Class XII – Biology – Paper – 2

Ans. c) Sunlight

Ans. d) Consap

Ans. b) Death of fish due to lack of oxygen.

Ans. c) S-shaped

Ans. b) Reporter

Ans. d) Viruses, bacteria and fungi

Ans. d) Grasshopper

Ans. c) Some amino acids as glycine and alanine

Ans. a) only in one direction

Ans. b) The female parent is heterozygous

Ans. a) Soil fertility

Ans. c) 1 and 3

Ans. a) Both A and R are true and R is the correct explanation of A.

Ans. a) If both Assertion & Reason are true but the reason is not the correct explanation of the assertion

Ans. b) Both A and R are true but R is not the correct explanation of A.

Ans. a) Both A and R are true and R is the correct explanation of A.

Ans. Transgenic animals that produce useful biological products can be created by the introduction of the portion of DNA. Rosie was the first transgenic cow and it was produced in 1997. The gene for human protein alpha-lactalbumin was introduced in this cow. Thus, the cow could produce protein-enriched milk. This milk was nutritionally more balanced than natural cow milk.

Ans. Valine: GUU, Proline: CCU

Ans. Nucleotides of DNA strand: TAC AAA TAC GGA CAA AGA ATT

Ans. UAA: Stop

Ans. A. represents the multi carpellary and syncarpous pistil of Papaver.

B. represents the multi carpellary and apocarpous gynoecium of Michelia.

Ans. A-Spermatogonium

B-Primary spermatocyte

C-Secondary spermatocyte

D-Spermatid

E-Spermatozoa

F-Sertoli cell

Ans. a. Monascus purpureus

b. Aspergillus niger

c. Penicillium notatum

d. Clostridium butylicum.

Ans. The order of arrangement of products according to their decreasing importance is: Penicillin- Biogas − Citric acid – Curd

Penicillin is the most important product for the welfare of human society. It is an antibiotic, which is used for controlling various bacterial diseases.

The second most important product is biogas. It is an eco-friendly source of energy.

The next important product is citric acid, which is used as a food preservative.

The least important product is curd, a food item obtained by the action of lacto bacillus bacteria on milk.

Ans. When the inducer is present, it combines with the repressor, coded by i gene.

After reacting with repressor it inactivates the repressor.

The repressor now cannot bind to the operator, hence the pathway for RA polymerase is open. The structural genes (z, y, a) are transcribed and the metabolism continues.

Ans. Lactose is inducer.

Ans. The snapdragon flower shows dominance. If a plant with red coloured flowers (RR) is crossed with a plant with white coloured flower (rr), the F1 progeny shows (Rr) the plant with pink coloured flowers. Hence, in the condition in which the selfing of the plant bearing red flower, they have RR genotype.

Phenotype: All plants are bearing red coloured flowers.

Phenotypic ratio: 100%

Genotype: RR

Genotypic ratio: RR (100%)

Ans. – Commensalism

– As egrets move, the cattle stir up and flush out from the vegetation the insects which otherwise might be difficult for the egrets to find and catch. Thus, the egrets are benefited while the cattle are neither benefited nor harmed.

Ans. Eli Lilly company prepares proinsulin chain A and B using separate DNA sequences corresponding to A and B, chains of human insulin and introduced them in the plasmid of E. coli to prepare insulin chains, chains A and B produced separately, extracted and combined by disulphide bond produces mature insulin.

Ans. The one important difference between the insulin produced by human pancreas and the one produced by Eli Lilly is that human insulin has an additional C peptide.

Ans. Extinction of species: The extinction of species is a natural process. Many species have disappeared and new ones have evolved to take over their place. There are three types of extinction processes:

i. Natural extinction: When there is a change in environmental conditions, certain species disappear and others, (which are more adapted to changed conditions) take their place. This loss of species that occurred in the geological past at a very slow rate is known as natural (background extinction).

ii. Mass extinction: There have been several periods in the earth’s geological history when a large number of species became extinct due to catastrophes.

iii. Anthropogenic extinction: Recently more number of species is disappearing from the face of the earth due to human activities. Man-made mass extinction represents a very severe depletion of biodiversity.

Ans. Biodiversity is not uniformly distributed throughout the world. Polar regions have very little biodiversity whereas South America has the greatest biodiversity on the earth. There are many hypothesis for higher biodiversity in tropics:

1. There are no unfavourable seasons or harsh climatic conditions in tropics. Continued favourable environmental condition has helped tropical organisms to flourish more.

2. There is more solar energy available in the tropics due to which productivity is higher and this contribute to greater diversity in both plants and animal species.

3. The tropical environment is older than other types of habitats. This has provided more time for the evolution of greater number of plants and animals.

Ans. It is a true and confirmed fact that the evolutionary history of man is similar to that of any other organism. Following are some of the points which support this theory.

i. Evolution continues from a simple form to complex form and this is true for human evolution as well as other organisms’ evolution.

ii. Evidence from fossils and embryological studies suggest the similarity in the development of different species including humans.

iii. Evidence from molecular studies shows similarities in the sequence of blood proteins and nucleic acids indicate a relationship with apes.

iv. Evidence from the banding pattern in a chromosomal study of man and apes confirm the ancestral relationship between the two.

v. Evidence from structural comparisons of haemoglobin from different species supports the evolution in humans being similar to other species.

