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AHSEC Class 12 Biology Solved Question Paper & Its Ans.
HS 2nd Year Biology Paper Solution
2012
PART- I (Botany)
(GROUP-A)
1. What is double fertilization? 1
Ans. Double fertilisation is the phenomenon in which two fusions i.e. syngamy and triple fusion occur in an embryo sea.
2. How can you determine the age of a fossil ? 1
Ans. The percentage of radioactive carbon (C14) and ordinary carbon present in the fossils helps in determining the age of a fossil.
3. Why grafting is not possible in Monocotyledonous plants? 1
Ans. Grafting is not possible in monocotyledonous plants because they do not possess cambium.
4. What is ecological succession? 1
Ans. The gradual and fairly predictable change in the species composition of a given area is called ecological succession'
5. Define organic farming. 1
Ans. The non use of artificial fertilizers and chemical pesticides and use of biopesticides as well as biofertilizers in agriculture is called organic farming.
6. Draw labelled diagram of L.Sx. of an angiospermic ovule showing different nuclei present in it. 2
Ans:-
7. Explain significance of mutation in evolution.
Ans. The significance of mutation is evolutiort are (i) Mutations are actually the source of all variations.
(ii) Mutation theory can explain both progressive and retrogressive evolution.
(iii) A number of mutations which are useful are selected by nature and induced. They have given rise to new species.
(iv) Mutation can explain the occurrence of both changed and unchanged forms.
8. What do you mean by coaccrvates? 2
Ans. Coacervates are regarded as primitive cell that contained different macromolecules like proteins, polysaccharides and some water in various combinations and in specific proportions.
9. Name the source organism from which T, plasmid is isolated. Explain the use of this in biotechnology. 2
Ans. T, plasmid is isolated from Agrobacterium tumefaciens.
The T-DNA transform normal plant cells into a tumour and direct these tumour cells to produce the chemical required by the pathogen. The Ti plasmid of Agrobacterium tumefaciens has now been modified into a cloning vector which is not pathogenic to the plant but is still able to use the mechanisms to deliver genes of our interest into a variety of plants.
10. How does transgenic crops technique differ from normal breeding? 2
Ans. Normal breeding activities in plants very often lead to inclusion and multiplication of undesirable genes along with the desired genes. While transgenic crops technique overcome this limitation and allows to isolate and introduce only one or a set of desirable genes without introducing undersirable genes.
11. What biotic abiotic ant) are components of ecosystern? 2
Ans. The abiotic components of ecosystem are temperature, water, light and soil. The biotic components include producers, consumers and decomposers.
12. Suggest any two techniques which can help in early detection of bacteria / virus infections much before the symptoms appear in the body. 2
Ans. Two techniques which help in early detection are
(i) Polymerase chain reactions In this method very low concentration of a bacteria or virus can be detected by amplification of their nucleic acid.
(ii) ELISA In this technique infection by pathogen can be detected by the presence of antigens or by detecting the antibodies synthesised against the pathogen.
13. What arc antibiotics? How they are able to prevent the growth of other microbes in media? 2
Ans. Antibiotics are chemical substances primarily produced by some micro organisms which in low concentration can kill or retard the growth of other disease causing microorganisms.
Antibiotics function either by killing the bacteria or inhibiting the growth of bacteria by acting on different metabolic pathways such as disruption of cell wall synthesis, disruption of plasmalemma repair and synthesis, inhibition of translation etc.
14. How do totipotency help in plant propagation and improvernent? 3
Ans. Totipotency is the capacity to generate a whole plant from any cell/explant. Thus when an explant is cultured in a nutrient media containing sucrose, inorganic salts, vitamins, amino acids and growth regulators like auxin and cytokinin, large number of plants can be propagated in short durations.
By this methods healthy plants can be recovered from diseased plants. Also somatic hybrid can be produced by fusing plants with desirable characters.
Or
Describe the major steps involved in gene cloning. 3
Ans. The major steps involved in gene cloning are-
(i) isolation of DNA.
(ii) fragmentation of DNA by restriction endonucleases.
(iii) isolation of a desired DNA fragment.
(iv) ligation of the DNA fragment into a vector.
(v) transferring the recombinant DNA into the host.
(vi) culturing the host cells in a medium at large scale.
(vii) Extraction of the desired product.
