Self Studies

Biology Mock Test - 8

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Biology Mock Test - 8
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Weekly Quiz Competition
  • Question 1
    5 / -1
    Which of the following pairs of organisms reproduce by budding?
    Solution
    Explanation:

    The correct option is 'c'.

    Yeast reproduction

    • Asexual reproduction via budding is the most common mechanism of vegetative growth in yeast, in which a tiny bud (also known as a bleb or daughter cell) is generated on the parent cell.
    • The parent cell's nucleus separates into two daughter nuclei, which migrate into the daughter cell.
    • The bud then grows until it separates from the parent cell and forms a new cell.
    • During the budding process, the daughter cell is usually smaller than the mother cell.
    • Some yeasts, such as Schizosaccharomyces pombe, reproduce through fission rather than budding, resulting in two daughter cells of the same size.

    Hydra reproduction-

    • Budding is hydras' most common asexual way of reproduction. Buds emerge from the intersection of the stalk and the stomach regions.
    • The bud begins as a hemispheric outpouching that elongates, becomes cylindrical, and produces tentacles as it grows.
    • After that, the bud pinches off and a new individual emerges.
    • Under ideal conditions, buds appear every two or three days.
    • Hydras occasionally reproduce through transverse and longitudinal fission in response to unfavourable situations, such as injuries or periods of scarcity of supplies.

  • Question 2
    5 / -1

    Which one of the following is an example of viviparous animal?

    Solution

    The correct answer is Kangaroo.

    Key Points

    • Animals that give birth to offspring are called viviparous.
      • In viviparous animals, both fertilization, as well as the development of the embryo, takes place inside the female reproductive system.
      • Once the fetus development is complete, the mother delivers the baby.
      • Kangaroo is an example of a viviparous animal.
      • Humans, dogs, cats, elephants, etc are few examples of viviparous animals.

    Additional Information

    •  Animals that lay eggs are called oviparous.
      • In oviparous animals, fertilization takes place internally but embryo development takes place externally.
      • Example- Fogs, birds, fishes, reptiles etc.
  • Question 3
    5 / -1
    The Pollen grains are covered with two concentric wall layers. The outer layer is termed as ________?
    Solution

    The correct answer is Exine.

    • Pollen grains are microscopic structures, which bear androecium i.e., a male reproductive organ of a flower.

    Key Points

    • They are generally spherical in shape measuring about 25-50 micrometres in diameter.
    • It has a prominent two-layered wall.
    • The hard outer layer called the exine and the inner wall of the pollen grain is called the intine.
    • Exine is made up of sporopollenin which is one of the most resistant organic material and can withstand high temperatures and strong acids and alkali.
    • Intine, on the other hand, is a thin and continuous layer made up of cellulose and pectin.

  • Question 4
    5 / -1
    Process of fusion between male & egg nuclei is
    Solution

    The correct answer is Syngamy.

    Key Points

    • Syngamy
      • The process by which two cells fuse is known as syngamy.
      • It results in a cell that has twice as many chromosomes.
      • Gametes are the two cells that are fused.
      • This fusion of gametes results in zygote formation.
      • The whole process is called fertilization.
      • The process of fusion between the haploid male nucleus and egg nucleus is known as syngamy. Hence, Option 1 is correct.
      • It is also known as fertilization which leads to the formation of a diploid zygote. 

    Additional Information

    • Triple fusion
      • It is the fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm.
      • The polar nuclei belong to the egg or female gamete.
      • It forms a triploid endosperm which helps in the development of the seed.
    • Double fertilization
      • It mainly takes place in angiosperms where a two sperm cell fuses with a single megagametophyte.
      • One sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the central large cell of the megagametophyte.
      • It is the combination of syngamy and triple fusion.
    • Conjugation
      • It is the transfer of genetic material between bacterial cells by direct cell-to-cell contact.
      • The donor bacteria has an F factor which is also known as the fertility factor.
      • The F factor is transferred from one bacteria to another by a connecting link known as a pilus. 
  • Question 5
    5 / -1
    The ratio of ploidy of chromosomes present in nuclei of antipodals, synergids, zygote and endosperm respectively are:
    Solution

    The correct answer is option 3, i.e., 1 : 1 : 2 : 3.

    • The ratio of ploidy of chromosomes present in nuclei of antipodals, synergids, zygote, and endosperm respectively are 1 : 1 : 2 : 3.
    • The 8- nucleate embryo sac (female gametophyte) is formed by the meiotic (reductional) division of megaspore mother cell (MMC), and mitotic (equational) division thereafter.
    • MMC is a diploid cell, so its meiotic division leads to two haploid cells. Then, 3 mitotic divisions take place which lead to the formation of 8 nucleate embryo sac.
    • Hence, the 3 antipodals at the chalazal end, 1 egg and 2 synergies at the micropylar end, and the 2 polar nuclei all are haploid structures, i.e. 'n'.
    • The Zygote is formed by the fusion of 1 male gamete and 1 egg (known as syngamy), therefore it is a diploid structure i.e. 2n.
    • Primary Endosperm Cell (PEC) is formed by the fusion of 1 male and 2 polar nuclei (known as triple fusion), therefore it is a triploid structure i.e. 3n.
    • Since the two fusions take place, hence the process is termed as Double fertilization.
    • PEC later develops into the endosperm and zygote later develops into the embryo.
  • Question 6
    5 / -1
    Edible part of mango is known as
    Solution

    Key Points

    • The fruit is a characteristic feature of flowering plants.
    • The fruit is a mature or ripened ovary, developed after fertilization.
    • The pericarp is the fruit wall and may be thick and fleshy or thick and hard or thin or soft.
    • The pericarp is made up of 3 layers-
      • Epicarp = Outermost layer
      • Mesocarp = Middle layer
      • Endocarp = Innermost layer

    Important PointsMango:

    • The scientific name of Mango is Mangifera indica.
    • It is a tropical fruit, common in South East Asian countries.
    • In mango fruit is known as a drupe.
    • They develop from monocarpellary superior ovaries and are one-seeded.
    • In mango, the pericarp is well-differentiated into an outer thin epicarp, a middle fleshy edible mesocarp and an inner stony hard endocarp.

    ​Thus, the edible part of the mango is known as mesocarp.

    Additional Information

    Fruit

    Type of fruit

    Edible part

    Mango

    Drupe

    Mesocarp

    Custard Apple

    Compound

    Fleshy part

    Sweet Orange

    Hesperidium

    Mesocarp or pulp

    Banana

    False Berry

    Placenta and Pericarp

    Guava

    Berry

    Whole fruit

    Litchi

    Nut

    Aril

    Pomegranate

    Babauta

    Aril

    Fig

    synchronous

    Fleshy receptacle or thalamus

    Grapes

    Berry

    Pericarp and Placenta

    Apple

    False Fruit

    Thalamus

    Mulberry

    Sorosis

    Entire fruit

    Strawberry

    etaerio of achenes

    Entire fruit

    Peach

    Drupe

    Entire fruit

    Date Palm

    Berry

    Epicarp and Mesocarp

  • Question 7
    5 / -1

    Consider the following sets of reproductive terms

    (A) Sperm, oviduct, egg, uterus

    (B) Ovulation, egg, oviduct, uterus

    (C) Sperm, testis, spermduct, penis

    (D) Menstruation, egg, oviduct, uterus:

    The sets of correct combination are :

    Solution

    The sets of correct combination are (B), (C) and (D)

    Key Points

    Justification for combination - (B)

    • Ovaries are the primary female sex organs that produce the female gamete (ovum) and several steroid hormones (ovarian hormones).
    • The ovaries are located on each side of the lower abdomen.
    • The ovaries contain thousands of immature eggs (ovum). On reaching puberty, some of these start maturing.
    • One egg is produced every month by one of the ovaries. This process is called Ovulation.
    • The produced egg is then carried from the ovary to the womb through a thin oviduct or fallopian tube.
    • The two oviducts unite into an elastic bag-like structure known as the uterus.
    • Thereby the correct order is Ovulation → Egg → Oviduct → Uterus.

