Biology Mock Test - 7

Concept-

• Reproduction is the biological process in which the organism gives rise to young ones or offspring similar to itself.
• It is responsible for the continuity of species generation after generation.
• Reproduction is mainly divided into three types- Asexual reproduction, Sexual reproduction, and vegetative reproduction.
• Asexual reproduction-
  • Asexual reproduction takes place by the formation of different types of spores.
  • These spores are formed by mitotic division.
  • Conidia-
  • The formation of conidia takes place exogenously. These conidia are formed at the tip of conidiophores.

Explanation-

• Reproduction by conidia occurs in Ascomyctes of fungi.
• The body of fungi is called mycelium.
• The asexual spores are conidia produced exogenously on the special mycelium called conidiophores.
• Conidia on germination produced mycelium.

Thereby Asexual reproduction by conidia occurs in penicillium.

Additional Information

Chlamydomonas-

• The asexual reproductive structure of the Chlamydomonas is zoospores.

Yeast-

• In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells).

The correct answer is Both 1 and 2.

Key Points

• All organisms have to reach a certain stage of growth and maturity in their life before they can reproduce sexually.
  • That period of growth is called the juvenile phase. It is known as a vegetative phase in plants. Hence statement 1 is correct.
• This phase is of variable durations in different organisms.
• The end of juvenile/vegetative phase which marks the beginning of the reproductive phase can be seen easily in the higher plants when they come to flower. 
• In some plants, where flowering occurs more than once.
• Plants –the annual and biennial types, show clear cut vegetative, reproductive and senescent phases, but in the perennial species it is very difficult to clearly define these phases.
• A few plants exhibit unusual flowering phenomenon; some of them such as bamboo species flower only once in their life time, generally after 50-100 years, produce large number of fruits and die. Hence statement 2 is correct.
• Another plant, Strobilanthus kunthiana (neelakuranji), flowers once in 12 years.

Additional Information 

• Its mass flowering transformed large tracks of hilly areas in Kerala, Karnataka and Tamil Nadu into blue stretches and attracted a large number of tourists.
• In animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour.
• The reproductive phase is also of variable duration in different organisms.

The correct answer is Anther.

Key Points

• The male sex cells of the seed plants or flowering plants are contained in tough capsules, called pollen.
• Pollen grains are produced by male organs, anthers, or stamens.
  • Sepal: The outer parts of the flower (often green and leaf-like) that enclose a developing bud. 
  • Petal: The parts of a flower that are often conspicuously colored. 
  • Stamen: The pollen-producing part of a flower, usually with a slender filament supporting the anther. 
  • Anther: The part of the stamen where pollen is produced. 
  • Pistil: The ovule producing part of a flower. The ovary often supports a long style, topped by a stigma. The mature ovary is a fruit, and the mature ovule is a seed. 
  • Stigma: The part of the pistil where pollen germinates. 
  • Ovary: The enlarged basal portion of the pistil where ovules are produced.

​Additional Information

Sexual reproduction is divided into three stages:

• Pollination
  • A process in which the pollen grains are transferred across the anther to the stigma of the same flower or flowers different plants.
  • There are two types of pollination- self-pollination, and cross-pollination.
• Zygote formation
  • After the transfer of pollen grains, the male gamete is transferred down through the style of the pistil to the ovary where the male gamete is fused with the female gamete to form a zygote.
• Fruit and seed formation
  • After fertilization, a formed zygote is developed into an embryo. The ovary develops into fruit and ovules into seeds.

The correct answer is Inbreeding.

Key Points

• Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant.
• Self-pollination leads to the production of plants with less genetic diversity, since genetic material from the same plant is used to form gametes, and eventually, the zygote.

Additional Information

• Self-pollination or cross-pollination can be an advantage when the number of flowers is small or they are widely spaced.
  • During self-pollination, the pollen grains are not transmitted from one flower to another.
  • As a result, there is less wastage of pollen.

The correct answer is option 4 i.e., Endosperm - 3n

Key Points

• In plant reproduction, the fusion of the second male gamete with secondary nucleus forms Endosperm - 3n.
• This is called Triple Fusion. The second male gamete with a secondary nucleus form triploid PEN (Primary Endosperm Nucleus).
• PEN develops to form endosperm.
• Please note as both male gametes participate in fertilization, it is also called double fertilization.
• The first male gamete fuses with the egg cell to form the zygote and the second male gamete fuses with the secondary nuclei to form the endosperm.

The correct answer is Ovary.

• A true fruit develops from the Ovary.

Key Points

• The fruit is a matured or ripened ovary developed after fertilization.
• Flower:
  • This is the reproductive part of the plant. In the flower Calyx, Corolla, Androecium, and Gynoecium are found.
  • Out of these, the androecium is a male sex organ and the Gynoecium is a female sex organ.
  • Pollination:
    • After the maturation of Anther, the process of reaching pollen grains to stigma is called pollination.
  • Fertilization:
    • Pollen tube reaches the egg cell after entering into the ovule through a pore called the micropyle.
  • After that, a male nucleus fuses with an egg cell. This is called fertilization.
  • The fertilized egg is called the zygote. In angiosperm, the fertilization is triple fusion whereas in other categories of plants it is double fusion.

The correct answer is None of these.

• Spermatogenesis is the process of the formation of sperms.

Key Points

• It takes place in the seminiferous tubule of the testes.
• The spermatogonia are the germ cells for synthesizing sperms.
• It matures and undergoes mitosis division to produce primary spermatogonia by obtaining nourishment from the germ cell.
• And each primary cell undergoes two successive meiosis divisions to form secondary spermatocytes and spermatids respectively.
• And the transformation of spermatids into spermatozoa is known as spermatogenesis. 
• One spermatogonium produces four sperms, It maintains the chromosome number of the species and FSH acts on spermatogonia to produce spears the significance of spermatogenesis. Hence, options 1, 2 and 3 are correct.

​

The correct answer is 2 only.

• The female eggs are made in the ovaries. 
• There are one ovary and one fallopian tube on each side of the uterus. (statement 1 is incorrect)
• The ovaries produce and release eggs into the female reproductive tract at the mid-point of each menstrual cycle.
• They also produce the female hormones oestrogen and progesterone.

Key Points

• One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube.
• The embryo gets nutrition from the mother’s blood with the help of a special tissue called the placenta.
• The placenta contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi.
• This is what provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
• The developing embryo also generates waste substances which can be removed by transferring them into the mother’s blood through the placenta. (statement 2 is correct)

Concept:

• The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. 
• Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth.
• These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes.
• Primary oocytes get surrounded by granulosa cells to form Primary follicles. Primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles.
• The secondary follicle soon transforms into a tertiary follicle 
• The tertiary follicle further changes into the mature follicle or Graafian follicle.

Explanation:

• The Corpus luteum is a structure formed from the Graafian follicle. After Ovulation, the ruptured Graafian follicle gets transformed into the Corpus luteum. 
• The Corpus luteum gets stimulated by the rising levels of LH and starts secreting the Progesterone hormone.
• Progesterone inhibits the uterine contraction so that the pregnancy can be maintained. For this reason, it is called the pregnancy hormone.
• In case if pregnancy does not occur after ovulation the levels of progesterone fall down and Corpus luteum gets transformed into Corpus albicans.

​

The correct answer is option 3.

Key Points

Concept

• Hormones are non-nutrient chemicals.
• A physical change occurs in the body by certain chemical substances are called hormones.
• The hormones are secreted by the endocrine glands into the blood.
• The major endocrine glands are the Pituitary, Pineal, Thyroid, Thymus, Gonads, etc.

Explanation:

• Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens, etc.
• In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary.
• The hCG, hPL and relaxin are produced in women only during pregnancy.
• In addition, during pregnancy, the levels of other hormones like estrogens, progestogens, cortisol, prolactin, thyroxine, etc., are increased several folds in the maternal blood.
• Thereby, the correct option is ''Relaxin, Human chorionic gonadotropin, Human placental lactogen''.