15. What is the full form of VAM? What is its role? Give two examples each of endo and ecto mycorrhiza. 3
Ans. The full form of VAM is vesicular arbuscular mycorrhiza. They help in obtaining nourishment.
1. e.g. of ectomycorrhiza - Boletus, Rhizopogon.
2. e.g. of endomycorrhiza - Glomus, Endogone.
16. What is embryo?' Discuss the development of a di- cot embryo. How do you differentiate a dicot embryo from a monocot embryo? 4
Ans. Embryo is the early stages of development of an offspring from the zygote.
Stages of development of a dicot embryo :-
1) The zygote undergoes transverse division to form a large basal cell and a small terminal cell.
2) Basal cell enlarges further and undergoes transverse division to form a group of 6-10 cells called suspensor.
3) The first cell of the suspensor towards the micropyle is called haustorium whereas the last cell towards the chalazal end is called hypophysis that later develop into radicle.
4) The terminal cell undergoes one transverse and two vertical divisions to produce 8-celled proembryo. Four cells of this proembryo towards the apex give rise to plumule and two cotyledons and another four gives rise to hypocotyl and part of radicle.
Difference between dicot and monocot embryo-
Dicot embryo
1) Consists of an embryonal axis and 2 cotyledons.
2) Portion of embryonal axis above cotyledons is epicotyl, which terminated with plumule
3) Portion below the levels of cotyledon is hypocotyl that terminates to radicle or root tip; covered with root cap.
Monocot embryo
1) Consists of only one cotyledon called scutellum
2) Portion of embryonal axis above the level of attachment of scutellum is epicotyl. Epicotyl has shoot apex and few leaf primordia as coleoptile.
3) Lower end of embryonal axis has radical and root cap enclosed in an undifferentiated sheath called coleorrhiya
OR
Pollination is an important phenomenon in the life cycle of a flowering plant', justify the statement and discuss the role of different agencies responsible for the event.
Ans. Pollination is an important phenomenon because without it the pollen grains will not reach the stigma and the male gametes will not reach the ovule to fertilise with the egg. Thus production of seeds and fruits to ensure continuity of the plant species will not take-place.
For effective pollination various pollinating agents are necessary.
They are categorised into two types biotic & abiotic.
(i) Biotic agencies Different biotic agents like birds, bats, snails, etc help in pollination but most common are the insects. They visit the flowers in search of nectar or a safe position to lay eggs. While picking up food the insect visitor deposits pollen grains brought from some other. flower over the stigma and gets dusted afresh with pollen grains from the present flower. Thus insect act as very good pollinators.
(ii) Abiotic agencies Some plants do not produce nectars so they have to develop some other mechanisms for pollination. These plants produce light, non sticky pollens so that it can be easily carried away by wind. Thus wind also play an important role as a pollinator.
17. Write short notes on (any two). 2 x 2 = 4
(a) Polyembryony
(b) Genetic Engineering
(c) Bio gas
(d) Hardy-Weinberg principle
Ans. (a) Polyembryony is the phenomenon of formation of more than one embryo during the development of seed. Polyembryony was discovered by Leeuwenhoek (1719) in case of citrus. Polyembryony is of three types-
(i) Simple- It is due to fertilisation of more than one egg cell in an ovule.
(ii) Cleavage Caused by splitting of proembryo into two or more parts and branching of proembryo.
(iii) Adventive It is the formation of additional embryos from different parts of ovule like synergids, antipodals etc.
(b) Genetic engineering: It is the technique to alter the chemistry of genatic material (DNA and RNA) to introduce these into host organisms and thus change the phenotype of the host organism. The various tools of genetic engineering are restriction enzymes, polymerase enzymes, ligases, vectors and host organisms.
(c) Bio gas: The gas produced by the anaerobic action of bacteria on biomass is known as biogas. It consists of methane, hydrogen sulphide and CO2. It is preferred over other conventional fuels because it is a cleaner fuel, has no foul smell and can be used as a source of energy as it is inflammable.
(d) Hardy Weinberg principle - Hardy
weinberg's principle states that allelic frequencies in a population are stable and remains constant from generation to generation. It can be expressed as p² + 2pq + q2 = 1 where p and q are frequencies of different alleles. Disturbances in genetic equilibrium results in evolution.
