The correct answer is an Oviparous animal.

Key Points

• Oviparous animals are the animals that lay eggs.
  • Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother.
  • This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and monotremes.

Additional Information

• Rhizomes are simply fleshy underground stems.
  • They grow underground or right at ground level with many growing points or eyes similar to potatoes.
  • Common examples of rhizomes include canna lilies, bearded Iris, ginger, and bamboo.
• Humans, fish, frogs, cats, and dogs, all reproduce by the method of sexual reproduction.

Explantion:

Sexual reproduction: 

• Involves the formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex.
• These gametes fuse to form the zygote which develops to form the new organism.
• It is an elaborate, complex and slow process as compared to asexual reproduction. (E.g. Mammals).
• The offsprings shows characteristic of both male and female and shows variation.

Asexual reproduction: 

• The reproduction in which an offspring is produced by a single parent without the fusion of gametes is called asexual reproduction. (E.g. Amoeba, Hydra)
• The offsprings is exact replica of their parents and genetically identical.

Asexual reproduction is carried out by a single parent through budding, fission, fragmentation, regeneration or spore formation.

• Since only a single parent is involved, there are negligible chances of variations in the progeny.
• As a result, the progeny appears morphologically and genetically identical to the parent. These are called clones.

The correct answer is Embryo sac.

• In a majority of flowering plants, one of the megaspores is functional while the other three degenerates.

Key Points

• The functional megaspore develops into the female gametophyte i.e. embryo sac.
• This method of embryo sac formation from a single megaspore is known as monosporic development.
• There is a characteristic distribution of the cells within the embryo sac. 
• Three cells are grouped together at the micropylar end and constitute the egg apparatus.
• The egg apparatus consists of two synergids and one egg cell.
• Three cells are at the chalazal end and are called antipodals.

Concept:

• Plants use various agents for pollination.
• The agents of pollination may be:
  • Biotic - Living organisms like bees, wasps, butterflies, birds or even small animals like rodents.
  • Abiotic - Non-living agents like wind and water.
• Plants produce morphologically different flowers for different types of pollination.
• Each type of agent requires different features in the pollens to effectively cause pollination.

Important Points

• Pollination by water is rare in angiosperms and is restricted to about 30 genera, which mostly comprise of monocots.
• Vallisneria, Zostera and Hydrilla are all pollinated by water.
• In Vallisneria:
  • The female flower reach the surface with the help of long stalk.
  • The pollens are released onto the surface.
  • Pollens are then carried to the stigma by water currents passively.
• In sea-grasses like Zostera:
  • The flowers remain submerged in water.
  • Pollens are released inside the water body.
  • Here, the pollens are long, ribbon-like which are passively carried by water currents inside the water.
• Water-pollinated pollen grains have a mucilaginous coating to prevent their wetting.

Additional Information

• Wind pollination -
  • It is the most common among abiotic pollinations.
  • Wind-pollinated pollens are light and non-sticky.
  • Stamens are well-exposed so that pollens are easily dispersed by the wind.
  • Stigma is usually large and feathery to trap the pollens from the air.
  • Example - Corn tassels represent feathery style that wave in the wind to trap pollens.
• Biotic pollination -
  • It is carried out by bees, flies, moths, wasps, butterflies, birds, bats or small animals.
  • Pollens are usually sticky or spiny to get stuck to the animal bodies.
  • Flowers are large, colourful and fragrant to attract the agents.
  • Flowers offer floral rewards in the form of nectar so that the agents visit repeatedly.
  • Some flowers may also provide a safe place to lay eggs in return for pollination.
  • Example - Yucca plant provides a place to lay eggs to the moth that pollinates it.

Explanation:

• A typical monocot seed has a short axis bearing plumule & a radical. The plumule differentiates to form the shoot while the radical forms the root system.
• The plumule is surrounded by a protective conical-shaped layer called the Coleoptile.
• The radical and root cap is surrounded by the protective undifferentiated sheath called the Coleorhiza.
• Both these sheaths provide protection to the developing root & shoot tips.
• Thus, the undifferentiated sheath which encloses the root cap in a monocot seed is termed as Coleorhizae.

Additional Information

• Calyptogen: It is a region of the root apical meristem that divides to form cap like protective structure, the root cap.
• Calyptra: It is a hood or cap-like structure present on the capsule of the sporophyte of certain mosses. It is formed by the expanded wall & neck of archegonium.

The correct answer is Apple.

• Apple is formed from the thalamus and not from the ovary. So, it is known as false fruit.

Additional Information

• False fruit is the fruits which are not derived from the ovary rather they are derived from some other reproductive part of the flower.
  • In apple, a major part of the fruit is formed from the thalamus, not from the ovary. So, it is known as false fruit.
• Parts of the plant involved in fruit formation are floral parts such as thalamus, peduncle and perianth.
  • False fruit is also referred to as Pseudo-carp or accessory fruit.
  • They are formed without fertilization.
  • False fruit is Parthenocarpic in nature and therefore do not contain seeds.
  • True fruit develops from the ovary which is mature and ripe. False fruits arise from alternative floral elements except for the ovary.
  • True fruits have seeds inside them. False fruits do not have seed in them as they are parthenocarpic in nature.

Concept:

• Menstrual cycle refers to the cyclical events that occur in a female primates, starting from puberty.
• The first menstruation is known as menarche and the end of it at the age of about 50 years is called menopause.
• The menstrual cycle in human females is about 28-30 days.
• Only one ovum is developed and released in each cycle.
• There are four phases of mensuration cycle:

Menstrual phase

• During this menstrual flow occurs and it lasts for 3-5 days.
• Menstrual flow results due to breakdown of endometrial lining of the uterus.
• The blood vessels and the tissue linings  break, which comes out through the vagina along with vaginal fluid.
• Menstruation only occurs if the released ovum is not fertilized.

Follicular phase (Proliferative phase)

• The menstrual phase is followed by the follicular phase.
• During this phase, the primary follicles in the ovary grow to a fully mature Graafian follicle.
• Simultaneously, the endometrium of the uterus regenerates through proliferation.
• The secretion of gonadotropins (LH and FSH) and ovarian hormones increases gradually during the follicular phase.
• These hormones stimulate follicular development as well as secretion of estrogens by the growing follicles.
• The ovary produces 5-20 follicles out of which 1 matures.

Ovulatory phase

• Pituitary hormones, LH and FSH attain a peak level in the middle of cycle (14th day).
• LH surge induces rupture of Graafian follicle release of ovum (ovulation).
• The mature egg is released from the ovary (13-17th day).
• If fertilization occurs within 24 hours, embryo develops otherwise the egg disintegrates.

