Biology Mock Test - 4

Concept:

• Asexual reproduction is a mode of reproduction in which new offspring are produced by a single parent without the involvement of gametes or fertilization.
• Offspring produced by such reproduction are genetically identical copies of the parents.
• Asexual reproduction is of the following types:
•  Binary fission
•  Budding
•  Fragmentation
•  Gemma-cup formation
•  Spore formation
•  Vegetative propagation.

Explanation:

Vegetative propagation:

• It is a form of asexual reproduction of a plant wherein a new plant grows from stems, roots, and leaves.
• Vegetative propagation can be natural and also can be done artificially.
• The parts which participate in vegetative propagation are called vegetative propagules.
• Vegetative propagules of different plants: 
   

Offset in Eicchornia (Water hyacinth)

Concept-

• Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
• The offspring grow, mature, and in turn, produce new offspring.
• Thus, there is a cycle of birth, growth, and death.
• Reproduction enables the continuity of the species, generation after generation.
• Based on whether there is the participation of one organism or two in the process of reproduction, it is of two types. Asexual and sexual reproduction.

Explanation- 

• Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures.
• The most common of these structures are zoospores that usually are microscopic motile structures. 
• Zoospores are thin-walled and formed during favourable conditions.
• Hence, statement 2nd is incorrect.

Additional Information

• When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual. 
• As a result, the offspring produced are identical to one another and are also exact copies of their parent.
• The term clone is used to describe such morphologically and genetically similar individuals.
• Common asexual reproductive structures are conidia (Penicillium), buds (Hydra), and gemmules (sponge).

The incorrect answer is a Fallopian tube.

Concept-

• A flower is the sexual reproductive organ in plants it consists of four basic parts, that are petals, sepals, stamens, and pistil.
• The petals attract insects and birds in order to pollinate(transfer pollen grains from stamen to stigma).
• The flower buds are protected by sepals (green color).
• The stamens which are the male part and the pistil that is the female part help in the reproduction system.

Explanation-

• The gynoecium is the female reproductive organ.
• The unit of gynoecium is called pistil or carpel.
• The carpel is differentiated into three parts-
  • (1) Stigma (2) Style (3) Ovary
• The stigma serves as a landing platform for pollen grains.
• The style is the elongated slender part beneath the stigma.
• The basal bulged part of the pistil is the ovary.

Therefore the Fallopian tube is not a part of the female reproductive system of the plants.

Additional Information

​Fallopian tube​

• The Fallopian tubes are found in the female reproductive system of humans.
• Fertilization of sperm and egg takes place in Fallopian tubes.
• In females, one fallopian tube is present on either side of the uterus.
• It is in the fallopian tube that the fertilization of the egg by the sperm takes place.
• The uterus has 3 mains parts, the upper part called the fundus, the main body called corpus, and the lower part called the cervix.

The Correct Answer is Transfer of pollen from anther to stigma of the same flower.

 Key Points

• The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination.
• When the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant), it is called self-pollination.

 Important Points

• A tube grows out of the pollen grain and travels through the style to reach the ovary helps the landed pollen grain to reach the female-germ cell.
• Thus, pollination is said to take place when pollen grains are carried from the anther to the stigma of the flower.
• If the transfers occur in a different flower it is called cross-pollination.
• Cross-pollination can be facilitated by insects, birds, animals, air, or water.

 Additional Information

• The flowers which contain only one sex organ, either stamens or carpels, are called unisexual flowers.
• The flowers of papaya and watermelon plants are unisexual flowers.
• The flowers which contain both the sex organs, stamens as well as carpel, are called bisexual flowers.
• The flowers of hibiscus and mustard plants are bisexual flowers.

The correct answer is through one of synergids.

Explanation-

• Pollen tube are the male reproductive part of the flowering plant.
• In plants, the pollen tube transfers the pollen grains from the stigma (male reproductive part) to the ovary (female reproductive part).
• The pollen tube enters the embryo sac through one of the synergids by the following mechanism.
  • The pollen tube grows through the tissues of the stigma and style and reaches the ovary.
  • As we know, that in some plants, pollen gains are shed at two-celled condition (a vegetative cell and a generative cell).
  • In such plants, the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma.
  • In plants which shed pollen in the three-celled condition, pollen tubes carry the two male gametes from the beginning. 
  • Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters the embryo sac through one of the synergids.
  • The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, in which the filiform apparatus is crucial in guiding pollen tubes into the synergid.

​

Thus, the Pollen tube enters the Embryo sac through the one of synergids.

Concept-

• The seeds are protected inside the fruit.
• The ripened ovule is known as a seed.
• A mature seed is having three main parts - Seed coat, embryo, and endosperm.
• Fruits are the results of fertilization, there are a few species in which fruits develop without fertilization. Such fruits are called parthenocarpic fruits.
• Parthenocarpy can be induced through the application of growth hormones and such fruits are seedless.

Explanation-

• In coconut parthenocarpy is useless.
• Because its edible part is the endosperm and endosperm is the part of the seed.
• Its edible endosperm is what it is valued for.

Therefore seedless fruits are of no use in Coconut.

Additional InformationTomato

• Tomato is a berry fruit. 
• These fruits develop from mono or multicarpellary, syncarpous ovary.
• Tomato is a true berry (Plant with superior ovary).

Banana

• Banana is a false berry (Plant with inferior ovary).

