Oswal 36 Sample Question Papers ISC Class 12 Biology Solutions


Answer 1.

  • (i) 1/3 land should be under forest in a country.
  • (ii) Dihybrid cross (F2) with independently assorting, completely dominant genes will give the ratio of 9 : 3 : 3 : 1.
  • (iii) Hunger, war, spread of epidemic diseases, other natural calamities like floods, earthquake and drought are positive checks on population.
  • (iv) The sequential arrangement of fossil as determined by their age and the rock strata in which they are found is known as fossil record.
  • (v) William Hornaday coined the term Wildlife.
  • (vi) A broad spectrum antibiotic is one which can inhibit the growth of both gram positive and gram negative bacteria. For example: Tetracycline.
  • (vii) The middle piece of human sperm contains mitochondria in order to provide energy for the movement of sperms. The absence of mitochondria makes the sperm immobile which in turn cause no fertilisation in the fallopian tube.
  • (viii) When pairs of genes are linked, they are carried on the same chromosome and are inherited together. Crossing over complicates the inheritance of linked genes; sometimes allele combinations differ from either parent. The inheritance pattern of non-linked genes is more predictable since it is not affected by crossing over. The inheritance of non-linked genes can be visualized by using a Punnett Square.

(ix) (a) 5

 Explanation :

A logistic (sigmoidal) growth curve has 5 phases. They are lag phase, log phase, deceleration phase, negative down acceleration phase, and stationary phase.

(x) (b) International Union for Conservation of Nature

 Explanation :

The International Union for Conservation of Nature is an international organization working in the field of nature conservation and sustainable use of natural resources.

(xi) (d) heterotrophs

 Explanation :

Decomposers are organisms that break down dead or decaying organisms to get energy. Decomposers speed up the decomposition process. Thus, they are heterotrophs.

(xii) (c) Assertion is true but Reason is false.

 Explanation :

Plant-animal interactions involve co-evolution of mutualists. E.g.: evolution of flower and pollinator. Plants need animals for pollination and seed dispersal and animals get rewards like pollen, nectar and juicy fruits. They evolve side by side.

  • (xiii) (a) T H Morgan gave the concept of Linkage.
  • (b) P Maheshwari gave the concept of Plant tissue culture.
  • (xiv) (a) Immunosuppressant
  • (b) Helper T-cells
  • (xv) (a) Ribosomal Ribonucleic Acid
  • (b) Expressed Sequence Tags
  • (xvi) (a) When the first line of defence fails, then the second line of defence i.e., the inflammatory response, takes over to prevent infection.
  • (b) In systemic inflammatory response, the number of white blood cells increases and fever is caused by the toxins released by pathogens or by compounds called pyrogens. These are released by WBCs to regulate body temperature. Fever if moderate stimulates the phagocytes and hence, inhibits growth of micro-organism.


Answer 2.

  • (i) Bioprospecting
  • (ii) Lungs of the planet

Answer 3.

(i) In self-pollinated species the seeds are not formed because of self-incompatibility where there is no growth of pollen tube on the stigma of a flower that prevents the fusion of gametes and thereby developing into an embryo. Hence, in such species seed could not be formed.


  • (ii) The probable reasons for this could be:
  • 1. Rapid decline in the death rate.
  • 2. Decreased maternal mortality rate.
  • 3. Decreased infant mortality rate.
  • 4. Increase in the number of individuals that have attained the reproductive age.

Answer 4.

  • A – Antigen binding site
  • D – Light chain
  • E – Heavy chain
  • F – Disulphide bridge.

Answer 5.

  • Physical agents, Chemical agents, Nutrient agent, Biological agent, Mechanical agents.

Answer 6.

  • 1. Raw material for biogas plant is mainly cow dung which is easily available in rural areas where cattle are used.
  • 2. The biogas is used for lighting and cooking in these areas as distribution is only in short distances.
  • 3. The spent slurry from the biogas plants is used as a fertilizer for agriculture hence are more suitable in rural areas.

Answer 7.

  • Filariasis disease is caused by two types of parasitic worms namely Wuchereria bancrofti and Burugia malayi. The disease shows the symptoms like chronic inflation of the lymphatic vessels of lower limbs and gross deformities of genital organs. This disease is transmitted through the bite of female mosquito vectors.

Answer 8.

  • (a) Zygote Intra Fallopian Transfer Technique (ZIFT)
  • (b) Human Immunodeficiency Virus (HIV)


Answer 9.


Answer 10.