Ans. Vaccination is the phenomenon of injection of killed or inactivated microbe to trigger the immune system to produce antibodies against a particular disease. Vaccination is the process of administering vaccines. Diseases can be prevented by vaccination. During vaccination inactivated or weakened microbes called as vaccines are introduced into the body. They trigger the production of antibodies. When disease-carrying microbes enter our body, self-protecting proteins called antibodies fight against the invader. Immunisation is the protection of individuals from communicable diseases by administration of a suspension of dead microorganisms. This is the stimulation of immune system in the body to produce memory cells which further can detect disease causing pathogens and immediately eliminate them before causing the disease. Generally vaccines are of two types:

(a) Attenuated Vaccines: They are prepared from live organisms (generally pathogen is made weak to make it non virulent). Examples : BCG and influenza vaccine.

(b) Killed Vaccines: They are prepared by killing the pathogenic organisms by heat or UV rays. Examples: Polio and Rabies vaccines.

Ans. X-FSH, Y-hCG

Ans. W- Hypothalamus but released through Posterior lobe of Pituitary.

Z- Contraction of smooth muscles during parturition.

Ans. The hormones produced only during pregnancy in human female are human Chorionic Gonadotropin (hCG), human Placental Lactogen (hPL) and relaxin.

The source of hCG and hPL is placenta and that of relaxin is ovary and placenta.

Ans. The two hormones secreted by placenta that are also present in a non-pregnant woman are oestrogen and progesterone.

Ans. Period of illness: The number of disease-causing microorganisms reaches its maximum during the period of illness so, there are maximum chances of a person transmitting a disease/infection at this stage.

Ans. Time period between infection and appearance of its symptoms is known as incubation period. AIDS/any other correct example

T lymphocytes are attack by the pathogen of this disease.

Ans.

Ans. Period of illness

Ans. B lymphocytes/B cells produces antibodies.

Ans.

Ans. Hypocotyl – The portion of embryonic axis between the radical and cotyledon

Epicotyl – The portion of embryonic axis between the plumule and cotyledon

Ans. Coleoptile – It is a conical protective sheath over the plumule in monocot seeds. 

Coleorrhiza – It is a protective sheath over the radical and root tip.

Ans. Integument is the covering of ovule, while testa is the outer seed coat developed from the outer integuments.

Ans. Perisperm is the residual persistent nucellus, while the pericarp is the fruit wall derived from the ovary wall.

Ans. Two approaches were involved in sequencing the human genome.

Using Expressed Sequence Tags (ESTs): In this approach, all the genes that are expressed as RNA are identified and then sequenced.

Blind Approach: This approach involved sequencing the whole set of the genome and then assigning different regions in the sequence with functions. This is referred to as sequence annotation. This approach is comprised of the following steps:

i. Total DNA from a cell is isolated and converted into random fragments of smaller sizes.

ii. These fragments are cloned in a suitable host by using specialized vectors. The cloning results in the amplification of each fragment and makes it easy to sequence the fragment. Bacteria and yeast are the commonly used hosts for this purpose. The vectors were called BAC (bacterial artificial chromosomes) and YAC (yeast artificial chromosomes).

iii. Automated DNA sequencers were used to sequence the fragments. Then these sequences were arranged on the basis of some overlapping regions present in them.

iv. For generating overlapping fragments in these sequences; help of computer programmes was taken because it was not possible for humans to do so.

v. Then the sequences were annotated and assigned to each chromosome.

vi. Genetic physical mapping of the genome was done on the basis of polymorphism in some segments of the DNA.

Ans. Ribosomes are also called as protein factories as they help in the protein synthesis.

Each ribosome has two unequal subunits named as small (40 s) and large (60 s) subunits.

The larger subunit of the ribosome has a groove for pushing out the newly formed polypeptide and protecting the same from cellular enzymes.

The smaller subunit fits over the larger one like a cap but leaves a tunnel for mRNA.

The two subunits come together only at the time of protein formation during the phenomenon known as association in which Mg2+ plays an important role.

Soon after the completion of protein synthesis, the two subunits separate by the process called dissociation.

The different parts of ribosome connected with protein synthesis are:

A tunnel for mRNA which lies between the two subunits.

A groove which is a part of large subunit; for the passage of newly synthesized polypeptide.

There are two reactive sites – P and A.

P-site (peptidyl transfer or donor site) is jointly contributed by two ribosomal subunits.

A-site (amino-acyl or acceptor site) is located on the larger subunit of the ribosome and faces the tunnel between the two subunits.

Smaller sub-unit of the ribosome has a point for recognizing mRNA and binding area for initiation factors.

Ans. (A) Denaturation, (B) Annealing, (C) Thermus aquaticus.

Ans. Denaturation: Heat denatures DNA to separate complementary strands.

Annealing: Primers hybridizes to the denatured DNA strands.

Thermus aquaticus: This enzyme induces denaturation of double-stranded DNA at high temperature.

Extension: Extension of primers resulting in the synthesis of copies of the target DNA sequence.

Ans. Denaturation: Heat denatures DNA to separate complementary strands. Annealing: Primers hybridizes to the denatured DNA strands. Thermus aquaticus: This enzyme induces denaturation of double-stranded DNA at high temperature. Extension: Extension of primers resulting in the synthesis of copies of the target DNA sequence.

Ans. ‘Rop’ codes for the proteins involved in the replication of plasmid.

Ans. Selectable marker: Ampicillin resistance gene. It will help distinguishing transformants from non-transformants after plating them on ampicillin containing medium.

Ans. Transformation: It is the phenomenon by which the DNA isolated frond one type of cell and introduced into another type, is able to bring about some of the properties of former to the later.