Explanation:

• Ovulation is the phase of the menstrual cycle where the ovum  gets released from the graffian follicle, this phase is regulated  by the activity of different hormones like FSH (follicle-stimulating hormone) and LH (luteinizing hormone)
• Both LH and FSH attain a peak level in the middle of the menstrual cycle (about 14th day). 
• Rapid secretion (increase) of LH leading to its maximum level during the mid-cycle (peak of ovulation) called LH surge induces rupture of graffian follicle and thereby the release of an ovum (ovulation)

Additional Information 

• After Ovulation, the ruptured Graffian follicle gets transformed into the Corpus luteum.
• The Corpus luteum gets stimulated by the rising levels of LH and starts secreting the Progesterone hormone.
• Progesterone inhibits the uterine contraction so that the pregnancy can be maintained. For this reason, it is called the pregnancy hormone.

The correct answer is ​Epididymis.

• Epididymisis a part of the male reproductive system.

​

Key Points

• The epididymis is a long-coiled Tubule that stores the sperm and also secretes a fluid that nourishes the sperms.
• The posterior end of the epididymis is called cauda epididymis and it lies along the inner side of each testis.
• Cervix, ampulla, and vagina are part of the female reproductive system.
• The ampulla is the longest part of the fallopian tube.
• Fertilization of egg or ovum takes place in the ampulla region.
• The cervix joins the part of the anterior wall of the vagina and opens into it whereas the vagina is the long tube structure that extends from the cervix to the outside of the body.

The correct answer is 1 and 3 only.

Key Points

• The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis.
  • Hence statement 1 is correct.
• Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth.
• These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes.
• Each primary oocyte then gets surrounded by a layer of granulosa cells and is called the primary follicle. 
• A large number of these follicles degenerate during the phase from birth to puberty.
• Therefore, at puberty, only 60,000-80,000 primary follicles are left in each ovary.
• The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles.
• The secondary follicle soon transforms into a tertiary follicle which is characterized by a fluid-filled cavity called the antrum.
• The theca layer is organized into an inner theca internal and an outer theca externa.
• It is important to draw your attention that it is at this stage that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division.
• It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.
• The secondary oocyte retains the bulk of the nutrient rich cytoplasm of the primary oocyte. 
• The tertiary follicle further changes into the mature follicle or Graafian follicle.
  • Hence statement 2 is not correct.
• The secondary oocyte forms a new membrane called zona pellucida surrounding it.
  • Hence statement 3 is correct.
• The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.

Concept:

• Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the foetus. This process of delivery of the foetus (childbirth) is called parturition.

Explanation:

Oxytocin is released during Parturition in human beings

• The posterior part of the pituitary gland also called Neurohypophysis (pars nervosa) releases oxytocin.
• Oxytocin is synthesized by the hypothalamus and is transported axonally to the neurohypophysis.
• Oxytocin acts on the smooth muscles of our body and stimulates their contraction. In females, it stimulates a vigorous contraction of the uterus at the time of childbirth, and milk ejection from the mammary gland. For this reason, it is also called the birth hormone.

Process of Parturition:

• Parturition is induced by a complex neuroendocrine mechanism.
• The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.
• This triggers release of oxytocin from the maternal pituitary.
• Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin.
• The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions.
• This leads to the expulsion of the baby out of the uterus through the birth canal – parturition

​

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. 
• Glucagon: The α cells of islets of langerhans of pancreas secrete glucagon. Glucagon is released into the bloodstream to prevent blood sugar levels from dropping too low (hypoglycemia)
• Prolactin: It is also called lactotrophic hormone. It regulates the growth and milk formation of mammary glands.

The correct answer is Neither 1 nor 2.

Key Points

In vitro fertilization​:

• In vitro fertilization (IVF–fertilization outside the body in almost similar conditions as that in the body) followed by embryo transfer (ET) is one of such methods.
• In this method, popularly known as the test tube baby program, ova from the wife/donor (female) and sperms from the husband/donor (male) are collected and are induced to form zygote under simulated conditions in the laboratory. Hence statement 1 is not correct.
• The zygote or early embryos (with up to 8 blastomeres) could then be transferred into the fallopian tube (ZIFT–zygote intrafallopian transfer) and embryos with more than 8 blastomeres, into the uterus (IUT – intrauterine transfer), to complete its further development.
• Embryos formed by in-vivo fertilization (fusion of gametes within the female) also could be used for such transfer to assist those females who cannot conceive.
• Transfer of an ovum collected from a donor into the fallopian tube (GIFT – gamete intrafallopian transfer) of another female who cannot produce one, but can provide a suitable environment for fertilization and further development is another method attempted.

​​Intracytoplasmic sperm injection

• Intracytoplasmic sperm injection (ICSI) is another specialized procedure to form an embryo in the laboratory in which a sperm is directly injected into the ovum. Hence statement 2 is not correct.
• Infertility cases either due to the inability of the male partner to inseminate the female or due to very low sperm counts in the ejaculates could be corrected by artificial insemination (AI) technique.
• In this technique, the semen collected either from the husband or a healthy donor is artificially introduced either into the vagina or into the uterus (IUI – intra-uterine insemination) of the female.

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

• GIFT stands for Gamete intra-fallopian transfer, which one of the ART procedures to help with infertility issues.
• It involves the transfer of ovum into the fallopian tube of the female.
• The ovum is collected from a female donor.
• The ovum is transferred to the fallopian tube as that is where fertilization takes place.
• It is effective for a female:
  • who cannot produce a gamete (ovum), but
  • who can provide a suitable environment for fertilization, and
  • who can retain the fertilized zygote or embryo inside the uterus.