    ​Justification for combination - (C)

    • The formation of germ cells or sperms takes place in the testes.
    • The sperms formed are delivered through the vas deferens which unites with a tube coming from the urinary bladder. 
    • The urethra thus forms a common passage for both the sperms and urine.
    • The urethra originates from the urinary bladder and extends through the penis to its external opening called the urethral meatus.
    • Thereby, the correct order is Sperm → testis → sperm duct → penis.

    Justification for combination - (D)

    • If the egg is not fertilised the uterus lining slowly breaks and comes out through the vagina as blood and mucous, this is called menstruation.
    • Thereby, the correct order is Menstruation → egg → oviduct → uterus
  • Question 8
    5 / -1
    Maturation of separmatozoa occurs in:
    Solution

    Concept-

    • Sperm(spermatozoa) is the male gamete. The sperm unites with (fertilizes) an ovum (egg) of the female to produce a new offspring.
    • A sperm has three main parts:
      • The head of the sperm contains an elongated haploid nucleus, which holds the DNA of the cell, and the anterior portion is covered by a cap-like structure acrosome.
      • The midpiece of the sperm is packed with mitochondria. Mitochondria are organelles in cells that produce energy. Sperm use the energy in the midpiece to move.
      • The tail of the sperm moves like a propeller, around and around. This tail is a long flagellum that pushes the sperm forward.
    • Spermatids are haploid cells formed by the meiotic division of spermatocytes and develop into spermatozoa after maturational events.

    Explanation-

    Image result for male reproductive organ ncert

    • Epididymis has 3 parts-
      • Upper, highly coiled part- Caput epididymis
      • Middle part- Corpus epididymis
      • Basal, least coiled part- Cauda epididymis
    • The epididymis can temporarily store the sperms for as long as one month and maturation also takes place.

    Therefore maturation of spermatozoa occurs in the epididymis.

    Important Points

    • The process of the formation of sperms is called spermatogenesis.
    • It involves 3 phases-
      • In the multiplication phase, male germ cells also called spermatogonia, which undergo mitotic divisions to form a large number of spermatogonia.
      • In the growth phase, spermatogonia prepare for meiotic division by increasing their size and called primary spermatocytes (46 chromosomes).
      • In the maturation phase, the primary spermatocyte undergoes the first meiotic division and produces 4 haploid cells called secondary spermatocytes (23 chromosomes), which after the second meiotic division produces four equal, haploid spermatids.

    Additional Information

    Prostate-

    • This gland is located below the urinary bladder.
    • It secretes a slightly alkaline prostatic fluid which is milky, thick, sticky, or jelly-like.
    • It makes about 30% part of semen and helps in sperm activation.

    Vas deferens-

    • The sperms reach the abdominal cavity due to the pulsation of the vas-deferens.
    • The wall of vas-deferens is made up of 2 layers outer circular muscle layer and the epithelium.
  • Question 9
    5 / -1
    Which of the following statements about human reproduction system is true?
    Solution

    The Correct Answer is Option (1) i.e. Menstrual cycle ceases during pregnancy.

    • The menstrual cycle is the regular natural change that occurs in the female reproductive system that makes pregnancy possible.
    • The menstrual cycle is the shredding of the uterine lining that would otherwise have housed a growing embryo in pregnancy.
    • When a woman becomes pregnant, that uterine lining is necessary to house the new embryo and is retained inside the womb. Since the lining doesn't shed, the woman doesn't menstruate during her pregnancy.
    • Androgens are produced by the Leydig cells that are present in the seminiferous tubules.
    • Leydig cells are present in the seminiferous tubules of the testis in the male.
    • Oogenesis is the phenomenon of formation of haploid female gametes known as ova from diploid oogonia in the ovary, Graffian follicles to be precised.
  • Question 10
    5 / -1
    Where does the fertilization in human females take place?
    Solution

    The correct answer is Fallopian tube.

    Concept:

    • Fertilization is the process of fusion of sperm (male gamete) with an ovum (female gamete).
    • Fertilization is of two types: External and internal fertilization
    • External fertilization: In external fertilization, eggs are fertilized outside of the organism's body.
    • Eg- amphibians and fishes.
    • Internal fertilization: In internal fertilization, eggs are fertilized within the female reproductive tract.
    • Eg- mammals and birds.

    Explanation:

    • The fertilization in human females takes place in the fallopian tube.
    • The Fallopian tubes are found in the female reproductive system of humans. 
    • Fallopian tubes are also known as oviducts.
    • These are two small tubes, about 10-12 cm in length, in which each one lies on either side of the uterus near the kidney.
    • Fallopian tubes serve as passageways for ova (egg cells) from the ovaries to the uterus.
    • The fallopian tubes are where an egg is fertilized by a sperm.
    • The fertilized egg then travels to the uterus and implants in the uterine lining.

    Thus, fertilization in human females takes place in fallopian tube.

    Additional Information

    • Blastocoel:
      • The blastocoel is a fluid-filled cavity found in animal embryos during the blastula stage.
    • Uterus (womb):
      • The uterus is a single, hollow, muscular, pear-shaped structure supported by ligaments, and attached to the pelvic wall.
      • Uterus is the home to a developing fetus.
      • It is present between the urinary bladder and the rectum.
    • Cervix:
      • It is the lower part of the uterus that opens into the vagina.
      • The cavity of the cervix is called the cervical canal, which forms the birth canal along with the vagina.
  • Question 11
    5 / -1
    One of the following, mentioned below, is not a contraceptive measure. Identify the same.
    Solution

    CONCEPT:

    • Contraception measure: It includes oral contraceptive pills, implants, injectables, patches, vaginal rings, Intrauterine devices, condoms, male and female sterilization, lactational amenorrhea methods, withdrawal, and fertility awareness-based methods.
      • The use of Copper T is also a contraceptive measure.

    EXPLANATION:

    • Medical termination of pregnancy is illegal and it is not a contraceptive measure. So option 2 is correct.

    Additional Information

    • Population Explosion is a sudden, large increase in the size of a population.
    • The major factors that are responsible for population explosion are illiteracy, reduced mortality, increased birth rate/fertility rate, and an increase in life expectancy.
    • The most simple method to control population explosion is to encourage small families about different control measures such as contraceptives. Periodic abstinence is the natural measure for control.
  • Question 12
    5 / -1
    The technique which makes use of amniotic fluid to detect prenatal disorder is called
    Solution
    Key Points
    • Amniocentesis is a procedure which uses some of the amniotic fluid to analyze the foetal cells.
    • This is useful in detecting some genetic disorders at the prenatal stage.
    • Some of the disorders that can be detected are - Down's syndrome, Haemophillia, Sickle-cell anaemia, etc.
    • Amniocentesis helps us to determine the survivability of the foetus.
    • This process uses karyotyping of the foetus, which provides the sex of the foetus.
    • This increases cases of female foeticide in countries like India.
    • Thus, amniocentesis has a statutory ban in India.
    • It is one of the measures to attain reproductive health in the society.

    Additional Information

    Strategies to achieve reproductive health

    • Use of media in creating awareness.
    • Sex education in schools for adolescent children. 
    • Pre-natal and post-natal care of both baby and mother.
    • Proper information dissemination about sexually transmitted diseases, safe sexual practices and reproductive organ-related knowledge.
    • Special opportunities or incentives for smaller families.
    • Medical assistance for problems related to reproduction and menstruation.
  • Question 13
    5 / -1

    Which of the following is/are correctly matched?

    1. Law of Dominance: Characters are controlled by discrete units called factors. 

    2. Law of Segregation: This law is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the F2 generation though one of these is not seen at the F1 stage. 

    Solution

    The correct answer is Both 1 and 2.

    Key Points

    • Mendel proposed two general rules to consolidate his understanding of inheritance in monohybrid crosses.
    • Today these rules are called the Principles or Laws of Inheritance the First Law or Law of Dominance and the Second Law or Law of Segregation.
      • Law of Segregation
        • This law is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the F2 generation though one of these is not seen at the F1 stage. Hence statement 2 is correct.
        • Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors.
        • Of course, a homozygous parent produces all gametes that are similar while a heterozygous one produces two kinds of gametes each having one allele with equal proportion.
      • Law of Dominance
        • Characters are controlled by discrete units called factors. Hence statement 1 is correct.
        • Factors occur in pairs.
        • In a dissimilar pair of factors, one member of the pair dominates (dominant) the other (recessive).
          • The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F1 and the expression of both in the F2.
          • It also explains the proportion of 3:1 obtained at the F2.
  • Question 14
    5 / -1
    Change in the base sequence within a gene is called
    Solution

    The correct answer is Mutation.

