Biology Mock Test - 3

The correct answer is the Oestrus cycle.

Key Points

• Oestrus cycle
  • Sexual reproduction in mammals involves cyclic changes in the ovaries, accessory glands, and reproductive hormones, during which the ovum is released.
  • In non-primate animals, it is called the oestrus cycle and in primates including human beings, it is called the menstrual cycle.
  • The females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase.
  • In non-primate mammals like cows, sheep, deer, dogs, tigers, etc., such cyclical changes during reproduction are called the oestrus cycle whereas in primates (monkey, apes, and humans) such cyclical changes are called the menstrual cycle. Hence, Option 2 is correct.

Additional Information

The correct answer is Rhizome.

Concept-

• Rhizome is a type of Vegetative propagation of asexual reproduction.
• Vegetative propagation is a mode of reproduction in which new plants are formed from vegetative parts (vegetative propagules) of the plant like root, stem, etc.
• Since the formation of these vegetative propagules does not involve two parents, the process involved is asexual.
• It is very common in higher angiosperms.

Following are some units of vegetative propagation:
Rhizome - Ginger
Bulb - Onion, Garlic
Tuber - potato
Bulbil - Agave
Leaf buds - Bryophyllum
Offset - Hyacinth and pistia
Runner - Oxalis
Sucker - Mint

Explanation-

• A rhizome is a form of plant stem that consists of nodes from which roots and shoots emerge. 
• Rhizomes can be found on the surface of the soil or underneath.
• Rhizomes are distinguished by their steep growth, which allows new shoots to emerge from the ground. 
• When a rhizome is separated, each component is capable of growing a new plant.
• Example-  As in Ginger, Rhizome are capable of giving rise to new offspring.

Concept:

• A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous
• Often a longitudinal groove runs lengthwise separating the theca
• The bilobed nature of an anther is very distinct in the transverse section of the anther.
• The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe

Explanation:

Structure of microsporangium:

• In a transverse section, a typical microsporangium appears near circular in outline.
• It is generally surrounded by four wall layers the epidermis, endothecium, middle layers and the tapetum.
• The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
• The innermost wall layer is the tapetum. It nourishes the developing pollen grains.
• Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.

Important Points

• The microsporangia develop further and become pollen sacs. They extend longitudinally all through the length of an anther and are packed with pollen grains. 

The correct answer is Both 1 and 2.

Important Points

• The flower has four main parts known as the calyx, corolla, androecium, and gynoecium.
• The calyx is the outermost whorl of a flower.
  • Sepals collectively called the calyx.
• Corolla:
  • Petals are collectively called the corolla.
  • The two main functions of the corolla are:
    • To attract pollinators. Hence statement 2 is correct.
    • To protect the reproductive parts of a flower.
• Androecium:
  • The stamens of the flower are collectively known as Androecium. Hence statement 1 is correct.
  • Stamens are the male reproductive organ of the flower and consist of anther and filaments.
• Gynoecium:
  • It is the innermost whorl of the flower.
  • Carpels are collectively called the gynoecium.
  • Carpels are the female reproductive organ of a flower.

Concept:

• The most important and unique characteristic of angiosperms is the participation of both male gametes in the act of fertilization. One male gamete fuses with the egg cell and forms the diploid Zygote. The process is called syngamy or generative fertilization. The  Zygote (2n)  develops into an embryo.
• The other male gamete fuses with two polar nuclei (or secondary nucleus) to form the triploid primary endosperm nucleus. The process is known as a triple fusion or Vegetative fertilization. 
• These two actions of fertilization are together called Double Fertilization.

Explanation:

• The endosperm is the food-laden tissue formed during the development of the angiospermous seed. In angiosperms, the endosperm develops from a triploid (3n) primary endosperm nucleus which is formed as a result of vegetative fertilization, triple fusion or the fusion of a male gamete with the secondary nucleus of the central cell.
• So, the central cell of the female gametophyte act as the endosperm mother cell.

​

​Additional Information

• Synergids: These are 2 elongated cells, present at the micropylar end of the ovule, one on each side of the ovule. The characteristic feature of the synergid cells is the presence of finger-like filiform apparatus. It guides the entry of the pollen tube inside the ovule.
• Antipodal cells: These are three in number present at the chalazal end of the embryo sac. These usually degenerate before/soon after fertilization. Antipodal cells serve to provide nutrition to the pro-embryo.
• Egg: It is a single haploid cell, at the micropylar end, between two synergids.
• It represents the female gamete.
• It, when fertilized by sperm (male gamete), forms a diploid zygote.

Concept:

Fruit Formation process in plants:

• Pollination: Pollen is transferred from a stamen to a stigma. The stamen is the male organ in a flowering plant and the stigma is the female part.
• Growth of Pollen Tube: A pollen tube develops to carry the pollen downward. Pollen travels from the stigma, down the style, and into the ovule of the plant.
• Fertilization: The male gamete (pollen) unites with a female gamete (ovule) to form a seed. The seeds are the embryo of the plant. 
• Fruit Formation: The ovary ripens and forms a fruit. The fruit may contain a single seed or multiple seeds.

Explanation:

• True Fruits- True fruits are those that are formed solely from the ovary with ovules inside it. No other flower parts form a part of this type of fruit. For example Cherries, plums, and peaches, mangoes etc.
• False Fruits-False fruits are formed from the ripened ovary along with some other flower parts like the base or receptacle, the perianth etc. For example apples, strawberries etc.

• The male reproductive system includes a pair of testes along with accessory ducts, glands and the external genitalia.
• Each testis has about 250 compartments called testicular lobules.
• Each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced.
• Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells.
• The male germ cells undergo meiotic divisions finally leading to sperm formation, while Sertoli cells provide nutrition to the germ cells.
• The regions outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells. 
• Leydig cells synthesise and secrete testicular hormones called androgens.

Solution

The correct solution is Spermatogonia

Key Points

• The immature cells are called  spermatogonia.
• A spermatogonium is an undifferentiated male germ cell.
• Spermatogonia undergo spermatogenesis to form mature spermatozoa in the seminiferous tubules of the testis.
• Spermatogonia are a heterogeneous group of proliferative cells in the testis that are the precursor cells for mature sperm.

 Important Points

Primary polar body

• Polar bodies are egg cells that cannot be fertilized and are therefore considered non-functioning
• A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis.
• when a primary oocyte undergoes meiotic division to produce a secondary oocyte and again when the secondary oocyte divides to produce an ovum
• Polar bodies are byproducts of meiosis and have no biological role in fertilization or in embryo development.

