Oswal Specimen Papers ISC Class 12 Biology Solutions (Specimen Paper - 9)

Section-A

1. (i) The diagram represents implants. These contain progesterone or progesterone-estrogen combination.
These are used for inhibiting ovulation and implantation of embryo in the uterine wall.
(ii) Difference between Exons and Introns.

	Exons	Introns
1.	The region of a split gene that becomes part of mRNA and codes for the different amino acids is known as exons.	The region of genes that do not form a part of mRNA and are removed during RNA processing during mRNA synthesis are known as introns.

(iii) The site from where DNA starts to replicate is called the origin of replication, or Ori site.
(iv) 23 Chromosomes are in sperm cells as sperm being the male gametes are haploid
(v) Baculovirus: Virus used in biological control of insects, pests, and other arthropods.
(vi) The commonly used vectors for genetic engineering are :

pBR322( Plasmid)
pUC19( Plasmid)
Bacteriophage M13

(vii) A genetic code comprises a triplet of nitrogen bases (A, G, C and U) which could translate the genetic information from DNA to a sequence of amino acids found in the proteins of an organism.
(viii) Tapetum provides nourishment to the developing pollen grains. The tapetal cells secretes granules that provides sporopollenin and other materials for exine formation.
(ix) (d) composed of all living organisms present on Earth which interact with the physical environment.

Explanation :

The biosphere is composed of all living organisms present on Earth which interact with their physical environment. In other words, a biosphere or ecosphere term is collectively used for all the ecosystems of world.

(x) (c) A zone of transition between two communities.

Explanation :

The adjacent biotic (natural) communities generally do not possess a fine demarcation edge or line between them. The adjacent two communities is represented by the population of both communities, and this transition zone between the two communities is referred to as ecotone. The rest of the options do not define ecotone (zone of transition).

(xi) (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation :

A population at its carrying capacity faces high intra specific competition due to limited resources. At this stage if any individual makes use of a new resource it will experience less competition and produce more offsprings. Hence, use of resources will increase through generations and niche will become longer. Thus, both assertion and reason are true and reason is the correct explanation of assertion.

(xii) (b) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

Explanation :

A single mRNA strand is capable of forming different polypeptide chains because it has different reading frame, (the way through which the reading of mRNA is done by tRNA).

(xiii) (a) Avery, MacLeod and McCarty identified DNA is the genetic material.
(b) Meselson and Stahl gave the Semi-conservative replication of DNA.

(xiv) (a) Salmonella typhi
(b) Antihistamines

(xv) (a) Gross Primary Productivity.
(b) Grazing Food Chain.

(xvi) (a) It is an established fact that the rich diversity of today’s organisms is the outcome of natural evolution stretching about 3.5 billion years. A species once lost cannot be retrieved. Therefore, it would be unethical on the part of man to be responsible for the destruction of a species.
(b) Lead in petrol inactivates the catalysts (platinum, palladium and rhodium) which convert harmful pollutants (CO, unburnt hydrocarbons, nitric oxide) to lesser harmful pollutants (CO₂, H₂O, N₂).

(xvii) A- Fertilised egg cell; B- Primary endosperm nucleus.
(xviii) DNA ligase joins the DNA fragments with same sticky ‘ends’, links okazaki fragments or discontinuously synthesised fragment, link the desired gene with plasmid to form recombinant DNA.

Section-B

2. A-Large aeration tank, B-Mechanical agitation, C-Reduced BOD, D-Activated sludge, E-Anaerobic sludge digesters.

3. (i) (a) (i) Pre-productive phase (ii) Reproductive phase (iii) Post-reproductive phase
(b) It exhibits the expanding type of population growth.

(ii) (a) The pyramid is inverted.
(b) T₃: Fishes, T₂: Zooplanktons, T₁: Phytoplanktons

4. Productivity is the rate of biomass production.
Gross productivity is the rate of production of biomass by green plants per unit time per unit area. It is the total amount of productivity.
NPP = GPP – R
Net primary productivity is the difference between gross primary productivity and the loss due to respiration.
Secondary productivity is the rate of formation of organic matter by the consumers.

5. Cryopreservation is a process of preserving the material for an extended period at a low temperature at which metabolism may cause damage to the biological materials e.g., cells, tissues can be effectively stopped and can effectively transport them over long distances. Cryopreservation is a method of preserving biological tissue or cells at extremely low temperatures. Although there are many applications of cryopreservation, the most common uses of the process are to preserve sperm, embryos, eggs, and plant seeds.

6. The introduction of genetically engineered lymphocytes into ADA deficiency patients is not a permanent cure because these cells are not immortal, and the patient requires periodic infusion of such genetically engineered lymphocytes.