Luteal phase (Secretory)

• Remaining parts of the Graafian follicle transform as the corpus luteum. 
• The corpus luteum secretes large amounts of progesterone which maintains endometrium.
• Endometrium is necessary for implantation of the fertilized ovum and other events of pregnancy.
• In the absence of fertilization, the corpus luteum degenerates.
• Endometrium lining disintegrates leading to menstruation, marking a new cycle.

Important Points

• The secretory phase is called as luteal phase as corpus luteum is formed during this time.
• This phase of menstrual cycle lasts for about 14 days.

The correct answer is L.H

Explanation-

• Placenta develops after implantation of embryo in human female in the uterus.
• After implantation, finger-like projections called chronic villi are formed which are surrounded by the uterine tissue and maternal blood.
• The chronic villi and uterine tissue together form a structural and functional unit between developing embryo and maternal body called placenta.
• The placenta also acts as an endocrine gland as it secretes the following hormones:
  • Human chorionic gonadotropin (HCG)
  • Progesterone
  • Estrogens
  • Human placental lactogen (hPL)
• Human chorionic gonadotropin- Its main function is to keep the corpus luteum's progesterone production up during early pregnancy.
• Progesterone- It is essential for maintenance of the endometrium for implantation of fetilised ovum and other events of pregnancy.
• Estrogen- It stimulates the proliferation of the endometrium of the uterine wall.

The increased production of these hormones during pregnancy is essential for supporting the fetal growth and metabolic change in the mother.

L.H-

• L.H (Luteinizing Hormone) is a gonadotrophic hormone.
• This hormone is produced and released by the cells of the anterior pituitary gland.
• It induces rupture of graffian follicle and thereby release of ovum (ovulation).

Additional Information Functions of placenta-

• Provides nutrients and oxygen to the developing embryo.
• Removes CO₂ and waste materials from the embryo.
• The placenta secretes hormones that are essential to maintaining pregnancy.

The correct answer is Lower than body temperature. Key Points

• For sperm development, the testes must maintain a temperature slightly cooler than normal body temperature. 

Important Points

• The penis is the male organ for sexual intercourse and urination.
• Semen and urine leave the penis through the urethra.
• The scrotum is a loose, pouch-like sack of skin that hangs behind the penis, containing the testes.
• The scrotum has a protective function, including the maintenance of optimal temperatures for sperm survival and function.
• Special muscles in the wall of the scrotum contract and relax in order to move the testes near the body.
• The epididymis is located at the back of the testis and connects it to the vas deferens.
• Its function is to store and carry sperm.
• The testis is the location for testosterone production.
• The coiled collection of tubes within the testes are the seminiferous tubules. Within these tubules, spermatogenesis takes place.

Key Points

• In human, fertilization takes place in the ampullary-isthmic junction of the fallopian tube.
• The zygote undergoes mitotic divisions by a process called cleavage.
• The cells formed after mitotic divisions are known as blastomeres.
• The dividing zygote gradually forms 2, 4, 8 and 16 celled stages.
• The 8-16 celled embryo is called morula, which continues to divide to form the blastocyst.

Therefore, the correct sequence of embryonic development in humans is Fertilization → Zygote → Cleavage → Morula → Blastocyst

Explanation:

• The developing embryo, in the meanwhile, keeps moving through the fallopian tube towards the uterine cavity.
• The blastomeres of the blastocyst are arranged into the outer layer of trophoblast and an inner cell mass.
• The inner cell mass later differentiates to form the embryo.
• The trophoblast gets attached to the endometrium as the uterine cells divide rapidly to cover it.
• This process is known as implantation, where the blastocyst gets embedded in the endometrium.
• After implantation, the inner cell mass or the embryo differentiates into 3 germinal layers (as humans are triploblastic animals):
  • Ectoderm - outer layer.
  • Mesoderm - middle layer.
  • Endoderm - inner layer.
• All the tissues and organs present in an adult body are formed from these 3 germinal layers.

Additional Information

• Human pregnancy lasts for about 9 months, which is known as the gestational period.
• It is usually divided into 3 trimesters, each of which shows some characteristic embryonic development.
• The process by which childbirth or delivery of fetus takes place is known as parturition.

The correct answer is Inside the uterus of a woman to block the fallopian tubes.

Concept:

Contraception:

• It is the method to prevent pregnancy in women.
• Any device or chemical which prevents pregnancy in a woman is called a Contraceptive.

Explanation:

Methods of contraception: 

• Barrier Method
  • Physical devices such as condoms (male) and diaphragm (female-covering on vagina) are used.
  • They prevent the fusion of sperm and egg.
• Chemical Method
  • The female uses 2 types of pills-oral and vagina.
  • Oral pills are made of specific hormones which prevent the release of the ovum (egg) into the oviduct.
  • Vaginal pills contain chemicals that kill the sperms.
• Intra-uterine contraceptive device(IUCD) 
  • The IUCD such as copper-T is placed inside the uterus to block the fallopian tube (oviduct).
  • It prevents the implantation of sperms from fertilizing the ovum. 
• Surgical method
  • In males, a small portion of sperm duct is removed by operation and both the cut ends are tied properly (Vasectomy). It prevents the sperms from coming out. 
  • In females, a small portion of the oviduct is removed and the cut ends are tied (Tubectomy). It prevents the egg from entering oviducts.

Concept:

• Assisted reproductive technologies or ART refers to the special techniques that are used to deal with infertility.
• The cause of infertility may be - physical, congenital, immunological, psychological, diseases or drugs.
• Specialized infertility clinics help in diagnosis and corrective treatments of couples to enable them in conceiving.
• Sometimes, medical assisted procedures are required for a couple to bear children.
• These ART procedures aim to resolve the specific issue that is restricting pregnancy.

Important Points

• In vitro fertilization (IVF) - It is the fertilization of sperm and ovum outside the body in laboratory conditions that is similar to that of the body.
• This is also known as the test tube baby programme.
• The ovum from the female and sperm from the male are collected.
• The gametes are then induced to fertilize and form zygote under simulated conditions in the laboratory (test tube).
• The next step is embryo transfer, where the fertilized zygote is transferred to the female body.
• This may take place by 2 ways:
  • ZIFT - Zygote intra-fallopian transfer is the transfer of the embryo, with less than 8 blastomeres, into the fallopian tube.
  • IUT - Intra-uterine transfer is the transfer of embryo with more than 8 blastomeres into the uterus, where implantation takes place.

Therefore, ZIFT is the ART method which is done after in-vitro fertilization.

Additional Information

• GIFT - Gamete intra-fallopian transfer is the transfer of only gamete into the female uterus.
• IUD - Intra-uterine devices are contraceptive devices that inserted into the uterus through the vagina of female by any medical professional.
• ICSI - Intra-cytoplasmic sperm injection is a method by which the sperm is directly injected into the ovum.

The correct answer is All (100 %).

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.

Phenotype: It refers to the external appearance. 