Biogas is a mixture of inflammable gases (Methane, SO2, CO2, etc.) produced by microbial activity that can be used as fuel.
  • Mechanism of Biogas production:
  • The mechanism of production of biogas can be completed in the following steps:
  • 1. The raw material for biogas production is excreta (dung) of cattle.
  • 2. The biogas plant has a concentrate tank (10-15 feet deep) in which bio-wastes and slurry of dung is collected.
  • 3. The tank has a floating cover which rises on production of gas in the tank.
  • 4. Methanobacterium in the dung act on the bio-waste to produce biogas.
  • 5. The gas produced is supplied to nearby houses by an outlet.
  • 6. Through another outlet, the spent slurry is removed to be used as fertilizers.
  • 7. Biogas is used as fuel for cooking and lighting.

Answer 11.

  • In genetics, the probability concepts decide the extent of agreement of the experimental results with a theoretically expected model, to predict the results of a hybridization programme.
  • Definition : Number of a possible outcomes (or happening) of an event divided by the total number of possible outcomes of that event. Probability is the study of the likelihood of the occurrence of a particular event or offspring. The chances or probability that an event will take place can be expressed as a fraction (1/4), ratio (1 : 4) or % (25%).
  • Example : In monohybrid cross heterozygous F1 hybrid (Tt) can produce two kinds of gametes (T) and (t). The probability of gamete that carries the (T) allele is 1/2. Similarly the probability of gamete that carries the (t) allele is 1/2.

Answer 12.

  • The following changes occur during spermiogenesis :
  • 1. The developing spermatozoa increase in their length.
  • 2. The weight of the gamete is reduced along with development of locomotory structures.
  • 3. Loss of water from the nucleus results in its compaction, wherein it forms the major part of head of spermatozoa. DNA, RNA and nucleolus become concentrated.
  • 4. Golgi complex of spermatid gives rise to acrosome on the head of the sperm.
  • 5. The two centrioles (proximal and distal) of the spermatid get arranged one after the other, behind the nucleus in the neck region.
  • 6. Distal centriole forms the axial filament of the spermatozoa.
  • 7. Mitochondria from different parts of the spermatid get arranged in the middle piece around axial filament and form nebenkern.
  • 8. Much of the cytoplasm of a spermatid is lost and forms a thin layer called manchette around middle piece.

Answer 13.

  • (i) The immunity that an individual acquires after the birth is called acquired, adaptive or specific immunity. It is specific and mediated by antibodies or lymphocytes or both, which make the antigen harmless. There are two types of adaptive responses: the cell-mediated immune response, which is carried out by T-cells, and the humoral immune response, which is controlled by activated B-cells and antibodies. Activated T-cells and B-cells that are specific to molecular structures on the pathogen proliferate and attack the invading pathogen. Their attack can kill pathogens directly or secrete antibodies that enhance the phagocytosis of pathogens and disrupt the infection.


  • (ii) Following are the series of events that are seen after the HIV gets entry in the body of the host:
  • 1. The virus enters into the macrophage.
  • 2. The RNA genome gets replicated and DNA is formed with the help of an enzyme called reverse transcriptase.
  • 3. The macrophage continues to produce virus particles on large scale.
  • 4. The virus then enters the helper T-lymphocytes, thus replicates and forms the progeny of the virus.
  • 5. Hence, the body of the host or person becomes susceptible for multiple infections including bacteria, virus, fungi and parasitic infections as immune cells are compromised.
  • 6. Multiple infections cause complications and the body fails to fight the pathogens.
  • 7. Due to such compromised immunity the person may also die.

Answer 14.

  • The primary productivity is the amount of biomass or the organic matter produced per unit area, per unit time by the plants during the process of photosynthesis. The factors that influence the primary productivity are:
  • 1. Availability of nutrients : More the nutrients available in the ecosystem, more is the primary productivity.
  • 2. Quality of light : The maximum photoperiod facilitates in photosynthesis. More the photoperiod, more will be the productivity.
  • 3. Availability of water : More the water available in the area, more will be the primary productivity of that area.
  • 4. Temperature : More the temperature less will be the primary productivity. Decomposition is an oxygen consuming process. The availability of oxygen increases the rate of decomposition. In the process of decomposition, the complex organic material is broken down into simpler and inorganic substances. This process needs oxygen. In presence of oxygen, the decomposers or saprotrophs secrete digestive enzymes and the process of decomposition completes.

Answer 15.

  • (a) Nutrition : Supply of nutrient material to foetus.
  • (b) Respiration : Supply of O2 to foetus and receives CO2 back from it.
  • (c) Excretion : Fluid nitrogenous waste products escape through the placenta.
  • (d) Barrier : The placenta is a barrier like semi-permeable membrane.
  • (e) Storage : The placenta stores fat, glycogen and iron for the embryo before the formation of liver.


