Bihar Board 12th Biology Important Questions Short Answer Type Part 2

Bihar Board 12th Biology Important Questions Short Answer Type Part 2

BSEB 12th Biology Important Questions Short Answer Type Part 2

Question 1. What is Semen? How is the secretion of accessory male sex glands significant?
Answer: Semen is the fluid mixture of spermatozoa and the secretions of the accessory male sex glands in the urethra.

The secretion of accessory glands:

• Provide fluid medium for transporting spermatozoa.
• Supply nutrients to spermatozoa.
• Maintain the viability and motility by providing proper pH and ionic strength.

Question 2. Name the hormones that control the growth, maintenance and functions of duct system, accessory glands, penis, seminiferous tubules and leydig cells.
Answer:

• Testosterone promotes the growth, maintenance and functions of duct system, accessory gland and penis.
• FSH regulates the growth maintenance and functions of seminiferous tubules.
• LH (Luteinizing Hormone) regulates the growth, maintenance and functions of leydig cells.

Question 3. Mention the functions of (i) Fallopian tubes (ii) Uterus and (iii) Vagina.
Answer:

1. Fallopian Tubes: These conducts the ovum towards the uterus and £vum may be fertilized by a sperm in it.
2. Uterus: The fertilized ovum at the blastocyst stage gets implanted on the wall of the uterus and develops into the growing foetus during pregnancy.
3. Vagina: It receives the semen from the male during mating. During child birth, it conveys child to the outside.

Question 4. Write down the major components of testis.
Answer:
In adult males, each testis is a small, structure. Each testis is a compound tubular gland and remains packed with numerous highly coiled tubules. The testes remain suspended in a skinny sac like pouch called scrotum or scrotal sacs. Scrotum acts as thermoregulator keeps the testicular temperature 2°C lower than the body. The scrotum is divided internally into right and left scrotal sacs by a muscular partition, the septum scroti. A scar like raphe marks the lining of septum.

Inguinal passage or inguinal canals in the passage through which the testes descend down into scrotal sac. Each testes is held in position in scrotum by a small, thick fibrous cord, the gubernaculum and spermatic cord.

Each testes is surrounded by 3 distinct coats, i.e. tunica vaginalis, tunica albuginea and the tunica vasculosa. Each seminiferous tubules is lined by a single layer of germinal epithelium, which give rise to spermatozoa. These are released into the lumen of the tubule.

Question 5. What is triple fusion?
Answer: The fusion of male gamete (n) with secondary nucleus (2n) to produce primary produce primary endosperm nucleus (3n) is known as triple fusion.

Question 6. What is conjugation?
Answer: This is a mode of sexual reproduction. Some acellular protist animals exhibul sexual reproduction by forming male and female gamete nuclei, which they exchange through temporary cytoplasmic bridge, later the cytoplasmic bridge disappears and the gamete nucleus of one individual fuse with that of the other to firm zygote nuclei.

Question 7. What is menstrual cycle? Write down the hormonal control over the menstrual cycle.
Answer: Menstrual cycle starts between 12 to 15 years and continues until about 40 – 50 years. On average, menstrual cycle continues for 28 days, after which some blood and other products of the disintegration of the uterine mucosa (the endometrium) are sloughed off and discharged form the uterus as menstrual bleeding. The process is called menstruation. During this period, the female reproductive system shows regular cycle changes. The cycle is known as menstrual cycle.

Hormonal Control: Estrogen plays a control role in the menstrual cycles. As the menstruation ceases, ovarian follicle secretes estrogens. It causes the formation of thick endometrium and more richy supplied with blood vessels and endometrium glands. A rising level of FSH stimulates the growth of ovarian follicles and formation of estrogens. The most immediate effect of FSH is the maturation of existing of late primary or secondary follicle.

Question 8. List various birth control measures.
Answer:

• Use of contraceptives such as condon, diaphargm, cervical cap, IUDs and oral pills and vaginal tablets, jellies, pastes and creams.
• Surgical operation, namely vasectomy and tubal ligation.
• Abortion.

Question 9. Write short note on RCH programmes.
Answer: RCH are reproductive and child health care programmes.
These programmes of health centres provide:

• necessary information, guidance and help to the mothers before and after delivery so that they can properly look after themselves and the infants.
• ensures safe delivery of infant and postnatal care.
• provides for immunization of infants and prophylaxis against anaemia and vitamin deficiency.
• arranges milk feeding programmes.
• training midwives.
• educating fertile couples about the benefits of small family.

Question 10. How do oral pills help in birth control? Name some commonly used pills.
Answer: Oral pills are a combination of progestins and estrogen. They inhibit ovulation and implantation. These alter the quality of cervical mucus to prevent or retard the entry of sperms, e.g. Combined pill, Mala D and Saheli.