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

Allele: The alternative form of genes for the same character. For example, the character height has two traits tallness and dwarfness determined by alleles T and t respectively. 

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.

•  All the progenies of the F1 generation have heterozygous Tt condition i.e., they all have two different alleles. 
• Thus, all (100 %) of the progenies have dissimilar alleles or factors to determine the height of the pea plant. 

The correct answer is that the results depend on whether factors A and B lie on the same chromosome.

Concept:

Linkage: 

• When two genes are present on the same chromosome, the proportion of parental gene combinations is much higher than the non-parental type.   
• This physical association of two genes is termed as linkage.                    

Explanation:

Inheritance of two genes: 

• Mendel studied the inheritance of two genes in a dihybrid cross between round yellow and wrinkled green seeds.
• Parental combinations: Round yellow, RRYY and wrinkled green, rryy.
• Non- parental combinations: Round green and wrinkled yellow
• In the first generation, all seeds were round yellow.
• In the second generation, the progenies were in the ratio 9 round yellow :3 round green :3 wrinkled yellow:1 wrinkled green.
• This dihybrid cross demonstrates the law of independent assortment i.e., the alleles of two (or more) different genes get sorted into gametes independently of one another.

Chromosomal theory of inheritance:

• This theory was supported by Thomas Hunt Morgan. 
• He experimented on fruit flies (Drosophila melanogaster).
• He made a cross between yellow-bodied white-eyed females and brown-bodied red-eyed males.
• He observed that the two genes did not separate independently of each other and the ratio deviated from 9:3:3:1 significantly. 
• Morgan observed that the two genes were present on the same chromosome and are thus linked.

Thus, In the cross of AABB × aabb, it will be seen that the results depend on whether the factors A and B lie on the same chromosome.

The correct answer is 'XX - XY'.

• Human beings have an XX-XY sex-determination system.
• In this, the males have XY sex chromosomes.
  • They produce two types of gametes having X and Y chromosomes.
• The females have XX chromosomes.
  • They produce only one type of gamete having an X chromosome.

Key Points

• The sex of a child is determined by the type of chromosome he/she receiving from the father.
  • If sperm is having an X chromosome, then the child will be a girl.
  • If sperm is having a Y chromosome, then the child will be a boy.
• The Y chromosome carries factors responsible for triggering male development.
• The X chromosome carries factors responsible for triggering female development.

Additional Information

• The sex of a human embryo is determined at the very start of the time of its conception.
• When a baby gets conceived, a chromosome X or chromosome Y from the sperm cells fuses with the X chromosome of the egg cell.
  • This determines whether the baby/ fetus/ child/ embryo would be genetically male (XY) or genetically female (XX).
• Genetically, to be a male, the chromosome XY bond is needed while to be a female, the chromosome XX is needed.
• The Y chromosome is essential for the growth and development of male reproductive organs and without the Y chromosome, the embryo develops into a female.
  • This happens because of the SRY gene, which is the presence of the sex-determining region of the Y chromosome.
• Once the SRY gene gets activated, the cells create the testosterone and the anti-mullerian hormone which ensures the development of a single, male reproductive system.
• In XX embryos, the cells secrete estrogen which helps in driving the body towards becoming a female. 

The correct answer is Down syndrome.

Key Points

Down syndrome -

• Down syndrome is also referred to as Trisomy 21. Hence option 3 is correct.
• This extra copy changes how the baby's body and brain develop, which can cause both mental and physical challenges for the baby.
• Even though people with Down syndrome might act and look similar, each person has different abilities.
• Down syndrome is a condition in which a person has an extra chromosome.
• Chromosomes are small “packages” of genes in the body.
• They determine how a baby’s body forms and functions as it grows during pregnancy and after birth.
• Typically, a baby is born with 46 chromosomes.
• Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21.
• A medical term for having an extra copy of a chromosome is ‘trisomy.’
• Even though people with Down syndrome might act and look similar, each person has different abilities.
• People with Down syndrome usually have an IQ (a measure of intelligence) in the mildly-to-moderately low range and are slower to speak than other children.
• There are three types of Down syndrome -
  1. Trisomy 21
  2. Translocation Down syndrome
  3. Mosaic Down syndrome
• Diagnosis - There are two basic types of tests available to detect Down syndrome during pregnancy -
  1. Screening tests
  2. Diagnostic tests
• Treatment -
  • Down syndrome is a lifelong condition.
  • Services early in life will often help babies and children with Down syndrome to improve their physical and intellectual abilities.

Key Points

• Haemophilia is a frequently inherited genetic disorder that impairs the body's ability to form blood clots, a process required to stop bleeding.
• This results in people bleeding longer after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain.
• Those with a mild case of the disease may have symptoms only after an accident or during surgery.
• Bleeding into a joint can result in permanent damage while bleeding in the brain can result in long term headaches, seizures or a decreased level of consciousness. 

Thus, Haemophilia is a genetic disorder that leads to the non-clotting of blood.

The correct answer is 1953.

Key Points

• Deoxyribonucleic Acid (DNA)  was first isolated, analysed and reorganised as a unique macro-molecule by Friedrich Miescher in 1869.
• In 1953 James Watson and Francis Crick, aided by the work of biophysicists Rosalind Franklin and Maurice Wilkins, determined that the structure of DNA is a double-helix polymer, the molecule containing human genes.
  • The DNA double-helix bio-polymer of nucleic acid, held together by nucleotides which base pair together.
  • The structure of the DNA model was first published in the journal Nature by James Watson and Francis Crick in 1953.
• DNA is called the blueprint of life because it contains the instructions needed for an organism to grow, develop, survive and reproduce.
• DNA does this by controlling protein synthesis.
• The information in DNA is stored as a code made up of four chemical bases: adenine) (A, guanine (G), cytosine (C), and thymine (T). 
• Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people.

Additional Information

Concept-

• 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.
• It is completed in three steps Initiation, Elongation & Termination.
• It is necessary for all forms of life.

Key Points

​After transcription, the DNA molecule reassociates to form its original structure.

• After transcription, the two strands of DNA pairs.
• And the formed RNA provides the site for protein synthesis i.e translation.
• The translation is the process that takes the information passed from DNA as messenger RNA and turns it into a series of amino acids.

Additional Information

• Reverse transcription-polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA and amplification of specific DNA targets using polymerase chain reaction (PCR).
• It is primarily used to measure the amount of a specific RNA.
• This is achieved by monitoring the amplification reaction using fluorescence, a technique called real-time PCR or quantitative PCR (qPCR).

Concept-

• DNA replication is a semi-conservative process in which two parental strands separate and each acts as a template for synthesizing a complementary strand over it. 
• After completion of replication, each DNA had one parental strand and one newly synthesized strand of DNA.

Explanation-

• Replication of DNA occurs in the S phase of the cell cycle.
• During the S phase, the amount of DNA present In each cell doubles.
• If the initial amount of DNA is denoted as 2C then it increases to 4C.