Additional InformationSome other ART methods: 

• ZIFT -
  • Zygote intra-fallopian transfer is the transfer of the embryo, with less than 8 blastomeres, into the fallopian tube.
  • This is performed after in-vitro fertilization of sperm and ovum.
  • The zygote is formed under simulated conditions in the laboratory (test tube).
  • It is effective for a female who cannot provide suitable environment for fertilization, but can retain the zygote in the uterus.
• IVF -
  • In vitro fertilization or IVF is the fertilization of sperm and ovum outside the body in laboratory conditions that is similar to that of the body.
  • 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.
• IUT -
  • Intra-uterine transfer is the transfer of embryo with more than 8 blastomeres into the uterus, where implantation takes place.
  • This is also an important part of IVF.
  • The ZIFT and IUT are types of embryo transfer techniques.
  • This method is also applicable for females who cannot provide suitable environment for fertilization, but can retain the zygote in the uterus.
• ICSI -
  • Intra-cytoplasmic sperm injection is a method by which the sperm is directly injected into the ovum.
  • It is a specialized procedure to form an embryo in-vitro.
  • It is effective where the male sperm is unable to fertilize the ovum normally due to low motility, etc.

The correct answer is plants were first cross-fertilised and then self-fertilised.

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 first 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.
• The F1 generation is then self-fertilized to get F2 generation.
• In F2 generation tall and dwarf plants can be seen in a ratio 3:1.  

Phenotype: It refers to the external appearance. 

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

Concept-

• Gene is the basic unit of inheritance.
• Genes are hereditary markers from which control various characteristics like skin colour, height, etc.
• Gene which controls more than one character is called a pleiotropic gene.
• This gene shows multiple phenotypic effects.

Explanation-

• Phenylketonuria (PKU) is one such disorder that is caused due to a single gene mutation.
• The mutation is caused in the gene encoding phenylalanine hydroxylase enzyme.
• Affected people lack this enzyme, which can convert phenylalanine to tyrosine.
• Lack of the enzyme results in accumulation of phenylalanine, which gets converted to phenylpyruvic acid.
• Phenylpyruvic acid has adverse effects on the body:
  • Mental retardation
  • Reduction of hair
  • Skin pigmentation
• Thus, we can see that a single gene mutation is causing multiple phenotypic expressions.

Additional InformationPolygenic Inheritance -

• Polygenic inheritance was first described by Nilsson Ehle.
• It is the inheritance of characters in which one character is controlled by many genes.
• Here, the intensity of character depends upon the number of the dominant alleles.
• For example, human skin colour which is spread across a gradient and not distinct.
• It is the result of the additive effect of each allele.

Explanation:

• Type of gametes or phenotypes in a cross can be calculated by the formula 2ⁿ
• Where n indicates the number of heterozygous pair (Dissimilar pair of alleles)
• The genotype AABbCC has only a single heterozygous pair Bb, so n = 1
• Now, 2ⁿ ⇒ 2¹ = 2
• Therefore, two different types of gametes will be produced ABC and, AbC​

Additional Information

• If the plant having the genotype AABbCC is self-pollinated, it would result in a 3:1 phenotypic ratio similar to a monohybrid cross.
• We can find the phenotypic and genotypic ratios of F2 generation from the following diagram.

Explanation:

Mutation:

• 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 
• Mutations are of two types - Chromosomal Mutations & Gene Mutations
• Gene Mutation is further divided into Point mutation & Frameshift mutation
• Point Mutation - When mutation takes place due to a single base pair change in DNA sequence, is called Point Mutation

Example:

• Sickle Cell Anemia - The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta-globin chain of the haemoglobin molecule.
• The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta-globin gene from GAG to GUG.
• The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle-like structure

Concept-

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

Explanation-

• Color blindness is a recessive sex-linked trait.
• Father transfers its X chromosome to the daughters.
• The colorblind father will transfer its carrier X chromosome to the daughter.
• The women will be a carrier for colorblindness XX^c.
• The colorblind man will be X^cY.
• The carrier female and color blind man will inherit the disease to 50% sons and 50% daughters. 

Thereby a color-blind man marries the daughter of a color-blind man. Then in their progeny, 50% of sons will be color blind.

Concept:

• DNA is a nucleic acid made up of several small monomeric units combined together called deoxyribose nucleotides 
• It was first discovered by Meischer and the term DNA was given Zacharis.
• A deoxyribonucleotide consists of three units:

1. Nitrogen base
2. Deoxy ribose pentose sugar
3. Phosphate group

• ​The nitrogen base forms an N-glycosidic linkage with the first carbon of pentose sugar to form a nucleoside. The nitrogen of third place (N3) forms a bond with sugar in the case of pyrimidine while in purines nitrogen of ninth place (N9) forms a bond with sugar. Phosphate forms 5' - phosphoester bond (covalent bond) with the fifth carbon of sugar to form a complete nucleotide.

Explanation:

• In DNA two types of nitrogen bases are present

1. Pyrimidines - Consist of one pyrimidine ring, Skeleton of the ring is composed of two nitrogen and four carbon atoms. Eg. Cytosine, Thymine 
2. Purines - Consist of two rings i.e. one pyrimidine ring (2N + 4C) and one imidazole ring (2N + 3C). eg. Adenine and Guanine.

• In RNA Thymine is not present, instead of that another nitrogen base called Uracil is there. 

​Explanation:

• Polypeptide chain synthesis is signaled by two initiation codons AUG & GUG.
• AUG codes for methionine amino acid in eukaryotes and it codes for N-formyl methionine in prokaryotes
• Sometimes GUG also functions as a start codon and codes for methionine amino acid otherwise, GUG codes for valine amino acid normally.
• So, it is clear that the first amino acid synthesized in polypeptide chain formation is methionine amino acid, hence the correct option will be 4. Methionine, glycine, valine, lysine are the correct sequence of amino acids.