Question 11. Name two new techniques for determining the condition of the foetus.
Answer:

1. Chorionic villus sampling (CVS): foetal cells are sucked into a catheter passed through the cervix without injuring the foetus. This provides a mass of rapidly dividing foetal cells for detection of any chromosomal disorders.
2. Ultrasound imaging or sonography technique uses high frequency sound waves ranging between 1 to 15 Mhz frequency. This technique is totally harmless, non-invasine and it does not use any ionic radiations.

Question 12. Why has amniocentesis been banned?
Answer: Amniocentesis is a prenatal diagnostic technique to determine the genetic disorders in the foetus. Small amount of amniotic fluid is drawn with a syringe. Amniotic fluid contains some foetal cells which can be examined for chromosomal abnormalities. Amniocentesis is being misused to kill the normal female foetuses. That is why this malpractice is banned.

Question 13. Who is a surrogate mother?
Answer: Surrogate mother is a mother who substitutes the real mother to nurse the embryo because some women can produce ovum but cannot support a full term pregnancy. Thus a embryo is implanted into the womb of another women who carries the term of pregnancy and give birth to a healthy baby.

Question 14. List some problems faced by adolescents.
Answer:

• Health matters
• Accidental injury
• Depression and suicide
• Substance abuse
• Eating disorders
• Unwanted pregnancy
• Violence
• Sexually transmitted diseases

Question 15. What are test tube babies?
Answer: A women who cannot conceive can have a baby by special technique. Ovum from mother is taken out, fertilized in the lab, the embryo is reimplanted into the uterus. Embryo develops into a normal baby. The offspring thus produced is called a test tube baby. It is done by IVF in-vitro fertilization and embryo transfer techniques.

Question 16. What are permanent methods for contraception?
Answer: Sterilization is a permanent and sure method for contraception. It is done by vasectomy in males and tubectomy in females. In the procedures a short segment of vas defens or oviduct is removed and tying the remaining ends with surgical thread. These methods do not interfere the normal healthy life of the individuals. They block the transport df gametes to avoid fertilization.

Question 17. Differentiate between vasectomy and tubectomy.
Answer: Vasectomy and tubectomy are both permanent methods of contraception. These are also known as sterilization.

Vasectomy	Tubectomy
1. Done in males.	1. Done in females
2. A short segment of vas deferens is removed.	2. A short segment of oviduct is removed

Question 18. Compare Genotype and Phenotype.
Answer:

Genotype	Phenotype
1. It is the genetic constitution of an organism.	1. It is the observable characteristics of an organism.
2. The genotype of a sexually produced diploid individual is established at the time the zygote is produced.	2. The phenotype of the genotype of individual changes with development and age.
3. It is not influenced by the environment.	3. It is influenced by the environment.

Question 19. If the offspring with the unknown dominant genotype is crossed with an individual homozygous recessive for the trait (e.g. green seed) and the phenotype of the F₁ progeny is examined, illustrate your answer with possibility.
Answer:
Possibility 1 : If the unknown is-homozygous (yy), crossing with green recessive (yy) gives all yellow offspring (Hybrid) i.e. Yy.

Possibility 11 : If the unknown is heterozygous (Yy), crossing with green recessive (yy) results in 50% yellow (Yy) and 50% green (yy) progeny.

Question 20. Epistatic interactions between ganes cause departures from Mendelian phenotypic dihybrid ratio. Support your answer with an example of flower colour in sweet pea, lathyrus odoratus.
Answer: In Lathyrus odoratus, the dominant allele determines the formation of purple flower cofbur. But neither PP or pp will express colour unless another gene C is present in the dominant’from i.e. CC or cc. Recessive cc will interfere with colour formation PP or PP, there by leading to white flowers.

A cross between purple PPCC and White PCCC gives all purple PPCC. F₁ hybrids, selling of the hybrids pp cc gives rise to purple and white flowered offsprings in the ratio 9 : 7. Instead of normal Mendelian ration i.e. 9 : 3 : 3 : 1.

Question 21. What is pedigree analysis? What are the symbols used in such an analysis?
Answer:
Pedigree analysis is a system to analyse the distribution and movement of the traits in the family tree.

Question 22. What are Mendelian disorders?
Answer: Mendelian disorders are determined by alteration or mutation in the single gene. These disorders one transmitted to the offspring on the principle of inheritance. The falter of inheritance of such mendelian disorders can be traced in a family by the pedigree analysis. Some Mendelian disorders are Haemophilia, Cystic fibrosis, Colour blindness, sickle cell anaemia etc.