    • A mutation is a change in a DNA sequence.
    • Mutations can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses.

    Important Points

    • Cloning:
      • Cloning is the process of generating a genetically identical copy of a cell or an organism.
    • Fission:
      • In the process, the parent organism starts the process by the division of its body into two. each part with a nucleus.
      • Example: Amoeba
    • Breeding:
      • The mating and production of offspring by animals are called breeding.
  • Question 15
    5 / -1
    In monohybrid cross of Mendel, when a pure tall plant was crossed with a dwarf plant, all the F1 progeny were tall, because of:
    Solution

    The correct answer is Dominance.

    Key Points

    • For the monohybrid cross, Mendel started an experiment with a pair of pea plants with two contrasting traits (one tall and another dwarf). 
    • Cross-pollination of tall and dwarf plants developed in tall plants.
    • This theory is known as the first hybrid generation (F1).
    • It is called Filial1 or F1 progeny.
    • Laws of inheritance can be summarized as under which was given by Mendel: 
      • Principles of Paired Factors. 
      • Principle of Dominance.
      • Law of Segregation or Law of Purity. 
      • Law of Independent Assortment.

    Additional Information

    • A monohybrid cross is the hybrid of two individuals with homozygous genotypes which result in the opposite phenotype for a certain genetic trait.
    • Mendel is known as the Father of genetics.
    • Mendel’s law of dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic.
  • Question 16
    5 / -1
    A zygote which has an X - chromosome inherited from the father will develop into 
    Solution

    The correct answer is girl.
    Key Points

    • There are XX Chromosomes in females and XY Chromosomes in males.
    • The male chromosome decides the sex of the zygote which develops into young ones.
    • When X-Chromosome inherited from the father it develops into a girl.
    • When Y- Chromosome inherited from the father it develops into a boy. 

    Important Points

    • Chromosomes are generally first discovered by Walther Flemming in 1882.
    • Chromosomes are thread-like structures located inside the nucleus of animal and plant cells.
    • Each chromosome is made of DNA( Deoxyribose nucleic acid) and protein, which is passed from parents to offspring.
    • In humans, 23pairs of chromosomes are found i.e. 46 in numbers.
    • 22 pairs of chromosomes are called autosomes, look the same in both males and females.
    • The 23rd pair of chromosomes is called sex chromosomes, which differ between males and females.
    • They play a vital role in cell division, heredity, variation, mutation, repair and regeneration.
  • Question 17
    5 / -1
    Which one is a sex-linked disease?
    Solution

    Concept-

    • The sex-linked disease is the transmission of characters and their determining genes along with sex-determining genes.
    • Sex-determining genes are borne on the sex chromosomes and, therefore, are inherited together from one generation to the next.
    • Most sex-linked genes are located on the X-chromosome, forming X-linkage.
    • Two important sex-linked human diseases are hemophilia and color blindness.

    Explanation

    • Colour blindness condition is usually passed down from the parents' side which is a common hereditary condition.
    • A man having color blindness can’t receive a color-blind ‘gene’ from his father, even if his father is color blind because his father can only pass an X chromosome to his daughters.
    • A daughter with color blindness, therefore, must have a father who is color blind and a mother who is a carrier (who has also passed the faulty ‘gene’ to her daughter).
    • If her father is not color blind, a ‘carrier’ daughter won’t be color blind.
    • A daughter can become a carrier in one of two ways – she can acquire the ‘gene’ from a carrier mother or from a color-blind father.

    Thereby color blindness is a sex-linked disease.

    Additional Information 

    Albinism-

    • Albinism is inherited as an autosomal recessive.
    • Albinism is a condition, which is genetically inherited and marks the deficiency of pigmentation in eyes, hair, and skin.

    Tylosis-

    • The persons with tylosis have excessively thick skin on their palms.

    Beriberi-

    • Beriberi is caused due to deficiency of vitamin B1.
    • This is also known as thiamine deficiency.
  • Question 18
    5 / -1
    According to Watson & Crick's model, one turn of DNA possess
    Solution

    Key Points

    Watson and Crick revealed the DNA double helix model:

    • DNA molecule is made up of two polynucleotide chains twisted around each other into a right-handed double helix.
    • Nucleotide = Deoxyribose sugar + a phosphate group + nitrogenous base.
    • The deoxyribose sugars of the polynucleotide chain are linked by phosphate groups forming an alternating sugar-phosphate backbone.
    • The two complementary strands are held together by adenine–thymine (A–T) and guanine-cytosine (G–C) base pairs.
    • Each complete turn of the double helix contains 10 base pairs.
    • Each complete turn of the DNA double helix = 3.4 nm (34Å)
    • Distance between each base pair = 0.34 nm (3.4Å)

    Therefore, one turn of DNA possess 10 base pairs.

  • Question 19
    5 / -1
    Gene is
    Solution

    The correct answer is A segment of DNA.

    Key Points

    •  Gene
      • It is the basic physical and functional unit of heredity.
      • These are passed from parents to offspring and contain the information needed to specify traits.
      • These are made up of DNA.
      • Genes are segments of DNA present within the chromosomes of a cell, provide the code for conversion RNA into proteins, the functional and structural units of the human body. Hence, a gene is a template.
      • These proteins determine the properties of our cells and their function, including the immune system.
      • In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.
      • Genes are arranged, one after another, on structures called chromosomes. A chromosome contains a single, long DNA molecule, only a portion of which corresponds to a single gene.

    Additional Information

    • DNA
      • It is Deoxyribonucleic acid
      • It is the hereditary material in humans and almost all other organisms.
      • The DNA molecule consists of two strands that wind around one another to form a shape known as a double helix.
      • Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups.
    • RNA
      • It is Ribonucleic acid.
      • The primary role of RNA is to convert the information stored in DNA into proteins.
      • An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups.
      • Unlike DNA, RNA is single-stranded.
    • Histones are a family of basic proteins that associate with DNA in the nucleus and help condense it into chromatin.
      • Nuclear DNA does not appear in free linear strands; it is highly condensed and wrapped around histones in order to fit inside of the nucleus and take part in the formation of chromosomes.
  • Question 20
    5 / -1
    The minimum length of cistron in base pairs, which synthesize a polypeptide chain of 100 amino acids is:
    Solution

    Explanation-

    • Cistron is a segment of DNA that specifies a single functional unit.
    • The Gene is called a cistron.
    • Cistron contains the information to determine the sequence of amino acids present in the protein.
    • A cistron is defined as the functional unit of the DNA or RNA molecule.

    Explanation-

    • Given that- 100 amino acids in a polypeptide chain.
    • 1 amino acid = triple codon
    • 100 amino acids  = 100  3 = 300 codons
    • 100 amino acids = 300 codons
    • Length of cistron = number of codon

    Thereby to synthesize the 100  amino acids in a polypeptide chain the minimum length of cistrons will be 300 (+1 stop codon).

    Additional Information

    • A codon is a sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis (Translation).
    • Each codon corresponds to a single amino acid (or stop signal), and the full set of codons is called the genetic code.
    • As the DNA and RNA molecules are written in a language of four nucleotides; whereas, the language of proteins includes 20 amino acids.
    • A nonsense codon is a codon for which no normal tRNA molecule exists, The presence of a nonsense codon causes the termination of translation (ending polypeptide chain synthesis) and is called a Stop Codon.
    •  The start codon is AUG.  Methionine is the only amino acid specified by just one codon.
    • The genetic code includes 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides.  
    • Out of 64 codons, 61 represent amino acids, and three are stop signals.
    • The genetic code is described as degenerate, or redundant, because a single amino acid may be coded for by more than one codon.
    • The conversion of codon information into proteins is conducted by transfer RNA.  Each transfer RNA (tRNA) has an anticodon that can base pair with a codon.

  • Question 21
    5 / -1

    Which of the following statements is/are correct?