A possible permanent cure can be obtained by isolating the gene-producing adenosine deaminase (ADA) from bone marrow cells and introducing it into cells at early embryonic stage cells.

7. Drug resistance : Due to continuous use of drugs in any population shows no effect of against such drug, this is called drug resistance. e.g., Original populations of mosquitoes had unique ability of resistance to DDT, but after continuous spraying of DDT, the new generation of mosquitoes becomes resistant to DDT.

8. (i) Hormone ‘X’: Luteinizing hormone
Hormone ‘Y’: Follicle-stimulating hormone.
(ii) 14^th day of the cycle : Ovulatory phase (release of ovum) followed by luteal phase.

Section-C

9. (i)

10. (i) Step-Termination
(ii) A-RNA polymerase, B-Rho factor

11. (a) Given cloning vector name is pBR322 and it is inserted in E. coli bacteria.
(b) Two restriction sites in the given diagram are Hind III and Bam H I
(c) In the cloning vector pBR322, ampicillin and tetracycline resistance genes are the selectable markers.

12. (i) Promoter : It is a region of DNA that contributes in initiating the process of transcription. It serves as the binding site for RNA polymerase.
(ii) t-RNA or Transfer RNA : It is a small RNA that reads the genetic code present in mRNA. It carries specific amino acids to mRNA on the ribosome during the translation of proteins.
(iii) Exons : Exons are coding sequences of DNA in eukaryotes that transcribe for proteins.

13. (a) Suppressor Cells: Prevent the immune system from attacking the body’s own cells.
(b) Stem Cells: Both kinds of lymphocytes, B-cells and T-cells originate from stem cells in the bone marrow.
(c) Complement System: Is composed of normal thermolabile protein constituents of blood serum that participate in antigen-antibody reactions. They assign the body’s defence mechanism.

14. (i) The number of double stranded DNA pieces is doubled in each cycle, so that after n cycles you have 2ⁿ copies of DNA. So, after 10 cycles you have 1024 copies.

(ii) PCR is based on three simple steps required for any DNA synthesis reaction: (1) denaturation of the template into single strands; (2) annealing of primers to each original strand for new strand synthesis; and (3) extension of the new DNA strands from the primers.

15. The three parameters used are:

Number of individuals at a trophic level.
Biomass of individuals at a trophic level.
Rate of flow of energy at a trophic level.

Section-D

16. (i) Here Phase C is the Ovulation phase and phase D is the Luteal phase.
(ii) The structure mentioned as label F is Corpus Luteum. The function of the Corpus Luteum is to produce the hormone progesterone that makes the uterus a healthy environment for a developing foetus.
(iii) The progesterone level at phase C is very less or minimum where as its level at phase D reaches maximum.
(iv) HCG hormone. [Human chorionic gonadotropin hormone]
(v) The structure labelled at E is a Graafian follicle. Estrogen hormone is released by the Graafian follicle.

17. Factors influencing infections caused by diseases are as follows :

The virulence of the organism : Virulence is a pathogen’s ability to cause damage to the host. It is referred as the degree of damage caused by a microbe. Similarly, the pathogenicity of an organism is determined by its virulence factor. This is why some strains of the influenza virus are easily spread and have serious consequences, while others are spread less readily and have a mild effect.
Immunity : Whether a person exposed to a disease takes the infection depends on the degree of his immunity. If he has recently had the disease or has been vaccinated or inoculated against it, he will have a high degree of immunity. Heredity also plays an important part. Some people are resistant
to certain diseases simply because they inherit a high degree of natural immunity. Age is also very important in this regard. Adults are highly immune to children’s diseases, yet may suffer greatly if they contact them; young people between the age of 17 and 25 are most susceptible to tuberculosis;
elderly people seem susceptible to pneumonia.

18. (i) Hershey and Chase conducted experiments on bacteriophages to prove that DNA is the genetic material.

Some bacteriophage viruses were grown on a medium that contained radioactive phosphorus (³²P) and some in another medium with radioactive sulphur (³⁵S).
Viruses grown in the presence of radioactive phosphorus (³²P) contained radioactive DNA.
Similar viruses grown in the presence of radioactive sulphur (³⁵S) contained radioactive protein.
Both the radioactive virus types were allowed to infect E. coli separately.
Soon after infection, the bacterial cells were gently agitated in a blender to remove viral coats from the bacteria.
The culture was also centrifuged to separate the viral particle from the bacterial cell.

(ii) In the replication process, while the original strands are 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 untravel 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. Each DNA polymerase is led 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.