Thereby DNA replication takes place during only one phase of the cell cycle.

​Additional Information

Interphase is divided into 3 phases:

• G1 phase/Post mitotic/Pre-DNA synthetic phase/Ist gap phase - Synthesis of different types of RNA and proteins.
• S-phase/Synthetic phase- Replication of DNA occurs in the S phase of mitosis.
• G2-phase/Pre mitotic/Post synthetic phase/IInd gap phase - Formation of tubulin protein required for the spindle fibre formation.

Concept-

• Gene expression is the mechanism at the molecular level by which a gene is able to express itself in the phenotype of an organism.
• The mechanism which stimulates the expression of certain genes and inhibits that of others is called regulation of gene expression.
• Francis Jacob and Monad proposed a mechanism called the operon model for the regulation of gene action in E.coli.
• An operon is a part of genetic material which acts as a single regulated unit having one or more structural gene, a promoter gene, a regulator gene.

Explanation-

• A regulatory gene is adjacent to the operator gene it controls.
• The regulator gene or inhibitor gene constantly transcribes mRNA to produce the repressor protein.
  • This repressor protein bind to the operator gene in the absence of an inducer. so no transcription of mRNA by the structural gene. Hence switch off operon.
  • In the presence of an inducer, the repressor has a higher affinity for the inducer than for the operator gene. The repressor-inducer fails to join with the operator gene, which is turned on.

So, Regulatory genes are involved in turning off or on, the transcription of a set of genes.

Additional Information

• Operator gene- It controls the synthesis of mRNA over the structural genes.
• The gene which has both non-functional and functional part called as a split gene.
  • The functional part is exon.
  • The non-functional part is intron.

The correct answer is DNA Polymorphism.

Key Points

• The basis of DNA fingerprinting is DNA Polymorphism.
• DNA polymorphism - These are inheritable mutations that occur at a high frequency in a population.
• Such variations occur frequently in non-coding DNA sequences and keep accumulating over generations.
• These mutations are the basis of variability or polymorphism in a population.
• Satellite DNA shows high degree of polymorphism and hence, was used by Alec Jeffreys for DNA fingerprinting.
• The DNA probes used were VNTRs.
• VNTR- Variable Number of Tandem Repeats or VNTRs are composed of 8-80 bp sequences which are tandemly repeated to form 1-30kb length of DNA.

Additional Information

• DNA fingerprinting is a laboratory technique used to establish a link between biological evidence and a suspect in a criminal investigation.
• A DNA sample taken from a crime scene is compared with a DNA sample from a suspect.
• If the two DNA profiles are a match, then the evidence came from that suspect.
• DNA profiling is the process of determining an individual's DNA characteristics.
• DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding.

The correct answer is Darwin.

Key Points

• The theory of evolution of species by natural selection was given by Darwin.
• Darwin conducted a sea voyage in a sailing ship called H.M.S Beagle as a part of his experiments on the theory of evolution.
• Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago
• Darwin's theory of natural selection is popularly known as 'Darwinism'.
• The evolution by natural selection, in a true sense, would have started when cellular forms of life with differences in metabolic capability originated on earth.
• Darwin went to the Galapagos Islands during his journey.
• Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution
• The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.
• Darwin’s finches represent one of the best examples of adaptive radiation.

Additional Information 

• Jagdish Chandra Bose is the inventor of the crescograph.
• Greger Mendel is the father of genetics.
• T H Morgan is the father of modern genetics.

Concept:

• The Earth was formed about 4.5 billion years ago in the solar system of the Milky Way galaxy.
• Life on Earth appeared about 4 billion years ago, which was 500 million years after the formation of Earth.
• But there has been a lot of speculation about how the first forms of life originated.

Important Points

• S. L. Miller conducted an experiment in 1953, which established the chemical theory of evolution as proposed by Oparin and Haldane earlier.
• Chemical evolution - refers to the formation of diverse organic molecules from the existing inorganic molecules.
• It was stated that the first form of life originated from non-living organic molecules, which were in turn formed from inorganic molecules.

Explanation:

• During the early years of formation of Earth, the climatic conditions were quite different from what it is in the present.
• Therefore, such conditions had to be created in the laboratory such as - high temperature, volcanic storms and reducing atmosphere with methane (CH4) and ammonia (NH3).
• To mimic the conditions, electric discharge was produced in a closed flask that contained CH₄, NH₃, H₂ and water vapour at 800°C.
• Formation of amino acids (organic molecules) were observed from this experiment, which supported the theory of chemical evolution.
• Formation of other organic molecules like sugars, nitrogenous bases, pigments and fats were also observed later by similar experiments.

​

The correct answer is Both 1 and 2.

Key Points

• In a given population one can find out the frequency of occurrence of alleles of a gene or a locus. Hence statement 1 is correct.
• This frequency is supposed to remain fixed and even remain the same through the generations. Hence statement 2 is correct.
• Hardy-Weinberg principle stated it using algebraic equations.
• This principle says that allele frequencies in a population are stable and are constant from generation to generation.
• The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium.
• The total of all the allelic frequencies is 1.
• Individual frequencies, for example, can be named p, q, etc. In a diploid, p and q represent the frequency of allele A and allele a.
• The frequency of AA individuals in a population is simply p². 
• This is simply stated in another way, i.e., the probability that an allele A with a frequency of p appears on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e. p². Similarly of aa is q², of Aa 2pq. Hence, p²+2pq+q²=1.
• This is a binomial expansion of (p+q)². When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change.
• Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.
• Five factors are known to affect Hardy-Weinberg equilibrium.
  • These are gene migration or gene flow, genetic drift, mutation, genetic recombination, and natural selection.
• When the migration of a section of the population to another place and population occurs, gene frequencies change in the original as well as in the new population.
• New genes/alleles are added to the new population and these are lost from the old population.
• There would be a gene flow if this gene migration, happens multiple times. If the same change occurs by chance, it is called genetic drift.
• Sometimes the change in allele frequency is so different in the new sample of the population that they become a different species.
• The original drifted population becomes founders and the effect is called the founder effect.
• Microbial experiments show that pre-existing advantageous mutations when selected will result in the observation of new phenotypes. Over a few generations, this would result in Speciation.
• Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave a greater number of progeny.
• The critical analysis makes us believe that variation due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in a changed frequency of genes and alleles in the future generation.
• Coupled to enhance reproductive success, natural selection makes it look like a different population.
• Natural selection can lead to stabilization (in which more individuals acquire mean character value), directional change (more individuals acquire value other than the mean character value), or disruption (more individuals acquire peripheral character value at both ends of the distribution curve).