Additional Information

             Table showing Codons coding for different amino acids

Concept-

• Deoxyribonucleic acid (DNA) is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth, and reproduction of all known organisms.
• Each DNA molecule consists of sequences of Genes.
• Each gene is a particular set of instructions for specific functions.
• Each gene naturally consists of a sequence of nucleotides and base pairs.

Explanation-

• Gene is the basic unit of inheritance.
• Genes are hereditary markers from which derive various characteristics like skin color, height, etc.
• It is the unit of recombination, mutation, and self-reproduction.
• Gene is expressed in genetic expression by transcription of mRNA to produce proteins.

Thereby the term 'gene' refers to a portion of DNA.

Additional Information

• The term 'gene' refers to A portion of DNA
• Gregor Mendel is the father of Genetics. 
• He experimented on Pea Plant (Pisum Sativum).
• Wilhelm Johannsen coined the word "gene". 
• William Bateson in 1905 coined the term genetics from the word "gene".
• The terms ‘Gene’ had already been coined by Wilhelm Johannsen (1857-1927), who described ‘gene’ as a carrier of heredity.
• Johannsen coined the terms ‘genotype’ and ‘phenotype’.
• ‘Genotype’ was meant to describe the genetic constitution of an organism, while ‘Phenotype’ was meant to describe actual organisms.
• The collective genotype of a population is known as the gene pool.
• The observable physical properties of an organism are known as the phenotype.
• It includes the behavior, appearance, and development of an organism.

Explanation:

• RNA ( Ribose Nucleic Acid) in a nucleic acid present in cells of living organisms.
• There are three types of RNA, as follows 

Types of RNA

So, If all the tRNAs within a cell were suddenly destroyed, the translation would be directly and immediately affected.

Explanation:

The DNA is a double-stranded structure made of deoxyribose-nucleotides.

The two chains of polynucleotides in a DNA are antiparallel to each other i.e. if one chain has the polarity 5', the other has 3'.

Some of the salient features of DNA are - 

1. It is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside.
2. The two chains have antiparallel polarity. It means if one chain has the polarity 5', the other has 3'.
3. The bases in two strands are paired through hydrogen bonds (H-bonds) forming base pairs (bp).
4. Adenine forms two hydrogen bonds with Thymine from the opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds.
5. As a result, always a purine comes opposite to pyrimidine. This generates an approximately uniform distance between the two strands of the helix
6. The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm (a nanometre is one-billionth of a metre, that is 10-9 m) and there is roughly 10 bp in each turn Consequently, the distance between a bp in a helix is approximately 0.34 nm.
7. The plane of one base pair stacks over the other in a double helix. This, in addition to H-bonds, confers stability of the helical structure

Important Points

• The double-stranded structure of DNA was first described by Crick & Watson.
• They proposed a scheme in 1953 that says DNA is a semi-conservative double-helical structure.

Explanation:

• Evolutionary biology: It is a field of science that deals with the study of evolutionary processes like natural selection, speciation & common descent that has led to the diversification of life on earth.
• Charles Darwin is known as the father of ''Evolutionary Biology''.
• Darwin proposed a theory of evolution called natural selection in the year 1859. According to it those populations which are a better fit (reproductively fit) in an environment will be selected by nature and will survive more.
• Charles Darwin wrote a book named ''The origin of species'' which is considered to be the foundation of evolutionary biology.

Additional Information 

• Herbert Spencer- He Was best known for the introduction and application of evolutionary theory to philosophy, psychology, and social sciences
• The famous phrase 'Survival of the fittest' to mean Natural Selection was coined by Herbert Spencer. He originated this phrase after the publication of famous biologist Charles Darwin’s book ‘Origin of Species’ which talked about ‘Natural Selection’.
• Julian Huxley was an English biologist, philosopher, educator, and author who greatly influenced the modern development of embryology, systematics, and studies of behaviour and evolution.
• Stanley Miller along with H.C. Urey provided experimental evidence of ''chemical evolution''

The correct answer is option 1.

Key PointsAdaptive Radiation 

• The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography is called adaptive radiation. Hence, option 1 is correct.
• Adaptive radiations are best exemplified in closely related groups that have evolved in a relatively short time.
• A striking example is a radiation, beginning in the Paleogene Period (beginning 66 million years ago), of basal mammalian stock into forms adapted to running, leaping, climbing, swimming, and flying.
• Other examples include Australian marsupials, cichlid fish, and Darwin’s finches (also known as Galapagos finches).
• The phenomenon of adaptive radiation was first observed by Darwin when he travelled to a place called Galapagos Island.
• There he observed that there were finches with different types of beaks. So, he concluded that all of these finches radiated on the same island from a single ancestor Finch.
• All of these finches developed beaks according to the kind of food available to them.
• Hence, they evolved from conventional seed-eating finches to vegetarian and insectivorous finches.
• They later came to be known as Darwin’s finches.

​

The correct answer is Homo habilis.

• Homo habilis is the first human-like being with a cranial capacity of 650 to 800cc.

Key Points

• Its fossil was discovered in Java in 1891.
• Homo erectus was discovered in 1.5 mya and it has a large cranial capacity of 900cc.
• Homo erectus ate meat but Homo habilis does not eat meat.
• Homo sapiens were discovered 10,000 to 75,000 years ago.
• It is the most recent species of human.
• Agriculture came during this period and their life settlement started.
• Australopithecines were in East African grassland discovered in 2 mya.
• They used stone weapons for hunting for food.

Hint

• It is based on Hardy-Weinberg equation: p² + q² + 2pq = 1​

Important Points

• G.H. Hardy and Wilhelm Weinberg independently described the basic principle of population genetics that is known as the Hardy-Weinberg principle.
• It states that allele frequencies in a population remains constant from generation to generation.
• The gene pool remains constant and is referred to as genetic equilibrium or Hardy-Weinberg equilibrium.
• Gene pool - It is the total of all genes and alleles in a population.
• This is supported by a mathematical equation that can be used to calculate genotype frequencies in a population at equilibrium.