Spermatid

• one of the haploid cells that are formed by the second division in meiosis of a spermatocyte and that differentiate into spermatozoa.
• A spermatid is the haploid male sexual cell formed after meiosis from spermatocytes that eventually matures into a spermatozoon.
• Spermatogenesis is the formation of male sexual cells or sperms in the testis, the male reproductive organ.
• Spermatids are immature, undifferentiated haploid male gametes.

Secondary polar body

• During oogenesis, the primary oocyte grows and produces a large secondary oocyte and a small polar body, both haploid
• The result of second meiotic division is the formation of a secondary polar body and a haploid ovum.
• The haploid nucleus of the sperm and the ovum fuse together to form a diploid zygote

Concept:

• Menstrual cycle: The rhythmic series of changes that occur in the reproductive organs of female primates (monkeys, apes, and human beings) is called the menstrual cycle.
• It is repeated after every 28/29 days. 
• The menstrual cycle has four phases:

1. Menstrual phase
2. Follicular phase
3. Ovulatory phase 
4. Luteal phase

Explanation:

• During the ovulatory phase, at about the 14th day of the cycle, there is a rupture of the graffian follicle and the ovum gets released.
• The ruptured Graffian follicle soon gets transformed into the Corpus luteum. 
• The Corpus luteum gets stimulated by the rising levels of LH and starts secreting the Progesterone hormone.
• Progesterone hormone is required for the maintenance of the endometrium lining of the uterus.
• In case if pregnancy does not occur after ovulation the levels of progesterone start to fall down and this leads to the disintegration of the endometrium lining causing menstruation.
• Thus, withdrawal of progesterone hormone is the immediate cause of menstruation

Additional Information

• Estrogen, or Oestrogen: It is a sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. 
• Follicle-stimulating hormone: It is one of the hormones essential to pubertal development and the function of women's ovaries and men's testes. In women, this hormone stimulates the growth of ovarian follicles in the ovary before the release of an egg from one follicle at ovulation

The correct answer is Neither 1 nor 2.

Solution:

Concept:

• The process of delivery of the foetus (childbirth) is called parturition.

• Hormone oxytocin (Pitocin) causes the uterus to contract during labour.

• Colostrum is the first form of breastmilk.

Explanation:

• Parturition is induced by a complex neuroendocrine mechanism. Hence statement 1 is correct.

• The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.

• This triggers the release of oxytocin from the maternal pituitary.

• Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates the further secretion of oxytocin.

• The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions leading to parturition.

• The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy by the process called lactation.

• This helps the mother in feeding the newborn.

• The milk produced during the initial few days of lactation is called colostrum which contains several antibodies absolutely essential to develop resistance in newborn babies. Hence statement 2 is correct.

• So, neither 1 nor 2 is incorrect.

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/ Hormonal contraceptives - Saheli
5. Injectables and Implants 
6. Surgical Methods - Vasectomy & Tubectomy

Explanation:

• The Hormonal contraceptive method prevents ovulation
• The oral pill contains hormonal preparations of either progestogens or progestogen-estrogen combination
• 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

Additional Information

 Barrier contraceptive method 

• 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.

​Surgical contraceptive method 

• For Men: Vasectomy, this method blocks sperm from moving into your semen. Many couples choose it because it works. Vasectomies have a 99% success rate in preventing pregnancy.
• It's also simple and safe. You can do it in a doctor's office and it only takes 15-30 minutes. The risks, like infection and bleeding, are low.
• For Women: Tubal Ligation, in this procedure, a surgeon closes off the fallopian tubes, which carry eggs from the ovaries to the uterus.
• It works and it's safe, but there are some risks, like bleeding, infection, damage to other organs, side effects from anesthesia, and ectopic pregnancy -- when a fertilized egg stays in the fallopian tube.

Natural contraceptive method ​

• Natural methods work on the principle of avoiding chances of ovum and sperms meeting.
• Periodic abstinence is one such method in which the couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected.
• As chances of fertilization are very high during this period, it is called the fertile period. Therefore, by abstaining from coitus during this period, conception could be prevented.

The correct answer is Typhus.

• Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus.
• Common symptoms include fever, headache, and a rash.
• The diseases are caused by specific types of bacterial infection.
• Chlamydia is a sexually transmitted infection (STI) caused by a bacteria called chlamydia trachomatis.
• Gonorrhoea is an infection caused by a sexually transmitted bacterium that infects both males and females.
• Hepatitis B is spread when blood, semen, or other body fluids from a person infected with the virus enters the body of someone who is not infected.

Additional Information

• Some common sexually transmitted diseases are - Pelvic Inflammatory Disease (PID), Genital Warts and Human Papillomavirus (HPV), Genital Herpes (HSV-1, HSV-2),
  Syphilis, etc.

The correct answer is 0% of the progeny plants was short.

Concept:

Monohybrid Cross: A cross between two types of plants of the same species considering only the transmission of one character is called a monohybrid cross.

Explanation:

• Gregor Johann Mendel used the monohybrid cross to determine the dominant and recessive traits in the case of peas.
• He crossed true-breeding tall pea plants with true-breeding dwarf pea plants.
• The homozygous allele for the tall pea plant is represented by TT, and the homozygous allele for the short/dwarf pea plant is represented by tt.
• A monohybrid cross between the two plants results in the production of a heterozygous genotype (Tt).
• In terms of phenotype, the F1 generation has all tall pea plants, thus indicating that the tall trait is the dominant trait and the short trait is a recessive trait.

Phenotype: It refers to the external appearance. 

Genotype: It refers to the genetic constitution i.e., the types of genes present in the organism. ​

The correct option is Carrier daughters and colour blind sons.

Concept:

• Colour blindness is a sex-linked recessive disorder due to a defect in either red or green cone of the eye resulting in failure to discriminate between red and green colour.
• This defect is due to mutation in certain genes present in the X chromosome.
• It occurs in about 8 per cent of males and only about 0.4 per cent of females.
• This is because the genes that lead to red-green colour blindness are on the X chromosome.
• Males have only one X chromosome and females have two.

Explanation:

As colourblindness is an x-linked recessive disorder so - 

1. For a woman to be colour blind both the X chromosomes should carry the mutated gene, it can be represented as - X^cX^c.
2. For a man to be colour blind the only one x chromosome present must carry the mutated gene, it can be represented as - X^cY.
3. A woman having one normal X chromosome and the other carrying the mutated gene for colour blindness is called the carrier, it can be represented as - X^cX.​

Now according to the question if a colour blind woman is married to a man of normal vision. Their children will be - Carrier daughters and colour blind sons.

