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Bihar BSEB Intermediate Biology study materials
Bihar BSEB Intermediate Biology study resources

Bihar BSEB Intermediate Biology practice questions

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Question 1Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In a typical angiosperm ovule, which structure gives rise to the megaspore mother cell?

  1. The funicle
  2. The integument
  3. The chalaza
  4. The nucellus Correct answer.

Explanation

The megaspore mother cell (megasporocyte) differentiates from a hypodermal cell of the nucellus, the nutritive tissue of the ovule. Integuments, funicle and chalaza are other ovular regions with different roles.

Question 2Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A mature angiosperm embryo sac is described as monosporic and eight-nucleate. Which cell of the egg apparatus carries the egg cell?

  1. The central cell
  2. The synergid Correct answer.
  3. The chalazal cell
  4. The antipodal cell

Explanation

The egg apparatus consists of one egg cell flanked by two synergids, so the synergids are the cells associated with the egg. The central cell holds the two polar nuclei, and antipodals lie at the chalazal end.

Question 3Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In a plant showing porogamy, how does the pollen tube enter the ovule?

  1. Through the micropyle Correct answer.
  2. Through the funicle
  3. Through the chalaza
  4. Through the integument

Explanation

Porogamy is entry of the pollen tube through the micropyle, the narrow opening of the integuments. Entry through the chalaza is chalazogamy and through the integuments is mesogamy.

Question 4Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which ploidy level correctly describes the primary endosperm nucleus formed after double fertilization in angiosperms?

  1. Triploid Correct answer.
  2. Diploid
  3. Haploid
  4. Tetraploid

Explanation

The primary endosperm nucleus arises from fusion of one male gamete with the two polar nuclei, giving three haploid sets. It is therefore triploid in most angiosperms.

Question 5Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A farmer wants to store pollen of a crop for later use in hybridization. Which condition best preserves pollen viability?

  1. Warm, humid air
  2. Direct sunlight with high humidity
  3. High temperature with free water
  4. Low temperature and low humidity Correct answer.

Explanation

Pollen viability is retained longest under cool, dry conditions because low temperature slows metabolism and low humidity prevents germination and microbial growth. Warmth and moisture accelerate loss of viability.

Question 6Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In an experiment, the embryo sac of a flower is destroyed before pollen tube entry but ovule and integuments remain intact. What is the most likely outcome?

  1. Only the endosperm develops
  2. No embryo or endosperm forms Correct answer.
  3. Only the seed coat fails to form
  4. Fertilization occurs normally

Explanation

Both the egg and the polar nuclei reside in the embryo sac, so its destruction removes the fusion partners for both male gametes. Without syngamy and triple fusion, neither embryo nor endosperm can form.

Question 7Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which type of ovule is described as having the micropyle directed downward and lying close to the funicle, with the embryo sac straight?

  1. Anatropous Correct answer.
  2. Orthotropous
  3. Amphitropous
  4. Campylotropous

Explanation

In an anatropous ovule the body is bent so the micropyle faces the funicle and the embryo sac lies parallel to the funicle. This is the commonest ovule type in angiosperms.

Question 8Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A pollen grain lands on a stigma of a different species and fails to germinate. This is an example of which phenomenon?

  1. Apomixis
  2. Self-incompatibility
  3. Interspecific incompatibility Correct answer.
  4. Parthenocarpy

Explanation

Failure of pollen from a different species to germinate or grow on the stigma reflects interspecific incompatibility, a barrier to cross-species fertilization. Self-incompatibility concerns pollen from the same species.

Question 9Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which structure of the male reproductive system produces testosterone?

  1. Leydig cells of the interstitial tissue Correct answer.
  2. Seminal vesicle
  3. Sertoli cells of the seminiferous tubules
  4. Epididymis

Explanation

Leydig (interstitial) cells located between seminiferous tubules secrete testosterone under LH stimulation. Sertoli cells support spermatogenesis and secrete inhibin and androgen-binding protein.

Question 10Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

During spermatogenesis, which cell division converts a secondary spermatocyte into spermatids?

  1. Meiosis I
  2. Differentiation without division
  3. Meiosis II Correct answer.
  4. Mitosis

Explanation

Secondary spermatocytes undergo meiosis II to yield haploid spermatids. Meiosis I produced the secondary spermatocytes from primary spermatocytes.

Question 11Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which hormone surge triggers ovulation in the human menstrual cycle?

  1. Progesterone
  2. Luteinizing hormone Correct answer.
  3. Prolactin
  4. Oxytocin

Explanation

A sharp surge of luteinizing hormone around mid-cycle induces rupture of the mature Graafian follicle and release of the oocyte. Progesterone rises later and supports the luteal phase.