Explanation:

• As the dominant (brown colour) and recessive (white colour) alleles as B and b respectively, the genotypic conditions will be:
  • BB - Homozygous dominant
  • bb - Homozygous recessive
  • Bb - Heterozygous

According to Hardy-Weinberg equation,

Sum of all allelic frequencies = 1

Therefore, p² + q² + 2pq = 1

or, (p + q)² = 1

where, p and q represent the frequencies of the alleles B and b respectively.

• Thus, the specific genotype frequencies are represented as:
  • p² - BB
  • q² - bb
  • 2pq - Bb

Calculation:

It is given that the frequency of recessive (white) butterflies is 40% or 0.4

Therefore, \(q^2 = 0.4\)

⇒ \(q = {\sqrt{0.4} = 0.63}\)

⇒ \((p + q)^2 = 1\) 

⇒ \(p = 1 - q \) 

⇒ \(p = 1 - 0.63 = 0.37\)

So, \(2pq = {2\times 0.63 \times 0.37} = 0.47\)

Therefore, the percentage of butterflies that are heterozygous will be 47%.

The correct answer is plasmodium falciparum.

Key Points

• Different species of Plasmodium (a tiny protozoan) are responsible for different types of malaria, of these, malignant malaria which is the most serious is caused by plasmodium falciparum.
• Plasmodia are a type of protozoa. Humans are usually infected with Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale. P falciparum is the most serious of the three.
• Plasmodium falciparum is a human unicellular protozoan parasite that causes malaria. It is the deadliest Plasmodium species.
• The parasite is spread via the bite of a female Anopheles mosquito, which produces falciparum malaria, the most deadly form of the disease.

Important Points

• Human malaria is caused by Plasmodium Malariae, a parasitic protozoan.
• Plasmodium vivax is a human pathogen and a protozoal parasite. This parasitic infection is the most common and widespread cause of recurrent malaria.

Additional Information

• Malaria is a parasitic disease spread by mosquitoes. Humans are infected with the parasite after being bitten by infected mosquitoes.
• Malaria makes people feel very sick, with a high fever and shivering chills.
• Malaria is still frequent in tropical and subtropical nations, despite its rarity in temperate settings.

The correct answer is option [4] i.e Metastasis is the property exhibited by benign tumours.

• Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually.
• The mechanisms that underlie the development of cancer or oncogenic transformation of cells, its treatment, and control have been some of the most intense areas of research in biology and medicine.
   

Direct exposure to disease-causing organisms as in the case of infection of germs provides active immunity.

Concept:

• Immunity-
  • The ability of an organism to resist infections and defend against disease-causing organisms.
  • Way of protecting oneself from the effects of toxins.
  • The capacity to recognize and tolerate self (own cells and tissues) and reject non-self (foreign cells, tissues, entities, bacteria, viruses, fungi, protozoa).
• Active Immunity - It results from the direct exposure to the disease-causing organism.
• Passive Immunity - It results from the introduction of antibodies against the disease, not the disease-causing organism.
• Natural Immunity - It results from exposure to the pathogen naturally, i.e., actual infection as opposed to artificial exposure by vaccination.

Concept-

• The development of several high-yielding varieties of wheat and rice in the mid-1960s, as a result of various plant breeding techniques, led to a dramatic increase in food production in our country.
• This phase is often referred to as the Green Revolution.
• The green revolution was dependent to a large extent on plant breeding techniques for the development of high-yielding and disease-resistant varieties in wheat, rice, maize, etc.
• Green Revolution was responsible for our country to not merely meet the national requirements in food production but also helped us even to export it.

Key Points

During the period 1960 to 2000, wheat production increased from 11 million tonnes to 75 million tonnes.

• This was due to the development of semi-dwarf varieties of wheat and rice.
• Nobel laureate Norman E. Borlaug, at International Centre for Wheat and Maize Improvement in Mexico, developed semi-dwarf wheat.
• In 1963, several varieties such as Sonalika and Kalyan Sona, which were high yielding and disease resistant, were introduced all over the wheat-growing belt of India.

Additional Information 

• During the period 1960 to 2000, rice production went up from 35 million tonnes to 89.5 million tonnes.
• This was due to the development of semi-dwarf varieties of wheat and rice. 
• Semi-dwarf rice varieties were derived from IR-8, (developed at International Rice Research Institute (IRRI), Philippines) and Taichung Native-1 (from Taiwan).
• The derivatives were introduced in 1966.
• Later better-yielding semi-dwarf varieties Jaya and Ratna were developed in India.

Explanation:

• Common carp is an edible freshwater fish. Other examples of  edible freshwater fishes are Catla & Rohu
• Some of the edible marine fishes are Hilsa, sardine, mackerel, and pomfrets.

Additional Information

• Fisheries is an industry that includes catching, processing, or selling fish, shellfish, or other aquatic animals.
• It is economically very important as:

1. A large part of the human population depends on fish & its products
2. It gives employment and income to a large number of fisherman in coastal areas.
3. Fish oil is used in medicines

The correct answer is option 2 i.e Tissue culture.

• Tissue culture is the phenomenon that many plants are grown from one parent in disease-free conditions.
• The production of plants by the method of tissue culture is also known as micropropagation 
• This technique is being used increasingly for the production of ornamental plants like orchids, dahlia, carnation, chrysanthemum, etc.
• The new plants produced by tissue culture are disease-free is an advantage of this technique.