PART - II (Zoology) (GROUP-B)
18. Fill in the blanks: (any two) 1 x 2 = 2
(a) Pebrine is caused by_____
(b) The milk of 'Rosie', the first transgenic cow, con- tains human alpha_____
(c) Ovulation is induced by a hormone called_____
(d) The total number of chromosomes in a human cell is ______
Ans. (a) Nosema bombycis
(b) lactalbumin
(c) Luteinising hormone
(d) 46
19. Answer any two:1 x 2 = 2
(a) What is frameshift mutation?
(b) Define algal bloom.
(c) Write the scientific name of African catfish.
(d) At which part of a pond ecosystem decomposers are abundant?
Ans. (a) Frameshift mutation is a gene mutation where the reading of codons is changed due to insertion or deletion of nucleotides.
(b) The excess growth of planktonic algae that causes colouration of water is called algal bloom.
(c) Clarias gariepinus.
(d) At the bottom of the pond.
20. Write answers of any four of the following: 2 x 4 = 8
(a) What are the changes that occur during follicular phase of menstrua cycle is human females?
(b) Why has arnniocentesis been banned?
(c) Write a note on Haemophilia.
(d) Discuss the structure of nucleosome.
(e) What are the different types of barriers in innate inununity?
(f) What is the causative organism of Flacherie? Write the symptoms of the disease.
Ans. (a) During this phase, the primary follicles in the way grow to become a fully mature graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and uterus are induced by changes in the levels of pituitary and ovarian hormones. The secretion of LH and FSH increases gradually during the follicular phase and stimulates follicular development as well as secretion of estogens by the growing follicles.
(b) Amniocentesis has been banned because it is misused for determining the sex of the foetus and then aborting the child if it is a female.
(c) Haemiophilia is a sex linked recessive disease which shows its transmission from unaffected carrier female to male progeny. In this disease a single protein that is a part of the caseade of proteins involved in blood clotting is affected. Due to this in an affected individual a simple cut will result in non stop bleeding. The possibility of a female becoming a haemoiphilic is extremely rare because mother of such a female has to be at least carrier and father shoube be haemophilic.
(d) The structure that is formed when negatively charged DNA is urapped around the positively charged histone octamer. A typical nucleosome contains 200bp of DNA helix. It constitutes the repeating unit of chromatin and are seen as beads on string.
(e) The different types of barrier are
(i) Physical barriers: These barriers do not allow pathogens and foreign agents to enter the body. e.g- skin, mucous membranes of digestive, respiratory and urinogenital tract trapping microorganisms.
(ii) Physiological barriers: Acid in the stomach saliva in the mouth, tears from eyes all prevent microbial growth.
(iii) Cellular barriers: WBCs (polymorphonuclear leukocytes and monocytes, natural killer lymphocytes) and macrophages phagocytose and destroy microbes.
(iv) Cytokine barriers: Interferons produced by virus infected cells protect non-infected cells from further viral infection.
(f) The causative organism of Flacherie is a virus symptoms- Flacherie is mostly prevalent in muga culture during summer. The infected larva soon die and sometimes the entire brood is completely destroyed. The infected larva cannot spin the cocoon properly and most of the larva die before sprinning the cocoon.
21. Write the difference between any two: 2 x 2 = 4
(a) T-lymphocyte and B-lymphocyte.
(b) Sex chromosome and autosome.
(c) Hydrarch and Xerarch.
(d) Spermatogenesis and Oogenesis.
Ans. (a) T-lymphocyte and B-lymphocyte
T-lymphocyte
1. T-lymphocytes are preprocessed in thymus gland.
2. Life span is long.
3. Memory persists in T-cells.
4. Antibodies are not produced
B-lymphocyte
1. lymphocytes are prepro- cessed in bone marrow.
2. Life span is short.
3. Memory is absent.
4. Plasma cells produce antibodies.
(b) Ans:- Sex chromosome
(i) Sex chromosomes singly or in pair determine the sex of the individual.
(ii) Sex chromosomes may be homomorphic or heteromorphic
Autosome
(i) Autosomes are thosc chromosomes which determine morphophysiological traits of the organism other than sex related characters.
(ii) No such differentiation is there.
(c) Hydrarch
(i) It occurs in freshly formed water body.
(ii) Pioneer species generally belong to phytoplankton.
