Biology Mock Test - 10

Explanation:

Flower:

• The Flower is the reproductive part of the plant.
• Flowers are of two types - unisexual flowers and bisexual flowers.
• The flower is the only part which takes part in the process of reproduction.

Unisexual Flower:

• The flower has only one reproductive system.
• They can have a male reproductive system or a female reproductive system.
• Pollination is always cross.

Examples: Papaya, watermelon, corn.

Bisexual Flower:

• Bisexual flowers have both sets of the reproductive system in them.
• Both male and female reproductive parts are present in this kind of flower.
• Pollination can be the self type or cross-type.

Examples: Hibiscus, rose, sweet pea, Mustard, Sunflower.

The correct answer is Microspores.

• The process of the formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis.

Key Points

• Microspores are the spores in plants that give rise to male gametophytes, whereas megaspores develop into female gametophytes.
• The male gametophyte gives rise to sperm cells, which are used for the fertilization of an egg cell to form a zygote.
• Microspores are haploid and are formed from diploid microsporocytes by the process of meiosis.

Concept:

• Pollination refers to the transfer of pollen grains from the anther of a stamen to the stigma of a carpel.
• Pollination is done by insects, wind, water, and birds.
• It occurs in 2 ways:
  • Self-pollination
  • cross-pollination
• Self-pollination refers to the transfer from the anther of a flower to the stigma of the same or genetically similar flowers on the same plant.
• Examples of self-pollinating plants are peanuts, wheat, rice, tomato, etc.
• Cross-pollination refers to the transfer from the anther of a flower on one plant to the stigma of the flower on another plant.
• Examples of cross-pollinating plants are grasses, maple trees, etc.
• In plants, pollination is followed by fertilization.
• Pollen grains contain 2 male gametes.
• The fusion of the male gamete with the female gamete or egg is called Syngamy and its product is a zygote.

Explanation:

• Anemophilous plants have light, non-sticky pollens produced in a large number.
• This plant have also long and feathery stigma.
• These modifications facilitate pollination by the wind.
• Examples are cannabis, maize, and many types of grass.

Therefore, from the above discussion, the correct answer is Wind.

Additional Information Pollination is carried by different agents-

• When a flowering plant's diploid number is 36, the chromosome number in its endosperm is 54. 
• In flowering plants, the number of chromosomes will be diploid, i.e. 2n. 
• 2n=36 and n=36/2 = 18 will be found in endosperm.
• Flowering plant endosperm has a triploid structure.
• The endosperm is formed by the fusion of 3 haploid nuclei i.e., two polar nuclei of central cell which belong to the female gametophyte ad the one male gametophyte. As a result, endosperm has 3n=18*3 = 54.

Thus, diploid number of a flowering plant is 36. So, chromosome number in its endosperm will be 54.

The correct answer is Antrum.

• The antrum is not a part of human sperm.

Key Points

Human Sperm:

• It is the male reproductive cell.
• A sperm has three main parts:
  • Head
  • Body
  • Tail
• The head:
  • It contains the nucleus. 
  • The nucleus contains the DNA of the cell.
• The body of the sperm is packed with mitochondria.
• The tail of the sperm helps for its propagation.
• The fine thread of sperm is called the axial filament.
  • It arises from the distal centriole and traverses the body and tail.

Explanation:

• The term Cleavage was given by Von Baer.
• The initial chain of cell divisions which a fertilized egg or zygote undergoes is known as Cleavage, segmentation, or cellulation and the daughter cells are called blastomeres.
• Cleavage produces a solid ball of small blastomeres and the embryo now looks like a mulberry is known as a morula.
• Morula is a 16-celled solid spherical ball-like structure formed by cleavage. It is formed after 3-4 days of fertilization.
• Morula further divides to form blastula which is a 128-celled stage.
• The blastula of mammals is called a blastocyst

​

Additional Information

• The Blastula undergoes division to form Gastrula.
• The gastrula stage is the most important stage in embryonic development because during this stage two major processes occur.
• Differentiation of the blastomere: as a result of differentiation three germinal layers are formed ectoderm, mesoderm, and endoderm.
• Morphogenic movement: Blastomere shows amoeboid movement and occupies their specific place in the embryo.
• Neurula: It is the next stage of embryonic development after the gastrula. In the neurula, the nervous tissues begin to differentiate 

Key Points

• Contraceptives are birth control devices that help in preventing unwanted pregnancies.
• An ideal contraceptive should have the following features:
  • User-friendly
  • Easily available
  • Effective
  • Reversible with little or no side effects
  • Not interfere with the sexual drive or desire and the act of the user

Therefore, all the given options are features of an ideal contraceptive.

