Oswal 36 Sample Question Papers ISC Class 12 Biology Solutions


Answer 1.

(i) Population density: Population density is the number of individuals per unit geographical area, for example, number per square meter, per hectare, or square kilometre.

(ii) Dihybrid cross (F) with independently assorting, completely dominant genes will give the 9 : 3 : 3 : 1 ratio.

(iii) Brood parasitism, also called social parasitism, is the unique population interaction in which the parasitic bird deposits its eggs in the nests or broods of another individual (host) and lets them incubate. For example- a cuckoo lays its eggs in the nest of a crow.

(iv) The body recognises ‘non-self’ organ and its immune system starts functioning against it.

(v) William Hornaday coined the term Wildlife.

(vi) (a) Mammals, (b) Amphibians

(vii) The given image represents the blastocyst which will be transferred to uterus in the procedure called intrauterine transfer (IUT).

(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 the parent. The inheritance pattern of non-linked genes is more predictable since it is not affected by crossing over does not affect it. The inheritance of non-linked genes can be visualised 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 organisation working in the field of nature conservation and sustainable use of natural resources.

(xi) (d) Both assertion and reason are false.

Explanation :

Plant- animal interactions involve co-evolution of mutualists. Eg: 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. Thus, both assertion and reason are false.

(xii) (d) Both assertion and reason are false.

Explanation :

Restriction endonucleases are used to cut foreign DNA and vector DNA while ligase seals the DNA pieces. Thus, both assertion and reason are false.

(xiii) (a) T H Morgan gave the concept of Linkage.

(b) P Maheshwari gave the concept of Plant tissue culture.

(xiv) Chromosomes assorting independently.

(xv) The commonly used vectors for transformation in plant cells are:

  1. Agrobacterium tumefaciens
  2. E. coli
  3. Cauliflower mosaic viruses (CaMV)
  4. Brome mosaic viruses (BMV)

(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) Saliva of the cow contains lysozyme which kills harmful bacteria.

(xvii) Ti plasmid is isolated from Agrobacterium tumifaciens. Ti plasmid of Agrobacterium tumifaciens has been modified into a cloning vector that is not pathogenic to plants and able to use the mechanisms to deliver genes of interest to plants.

(xviii) Statin is produced by the yeast Monascus purpureus. It acts as a blood cholesterol lowering agent by competitively inhibiting the enzyme responsible for synthesis of cholesterol.


Answer 2.

(i) The naturalist Alexander Von Humboldt explained about the above given graph. His observations suggested that, the species richness increases with an increase in explored area but upto certain limit.

(ii) The slope of line ‘b’ becomes steeper when the species richness will be between 0.6 to 1.2.

Answer 3.

(i) (a) A-Male gametes; B-Tube nucleus

(b) The main function of a tube nucleus is to control and direct the growth of the pollen tube.


(ii) (a) P-Primary spermatocyte; R-Spermatids

(b) Testosterone

Answer 4.

(i) The above diagram shows the action of restriction endonuclease and thus forms a recombinant DNA after completion of entire process.

(ii) Eco stands for Escherichia coli, R stands for the name of the strain and Roman I indicates the order in which the enzymes were isolated from the strains of the bacteria.

Answer 5.

A bat’s wing and a bird’s wing have similar structures and origins i.e., they have bony structures hence, they are called homologous organs. A bat’s wing is analogous to the wing of an insect because the wing of an insect does not have a bony structure, it has a membranous wing. So, a bat’s wing and an insect’s wing are analogous because they have similar functions but do not have the same origin and structure.

Answer 6.

  1. Raw material for biogas plants is mainly cow dung, readily available in rural areas where cattle are used.
  2. 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 fertiliser for agriculture, and 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.

Ecologist Paul Ehrlich gave rivet popper hypothesis to help in understanding the contribution of species richness of the ecosystem. He compared each species with rivet in the body of an aeroplane. This hypothesis explains that ecosystem is an aeroplane and the species are the rivets joining all parts together. If every passenger travelling in the aeroplane starts taking rivets home (causing a species to become extinct), initially it may not affect flight safety (proper functioning of ecosystem), but over a period of time the plane becomes weak and dangerous (species become endangered and then extinct). In an ecosystem, the role of each species is important.