Question 12Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A woman with a regular 28-day cycle ovulates around day 14. On which days is the chance of conception highest?

  1. Days 12 to 16 Correct answer.
  2. Days 1 to 4
  3. Days 6 to 8
  4. Days 22 to 26

Explanation

The oocyte survives only about 24 hours after ovulation, while sperm can survive a few days in the female tract. Conception is therefore most likely around the days immediately before and after ovulation, roughly days 12 to 16.

Question 13Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which layer of the blastocyst gives rise to the embryo proper?

  1. Zona pellucida
  2. Trophoblast
  3. Inner cell mass Correct answer.
  4. Blastocoel

Explanation

The inner cell mass of the blastocyst differentiates into the embryonic disc, which forms the embryo. The trophoblast forms extraembryonic membranes and the placenta.

Question 14Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which extraembryonic membrane encloses the fetus in a fluid-filled sac that cushions mechanical shocks?

  1. Allantois
  2. Chorion
  3. Yolk sac
  4. Amnion Correct answer.

Explanation

The amnion is a thin membrane that surrounds the embryo with amniotic fluid, protecting it from desiccation and mechanical injury. The chorion contributes to the placenta.

Question 15Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which hormone is chiefly responsible for milk ejection during breastfeeding?

  1. Estrogen
  2. Oxytocin Correct answer.
  3. Prolactin
  4. Follicle-stimulating hormone

Explanation

Oxytocin causes contraction of myoepithelial cells around alveoli of the mammary gland, forcing milk into ducts for ejection. Prolactin stimulates milk synthesis but not ejection.

Question 16Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A couple wishes to avoid pregnancy for several years but wants a permanent, highly reliable method. Which of the following is a surgical method?

  1. Copper T intrauterine device
  2. Oral contraceptive pills
  3. Vasectomy Correct answer.
  4. Condom

Explanation

Vasectomy is surgical ligation of the vas deferens, preventing sperm from reaching the ejaculate and providing permanent contraception. The other options are reversible barrier, hormonal or intrauterine methods.

Question 17Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which sexually transmitted infection is caused by Treponema pallidum and presents initially with a painless genital ulcer called a chancre?

  1. Chlamydiasis
  2. Syphilis Correct answer.
  3. Trichomoniasis
  4. Gonorrhoea

Explanation

Syphilis is caused by the spirochaete Treponema pallidum and its primary stage is marked by a painless chancre. Gonorrhoea is caused by Neisseria gonorrhoeae and chlamydiasis by Chlamydia trachomatis.

Question 18Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which assisted reproductive technique involves transferring an embryo into the uterus after fertilization outside the body?

  1. Zygote intrafallopian transfer
  2. In vitro fertilization with embryo transfer Correct answer.
  3. Intrauterine insemination
  4. Gamete intrafallopian transfer

Explanation

IVF involves fertilizing the oocyte with sperm in the laboratory and transferring the resulting embryo into the uterus. ZIFT and GIFT place the zygote or gametes into the fallopian tube instead.

Question 19Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A woman is prescribed oral contraceptive pills. Which mechanism contributes most directly to preventing ovulation?

  1. Thickening of cervical mucus only
  2. Inhibition of FSH and LH secretion by negative feedback Correct answer.
  3. Blocking of the fallopian tube
  4. Direct destruction of the corpus luteum

Explanation

Combined pills contain estrogen and progestogen, which exert negative feedback on the hypothalamus and anterior pituitary. Reduced FSH and LH prevents follicular maturation and the mid-cycle LH surge needed for ovulation.

Question 20Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which event marks the onset of the luteal phase of the menstrual cycle?

  1. Rupture of the Graafian follicle and formation of the corpus luteum Correct answer.
  2. Desquamation of the endometrium
  3. Maturation of the primary follicle
  4. Peak of follicle-stimulating hormone

Explanation

After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone and defines the luteal phase. Endometrial shedding marks the start of menstruation, not the luteal phase.

Question 21Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In humans, the secondary oocyte completes meiosis II only after which event?

  1. Degeneration of the corpus luteum
  2. Formation of the first polar body
  3. Entry of the sperm into the cytoplasm Correct answer.
  4. Release of the oocyte from the ovary

Explanation

The secondary oocyte is arrested in metaphase II and completes the second meiotic division only when a sperm penetrates it. This releases the second polar body and forms the female pronucleus.

Question 22Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A plant species produces seeds without fertilization, and the embryo develops directly from a diploid nucellar cell. Which term best describes this condition?