Additional InformationContraceptive Methods - 

• Natural Methods -
  • These include natural ways by which the meeting of sperm and ovum can be avoided.
  • There are 3 major ways - Periodic abstinence, Coitus interruptus and Lactational amenorrhea.
• Physical Methods/ Barriers -
  • Males can use condoms, while females can use diaphragm, cervical caps or vaults.
  • They block the entry of sperms through the cervix.
• IUDs -
  • Intra-uterine devices are inserted into the uterus through the vagina.
  • These can be non-medicated, copper-releasing or hormone-releasing.
  • Examples - Lippes loop, CuT, Cu7, Progestasert.
• Oral Contraceptives -
  • This involves oral administration of contraceptives which are also known as oral pills.
  • They are usually small doses of progesterone or a combination of progesterone and estrogen.
  • They prevent the release of ovum from the ovary.
• Surgical Methods -
  • This includes sterilization processes of tubectomy and vasectomy.
  • It is a terminal method and often irreversible.
  • It interferes with gamete transfer and thus prevent pregnancies.

Key Points

• An allele is an alternative form of the same gene.
• It is a slightly different DNA sequence present at the same locus (position on chromosome) on the homologous chromosomes.
• The gene variants still code for the same trait (e.g. hair color), but they differ in how the trait is expressed (i.e., brown, black, red, blonde hair).

Explanation:

• There are many variations of the same gene called alleles.
• Any diploid individual will have at least two alleles. Another individual can have a different set of alleles.
• But they will have the same location on the chromosome.
  • Any gene has a fixed position on DNA.
• So, the position of all the alleles on the DNA is also fixed.

Therefore, alleles are located on the same locus on homologous chromosomes.

Additional Information

1.  Homologous chromosomes
   • The chromosomes which pair with each other during meiosis.
   • They are made up of chromosome pairs of the same length, centromere position, and staining pattern.
   • They have the same genes with the same corresponding loci.
   • A pair of homologous chromosomes is formed by each homologue coming from each of the parent.
2. Non-homologous chromosome
   • They do not pair during meiosis.
   • They have different lengths, different centromere positions, and staining pattern.
   • They mostly have different sets of genes.

Key Points

Gregor Mendel gave the Laws of Inheritance based on his plant hybridization experiments on Pisum sativum (garden pea):

• Law of Dominance -
  • It states that characters are controlled by discrete units called factors (alleles) which occur in pairs.
  • It also states that in a dissimilar pair of alleles, one of the alleles is expressed (dominant) over the other (recessive).
• Law of Segregation - 
  • It states that alleles do not show any blending and both parental characters are recovered in the F2 generation.
  • It also states that during gamete formation, alleles of a pair separate in such a way that one gamete receives only one of the two alleles of a pair.
  • It is also known as the Law of purity of gametes.
  • It can be proved with a monohybrid cross.
• Law of Independent Assortment -
  • It states that when 2 pairs of traits are combined in a hybrid, segregation of one pair is independent of the other pair.
  • It can be proved with a dihybrid cross.

Therefore, the law that Mendel did not propose was law of blending inheritance.

Additional Information

• In a monohybrid cross, the phenotypic ratio is 3:1.

• In a dihybrid cross, the phenotypic ratio is 9:3:3:1.