Question 23. Distinguish between a leading strand and a lagging strand.
Answer:

Leading Strand	Lagging Strand
1. A leading strand which is formed in a continuous stretch in the 51−31 direction with the help of DNA polymers on one of the parent strand of DNA.	1. A lagging strand is formed in small pieces of DNA referred to as OKAZAKI fragments and then join together by DNA ligase.
2. The overall direction of this strand 51−31 is established at the time the zygote is produced.	2. Though the small pieces grow in

Question 24. What is genetic code? Give its characteristics.
Answer: Genetic code refers to the sequence of the four bases adenine, guanine, cytosine and thymine on a strand of DNA which represent a code that controls the construction of proteins and enzymes to make up cytoplasm of the organism and directs its functioning.

Characteristics:

1. Triplet code – A particular sequence of 3 bases would code for particular amino acids and this triplet is called CODON. Three codon i.e. UAA, UAG and UGA serve as STOP CODONS and one codon AUG serves as INITIATING CODON.
2. Non-overlapping – In a mRNA molecule, the sequence of three at a time shorting from a specific position in a non-overlapping fashion.
3. Degenerate – Many amino acids may have more than one codon and codons specifying the some aminoacids are called degenerate. They differ in only the third base.
4. Universal – The same code dictionary is used by all organisms irrespective of their phylogenies and so it is called universal. Exception to this found in m-DNA.

Question 25. How are chromosomal disorders caused?
Answer: Chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. The total number of chromosome of a normal human being is 46 (23 pairs). Out of there 22 pairs are autosomes and one pair of chromosomes are sex chromosome. Sometimes other an additional copy of a chromosome may be included in an individual or an individual may lack one of any one pair of chromosomes.

Question 26. What are three types of RNA molecules? How is each related to the concept of information flow?
Answer: There are three major types of RNAs: messenger RNA (mRNA), tRNA (transfer RNA) and ribosomal RNA (rRNA). These three are required for the process of protein synthesis (translation). The mRNA provides the template for protein synthesis, tRNA brings amino acids and reads the genetic code and rRNA plays structural and catalytic role during translation.

Question 27. What are three essential requirements of the genetic material?
Answer: Genetic material must fulfill the following criteria:

1. It should be able to replicate.
2. It should be chemically and structurally stable.
3. It should provide the scope for mutation and evolution.

Question 28. What is a peptide bond? How is it formed?
Answer:
In a polypeptide chain, the adjust amino acids are linked to each other by a peptide bond.

Question 29. What is the role of nonsense codon in protein synthesis?
Answer: Nonsense codon as the name indicates, code for nothing in a growing polypeptide chain thus the addition of new amino acid stops and the process of translation stops. Thus nonsense codons act as stop signals and terminate the translation process. There are three nonsense codons viz. UAG, UAA and UGA.

Question 30. Differentiate between DNA and RNA.
Answer: Differences between DNA and RNA:

Question 31. Enlist different types of DNA.
Answer:

1. A-DNA: It has 11 base pairs, which are tilted from the axis of the helix (γ 20.2°). It is found at 75% relative humidity in the presence of Na⁺, K⁺ or Cs⁺ ions.
2. B-DNA: It has 10 base pairs which are tilted from the helix axis (γ = 6.3°). It is found at 92% relative humidity and low ionic strength.
3. C-DNA: It has 9.33 base pairs which is negatively tilted from helix axis (γ = 7.8°). It is found at 66% relative humidity in the presence of lithium.
4. D-DNA: It has 8 base pairs. negatively tilted from the helix axis (γ = 16.7°).
5. Z-DNA: It is left handed double helix DNA with a zig-zag sugar phosphate backbone in antiparallel manner. It has 12 base pairs, which are tilted from helix axis (γ = 70).

Question 32. What happens in haemophilia?
Answer: Haemophilia is called bleeders disease. The time taken in blood clotting of Haemophilic persons in from 1 – 24 hrs. Hence, blood loss takes place in such person after an ordinary cut or injury. The death may occurs of such person due to excessive blood loss.

Question 33. What are the characteristics of genetic code?
Answer:

• The codons are tripled.
• One codon codes for only one amino acid. So genetic code is specific and unambiguous (clear).
• Genetic code is degenerate i.e., some amino acids are coded by more than one codon.
• The codon is read in a continuous manner, without any punctuations.
• The codon is universal.

Question 34. What is the purpose of proof-reading in DNA synthesis?
Answer: The process of replication is efficient and accurate. Specificity of base pairing ensures exact replication. Sometimes if any wrong base is present (1 in 10,000), it can be removed by the proof-reading activity. It is done by the enzyme DNA-polynucleotide.

Question 35. What are important features of DNA structure?
Answer:

• DNA, double helix is made up of two polynucleotide chains. The backbone is made up of sugar-phosphate and the bases project inside.
• The two strands are antiparallel i.e. one with 5′ → 3′ polarity and the other with 3′ → 5′ polarity.
• The bases pair with each other via hydrogen bonds. Adenine forms two hydrogen bonds with thymine and guanine pairs with cytosine by three hydrogen bonds.
• The two strands are coiled in right handed fashion. One turn contains 10 base pairs.