Additional Information

Explanation:

• Amniocentesis is a fetal sex determination method based on the chromosomal pattern (karyotyping) in the amniotic fluid surrounding the developing embryo.
• In the 14th or 15th  week a small amount of amniotic fluid is taken out from the uterus, using a surgical needle. In this fluid, few cells of embryo-like skin, liver & placenta are present.
• They are tested to know:

1. Genetic anomalies like Down syndrome
2. Metabolic disorders
3. Determining fetal sex

Important Points

• There is a statutory ban on amniocentesis for sex determination to legally check increasing female foeticides

​Additional Information

• Umbilical cord blood sampling: It is a prenatal diagnostic test used for determining fetal abnormalities by examining the blood from the fetal umbilical cord.
• It is also used to check the fetal oxygen level
• Chorionic villus sampling: It entails sampling of the chorionic villus (placental tissue) and testing it for chromosomal abnormalities, usually with FISH or PCR. CVS usually takes place at 10–12 weeks' gestation, earlier than amniocentesis or percutaneous umbilical cord blood sampling.
• Ultrasound imaging: It uses ultrasound waves to produce an image of the fetus on the monitor screen. It is usually done between the 18^th to 20^th week of pregnancy 

Concept:

• The devices that are used to prevent unwanted pregnancies are called Birth control devices or Contraceptives.
• Various Contraceptive methods are:

1. Natural/traditional methods
2. Barrier methods - Condoms, Diaphragms, Cervical caps
3. Intra uterine devices (IUDs) - Lippes loop, Copper T, Copper 7
4. Oral contraceptives - Saheli
5. Injectables and Implants 
6. Surgical Methods - Vasectomy & Tubectomy

Explanation:

• Condoms are barriers made of thin rubber/latex sheath used to cover the penis in the male or vagina and cervix in females.
• It prevents the deposition of ejaculated semen into the vagina of the female.
• Condoms are generally used by males.
• All the other three are specifically used by females.

Additional Information

• Copper T is an intra uterine device inserted by doctors in the uterus through the vagina.
• It increases the phagocytosis of sperms in the uterus, along with this it also releases copper ions which suppress sperm motility and fertilizing capacity.
• Diaphragms are the barrier made of rubber that is inserted into the female reproductive tract to cover the cervix during coitus.
• Oral pill or contraceptive - This involves uptake of hormonal preparations of either progestogens or progestogen-estrogen combination in the form of pills.
• They inhibit ovulation and implantation as well as the alter quality of cervical mucus to prevent the entry of sperms. Eg. The Saheli pill developed by CDRI, Lucknow

The correct answer is a Dihybrid cross.

• Mendel's law of independent assortment can be demonstrated by the Dihybrid cross.

Key Points

• Mendel's law of independent assortment:
  • Independent assortment is a fundamental principle of genetics evolved by Gregor Mendel in the 1860s.
  • Mendel formulated this principle after discovering another principle known as Mendel's law of segregation, both of which govern heredity.
  • The law of independent assortment asserts that an assortment of each pair of traits is independent of the other, i.e.during gamete formation, one pair of traits segregates from another pair of traits independently. 
  • Dihybrid cross – Cross is made between a homozygous dominant parent to another homozygous recessive parent on the basis of twocharacters.
  • By using this cross, Mendel postulated the Law of Independent Assortment.

​

Explanation:

• Mendel selected traits for dihybrid cross for his experiments-
  • Colour of cotyledons- Yellow (Y) and Green (y).
  • Seed shape - Round (R) and Wrinkled (r).
• The phenotypic ratio produced is 9: 3: 3: 1.
• The genotypic ratio produced is 1: 2: 2: 4: 1: 2: 1: 2: 1.
• This proved that two pairs of alleles assorted independent of each other.

Therefore, Mendel's law of independent assortment can be demonstrated by a dihybrid cross.

Additional Information 

• Monohybrid cross – Cross is made between a homozygous dominant parent to another homozygous recessive parent on the basis of one character.
  • By using this cross Mendel postulated the Law of dominance and the Law of Segregation.

The correct answer is Option 3.

Key Points

• Pleiotropy is the phenomenon of a single gene influencing two or more distinct phenotypic traits. Hence Statement 1 is correct.
• An example of a Pleiotropy is phenylketonuria which is a genetic disorder caused by the low metabolism of the amino acid phenylalanine in the body cells. 
• Phenylketonuria (PKU) is a rare genetic condition that causes an amino acid called phenylalanine to build up in the body.
  • It is caused by a mutation of the gene responsible for the production of an enzyme called phenylalanine hydroxylase. Hence statement 2 is correct.
  • This enzyme breaks down the amino acid phenylalanine that we get from protein digestion.
  • Without this enzyme, levels of the amino acid phenylalanine increase in the blood and damage the nervous system in infants.
  • This disorder may result in several conditions in infants including intellectual disabilities, seizures, heart problems, and developmental delays.

The correct answer is Female.

 Key Points

• Humans have one pair of allosomes. X and Y are the one pair of sex chromosomes.
• These chromosomes contain genes that determine the biological sex of an organism.
• In the XY sex-determination system, the female-provided ovum contributes an X chromosome.
• The male-provided sperm contributes either an X chromosome or a Y chromosome.
• Thus resulting in female (XX) or male (XY) offspring, respectively. 

Additional Information

• An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes.
• All the chromosomes other than the sex hormones are autosomes.
• Chromosomes is a thread-like structure found in the nucleus. It becomes visible during cell division.
• In Humans, there are 23 pairs of  chromosomes in total (46 chromosomes)
• 22 pairs of autosomes (total 44) and one pair of allosomes.
• An allosome is a sex chromosome that differs in size, form, and behavior from an autosome.

Concept:

• Genotype:
  • The genetic constitution of an individual representing a single character or a set of characters.
  • This represents whether a particular character is controlled by dominant or recessive alleles.
  • It also shows if the character is homozygous or heterozygous in nature.
  • E.g. - Tall (TT or Tt), Dwarf (tt).
• Phenotype:
  • The external appearance of an individual with respect to a particular trait.
  • E.g. - Tallness, dwarfness.
• Test Cross:
  • In a test cross, an organism showing a dominant phenotype (but genotype is unknown) is crossed with the recessive parent.
  • Test cross is performed to identify the genotype of any plant showing a dominant trait when it is unknown whether the plant is homozygous i.e., pure or heterozygous for that particular trait.

Key Points

• For example, a pea plant having round seeds (F₁ hybrid with unknown genotype) is crossed with a pea plant with wrinkled seeds (recessive parent).
• We should note here that round seeds are dominant over wrinkled seeds in pea plant.
• If all the seeds produced are round, we can conclude that plant is pure or homozygous and if we get round and wrinkled seeds in 1:1 ratio, then we can conclude that plant is heterozygous.

Explanation:

• Case 1 - Consider that round seeds are homozygous dominant (RR):

• All seeds produced are round.
• Thus, the genotype of a hybrid is homozygous dominant (RR).
• Case 2 - Consider that round seeds are heterozygous dominant (Rr).

• Half of the seeds are round and half are wrinkled or, Round : Wrinkled = 1 : 1.
• Thus, the genotype of a hybrid here is heterozygous dominant (Rr).

Additional Information

Significance of Test Cross:

• It is useful for determining whether individuals displaying dominant character are genotypically homozygous or heterozygous.
• It has applications in various plant breeding experiments.
• It is used to introduce a useful recessive trait in the hybrids for rapid crop improvement programs.

