CBSE ANNUAL PAPER - 1998

BIOLOGY

(SET-I)

Time Allowed : 3 Hours

Section--A

Question No. 1-8 are of very short answer type carrying 1 mark each. Answer threw in one word/one sentence having 1-20 words each.

What is the term used for the regions of gene which become part of RNA and code code for the different regions of the proteins?

The venous blood in the lung has a PCO₂ of 46 mmHG. Should the alveolar PCO₂ exceed or be less than 46 mmHG to result in diffusion of CO₂ from the blood into the alveolus?

Which part of the plant leaf is modified to form spines of Acacia and the sheath covering the leaf of Ficus elastica?

Name the enzyme that can break and reseal one stand of DNA?

What does J-shaped growth curve of a population indicates?

J-shaped growth curve of a population indicate tremendous increase in population followed by population explosion.

What forms the combialring in a doctor stew during the secondary growth?

Name the principal mineral anion in the extracellular fluid.

Section - B

Question No. 9-18 are of short answer type carrying 2 marks each. Answer them in 20-30 words each.

A mother with O type blood group has conceived. The expected blood group of the factus is B. Will there be any problems to the mother or the factus? If so, specify the problems.

Since there is connection between mother and the factus through placenta, it may so happen that the some of the RBC's of blood group B enter the mother. The result in production of antibodies against blood group B. These antibodies will now enter the factus body and will cause haemolysis of factus resulting in Jaundice.

What are the two types of fibres of the connective tissue? Differentiate between the two.

The two types of fibres of the connective tissue are white fibrousand yellow elastic. White fibrous are longer, highly organised and made up of collagen fibres. They are strong, flexible with great strength. Yellow elastic are irregularly arranged with elasticity. It provides elasticity to the tissue.

A farmer observed drops of water along the margins of leaves of tomato plants growing in his well irrigated field on a winter morning. Give reasons for this occurrence. Why had the water drops appeared only along the leaf margins?

Since the field is well irrigated and it is winter, the water loss due to evaporation is very low. Due to root pressure water is lifted to the leaves and this excess of water is seen on the leaf margins of tomato leaves. The water drops had occurred at the margins because hydathodes are located at the margins of the leaves.

Give the scientific name of the modern wheat why is it coated as a typical example of rapid specialion?

Triticum aestivum is the name of the modern wheat. it is coated as a typical example of rapid speciation as it is produced by crossing original wheat variety with grass. It is hexaploid plant that is different from the diploid parent. It have the characteristics of the both the parents but it is a new species artificially made by man.

Name any two cyanobacteria and explain how they serve as main sources of bio-fertilizers.

Cyanobacteria - Nostoc, Anabena. They are nitrogen fixers that are present freely in the soil. they fixes nitrogen as nitrates, nitrates are easily available for plants for synthesing proteins.

What are the two striking observations when different stages of embroys of different classes of vertebrates are studied comparatively? How does this study support evolution?

All the embroys have two common features is notochord and gills. Notochord get transformed to vertebral column and gills to lungs. According to this theory all the organisms have same common ancestor. Therefore all the embroys notochord and gills during certain stages of development. As evolution took place there was replacement of notochord by vertibral column and gills by lungs.

(i) An animal should possess atleast one out of the three possible characteristics to enable it to function as a ureitelic organism. List these characteristics.

(ii) Which among the following is/are ureotelic animals? Whale, Camel, Toad, Shark.

(i) The animals should be semiquatics as urea formed by the interaction of ammonia CO₂ is exerted out.

(ii) Whale.

Pick out the plant with whorled arrangement of leaves from the list given below and say why it is categorised so? Neem; Nerium; Nepenthes.

Nerium.

(i) In Nerium 3-5 leaves are borne at the nodes forming whorl at each node.

How is elongation carried on during protein synthesis in a cell?

When RNA comes in the cytoplasm. The smaller subunit of Ribosome get attached to it with the help of Mg⁺⁺ ions. Soon bigger subunit get attached at the upper position. Bigger subunit have two sites P site A site. The first RNA carrying the first amino acid methionine binds at P site and the second RNA amino acyle complex binds at A site. The first RNA amino acid complex donates amino acid to the second RNA forming a peptide bond leaves the ribosome. At the same time ribosome moves along the RNA by three bases. Likewise one by one other RNA amino acid complex comes at A site and second RNA carrying two amino acids moves to P site. The process is repeated and it results in chain elongation.

What category of pathogens causes poliomyclitis. How is cripping caused in the victim of this disease? How can this disease be prevented?

Poliomelyit is caused by virus. the virus attack the motor pathways of the spinal cord resulting in cripling. This disease can be prevented by avoiding contaminated food and water.

To which category of cells do B-cells and T-cells belong? How do they differ from each other with reference to their formation and response to antigens?

B-cells and T-cells belong to the category of lymphocytes. B-cells and T-cells are formed in bone marrow but B-cells are differentiated in bone marrow while T-cells are differentiated in thymus gland. B-cells produces antibodies to kill the antigenswhile T-cells produces killer cells, helper cells and supressor cells to fight against antigens.

How did Urey and Miller provide the conditions of primitive earth to prove the origin of life in their experiments?

Stanley Miller and Herold C. Urey (1953) conducted an experiment to test the theory

of A.I. Oparin. (1923) and J.B.S. Haldane (1928) on origin of life. In their experiment

they used Hydrogen (H₂), water Vapours (H₂), Ammonia (NH₃) and Methane (CH₄).