Question 36. Which molecule bears codons and which molecule anticodons?
Answer: mRNA bears codons, it acts as the reading frame. mRNA codes information in the form of codons for the synthesis of proteins. One codon consists of three nucleotides, it codes for a specific amino acid on a growing polypeptide chain. tRNA bears anticodons on its anticodon loop which is having complementary bases to the codon present on mRNA.

Question 37. Describe the benifits of transgenic animals.
Answer: The advantages of transgenic animals are as follows:

• Normal physiology and development
• Stydy of diseases.
• Biological product.
• Immunisation safety and
• Chemical safety test.

Question 38. Briefly describe the process of replication.
Answer: The process of replication starts from unwinding of two strands, which will act as a template for the synthesis of new complementary strands. DNA dependent DNA polymerase enzyme catalyzes the polymerization of deoxynucleotides. Replication occurs at small opening of the DNA helix called as replication fork. DNA polymerase can catalyze polymerization only in one direction i.e., 5′ → 3′ which is called continuous replication. The other strand replicated by discontinuous mechanism. So the continuous strand is with polarity (3′ → 5′) and discontinuous strand is with polarity (5′ → 3′). The discontinuous fragments are joined by DNA ligase enzyme.

Question 39. What are introns and exons? What process ensures a linear arrangement of amino acids although the genes are discontinuous?
Answer: The eukaryotic gene is split into coding and non-coding sequences. The coding sequences also called as exons are those which are expressed in the mature RNA. They are flanked by non-coding sequences, termed Introns or intervening sequences Which do not appear in mature or processed RNA. Splicing is the process which removes the unwanted mRNA regions and joins the functional regions responsible for coding.

Question 40. What does the Big Bang theory explain to us?
Answer: The Big Bang theory attempts to explain to us the origin of universe. It tells us of a singular huge explosion. Hydrogen and Helium formed sometime later. The gases condensed under gravitation and formed the galaxies of the present day universe.

Question 41. When was the earth formed? What was its condition at that time?
Answer: The earth was supposed to have been formed 4.5 billion years ago. At that time, there was no atmosphere on the earth. Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the surface.

Question 42. What changes took place on the earth when life appeared on earth?
Answer: The UV rays from the sun broke up water into hydrogen and oxygen and the lighter H₂ escaped. Oxygen combined with ammonia and methane from water, CO₂ and others. The ozone layer was formed. As it cooled, the water vapour fell as rain, to fill all the depressions and forms oceans. Life appeared 500 million years after the formation of earth.

Question 43. Write in brief about Louis Pasteur’s experiments about evolution.
Answer: Louis Pasteur experiments demonstrated that life comes only from pre-existing life. He showed that in pre-sterilised flasks life did not come from killed yeast while in flask open to air, new living organisms arose from killed yeast.

Question 44. What was the contribution of Oparin of Russia and Haldane of England regarding evolution?
Answer: Both Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (eg. RNA, protein etc.) and that formation of life was preceded by chemical evolution i.e., formation of diverse organic molecules from inorganic constituents.

Question 45. Explain homology and analogy will examples.
Answer: Homology is based on divergent evolution whereas analogy refers to a situation exactly opposite. For example sings of butterfly and of birds look alike. They are not anatomically similar structures though perform similar functions. Analogous structure are a result of convergent evolution – different structures evolving for the same function and thus, having similarity.

Question 46. What do you mean by evolution by anthropogenic action?
Answer: Anthropogenic action tells us that evolution is not a direct process in the sense of determinism. It is a stochastic process based on chance events in nature and chance mutation in the organisms. For example, excess use of herbicides, pesticides etc. has only resulted in selection of resistant varieties in a much lesser tonic scale.

Question 47. What is the essence of Darwinian theory about evolution?
Answer: The essence of Darwinian theory about evolution is national selection. The rate of appearance of new forms is linked to life cycle or life span. Microbes that divide fast have the ability to multiply and become millions of individuals within hours.

Question 48. Name the hormones that control the growth, maintenance and functions of duct system, accessory, glands, penis, seminiferous tubules and leydig cells.
Answer:

• Testosterone promotes the growth, maintenance and functions of duct system, accessory gland and penis.
• FSH regulates the growth maintenance and functions of seminiferous tubules.
• L. H (Luteinizing Hormones) regulates the growth maintenance and functions of leydig cells.

Question 49. Mention the functions of (i) Fallopian tubes, (ii) Uterus and (iii) Vagina.
Answer:

• Fallopian tubes: These conducts the ovum towards the uterus and ovum may be fertilized by a sperm in it.
• Uterus: The fertilized ovum at the blastocyst stage gets implanted on the wall of the uterus and develops into the growing foetus during pregnancy.
• Vagina: It receives the semen from the male during mating. During childbirth, it conveys child to the outside.