  1. Vegetative propagation
  2. Adventive embryony Correct answer.
  3. Parthenocarpy
  4. Double fertilization

Explanation

Adventive embryony is a form of apomixis in which embryos arise from somatic cells such as nucellus or integument, producing seeds without fertilization. Parthenocarpy refers to fruit development without seeds.

Question 23Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

An embryo sac contains an egg cell with a haploid chromosome number of 12. What is the chromosome number of the endosperm formed after normal double fertilization?

  1. 48
  2. 12
  3. 24
  4. 36 Correct answer.

Explanation

The primary endosperm nucleus receives two polar nuclei (each 12) plus one male gamete (12), giving 36 chromosomes. The zygote in the same plant would have 24 chromosomes.

Question 24Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A couple is infertile because the woman's fallopian tubes are blocked but her uterus and ovaries are normal. Which technique is most appropriate?

  1. Gamete intrafallopian transfer
  2. In vitro fertilization with embryo transfer Correct answer.
  3. Vasectomy reversal
  4. Intrauterine insemination

Explanation

With blocked fallopian tubes, fertilization cannot occur in vivo, so IVF in the laboratory followed by embryo transfer into the uterus bypasses the tubes. GIFT and insemination both depend on functional tubes.

Question 25Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

Which statement best explains why self-pollination in a cleistogamous flower guarantees fertilization?

  1. Anthers dehisce and pollen reaches the stigma while the flower remains closed Correct answer.
  2. The stigma matures after the flower has withered
  3. The flower opens widely before anther dehiscence
  4. Pollen is carried by wind to a distant flower

Explanation

In cleistogamous flowers the buds never open, so anthers shed pollen directly onto the stigma within the closed flower. This ensures self-pollination and seed set without any pollinating agent.

Question 26Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In a typical angiosperm ovule, which structure directly gives rise to the megaspore mother cell?

  1. The chalaza
  2. The nucellus Correct answer.
  3. The integument
  4. The funicle

Explanation

The megaspore mother cell (megasporocyte) differentiates within the nucellus, the nutritive tissue of the ovule. It then undergoes meiosis to form a linear tetrad of megaspores, of which usually the chalazal one survives to form the embryo sac.

Question 27Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A pollen tube enters the ovule through the micropyle in most angiosperms. Which term describes this route of entry?

  1. Apogamy
  2. Chalazogamy
  3. Mesogamy
  4. Porogamy Correct answer.

Explanation

Entry of the pollen tube through the micropyle is called porogamy and is the common condition in angiosperms. Chalazogamy refers to entry through the chalaza and mesogamy through the integuments or funicle.

Question 28Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

During double fertilization in angiosperms, one male gamete fuses with the egg cell. What is the product of this fusion called?

  1. Primary endosperm nucleus
  2. Antipodal cell
  3. Synergid
  4. Zygote Correct answer.

Explanation

Syngamy, the fusion of one male gamete with the egg cell, produces the diploid zygote, which develops into the embryo. The other male gamete fuses with the two polar nuclei to form the triploid primary endosperm nucleus.

Question 29Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A seed is described as albuminous. Which feature defines such a seed?

  1. It contains two embryos within one seed coat
  2. It lacks a seed coat and is dispersed naked
  3. It stores food only in the cotyledons at maturity
  4. It retains a persistent endosperm that stores food at maturity Correct answer.

Explanation

An albuminous (endospermic) seed retains the endosperm as the main food store at maturity, as in castor and wheat. In non-albuminous seeds the endosperm is fully consumed and food is stored in the cotyledons.

Question 30Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

In the human ovary, the antrum of a mature tertiary follicle is a space filled with fluid. Which cells secrete this follicular fluid?

  1. Granulosa cells Correct answer.
  2. Oogonia
  3. Theca interna cells
  4. Stromal fibroblasts

Explanation

The granulosa cells lining the follicle secrete the fluid that accumulates in the antrum, forming the liquor folliculi. The theca layers are steroidogenic connective-tissue sheaths and do not form this fluid.

Question 31Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A woman in the late follicular phase shows a rising level of estrogen. Which feedback action does this estrogen exert on the hypothalamus and anterior pituitary at this stage?

  1. No effect on gonadotropin release
  2. Negative feedback that lowers GnRH and LH secretion
  3. Positive feedback that triggers an LH surge Correct answer.
  4. Direct inhibition of progesterone secretion by the corpus luteum

Explanation

High estrogen from the mature Graafian follicle exerts positive feedback on the hypothalamus and anterior pituitary, producing the mid-cycle LH surge that induces ovulation. Earlier, low estrogen levels maintain negative feedback on gonadotropins.