    1. Genes contain the information that is required to express a particular trait in an organism.

    2. DNA’s molecular structure was first identified by James Watson and Francis Crick in 1953. 

    Solution

    The correct answer is Both 1 and 2.

    Key Points

    Genome:

    • A genome is all the genetic matter in an organism.
      • It is defined as an organism’s complete set of Deoxyribose Nucleic Acid (DNA), including all of its genes.
    • Genes contain the information that is required to express a particular trait in an organism. Hence statement 1 is correct.
      • Genes are the unit of inheritance.
    • Genes that code for a pair of contrasting traits are known as alleles, i.e., they are slightly different forms of the same gene
    • Every organism’s genetic code is contained in its DNA, the building blocks of life.
    • Each genome contains all of the information needed to build and maintain that organism.

    DNA:

    • DNA (Deoxyribonucleic acid) is the hereditary complex molecule present in humans and almost all other organisms.
    • Nearly every cell in a multicellular organism possesses the full set of DNA required for that organism.
    • Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix.
    • The two strands are called polynucleotides since they are composed of simpler monomeric units called nucleotides.
    • Each nucleotide is composed of one of four chemical bases: cytosine (C), guanine (G), adenine (A), thymine (T).
    • It also has a sugar called deoxyribose and a phosphate group. These nucleotides create proteins that are needed for the cell.
    • Although 99.9% of human DNA sequences are the same in every person, some of the DNA is unique that makes it possible to distinguish one individual from another.
    • DNA can be extracted from the saliva, hair, blood samples, any small amount of the muscles or tissues of a person, nail scraping.
    • DNA’s molecular structure was first identified by James Watson and Francis Crick in 1953Hence statement 2 is correct.
      • They won the Nobel prize for the same in 1962.
  • Question 22
    5 / -1

    Regarding DNA fingerprinting, consider the following statements:

    1. It is a technique to find out variations in individuals of a population at the DNA level.
    2. It works on the principle of polymorphism in DNA sequences.
    3. DNA fingerprinting can be used for paternity testing.

    Which of the statements given above is/are correct?

    Solution

    The correct answer is 1, 2 and 3 only.

    Key Points

    • DNA fingerprinting is a technique to find out variations in individuals of a population at the DNA level.
    • It works on the principle of polymorphism in DNA sequences.
    • Polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.
    • Hence, all the statements are correct.

    Additional Information

    • DNA fingerprinting involves identifying differences in some specific regions in the DNA sequence called repetitive DNA because, in these sequences, a small stretch of DNA is repeated many times.
      • These repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation.
      • The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA.
    • Polymorphism (variation at the genetic level) arises due to mutations.
      • New mutations may arise in an individual either in somatic cells or in the germ cells (cells that generate gametes in sexually reproducing organisms).
    • Since DNA from every tissue (such as blood, hair follicle, skin, bone, saliva, sperm, etc.), from an individual, show the same degree of polymorphism, they become a very useful identification tool in forensic applications.
    • DNA fingerprinting has immense applications in the field of forensic science, genetic biodiversity, and evolutionary biology.
  • Question 23
    5 / -1
    Evolution occurs as a result of mutations in
    Solution

    Concept:

    Mechanism of evolution according to Hugo de Vries - 

    • According to Darwin, variations are small and directional.
    • He did not propose how these small variations happened but they were thought to be influenced by the environment.
    • Hugo de Vries suggested that the variations are caused by mutations.
    • They are random and directionless.
    • Organism carrying a mutation that helps in adapting to an environment survives.
    • Mutations are not influenced by the environment, they happen randomly.
    • But the mutations which are carried to the next generation are influenced by the environment.
    • This is because harmful mutations are eliminated due to less adaptability and competitive ability.

    Key Points

    Somatic DNA mutation

    • The mutations occur anywhere in the body other than in germ cells. 
    • Germ cells are sperm cells, egg cells and their progenitor.
    • These mutations are not inherited because only germ cells combine to form a new zygote.
    • They occur after conception or formation of a zygote.

    Germplasm DNA mutation

    • These mutations occur in germ cells, like sperm cells, egg cells and their progenitor.
    • They are inherited from one generation to another.
    • They occur before zygote formation.

    Explanation:

    • Since the mutation in somatic cells cannot be carried to the next generation, it cannot cause evolution.
    • Mutations occurring in germ cells can be carried to next-generation and thus play a role in evolution.

    Additional InformationMutation

    • Mutation is when DNA is changed or damaged in such a way that the genetic message carried by the is altered.
    • It is caused by a change in the nucleotide sequence in the DNA.

    RNA Mutation

    • RNA does not carry genetic message.
    • Any change in the sequence of nucleotides in RNA changes the protein code.
    • But neither RNA nor protein are carried into the next generation as genetic material.
    • Thus, RNA mutation does not affect evolution.
  • Question 24
    5 / -1

    Which one of the following statements given below regarding homologous organs is/are correct?

    1. Organs with anatomical similarities perform different functions.

    2. These organs are modified to perform different functions as an adaptation to different environments.

    3. These structures are a result of convergent evolution.

    Select the correct answer using the codes given below.

    Solution

    The correct answer is 1 and 2 only.

    Key Points

    • Homologous organs 
      • These are organs that have the same fundamental structure but are different in functions. Hence, statement 1 is correct.
      • These organs follow the same basic plan of the organization during their development.
      • In adult conditions, these organs are modified to perform different functions as an adaptation to different environments. Hence, statement 2 is correct
      • These structures are a result of divergent evolution or adaptive radiation. Hence, statement 3 is incorrect
      • It indicates common ancestry.
      • Example: Forelimbs of man, horse, whale, and bat.

    Additional Information

    •  Analogous organs
      • These organs have an almost similar appearance and perform the same function.
      • These develop in totally different groups are totally different in their basic structure and development origin.
      • These structures are a result of convergent evolution.
      • Example: Wings of a butterfly, bird, and bat.
    • Vestigial or Rudimentary organs 
      • They are the useless remnants of structures or organs.
      • They might have been large and functional in ancestors.
      • Example: Vermiform appendix in man.
  • Question 25
    5 / -1
    Some dinosaurs had feathers although they could not fly, but birds have feathers that help them to fly. In the context of evolution this means that
    Solution

    Key Points 

    • Evolution: Evolution is a process of change happening over generations.
    • During the course of evolution, a change that is useful for one property to start with can become useful later for quite different functions.
    • For example - some dinosaurs had feathers, although they could not fly using the feathers. Birds seem to have later adapted the feathers to fly.
    • This indicates that feathers become useful during the course of evolution.
    • This also means that birds are very closely related to reptiles since dinosaurs were reptiles it can be said that birds have evolved from reptiles.

    Important Points

    • Charles Darwin is known as the father of ''Evolutionary Biology''.
  • Question 26
    5 / -1
    Which of the following era is called age of mammal ?
    Solution
    Key Points
    • Geological time refers to that period of Earth's history which can be studied geologically from the rocks.
    • Geological time scale is how that timeframe is sub-divided like a calendar for our understanding.
    • The fossils that are found in the rock strata helps in establishing the timeline for appearance or disappearance of species.
    • It also helps us in studying the timelines of biological evolution of different species.
    • It is divided into eons, eras, periods and epochs.

    Important Points

    • The cenozoic era is known as the 'Age of Mammals'.
    • This era indicates the period from 65 million years ago to present day.
    • Many significant changes occurred during this era:
      • Mammals became a more prominent life form.
      • Flowering plants diversified to form the present day Angiosperms.
      • Humans evolved.
      • Climatic zones became sharply differentiated.
      • Some of the great mountain ranges were formed like the Himalayas and the Alps.
    • The diversification of mammals is largely owed to the continental shifts of landmasses that allowed migration and evolution of species.
  • Question 27
    5 / -1
    Name the parasitic worm that causes a slowly developing chronic inflammation of the organs in which they live for many years, usually the lymphatic vessels of the lower limbs.
    Solution

    Explanation:

    • Wuchereria malayi & Wuchereria bancrofti are two filarial parasitic worms that cause the disease filariasis.
    • It causes the inflammation of the organs in which they live for many years, usually, lymphatic vessels of the lower limbs are affected.
    • Blockage of lymph vessels occurs that results in intense swelling. The lower limbs of the infected person appear like the legs of an elephant, thus it is also called Elephantitis.
    • The genital organs may also get affected, leading to severe deformation.