Question 50. Distinguish between Menstrual and Oestrous cycle.
Answer:
Menstrual cycle:

1. It occurs only in primates.
2. Menstruation occurs at the end of cycle.
3. Endometrium goes out with menstrual flow.
4. Copulation can be any time of year

Oestrous cycle:

1. Occurs in most of the mammals.
2. Menstruation does not occur.
3. Endometrium is reabsorbed.
4. Copulation occurs only when female in oestrous or heat period.

Question 51. Differentiate between insitu and exsitu conservation.
Answer:
Insitu Conservation – It include protection or conservation of whole ecosystem and its biodiversity in natural condition.
Exsitu conservation – It includes conservation of rare plant/animal in place outside their natural home.

Question 52. Name and assign the aim of different zones of biosphere reserve.
Answer:

• Corse or Natural zone
• Buffer zone
• Transition zone.

Question 53. Giving example of each differentiate between biodegradable and non-degradeble pollutants.
Answer:
Biodegradable Pollutants – Garbage, Sewage, Livestock, Wastes.
Nonbiodegradable Pollutants – DDT, BHC, Plastics, Polyethylene, Cans, broken glass.

Question 54. Mention any two effects of air pollution on plants.
Answer:

1. Closing of Stomata
2. Chlorosis
3. Defoliation
4. Necrosis
5. Silvering.

Question 55. Write a note on puberty.
Answer: Puberty is the period of sexual maturity. It comes between 13 to 16 years in the male and between 10 to 14 years in the female. It is controlled by testosterone in the male and estrogens in the female. It is characterized by the development of secondary sexual characters.

Question 56. What is parthenogenesis?
Answer: Parthenogenesis is the development of an unfertilized ovum into a fully formed haploid organism. It is nonparental i.e. honey bees, wasps, aphids. The offsprings thus produced are exactly similar to the parents. It permits. triploid and aneuploid chromosomal combination. At the same time it stops the chances of new combinations of genes.

Question 57. Draw well labelled diagram of male reproductive system.
Answer:

Question 58. Mention three advantages of sexual reproduction.
Answer: Sexual reproduction involves formation and fusion of sex called (gametes). Its main advantages are:

1. The haploid (n) gametes fuse together and the chromesome number of the species (2n) is restored
2. Variations are produced in the off-springs
3. Off-springs are better adapted to the environment and it leads to evolution.

Question 59. Draw a labelled digram of a human sperm.
Answer:

Question 60. Give a diagramatic representation of female reproductive system.
Answer:

Question 61. Name two basic processes involved in sexual reproduction.
Answer: Two basic processes involved in sexual reproduction are:

1. Gametogenesis: It involves the formation of haploid gametes (sperms and ova) in the primary sex-organs called gonads.
2. Syngamy: Syngamy (fertilization) involves the complete and permanent fusion of two haploid gametes to form a diploid zygote.

Question 62. Differentiate between fission and budding.
Answer:
Fission:

1. It involves the division of whole organism into more than one new organism. It may be binary fission or multiple fission.
2. Binary fission may be longitudinal or transverse fission.
3. There is neither proliferation nor differentiation of some vegetative cells, e.g. Planaria.

Budding:

1. It involves the enlargement of a vegetative part of the body to form a bud, which detaches from the parent body to form a new organism.
2. A bud is constructed to the parent body.
3. Proliferation and differentiation of some ordinary vegetative cells on the body surface form a bud. e.g. Hydra.

Question 63. Why is endosperm in angiospermic ovule considered as more efficient?
Answer: In angiosperms, the cells of endosperm are triploid due to double fertilization. Thus they are considered more efficient in supplying food materials to the developing embryo.

Question 64. Why is the process of fertilization in a flowering plant referred to as double fertilization? Explain. 
Answer: Fertilization in flowering plants is referred to as double fertilization because two male gametes from the same microspore takes part in fusion. One male gamete fuses with the egg to form a diploid zygote and the other male gamete fuses with the two polar nuclei or secondary nucleus to form the triploid primary endosperm nucleus.

Question 65. Write the functions of flowers.
Answer: Functions of a flower are as follows:

• Flowers are modified to perform the function of sexual reproduction.
• They are shaped variously to help in pollination.
• They provide seat for germination of pollen, development of pollen, tube, formation of gametes and fertilization.
• Some floral parts help in dispersal of fruits and seeds.
• The ovary transforms into fruit and ovules into seeds after fertilization in flowers.

Question 66. Differentiate between self pollination and cross pollination
Answer:

Self pollination	Cross pollination
1. Migration of pollen grains from to the stigma of the same flower (or same plant) is called self pollination.	1. Migration of pollen grains from to the stigma of another flower to another plant is called cross pollination.
2. Mode of pollination is always wind or by touch.	2. Modes of pollination are external e.g. wind, water or animals.
3. Anthers and stigma mature at same time and lie close to each other.	3. Anthers and stigma may mature at different times and not essentially lie in proximity.
4. No chances of new varieties.	4. Variations occurs at every new generation and thus leads to evolution.