Concept:

• The genetic constitution of a normal human being is 44 Autosomes + 2 Sex Chromosomes = 46 Chromosomes.
• The genetic constitution of a normal male is 44 Autosomes + XY and that of a normal female is 44 Autosomes +XX.
• The genetic constitution of the person suffering from Turner syndrome is 44 Autosomes + XO Chromosome = 45 Chromosomes.
• These types of disorders that result from absence or excess or abnormal arrangement of chromosomes, are known as chromosomal disorders.
• It is of two types:
  • Aneuploidy - This refers to the gain or loss of chromosome(s) due to the failure of segregation of chromatids during cell division.
  • Polyploidy - This refers to the gain of a whole set of chromosomes in an organism, mainly plants. E.g. - triploid (3n) or tetraploid (4n), meaning 3 or 4 sets of the chromosomes respectively.
• Monosomy is a type of aneuploidy that is caused due to loss of one copy of a chromosome, forming 2n-1 condition. Example - Turner's syndrome.

Explanation:

• Turner syndrome is a sex chromosomal disorder caused due to non-disjunction of the chromosome during gamete formation i.e., meiosis.
• It is also known as monosomy of the X chromosome.
• Affected individuals are females because of the lack of Y-chromosome, which reinforces the fact that presence or absence of Y-chromosome is the sex determining factor in humans.
• Affected females with Turner syndrome fail to develop secondary sexual characteristics.
• They tend to have short stature.
• They have low intelligence, weblike necks, poorly developed breasts and immature sexual organs.
• They are usually infertile.

Additional Information

Down Syndrome (Trisomy-21) - 

• It occurs when there are three copies of chromosome 21. [Genetic Constitution: 45 Autosomes + 2 Sex Chromosomes= 47 Chromosomes]
• Individuals with Down syndrome have the following characteristics:
  • Low IQ and mental retardation
  • Epicanthal folds (the skin of the upper eyelid forms a layer that covers the inner corner of the eye)
  • Flat hands and stubby fingers
  • Palm is broad with a single palmar crease
  • Below-average height.
• Down syndrome is named after English physician John Langdon Down who became the first to publish a precise description of a person with Down syndrome.

Klinefelter Syndrome (44 Autosomes + XXY) - 

• It is a sex chromosomal disorder caused due to an extra X chromosome in males.
• The genotype of an individual is 44 + XXY.
• Additional sex chromosome is a result of the non-disjunction of X-chromosomes during meiosis.
• An individual suffering from Klinefelter syndrome is male and has overall masculine development, and has harsh voice pitch.
• They have underdeveloped testis.
• They show feminine features such as the development of breasts i.e., Gynaecomastia.
• Spermatogenesis does not occur; hence, individuals are sterile.

Colour-blindness - 

• It is an X-linked recessive disorder, which is classified as a Mendelian disorder.
• The affected individual is unable to differentiate between the colors red and green because of a defect in light-sensing cells in the retina.

The correct answer is 1, 2, and 3.

Key Points

The salient features of the Double-helix structure of DNA are as follows:

• It is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside.
• The two chains have antiparallel polarity. It means, if one chain has the polarity 5'à3', the other has 3'à5'. Hence statement 1 is correct.
• The bases in two strands are paired through hydrogen bonds (H-bonds) forming base pairs (bp). Hence statement 2 is correct.
  • Adenine forms two hydrogen bonds with Thymine from the opposite strand and vice-versa.
  • Similarly, Guanine is bonded with Cytosine with three H-bonds.
  • As a result, always a purine comes opposite to a pyrimidine.
  • This generates an approximately uniform distance between the two strands of the helix.
• The two chains are coiled in a right-handed fashion. Hence statement 3 is correct.
• The pitch of the helix is 3.4 nm (a nanometre is one-billionth of a metre, that is 10-9 m) and there is roughly 10 bp in each turn. Consequently, the distance between a bp in a helix is approximately 0.34 nm.
• The plane of one base pair stacks over the other in a double helix. This, in addition to H-bonds, confers the stability of the helical structure.
• The proposition of a double helix structure for DNA and its simplicity in explaining the genetic implication became revolutionary.
• Francis Crick proposed the Central dogma in molecular biology, which states that genetic information flows from DNA to RNA to Protein.
• In some viruses the flow of information is in the reverse direction, that is, from RNA to DNA.

The correct answer is Both 1 and 2.

Key Points

• A nucleosome is the basic repeating unit of eukaryotic chromatin. 
  • The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called a nucleosome.
  •  Nucleosomes constitute the repeating unit of a structure in the nucleus called chromatin, threadlike stained (coloured) bodies seen in the nucleus.
  • The nucleosomes in chromatin are seen as ‘beads-on-string’ structures when viewed under an electron microscope.
    • The beads-on-string structure in chromatin is packaged to form chromatin fibres that are further coiled and condensed at the metaphase stage of cell division to form chromosomes.
    • The packaging of chromatin at a higher level requires an additional set of proteins that collectively are referred to as Non-histone Chromosomal (NHC) proteins.
    • In a typical nucleus, some regions of chromatin are loosely packed (and stains light) and are referred to as euchromatin. Hence, statement 1 is correct.
    • The chromatin that is more densely packed and stains dark are called as Heterochromatin. Hence statement 2 is correct.
      • Euchromatin is said to be transcriptionally active chromatin, whereas heterochromatin is inactive.

Concept:

• The Non-genetic RNA is of 3 types: 

1. r RNA
2. t RNA
3. m RNA

​Explanation:

Transfer RNA (tRNA):

• It is the smallest type of RNA (4s)
• It is 10-15% of total RNA.
• It is synthesized in the nucleus by DNA.
• It is also known as soluble RNA (sRNA) and Adapter RNA.
• Functions:

1. Carry amino acids to mRNA codons at the time of protein synthesis i.e. it carries information in its anticodons.
2. Reading of mRNA codons.

• Structure: It has a very complicated structure, the scientist Holley presented the Cloverleaf model of its structure.
• In 2D/secondary structure the t RNA appears clover leaf-like but in 3D/tertiary structure it appears like an inverted L-shaped
• There are about 60 different types of t RNA

​

Additional Information

Concept:

• Gene expression refers to the process by which the information in the genes is expressed in the form of a protein product.
• Regulation of gene expression may take place at various levels, and may be controlled by metabolic, physiological or environmental conditions..
• One of the regulation mechanism is transcriptional regulation system.
• In prokaryotes, we find polycistronic genes, which are mostly regulated at the transcription initiation site.
• In a transcription unit, the function of RNA polymerase is regulated by interactions with some regulatory proteins.
• This is known as an operon system, which can be either positively (by activators) or negatively controlled (by repressors).

Key Points

• Francois Jacob and Jacques Monod described the lac operon system in bacteria.
• An operon is a part of genetic material which acts as a single regulated unit having one or more structural genes.
• The lac operon consists of the following parts:

1. Structural Gene - It consists of 3 genes:
   • z - codes for β-galactosidase
   • y - codes for permease
   • a - codes for transacetylase
2. Operator -
   • It is present adjacent to the structural gene.
   • It is the site for the binding of repressor protein.
3. Regulator -
   • It comprises of the i-gene, which codes for the repressor protein.
   • The repressor protein is synthesized all the time constitutively.
4. Promoter -
   • It is the transcription initiation site where RNA polymerase binds.
5. Inducer -
   • It is the molecule that determines whether the repressor will bind to the operator or not.
   • Hence, it regulates the operon.
   • Example - Lactose in lac operon.

• Lac operon is regulated by a repressor and hence it is a negative regulation.

Explanation:

• In the absence of lactose, the repressor protein binds at the operator site and prevents RNA polymerase to transcribe the structural genes.
• But in the presence of lactose, transcription of the genes take place.
• Inducer binds to the repressor and inactivates it by forming the repressor inducer complex.
• This complex prevents the repressor from binding with the operator.
• Thus, the RNA polymerase slides along the DNA without any hindrance and thus, the genes get expressed.

Therefore, Francois Jacob and Jacques Monod - Lac operon is the CORRECT pair.

