Oswal Specimen Papers ISC Class 12 Biology Solutions (Specimen Paper - 8)

Section-A

1. (i) (a) and (d) represent increase of population.
(b) and (c) represent decrease of population.
(ii) Reproductive health means total well being in all aspects of reproduction i.e., physical emotional, behavioural, social and physiological.
(iii) Penicillium notatum
(iv) Reproductive fitness is the individual’s reproductive success (equal to the average contribution to the gene pool). For example : Ascaris lays 2 crore eggs.
(v) Helper T-cells stimulate antibody production by B-cells.
(vi) (a) Fungi (b) Angiosperm
(vii) Propionibacterium shermanii
(viii) Zygote
(ix) (a) Antibody-Mediated Immunity

Explanation :

The full form of AMI is Antibody-Mediated Immunity. Antibodies are immunoglobulins which are produced in response to antigenic stimulation.

(x) (d) Lysergic acid dimethylamide

Explanation :

LSD is a potent synthetic hallucinogenic drug that can be derived from the ergot alkaloids (such as ergotamine and ergonovine, principal constituents of ergot, the grain deformity and toxic infectant of flour caused by the fungus Claviceps purpurea).

(xi) (b) Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation :

In the structure of immunoglobulin, two heavy and light chains are present and connected by disulphilde linkages.

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

Explanation :

Species diversity decreases as we increase in altitude or ascend mountains due to decrease in temperature.

(xiii) Advantages of Ex-situ conservation:

Efficient and reproducible.
Feasible for medium and long-term secure storage.

(xiv) Gel electrophoresis
(xv) International Union for Conservation of Nature and Natural Resources.
(xvi) (a) Transgenic plants are also proposed to be used in factories or bioreactors for manufacturing special chemicals or pharmaceuticals.
(b) Transgenic animals are so called because these animals have had their DNA manipulated.

(xvii) Biodiversity is the variety of life on earth and includes variation at all levels of biological organisation from genes to species to ecosystems.
(xviii) The DNA molecule created in the laboratory by ligating two different pieces of DNA from two different organisms is called recombinant DNA or rDNA.

Section-B

2. (a) The Red Data book is a compilation of data on species threatened with extinction (endangered) and is maintained by IUCN.
(b) The species which are in danger of extinction and whose number has been reduced to a critical level are called endangered species.

3. Difference between Spermatogenesis and Oogenesis.

	Spermatogenesis	Oogenesis
1.	It occurs in the male gonads i.e., testes.	It occurs in the female gonads i.e., ovaries.
2.	Each primary spermatocyte gives rise to spermatozoans.	Each primary oocyte gives rise to one ovum and three polar bodies.

4. (i) (a) A is seminal vesicle; B is prostate, and C is bulbourethral gland, D is urethra
(b) Urethra (D) conducts sperms through the penis to the outside of the body.

(ii) (a) a – Ovum
(b) c- Zona pellucida. It protects ovum and regulates interaction between ovum and sperm during fertilisation.
(c) d – Cells of corona radiata

5. The two types of ‘biological tools’ used in recombinant DNA technology are:

Enzymes: These include restriction enzymes (Endonucleases), which act as molecular scissors; Ligases, which are responsible for joining DNA fragments together and Reverse Transcriptase, which is used for converting mRNA to cDNA.
Vectors: They serve as a medium or vehicle to carry recombinant DNA into the host cell. The most commonly used vectors are Plasmids, Cosmids and Bacteriophages.

6. (i) (a) Deletion (b) Duplication

(ii) The above diagram represent mutation in bases of DNA.

S. No.	Autogamy	Allogamy
1.	Pollination by the pollen grains of the same flower is termed as autogamy.	Pollination by the pollen grains of another flower of a different plant is termed allogamy.
2.	It does not provide opportunity for genetic recombination and genetic variability.	It provides opportunity for genetic recombination and genetic variability.

8. (i) A-N-glycosidic bond, B-Phosphoester bond, C-Hydrogen bond
(ii) Adenine pairs with thymine, and cytosine pairs with guanine.

Section-C

9. (i) The curve ‘a’ would depict the prey population as there would be no competition for food and shelter resources in the absence of predators, leading to their exponential growth with time.

(ii) The dotted line in the above graph represents the carrying capacity (K) of the population. It represents the size of a population that the environment can hold by providing necessary resources.

10. (i)

11. (i) Father genotype is Hb^AHb^S
(ii) Mother is affected with sickle cell anaemia.

12. Food chain and Food web:

S. No.	Food Chain	Food Web
1.	Transfer of energy from producer to top consumers through a series of organisms is called a food chain.	A number of foods chain interconnected with each other forming a web-like pattern is called a food web.
2.	One organism holds only one position.	One organism can hold more than one position.
3.	The flow of energy can be easily calculated.	The flow of energy is very difficult to calculate.

13. An ideal cloning vector must have the following characteristics :

It must have an Origin of Replication (ori). It is the sequence from which replication starts and the foreign gene linked to it will clone itself and it also controls the copy number of the linked DNA.
It must be small less than 10 kB.
It must be self-replicating inside the host cell.
It must possess a restriction site for Restriction Endonuclease enzymes.
It must have the cloning sites for the ligation of the alien DNA which is carried out at the recognition site.
Introduction of donor DNA fragments must not interfere with the replication property of the vector.
It must possess some marker genes for later identification of recombinant cells. These will help in identifying and eliminating non-transformants and selectively permitting the growth of transformants.

14. The sex determination in grasshoppers is found to be of XX-XO type. The females have two copies of the sex chromosome represented by XX, while the males have only one copy of the sex chromosome and can be represented as XO. Here, the O shows the absence of a second sex chromosome. When the X chromosome from a female, fuses with the X chromosome of a male, a female offspring is produced.
And when the X chromosome from the female, fuses with no chromosome of the male, then a male is produced having chromosomes XO. This method depends upon the number of genes expressed between the two chromosomes.

15. (i) A-Exine, B-Intine, C-Germ pore, D-Generative cell, E-Tube nucleus.
(ii) The exine is made up of sporopollenin.

Section-D

16. 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 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 synthesised in the 5’ to 3’ direction is called the leading strand. The opposite strand is the lagging strand, and it is synthesised 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.

17. (i) (a) Population explosion
(b) Infertility
(c) MTP (Medical Termination of pregnancy)
(d) Amniocentesis
(e) Vasectomy

(ii)

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

The events occurring during this phase are:

Corpus luteum is formed from empty Graafian follicles 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.
It secretes progesterone by suppressing the secretion of FSH, and LH inhibits the maturation of follicles and ovulation. It also inhibits uterine movements.
The uterine endometrium proliferates (5-6 mm) and is ready for implantation.
If fertilisation occurs, the uterine endometrium implants the zygote after 7 days by maintaining high levels of progesterone.
If fertilization does not occur, the high progesterone concentration inhibits GnRH production from the hypothalamus. In the absence of GnRH, levels of FSH and LH fall, thus the endometrium starts detaching. Due to decreasing progesterone level, corpus luteum converts to corpus albicans and
prepares to start the next menstrual phase.

18. (i) Sexual phase: Female Anopheles mosquito. Asexual phase: Human being.
(ii) The gametocyte is the infective stage where the uninucleate, lancet-shaped sporozoite (approximately 1 × 7 μm). The Sporozoites are produced by sexual reproduction in the midgut of vector Anopheles mosquitoes and migrate to the salivary gland.
(iii) Label A: Liver, Label E: RBC
(iv) Symptom: Shaking chills.
(v) Malaria fever is caused by a protozoan Plasmodium.