Key Points

• Every gene contains the information to express a particular trait.
• Genes code for RNA and proteins that act as enzymes or metabolites.
• These enzymes and metabolites are a part of a biochemical reaction that presents a particular trait.
• DNA contains many genes → transcribed to RNA → translated to protein → RNA and protein act as enzymes and metabolites → biochemical reaction → trait expressed 
• In a diploid organism, there are two copies of each gene, i.e., as a pair of alleles.
• One allele is received from one parent (father) and another from another parent (mother).
• In a heterozygote, one allele is dominant and another is recessive.
• In presence of the dominant allele, the recessive is not able to express.
• Different alleles produce slightly different proteins, which function in different ways.  
• In dominant/recessive relationships, the recessive allele produces a non-functional protein. The dominant allele produces a functioning protein.
• In incomplete dominance, it is thought that in a heterozygote, the dominant allele is functioning properly and the recessive allele is malfunctioning.
• The normal or dominant allele produces the normal enzyme but the modified or recessive allele could be responsible for the production of –
  •   the normal/less efficient enzyme, or
  • a non-functional enzyme, or
  • no enzyme at all

Additional Information

• Incomplete dominance is a form of gene interaction in which both alleles of a gene at a locus are partially expressed.
• It results in an intermediate or different phenotype.
• When dominant (RR) and recessive (rr) genotypes are crossed, F1 (Rr) has a phenotype that did not resemble either of the two parents and was in between the two.
• Example - inheritance of flower color in the dog flower (snapdragon or Antirrhinum sp.)
• In a cross between a homozygous dominant (RR) red flowering snapdragon and a homozygous recessive (rr) white snapdragon, the F1 (Rr) was pink.
• When the F1 (Rr) was self-pollinated the F2 resulted in the phenotypic ratio of 1 (RR) Red: 2 (Rr) Pink: 1 (rr) White.
• Here Mendelian monohybrid phenotype ratios change from the 3 (dominant):1(recessive) ratio to 1(dominant): 2(incompletely dominant): 1(recessive).
• R is not completely dominant over r and this made it possible to distinguish Rr as pink from RR (red) and rr (white).

The correct answer is option 2 i.e., Downs Syndrome.

• Down's Syndrome is the name of the disorder caused by the presence of an extra chromosome.
  • Down's syndrome is a genetic disorder caused when abnormal cell division results in extra genetic material from chromosome 21.
• Klinefelters syndrome is a genetic condition in which a male is born with an extra copy of the X chromosome.
• Turners Syndrome is a chromosomal disorder in which a female is born with only one X chromosome.
  • Turner syndrome results from a missing or incomplete sex chromosome.

Polynucleotide is a molecule is a biopolymer composed of 13 or more nucleotide monomers covalently bonded in a chain.

Concept-

• The analogy is the study of organisms with structures that are not anatomically similar but perform similar functions.
• There is no common ancestor between the two organisms.
• They are actually a product of convergent evolution.
• Analogous organs are defined as the organs of different animals having different structures but perform the same functions.
• An example of analogy includes the wings of a butterfly or insects and birds that are not looking anatomically similar but perform similar functions.

Key Points

The wings of insects and feathers of birds are analogous organs as these differ in structure but both of them perform the function of flight.

• Homologous and analogous structures are often confused.
• Homologous organs have the same origin but perform different functions while analogous organs have different origins but perform the same functions.
• Analogous organs which are different anatomically but similar functionally are called analogous organs.
• Eg- Wings of butterflies, birds, and bats, Eyes of octopus & mammals, Flippers of penguins & dolphins.
• All these have different anatomical structures but they perform the same function like Wings of butterfly, birds & bats differs in structure but all of them perform the function of flight.
• Analogous organs always show convergent evolution.
• In convergent evolution, the species of different ancestry start sharing analogous traits because of selection pressure or shared environment.

Concept:

• The 'theory of organic evolution' was given by Charles Darwin and Alfred Wallace independently. 
• It states that 'changes in the genetic makeup of species in a population as a result of responding to environmental changes is organic evolution'.
• It means that the variations in the genes of a population due to competition and environmental changes lead to evolution into a more adapted and competitive species.
• The sequence of organic evolution theory:

​Overpopulation → Constancy of population size → Variation → Natural Selection

Key Points

Overpopulation -

• Most organisms produce more offspring than the resources can carry.
• Reproductive rate is high and the resources are limited.
• More offspring means more variation in the next generation.
• Example - Starfish produces 1 million eggs, E. coli divides every two minutes.

Constancy of Population size -

• Despite a large number of offspring the population size remains constant.
• This is due to three reasons:
  • Intraspecific competition - competition within the species.
  • Interspecific competition - competition between the species.
  • Environmental factors - elimination of offspring due to adverse environmental factors.
• A vast majority of offspring who are weaker, less adapted and less competitive are eliminated or die.