Concept-

• The fungi constitute a unique kingdom of heterotrophic organisms.
• True fungi are divided into the following classes-
  • Phycomycetes- Examples are mucor, rhizopus.
  • Ascomycetes- Examples are Neurospora, Claviceps, yeast.
  • Basidiomycetes- Examples are Agaricus, ustilago.
  • Deuteromycetes- Examples are Alternaria, Colletotrichum.

Explanation-

• Yeast is a unicellular fungus.
• Yeast grows on ripened fruits like grapes, sugarcane, date palm, and flowers.
• Mycelium is absent in yeast.
• If the yeast is dissolved in sugar solution then pseudomycelium is formed. Because in a sugar solution, it grows very fast i.e. it reproduces fast.
• Yeast is also called fermentation fungi because different types of products are formed by fermentation with the help of yeast.

Yeast is used as a fermentation agent in breweries (wine industry).

Additional Information

• Rhizopus and Mucor are known as bread mold.
• Neurospora is red or pink mold. is used for the study of genetics in the Plant Kingdom.

The correct answer is Biogas.

Explanation:

• Biogas is produced by the anaerobic fermentation of biomass.
• Biogas consists of methane gas, carbon dioxide, and trace amounts of nitrogen, hydrogen, and carbon monoxide.
• Anaerobic fermentation is a degradation process of organic material into biogas by microorganisms, in the absence of oxygen.
• Anaerobic fermentation can be used for the production of various chemicals, such as ethanol, butyl alcohol, lactic acid, acetic acid, and hydrogen gas.
• The conversion of organic waste and biomass into biogas reduces the production of the greenhouse gas methane as efficient combusting gas.
• It also replaces methane with carbon dioxide. 

Additional Information

• Compressed natural gas is a fuel that can be used in place of gasoline, diesel fuel, and liquefied petroleum gas (LPG).
  CNG is made by compressing natural gas, which is mainly composed of methane (CH₄).
•  

Key Points

Plasmid-

• 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.

​

​Explanation:

Genetic Engineering/Gene cloning/Recombinant DNA (R-DNA technology)

Genetic Engineering is the (1)isolation (2)introduction and (3) expression of foreign DNA into an organism.

1. Isolation 
   • The DNA is isolated from the organism that has the gene of interest.
   • The gene of interest from DNA is cut using 'Restriction endonucleases'- molecular scissors.
   • Restriction endonucleases can cut DNA molecules at specific sites.
   • The few cut DNA are amplified or increased in number to millions by using Polymerase Chain Reaction (PCR).
2. Introduction
   • The cut gene is first inserted into a vector.
   • The vector is cut using the same restriction enzyme as the gene of interest.
   • Cutting with the same restriction enzyme make the cut ends of vector and gene of interest complementary and helps in joining.
   • Joining is done by DNA ligase.
   • The vector, now inserted with the gene of interest are introduced into a host cell.
   • The host cell is made compatible using chemicals such a polyethylene glycol or by physical methods such as microinjection, electroporation, gene-gun, etc.
3. Expression
   • After introduction the cells which have been introduced with the vector containing the gene of interest are identified using selectable markers.
   • The recombined host cells can multiply the plasmid and produce the desired product from the gene.

Additional Information

• Vectors are the medium using which gene is transferred.
• They carry the gene of interest within them.
• They should have an origin of replication, to initiate replication independent of chromosomal DNA
• They should have selectable markers so as to facilitate the identification of transformed cells from non-transformed cells. 
• Genes giving antibiotic resistance are good selectable markers for host cells which are not naturally resistant to the antibiotic.
• So, if all cells are treated with the antibiotic, the cells carrying the vector will only survive because they have resistance genes.
• They should have cloning sites where the gene of interest can be joined.

Concept:

• Selectable markers are the genes that can help identify 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.

Explanation:

• After the vectors are introduced into the host cell, the transformed cell is selected using selectable marker.
• This selection of transformants is done on the basis of insertional inactivation of a 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.
• The non-transformed cells do not have any recombinant DNA.
• Therefore, non-transformed cells are resistant towards 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.
• We first grow the cells in a medium containing ampicillin where 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.
• Thus we can select the transformed colonies from the ampicillin medium.

• Therefore, antibiotics can be used as selectable markers in genetic engineering.

  

Concept:

• During polymerase chain reaction, the temperature in the machine can range from 4ºC to 95ºC.
• The DNA polymerase found in most organisms cannot withstand such high temperatures.
• Taq polymerase, a polymerase isolated from Thermus aquaticus, can withstand such high temperatures and can be used in PCR as a thermostable DNA polymerase.

• The polymerase chain reaction is a laboratory method used to multiply a specific region of DNA and produce millions of copies.​

Key Points

Components of PCR -

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

Steps -

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

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

​

Correct answer is cotton.

Key Points

Bt toxin -

• Bt stands for Bacillus thuringiensis.
• Bt toxin gene is present in a bacteria, B. thuringiensis.
• This bacteria produces toxins against lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes).
• During a particular phase of their growth, B. thuringiensis forms protein crystals.
• These crystals are insecticidal.
• They are inactive inside the bacteria as pro-toxin.
• When a target insect ingests it, it converts into an active form due to the alkaline pH in the gut of these insects.
• The active toxin binds to the surface of the midgut epithelial cells and creates pores in the gut of the insect. 
• It causes swelling and lysis and the insect dies.