    Additional Information

    • Ascaris lumbricoides is an intestinal endoparasite of humans that causes a disease, Ascariasis.
    • These worms are commonly known as roundworms. The person gets infected by consuming contaminated vegetables, fruits, and water.
    • The symptoms include Abdominal pain, Internal bleeding, Fever & blockage of the intestinal passage.
    • Ancylostoma or commonly known as hookworms are intestinal endoparasites of humans that cause intestinal diseases.
    • The person gets infected with hookworms by walking barefoot on the contaminated soil. The larvae of ancyclostoma can penetrate the skin and cause infection.
    • The symptoms include abdominal pain, diarrhea, loss of appetite, and weight loss.
    • Taenia solium belongs to the class Cestoda of phylum Platyhelminthes. These are Endo-Parasite of Intestines.They are commonly referred to as Pork Tapeworms. It may cause the disease Taeniasis. The primary reason for the disease is the consumption of undercooked pork containing tapeworms. The symptoms include abdominal pain, diarrhea, loss of appetite, and weight loss.
  • Question 28
    5 / -1
    A non-infection unnatural and unusual reaction of a person to any substance or condition for which he is hypersensitive is termed as
    Solution

    Concept:

    • Allergy - 
      • An exaggerated response of the immune system to certain antigens present in the environment is called allergy.
      • The substances to which such an immune response is produced are called allergens.
      • The allergens do not usually cause disease and hence are non-infectious.
      • The reaction is not present in everyone and only some people show it, so it is unusual.
      • Such persons are hypersensitive to allergens.
      • Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
      • The antibodies produced to these are of IgE type.

    Therefore, non-infection unnatural and unusual reaction of a person to any substance or condition for which he is hypersensitive is termed as allergy.

    Additional Information

    1. Infection
      • Infection is the introduction and invasion by another organism like bacteria, viruses, fungi, worms, etc. into the body.
      • The introduced organism is called a pathogen or parasite.
      • They live off their host and make them weak.
    2. Immunity
      • The ability of the host to fight the disease-causing organisms is called immunity.
      • It is conferred by the immune system.
    3. Toxin
      • Toxins are proteins that when introduced in small amounts to other organisms cause harm to them.
      • They are naturally occurring compounds which are toxic to other organisms.
      • They are usually produced by pathogen and parasite.
      • They may be present in plant and used for defense.
  • Question 29
    5 / -1
    Widal test is used for susceptibility of
    Solution

    Key Points

    • Widal Test
      • Widal test is used to confirm typhoid.
      • The test detects the antibodies present in blood serum against the causal organism, Salmonella typhi.
      • Salmonella typhi is the pathogen against which antibodies are produced by B-cells.
    • Typhoid
      • It is caused by a bacteria, Salmonella typhi.
      • They enter small intestine through contaminated food and water.
      • From small intestine, they migrate to other organs through blood.
      • Symptoms:
        • Sustained high fever (39° to 40°C)
        • Weakness
        • Stomach pain
        • Constipation
        • Headache
        • Loss of appetite
      • In severe cases, intestinal perforation and death occurs.

    Additional Information

    1. Malarial - caused by Plasmodium, a protozoan.
    2. Cholera - caused by Vibrio cholerae, a bacterium.
    3. Yellow fever - caused by a virus carried by mosquito vector.
  • Question 30
    5 / -1
    Which of the following features gives resistance against bollworms in cotton plants?
    Solution

    Concept:

    • Several bacterial, fungal or viral pathogens affect the crop plants, reducing their yield.
    • Crop losses can sum up to 20-30% or even total loss.
    • Thus, development of disease-resistant cultivars are essential to enhance food production.
    • Resistance of host plant refers to the ability of the plant to prevent the infection and this is determined by the genetic constituent of the plant.
    • The resistance of the host crop plant can be achieved by different types of characteristics:
      • Morphological - Resistance is achieved due to some morphological features.
      • Biochemical - The pest resistance is achieved by some biochemical agents.
      • Physiological - The host plant prevents pest infection by physiological processes.

    Important PointsSome Common Resistance Features:

    FeatureResistance AgainstPlant
    Hairy Leaves
    JassidsCotton
    Cereal Leaf BeetleWheat
    Solid StemStem SawflyWheat
    Smooth-leaved, Nectar-lessBollwormsCotton
    High Aspartic Acid, Low Sugar Content, Low NitrogenStem BorersMaize
    Explanation:
    • From the above table we can see that smooth leaved and nectar-less cotton plants are resistant against bollworms.
    • The crop varieties having these features are found to be naturally resistant to the respective pest insects.
  • Question 31
    5 / -1
    Which of the following is not achieved under biofortification of crops?
    Solution
    Concept:
    • Plant breeding is the intentional manipulation of plant species to create desirable varieties that are better suited for cultivation, can give better yield and are disease resistant.
    • Breeding can be achieved by conventional methods or mutation breeding.
    • It is performed for disease resistance or improved food quality.
    • Food quality is an important factor that contributes to malnutrition and diseases.

    Key Points

    • Biofortification - Breeding of crops with higher levels of vitamins, minerals, proteins or healthier fats, in order to improve public health.
    • Biofortification aims at eradicating hidden hunger in human population.
    • Hidden hunger - refers to the deficiencies of micronutrients, proteins and vitamins in our food.
    • The objectives are to improve:
      • Protein content and quality
      • Oil content and quality
      • Vitamin content
      • Micronutrients and mineral content

    Some biofortified foods

    • Atlas 66 - wheat variety with high protein content.
    • Maize hybrids - with twice the amount of lysine and tryptophan (amino acids).
    • Iron-fortified rice varieties - with 5 times the iron content of previous varieties.
    • Vitamin A enriched carrots, spinach and pumpkin.
    • Vitamin C enriched bitter-gourd, bathua, mustard and tomato.
    • Calcium and iron enriched spinach and bathua.
    • Protein enriched beans of various kinds - broad, French, lablab and garden peas.

    Therefore, production of pest-resistant crop varieties is not achieved under biofortification.

    Additional Information

    • About 840 million people do not have adequate food to meet daily dietary requirements.
    • About 3 billion people suffer from hidden hunger as they cannot afford to buy adequate food.
    • This hidden hunger increases the risk for diseases, reduce lifespan and mental ability.
  • Question 32
    5 / -1
    Which of the following statements is not correct regarding microbes?
    Solution

    Concept:

    • Microbes play an important role for the production of industrial products.
    • They are used for fermented beverages, antibiotics, bioactive molecules as well as food products like cheese.
    • Microbes may include bacteria as well as fungi.
    • Microbes may also be used in other processes related to human welfare.


    Key Points

    • They are used in sewage treatment plants : CORRECT
      • ​Secondary treatment in sewage treatment plants is a biological process.
      • Thus, aerobic as well as anaerobic microbes are used to remove the organic wastes.
    • They are used to obtain bioactive molecules for industrial purpose : CORRECT
      • Bioactive molecules are compounds which have some effect on living organisms.
      • Several such molecules are produced industrially by the action of microbes.
      • Example - Citric acid from Aspergillus niger, Acetic acid from Acetobacter aceti.
      • Some pharmaceutically important compounds are also obtained.
      • Example - Streptokinase from Streptococcus, Statins from Monascus purpureus.
    • Fermented beverages are obtained by the action of microbes : CORRECT
      • Microbes like yeast helps in the fermentation of malted cereals and fruit juices to yield wine and beer.
    • No antibiotics have been obtained from microbes : INCORRECT
      • Antibiotics are chemical substances that are produced by some microbes that may function against some other microbes.
      • The first antibiotic to be discovered was Penicillin from the fungus Penicillium notatum.
      • Penicillin stops the growth of the bacteria Staphylococcus.
  • Question 33
    5 / -1
    In which of the following processes, Bacteria is NOT used?
    Solution

    The correct answer is Baking bread

    Key Points

    • Bacteria are microscopic, single-celled organisms that thrive in diverse environments. Bacteria was discovered by AV Leeuwenhoek. Bacteria are organisms that exist in their millions, in every environment, both inside and outside other organisms. 
      • Bacteria are found almost everywhere on Earth and are vital to the planet's ecosystems.
      • Some bacteria are harmful but must serve a useful purpose. They support many forms of life, both plant, and animal, and they are used in industrial and medicinal processes.
      • Bacteria can use most organic and some inorganic compounds as food and some can survive extreme conditions.