• The theory of evolution by natural selection was proposed by Charles Darwin.
• It stated that all life forms arise due to natural selection of small inheritable changes that increase the survivability of a species.
• Darwin also defined evolution as descent with modification, meaning we have evolved from our ancestors through inheritable variations of characteristics.
• The evidences for evolution include:
  • Paleontological Evidence - Study of fossils have revealed that different life forms existed in different geological time-periods and similarities exist between existing and pre-existing life forms.
  • Anthropogenic Evidence - Overuse of pesticides and herbicides have resulted in natural selection of resistant varieties in much lesser time.
  • Comparative Anatomy & Morphology - Homology and analogy are based on comparisons between structure and functions of organs that show evolutionary adaptations in nature.
  • Embryological Evidence - The presence of some features in embryonic stages of all vertebrates and their absence in adult stages suggest common ancestry.

Key Points

• Homologous structures refer to the similar structures that differ in functions.
• These structures have evolved from a common ancestor.
• They show divergent evolution, meaning that they have undergone evolutionary modifications to perform different functions due to varying needs.
• Example - Thorns of Bougainvillea and tendrils of Cucurbita:
  • Both have evolved from branches by modification.
  • They have evolved for different functions - thorns for protection and tendrils for support.
• Homologous structures provide evidence in support of biological evolution.

Additional Information

• Analogous structures - refer to different structures that perform similar functions.
• Vestigial structures - refer to those structures that do not have a defined function in some species, but are completely functional in some other.
• Convergent evolution - is the evolution of species towards a common need, as shown by analogous structures.

The correct answer is Protozoa.

Mistake Points

• Dysentery can be caused by both bacteria and protozoa.
• Since the question asks about malaria along with dysentery, the correct answer will be Protozoa because malaria is always caused by a protozoa.

Key Points

• Protozoa are a group of unicellular eukaryotic organisms.
• Diseases like dysentery and malaria are caused by protozoa.
• The protozoa causing malaria is Plasmodium.
• The mosquito spreading malaria is anopheles mosquito.
• The dysentery caused by the protozoa Entamoeba histolytica is known as amoebic dysentery.

Additional Information 

• Disease caused by protozoa are - 
  • African trypanosomiasis.
  • Amoebiasis.
  • Malaria.
  • Chagas disease.
  • Leishmaniasis.
• Important diseases

Concept:

• Typhoid is caused by the pathogenic bacteria Salmonella typhi. 
• It is spread through contaminated food and water.
• It generally enters the small intestine and then migrates or moves to other organs through blood.
• The symptoms include: Constant high fever (39oC to 40oC), Stomach pain, Constipation, Loss of appetite, Weakness, Intestinal perforation, and death may occur in severe cases.

Explanation:

• Typhoid fever is confirmed by the Widal test.
• In this test bacteria causing typhoid is mixed with a serum containing specific antibodies obtained from an infected individual.
• Note: The test is named after its inventor, Georges-Fernand Widal.

​ Additional Information

Explanation:

• The thymus is a lobed organ situated near the heart and, beneath the breastbone.
• It is quite large at the time of birth but it gradually gets reduced with age.
• The thymus provides the micro-environment needed for the maturation & development of T-lymphocytes.
• The T-lymphocyte cells originate in the bone marrow but migrate or move to the thymus for maturation & development, hence if the thymus gland is removed from the new-born baby T-lymphocyte cells will not form.

​Additional Information 

• There are two main categories of WBCs – granulocytes and agranulocytes. Neutrophils, eosinophils, and basophils are different types of granulocytes, while lymphocytes and monocytes are agranulocytes.
• Neutrophils and monocytes (6-8 percent) are phagocytic cells that destroy foreign organisms entering the body.
• Eosinophils (2-3 percent) resist infections and are also associated with allergic reactions

Option 4 is the correct answer: Mule is a hybrid derived by crossing male donkey and a female horse.

• Usually in the name of hybrid animals first half is derived from the male and the second half is that of the female.
• The hybrids obtained are usually sterile.

Extra facts:

• Liger and Tigon are also a hybrid derived by crossing Lion and Tiger.

The correct answer is Fishing.

Key Points

• The term Blue revolution refers to the remarkable emergence of aquaculture as an important and highly productive agricultural activity.
• Dr. Hiralal Chaudhuri and Dr. Arun Krishnsnan are known as the Father of the Blue revolution.
• Aquaculture refers to all forms of active culturing of aquatic animals and plants, occurring in marine, brackish, or freshwaters.

Additional Information

• List of all the important Revolutions in India

The correct answer is 1, 2 and 3.

Key Points

Microorganisms

• It is also known as Microbes.
• It is the major components of biological systems on the planet earth, that are present everywhere, around us, in the soil, water, air, and both in and on our body.
• It is also found in other animals and plants.
• These organisms are so minute and vary in their size and shapes, that cannot be seen by naked eyes.
• They can only be seen through the microscope, therefore, they are also referred to as microscopic organisms.
• Industrial Uses of different types of microbes are:
• Algae
  • Algae are being used for a long period of time due to their high biomass production rate in different extreme habitats as compared to cereal-based crops.
  • Algae are categorized as third-generation biofuels due to their many advantages over different agricultural-based crops. 
• Bacteria
  • It is used in industry in a number of ways that generally exploit their natural metabolic capabilities.
  • They are used in the manufacture of foods and the production of antibiotics, probiotics, drugs, vaccines, starter cultures, insecticides, enzymes, fuels and solvents.
• Fungi
  • It is used in many industrial fermentative processes, such as the production of vitamins, pigments, lipids, glycolipids, polysaccharides and polyhydric alcohols.
  • They possess antimicrobial activities and are used in biomineralization, as a food for its high protein contents and as biofertilizers.
• Protozoa
  • It plays important role in wastewater treatment processes, in both activated sludge and slow percolating filter plants.
• Virus
  • It can also be used for different applications in pharmacology, cosmetics, electronics, and other industries. Thus, viruses are no longer only seen as enemies.
• Hence, Option 4 is correct.

Concept-

• Fermentation is a chemical process in which bacteria and other micro-organisms break down starches and sugars within the foods.
• Bacteria alone or in combination with yeasts were found to be responsible for the fermentation of dosa.

Key Points

• Lactobacillus bacteria causes fermentation in dosa batter releasing CO₂ gas.
• Saccharomyces cerevisiae(Baker's yeast) is also used in making dosa for making the batter soft and fluffy.

Additional Information

• Anaerobic respiration is similar to aerobic respiration, except, the process happens without the presence of oxygen. Aerobic respiration takes place in presence of oxygen gas.

The correct answer is Fungi.

Key Points

• The penicillin is a type of antibiotic.
• It is produced from a fungus called as Penicillium notatum.
• Penicillin was the first antibiotic to be discovered.
• Penicillin was discovered by Alexander Fleming.
• Fleming, Chain and Florey were awarded the Nobel Prize in 1945.
• Penicillin was extensively used to treat American soldiers wounded in World War II.
• Penicillin works by interfering with bacteria cell walls.
• Antibiotics like penicillins produced by useful microbes are used to kill disease-causing harmful microbes.