Xerarch
(i) It occurs over bare rock.
(ii) Pioneer species are generally lichens.
(d) Ans: Spermatogenesis
1. It occurs inside testis
2. Spermatogonia develop from germinal epithelium linning the seminiferous tubules.
3. All the spermatogonia divide to form spermatocytes
4. A spermatocyte forms four spermatozoa
5. Sperms are smaller than spermatocytes.
6. It produces motele male gametes
Oogenesis
1. It occurs inside ovary
2. Oogonia develop from the germinal epithelium overlying the ovary.
3. Only some oogonia give rise to oocytes.
4. An oocyte forms only one egg or ovum.
5. Eggs are larger than oocytes.
6. It produces non-motile female gametes.
22. What do you understand by STD? Name two STD in man. Mention two preventive measures of SID. 1+1+1=3
Ans. Diseases or infections which are transmitted through sexual intercourse are called sexually transmitted diseases (STD).
Three STD in man are AIDS, Gonorrhoea and Syphilis.
They can be prevented by
(i) Avoid sex with unknown partners/multiple partners.
(ii) Always use condoms during coitus.
(iii) In case of doubt go to a qualified doctor for early detection and get complete treatment if diagnosed with disease.
OR
Draw and label the internal structure of the semin Herous tubules. 3
Ans.
23. Write the goals of human Genome Project. 3
Ans. (i) To identify all the approximately 20,000-25,000 genes in human DNA.
(ii) to determine the sequences of the 3 billion chemical bases pairs that make up human DNA.
(iii) Store this information in databases.
(iv) Improve tools for data analysis.
(v) Transfer related technologies to other sectors, such as industries.
(vi) To solve the ethical, legal and social issues that may arise from the project.
OR
Write the Mendel's laws of Inheritance. 3
Ans. (i) Law of dominance It states that when two alternative forms of a trait are present in an organism only one factor expresses itsely in F₁ progeny and is called dominant while the other is recessive.
(ii) Law of segregation: It states that the alleles of a pair segregate from each other during gamete formation such that a gamete receives only one of the two factors.
(iii) Law of independent assortment: The two factors of each character assort independently at the time of gamete formation and get randomly rearranged in the offsprings
24. Discuss the causes of cancer.
Ans. The cancer causing agents are called carcinogens.
They are of following types-
(i) Chemical agents Aniline dyes, benzopyrene, chemicals in cigarette smoke.
(ii) Physical agents Ionising radiations like X-rays and gamma rays, non-ionising radiatins like W-rays.
(iii) Biological agents Oncogenic viruses, some parasites.
OR
Write a note on Biosphere Reserves of Assam. 3
Ans. Biosphere reserves are large tracts of protected land with multiple use preserving the genetic diversity of representative ecosystem by protecting wildlife. In Assam there are two biosphere reserves Manas and Dibru Saikhowa. Manas is known for its rare and endangered endemic wildlife. A total of 543 plan Species have been recorded 374 sp are dicots. 139 sp monocots and 30 sp of pteridophytes and gymnosperms. Among yauna species 55 sp of mammals, 380 sp of birds, 50 reptiles and 3 sp of amphibeans are recorded.
Dibru Saikhowa provides natural habitats to a large variety of flora and fauna species. It is one of the 19 biodiversity hotspots in the world. The reserve was primarily established for conserving the white winged wood duck in its natural habitat. Almost 36 sp of mammals and 350 species of birds are recorded so far. A large number of orchids also blossom here.
25. What is the infective stage of malarial parasite? De- scribe the life cycle of malarial parasite in brief. 1+4=5
Ans. The infectious stage of malarial parasite is sporozoites. Plasmodium enters the human body as sporozoites through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells resulting in their rupture. The rupture of RBC is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days. When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito's body and undergo further development. The parasites multiply within them to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into the human body and the cycle is repeated again.
26. Discuss the various applications of DNA ing. fingerprint- 5
Ans. (i) DNA fingerprinting is used as a tool in forensic tests to identify criminals.
(ii) To identify the true biological father a mother in case of disputes.
(iii) It is used to determine population and genetic diversities to study evolution.
(iv) It can be used to study the breeding pattern of animals facing the danger of extinction.
(v) It can identify racial groups, their origin, historical migrations and invasions.
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