Oswal Specimen Papers ISC Class 12 Biology Solutions (Specimen Paper - 10)

Section-A

1. (i) B-cell and T-cell are formed in the bone marrow.
(ii) Any changes in somatic cells (or non-reproductive tissues) cannot be passed on to the DNA of germ cells. Hence, these traits are not inheritable.
(iii) Genetic diversity
Species diversity
Ecosystem diversity
(iv) 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.
(v) Flocs are masses of bacteria associated with fungal hyphe, which form mesh-like structures during secondary treatment of sewage.
(vi) Mutual exchange of chromosome segments between non-sister chromatids during production of gametes is called crossing over.
(vii) Immunosuppression : The process of suppressing the immune system and stop the production of antibodies against the transplant organ is known as immunosuppression.
(xiii) Poverty is directly related to population. With increase in population, there develops a need for more resources leading to poverty.
(ix) (b) Logistic growth curve

Explanation :

A sigmoid growth curve is also called a logistic growth curve. It is considered to be a realistic curve. It is obtained due to the finite and limited source of resources in a population. It is also called a Verhulst-Pearl Logistic growth curve.

(x) (b) South Africa

Explanation :

The ‘World Summit on Sustainable Development’-2002 took place in Johannesburg, South Africa, from 26th August to 4th September 2002. It was held to discuss sustainable development by the United Nations.

(xi) (c) Assertion is true, but reason is false.

Explanation :

The gynoecium represents the female reproductive part of the flower consisting of pistil. Thus assertion is true, but reason is false.

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

Explanation :

Communities with more species are more stable due to variety of complex inter-relationships and interactions and hence there are less year to year variations in total productivity. Thus, both assertion and reason are true and reason is the correct explanation of assertion.

(xiii) (a) Henking Discovered X-chromosome.
(b) F. Meischer isolated nucleic acid from pus cells, called Nuclein.

(xiv) B- Funicle; E- Embryo sac

(xv) Biogas consist of 60-70% of methane and 30-40% of carbon dioxide.

(xvi) (a) The middle piece of human sperm contains mitochondria to provide energy for the movement of sperm. The absence of mitochondria makes the sperm immobile which in turn cause no fertilisation in the fallopian tube.
(b) In the absence of acrosome, spermatozoa will fail to enter the ovum hence no fertilisation will not take place.

(xvii) A - Antigen binding site D - Light chain E - Heavy chain F – Disulphide bridge.

(xviii) Chain, Florey and Fleming won the Nobel Prize for the discovery of penicillin in 1945.

Section-B

2. (i) (a) A-Exine; E-Tube nucleus.
(b) Generative cell is act as the reproductive cell of the pollen grain.

(ii) (a) anatropous ovule
(b) A- Chalazal pole
(c) The body of the ovule fuses with funicle in the region called hilum. Thus hilum represents the junction between ovule and funicle.

3. (i) Plasmids are DNA molecules, usually circular, that are independent of the chromosomal DNA.
(ii) Enzyme called lysozyme digests the cell wall.

4. (i) A-Promoter, C-Coding strand
(ii) Terminator is a section of nucleic acid sequence that marks the end of a gene or operon in genomic DNA during transcription.

5. Nucleopolyhedrovirus is very useful for species-specific narrow spectrum insecticidal applications (IPM). They have been seen to show no negative impact on plants, mammals, birds, fish or even on-target insects.

6. Causes of infertility in males are :

Y chromosome deletion and other genetic problems lead to infertility in males.
Blockage in the Vas deferens, acidity in urethra cause infertility.
Deformities in the shape and size of the sperm.
Age, senility and injury to reproductive system are some other causes of infertility

7. (i) The high proportion of pre-reproductive individuals.
(ii) Set the minimum age of marriage and strictly enforce the same.