This can be explained as - 

Concept:

• Collective inheritance of character is called linkage.
• The Genes showing linkage are called Linked genes.
• Linkage first time is seen by Bateson and Punnett in Lathyrus odoratus.
• They gave coupling and repulsion phenomena.

Explanation:

• Crossing over (C.O) or recombination is the phenomena in which the non-sister chromatids of the homologous chromosomes exchange their genetic parts carrying genes
• Linkage has an inverse relation with crossing over i.e. the higher the linkage the lower will be the chances of crossing over.
• So if two genes are located very close to each other in a chromosome i.e., they are linked genes there are very little chances of crossing over and hardly any cross over can be detected.​

Additional Information

Other factors affecting linkage:

• Distance between linked genes ↑ = C.O ↑
• Temperature ↑ = C.O ↑
• Age ↑ = C.O ↓

Concept:

• The phenomena when more than two alternate alleles of a single gene govern a character is called multiple allelism. All the multiple alleles occupy their respective loci or position on the homologous chromosomes.
• All the multiple alleles exhibit alternate traits of a single character.
• Examples of multiple allelism are: ABO blood group (3 alleles), Coat color in rabbits (4-alleles), Eye color in drosophila (12-alleles)

Explanation:

• The human blood group (ABO blood group) shows multiple allelism where one character is governed by three alleles
• The ABO blood group gene I (Iso agglutinogen) is present on the 9th chromosome. Gene I has three alleles IA, IB, IO 
• IA allele forms a sugar on the plasma membrane of RBC called a-antigen.
• IB allele forms a different sugar on the RBC called b-antigen.
• IO does not form any antigen.
• Alleles IA and IB are dominant over allele IO but co-dominant to each other.
• The ABO blood grouping is used to determine the blood group of an individual based on the presence or absence of antigens A & B.

Important Points

• People with O blood group are termed as universal donors as they have neither antigens A nor B in their bloodstream which is why they can donate blood to any other blood type.
• On the other hand, individuals with blood group AB are called universal recipients as they can receive blood from any other type.

Additional Information

• Linkage: The tendency of genes present in the same chromosomes to stay together in the hereditary transmission is known as linkage.
• The genes located in the same chromosomes are called linked genes, and those present in different chromosomes are termed unlinked genes
• Polygenic Inheritance: It deals with quantitative traits such as height, weight, and number.
• It is controlled by more than one pair of non-allelic genes (Polygenes)

Concept:

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• According to the complementarity of bases:
  • A is complementary to U in mRNA.
  • C is complementary to G in mRNA.

Important Points

• Sickle-cell anaemia is caused by a point mutation that causes a substitution of amino acid.
• The β-globin chain of haemoglobin (Hb) has Glutamic acid at the 6th position of its peptide chain.
• This Glutamic acid (Glu) is substituted by Valine (Val) due to the point mutation.
• A single base pair of A-T in the normal Hb gene (Hb^A) is replaced by T-A in the mutated gene Hb^S.
• Thus, the codon that is transcribed changes from CTC to CAC.
• The CAC codon is transcribed to GUG in the mRNA.
• The GUG codon of mRNA is then translated into Valine (Val).
• Therefore, the Glu is changed to Val in haemoglobin of sickle-cell anaemic patients.

Concept:

Features of DNA & RNA:

• Both DNA and RNA are genetic materials.
• DNA and RNA are both large biological polymers of nucleotides.
• Both DNA and RNA consist of sugar, nitrogenous bases, and a phosphate backbone.
• DNA consist of nitrogen bases -  Adenine, Guanine, Cytosine & Thymine while RNA has Adenine, Guanine, Cytosine & Uracil.
• RNA has Uracil in place of Thymine.
• On both DNA & RNA Guanine & Cytosine are complementary to each other i.e. they form pair
• Complementary base pairs are connected by hydrogen bonding.
• Two hydrogen bonds form between adenine and either thymine or uracil, while three hydrogen bonds form between cytosine and guanine.

Explanation:

• The process of copying genetic information from one strand of DNA into RNA is termed transcription or mRNA synthesis.
• The process of transcription begins when an enzyme called RNA polymerase attaches to the template DNA strand and begins to catalyze the production of complementary RNA.
• Hydrogen bonds are formed between the nitrogen bases of the template DNA strand and the complementary RNA strand.
• Adenine forms two H2 bonds either with Uracil or Thymine.
• Cytosine forms three H2 bonds with Guanine.
• Therefore the transcribed RNA of a segment of DNA with the codons TAGCATACT is  AUCGUAUGA.

Important Points 

• Transcription is completed in three steps Initiation, Elongation & Termination.

The correct option is ''4''

Explanation:

• Transcription is the process of copying genetic material from one strand of the DNA to RNA. It is also called m-RNA synthesis. 
• Transcription is carried out by the activity of an enzyme called the RNA polymerase along with its several accessory proteins called the transcription factors
• During transcription one of the strands of the double-stranded DNA is used as a template onto which new mRNA is synthesized. This strand is called the template strand or the antisense strand. It has a 3' to 5' polarity i.e. it runs in a 3' to 5' direction.
• The second strand of the DNA is called the coding strand because it has the base pair sequence corresponding (similar) to the base pair sequence of the newly synthesized mRNA which will be later translated into proteins. It has a 5' to 3' polarity i.e. it runs in a 5' to 3' direction.

Important Points

• The coding strand does not code for anything, it got its name because it corresponds to the same sequence as the mRNA that contains the codon sequences required for protein synthesis
• Thus, the polarity of the coding strand is 5' ........ > 3' direction.

​Additional Information

• The polarity of coding is always 5' to 3', it cannot run in a 3' to 5' direction.

Concept:

• Synthesis of proteins is a very elaborate process consisting of different steps like

1. Activation of Amino acids
2. Charging of tRNA
3. Activation of Ribosomes
4. Assembly of Amino acids (Polypeptide Formation)
5. Modification of the released polypeptide

Explanation:

• The assembly of amino acids involves 3 stages: initiation, elongation, and termination.
• The initiation stage brings together an mRNA, a tRNA having the first amino acid (methionine) of the polypeptide, and two subunits of ribosomes. The union of all these components forms the translation initiation complex. 
• First, small subunit (the 30s) of ribosome attaches to the 5’ end of the mRNA and a specifically charged initiator tRNA.
• Downstream on the mRNA lies the initiator codon, AUG, which signals the start of translation. The initiator tRNA joins the initiator codon by its anticodon through hydrogen bonds. It carries the amino acid methionine in eukaryotes and formylmethionine in prokaryotes. Now the large subunit of ribosome joins the small subunit. This completes the translation initiation complex.
• Thus, methionine amino acid initiates the formation of polypeptide chains in protein synthesis.