Key Points

• Reverse transcription-PCR-Many copies of DNA sequence - CORRECT
  • Reverse transcriptases are RNA-dependent DNA polymerase.
  • It is a type of DNA polymerase enzyme that transcribes single-stranded RNA into DNA.
  • mRNA is used as a template for a DNA product.
  • Mature mRNA do not contain introns. 
  • Because of the removal of introns, the DNA produced is not an exact copy of genetic DNA, called cDNA.
  • This cDNA can be used in a Polymerase Chain Reaction (PCR).
  • The polymerase chain reaction is a laboratory method used to amplify a specific region of DNA and produce millions of copies.
  • The PCR can then produce many copies of the cDNA sequence.
  • After reverse transcription of mRNA into cDNA, cDNA can be used in PCR amplification.
  • mRNA is not directly used for PCR and is reverse transcribed into cDNA first.
  • This is because RNA cannot be polymerized by DNA polymerase.​
  • This process is specifically called reverse transcription PCR or RT-PCR.

​​

Additional Information

• Central dogma-RNA -DNA Protein -RNA - INCORRECT
  • The central dogma is the explanation of the flow of genetic information in all biological systems.
  • The central dogma of molecular biology as proposed by Francis Crick states that the genetic information flows thus:

• Transcription-Formation of RNA and proteins - INCORRECT
  • Transcription is the process by which the information in a strand of DNA is copied into a new molecule of mRNA.
  • Transcription is carried out by DNA-dependent RNA polymerase.
  • Proteins are formed by the translation process and NOT transcription.
  • We can also see this from the central dogma mentioned above.
• RNA silencing-Use of dsRNA - INCORRECT
  • RNA interference (RNAi) technology is used to silence a gene.
  • This technology is used to obtain disease resistance in plants.
  • After an infection, the infectious organism produces RNA in the host cell to express toxins, produce more progeny, virus coat protein, etc.
  • This RNA produced by the infectious agent can be silenced using a complementary dsRNA produced by the host.
  • This dsRNA, helps in recognizing and transferring to the target RNA from nematodes, bacteria, or viruses.
  • One of the strands is degraded and a single-stranded complementary RNA binds to the target RNA.
  • The binding of ssRNA (from host) prevents the translation of the mRNA (silencing).
  • This option is incorrect because the silencing of the infectious RNA is carried out by ssRNA.

Concept:

Antibiotic resistance

• Antibiotic resistance gene is a gene that can help the bacteria survive even in presence of an antibiotic.
• The bacteria becomes resistant to the antibiotic.
• Antibiotic resistance genes are also selectable marker for the identification of transformed bacteria.
• Selectable markers are the genes that can help identity transformed cells and differentiate them from non-transformed cells. 
• Genes giving antibiotic resistance are good selectable markers.
• So, if all cells are grown on a medium containing the antibiotic, only the cells having the resistant genes will grow.
• Such transformed cells can then be isolated from non-transformed cells that do not contain resistance genes.

Key Points

• After the vectors are introduced into the host cell, the transformed cell is selected using a selectable marker.
• This selectable marker can be an antibiotic resistance gene.
• The selection of transformants is done on the basis of insertional inactivation of a gene, in this case the antibiotic resistance gene..
• Insertional Inactivation - When a DNA fragment is inserted within the coding sequence of a gene, the gene gets inactivated and can not be expressed.
• So, after insertional inactivation, the antibiotic resistance property will be lost.
• The non-transformed cells do not have any recombinant DNA.
• Therefore, non-transformed cells are resistant to both ampicillin and tetracycline.
• For example, if we insert a DNA fragment into the plasmid pBR322 at the BamHI site, there will be insertional inactivation of the tetracycline resistance gene.
• So, the transformed cell with the recombinant DNA will have only ampicillin resistance and not tetracycline resistance.
• To identify transformants and non-transformants, we first grow the cells in a medium containing ampicillin.
• Here, both transformed and non-transformed cells will form colonies.
• These colonies are then transferred to a medium containing tetracycline, where only the non-transformed cells will grow.
• This is because, in transformed cells, there is insertional inactivation of tetracycline resistance due to the introduction of the gene of interest at the BamHI site.
• Thus we can select the transformed colonies from the ampicillin medium.

• Therefore, an antibiotic resistance gene can be used in the selection of transformed bacterial cells.

  

Additional InformationCompetent Bacteria Cell

• The bacteria that are able to uptake the recombinant DNA vector are called competent bacterial cells.
• Cells are made competent by subjecting them to polyethylene glycol, calcium chloride, heat shock, etc.

Transformed bacterial cell

• Transformation is the genetic alteration of a cell by taking up foreign genetic material.
• The source of foreign genetic material can be genetically engineered genes, vector carrying genes of interest, or horizontal transfer of genes. 
• The cell can directly uptake genes from its surroundings or genes can be penetrated by the cell membrane. 
• Transformed cell is a more appropriate term for cells carrying genes modified by genetic engineering.
• The transformed cells may or may not produce any gene product.

Recombinant Bacterial cell

• The word recombinant is more frequently used for DNA rather than an entire cell.
• A recombinant cell is a cell containing a modified gene, other than what was originally present in it. 
• The recombinant cell refers to the bacterial cell containing the recombinant DNA that can efficiently produce the recombinant protein product.

Concept:

• Plasmid is a small, circular, extra-chromosomal, self-replicating double-stranded DNA molecule.
  • Small - Smaller than the chromosomal genetic material with a lesser number of genes as compared to the chromosomal genetic material
  • Circular - plasmid is not linear, its ends are covalently joined to each other
  • Extra-chromosomal - it is physically detached from the chromosomal DNA, separate from chromosomal DNA
  • Self-replicating plasmid replication is independent of chromosomal DNA replication.
  • ds DNA - there are two strands of DNA joined by hydrogen bonds between the nitrogenous bases
• The plasmid is most commonly found in prokaryotes like bacteria, but some archaea and yeast may also have it.

• Plasmid is a cellular component found in bacteria which are suitable to use as vector to transfer genes from one organism to another.​

Important Points

Assertion - INCORRECT

• Plasmids are extrachromosomal but they are NOT single stranded.
• They are double-stranded.

Reason - INCORRECT

• Plasmids are found in prokaryotic cells and not in eukaryotic cells.

Therefore, both assertion and reason are false.

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.