Question 67. Draw a labelled diagram of the longitudinal section of a maize grain to show the structure of mature embryo.
Answer:

Question 68. Name the pollinating agents of flowers like maize and wheat. Give any two favourable features of such a flower.
Answer: In case of maize, the pollinating agent is wind. These flowers are unisexual, small, colourless, inconspicuous and odourless. Whereas in wheat, its self-pollination. Both anthers and stigma of bisexual flowers from the same plant mature before the bud opens, thus to ensure complete self-pollination.

Question 69. Name a plant where vegetative propagation occurs from reproductive organs. What is the special name of the reproductive part of this plant.
Answer: In Agave sp. (century plant), the floral buds get modified into bulbils. When these bulbils get detached from the mother plant, they form a new plant. Thus its a form of vegetative propagation which occurs from reproductive organs (fower).

Question 70. What are the advantages of using plant tissue culture for propagation?
Answer: Plant tissue culture is a technique employed for quick, multiplication of plants. It is also used in producing virus-free plants, disease-free plants and homozygous diploids. This technique is highly useful in commercial micropropagation of orchids, carnation, gladiolus, chrysanthemum and some ornamental plants.

Question 71. Draw a labelled diagram of the longitudinal section of a pistil showing pollen germination.
Answer:

Fig.: Diagram of sectional view of flower to show germination of pollen grains (male gametophyte)

Question 72. What are the characteristics of wind pollinated flowers?
Answer: Pollination by wind is called Anemophilous. It happens in coconut palm, date palm, maize, grasses etc. Their some characters are as such:

• Flowers are inconspicuous and not showy.
• They are colourless and odourless.
• Produce large quanities of dusty pollens.
• Flowers grow in large groups.
• Stigmas are stickly, hairy, feathery or branched.

Question 73. Some crop plants can be grown from a seed as well as vegetatively from stem cutting. List any four advantages of vegetative propagation in such cases.
Answer: Plants which are grown vegetatively from stem cuttings have following advantages than those produced from seeds.

• They mature early and grow very fast.
• They are healthy and robust.
• The produce flowers and fruits much early.
• They characteristics of parent plant are preserved in them as no recombination occurs.

Question 74. Draw a labelled sketch of the section of a mature pollen grain.
Answer:

Question 75. Name one example for each of the following:
(a) A Plant in which both male and female sex organs occur in the same flower.
(b) A plant in which separate male and female flowers are borne on the same individual at different positions.
(c) A cultivated plant which neither fruits nor seeds are formed.
(d) A species in which the individual plant is either male or female.
Answer:
(a) Hibiscus rosa-sinensis
(b) Zea-mays (maize)
(c) Sugar cane
(d) Date-palm.

Question 76. Trace the development of microsporocyte in the anther to a mature pollen grain.
Answer: Microsporocyte or microspore mother cells are polygonal and closely packed initially. Pollen grains develop from them in pollen sacs of anthers. As anther enlarges, pollen sac becomes loosely arranged. A few microsporocytes become non-functional and are absorbed by developing microspores. Each microsporocyte undergoes meiosis and form four haploid nuclei (microspores or pollen grains). They arrange in a tetrahedral manner. Later on each microspore separates and develops into a mature pollen grain.

Question 77. What are the fundamental methods of reproduction?
Answer: There are two fundamental methods of reproduction:

1. Asexual – A single parent is involved. In this case a single celled parent individual either splits or buds or fragments into two identical daughter cells or individuals, for example amoeba, paramoecium etc.
2. Sexual – The two parents, each capable of producing gametes, spermatozoa and ova, are required. Many acellular protists, like monocystis plasmodium and all metazoans employ sexual reproduction.

Question 78. Trace the development of a mature ovule from a megaspore mother cell.
Answer: The process of formation of megaspores from megaspore mother cell is called as megasporogenesis. Megaspore mother cell undergoes meiosis to form four haploid megaspores. They arrange in a linear tetyrad, usually the upper three degenerate and lowermost becomes a functional megaspore. This functional megaspore forms female gametophyte or embryo sac.

Question 79. Write on the roles of lymphocyte in immunity.
Answer: Xymphocyte is a main cell of immune system.
It is two types –

1. T-Lymphocyte
2. B-Lymphocyte

1. T-Lymphocyte makes antibody molyced immune system.
2. B-Lymphocytes cells make mediated immune system. These two lymphocytes want antigens for their working but these two lymphocytes do their work separately. Hence, lymphocytes play their role in immunity.