Additional Information

• Aspartic acid is a non-essential amino acid in humans. It has codons GAC and GAU
• Glutamic acid or glutamate (the ionic form) is an alpha-amino acid used in the biosynthesis of proteins. It is a non-essential amino acid in humans. It has codons GAA and GAG.
• Valine is an alpha-amino acid used in the biosynthesis of proteins, It is used to break down tryptophan and vitamin B6. Valine has codons GUU, GUC, GUA and GUG

The correct answer is Frederick Griffith.

• Frederick Griffith performed this transformation experiment with Streptococcus pneumoniae in 1928.

Key Points

• In this experiment, bacteria are grown in a suitable culture medium; it produces smooth-walled strain as well as rough-walled strain.
• The smooth-walled strain has a polysaccharide coating and is also disease-causing.
• When S Strain is injected mice die whereas when R strain is injected mice do not die. And when S heat-killed is injected mice remain alive. 
• But, when S heat-killed and R strain is injected into mice, Mice die.
• Hence the conclusion is R strain bacteria transformed by heat-killed S strain.

Explanation:

• The Human genome represents the entire set of nucleic acid sequences present in the 23 pair of chromosomes in a human cell.
• There are approximately 3 billion nucleotides present in the human genome.

The salient features of the Human genome are:

1. The human genome contains 3164.7 million bp.
2. The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.
3. The total number of genes is estimated at 30,000–much lower than previous estimates of 80,000 to 1,40,000 genes. Almost all (99.9 per cent) nucleotide bases are exactly the same in all people.
4. The functions are unknown for over 50 per cent of the discovered genes.
5. Less than 2 per cent of the genome codes for proteins.
6. Repeated sequences make up a very large portion of the human genome.
7. Repetitive sequences are stretches of DNA sequences that are repeated many times, sometimes a hundred to thousand times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution.
8. Chromosome 1 has the most genes (2968), and the Y has the fewest (231).
9. Scientists have identified about 1.4 million locations where single-base DNA differences (SNPs – single nucleotide polymorphism, pronounced as ‘snips’) occur in humans. This information promises to revolutionise the processes of finding chromosomal locations for disease-associated sequences and tracing human history.

Concept:

• Evolution: Evolution is a process of change happening over generations.
• Darwin published his theory of evolution with evidence in his book 'On the Origin of Species' in 1859.
• The book introduced the scientific theory of evolution over the course of generations through the process of Natural Selection.
• Kinds of evolution:

1. Divergent evolution
2. Convergent evolution
3. Parallel evolution

Explanation:

• The organs which are different anatomically but similar functionally are called analogous organs. Eg. Wings of butterflies & birds, Eyes of octopus & mammals, Flippers of penguins & dolphins. All these have different anatomical structures but they perform the same function like Wings of butterfly & birds differs in structure but both perform the function of flight.
• Due to their same function, different structures evolve similarly. This is known as convergent evolution. In convergent evolution, the species of different ancestry start sharing analogous traits because of selection pressure or shared environment.
• Thus two genetically different organisms like a bat & an insect having different skeletal structures adapt their wings to fly due to convergent evolution.

Additional Information 

• Divergent evolution: The organs which are similar in structural design & origin i.e. same anatomical structure but different in functions are called Homologous organs. Eg. The forelimbs of some animals like whales, bats & cheetah have similar anatomical structures i.e., humerus, radius, ulna, metacarpals, and phalanges but different functions. The forelimb of the whale is used in swimming, a bat's forelimb is used for flight while a cheetah uses the forelimb for running.
• Due to their different needs, some structures evolve differently. This is called divergent evolution.
• Co-evolution: It is a process of evolution occurring between two species or more in which both the species are mutually dependent on each other for their needs & survival. It occurs due to the pressure of natural selection on species. Eg. coevolution of flowering plants and associated pollinators (e.g., bees, birds, and other insect species).
• Mutation: It is defined as the change of gene sequence in the organism’s genome by deletion, addition, or translocation such that it alters the genetic message carried by that gene.

The correct answer is option 2.

• J.B.S. Haldane opinioned that life must have developed from the simple inorganic molecule in the Oparin-Haldane Hypothesis.
• According to him the process of evolution from inorganic to organic would have taken in multiples events owing to change of conditions on earth.

Concept:

Mutation:

• It is defined as the change of gene sequence in the organism’s genome by deletion, addition, or translocation such that it alters the genetic message carried by that gene.
• Mutations are permanent irreversible inheritable changes i.e. they are carried forward in the next generation & cannot be reversed thus, mutations are referred to as the ultimate source of organic variation 

​Explanation:

• The mutation theory of evolution was proposed by Hugo de vies in 1901
• He studied mutation in the Oenothera lamarckiana (Evening Primrose) plant. 

Some of the salient features of this theory are:

• Mutation forms the raw material for evolution
• These are sudden and inheritable changes that immediately become operational
• The mutations occur in all the possible directions and the same type of mutation can occur in n number of individuals within a species
• The useful mutation are selected by nature while the lethal ones are eliminated

Important Points 

• The word mutation was also coined by Hugo de Vries

Additional Information 

Explanation:

• The creature that is called the first human-like being (hominid) is Homo habilis.
• Homo habilis means ''able man'' or ''handyman'' in Latin.
• They had human-like hands & feet, which indicates their ability to handle objects with great precision.
• Their first fossils were found at Olduvai Gorge in northern Tanzania (East Africa)
• Homo habilis had a brain capacity of 650 - 800 cc.
• They did not eat meat.

Additional Information 

The correct answer is Hemozoin.

Key Points

• Hemozoin:-
  • Hemozoin is an iron porphyrin proteinoid complex formed by the parasite from the breakdown of haemoglobin.
  • It does not react with a Prussian blue stain and can be removed from tissue sections by a saturated alcoholic solution of picric acid.
• In order to know about the poisonous substance hemozoin, which is released as a result of RBS’s rupturing, let us know about the complete cycle of malarial parasite:
  • The sporozoites of plasmodium are injected into the human blood when its vector, a female anopheles mosquito bites the person.
  • These sporozoites then enter the liver through blood circulation.
  • When the schizont is mature, the RBCs burst to release merozoites into the blood.
  • The rupture of RBCs is associated with the release of a toxic substance, hemozoin.
  • This hemozoin is responsible for the chills and high fever recurring every three to four days.

