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 Bihar Board 12th Biology Important Questions Short Answer Type Part 4

Bihar Board 12th Biology Important Questions Short Answer Type Part 4

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.