Additional Information

• Matthew Meselson and F. Stahl - Pisum sativum : INCORRECT
  • Meselson and Stahl proved semi-conservative mode of DNA replication by experimenting with E. coli.
  • Pisum sativum (garden pea) was the model organisms for Mendel's hybridization experiments.
• Alfred Hershey and Martha Chase - TMV : INCORRECT
  • Hershey and Chase used bacteriophages to prove experimentally that DNA is the genetic material.
• Alec Jeffreys - Streptococcus pneumoniae : INCORRECT
  • Alec Jeffreys is known for developing DNA fingerprinting technique.
  • Streptococcus pneumoniae was used by Frederick Griffith for his experiments on 'transforming principle'.

The correct answer 1 and 3 only.

Key Points

• Genome Sequencing 
  • Genome sequencing is figuring out the order of DNA nucleotides, or bases, in a genome—the order of Adenine, Cytosine, Guanines, and Thymine that make up an organism's DNA.
    • Hence statement 1 is correct.
  • Human genome
    • It is made up of 23 chromosome pairs with a total of about 3 billion DNA base pairs. Hence statement 2 is not correct.
    • There are 24 distinct human chromosomes: 22 autosomal chromosomes, plus the sex-determining X and Y chromosomes. Hence statement 3 is correct.
    • Chromosomes 1-22 are numbered roughly in order of decreasing size.
    • Somatic cells usually have one copy of chromosomes 1-22 from each parent, plus an X chromosome from the mother and either an X or Y chromosome from the father, for a total of 46.
    • There are an estimated 20,000-25,000 human protein-coding genes.​

Important Points

• Genome Mapping
  • It describes the methods used to identify the locus of a gene and the distances between genes.
    • Gene mapping can also describe the distances between different sites within a gene.
  • Taking inspiration from the Human Genome Project, the Department of Biotechnology (DBT) initiated the ambitious “Genome India Project” (GIP) in January 2020.
    • ​The GIP aims to collect 10,000 genetic samples from citizens across India, to build a reference genome.

The correct answer is Charles Darwin.

Key Points

• The Galapagos Islands is a volcanic archipelago in the Pacific Ocean. It's considered one of the world's foremost destinations for wildlife viewing.
• A province of Ecuador, it lies about 1,000 km off its coast. Its isolated terrain shelters a diversity of plant and animal species, many found nowhere else.
• Charles Darwin visited in 1835, and his observation of Galapagos species later inspired his theory of evolution.
• During the second voyage of the HMS Beagle, Charles Darwin researched a huge number of indigenous species on the Galapagos Islands. Charles Darwin backed up the idea that mutations occur throughout time.
• Finches' beaks have astonishing variety, according to Charles Darwin. These finches were born in one place but spread to the other. The Galapagos finches, sometimes known as Darwin's finches, are a group of roughly fifteen species of passerine birds.
• The Geospizinae subfamily is frequently used to classify them. Which bird family the passerine birds belong to is yet unknown.
• Darwin discovered endemic species in the Galapagos islands, including passerine birds.

Important Points

• Charles Robert Darwin was an English naturalist, geologist, and biologist best known for his work on evolution.
• Carl Linnaeus, also known as Carl von Linné following his ennoblement, was a Swedish botanist, zoologist, taxonomist, and physician who helped to establish binomial nomenclature, the modern way of identifying species.
• Ernst Haeckel discovered, characterised, and named thousands of new species, built a genealogical tree connecting all life forms, and linked several biological words such as ecology, phylum, phylogeny, and Protista. He was a strong proponent of Darwinism and proposed new notions of the evolutionary descent of human beings.
• Gregor Johann Mendel was an Augustinian monk and abbot of St. Thomas' Abbey in Brünn (Brno), Margraviate of Moravia. He was a meteorologist, mathematician, biologist, and Augustinian friar. Through his careful breeding of garden peas, Gregor Mendel discovered the basic principles of heredity and laid the mathematical foundation of the science of genetics.

Concept-

• Evolution is a process of change happening over generations.
• Generally, this gradual change moves towards the complex organism from the simpler ones.

• Firstly single-celled organisms were formed. But in gradual development became complicated.
• The arrangements of animals according to evolution.
  • Animals without backbone ⇒   Fishes ⇒ Amphibians ⇒ Reptiles ⇒ Aves ⇒ Mammals.
• There is evidence that all organisms evolved from a common ancestor. Example- Homologous and analogous organ.

Explanation-

• Mammals have four limbs, as do birds, reptiles, and amphibians.
• The basic structure of the limbs is similar though it has been modified to perform different functions in various vertebrates.
• There is a difference between the external structure of forelimbs of all of these due to different types of habitat and functions performed by them.
• The basic structure of the skeleton and origin of these animals is the same. The difference between functions and the external structure of forelimbs of these animals. Such organs are called homologous organs.
• This proves that the ancestors of all of them are the same.

The forelimb of the whale is modified into flippers.

Additional Information

• The forelimb of the human is modified into an arm.
• The forelimb of the bird is modified into wings.
• Theories regarding evolution-
  • Darwin gave the theory of natural selection for organic evolution.
  • Hugo de Vries gave the theory of mutation.
  • Lamarck gave the theory of acquired characters.

Concept-

• Darwinism is the term coined for the Darwin theory.
• Darwinism never explained what evolution is but how evolution occurred in nature.
• Darwinism gives the theory of natural selection.

Explanation-

• Neo-Darwinism is a modified form of Darwinism along with recent researches by Weismann, Mendel, Devries, Huxley, Gates, Stebbins, etc.
• They performed experiments to remove the objections against Darwin's theory.
• According to neo-Darwinism natural selection is the main agent of evolution along with mutations, variations.
• Organism more fittest to environmental conditions will survive and get selected.
• Organisms that have useful mutations are selected in nature.
• An isolated population (naturally selected) independently develops mutations. And accumulate in its gene pool.
• After several generations, the isolated populations becomes genetically and reproductively different from another and i.e. form the new species which is evolution.

Therefore according to neo-Darwinism mutation and natural selection are responsible for the evolution of organisms.

Additional Information

Mutation

• Mutation theory was proposed by Hugo-de-Vries.
• The mutation is a phenomenon that results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism.
• Mutation is a phenomenon that leads to variation in DNA.
• The mutation is the raw material of evolution.
• Mutations are random.
• Mutation can be harmful, beneficial, and neutral depending on the alteration.
• The mutation in which characters take part in evolution is dominant.

Natural selection

• Charles Robert Darwin gave the theory of evolution by natural selection.
• The theory was known as the theory of natural selection.
• He explained the process by which organisms change over time as a result of changes in behavioral traits.
• He proposed this theory in his book “The Origin of Species”.
• He gave an explanation of the formation of new species i.e. various species evolve from single species through adaptation to the environment.
• He is also known as the father of evolution.

Concept:

• Hardy–Weinberg Equilibrium(HWE) is a model of the relationship between allele(represents gene) and genotype(gene ratio) frequencies in a random mating population.
• It was formulated independently in 1908 by both G. H. Hardy and Wilhelm Weinberg.

Key Points Hardy–Weinberg Equilibrium is based on several assumptions-

• The population is infinitely large
• The population is closed, meaning that there are no individuals immigrating into or emigrating out of the population.
• There are no mutations occurring on the gene in question.
• Individuals within the population are mating at random - individuals are not choosing their mates.
• Natural selection is not occurring.

Additional Information

• It is a null hypothesis i.e., it does not apply to real population.
• The Hardy-Weinberg equation used to determine genotype frequencies is: p² + 2pq + q² = 1. Where 'p²' represents the frequency of the homozygous dominant genotype (AA), '2pq' the frequency of the heterozygous genotype (Aa) and 'q²' the frequency of the homozygous recessive genotype (aa).