​

The correct answer is 1 only.

Key Points

Bone Marrow

• A bone marrow transplant is a medical treatment that replaces one’s bone marrow with healthy cells. The replacement cells can either come from the person’s own body or from a donor.
• A bone marrow transplant is also called a stem cell transplant or, more specifically, a hematopoietic stem cell transplant.
• Both B and T lymphocytes originate in the bone marrow. Hence, statement 1 is correct.
  • T lymphocytes migrate to the thymus to undergo their maturation.
  • Thus B lymphocytes are so-called because they are bone marrow-derived, and T lymphocytes because they are thymus-derived.
• B cells are involved in humoral immunity, whereas T cells are primarily responsible for cell-mediated immunity. Hence, statement 2 is not correct.

Concept:

Tobacco:

• Tobacco smoke is made up of thousands of chemicals, including at least 70 known to cause cancer.
• The cancer-causing chemicals are known as carcinogens.
• Some of them are:-
  • Nicotine
  • Hydrogen cyanide
  • Formaldehyde
  • Lead
  • Arsenic

• Tobacco contains a large number of chemical substances including nicotine (an alkaloid).
• Tobacco chewing is associated with an increased risk of cancer of the oral cavity.
• Smoking is associated with an increased incidence of cancers of the lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer, etc.​

​Explanation:

• Smoking increases carbon monoxide (CO) content in the blood.  
• Carbon monoxide has more affinity towards haemoglobin than oxygen (O₂).
• This carbon monoxide gas is fatal to health, can lead to coma and even death of the persons sleeping in that room.
• Carbon monoxide is a poisonous gas and causes asphyxiation.
• It binds to haemoglobin to form carboxyhemoglobin, which is about 300 times more stable than the oxygen-haemoglobin complex.
• This carboxyhemoglobin decreases the oxygen-carrying capacity of blood in our bodies.
• Thus the brain gets deprived of oxygen.
• This leads to suffocation and eventually leads to death.

Thus, tobacco smoke contains carbon monoxide which reduces the oxygen-carrying capacity of the blood.

Concept:

• In the mid-1960s Green revolution started in India which led to the introduction of several high-yielding hybrid varieties of different crops like Wheat & Rice.
• The green revolution led to a dramatic increase in food production in our country
• The green revolution helped India to become Self-reliant in Agriculture.

Explanation:

• Kalyan sona is a variety related to wheat. Kalyan sona is a double gene dwarf variety of wheat developed from Kalyan 227 and Sona 227 by Indian Agriculture Research Institute (IARI).
• Kalyan sona is resistant to rusts, it was introduced in India in the year 1966

Additional Information

• Jaya & Ratna are semi-dwarf hybrid varieties of rice developed in India during the Green revolution. Due to these hybrid varieties production of Rice increased from 35 million tonnes to 89.5 million tonnes.
• Pusa swarnim is a hybrid variety of Okra (bhindi) that is resistant to pests such as Shoot & fruit borers

Concept-

• The fishery is an industry devoted to the catching, processing, or selling of fish, shellfish, or other aquatic animals.
• A large number of our population is dependent on fish, fish products, and other aquatic animals such as prawns, crab, lobster, edible oysters, etc., for food.
• Fishes can be divided into two broad categories - freshwater fishes & marine fishes.
• Some of the freshwater fishes which are very common include Catla, Rohu, and common carp.

Key Points

Some of the marine fishes that are eaten include – Hilsa, Sardines, Mackerel, and Pomfrets.

Additional Information 

• Fisheries have an important place in the Indian economy.

• It provides income and employment to millions of fishermen and farmers, particularly in the coastal states.
• For many, it is the only source of their livelihood. In order to meet the increasing demands on fisheries, different techniques have been employed to increase production.
• For example, through aquaculture and pisciculture, we have been able to increase the production of aquatic plants and animals, both fresh water and marine.
• This has led to the development and flourishing of the fishery industry, and it has brought a lot of income to the farmers in particular and the country in general.

The correct answer is All of the above.

Key Points

• Biofortification is breeding crops with higher levels of vitamins and minerals, or higher protein and healthier fats.
• It is the most practical means to improve public health.
• Breeding for improved nutritional quality is undertaken with the objectives of improving –

1. Protein content and quality; Hence, Statement 1 is correct.
2. Oil content and quality; Hence, Statement 2 is correct.
3. Vitamin content; and Hence, Statement 3 is correct.
4. Micronutrient and mineral content. Hence, Statement 4 is correct.

• In 2000, maize hybrids that had twice the amount of the amino acids, lysine and tryptophan, compared to existing maize hybrids were developed.
• Wheat variety, Atlas 66, having a high protein content, has been used as a donor for improving cultivated wheat. 
• It has been possible to develop an iron-fortified rice variety containing over five times as much iron as in commonly consumed varieties.
• The Indian Agricultural Research Institute, New Delhi has also released several vegetable crops that are rich in vitamins and minerals, e.g., vitamin A enriched carrots, spinach, pumpkin; vitamin C enriched bitter gourd, bathua, mustard, tomato; iron and calcium-enriched spinach and bathua; and protein-enriched beans: broad, lablab, French and garden peas.

The correct answer is Lactobacillus.

Key Points

• Lactobacillus is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria.
• There are many species of lactobacillus.
• These are "friendly" bacteria that normally live in our digestive, urinary, and genital systems without causing disease. 
• Curd contains a wide variety of bacteria like Lactobacillus, Lactococcus lactis, etc, whereas yogurt contains Streptococcus thermophilous and Lactobacillus bulgaricus.

Additional Information

• Salmonella is a type of bacteria that commonly causes diarrhea.
• Clostridium is a bacterium that can cause symptoms ranging from diarrhea to life-threatening inflammation of the colon. 

Concept -

• Organic farming is a technique that entails growing plants and raising animals in a natural environment.
• To preserve soil fertility and ecological balance while minimizing contamination and waste, this method employs biological materials while avoiding synthetic substances.
• Different techniques followed in organic farming are - 
  • CATCH CROP: A catch crop is a fast-growing crop that is planted in between main crop plantings. It allows better use of available growing space and prevents mineral runoff. 
  • MIXED CROP: Instead of one crop, two or more crops are grown on the same piece of land during the same growing season.
  • ​MANURE: Manure is purely organic and is used in agriculture. Animal faeces makes up the majority of manure and other sources include compost that is together used to make manure. 
• It forbids the use of synthetic fertilizers, pesticides, growth regulators, genetically modified organisms, and livestock feed additives.
• The use of fertilizers in crop filed causes a number of harmful effects to the environment as well as the on human health. 
  • It releases harmful heavy metals in the water that then undergoes the process of biological magnification causing severe harm to human life. 
  • Fertilizers seeping in vegetables and other crop feed causes cancer in humans. 
  • The seepage of harmful chemicals in soil and water cause land and water pollution. 