Key Points

Tools required for constructing recombinant DNA:

1. Restriction Enzyme 
   • Restriction enzyme is a protein that cleaves DNA strands.
   • It cuts DNA at sequence-specific sites.
   • It produces DNA fragments with a known sequence at each end. 
   • The DNA is isolated from the organism that has the gene of interest.
   • The gene of interest from DNA is cut using these enzymes, which are also known an Restriction endonucleases or molecular scissors.
   • The vector to which the gene of interest is joined is also cut using the same restriction enzyme.
   • Cutting with the same restriction enzyme makes the cut ends of vector and gene of interest complementary, which can then bind to each other.
2. DNA fragment
   • DNA fragments are produced by restriction digestion.
   • The action of restriction enzyme on a DNA strand is called restriction digestion.
   • To produce a recombinant DNA, cut DNA  fragments are amplified or increased in number to millions by using Polymerase Chain Reaction (PCR).
3. ​DNA ligase
   • The DNA fragments from different sources can be joined to each other by DNA ligase.
   • 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.

Explanation:

• In genetic engineering, E. coli acts as a host cell for the vector carrying the gene of interest or recombinant DNA.
• After the production of the recombinant DNA, it is introduced into E. coli.
• The host cell helps in expressing the gene of interest or the recombinant DNA .
• The protein product can then be extracted from the host cell.
• Therefore, E. coli is not required in the preparation of a recombinant DNA molecule.

​Confusion Points

• Though the plasmid is used as vector for preparing a recombinant DNA molecule, the entire bacteria like E. coli is not required.
• The plasmid is an extra-chromosomal DNA present in a bacterial cell.

Key Points

• Bt-cotton is a genetically modified crop plant, which carries the gene for Bt-toxin.
• Bt-toxin is an insecticidal protein produced by Bacillus thuringiensis.
• The gene encoding this toxin is named as 'cry' gene and so Bt-toxin is also known as Cry protein.
• This toxin is effective in killing several insect groups like -
  • Lepidopterans - Tobacco budworm, armyworm.
  • Coleopterans - Beetles.
  • Dipterans - Flies, mosquitoes.
• These genes produce insect-group specific toxins and thus can be introduced into crop plant genomes to make them pest-resistant.
• For example, the genes cryIAc and cryIIAb are effective against cotton bollworms, while the gene cryIAb is effective against corn borers.
• Thus, Bt-cotton is resistant only against cotton bollworms.

Additional Information

Mechanism of Action of Bt-toxin:

• The bacteria produce crystals containing insecticidal Cry proteins during a particular growth phase.
• The protein exists in the inactive protoxin form in the bacteria.
• It gets activated in the alkaline gut of insects, where the crystals get solubilized.
• This releases the active toxin, which binds to the midgut epithelial cells of insects.
• This creates pores causing cell swelling and lysis.
• This leads to the death of the insect.

Key Points

• To produce antibiotics on a large scale, bacteria like E. coli, can be used.
• The gene encoding the antibiotic can be inserted into the bacterial cell.
• After incorporation, the bacteria will express the gene and produce the antibiotic.
• To achieve this, first we need to find the gene which can produce the antibiotic of concern.
• Once we find an organism which produces the said antibiotic, we can isolate the gene from the organism using the biotechnological tools.
• The isolated gene can then be expressed in E. coli using recombinant DNA technology.
• The gene is inserted into the bacterial plasmid.
• The expressed gene will produce the antibiotic which can then be manufactured commercially.

Steps:

Finding the organism which produces the antibiotic → identifying the gene which encodes antibiotic production → isolation of identified gene → insertion of gene into plasmid of bacteria

The correct answer is 1(A), 2(C), 3(D), 4(B).

Key Points

• Regulate:
  • Some organisms can maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc.
  • All birds and mammals and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation). 
• ​Conform:
  • An overwhelming majority (99 per cent) of animals and nearly all plants cannot maintain a constant internal environment.
  • Their body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids changes with that of the ambient air, water osmotic concentration. These animals and plants are simply conformers.
  • Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and hummingbirds. 
• ​Migrate:
  • The organism can move away temporarily from the stressful habitat to a more hospitable area and return when the stressful period is over.
  • Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas.
  • Every winter the famous Keoladeo National Park (Bharatpur) in Rajasthan host thousands of migratory birds coming from Siberia and other extremely cold northern regions.
• Suspend:
  • In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them to survive unfavourable conditions – these germinate on the availability of a suitable environment.
  • In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions.

Key Points

• A population at any given point of time comprises of individuals of different age groups.
• The percentage of individuals of a given age or age group is known as age distribution, which is an important population attribute.
• Age pyramid is a structure that results from the plotting of the age distribution of a population.
• For a human population, 3 age groups are considered:
  • Pre-reproductive
  • Reproductive
  • Post-reproductive

Important Points

• The age pyramids usually include both male and female individuals.
• The shape of the pyramid shows the growth status of a population.
• They can be of 3 basic types:
  • Expanding - Pre-reproductive group is maximum and post-reproductive group is minimum.
  • Stable - The pre-reproductive and reproductive groups are almost equal, while the post-reproductive is less.
  • Declining - Pre-reproductive group is lesser than the other age groups.

Explanation:

• In the given question, the diagram is showing less pre-reproductive than reproductive group.
• Therefore, it represents a declining population.

Concept:

• A habitat always has more than one species, which interact with the environment as well as among themselves.
• These interactions help in forming a functional biotic community.
• The interactions can be:
  • Intraspecific - takes place among the individuals of the same species.
  • Interspecific - takes place among populations of two different species.
• Based of their effects, the interspecific interactions can be of 3 types:
  • Beneficial - These are positive interactions where either one or both of the species are benefitted.
  • Detrimental - These are the negative interactions where one or both of the species are harmed.
  • Neutral - These are interactions where the species is not affected.
• It is important to note here that an interaction that is beneficial to one species may or may not be beneficial to the other species.

Major Types of Interactions:

Important Points

• Competition is a type of interaction in which both the species is negatively affected.
• In competition, each species significantly lowers the fitness of another species to get an advantage over the available resources.
• Example - When goats were introduced on the Galapagos island, it led to the extinction of the Abingdon tortoise because of the greater browsing efficiency of the goats.
• Competition may take place for a number of reasons like -
  • Food
  • Habitat space
  • Breeding ground

Explanation:

• There are may theories regarding interspecific competition like Gause's 'Competitive Exclusion Principle'.
• It states that when resources are limiting and two closely related species compete for the same resources, they cannot co-exist indefinitely.
• The competitively inferior species gets eliminated.
• Elimination of any species from a functional habitat or ecosystem will eventually change the dynamics of that ecosystem.
• Therefore, competition affects both the species negatively.