Question 80. Where do you find corpora cavernosa?
Answer: Corpora cavernosa is found under the skin of penis. It is a column of erectile tissue.
Under the skin, the penis contains three columns of erectile tissue: Two cylinders of the corpara cavernosa of the penis, placed dorsally, one cylinder the corpus cavemosum of the urethra or corpus spongiosum, along the ventral side.

Question 81. How is corpus luteum formed? What is its function?
Answer: After ovulation the granulosa cells and the interstitial cells form a mass of large and yellowish conical cells. This is named as corpus luteum.
Functions: It serves as temporary endocrine gland by releasing progesterone and estrogen.

Question 82. What is follicular atresia?
Answer: Most of the follicular in the two ovaries undergo regression and disappear due to death and disposal by phagocytes. This is referred to as follicular atresia.

Question 83. Name the accessory structures of female reproductive system.
Answer: Vulva or external genitalia are the female accessory genital glands. Vulva has small depression in front of the anus called vestibule.

Vestibule contains following structures:

• Labia Majora: These are two outer skinny, moist hair covered folds forming the outer boundaries of the vulva. Anteriorly the two folds are joined to form monus pubis. A fleshy elevation above the labia is called mons veneris.
• Labia Minora: These are two thin, small, moist folds of connective tissue covered with skin. On stretching over the clitoris to form the prepuce and beneath in form frenulum. The smooth, almond shaped area into which opens the vagina and urethra between the labia minora is called the vestibule.
• Clitoris: It is capable of enlargement but serves no reproductive function.
• Barthclin’s Glands: These secretes clear viscous mucus containing alkaline fluid to lubricate the vulva and vagina during copulation.
• Perineum Jt lies between the anus and vaginal artifice.

Question 84. How do leyding cell help in spermatogenesis?
Answer: Interstitial cells or leyding cells that lie between the seminiferous tubules secrete testosterone. Testosterone is essential for making sperm interstitial cell or leyding cell stimulating hormone (ICSH).

Question 85. What is spermatogenesis? Write down its steps.
Answer: It is process of formation and differentiation of haploid sex cells or garmetes in sexually reproducing animals form undifferentiated diploid germ cells. completed in three major steps:
(a) Spnrmatocutownesis: During this process spermatogonia divide and produce successive generations of cells, which give rise to spermatocytes.
(b) Meiosis: During which the spermatocytes go through one reduction division (meiosis-I) and one equational division (meiosis-II).
(c) Spcrmiogenests: During which the spermatids differentiate into spermatozoa.

Question 86. What is capacitation?
Answer: Sperm motivity occurs due to activation of the sperm by the viscous liquid secreted from the secretory cells of the epithelial lining of oviductal mucosa. The phenomenon of sperm activation in mammals is known as capacitation.

Question 87. What is cortical reaction?
Answer: Cortical reaction are the reaction by which egg-sperm binding takes place.
First: The egg becomes activated and undergoes depolarization of its membrane.
Second: The egg exhibits cortical reaction and shows zona reaction, which makes the egg impervious to any second sperm.

Question 88. Name some chemicals that are released by acrosome during fertilization.
Answer: The activated spermatozoa undergo acrosomal reaction and release various chemicals, like hyaluronidase that acts on the ground substances of follicle cells, corona penetrating enzyme that dissolves corona radiata and zona lysine or acrosin helps to digest the zona pellucida. All these chemicals are collectively termed sperm lysin. Fretilin proteins are present on the sperm surface.

Question 89. Explain why secondary immune response is very quick and intense?
Answer: Secondary immune response is very quick and intense because the memory B-cells persisting from the primary immune reaction quickly form antibodies to deal with microbes.

Question 90. Why skin is called a self-disinfecting organ?
Answer: Skin is called a self-disinfecting organ because sweat and sebum, which are secreted by sudoriferous glands and sebaceous glands contain lactic acid and fatty acids which check microbial growth on the skin. Sweat also contains lysozyme which kills bacteria.

Question 91. What is passive immunity?
Answer: Immunity is called passive when antibodies produced in other organism are injected into a person who already has a potential antigen in his body. For example passive immunity is developed to counteract snake venom and rabies.

Question 92. In case of infectious disease, having fever is beneficial for the body?
Answer: In case of severe infection, body temperature rises, causing fever. Mild fever strengthens the defense mechanism by activating the phagocytes and inhibiting the growth of the microbes.

Question 93. What are interferons?
Answer: Interferons are antiviral proteins secreted by virus infected cells. It is released from the infected cells and makes the nearby uninfected cells more resistant to the viral infection.

Question 94. With examples, define distilled and undistilled alcohols.
Answer: Alcohol produced by mere fermentation of raw material is called undistilled alcohol, e.g. beer, champagne, Alcohol formed by distilling the fermented product of raw material is called distilled alcohol, e.g. whisky, brandy etc.