Explanation -

• Organic farming introduces a completely natural process of agriculture to help save the environment and human health and to produce good quality crops too. 
• It forbids the use of harmful chemical fertilizers.

Hence the correct answer for this question is - fertilizer. 

The correct answer is the Polymerase chain reaction.

• The polymerase chain reaction is most useful for the enzymatic amplification of specific gene segments of DNA.

Key Points

• The polymerase chain reaction is a technique to make copies of a specific DNA region in vitro.
• It is used to make enough of the target DNA region so that it can be analyzed or used in some other way. 
• It is based on a thermostable DNA polymerase, Taq polymerase, and requires DNA primers designed specifically for the DNA region of interest.

Additional Information

• DNA hybridization is the process of combining two complementary single-stranded DNA or RNA molecules and enabling them to form a single double-stranded molecule through base pairing.
• Nucleotide sequencing is defined as a process of determining the order of nucleotides.
  • Nucleotides are defined as organic molecules that act as monomers or the subunits of nucleic acids.
  • They are known as the building blocks for nucleic acids.
• Reverse transcription is the enzyme-mediated synthesis of a DNA molecule from an RNA template.
  • The resulting DNA is known as cDNA and can be used as a template for PCR amplification.
  • Reverse transcription followed by PCR is known as RT-PCR (reverse transcription-PCR).

Key Points

• Recombinant DNA Technology - Genetic Engineering
  • Genetic engineering involves the creation of recombinant DNA.
  • Thus, it is also known as recombinant DNA technology.
  • It involves various techniques by which a DNA fragment from one cell can be introduced into another.
• Cloning Vehicles - Vector
  • Gene cloning is one of the processes of genetic engineering.
  • This requires some cloning vehicles, which can be used for transferring the foreign DNA into the host cell.
  • These are also known as cloning vectors and are usually bacterial plasmids.
• Macromolecular Separation - Electrophoresis
  • Electrophoresis is a process by which DNA fragments are separated by their size after they have been cut by restriction enzymes.
  • Thus it is a process of macromolecular separation, the macromolecule here being the DNA.
• DNA Ligase - Sealing Enzyme
  • DNA Ligase is an enzyme that helps in joining two DNA fragments by forming a phosphodiester bond between the 5'-phosphate group of one chain and the 3'-OH of another.
  • Thus it is known as the sealing enzyme as it ligates or "seals" together two DNA strands.

Therefore, the correct answer is I - D, II - A, III - C, IV - B.

Concept:

• Isolation of DNA from a cell is the first step for any genetic engineering process.
• Restriction enzymes can work only when the DNA molecule is in the pure form, free from other macromolecules.
• Thus DNA needs to be isolated from a cell before proceeding with restriction digestion.

Key Points

Steps of Isolation of DNA:

1. Treatment with Digestive Enzymes -
   • Digestive enzymes help to break down the cell wall of bacterial, plant or fungal cell.
   • Lysozyme- digests the bacterial cell wall.
   • Cellulase- digest the plant cell wall.
   • Chitinase- digest the fungal cell wall.
2. Removing other macromolecules -
   • RNA and proteins are removed by this process.
   • Protease- cleaves protein molecules.
   • Ribonuclease- removes the RNA.
3. Precipitation of purified DNA -
   • This is achieved by the addition of chilled ethanol.
   • The charged DNA molecules move away from ethanol and precipitate.
4. Removal of DNA -
   • Fine threads of purified DNA can be observed in the suspension.
   • This can be removed by a process called spooling.
   • Spooling is the process that helps to scoop up long DNA threads by swirling it around a glass rod or spooling stick.

Therefore, chilled ethanol is added to precipitate DNA.

The correct answer is option 2.

Key Points

• GMO (Genetically Modified Organisms)
  •  Techniques to alter the chemistry of genetic material (DNA and RNA), to introduce these into host organisms and thus change the phenotype of the host organism.
  • The techniques of genetic engineering include
    • the creation of recombinant DNA, use of gene cloning, gene transfer, overcome this limitation and allow us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism.
  • In this technique, a gene from one organism is isolated and transferred to the cell of another organism. Hence statement 1 is correct.
  • A genetically modified organism (GMO) is an animal, plant, or microbe whose DNA has been altered using genetic engineering techniques. Hence statement 2 is not correct.
  • Genes for insect resistance may spread from crop plants to wild plants. Hence statement 3 is correct.
  • Animals that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals.
  • To produce a transgenic animal the novel genes are inserted at a very early stage of development. Hence statement 4 is correct.

Concept-

• ELISA means Enzyme-Linked Immuno-sorbent Assay.
• ELISA techniques serve the purpose of early diagnosis.
• ELISA is based on the principle of antigen-antibody interaction.
• Infection by a pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesized against the pathogen.

Explanation-

• ELISA uses an enzyme to detect the binding of antigens and antibodies.
• The enzyme converts a colorless substrate to a colored product, indicating the presence of Ag: Ab binding.
• An ELISA can be used to detect either the presence of Antigens or antibodies in a sample depending on how the test is designed.
• ELISA was developed in 1970 and became rapidly accepted.
• ELISA is used for the diagnosis of AIDS.

Therefore the working principle of ELISA is antigen-antibody interaction.

Additional Information

• Phagocytic process: Phagocytosis is a process for ingesting and eliminating materials, including, foreign substances, and apoptotic cells, etc.
• Amplification process: PCR is a method for amplifying a specific region of DNA molecule without the requirement for time-consuming cloning procedures.
• Magnification process: Magnification is for enlarging the apparent size.

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.

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

Important Points

• ADA is mostly produced in the lymphocytes and thus lymphocytes are used in gene therapy technique.
• The lymphocytes are first obtained from the patient blood and then grown in culture medium in vitro.
• A cDNA (complementary DNA) for functional ADA is introduced into the lymphocytes using retroviral vectors.
• These genetically engineered lymphocytes are then returned to the patient.
• These lymphocytes, having the functional ADA gene, produce ADA in the patient.
• But the patient would still require periodic infusion of such genetically engineered lymphocytes.

Explanation:

• 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 vector in gene therapy for SCID.