Answer 16.

A bioreactor is a vessel or a fermenter like an apparatus that is used to grow organisms such as bacteria or fungi under controlled environmental conditions e.g. pH, temperature, dissolved oxygen, etc. It can be used for the production of compounds of pharmaceutical importance, antibodies or vaccines.


A stirred tank reactor is cylindrical has a curved base that assists in the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor. Alternatively, air can be bubbled through the reactor. The function of the agitation system is to provide good mixing and thus increase mass transfer rates through the bulk liquid. The agitation system consists of the agitator and the baffles that are used to break the liquid flow to increase turbulence and mixing efficiency.

  • The components of a bioreactor are:
  • 1. An agitator system
  • 2. An oxygen delivery system
  • 3. A foam control system
  • 4. Temperature control system
  • 5. pH control system
  • 6. Sampling ports to withdraw small volumes of culture periodically.

Answer 17.

Luteal phase is the period between ovulation and the onset of the next menstrual flow. It lasts for about 12-14 days (from 16th–28th day) of menstrual cycle.

  • The events occurring during this phase are:
  • 1. Corpus luteum is formed from empty graafian follicle which increase in size. The follicular cells are converted to lutein cells by deposition of yellowish lipid inclusions, giving it a yellow colour, so called Luteal phase.
  • 2. It secretes progesterone by suppressing the secretion of FSH, and LH inhibits the maturation of follicle and ovulation. It also inhibits uterine movements.
  • 3. The uterine endometrium proliferates (5-6 mm) and is ready for implantation.
  • 4. If fertilisation occurs, the uterine endometrium implants the zygote after 7 days by maintaining high levels of progesterone.
  • 5. If fertilisation does not occur, the high progesterone concentration and inhibin inhibits GnRH production from hypothalamus. In absence of GnRH, levels of FSH and LH falls, thus the endometrum starts detaching. Due to decreasing progesterone level, corpus luteum converts to corpus albicans and prepares to start the next menstrual phase.

Answer 18.

  • (i) In the replication process, while the original strands unwound, new nucleotides are added to form pairs with the bases of the original strand. To begin with, DNA duplex is nicked by the enzyme DNA topoisomerase, allowing part of the molecule to unravel to form a replication fork. Next, the enzyme DNA helicase splits the two strands by breaking the hydrogen bonds. This exposes the bases. Because of the characteristic Y-shape of the replicating DNA, it is often referred to as a “replication fork.”
  • DNA polymerase enzyme then moves along the exposed base sequences, and creates a new complementary strand. DNA polymerase reads the exposed code from the 3′ to the 5′ end and therefore assembles the new strand from the 5′ to the 3′. The DNA strand that is synthesized in the 5′ to 3′ direction is called the leading strand. The opposite strand is the lagging strand, and it is synthesized in the 3’ to 5’ direction. This brings us to the first rule of DNA replication : DNA synthesis only occurs in one direction, from the 5′ to the 3′ end.
  • Several molecules of DNA polymerase act simultaneously, each assembling a separate section of the new strand of DNA, called Okazaki fragments. Each DNA polymerase is lead by an RNA polymerase enzyme, which constructs an RNA primer to guide the action of the DNA polymerase. All Okazaki fragments are subsequently joined together by DNA ligase to form a long continuous DNA strand.


  • (ii) When Griffith conducted experiments on transformation, protein was believed to be genetic material. Since transforming material in Griffith’s transformation principle was the genetic material, three scientists, Oswald T. Avery, Colin Macleod and Maclyn McCarty (1944) set out to find the chemical nature of the transforming material.
  • Their experiment was :
  • 1. They killed S-type bacterial strain with heat and separated its components DNA proteins and carbohydrates. DNA components were subdivided into two-one parts with hydrolysing enzyme DNAase and the other without the enzyme.
  • 2. They added the four different components to the culture medium supporting R-type bacteria.
  • 3. After an interval, the bacteria were analysed.
  • 4. There was no change in the three cultures having additions of S-type carbohydrates, S-type proteins and S-type DNA with DNAase.
  • 5. The fourth culture having S-type DNA without DNAase was found to have some bacteria of S-type. They must have been formed from R-type bacteria with the help of DNA of S-type.
  • Thus, this experiment of Avery, Macleod and McCarty gave experimental proof that DNA is the genetic material in most living organisms.

ISC 36 Sample Question Papers

All Subjects Combined for Class 12 Exam 2023

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