    Additional Information

    • Some Uses of Bacteria:
      • Bacteria are used in the manufacture of foods and the production of antibiotics, probiotics, drugs, vaccines, etc.
      • Bacteria are used in the formation of curd.
      • lactic acid bacteria such as Lactobacillus, Lactococcus, and Streptococcus are used in the manufacture of dairy products.
      • Bacteria convert milk into useful dairy products, such as buttermilk, yoghurt, and cheese.
      • Bacteria are used in the fermentation of Sugarcane juice.
      • Coliform bacteria are used to measure the level of contamination of a water body.
      • Bacteria are present in the nodules of the legumes where the process of nitrogen fixation is done by the bacteria and the NH3 produced is absorbed by the plant. Rhizobium bacterium is responsible for nitrogen fixation.

    Mistake Points

    • Baking soda and baking powder help in baking bread.
    • The microbe responsible for baking bread is a fungus named Saccharomyces cerevisiae for this reason it is also called baker's yeast.
    • Hence, from the above-mentioned points, it becomes clear that bacteria are not used in the baking of bread.
  • Question 34
    5 / -1
    Secondary sewage treatment is mainly a
    Solution

    Concept:

    • A huge amount of waste water is produced everyday.
    • It contains organic matter as well as microbes, which may even be pathogenic.
    • This waste water needs to be treated in sewage treatment plants (STPs) before disposing it into water bodies.
    • This treatment is carried out with the help of the heterotrophic microbes present in the sewage.
    • The treatment takes place in 2 stages - primary and secondary treatments.

    Important Points

    Steps of Sewage Treatment - 

    1. Primary Treatment -
      • All the solid particulate matter are removed by primary treatment.
      • Floating debris is removed by sequential filtration.
      • The grit (soil and small pebbles) are removed by sedimentation.
      • The solids settle as primary sludge and the supernatant as effluent.
      • The effluent moves from primary settling tank to large aeration tanks for secondary treatment.​
    2. Secondary Treatment -
      • ​​The effluent is continuously agitated mechanically and air is pumped into it.
      • This allows vigorous growth of aerobic microbes into flocs.
      • These microbes use up most of the organic matter for their growth.
      • This reduces the BOD (biological oxygen demand) of the effluent.
      • Effluent is then passed into a settling tank, where the bacterial flocs sediment to form the activated sludge.
      • Most of the activated sludge is moved into large tanks called anaerobic sludge digesters, and the rest is used as inoculum in the aeration tanks.
      • Next, the anaerobic bacteria digest the other bacteria and fungi in the sludge.
      • The effluent is then discharged into water bodies.

    As the secondary treatment involves the use of microbes, it is a biological process.

  • Question 35
    5 / -1
    PCR and Restriction Fragment Length Polymorphism are the methods for
    Solution

    Concept:

    • Genetic fingerprinting is the analysis of DNA from samples of body tissues or fluids, especially when conducted in order to identify individuals.
    • The human gene is composed of a relatively small region having transcribable genes and their regulators, promoters, etc.
    • The rest of the genome is a vast region of non-coding DNA that is not affected by changes in DNA sequence because it does not code for protein or RNA.
    • This region can vary in different individuals without affecting function and causing any harm.
    • Related individuals will have more similarities in these regions than unrelated individuals.
    • Restriction enzymes cut DNA at specific sequences.
    • In non-coding regions, sequences recognized by restriction enzymes can be absent or their placement can vary, generating cuts of different lengths in different individuals.
    • This property can be used to identify an individual from their DNA or related individual can be recognized.
    • First DNA is amplified using PCR, then amplified DNA is cut using restriction enzymes.
    • These restriction enzymes digested DNA is visualized by agarose gel electrophoresis.

    Key Points

    Polymerase Chain Reaction (PCR) - 

    • The polymerase chain reaction is a laboratory method used to multiply a specific region of DNA and produce millions of copies.
    • A few strands of DNA can be amplified or increased in number to billion copies within a few hours using a PCR machine.
    • Components of PCR -
      1. DNA template - the sample DNA containing the gene of interest which has to be multiplied.
      2. Primer - Primers are short pieces of single-stranded DNA that are complementary to the target gene sequence.
      3. DNA polymerase - a heat-resistant, thermostable DNA polymerase is required to replicate the template DNA.
      4. Nucleotides or dNTPs - nucleotides are the building blocks of DNA, they are required to make the DNA when template DNA is replicating.

    Restriction fragment length polymorphism (RFLP) - 

    • Restriction enzyme is a protein that cleaves DNA strands at sequence-specific sites.
    • Restriction Fragment Length Polymorphism (RFLP) works on the principle that different individuals have variations in DNA sequence at sites recognized by restriction enzymes.
    • This variation leads to the production of different length fragments when cut by restriction enzymes.
    • The restriction enzyme digested DNA can be visualized by agarose gel electrophoresis and can be compared to another individual to find relatedness or matching DNA.

    Additional Information

    1. The study of enzymes is learning about the enzymes present in the cells and involved in the metabolic process.
    2. Genetic transformation is a process that involves the introduction and expression of foreign genes in a host organism.
    3. DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA.
  • Question 36
    5 / -1
    Each Restriction enzyme cleaves a DNA molecule only at :
    Solution

    Concept:

    • A restriction enzyme is a protein produced by bacteria that cleaves DNA at specific sites along with the molecules.
    • It is also known as restriction endonuclease and "molecular scissors".
    • The first restriction endonuclease is Hind II.
    • In the bacterial cell, restriction enzymes cleave foreign DNA, thus eliminating infecting organisms.
    • This enzyme can be isolated from the bacterial cells and used in the laboratory to manipulate fragments of DNA.
    • Restriction enzymes were characterized by molecular biologist Werner Arber.
    • Work of Restriction enzyme:
      • A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages.
      • When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated.
      • It prevents replication of the phage DNA by cutting it into many pieces.
      • Restriction enzymes were named for their ability to restrict.

     

    Explanation:

    •  A restriction enzyme is used to cut DNA molecules.
    • It is of 3 types: Exonucleases, Endonucleases, and Restriction endonucleases.
      • Exonucleases-  They cut off nucleotides from 5" or 3" ends of DNA molecules.
      • Endonucleases-  They break DNA duplexes at any point except ends.
      • Restriction endonucleases- They cleave DNA duplexes at a  specific point.
    • Each restriction endonucleases functions by inspecting the length of a DNA sequence.
    • And each restriction endonucleases cleave DNA molecules at a specific nucleotide sequence. So, it recognizes a specific palindromic nucleotide sequence in the DNA.

    ​Therefore, the correct answer is a specific nucleotide sequence.

    Key Points

    • DNA (Deoxyribonucleic aid) is a nucleic acid made up of nucleotides.
    • It is a long polymer of deoxyribonucleotides.
    • DNA was first identified by Fredrich Meischer in 1869. He named it Nuclein.
    • DNA acts as the genetic material in most organisms.
    • It is a double-helix structure of protein and nucleic acid which carry all the genetic information in the form of genes.
    • A nucleotide has 3 components: a nitrogenous base ( A, T, G, C), a pentose sugar, and a phosphate group.
    • The length of the DNA is usually defined as the number of nucleotides in it.
  • Question 37
    5 / -1

    Which of the following pairs is correctly matched ?

    Solution

    The correct answer is Ligases - Molecular Stitchers.

    Key Points

    • Ligase is like a molecular stitcher, they are ubiquitous and essential for all cells and perhaps at all times.
    • DNA ligase (polydeoxyribonucleotide synthase) is the enzyme that joins two single-stranded DNA fragments by catalyzing the formation of an inter-nucleotide ester bond between phosphate and Deoxyribose.
      • It is active during DNA replication, DNA repair, and DNA recombination.
    • There are two forms of DNA ligase: one requires ATP and the other NAD. NAD (+) dependent DNA ligases are present in bacteria, some Entomopox viruses, and Mimivirus while ATP-dependent DNA ligases are ubiquitous.