​Explanation:

Bt cotton -

• Bt toxin gene were isolated from Bacillus thuringiensis and incorporated into crop plants that are prone to infestation of these insects.
• This was done using recombinant DNA technology.
• There are specific Bt genes against specific insects.
• The toxin coded by genes named cryIAc and cryIIAb are effective against cotton bollworm, and cryIAb is effective against corn borer.
• The Bt toxin gene has been cloned from the bacteria and has been expressed in plants.
• This lets the plant express Bt toxin and kills the insects attacking them.
• It provides resistance from insects without the need for insecticides; in effect resulting in a bio-pesticide.

Although other Bt crops have also been produced by genetic engineering, ​Bt cotton is the only Bt crop grown by farmers in India.

Concept

• RNA interference (RNAi) technology is used to silence a gene.
• After an infection, the infectious organism produces RNA in 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, being complementary will recognize and bind to the target RNA from nematode, bacteria or virus.
• To make a double-stranded RNA both sense and anti-sense RNA should be produced from the DNA.
• This method involves the silencing of a specific mRNA (from infection) due to a complementary dsRNA molecule (from host).
• The binding of dsRNA (host) prevents the translation of the mRNA (silencing) of the virus, bacteria or nematode.
• RNAi takes place in all eukaryotic organisms as a method of cellular defense.

Additional Information

RNAi silencing for disease control

• A nematode Meloidegyne incognita infects the roots of tobacco plants.
• Nematode-specific genes were isolated and inserted into an Agrobacterium vectors
• Agrobacterium vectors were used to transfer those nematode-specific genes into the host plant. 
• The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells.
• These two RNAs being complementary to each other formed a double-stranded (dsRNA).
• This dsRNA could bind to nematode mRNA produced after infection. 
• That initiated RNAi and thus, silenced the specific mRNA from Meloidegyne incognita.

Key Points

Transgenic Animals -

• Animals that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals.
• A foreign gene is deliberately inserted into their genome.
• This is done by using a micro-injection.
• Microinjection is used to inject the foreign gene into the nuclei of the fertilized egg.
• Injecting the gene into a fertilized egg makes sure that all the cells of the transgenic animal contain the foreign gene. 

Additional Information

1. Study of Physiology & Development -
   • Study of how genes and their regulation affects the physiological functioning of the body.
   • Complex growth factors like insulin can be studied.
2. Study of Diseases -
   • Transgenic animals serve as model organisms for studying human diseases.
   • They help in understanding the disease development process from genes.
   • They are also used for investigating new treatment methods.
   • Transgenic models exist for diseases like cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's.
3. Biological Products -
   • Many biological products that are essential for formulating medicines of use are often expensive.
   • These products can be obtained easily from transgenic animals.
   • This can be achieved by just introducing the gene responsible for the desired product into a suitable organism.
   • Example - Alpha-1 antitrypsin is a human protein that is required for emphysema treatment.
4. Vaccine Safety -
   • Transgenic mice can be used to test safety of vaccines before using for humans.
5. Toxicity Testing -
   • Transgenic animals can be made more sensitive to certain chemicals or drugs.
   • These animals are exposed to the toxic substances and their effects are then studied

The correct answer is Cladode & Leaf spine.

• Adaptations found in the cactus are Cladode & Leaf spine.
  • A cactus has special adaptations in its roots, leaves, and stems that enable it to thrive in a desert environment.
  • These adaptations include spines, shallow roots, deeply layered stomata, thick and extensible stems, waxy skin and a short growing season.

Key Points

• Cladodes are shoot systems in which leaves do not develop.
  • Rather, the stem flattens out and takes over the photosynthetic functions of the plant.
  • In asparagus, the scales found on asparagus spears are the true leaves.
• Leaf spine:
  • By shading the cactus, these spines also help prevent the cactus from losing water through evaporation.

Concept:

• Interspecific interactions are the interactions of the population of two different species.
• These interactions may be Positive, Negative, or Neutral.​​
• Positive interaction: Both the species are benefited. For example- Mutualism, Protocooperation.
• Negative interaction: One species is harmed. For example- Ammensalism, Parasitism, predation.
• Neutral interaction: Neither species benefits nor suffers. For example-  Lactobacillus and Streptococcus.

Explanation:

• Mutualism: It is referred to as the interspecific interaction in which both the interacting species are benefited.
• Algae and fungi remain in a close association where the fungus helps in the absorption of nutrients and provides protection while algae or cyanobacterium prepares the food. This association is called ''lichen''. Both the species are benefited here thus it is an example of mutualism.​

Additional Information

• The rest options are examples of Commensalism where one species is benefitted while the other is neither benefitted nor harmed
• Barnacles growing on the back of the whale. Barnacles are benefited to move to a location for food as well as shelter while the mango tree is neither benefited nor harmed.
• An orchid growing as an epiphyte on a mango tree. The orchid gets shelter and nutrition from the mango tree while the mango tree is neither harmed nor benefited
• The sea anemone eats scraps of food that the hermit crab releases as she eats, and the hermit crab is protected from predators like the octopus by the painful sting of the sea anemone's tentacles.

Key Points

Total population = 10,000

Birth per year = 1500

Deaths per year = 500

Net Births = 1500 - 500 = 1000 per year

Therefore, Population growth rate = Net births per year / Total population 

⇒ Growth rate = 1000 / 10000 = 0.10

The correct answer is always upright

Key Points

• An ecosystem is the basic ecological unit in which living organisms interact among themselves and with their surrounding physical environment.
• In an ecosystem, an organism occupies a specific place in the food chain called trophic level like Producers, Consumers, Decomposers.
• Each trophic level has a certain mass of living material at a particular time called the standing crop, this standing crop is measured as the biomass of living organisms, as the number in a unit area.
• An ecological pyramid is a pictorial representation of the relationship between different organisms in an ecosystem.
• It is of three types: Pyramid of the number, Pyramid of biomass, and Pyramid of energy.