Concept:

• Saprophyte - 
  • Any organism that survives or feeds on dead and decaying organic matter.
  • They convert complex organic compounds of a decomposing body into simpler ones.
  • This helps in the process of decomposition.
  • They are mostly fungi and bacteria.
• Parasite - 
  • Organisms that attack living organisms rendering them weak.
  • Parasites live off other organisms called hosts, harming them and sometimes causing death.
  • Parasites live in or on the host and get their food from the host.
• Lichens - 
  • A close symbiotic association between algae and fungi.
  • The fungi provide shelter and protection to algae and the algae provide photosynthetic products to the fungi.
  • Lichens only grow in pollution-free environments and hence are used to detect pollution.
• Mycorrhiza - 
  • Symbiotic association between the plant roots and fungi.
  • Fungi absorb nutrients from the soil and provide them to the plant.
  • Plants in turn provide fungi with photosynthetic products.

Key PointsThe correct match is as follows:

So, option (1) is the correct answer.

Key Points

• Ecological pyramids are graphical representations of trophic systems in an ecosystem.
• Shape of pyramid can be upright (base broader than top), inverted (top broader than base) or variable.
• They are mainly of 3 types:

1. Pyramid of Number -
   • It is based on the number of individuals in each trophic level.
2. Pyramid of Biomass - 
   • It is based on the quantitative biomass of organisms present in unit area (standing crop), for each trophic level.
3. Pyramid of Energy -
   • It is based on the energy content available at each trophic level.

Explanation:

• Trophic system refers to the system in which energy flows from one trophic level to another.
• Trophic level is the specific place in the food chain that is occupied by an organism based on their source of food.
• In an ecosystem, the trophic level starts with a producer and is succeeded by different levels of consumers.
• In a lake ecosystem, the usual food chain is like:

Phytoplankton → Zooplankton → Small fish → Big fish

• When we consider the quantitative biomass of each of the trophic levels, we find that the biomass produced by phytoplanktons is the minimum.
• Phytoplanktons are autotrophic planktons that act as producers for this ecosystem.
• As we gradually move up the trophic levels, we find the biomass to be increasing.
• The big fishes will have the maximum biomass in this ecosystem.
• Therefore, the pyramid of biomass is inverted in a lake ecosystem.

​

Concept:

• Food chain - is a linear sequence of flow of energy takes place between different organisms that are related to each other by the food they consume.
• Food chains outline who eats whom in an ecosystem.
• There are two main types of food chains:
  • Grazing - These food chains start with the producers and are the major system of energy flow in aquatic ecosystems and grasslands.
  • Detritus - The starting point is dead organic matter from other food chains and is the major energy flow system in forest ecosystems.

Key Points

• The organisms are classified into different categories according to their feeding order:
  • Producers - synthesize food from solar energy. This covers all photosynthesizing plants and algae.
  • Primary consumers - come immediately after producers and comprise herbivores that feed on the producers directly.
  • Secondary consumers - feed on primary consumers and hence comprise of carnivores.
  • Tertiary consumers - feed on secondary consumers and are also carnivores.
  • Decomposers - break down dead, decaying organisms into simpler inorganic substances. E.g. - Fungi.

Explanation:

• Among the given food chains of grassland ecosystem, the correct sequence is: Grass → Insect → Snakes → Birds
• Here:
  • ​Grass - Producer
  • Insect - Primary Consumer
  • Snakes - Secondary Consumer
  • Birds - Tertiary Consumer
• This food chain is similar to the one given in the diagram below:

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.

Key Points

• Biodiversity can be studied at all levels of biological organizations.
• Depending on these levels, biodiversity can be categorized into 3 types:

1. Genetic Diversity -
   • It is the diversity in the genetic make-up of a species due to variations in the gene pool.
   • Example - India has >50,000 genetic strains of rice and about 1000 varieties of mango.
   • Therefore, this refers to the study of diversity at below species level.
2. Species Diversity -
   • It refers to the richness of species in an ecosystem.
   • This refers to the study of diversity at the species level.
   • Example - The Western ghats have greater amphibian species diversity than the eastern Ghats.
3. Ecosystem Diversity -
   • It is the diversity of ecosystems in a particular geographical area.
   • Each ecosystem comprises of diverse communities of organisms.
   • Example - India has greater ecosystem diversity than a Scandinavian country like Norway as it has deserts, rain forests, mangroves, coral reefs as well as alpine meadows.

Key Points 

• Red Data Book is the sourcebook that keeps a record of all the endangered animals and plants.
• There are different Red Data Books for plants, animals and other species.
• The Red Data Book is also known by the name ''Red List of Threatened Species''.
• The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
• Some examples of recent extinctions include:
  • Dodo (Mauritius)
  • Quagga (Africa)
  • Thylacine (Australia)
  • Steller’s Sea Cow (Russia)
  • Three subspecies (Bali, Javan, Caspian) of the tiger.
• The last twenty years alone have witnessed the disappearance of 27 species.

Concept:

• Biochemical Oxygen Demand (BOD) is defined as the amount of dissolved oxygen needed by aerobic microorganisms in a water body to break down the organic matter.
• Dissolved Oxygen is the amount of oxygen in a water body that is available to all aquatic organisms.
• When sewage is discharged into a flowing river, the amount of organic matter increases.
• This leads to an increase in the number of microbes that can degrade the organic matter.
• Thus there is an increase in the uptake of oxygen by the micro-organisms.

Explanation:

• Statement I : INCORRECT
  • Sewage discharge in a flowing river causes an increase in biochemical oxygen demand (BOD) due to the biodegradation of organic matter by microbes.
• Statement II : INCORRECT
  • Sewage discharge in a flowing river causes a sharp decrease in dissolved oxygen (DO) downstream from point of discharge due to increased consumption of DO by microbes. This causes the mortality of fish and other aquatic creatures.
• The increase in BOD and decrease in DO leads to the mortality of fish and other aquatic creatures.

Additional Information:

• During the 1970s, scientists proved that the fertilizer and sewage runoff from farms adds significant amount of nutrients to lakes which promotes the growth of primary producers.
• When the primary producers die, detritivores decompose them which results in reduced dissolved oxygen content of the lake water.
• The ecological impacts of this process is called eutrophication (Greek eutrophos: well nourished) and include the loss of many fish species from the lakes.

​Option 1, 3 and 4 contain only biodegradable commodities while option 2 has plastic which is a non-biodegradable item hence, the correct option is 2 i.e. ''Grass, Wood and Plastic''.

Key Points 

• The wastes can be broadly divided into two main categories -  biodegradable waste and non-biodegradable waste.

Biodegradable wastes:

• The wastes that can be degraded or decomposed in nature by the action of different microbes and other living things using processes like composting, aerobic digestion, anaerobic digestion, etc are called Biodegradable wastes.
• Examples - wood, fruits, grass, flower, cakes, vegetables, dead animals and plants, etc.

​Non-biodegradable wastes:

• The wastes that cannot be degraded or decomposed in nature by the action of different microbes and other living things using processes like composting, aerobic digestion, anaerobic digestion, etc are called Non-Biodegradable wastes.
• Examples include plastic, glass, metallic wastes, etc.