Concept:

• Plasmodium is a protozoan that causes the disease malaria. There are different plasmodium varieties like P. vivax, P. malaria, and P. falciparum
• P. falciparum is the most fatal one.
• Plasmodium requires two hosts to complete its Life cycle:

1. Human
2. Female Anopheles Mosquito

Explanation:

• The infective stage of malarial parasite plasmodium is ''Sporozoite''

The life cycle of Plasmodium: 

Ist phase in the Human:

• The infected female Anopheles mosquito transfers the sporozoites i.e. an infectious form of plasmodium to the human body by biting.
• The sporozoites reach the liver cells and multiply themselves and become merozoites.
• These merozoites now attack the red blood cells and soon they get transformed into the trophozoites.
• They reproduce asexually in the RBCs producing male & female gametes.
• After this, they rupture the RBCs and release a toxin called hemozoin, which is responsible for high recurring fever, chills, and shivering.

IInd phase in Mosquito:

• The plasmodium again enters the Female Anopheles mosquito when it bites another infected person.
• Now the male and female gametes get fertilized in the mosquito's intestine and migrate to the salivary glands.

Additional Information 

• Cyst: It represents a stage in the life cycle of protozoans where a thick wall develops around them that helps them to withstand harsh and unfavourable conditions.

Concept:

• Immunity: It is the ability to resist or defend itself from the development of a disease.
• Immunity can be divided into two types:

1. Innate or Natural immunity: It is present from birth and is inherited from parents. It is non-specific.

• It can be of two types active or passive

      2. Acquired or Artificial immunity: It is not present from birth and develops during an individual's lifetime. It is pathogen-specific.

• It can also be divided into active and passive.

Note:

• Active immunity is developed due to contact with a pathogen or its antigen.
• Passive immunity is developed when ready-made antibodies are injected into the body.

Explanation:

• A person, who is transfused with blood plasma proteins (antibodies) from someone who has been actively immunized against a specific antigen, is considered to have passive immunity because readymade antibodies are being injected into the person's body.
• The antibodies present in the blood of the person actively immunized are directly injected into the other person which is considered passive immunity.   
• This type of immune response is faster as the body is getting readymade antibodies, but it lasts only a few days.
• Passive immunity is given in infections like tetanus where a quick response is needed.

Additional Information

• Auto-immunity: It is an unusual type of immune response developed in the body where it starts rejecting its own body cells or self-cells and molecules. Eg. Addison's disease, Hashimoto disease, Rheumatoid arthritis.
• Antibody: These are the protein molecules called immunoglobulins (Ig) that act against the foreign antigens entering the body. These are of five types - IgA, IgM, IgE, IgG & IgD.

Concept:

• When drugs & alcohol are taken for purposes other than medicinal use or taken in amounts that impair the physiological, psychological & physical functions of the body is called drug abuse.
• Drugs belong to various categories like Opioids, Cannabinoids, Coco alkaloid, Hallucinogens, etc.

Explanation:

• The poppy plant (Papaver somniferum) is a source of many alkaloids like morphine, codeine, narcotine, thebaine.
• Morphine is extracted from the latex of the poppy plant.
• It is named after Morpheus, the Greek god of dreams, morphine provides a feeling of euphoria oft-described as a dreamlike state.
• They bind to the specific opioid receptors in the central nervous system (CNS) and gastrointestinal tract.
• Morphine is an effective sedative and painkiller.
• Codeine is prepared by the methylation of morphine. The hydroxyl group of morphine is replaced by methyl. It is a white crystalline powder that is odourless and bitter in taste.
• Codeine is primarily used as a pain reliever for mild to moderate cough. It is not used as a severe painkiller.

  Morphine 

  Codeine

Additional Information

• Cocoa leaves (Erythroxylum coca): Alkaloid cocaine is extracted from its leaves, It has a potent stimulating action on the central nervous system and interferes with the transport of the neurotransmitter dopamine.
• It is a strong stimulant and when taken in overdoes causes headache, convulsions, hallucination and death due to cardiovascular or respiratory failure.
• Cannabis sativa: Flower tops, leaves and resins of C. Sativa in various combinations produce hashish, charas, marijuana and ganja.
• They interact with the cannabinoid receptors present in the brain. It affects the cardiovascular system of the body.
• Penicillin: It is known as the first discovered antibiotic from the fungus Penicillium notatum

The correct answer is option 3

Apiculture or Beekeeping

• Apiculture or Beekeeping is the production of honey and the wax by care and management of honey bees.
• In apiculture, bees are bred commercially in apiaries, where a lot of beehives can be placed.
• Apiaries can be set up in areas where there are sufficient flowering plants available.
• Working at Beehive

1. Sterile diploid females as workers. Hence statement 2 is correct.
2. Worker bees do all of the works from tending to, feeding young larvae, gathering water, pollen, and nectar, making wax comb, making honey, and guarding the hive. Hence statement 4 is incorrect.
3. Fertile haploid males as drones. Hence statement 1 is correct.
4. The only purpose of the drone is to mate with a virgin queen even he can not feed himself.
5. Haploid that is, they have only half the genes possessed by the queen, all of them derived from the mother.
6. Diploid drones (biparental males) develop from fertilized eggs. Diploid drones do not survive until the end of larval development. The larvae of diploid drones are eaten by workers within a few hours after hatching from the egg.
7. Both haploid and diploid individuals formed as a result of incomplete(cyclic) parthenogenesis i.e. reproduction from an ovum without fertilization.
8. fertilized eggs (zygote) give rise to queen and workers (both are females) by the process of sexual reproduction and unfertilized eggs (ova) develop into drones (males) by the process of parthenogenesis.
9. The difference between a worker and the queen bee is made three days after the egg transforms into larvae and six days after the egg is laid in the beehive.
   • The “royal jelly” is fed to all the larvae.
   • The larva sheds skin multiple times throughout this stage.
   • Later the royal jelly is fed only to the female larvae, which eventually becomes a queen bee. Hence statement 3 is correct. 

The correct answer is 1, 2, and 3

Key PointsPlant tissue culture

• Plant Tissue culture is the in vitro aseptic culture of cells, tissues, organs, or whole plant under controlled nutritional and environmental conditions often to produce the clones of plants.
• It refers to a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of the known composition. 
• The resultant clones are true-to-type of the selected genotype.
• In tissue culture, new plants are grown by removing tissue or separating cells from the growing tip of a plant. Hence, statement 1 is correct. 
• The cells are then placed in an artificial medium where they divide rapidly to form a small group of cells or callus.
• The callus is transferred to another medium containing hormones for growth and differentiation.
• The plantlets are then placed in the soil so that they can grow into mature plants.
• Using tissue culture, many plants can be grown from one parent in disease-free conditions. This technique is commonly used for ornamental plants. Hence, statement 3 is correct. 
• Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. Hence, statement 2 is correct. 

​

Key Points

• Saccharomyces cerevisiae is the name of Brewer’s yeast. 
• The dough, which is used for making bread, is fermented using baker’s yeast. 
• CO₂ gas is released in fermentation. 
• Different kinds of traditional drinks and foods are also made by fermentation by microbes.
• Brewer’s yeasts are used for fermenting malted cereals and fruit juices, to produce ethanol.

Additional Information

1. Penicillium notatum is mould used to prepare antibiotic ​Penicillium. 
2. Lactobacillus is used for the fermentation of milk and producing curd out of it. 

Key Points

• Enzymes are catalysts that help in increasing the rate of a chemical reaction.
• Enzymes are essential for various metabolic activities in our body.
• However, enzymes are also important in the industries, where they are used for various processes.
• Example - 
  • Lipases - are used in detergent formulations as they help in removing oily stains from our laundry.
  • Pectinases & Proteases - are used to clarify bottled juices.
  • Streptokinase - is an enzyme that is used as a 'clot-buster' medicine for patients who have had heart attacks.
• These enzymes are obtained from various microbes for industrial production.