Additional Information

• The pyramid of energy represents the total amount of energy consumed by each trophic level in a given food chain.
• According to the 10% law of energy transfer, only 10% of the total energy is transferred from one trophic level to another.
• Therefore the total amount of energy available for utilization in the layers above is less than the energy available in the lower levels, so the pyramid is always upright.

​​

the correct answer is 2 only.

Key Points

• An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions.
• This change is orderly and sequential, parallel with the changes in the physical environment.
• These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.
• The gradual and fairly predictable change in the species composition of a given area is called ecological succession. Hence, Statement 1 is incorrect.
• During succession, some species colonize an area and their population becomes more numerous whereas populations of other species decline and even disappear.
• The entire sequence of communities that successively change in a given area is called sere(s). Hence, Statement 2 is correct.
• The individual transitional communities are termed seral stages or seral communities.
• In the successive seral stages, there is a change in the diversity of species of organisms, an increase in the number of species and organisms as well as an increase in the total biomass.
• The present-day communities in the world have come to be because of succession that has occurred over millions of years since life started on earth.
• Actually, succession and evolution would have been parallel processes at that time.
• Succession is hence a process that starts in an area where no living organisms are there – these could be areas where no living organisms ever existed, say bare rock; or in areas that somehow, lost all the living organisms that existed there. 
• The former is called primary succession, while the latter is termed secondary succession. 

The correct answer is Sweating and Shivering.

• Sweating & Shivering is one of the techniques by the means of which organisms maintain homeostasis by the regulation process.
• Homeostasis is a condition of optimal functioning of steady internal, physical, and chemical conditions maintained by living systems.
• It refers to stability, balance, or equilibrium within a cell or the body and an organism can keep a constant internal environment.
• Homeostasis is an important characteristic of living things which means the adjusting of systems within a cell because keeping a stable internal environment requires constant adjustments as conditions change inside and outside the cell.

The correct answer is Endangered.

Concept:

• IUCN, International Union for Conservation of Nature, was established on 5 October 1948.
• The IUCN Red List of Threatened Species founded in 1964, is the world's most comprehensive inventory of the global conservation status of biological species.
• The red list has eight categories of species:
• 1. Extinct, 2. Extinct in Wild, 3. Endangered, 4. Critically Endangered, 5.  Vulnerable, 6. Lower Risk, 7. Data deficient, 8. Not evaluated

Explanation:

Endangered species:

• Animal or plant species that are likely to become extinct in the near future, either worldwide or in a particular country are called Endangered species.
  Endangered species are not found in their natural habitat, they are conserved and bred in areas like a national park, sanctuaries, zoos, etc
• Example - Bengal tiger in Jim Corbett national park.
• This tag is given by the International Union for Conservation of Nature (IUCN). 
• These tags are used to identify species which are needed to be protected.  

Additional Information 

• Extinct Species is defined as the moment of extinction is generally considered to be the death of the last individual of the species. Extinct species can be also called Vanished species

The correct answer is All.

Explanation-
Algal bloom-

• Domestic sewage contains nutrients like nitrogen and phosphorous which favour the excessive growth of planktonic (free-floating) algae called an algal bloom which imparts a distinct odour to the water bodies.
• Algal bloom causes fish mortality and causes deterioration of the water quality.
• Algal blooms lead to death of aquatic organisms due to oxygen depletion.
• Some bloom-forming algae are extensively toxic to human beings and animals.

Water hyacinth-

• Excessive growth of water hyacinth (Eichhornia crassipes), the world's most problematic aquatic weed, also called "Terror of Bengal".
• They grow abundantly in eutrophic water bodies and lead to an imbalance in the ecosystem dynamics of the water body.
• Due to the excessive growth of water hyacinth, it causes blocks in our waterways.

Sewage- 

• Sewage from our homes as well as from hospitals are likely to contain many undesirable pathogenic microorganisms, and its disposal into the water without proper treatment causes serious diseases, such as dysentery, typhoid, cholera, jaundice, etc.
• Unlike domestic sewage, waste water from industries like petroleum, paper manufacturing, metal extraction and processing, etc., often contains toxic substances.
• The disposal of these toxic substances into the water is harmful to aquatic organisms.

Thus, all three are bad for the aquatic ecosystem.

Key Points

• Realizing the significance of participation by local communities, the Government of India in the 1980s has introduced the concept of Joint Forest Management (JFM) so as to work closely with the local communities for protecting and managing forests.
• In return for their services to the forest, the communities get the benefit of various forest products (e.g., fruits, gum, rubber, medicine, etc.), and thus the forest can be conserved in a sustainable manner. 

Additional Information

The correct answer is All of the above 

Key Points

• Concept:
• Ozone is a gas that is present naturally within Earth’s atmosphere. It is formed of three oxygen atoms (O3). It is much less stable than oxygen and is thus much more reactive, which means it can be more easily formed and broken down through interaction with other compounds.
• Ozone protects the environment from harmful UV-B radiation
• Ozone is mainly found in two regions of the Earth's atmosphere: Stratosphere & Troposphere. 
• Explanation:
• About 90% of the ozone lies in the stratosphere region and the rest 10% in the Troposphere.
• So the ozone gets maximum damaged in the stratosphere. Although ozone depletion is occurring widely in the stratosphere, the depletion is particularly marked over the Antarctic region.
• This has resulted in the formation of a large area of the thinned ozone layer, commonly called the ozone hole

Additional Information

• The bad effect of ozone hole includes:
• Damage to skin cells and various types of skin cancers
• In the human eye, the cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of the cornea, called snow-blindness, cataracts, etc.
• Thus, the correct option is all of the above