Variation - 

• Variation means that the offspring is not a clone of either parent and is different and unique.
• The offspring who survive, have genes that are best suited to the environment.
• They have genetic variations that are more adapted to the external environment and have more competitive ability.
• Useful variations are selected and harmful variations are removed.​

​Natural Selection - 

• This leads to natural selection of progeny.
• Nature in each successive generation selects for the progeny which is more suited to the external environment.
• There is selective pressure on the individuals, due to limited resources, competition and adverse environment.
• This is called struggle for existence.​
• Natural selection takes place in favor of those that higher reproductive fitness and survive better.

The correct answer is adaptive radiation.

• Adaptive radiation (divergent evolution) is the evolution from one species of animals or plants of many different forms.
• The original population increases in size and it spreads out from its center of origin to exploit new habitats and food sources.
• This results in many populations each adapted to its particular habitat. Eventually, these populations will differ from each other sufficiently to become new species.

Key Points

• Adaptive evolution is natural selection that acts to increase the frequency of beneficial alleles and traits while decreasing the frequency of deleterious qualities.
• Natural selection acts at the level of the individual, selecting for those that have a higher overall fitness compared to the rest of the population.
• There are several ways evolution can affect population variation: stabilizing selection, directional selection, diversifying selection, frequency-dependent selection, and sexual selection.
• Genetic drift produces random changes in the frequency of traits in a population. An evolution that arises from genetic drift is called neutral evolution.

The correct answer is 1 only.

• The term ‘Founder effect’, in population genetics, is used to indicate reduced genetic variation as compared to the original population.

Key Points

• The term "founder effect" refers to the observation when a small group of individuals breaks off from a larger population and establishes a new population.
  • The particular alleles may not be representative of the larger population.
  • As the new population grows, the allele frequencies will usually continue to reflect the original small group.
• A founder effect occurs when a new colony is started by a few members of the original population.
• This small population size means that the colony may have:
  • reduced genetic variation from the original population.
  • a non-random sample of the genes in the original population.

Important Points

• A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population.
  • It is due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts or human activities such as genocide and human population planning.
  • The frequency of certain alleles in a population change because the organisms that carry them are eliminated.
  • The others increase in number because they are the only alleles left.

Concept:

•  Amoebiasis
  • Entamoeba histolytica, a protozoan parasite in the large intestine of human causes amoebiasis (amoebic dysentery).
  • Symptoms:
    • Constipation
    • Abdominal pain and cramps
    • Stools with excess mucous and blood clots
  • Houseflies act as mechanical carriers.
  • They transmit parasites from the feces of infected persons to food.
  • Drinking water and food contaminated by fecal matter are the main sources of infection.

Additional Information

1. Plasmodium vivax - a protozoan, causes Malaria.
2. Entamoeba gingivalis -  a protozoan, resides in the gingival pocket near the base of teeth, causing oral inflammation.
3. Trypanosoma gambiense - a protozoan, causes African sleeping sickness.

Key Points

• Antibodies are a specific types of proteins produced by B-cells against antigens.
• Antigens are any foreign organism, object, or toxin that enters our body and the body thinks is harmful.
• The antibodies are proteins, so they have amino acid sequences that form a peptide chain.
• Each antibody is made up of four peptide chains.
• Two small chains are called light chains and two longer chains are called heavy chains.
• The antibody is represented as H₂L₂. [H for heavy chain and L for light]
• Both chains are joined by disulfide bond. 
• The chain has a constant region which is same for all antibodies and a variable region having different amino acid sequence in different antibodies.
• The variable part of the sequence recognizes the antigens and eliminates them.
• They also have specific antigen-binding sites at the N-terminal of the peptide chains.
• They also recognize the cancerous cells, pathogen-infected cells, cells from grafts, etc.
• IgA, IgM, IgE, IgG are the different types of antibodies produced in our body.

Additional Information

1. Lipid - 
   • It denotes a class of organic compounds that are fatty acids, ester of fatty acid or their derivatives.
   • They include fats, waxes, oils, etc.
2. Carbohydrates - 
   • A carbohydrate is a biomolecule consisting of carbon, hydrogen, and oxygen atoms.
   • They form the biomolecules which are commonly called sugars.