8. (i) Species Area Relationship
(ii) Alexander Van Helmboldt

Section-C

9. The amount of energy flow decreases with successive trophic levels as only 10% of energy is transferred from one trophic level to the next successive level. The energy is lost in the form of respiration and other vital activities to maintain life. If more trophic levels are present, the residual energy will be limited and decreased to such an extent that it cannot further support any trophic level through the flow of energy. So the food chain is generally limited to 3-4 trophic levels only.
For e.g.,

10. (i) Nucleosome
(ii) a – Histone octamer
b – DNA
c – H1 Histone
(iii) In bacterial cells, DNA in nucleoids is organised in large loops held together by protein.

11. The DNA-dependent RNA polymerase plays a role as a catalyst in RNA synthesis. To transcribe a gene, the RNA polymerase proceeds through the steps grouped as:

Initiation : In this step, the RNA polymerase binds with the promoter region of the DNA. The promoter polymerase complex, then undergoes structural changes that are essential for transcription.
Elongation : In this step, the RNA polymerase unwinds the DNA in front and tunnels it behind. It dissociates the growing RNA chain from the template as it moves along.
Termination : Once the polymerase transcribes the length of the gene, it stops and releases the newly produced molecule RNA.

12. (i) The genetic disorder showing 44 + XO type shows Turner’s syndrome. Such females are sterile as ovaries are rudimentary. Other features include a lack of other secondary sexual characters, short stature and under developed feminine characters. This disorder is caused due to the absence of one of the X chromosomes.
(ii) It suggests that the pairing and separation of the pair of chromosomes will always lead to the segregation of the pair of factors they carry.
(iii) It is the cross between the individual of F1 progeny with the recessive parent, such cross is known as the test cross.

13. (i)

14. The pyramid of biomass in the sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton and the number of big fishes eating the small fishes is also greater than the small ones. Also in pyramid of number, the number of insects feeding on a big tree is far greater than the tree. Now the number of small birds depending on the insect and the number of larger birds eating the smaller ones also increase in the order.

15. (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 9 cycles you have 512 copies.
(ii) PCR stands for Polymerase chain reaction, is a technique used to synthesize multiple copies of DNA on a template DNA that is similar to the parent DNA. The discovery of PCR was done by Kary Mullis.

Section-D

16. (i) The above-given diagram is the E. coli cloning vector pBR322 depicting the restriction sites.
(ii) A is Hind III and B shows BamH1 which are the restriction sites on the vector.
(iii) Rop codes for the proteins that are involved in the replication of the plasmid.
(iv) Yes, ori is important as it is a starting site of replication. Then the target DNA should be cloned in such a vector whose origin supports high a copy number.

17. Helminths cause numerous diseases such as Taeniasis, Ascariasis, and Filariasis.
Taeniasis : Causative agent Taenia solium. It is the parasite of human intenstine.

Mode of infection : Eating pork of an infected pig.
Signs and symptoms : (a) abdominal pain, (b) weakness, (c) loss of weight, (d) diminished appetite, (e) chronic indigestion.
Prevention and control : (a) Well-cooked pork eaten, (b) Disposal of infected sewage.
Treatment : Administering drugs to kill worms.
Ascariasis : Causative agent Ascaris lumbricoides. It is an infection of the intestinal tract.

18. (i) 1. Multiplication Phase: At sexual maturity, the undifferentiated primordial germ cells divide several times by mitosis to produce many spermatogonia. These spermatogonia move towards the lumen of seminiferous tubules and enter the growth phase.

2. Maturation Phase: Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic. Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo a second maturation division which is an ordinary mitotic division to form, four haploid spermatids, by each primary spermatocyte.

(ii) 1. Growth Phase: Each spermatogonium actively grows to a larger spermatocyte by obtaining nourishment from the nursing cells. They are now called primary spermatocytes.

2. Spermiogenesis: It is the process of transformation of a circular spermatid to a spermatozoan. The head of the sperm, it shrinks with closely packed DNA and the Golgi apparatus, containing proteospermatozoa are later known as sperms. In this process the nucleus of the spermatid becomes
the head of the sperm, it shrinks with closely packed DNA and the Golgi apparatus, containing proteolytic enzymes, becomes the acrosomal cap. Axial filaments are formed from distal centrioles and from the mitochondria, the mitochondrial spiral is formed. Also the loss of cytoplasm takes place
and only a sheath remains around mitochondria.