    Additional Information

    • Restriction endonucleases are the restriction enzymes that cleave the DNA at specific sites so they are known as molecular scissors.
    • DNA polymerases are enzymes that play a key role in DNA replication.
      • DNA replication is the process of splitting an existing double-stranded DNA molecule into two single strands of DNA.
  • Question 38
    5 / -1
    The genetically modified (GM) brinjal in India has been developed for:
    Solution

    The correct answer is 'Insect Resistance'

    • Genetic engineering is the technique in which the genes of the organisms are modified in order to enhance the quality of the products.
    • Crops produced with desirable traits by introducing the foreign gene with their genetic pool are called as genetically modified crops that causes high yielding varieties with resistance to environmental stress, diseases, cold and drought.
    • BT Brinjal is also a genetically modified crops which developed by using the gene isolated from bacteria Bacillus thuringiensis and introduce into the genome of brinjal.
    • The modified gene in BT brinjal is responsible for production of toxin which is fatal (harmful) for insects, Hence insects unable to destroys the crops due to become insect resistance.
  • Question 39
    5 / -1
    Which bacterium is used in the production of insulin by genetic engineering?
    Solution

    The correct answer is Escherichia.

    Key Points

    • Escherichia is a genus of Gram-negative, non-spore-forming, rod-shaped bacteria from the family Enterobacteriaceae.
    • Escherichia coli is a bacterium found in the intestines of foods, humans, and animals.
    • E. coli bacteria is a transgenic bacterium that produces insulin for the diagnosis of diabetes.
    • Although these bacteria are mostly not harmful, some of them can cause diseases like 'diarrhea'.
    • While some others can cause diseases such as respiratory disease and pneumonia.


    Additional Information

    • Rhizobium -
      • This is a genus of bacteria related to the formation of root nodules on plants.
      • This is the bacterium of the soil, which fixes nitrogen.
      • This is the most suitable organic fertilizer for a pulse crop.
      • Rhizobium bacteria stabilize the circulating nitrogen in the environment and reach the roots of the plants.​
    • Mycobacterium -
      • Mycobacterium is a biological genus of Actinobacteria.
      • This is a bacterium causing tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae) in humans.
    • Saccharomyces -
      • This is a genus of fungi that includes many species of yeasts. 
      • Its members of this genus are very important in food production. 
      • It is known as the brewer's yeast or baker's yeast.​
  • Question 40
    5 / -1

    'RNA interference (RNAi)' technology has gained popularity in the last few years. Why?

    1. It is used in developing gene silencing therapies

    2. It can be used in developing therapies for the treatment of cancer.

    3. It can be used to develop hormone replacement therapies.

    4. It can be used to produce crop plants that are resistant to viral pathogens.

    Select the correct answer using the code given below.

    Solution

    The Correct Answer is Option 1 i.e. 1, 2 and 4.

    • 'RNA interference (RNAi)' technology is a technique that became popular because of its use of gene silencing therapies linked to disease such as cancer.
    • RNAi is a gene-silencing technology that inhibits protein synthesis in target cells using double-stranded RNA.
    • RNAi is also used to produce crop plants that are resistant to plant viruses such as RNA and DNA viruses, viroids, insects, and other fungal pathogens.
    • a process using recombinant DNA technology to join, by attachment or insertion, a DNA segment from one source to a DNA segment from another source.
    • Gene Silencing -
      • Gene silencing refers to a mechanism by which cells shut down large sections of chromosomal DNA.
      • It is generally used to describe the “switching off” of a gene by a mechanism other than genetic modification.
  • Question 41
    5 / -1
    The ecological niche of the population is an
    Solution

    Key Points

    • Ecological Niche - 
      • Many organisms live together in the same habitat which can cause competition among them.
      • So, each species develops its own niche to avoid competition.
      • Niche is the function of a species, the role it plays in a habitat.
      • Niche is a defined physical condition, particular kind of resources, and distinct functional role in the habitat, for each organism.
      • Physical conditions like time of foraging, optimum temperature, water required, etc., and resources needed are different from any other organism in the same habitat.
    • Over the course of evolution, organisms evolved to optimize survival in a particular set of environmental conditions which is their habitat.
    • They also evolve to develop a unique niche for each species residing in the same habitat. 
    • If the niche for any two species is the same, competition leads to the elimination of one of them.

    Additional Information

    1. The geographical area that a species covers - Habitat
    2. A place where species lives - Habitat
    • Habitat - 
      • Habitat is the natural home or environment where an organism lives.
      • It is the selection of resources, biotic and abiotic factors present in an area suitable for organisms who live there.
      • For a particular animal, its habitat will be where it can find everything it needs to locate and gather food, select a mate, and successfully reproduce.
      • Habitat is the geographical limit within which a population is found.
  • Question 42
    5 / -1
    Natality refers to
    Solution
    Key Points
    • Population size keeps changing with time due to a number of factors.
    • The basic factors that contribute towards the fluctuations in population density are:
      • Immigration (I) - is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
      • Emigration (E) - is the movement of a few individuals of a population from one habitat to another during the time period under consideration.
      • Natality (B) - is the number of births in the given population for a given period of time.
      • Mortality (D) - is the number of deaths in the given population during a given period of time.

    Therefore, natality refers to the birth rate.

    Explanation:

    Among these factors, immigration and natality leads to an increase in population, while emigration and mortality leads to the decrease.

    We can express the relation between these factors in the following equation:

    Nt+1 = Nt + [ (B + I) - (D + E) ]

    where, N = Population density

  • Question 43
    5 / -1
    Desert biome does not support much vegetation as it lacks
    Solution

    Concept:

    • Desert biome has a very extreme climate.
    • They can be very hot or very cold with very little precipitation.
    • The soil quality is very poor and thus, vegetation is very sparse.
    • The flora and fauna have modifications to adjust to the extreme temperatures and lack of precipitation.

    Key Points

    • Option 1 - Sufficient light - INCORRECT
      • Vegetation requires sufficient sunlight to grow.
      • Desert biome has sufficient sunlight during the day.
      • Hence, desert biomes do not lack sufficient light.
    • Option 2 - Favorable temperature - INCORRECT
      • Desert biome has extreme temperature.
      • This extreme climate is not favorable for the growth of most vegetation.
      • Though the desert biome lacks favorable temperature, this is NOT the major contributing factor for lesser vegetation.
    • Option 3 - Sufficient water - CORRECT
      • Deserts have very little precipitation and hence do not have sufficient water.
      • Vegetation requires water to grow and perform photosynthesis.
      • Little precipitation is the characteristic feature of the desert biome.
      • Lack of sufficient water is the major cause of the lack of vegetation in the desert biome.
    • Option 4 - Sufficient nutrients - INCORRECT
      • Desert biome has poor quality soil.
      • To develop a proper vegetation cover the soil needs to be rich.
      • Though poor soil is a contributing factor to lack of vegetation, it is NOT the most important factor.
  • Question 44
    5 / -1
    How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?
    Solution

    Key Points

    • The energy in an ecosystem flows from the Producer → Herbivore/Primary Consumer → Carnivore/Secondary consumer
    • At each successive trophic level, there is only a 10% transfer of energy from lower to higher trophic levels.
    • This is called the 10 percent law.
    • The amount of energy available decreases as the food chain goes to higher levels.
    • Herbivores only consume 10% of all the energy captured by the producers.
    • Carnivore consumes only 10% of energy captured by the herbivore.
    • Of the total energy available at one trophic level, most of it is lost in metabolism or heat.
    • The lost energy is 90% of all the energy consumed and only 10% is transferred to the next trophic level.
    • This loss of energy limits the length of the chain or the number of trophic levels.