Question 32Reproduction (sexual reproduction in flowering plants, human reproduction, reproductive health)

A student argues that a vasectomy provides immediate and complete contraception. Which statement best evaluates this claim?

  1. It is incorrect, because vasectomy only blocks the urethra and leaves the vas deferens open
  2. It is correct, since sperm production stops at once after the operation
  3. It is incorrect, because stored sperm may remain in the ducts for weeks and other contraceptive cover is advised initially Correct answer.
  4. It is correct, because vasectomy also suppresses testosterone secretion

Explanation

Vasectomy ligates and cuts the vas deferens, preventing sperm from reaching the urethra, but sperm already stored in the distal duct can be ejaculated for a period after surgery. Couples are therefore advised to use another method until a semen analysis confirms azoospermia. Spermatogenesis and testosterone secretion continue normally.

Question 33Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

In a monohybrid cross between two heterozygous tall pea plants (Tt × Tt), what phenotypic ratio is expected in the offspring?

  1. 1 tall : 1 dwarf
  2. 1 tall : 3 dwarf
  3. 3 tall : 1 dwarf Correct answer.
  4. 9 tall : 3 dwarf

Explanation

A Tt × Tt cross produces genotypes TT, Tt, Tt and tt in the ratio 1:2:1. Since T (tall) is completely dominant over t, both TT and Tt appear tall, giving three tall to one dwarf plant.

Question 34Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

Which term describes an organism carrying two identical alleles for a given gene?

  1. Heterozygous
  2. Hybrid
  3. Hemizygous
  4. Homozygous Correct answer.

Explanation

Homozygous individuals carry two copies of the same allele, such as TT or tt, and breed true for that trait. Heterozygous individuals carry two different alleles, and hemizygous refers to a single copy as in male X-linked genes.

Question 35Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

A cross between a heterozygous tall pea plant and a dwarf pea plant yields approximately equal numbers of tall and dwarf offspring. This result is characteristic of which cross?

  1. Back cross with the dominant parent
  2. Test cross Correct answer.
  3. Reciprocal cross
  4. Dihybrid cross

Explanation

Crossing an individual of unknown genotype with the homozygous recessive parent is a test cross. A 1:1 phenotypic ratio reveals that the tested plant was heterozygous, because half its gametes carry T and half carry t.

Question 36Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

In a dihybrid cross of two plants heterozygous for both seed shape and seed colour (RrYy × RrYy), assuming independent assortment, what fraction of offspring is expected to be homozygous recessive for both traits (rryy)?

  1. 1/16 Correct answer.
  2. 9/16
  3. 3/16
  4. 1/4

Explanation

Each parent produces ry gametes with probability 1/4. Independent assortment lets the two 1/4 probabilities multiply, giving 1/16 rryy offspring, the double recessive class of the classic 9:3:3:1 ratio.

Question 37Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

The law of independent assortment applies to genes that are located where?

  1. Very close together on the same chromosome
  2. On different chromosome pairs Correct answer.
  3. On the same chromosome at opposite ends
  4. Within the same operon

Explanation

Independent assortment holds when gene pairs lie on separate chromosomes, so their alleles segregate into gametes independently. Genes on the same chromosome are linked and tend to be inherited together unless crossing over separates them.

Question 38Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

A woman who is a carrier of an X-linked recessive disorder marries an unaffected man. What is the probability that a son born to them will be affected?

  1. 1
  2. 0
  3. 1/2 Correct answer.
  4. 1/4

Explanation

A son inherits his single X chromosome from his mother and a Y from his father. Since the carrier mother passes the mutant allele to half her sons, each son has a 1/2 chance of being affected.

Question 39Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

In human ABO blood grouping, a cross between a person of blood group AB and a person of blood group O can produce which blood groups in the children?

  1. A, B, AB and O
  2. A and B only Correct answer.
  3. A and AB only
  4. AB and O only

Explanation

The AB parent has genotype IAIB and the O parent has ii. Children receive either IA or IB from the first parent and i from the second, giving IAi (group A) or IBi (group B).

Question 40Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

A cross between a red-flowered and a white-flowered snapdragon produces pink-flowered offspring. When two pink plants are crossed, the offspring appear in the ratio 1 red : 2 pink : 1 white. This pattern illustrates which phenomenon?