• Planktons constitute the upper part of the aquatic ecosystem like water.
• Planktons are a diverse collection of organisms that live in large bodies of water unable to swim against the current.
• They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

Additional Information

• Planktons:
  • They are very minute or microscopic organisms freely floating on the surface of the water in a pond, lake, river, or ocean.
  • Planktons float near the surface of the water and provide food for many fish and other aquatic animals.
• There are two types of planktons:
  • Phytoplanktons:
    • The microscopic aquatic plants freely floating on the surface of the water in a pond, lake, river, or ocean.
    • The free-floating alga is an example of phytoplanktons.
    • Phytoplanktons are capable of producing food by the process of photosynthesis.
  • Zooplanktons: ​
    • The microscopic aquatic animals freely floating on water are called zooplanktons.
    • The free-floating protozoa are an example of zooplanktons.
    • A very, very small fish is also zooplankton.

Explanation:

• Hibernation is defined as the dormancy period of the cold-blooded animals in winters.
• The cold-blooded animals such as Lizards, Frogs, Bats, Hamster, Bear etc. tend to go under a dormancy period in winters in order to survive the cold temperature.
• Aestivation is defined as the slowing down of activity during the summer by some animals in order to cope with high temperatures.
• Regeneration is defined as the growth of new tissue from a destroyed one.
• The alteration in the genetic material that tends to change the characteristics of an organism is called Mutation.

Key Points

• Hibernation is defined as a state of reduced metabolic activity during the winter season 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.
• Some animals become dormant in the summer season which is called Aestivation.

• Mycorrhizae is a symbiotic association between a fungus and roots of higher plants.
• The term mycorrhiza refers to the role of the fungus in the plant’s rhizosphere, its root system.
• Mycorrhizal fungi allow plants to draw more nutrients and water from the soil.
• They also increase plant tolerance to different environmental stresses.
• They play a major role in the soil aggregation process and stimulate microbial activity.
• Fungistatic: It is a process that stops the growth of fungus. 
• Mutualism: It is an interaction between two organisms in which both are being benefitted. 
• Amensalism: It is a process in which one organism is harmed and the other has no effect. 

 Additional Information

Mycorrhiza is of two types:

1. Ectomycorrhiza - In this, the fungus forms a covering around the plant's roots. In this way, a layer like structure is formed on the surface of the roots, which is called peudoparenchymatous sheath. Ex - Pinus, Abies, Eucalyptus and Oak
2. Endomycorrhiza - In this the fungus does not form a layer on the roots of plants. They enter intracellularly in the roots. Intracellular fungal hyphae form branched structures in cells of roots called ''arubscule'' and unbranched structures called vesicles so these are also called Vesicular arbuscular mycorrhizal (VAM). Ex - Orchids

Explanation:

Ecological succession :

• It refers to the gradual changes that occur in an ecosystem over time.
• It may either begin with the formation of a new habitat or by damage to the existing habitat due to fires, floods, etc.
• For example, Acadia National Park suffered a wildfire and was completely destroyed.
• Initially, the forests had evergreen trees, but after the ecological succession, deciduous forests dominated the area.
• Ecological succession is of two types :
  • Primary succession
  • Secondary succession

• Primary succession- occurs in the barren area where there was no previously any type of living matter.
• Examples of primary succession are volcanic lava, igneous rock, sand dunes.
• Secondary succession- This type of succession occurs where vegetation was present previously but the vegetation was destroyed due to natural or artificial causes i.e. fire, flood, sudden changes in climate, and landslide.

​

• The causes of ecological succession are :       

         1. Climatic causes: E.g. rainfall, temperature, variations, humidity, etc.

         2. External causes: Soil conditions are affected by the process of migration, invasion, and competition among various aspects.

So, the correct answer is an option (4). Both A and R are false.

Additional Information

• Autogenic and Allogenic Succession:
  • When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession while change is brought about by outside forces known as allogenic succession.
• Autotrophic and Heterotrophic succession:
  • Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession and the ones in which the heterotrophs are greater in quant is known as heterotrophic succession.

Concept:

• Organisms need a constant supply of nutrients to grow, reproduce and regulate various body functions. The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state. It varies in different kinds of ecosystems and also on a seasonal basis.
• Nutrients are never lost from the ecosystems, rather they are recycled time and again indefinitely. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling.
• Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo rocks, air, water).
• Nutrient cycles are of two types
• Gaseous- the reservoir for the gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the atmosphere
• Sedimentary- for the sedimentary cycle (e.g., sulfur and phosphorus cycle), the reservoir is located in Earth‟s crust.
• Environmental factors, e.g., soil, moisture, pH, temperature, etc., regulate the rate of release of nutrients into the atmosphere. The function of the reservoir is to meet the deficit which occurs due to an imbalance in the rate of influx and efflux.

Explanation:

• The sulphur reservoir is in the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and sulphur rock) in the form of sulphates, sulphides and organic sulphur.
• It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in a salt solution.
• The sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide (H2S) and sulphur dioxide (SO2) add a gaseous component to its normal sedimentary cycle.
• Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels, from the surface of the ocean and from gases released by decomposition. Atmospheric hydrogen sulphide also gets oxidised into sulphur dioxide.
• Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid.

Additional Information

• Carbon is a minor constituent of the atmosphere as compared to oxygen and nitrogen. However, without carbon dioxide life could not exist, because it is vital for the production of carbohydrates through photosynthesis by plants. It is the element that anchors all organic substances from coal and oil to DNA (deoxyribonucleic acid the compound that carries genetic information).
• Carbon is present in the atmosphere, mainly in the form of carbon dioxide (CO₂). The carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. Carbon from the atmosphere moves to green plants by the process of photosynthesis, and then to animals. By process of respiration and decomposition of dead organic matter returns back to the atmosphere. It is usually a short term cycle.
• Some carbon also enters a long term cycle. It accumulates as un-decomposed organic matter in the peaty layers of marshy soil or as insoluble carbonates in bottom sediments of aquatic systems which take a long time to be released.
• In deep oceans, such carbon can remain buried for millions of years till geological movement may lift these rocks above sea level. These rocks may be exposed to erosion, releasing their carbon dioxide, carbonates and bicarbonates into streams and rivers.
• Fossil fuels such as coals, oil and natural gas etc. are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When they are burned the carbon stored in them is released back into the atmosphere as carbon dioxide.

• Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins that is, converted to ammonia, nitrites or nitrates before it can be taken up by plants.
• Nitrogen fixation on earth is accomplished in three different ways:
  a) By microorganisms (bacteria and blue-green algae)
  b) By man using industrial processes (fertilizer factories) and
  c) To a limited extent by atmospheric phenomena such as thunder and lighting
• Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions. These include free-living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root nodule plants (e.g. Rhizobium) as well as blue-green algae (e.g. Anabaena, Spirulina).
• Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialised bacteria: Nitrosomonas bacteria promote the transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.
• The nitrates synthesised by bacteria in the soil are taken up by plants and converted into amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem. During excretion and upon the death of all organisms nitrogen is returned to the soil in the form of ammonia.
• Certain quantities of soil nitrates, being highly soluble in water, are lost to the system by being transported away by surface run-off or groundwater. In the soil as well as oceans there are special denitrifying bacteria (e.g. Pseudomonas), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus completing the cycle.
• The periodic thunderstorms convert the gaseous nitrogen in the atmosphere to ammonia and nitrates which eventually reach the earth’s surface through precipitation and then into the soil to be utilized by plants.

Hydrogen Cycle-

• The hydrologic cycle is the continuous circulation of water in the Earth-atmosphere system which is driven by solar energy. Water on our planet is stored in major reservoirs like the atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater. Water moves from one reservoir to another by the processes of evaporation, transpiration, condensation, precipitation, deposition, runoff, infiltration, and groundwater flow.
• Water as an important ecological factor determines the structure and function of the ecosystem. Cycling of all other nutrients is also dependent upon water as it provides their transportation during the various steps. It acts as a solvent medium for their uptake of nutrients by organisms.

The correct option is ''Alien species invasion''

Concept:

• Causes of biodiversity losses: The accelerated rates of species extinctions that the world is facing now are largely due to human activities.
• There are four major causes called ''The Evil Quartet'' - Over-Exploitation, Alien species invasion, Habitat loss and fragmentation & Co-extinction.

Explanation:

Alien species invasions:

• When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive and cause the decline or extinction of indigenous species.
• The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.
• The introduction of African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.

Additional Information 

The other three major causes for biodiversity loss:

Over-exploitation:

• Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.
• Presently many marine fish populations around the world are over-harvested, endangering the continued existence of some commercially important species.

Habitat loss and fragmentation:

• This is the most important cause driving animals and plants to extinction.
• The most dramatic examples of habitat loss come from tropical rainforests.
• Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent. They are being destroyed fast.
• Besides total loss, the degradation of many habitats by pollution also threatens the survival of many species.
• When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to population declines.

Co-extinctions:

• When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.
• When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate.
• Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

The correct answer is A, C, D.

Explanation:

Statement A is correct.

• The species which are in danger of extinction and whose number have been reduced to a critical level are called endangered species. 
• Thus, endangered species are in danger of extinction.

Statement B is incorrect.

• Endemic species are species of plants and animals that can only be found in a particular area.

Statement C is correct.

• Increasing population and the introduction of new species may affect the natural habitat of endemic species and endanger their existence.
• Thus, endemic spices may come under the threat of extinction on introduction of new species in that region.

Statement D is correct.

• A hotspot is an area having endangered endemic species with very high levels of species richness.
• Criteria used for determining hotspot:

1. Number of endemic species, i.e., species that are not found anywhere else.
2. Degree of threat is measured in terms of habit loss.

• Thus, hotspots have numerous endemic species.

Key Points 

• The biosphere reserves are the areas meant for the conservation of biodiversity.
• These are large areas of protected land for the conservation of wildlife, plant and animal resources and traditional life of the tribals living in the area.
• The biosphere reserves help to maintain the biodiversity and culture of that area.
• A biosphere reserve may also contain other protected areas.
• The Pachmarhi Biosphere Reserve consists of one national park named Satpura and two wildlife sanctuaries named Bori and Pachmarhi

Additional Information

• There are a total of 18 biosphere reserves in India Eg. Nilgiri biosphere reserve, Nanda biosphere reserve, Pachmarhi biosphere reserve

Concept-

• Solid wastes refer to everything that goes out in the trash.
• Municipal solid wastes are wastes from homes, offices, stores, schools, hospitals, etc., that are collected and disposed of by the municipality.
• The municipal solid wastes generally comprise paper, food wastes, plastics, glass, metals, rubber, leather, textile, etc.
• Burning reduces the volume of the wastes, although it is generally not burnt to completion and open dumps often serve as the breeding ground for rats and flies.

Explanation-

• Hospitals generate hazardous wastes that contain disinfectants and other harmful chemicals, and also pathogenic micro-organisms.
• Such wastes also require careful treatment and disposal.
• The use of incinerators is crucial to the disposal of hospital waste.
• Incineration is a waste treatment process that involves the combustion of substances contained in waste materials.

Therefore Incineration is the technique that is most suitable for the disposal of biomedical waste.

Additional InformationLandfill

• Sanitary landfills were adopted as the substitute for open-burning dumps.
• In a sanitary landfill, wastes are dumped in a depression or trench after compaction and covered with dirt every day.
• Landfills are also not really much of a solution since the amount of garbage generation especially in the metros has increased so much that these sites are getting filled too. 

Recycling

• A solution to all this can only be in human beings becoming more sensitive to these environmental issues.
• All waste that we generate can be categorized into three types – (a) bio-degradable, (b) recyclable, and (c) non-biodegradable.
• It is important that all garbage generated is sorted.
• What can be reused or recycled should be separated out our kabadiwallahs and rag-pickers do a great job of separating materials for recycling.

The correct option is Both nitrates and phosphates.

Concept:

• Eutrophication is the natural ageing of a lake by nutrient enrichment of its water.
• In a young lake, the water is cold and clear, supporting little life.
• With time, streams draining into the lake introduce nutrients such as nitrogen and phosphorus, which encourage the growth of aquatic organisms.
• As the lake’s fertility increases, plant and animal life burgeons, and organic remains begin to be deposited on the lake bottom.
• Over the centuries, as silt and organic debris pile up, the lake grows shallower and warmer, with warm-water organisms supplanting those that thrive in a cold environment.
• Marsh plants take root in the shallows and begin to fill in the original lake basin.
• Eventually, the lake gives way to large masses of floating plants (bog), finally converting into the land.
• Depending on the climate, size of the lake, and other factors, the natural ageing of a lake may span thousands of years.

Explanation:

• Pollutants from man’s activities like effluents from industries and homes can radically accelerate the ageing process.
• This phenomenon has been called Cultural or Accelerated Eutrophication.
• The prime contaminants are nitrates and phosphates, which act as plant nutrients.
• They overstimulate the growth of algae, causing unsightly scum and unpleasant odours, and robbing the water of dissolved oxygen vital to other aquatic life.
• At the same time, other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved oxygen content. In such a fashion, a lake can literally choke to death.