Additional InformationOther uses of microbes: 

• Penicillin - It is an antibiotic that is obtained from the fungus Penicillium notatum.
• Cyclosporin A - It is an immunosuppressive agent that is obtained from the fungus Trichoderma polysporum.
• Statins - are blood cholesterol-lowering agents that are obtained from a type of yeast called Monascus pupureus.
• Biogas production - is done with the help of anaerobic methanogenic bacteria like Methanobacterium.
• Swiss cheese - is produced by the action of Propionibacterium shermanii.

The correct answer is  Acetobacter aceti.

Key Points

• Microorganisms are too small and are not visible to naked eyes.
• Microorganisms are found in air, water, and in the bodies of plants and animals.
• They may be unicellular or multicellular.
• Some microorganisms are useful for the commercial production of medicines and alcohol.
• Microorganisms are classified into four major groups.
  • Bacteria- Bacteria are unicellular microorganisms. Found in air, water, and soil.
  • Fungi- Fungi are cosmopolitan and occur in air, water, soil, and on animals and plants.
  • Protozoa- Protozoans are heterotrophs and live as predators or parasites.
  • Algae- Algae are largely aquatic both fresh water and marine organisms.

Explanation:
Acetobacter aceti-

• Acetobacter aceti is a type of bacteria.
• It is a type of Gram-negative bacteria.
• It is used for the large-scale production of vinegar by the conversion of ethanol to acetic acid.

Aspergillus niger-

• Acetobacter aceti is a type of fungi.
• it is used in the production of citric acid.
• Acetobacter aceti is mainly used in the manufacturing industries.

Clostridium butylicum-

• Clostridium butylicum is a type of bacteria.
• It is a type of Gram-positive bacteria.
• It is used for the large-scale production of butyric acid.

Lactobacillus-

• Lactobacillus is a type of bacteria.
• Lactobacillus and lactic acid bacteria (LAB) are present in starter, multiply at a suitable temperature and convert milk into curd.
• Curd if formed by adding a small amount of curd to milk which acts as a starter.
• Lactobacillus helps in checking disease-causing microbes in stomach.
• It is mainly used for the production of lactic acid.

Concept:

• Recombinant DNA molecule refers to a DNA molecule that is made in a laboratory by combining DNA from two or more sources.
• Preparing recombinant DNA is a primary procedure for genetic engineering techniques.

Explanation:

Steps - 

1. Isolation  -
   • The DNA is isolated from the organism that has the gene of interest.
   • To isolate the DNA from a cell lysozyme are used.
   • Lysozyme breaks down the bacterial cell wall and makes DNA accessible for further isolation steps.
   • Proteases are used to degrade the proteins and ribonuclease are used to degrade RNA component of cell.
   • Removal of the cell wall, protein, and RNA leaves the DNA, which can then be isolated with ease.
2. Restriction digestion - 
   • The gene of interest from DNA is cut using 'Restriction endonucleases'- molecular scissors.
   • Restriction endonucleases like EcoRI can cut DNA molecules at specific sites.
   • In a test-tube isolated DNA and restriction enzymes are added and left to incubate. 
   • This creates a mixture of DNA fragments of different lengths.
3. Separation - 
   • The fragments are separated using Agarose gel electrophoresis.
   • The desired DNA length is determined and eluted from the gel by cutting and extracting it from gel piece.
   • The few cut DNA are amplified or increased in number to millions by using Polymerase Chain Reaction (PCR).
4. Introduction - 
   • The cut gene is first inserted into a vector.
   • The vector is cut using the same restriction enzyme as the gene of interest.
   • Cutting with the same restriction enzyme makes the cut ends of vector and gene of interest complementary and helps join.
   • Joining is done by DNA ligase.
   • The vector, now inserted with the gene of interest is introduced into a host cell.
   • The host cell is made compatible using chemicals such as polyethylene glycol or by physical methods such as microinjection, electroporation, gene-gun, etc.
5. Expression - 
   • Introduction of the vector carrying the gene of interest into the host cell produces recombinant cells.
   • After introduction, the cells which have been introduced with the vector containing the gene of interest are identified using selectable markers.
   • The recombined host cells can multiply the plasmid and produce the desired product from the gene.

Therefore, the correct sequence of steps are:

Lysozyme for isolation of the genetic material (DNA) → Protease and ribonuclease for removal of proteins and RNA from DNA → EcoRI to cut the isolated genome → Gel electrophoresis for separation and isolation of DNA  → DNA ligase → Production of recombinant hosts

Key Points

• DNA is a hydrophilic molecule and thus, it cannot pass through the cell membrane and cell wall easily.
• Thus for a cell to be transformed with a recombinant DNA, some special insertional techniques are required.
• Gene gun or biolistic is one such technique that helps in bacterial transformation:
  • In this process, cells are bombarded with high-velocity micro-particles coated with DNA.
  • The micro-particles are made up of gold or tungsten.
  • This process is particularly useful for plant cell transformation.

Additional Information

Some other insertional techniques:

• Microinjection -
  • Recombinant DNA is directly injected into the nucleus of the cell.
• Pathogen vectors -
  • Disarmed pathogens can be used to infect the cells, allowing successful transfer of rDNA into host cell.
• Heat shock Technique -
  • Cells are treated with divalent cations like Ca²⁺.
  • Cells are then incubated with rDNA on ice.
  • These cells are then briefly exposed to a heat shock at 42°C and are again transferred back to the ice.
  • This process creates some pores on the bacterial cell wall, which facilitates the uptake of DNA.

Concepts:

• 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 -

• DNA template - the sample DNA containing the gene of interest which has to be multiplied
• Primer -
  • DNA polymerase needs a short length of DNA or RNA at the starting point of replication to begin replication.
  • Primers are short pieces of single-stranded DNA that are complementary to the target gene sequence.
  • Since primers are complementary to the target gene sequence, they can bind to both ends of template, and DNA replication can begin.
• DNA polymerase -
  • a heat-resistant, thermostable DNA polymerase is required to replicate the template DNA.
  • This is usually Taq polymerase which is isolated from Thermus aquaticus.
• Nucleotides or dNTPs - nucleotides are the building blocks of DNA, they are required to make the DNA when template DNA is replicating.

Key Points

Steps -

A mixture of all the above components is kept in a PCR machine which cyclically gives different temperatures to the mixture for the PCR to happen.

1. Denaturation - both the strands of DNA are separated by subjecting the template DNA to a high temperature of 90 ºC to 95 ºC
2. Annealing - the temperature is bought down to 50 ºC to 55 ºC to allow the primers to bind to the DNA template
3. Extension - the temperature is raised to 72 ºC because the Taq polymerase functions most efficiently at this temperature. It extends the primer and synthesized new strands.​

These steps are repeated for 30 cycles to get about a billion copies of the DNA. Therefore, PCR is useful in amplification of DNA.

​

Concept:

• Recombinant DNA molecule refers to a DNA molecule that is made in a laboratory by combining DNA from two or more sources.
• Preparing a recombinant DNA is a primary procedure for genetic engineering techniques.
• Various tools are required in constructing a recombinant DNA molecule.

Key Points

Construction of Recombinant DNA:

• Restriction Digestion - 
  • Restriction enzymes are used to cut DNA at specific sites.
  • Same restriction enzymes are used for the cleaving vector DNA and gene of interest.
  • This creates same cohesive ends in the DNA fragments.
• Ligation - 
  • The DNA fragments produced are then joined to each other by ligation.
  • This is carried out by the enzyme DNA ligase.
• This produces the recombinant DNA molecule.

Explanation:

• DNA ligase is a specific type of enzyme that facilitates the joining of DNA strands.
• It catalyzes the formation of a phosphodiester bond between the two strands.
• The bond is formed between the 5'-phosphate group of one chain and 3'-OH group of another.
• The complementary ends of the vector and gene of interest are joined using DNA ligase.