Question 95. Write a note on cirrhosis.
Answer: Liver converts alcohol into fat that is stored in liver cells. Excess fat reduces formation of glycogen, enzymes and structural proteins. The fatty liver then hardens and dries up as its cells are replaced by fibrous tissue. The degeneration of liver is known as cirrhosis.

Question 96. What are intervarietal and interspecific hybridisation?
Answer: Intervarietal hybridisation is a cross between the two varieties of the same species whereas interspecific hybridisation is a cross between the different species of the same genus.

Question 97. Name the two main classes of general drugs. Give their source and one example of each.
Answer:

1. Natural drugs obtained from plants, e.g. quinine and morphine, from animals, e.g. heparin and liver extract, and microorganisms, e.g. penicillin and streptomycin.
2. Synthetic drugs which are manufactured in the laboratory, e.g. aspirin, chloroquine etc.

Question 98. What are endogenous and exogenous chemical agents of disease?
Answer: Endogenous chemical agents are those which are formed in the body itself. These may be hormones, urea etc. Exogenous chemical agents are those which enter the body from environment through water, air, food etc. for example fumes, spores etc.

Question 99. How infection is different from infestation?
Answer: Infection is the entry of a pathogen inside the host’s body, whereas infectation is the presence of pathogens, generally arthropods on the body Surface or on the clothes, e.g. louse infestation.

Question 100. What are the aims of plant breeding?
Answer: Plant breeding is mainly concerned with the production of plants having desired characters such as high yield, better adaptation, resistance to diseases and pests etc.

Question 101. What are stem cells? What is stem cell therapy?
Answer: The cells of young embryo (approx 40) are called stem cells. They are capable of transforming into any of the 220 cell types human body, they are pluripotent. These are used in therapy called stem cell therapy. For example, if injected into various organs, stem cells can rejuvenate them like stem cells transformed to islet cells can cure diabetes, stem cells that form nerve cells can cure spinal cord injuries. Alzheimer etc.

Question 102. What are plasmids, why they are suitable for use as a vehicle DNA?
Answer: Plasmids are circular, double stranded DNA molecules which occurs as extrachromosomal material and can replicate independently. They serve as vectors or cloning vehicles in prokaryotes like bacteria. The ideal plasmid vector has three properties for suitable use as cloning vector:

• low molecular weight, it makes handling easy
• ability to confer readily with selectable phenotypic traits on host cells
• single sites for a large number of restriction enzymes.

Question 103. What is antisense nucleic acid?
Answer: This is single stranle stranded molecule of DNA or RNA, which base pairs with mRNA molecules and block its translation. This process of inactivation of specific in RNA is used against viral replication and transformation on normal cells into cancerous cells and this can stop the further spread of the disease.

Question 104. Diagramatically show the construction of a chemeric plasmid.
Answer: Chemeric or recombinant plasmids have an additional foreign fragment of DNA. It can be shown like this:

Question 105. What are cDNA libraries? How they are made?
Answer: A complete library of genome fragments is a set of independent clones, that contains the entire genome among the recombinant DNA molecules. Genomic libraries are also called gene banks. Construction of cDNA library involves following steps:

• the generation of DNA segments
• introduction of DNA fragments into a cloning vector like plasmid, cosmid or virus
• introduction of cloned DNA into a bacterium like E. Coli.

Question 106. What are second generation vaccines?
Answer: With the help of genetic engineering vaccines of immense importance are synthesized, called second generation vaccines. These consist of a few antigens present on the surface of the infecting agents rather than the whole inactivated organism (fifst generation vaccine).

The surface antigens are produced in large quantities with the help of recombinant DNA technique. These are injected in safer dozes to healthy individuals for development of immunity. These are more uniform in quality and have less side effects than first generation vaccines. For example, vaccine for Hepatitis-B.

Question 107. Show diagramaticallv how monoclonal antibodies are produced.
Answer:

Question 108. What are monoclonal antibodies ? Write down their characteristics.
Answer: In 1970, Georges Kohler and Cesar Milstein developed the technique of producing monoclonal antibodies by fusing normal antibody producing cells with cells from cancerous tumours. Their main characteristics are:

• Monoclonal antibodies are pure and highly specific for specific antigens
• These can be easily cultured outside the body
• These antibodies are more effective and ideal for diagnosis of specific diseases.

Their most effective clinical application is immune suppression for kidney transplantation.

Question 109. How biotechnology helped in developing herbicide tolerance in plants?
Answer: Herbicides are chemicals with destroy weeds, but they also have adverse affects on crop plants. With the help of biotechnology, scientists develop such transgenic crops which are resistant to the herbicides, and continue to produce normal yield. This may be achieved by –

• Overproduction of those enzymes which are inactivated by herbicide,
• Mutating the enzymes and making them less sensitive to herbicide,
• Introducing such enzymes which cause detoxification of herbicides. Production of herbicide resistant plants, reduce the use of weeding labour, farmer’s cost and increase yield.