    Additional Information

    • The 10 percent law was given by Lindeman.
    • Of all the solar energy falling on the earth, only 1-2% is captured by all the plants.
  • Question 45
    5 / -1
    Which of the following would appear as the pioneer organisms on bare rocks
    Solution

    Concept:

    • Ecological succession - the gradual change in the species composition of a given area caused due to successive colonization of different groups or communities of plants.
    • Sere or seral stage - refers to the individual transitional communities that successively change in a given area.
    • Succession can be of 2 types:
      • Primary - It starts in areas where no living organisms ever existed. Example - Bare rocks, cooled lava.
      • Secondary - It starts in areas where organisms existed previously, but is not present currently. Example - Flooded land, burned forest.
    • Primary succession requires the formation of soil and hence is a much slower process than secondary succession.

    Important Points

    • For primary succession to take place, a bare area needs to be colonized first.
    • Pioneer species -
      • They are species that can invade and colonize a bare area.
      • They have the ability to survive with minimum resources.
      • These also cause modifications of the habitat such that successful establishment of the next seral stage species becomes possible.
    •  Climax community
      • It denotes a stable community that stays in equilibrium with the environment.
      • The equilibrium shifts only when the environment changes.
      • It is usually represented by a forest community.

    Explanation:

    • A bare rock represents a xeric condition and consequently, the succession starting from here is known as xerarch succession.
    • In xerarch succession, lichens form the pioneer species.
    • Lichens have the ability to colonize barren rocks as they can grow without soil and with limited resources.
    • They also secrete acids to dissolve the rocks, leading to weathering and formation of soil.
    • This, in turn, facilitates new species to invade and colonize the area and form the next seral stage.
  • Question 46
    5 / -1
    What is the main cause for the extinction of some species in tropical forest?
    Solution

    Concept:

    • Extinction of any species is an event wherein no individuals of that species survive.
    • For any species to survive, they need food and shelter.
    • Habitat provides food, shelter, and mating opportunity to any species.
    • Tropical forests are the habitat of many tropical species.
    • Deforestation is the act of cutting trees in the forest on a very large scale.
    • Deforestation causes the loss of habitat  to the animals that live in the tropical forest.
    • They lose food sources, and shelter and are unable to find mating partners.
    • This leads to the death of existing individuals and the production of lesser progeny leading to a reduction in their numbers.
    • If their habitat is not restored then the number of individuals keeps reducing and go to extinction.

    Additional Information

    1.  Afforestation
      • It is the process of planting a forest in an area where there was no forest before.
    2. Pollution
      • Pollution is the introduction of harmful materials into the environment.
      • The introduction of contaminating materials in the environment above a certain limit that can harm the species living there is called pollution.
    3. Soil erosion
      • The removal of the top layer of soil.
      • the topmost layer of the soil is the most fertile and is removed by rain and wind in the absence of vegetation.
  • Question 47
    5 / -1
    Biodiversity of a geographical region represents
    Solution

    Key Points

    • Biodiversity is all the different kinds of life found in an area, the variety of animals, plants, fungi, and even microorganisms.
    • Biodiversity varies from place to place because of changing temperature, altitude, topology, latitude, soil type and quality, precipitation and coexistence of other organisms.
    • Biodiversity is a measure of variation at the genetic, species, and ecosystem level. 
    1. Genetic Diversity - 
      • It is the variation in the genetic pool of population present in the region.
      • Genetically diverse regions are able to withstand changes around them by adaptation.
      • Example - India has >50,000 genetic strains of rice and about 1000 varieties of mango.
    2. Species Diversity - 
      • It is the number of species of organisms in the region.
      • It refers to the richness of species in an ecosystem.
      • Species diverse regions make a healthy and balanced ecology.
      • Example - The Western ghats have greater amphibian species diversity than the eastern Ghats.
    3. Ecosystem Diversity - 
      • It is the diversity of ecosystems in a particular geographical area.
      • Each ecosystem comprises of diverse communities of organisms.
      • Example - India has greater ecosystem diversity than a Scandinavian country like Norway as it has deserts, rain forests, mangroves, coral reefs as well as alpine meadows.

    Additional Information

    • Biodiversity hotspots are the regions which are species rich and have many endemic species.
    • At the same time they also need maximum protection, because they are threatened and require conservation.
    • They have many species endemic to that regione.g., western ghats macaque monkeys.
    • Biodiversity hotspots have also lost about 70% of their area and are under protection because they have many endangered species.
  • Question 48
    5 / -1
    What is the most effective way to conserve plant diversity of an area?
    Solution

    Key Points

    • Biodiversity is the variety of species living in a region.
    • The more the number and type of species residing in a region, the more the diversity.

    Biosphere reserves - 

    • They are large protected areas meant for the conservation of plants and animals.
    • It also restores the traditional life of the tribal living in that vicinity.
    • The tribal people living off the reserve conserve the biodiversity of that area.
    • It is an in situ conservation method.
    • It is on-site conservation of all the species of plants or animals in their natural habitat.
    • It protects all the organisms in their own environment along with the people living with it and is sustainable.
    • It is effective because it preserves genetic diversity, protects species populations, traditional lifestyles, and domesticated plant genetic resources.
    • Seed banks, botanical gardens, and tissue culture are all ex-situ methods of conservation where they are taken away from the natural habitat.

    Hence, the most effective way to conserve plant diversity in an area is through biosphere reserves because the plants are conserved in their natural habitat.

    Additional Information

    1. Tissue culture is the in vitro culture of cells, tissues, or organs of plants for their maintenance and study.
    2. A botanical garden is a collection of a large number of living plants in a single place maintained for ex-situ conservation of the plant species.
    3. Seed banks are a type of gene banks that are meant for the preservation of seeds of various types of plants from a variety of sources.
  • Question 49
    5 / -1
    Which one of the following is not correct regarding the harmful effect of particulate matter of the size 2.5 micro meters or less
    Solution

    Key Points

    • Particulate matter is a mixture of a variety of microscopic particles of solid or liquid matter suspended in the air.
    • Together they are called suspended particulate matter (SPM).
    • They lie in the size range of <0.1 µm and up to some 100 µm.
    • Exposure to such fine particles can cause eye, nose, throat irritation, coughing, sneezing, shortness of breath, and can affect lung function.
    • SPM less than 2.5 µm are very difficult to filter from vehicular and industrial exhaust
    • According to Central Pollution Control Board (CPCB), particulate sizes 2.5 micrometers or less are responsible for causing the greatest harm to human health
    • These fine particulates can 
      • cause breathing and respiratory symptoms
      • irritation
      • inflammations and damage to the lungs
      • premature deaths
      • be inhaled deep into the lungs

    According to the above information, the only thing the particulate matter of the size 2.5 micrometers or less do not cause is that they do not enter our circulatory system directly.

    Hence, option 2) It can directly enter into our circulatory system is correct.

  • Question 50
    5 / -1
    Identify the incorrect statement among the following statements on the effects of deforestation
    Solution
    Key Points
    • Deforestation is the process by which a forested area is converted into a non-forested area.
    • In simpler terms, it refers to the loss of a forest.
    • Deforestation is caused mainly due to human activities like felling of trees for various purposes:
      • Forests are often cut down to turn it into an agricultural field, so that agricultural produce can meet the food demand of the increasing human population.
      • Trees are also fell in order to obtain timber, which is crucial for construction purposes, firewood, etc.
      • Forests are also cleared to make grasslands where cattle can be reared.
    • Effects of deforestation:
      • Increased CO2 concentration in the atmosphere.
      • Habitat destruction for wildlife
      • Soil erosion
      • Disturbance in the hydrologic cycle (water cycle), which may affect the weather patterns of a region.
      • Desertification in extreme cases.
    • Deforestation effects can be reduced by reforestation.
    • Reforestation - It is a process by which a previously forested area is restored to its previous stage.
    • Reforestation can occur naturally, but the rate can be increased by human intervention.
    • We can plant more trees in accordance with the ecosystem and biodiversity that previously existed there.

    Therefore, deforestation does not speed up nutrient recycling.

    Additional Information

    • It is estimated that the loss of forests in the tropics is about 40%, whereas in the temperate it is only 1%.
    • In India, forests covered about 30% of the total land area at the beginning of 20th century, but at the end of the century it came down to 21.54%.
    • The National Forest Policy (1988) recommends 33% forest cover in the plains and 67% in the hills.
    • The 'Slash and burn' agriculture or Jhum cultivation has led to considerable deforestation in the North-eastern part of the country.
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