Additional Information

• DNA is formed by joining together nucleotides.
• A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group.
• The phosphate moiety at 5' -end of sugar is referred to as 5’-end of the polynucleotide chain.
• At the other end, the sugar has a free OH of 3'C group which is referred to as 3' -end of the polynucleotide chain.
• Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.
• DNA ligases are able to catalyze the formation of such 3'-5' phosphodiester linkage.
• Many such nucleotides join together to form a polynucleotide or DNA.

Concept:

• Genetic engineering is important for producing more effective and safer therapeutic drugs.
• Recombinant therapeutics are advantageous because they do not induce any unwanted immunological responses.
• Diabetes is one such disease where the patients need to take insulin at regular intervals.
• This necessitates use of insulin from non-human sources.
• Insulin was previously extracted from the pancreas of slaughtered cattle and pigs.
• But this caused allergies and other reactions in the patients.
• This problem was solved by producing human insulin by genetically engineered bacteria.

Important Points

• Human Insulin:
  • Human insulin consists of 2 short peptide chains - peptide A and B.
  • These are linked to each other by disulphide bridges.
  • Insulin is produced as proinsulin, which is a prohormone.
  • Proinsulin contains an extra C-peptide that needs to be cleaved during maturation of proinsulin to insulin.

Explanation:

• Human insulin was produced by genetic engineering for the first time by an American company called Eli Lilly in 1983.
• They prepared 2 DNA sequences corresponding to the A and B peptides using the bacterium Escherichia coli.
• These DNA sequences were then inserted into E. coli plasmids.
• The A and B peptides were produced separately and extracted.
• These peptide chains were then linked by forming disulphide bonds between them.
• This produced the human insulin.

Therefore, genetically engineered bacteria are being employed for production of human insulin.

Concept:

• Gene therapy refers to a collection of methods involving genetic engineering techniques that allows correction of a gene defect by alteration or replacement.
• Correction of a gene defect involves the delivery of a normal gene that could compensate for the non-functional gene.
• This is achieved by inserting the genes into cells using retroviral vectors.

Important Points

• In gene therapy -
  • The host cells are first obtained from the patient and then grown in culture medium in vitro.
  • A cDNA (complementary DNA) for the functional protein is introduced into the host cells using retroviral vectors.
  • These genetically engineered cells are then returned to the patient.
  • These engineered cells, having the functional gene, produce the protein product in the patient.
• Retroviruses have the special feature of having RNA as the genetic material, which is converted to DNA by reverse transcriptase enzyme.
• This feature of retrovirus helps in introducing the cDNA into the vectors.
• Retroviruses also have the ability to replicate efficiently within cells of higher animals.

Therefore, Retrovirus is used as a vector to replace the defective gene in gene therapy.

Additional Information

• The first clinical gene therapy was done in 1990 to a 4 years old girl for the treatment of ADA deficiency.
• ADA stands for adenosine deaminase, an enzyme crucial for the immune system.
• The deficiency of ADA is a severe combined immunodeficiency (SCID) disorder.
• It is caused by the deletion of the gene encoding ADA.
• ADA is mostly produced in the lymphocytes and thus lymphocytes were used for gene therapy.

Explanation:

Hibernation:

• Hibernation is defined as the dormancy period of cold-blooded animals in winters.
• It is a state of reduced metabolic activity among some animals.
• Many organisms are hibernators such as fishes, amphibians and reptiles.
• Snakes, frogs and lizards hibernate in cold weather because they are cold-blooded animals.
• The Hibernators relies on a combination of reserve body fat, stored food supplies etc.

Thus, Lizards goes into a long, deep sleep in the winter season.

Aestivation

• Aestivation is the opposite process of hibernation.
• Some animals go under the ground during the dry season of summer.
• In zoology, it is a state of inactivity and reduced metabolic activity that occurs during the dry season in species such as lungfish and snails.

Diapause

• A temporary pause in the growth and development of an organism is called diapause.
• It is due to adverse environmental conditions.
• It is found especially in insects and in the embryos of many of the oviparous species of fish in the order Cyprinodontiformes.

Concept:

• Growth models help us understand if the growth of any population over time follows a particular pattern or not.
• This also helps us to understand several other attributes of the population.
• Growth models explain 2 types of growth curves:
  • Exponential - This takes place when the resources are unlimited and the population keeps growing.
  • Logistic - This is a growth model that takes the limitations of resources into account.

Key Points

• Human population growth shows an exponential growth curve.
• Exponential growth takes place when the resources available are unlimited.
• But resources are not available to any species population in unlimited amount.
• Thus, the species compete for the available resources to survive.
• This competition for the limited resources restricts the exponential or unlimited growth of any population.
• The maximum number of individuals that can be sustained by a habitat is represented as the carrying capacity (K) of that habitat.
• Interestingly, humans have increased the carrying capacity of their habitats by various methods like agriculture and advanced medicine.
• Scientific advancements have increased the human life span and improved the reproductive abilities.
• Hence, human population is still able to grow exponentially.
• Human population growth produces a J-shaped curve.

Explanation:

Exponential growth can be denoted by the equation:

\({dN \over dt} = rN\)

where, N = Population Density

\(r \) = Intrinsic rate of natural increase = The difference between the per capita birth and death (b-d)

\(dN \over dt\) = Rate of change of population density.

The correct answer is Thunder.

Concept:

Ecology:

• The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of’ or ‘the study of ’.
• Ecology is the study of the earth as a ‘household’, of plants, human beings, animals, and micro-organisms.
• They all live together as interdependent components. 
• The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water, and air, are called ecological systems.

Explanation:

Abiotic factors:

• They refer to all the non-living components like physical conditions (temperature, pH, humidity, salinity, sunlight, etc.) and chemical agents (different gases and mineral nutrients present in the air, water, soil, etc.) in an ecosystem. 

Abiotic factors affecting the life of living organisms:

• Rainfall,
• Temperature,
• Sunlight,
• Wind
• Atmospheric humidity,
• Soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.).

Thus, thunder is not an abiotic factor affecting animal life.  

Concept:

• Planktons are the diverse collection of microorganisms found in water.
• Their composition varies depending on the water-salt level and the environment.
• They are autotrophic or heterotrophic.
• They are non-motile or weak swimmers and drift in the water.

 Important Points

• The aqueous environment like lakes, rivers, and oceans are called hydrarch ecosystem.
• The primary producer in any hydrarch ecosystem is autotrophic plankton called phytoplankton.
• They can colonize the water body and makes it suitable for survival of other organisms.
• Therefore they act as the pioneer community in a hydrarch succession.
• They interact with the environment in a way that facilitates the establishment of the next seral communities of ecological succession. 

Additional Information 

• Herbivores - heterotrophic organisms that feed on plants and other autotrophs.
• Carnivores  - heterotrophic organisms that feed on animals and other heterotrophs.
• Flora - a list of plants in an area or region or time period.
• Fauna  - a list of animals in an area or region or time period.

Concept:

• Organisms need a constant supply of nutrients for various metabolic activities.
• The nutrient amount varies in different ecosystems and also due to seasonal variations.
• The amount of nutrients present in the soil at any given point of time is known as the standing state.
• Though variable, but nutrients are never lost from the ecosystem.
• This is due to the process of nutrient cycling, which refers to the movement of nutrient elements through the different components of the ecosystem.
• They are also known as biogeochemical cycles.
• The rate of release of nutrients into the atmosphere is controlled by environmental factors like soil, moisture, pH and temperature.

Important Points

• Biogeochemical cycles are of 2 types:

1. Gaseous -
   • These include the nitrogen and carbon cycles.
   • The main reservoir for these cycles is in the atmosphere.
2. Sedimentary -
   • These include the sulphur and phosphorus cycles.
   • Their reservoir is in the Earth's crust.

• The function of these reservoirs is to meet the deficit that might be caused due to imbalance in the rate of influx and efflux.