  1. Incomplete dominance Correct answer.
  2. Epistasis
  3. Codominance
  4. Complete dominance

Explanation

In incomplete dominance the heterozygote shows an intermediate phenotype because neither allele fully masks the other. The 1:2:1 ratio reflects the underlying genotypes directly, since each genotype has its own distinguishable phenotype.

Question 41Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

Which of the following provides the best evidence for the chromosomal theory of inheritance?

  1. Presence of multiple alleles in a population
  2. Discovery of the double-helical structure of DNA
  3. Parallel behaviour of chromosomes and Mendelian factors during meiosis Correct answer.
  4. Observation of blending inheritance in flower colour

Explanation

Sutton and Boveri noted that chromosomes and Mendelian factors both occur in pairs, segregate at meiosis and recombine at fertilisation. This parallel behaviour linked genes to chromosomes and founded the chromosomal theory.

Question 42Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

A male with haemophilia marries a homozygous normal woman. What is the expected status of their children?

  1. All daughters are carriers and all sons are normal Correct answer.
  2. All daughters are affected and all sons are normal
  3. Half the daughters are affected and half the sons are affected
  4. All sons are affected and all daughters are normal

Explanation

The affected father contributes his X carrying the mutant allele to every daughter and his Y to every son. Daughters therefore become carriers, while sons receive the mother's normal X and are unaffected.

Question 43Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

Which of the following is a sex-linked trait in humans?

  1. Phenylketonuria
  2. Red-green colour blindness Correct answer.
  3. Cystic fibrosis
  4. Sickle-cell anaemia

Explanation

Red-green colour blindness is caused by a recessive allele on the X chromosome, so it appears far more often in males. Sickle-cell anaemia, cystic fibrosis and phenylketonuria are autosomal disorders.

Question 44Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

In a pedigree, a trait appears in every generation, affects about half the children of an affected parent, and affects males and females equally. Which mode of inheritance best fits this pattern?

  1. Y-linked
  2. X-linked recessive
  3. Autosomal recessive
  4. Autosomal dominant Correct answer.

Explanation

Appearance in every generation with roughly half the offspring of an affected parent affected indicates a dominant allele on an autosome. Equal involvement of both sexes rules out X-linked and Y-linked transmission.

Question 45Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

Which nitrogenous base is found in RNA but not in DNA?

  1. Thymine
  2. Guanine
  3. Uracil Correct answer.
  4. Adenine

Explanation

RNA contains uracil in place of the thymine found in DNA. Adenine, guanine and cytosine occur in both nucleic acids.

Question 46Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

According to the Watson–Crick model, the two strands of a DNA molecule are held together by which bonds?

  1. Ionic bonds between phosphate groups
  2. Peptide bonds between sugar molecules
  3. Hydrogen bonds between complementary bases Correct answer.
  4. Phosphodiester bonds between bases

Explanation

The two antiparallel strands are joined by hydrogen bonds between complementary base pairs: two between A and T, and three between G and C. Phosphodiester bonds instead link nucleotides along each strand.

Question 47Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

A DNA sample contains 30% adenine. What percentage of its bases is guanine?

  1. 40%
  2. 70%
  3. 20% Correct answer.
  4. 30%

Explanation

By complementary base pairing, adenine equals thymine, so thymine is also 30%, making A + T = 60%. The remaining 40% is shared equally by guanine and cytosine, giving 20% guanine.

Question 48Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

In the semi-conservative replication of DNA, each daughter molecule consists of which strands?

  1. Two parental strands
  2. Fragments of both parental strands joined together
  3. One parental strand and one newly synthesised strand Correct answer.
  4. Two newly synthesised strands

Explanation

Meselson and Stahl showed that replication is semi-conservative: the double helix unwinds and each old strand serves as a template for a new strand. Every daughter duplex therefore retains one parental strand.

Question 49Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

Which enzyme is responsible for joining Okazaki fragments on the lagging strand during DNA replication?

  1. RNA primase
  2. DNA helicase
  3. DNA polymerase III
  4. DNA ligase Correct answer.

Explanation

DNA ligase seals the nicks between adjacent Okazaki fragments by forming phosphodiester bonds. Helicase unwinds the duplex, primase lays RNA primers and polymerase extends the new strand.

Question 50Genetics and Evolution (principles of inheritance and variation, molecular basis of inheritance, evolution)

During transcription in bacteria, which enzyme synthesises the RNA copy from the DNA template?

  1. Ribonuclease
  2. Reverse transcriptase
  3. DNA polymerase
  4. RNA polymerase Correct answer.

Explanation

RNA polymerase binds the promoter, unwinds the DNA and polymerises ribonucleotides complementary to the template strand. It does not require a primer, unlike DNA polymerase.