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 cattle excreta (dung).
  2. The biogas plant has a concentrate tank (10-15 feet deep) in which bio-wastes and the slurry of dung is collected.
  3. The tank has a floating cover which rises on the production of gas in the tank.
  4. Methanobacterium in the dung acts on the bio-waste to produce biogas.
  5. The gas produced is supplied to nearby houses by an outlet.
  6. The spent slurry is removed through outlet to be used 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 hybridisation programme.

Definition : Number of 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 a gamete that carries the (T) allele is 1/2. Similarly, the probability of a gamete that carries the (t) allele is 1/2.

Answer 12.




Answer 13.

(i) It is a type of antibody (Immunoglobulin).

(ii) ‘A’ denotes the antigen binding site and ‘B’ denotes the heavy chain.

(iii) The B-cells or B–lymphocytes produce such type of molecules.

Answer 14.

The primary productivity is the amount of biomass, or organic matter produced per unit area, per unit time by the plants during the process of photosynthesis.

The factors that influence primary productivity are:

  1. Availability of nutrients : More the nutrients available in the ecosystem, the more is the primary productivity.
  2. Quality of light : The maximum photoperiod facilitates in photosynthesis the more the photoperiod, more will be the productivity.
  3. Availability of water : More the water available in the area,the 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 the presence of oxygen, the decomposers or saprotrophs secrete digestive enzymes and the process of decomposition completes.

Answer 15.

(i) Fig 1 to 5 specify the passage of a growing embryo, the stages occurring through the fallopian tube.

(ii) Blastomeres.

(iii) It is known as morula.


Answer 16.

Recombinant DNA technology involves several important steps that include:

  1. Isolation of Gene of Interest: The first step in rDNA technology is to isolate the desired DNA in its pure form i.e. free from other macromolecules. Since DNA exists within the cell membrane along with other macromolecules such as RNA, polysaccharides, proteins, and lipids, it must be separated and purified which involves enzymes such as lysozymes, cellulase, chitinase, ribonuclease, proteases etc.
  2. Restriction Enzyme Digestion: Once DNA is purified; restriction enzymes are used to isolate the gene of interest. Restriction enzymes act as molecular scissors that cut DNA at specific locations. This step involves the incubation of the purified DNA with the selected restriction enzyme, at conditions optimal for that specific enzyme. The vector DNA is also processed using the same procedure.
  3. Amplification Using PCR: Polymerase Chain Reaction or PCR is a method of making multiple copies of a DNA sequence using the enzyme – DNA polymerase in vitro. It helps to amplify a single copy or a few copies of DNA into thousands to millions of copies. The cut fragments of DNA can be amplified using PCR and then ligated with the cut vector.
  4. Ligation of DNA Molecules: The purified DNA and the vector of interest are cut with the same restriction enzyme and ligated using the enzyme ‘DNA ligase’. The resulting DNA molecule is a hybrid of two DNA molecules – the interest molecule and the vector. Hence, this new hybrid DNA molecule is also called a recombinant DNA molecule.
  5. Insertion of Recombinant DNA into Host: In this step, the recombinant DNA is introduced into recipient host cells which are mostly, bacterial cell. This process is called transformation. Hosts are treated to make them competent to accept new DNA. The processes used may be thermal shock, Ca2+ ion treatment, electroporation etc.
  6. Isolation of Recombinant Cells: The transformation process generates a mixed population of transformed and non-transformed cells. The selection process involves filtering the transformed host cells only. Gel electrophoresis is often used to separate pieces of DNA which in turn makes it possible to determine which plasmids took up the gene of interest. Several other methods involve growing the cells on antibiotic (e.g., tetracycline) agar plates.

Answer 17.

(i) They are situated on the inside wall of the seminiferous tubule.

(ii) When primary spermatocytes undergo their first meiotic division they form two equal haploid cells known as secondary spermatocytes.

(iii) They are four haploid cells formed when the secondary spermatocytes undergo the second meiotic division. Such haploid cells are called spermatids.

(iv) It is the process by which the spermatids are transformed into spermatozoa or sperms.

(v) After the process of spermiogenesis, the heads of the sperms get embedded into sertoli cells and are finally released from seminiferous tubules through the process of spermiation.

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, the protein was believed to be a 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 the 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

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