Carbon Cycle -

• We know that carbon is vital for the formation of organic molecules.
• Hence, it constitutes 49% of the dry weight of organisms.
• About 71% of the global carbon is dissolved in the oceans.
• The oceanic reservoir regulates the amount of carbon in the atmosphere.
• The atmosphere contains about 1% of total global carbon.
• The main reservoir for gaseous cycles are in the atmosphere.
• Thus, carbon is released into the atmosphere through various processes:
  • Respiration
  • Decomposition
  • Burning of wood and fossil fuels
  • Forest fire
  • Combustion of organic matter
  • Volcanic activity

Concept:

• Ecosystem Services - refer to the products of ecosystem processes.
• They may include economic, environmental and aesthetic goods and services.
• Some of the ecosystem services are:
  • Purification of air and water
  • Mitigation of droughts and floods
  • Recycling of nutrients
  • Fertility of soils
  • Pollination
  • Wildlife habitat
  • Maintenance of biodiversity
  • Storage site for carbon
  • Aesthetic, cultural and spiritual values

Key Points

• These ecosystem services are often taken for granted as they are free to use.
• Robert Constanza and his colleagues tried to put a price value to these to show how invaluable they actually are.
• It was estimated to be US $ 33 trillion per year.
• This value is nearly twice the global gross national product (GNP), which stands at US $ 18 trillion.
• According to Constanza, of the total cost, each service would account for:
  • Soil formation - 50%
  • Nutrient cycling - <10%
  • Recreation - <10%
  • Climate regulation - 6%
  • Habitat for wildlife - 6%

Concept:

• Biodiversity has been defined by Edward Wilson as the combined diversity of all the levels of biological organization.
• It has taken millions of years to accumulate the current biodiversity that we observe on Earth today.
• However, biodiversity is not uniformly distributed throughout the world.
• There are certain patterns of distribution, which can be explained by:
  • Latitudinal Gradients - This shows that species diversity decreases as we move away from the equator.
  • Species-area relationship - This is a mathematical approach to explain the relation between species richness and the area covered.

Key Points

Latitudinal Gradient -

• Species diversity gradually decreases as we move away from the equator.
• This indicates that the tropics (23.5°N to 23.5°S) would have the greatest biodiversity.
• Reasons for greater biodiversity in the tropics:

1. Speciation - 
   • It is a function of time, meaning that formation of new species happens over a long period of time.
   • It has been observed that temperate regions have had frequent glaciations, whereas tropical regions have remained fairly undisturbed for millions of years.
   • This has allowed species diversification in the tropics over a long periods of time.
2. Niche Specialization - 
   • The tropics are less seasonal, meaning they have a more or less constant and predictable environment.
   • These constant conditions promote niche specialization for species.
   • Niche specialization ensures resource partitioning among different species.
   • This allows competing species to co-exist even with limited resources.
   • Thus, it leads to greater biodiversity.
3. Solar energy - 
   • We know that energy enters into an ecosystem as solar energy, which gets converted to biomass (organic matter) by producers.
   • The tropics receive more solar energy, which leads to higher productivity.
   • This higher productivity supports greater biodiversity.

Therefore, the tropical rain forests have a high diversity of organisms.

Additional Information

• Amazonian rain forests have the highest biodiversity on Earth, having the following number of species:
  • Plants - 40,000
  • Fishes - 3,000
  • Birds - 1,300
  • Mammals - 427
  • Amphibians - 427
  • Reptiles - 378
  • Invertebrates - 1,25,000
• It is also estimated that about 2 million insects are yet to be discovered from these rain forests.

Concept:

• Loss of biodiversity can be caused due to a number of factors but has been accelerated by several human activities.
• Several species have become extinct in just the last century.
• We are currently in the phase of the 'Sixth extinction', which is happening at a much faster rate than the previous mass extinctions.
• The previous extinctions happened in pre-human era, thus proving that human activities are responsible for the higher rate of extinction.
• The major causes for loss of biodiversity is referred to as the 'Evil Quartet'.

Important Points

• Passenger pigeon is an extinct species of pigeon that was native to North America.
• It was a migratory bird that nested in large flocks, which made them more vulnerable.
• It was once considered to be the most abundant bird in the entire world.
• They were hunted for their meat and their overexploitation made them extinct.

Additional Information

Evil Quartet - 

• Habitat Loss & Fragmentation -
  • Loss of habitat may be caused by human activities which require more land area.
  • Forest areas are cleared for urbanisation and infrastructural developments.
  • This is the reason tropical forests have reduced to 6% from 14% of total land surface.
  • For example, Amazon rainforests are increasingly being cleared for cultivation of soya beans and conversion to grasslands for raising beef cattle.
  • Some of the habitat loss is also caused due to increasing levels of pollution.
  • Fragmentation refers to the breaking up of a large area into smaller fragments of habitats.
  • For example, if a road is built across a forest, the forest gets divided into at least 2 different fragments of habitat.
  • This also increases the perimeter area, which reduces the habitat area even further.
• Overexploitation -
  • This refers to the overuse and overexploitation of living organisms for human needs.
  • Example - Passenger pigeon, Stellar's sea cow.
  • Marine fishes are highly over-harvested for consumption as well as for obtaining other products like fish oils, etc.
• Alien Species Invasion -
  • When any species from a different habitat (alien species) is introduced into another habitat, it tends to grow exponentially in absence of its natural predator.
  • This reduces the resources available for the native species of that habitat.
  • The native species present in the habitat are not equipped to compete with these alien species and hence, face a threat of extinction.
  • For example, introduction of Nile perch in Lake Victoria in east Africa led to the extinction of more than 200 species of cichlid fishes there.
  • Illegal introduction of African catfish Clarias gariepinus for aquaculture has posed a threat to the indigenous catfishes in Indian rivers.
• Co-extinction -
  • When two species live in obligatory associations, extinction of one species leads to the extinction of another.
  • Example - Host fishes and their parasites, co-evolved plant-pollinator mutualistic species.

The correct answer is 2 only.

Important Points

• There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator, which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant. Hence, Statement 1 is incorrect.
  • It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. Hence statement 2 is correct.
  • These electrons attach to dust particles giving them a net negative charge.
  • The collecting plates are grounded and attract the charged dust particles.
  • The velocity of air between the plates must be low enough to allow the dust to fall. 
• A scrubber can remove gases like sulfur dioxide.
  • In a scrubber, the exhaust is passed through a spray of water or lime.
  • Recently we have realized the dangers of particulate matter that are very very small and are not removed by these precipitators.

The correct answer is option 4 (In a forest, trees form the uppermost and shrubs form the lowest layer of vegetation).

Explanation:

Forests protect the soil from erosion. (TRUE)

• The term "forest" refers to a large area dominated by trees.
• Many animals need forests to live and survive. 
• They are important for preventing soil erosion and retaining water on the earth's surface.
• Roots of trees hold the soil strongly. This prevents wind and water from eroding the soil. The presence of forests improves the overall quality of land.
• They protect the soil and provide habitat for a variety of animals.

Forests help in bringing good rain fall in neighbouring areas. (TRUE)

• Forests help to keep the surrounding air cool and bring rain.
• Forests, as we all know, have a diverse range of plants and trees. Plants lose water in the form of water into the atmosphere every day through transpiration. Every day, a tree loses more than 30 litres of water.
• As a result, forests release a large amount of water into the atmosphere. This increases the amount of moisture in the atmosphere, resulting in more frequent rains.

Forests influence climate, water cycle, and air quality. (TRUE)

• Forests play an important role in climate change and the water cycle because they provide fresh air to people.
• Forest trees have a very positive effect on climate, water cycle, and air quality. Trees absorb harmful gases, improving both air quality and climate. The water cycle is improving as a result of climate change.

In a forest, trees form the uppermost and shrubs form the lowest layer of vegetation. (FALSE)

• In forests, the uppermost layer is formed by trees, the second layer is formed by shrubs
• And the lowest layer is formed by herbs of the vegetation.