The source of energy available to these energy requiring processes were : (i) electric Picture

discharge, (ii) Heat-high temperature of earth, (iii) Ultra-violet radiations from the sun,

(iv) Ionizing radiations (Protons, electrons, X-rays), (v) The experiment was allowed

to sun for few days, (vi) The liquid obtained after the reaction was tested and they

found that it contained amino acids like glycine, serine, sugars like rebose.

Human skin, coloured is believed to be controlled by at least three separate genes :

(i) What do you call this type of inheritance?

(ii) Suppose the gene are designated as A, B and C and darkness is dominant over fairness, what shall be the genotypes of the darkest, fairest and intermediate skin color?

(iii) What will be the number of allete combinations in the gametes of a person heterogeneous, all the three genes.

(ii) Gynotype of darkest - AABBCC

Gynotype of fairest - aabbcc

Gynotype of intermediate - AaBbCc

(iii) 62.

Draw a lebeled diagram of the vertical section of human heart and the show the pulmonary circulation in it by means of arrows.

Expand PEP, where is it produced in C₄ plants ? What is its role in the biosynthetic process ?

(ii) It is produced in the mesophyll cell.

(iii) It functions in carboxylation and form exaloacctate that latter forms malachite. Malate producesCO₂ in bundle sheath cell to derive calvin cycle.

What type of striated muscles constitute the muscles of the eye ball. How is this specific type of muscles advantageous ?

The eye ball is made up of ciliary muscle. It enables the eye to see objects at varying distance from it. It also helps in the secretion of aqueous humour.

The base sequence on one of the strand of DNA is TAC TAG GAT.

(i) Write the base sequence of its complementary stand.

(ii) what is the distance maintained between the two consecutive paired bases in the DNA molecule ?

(iii) who contributed the base complementary rule.

(I) Complementary Strand of DNA have the base sequence as ATG ATC CTA.

(ii) The distance between two consecutive paired bases is 0.34 mm.

(iii) Watson & Crick gave the base complementarity rule.

Name the parasympathetic nerve from the brain that innovates most of the visceral organs. List any four functions of this nerve.

Vague nerve innovates most of the visceral organs.

Functions (i) Stimuatles secretion of alimentary juices, (ii) decreases the heart beat, (iii) stimulates peristalsis, (iv) decreases the bronchial rate.

Sometimes natural selection is not operative if the abnormal allelle is somehow advantageous to the individual. Explain this mechanism with a suitable example.

Sometimes natural selection is not operative if the abnormal allele is somehow advantageous to the individual. For eg. sickle cell anemia is caused by a gene in heterozygous condition.

In the disease RBC's become sickle - shaped and are not able to transport oxygen. Such persons cannot survive for a longer period in general. Further it has been observed that such individuals are enjoying their lives well in malaria prone regions like Africa.

Reason - The RBC'c of heterozygotes (HB^A Hb^S) when it becomes sickle shaped due to low tension of oxygen it kills the malarial parasite which is found in the RBC's. This stage of parasite is signet ring stage. The heterozygous individuals cope better with material infections in comparison to normal homologous. Thus, the process of natural selection maintains this abnormal form of hemoglobin along with the normal form of hemoglobin in the regions where malaria is a common.

Section - D

Questions No. 28-30 are of long answer type carrying 5 marks each Answer them in 80-120 words each.

What develops into a micro spore mother cell in a flower ? Trace the development of the cell into a pollen grain which is ready for germination. Draw a labeled figure of a nature pollen grain.

Anther consists of four anther sacs. Anther sac is made up of sporogenous tissue. It consists of cytoplasmic cells. The cells divide mitotically and forms microspore mother cells. EAch microspore mother cell undergoes meiosis to from four haploid microspore.

The four microspores formed from a microspore mother cell are arranged in a tetrahedral form. Each microspore or pollen grain has two layers, an outer thick exuin and an inner thin intine. The pollen grain divides to form a generative cell and a vegetative cell. The generative cell give rise to two male gametes and a vegetative cell forms pollen nucleus that directs pollen tube towards micropyle for fertilization.

What envelops of mammalian ovum preventing the entry of sperm into it easily ? How does the sperm gain the entry eventually. What is the significance of the point of entry of the sperm ?

The mammalian ovum is surrounded by two layers (a) Zone pellucida (b0 Corona radiata. It prevents the entry of sperm into it easily. When sperm acquires contact with the ovum the acrosomal membrane ruptures releasing sperm lysin consisting of enzyme hyaruonidase. It helps in the removal of follicle membranes and facilitate the entry of the spermatozoon into the ovum. At the point of entry of sperm, the cortical granules below the zona pellucida forms a thick covering called fertilization membrane. The fertilization membrane prevents polyspermy.

Who demonstrated the semi conservative replication of DNA ? Explain the experiment in detail.

Meshelson nd Staheol demonstrated the semiconservative replication of DNA.

(i) They grew E-Coil in a medium containing heavy isotope of nitrogen salts (N¹⁵)¹⁵. N got incorporated into both strands of DNA. The DNA was found to be heavier than N¹⁴ one.

(ii) He now transferred E-coli with N¹⁵ to a medium containing N¹⁴. After one division it was found to have 50 %

15N and 50 % N¹⁴ . This proves that DNA replication is semi - conservative where one strand is old and the other strand formed on it is new.