over-exploitation and co-extinctions.
(iii) Hint: As per scientists, the following would have triggered the mass extinction:
• Temperature fluctuation
• Meteorite/Asteroid hitting the planet
• Emission of lethal hydrogen sulphide from the sea
• The outburst of gamma radiations/supernova
OR
Human activities cause loss to biodiversity at a very fast rate. According to IUCN Red list (2004) , a number of invertebrates, vertebrates and plants have become extinct in last 500 years. The main cause of the loss of biodiversity can be attributed to the influence of human beings on the world’s ecosystem, In fact human beings have deeply altered the environment, and have modified the territory, exploiting the species directly, for example by fishing and hunting, changing the biogeochemical cycles and transferring species from one area to another of the Planet.
(i) Why are certain regions on the earth called hot -spots? Name any one hotspots in India.
(ii) State a difference between endemic and exotic species.
(iii) In comparison to other animal groups, why are amphibians more vulnerable to extinction?
(iv) What is Red list? Give two uses of the red list.
Answer : (i) Regions of rich biodiversity especially habitats for many endemic species. Generally these regions also are vulnerable to major biodiversity losses. Examples: Western ghats.
(ii) Endemic species are confined to one particular region mostly where it would have originated. Exotic species are species that have been shifted from another region.
(iii) Hint: It is because of the following:
• Habitat fragmentation
• Habitat destruction or modification
• Large scale climate change
(iv) Hint: IUCN maintains a red data book or red list which is a catalogue of taxa facing risk of extinction.
It aims to convey the urgency of conserving threatened species to the public and policy makers so as to reduce species extinction.
Uses:
(a) Identification and documentation of endangered species of plants and animals.
(b) Creating awareness about the importance of preserving the threatened biodiversity.