Key Points

​Innate immunity - is a non-specific type of defence that consists of 4 types of barriers:

1. Cellular barriers - 
   • Innate immunity is provided by barriers in our body, one of which is cellular barriers which consists of cells that protect our body from infection
   • It includes leukocytes and lymphocytes cells which attack the pathogen.
   • e.g., White blood cells (WBC), natural killer cells, monocytes. 
2. Passive Immunity -
   • It results from the direct introduction of antibodies against the disease
   • The antibodies fight off the infection and the body does not need to make its own antibody
   • This type of direct injection of antibodies is used for faster protection because the body takes time to make its own antibody.
   • The immunity is short-term (few weeks), until the introduced anti-bodies last
   • e.g., preformed antibodies given against snake-bites, preformed antibodies are given in case of Tetanus
3. Physiological barriers - 
   • These barriers are related to the functions of body organs like maintaining temperature, pH, etc.
   • They are also produced in response to pathogens.
   • e.g., acid in stomach, saliva in mouth, tears in eyes
4. Physical barriers -
   • It is the structural obstruction that prevents entry into the body or target organ/tissue.
   • They do not necessarily kill the pathogen.
   • They just inhibit the movement by acting as a hurdle or obstacle.
   • e.g., skin, mucus coating in respiratory and gastrointestinal tract.​

Active Immunity - It is a specific type of immunity that results from the direct exposure to the disease-causing organism.

​Passive Immunity - It is also a specific type of immunity that is provided by ready-made antibodies that are directly introduced into a body to protect against antigens.

Important Points

• Polymorphonuclear leukocytes and monocytes - Cellular barriers : CORRECT
  • Leukocytes, monocytes, natural killer cells, B-cells, T-cells are cellular barriers
• Anti-tetanus and anti-snake bite injections - Active immunity : INCORRECT​
  • Anti-tetanus and anti-snake bite injections are examples of passive immunity.
  • Active immunity is provided by the production of antibodies in the body in response to antigens.
• Saliva in mouth and Tears in eyes -  Physical barriers : INCORRECT
  • Saliva in mouth and Tears in eyes are the examples of physiological barriers.
• Mucus coating of epithelium lining the urogenital tract and the HCI in stomach - Physiological barriers : INCORRECT​
  • Mucus coating of epithelium lining the urogenital tract and the HCI in stomach are examples of physical barriers.

Key Points

• AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV).
• HIV virus is an RNA virus and carries reverse transcriptase.
• It causes deficiency of the immunity in the body.

HIV Infection - 

• After infection, the virus enters macrophages and removes protein coating (uncoating).
• RNA forms DNA using reverse transcriptase and DNA replicates to become double-stranded. 
• The viral DNA gets incorporated into the host DNA and becomes latent.
• The latent period can be very long ranging from few months to many years (5-10 years).
• When the latent period ends, the viral DNA directs the infected cells to produce new virus particles.
• New virus particles are produced and they bud out of the cell.
• HIV enters into helper T-lymphocytes where it replicates and produces progeny viruses.
• Attack on T-lymphocytes leads to a decrease in immunity in infected persons.
• The disease spreads by the transfer of bodily fluids.
• Transmission:
  • sexual contact with an infected person
  • transfusion of contaminated blood
  • by sharing infected needles 
  • from an infected mother to her child through the placenta.

Explanation

1. Option 1) - CORRECT
   • ​​HIV is a retrovirus that has a single-stranded RNA as its genetic material.
2. Option 2) - CORRECT
   • Replication in helper T-lymphocytes reduces the number of T-lymphocytes in the body.
   • T-lymphocytes help protect our bodies from diseases.
   • Their reduction causes a loss of immunity in the infected person causing immunodeficiency.
3. Option 3) - INCORRECT
   • The time lag between the infection and appearance of AIDS symptoms may vary from a few months to many years.
   • The latent period is almost always very long, up to 5-10 years.
4. Option 4) - CORRECT
   • HIV only spreads by the transfer of bodily fluids like blood, semen, vaginal fluid, anal fluid, and breast milk.
   • It cannot be spread by saliva, sweat, skin, feces, or urine.

The correct answer is option 1 i.e Hybridisation.

• Hybridisation is the process of crossing dissimilar plants of different varieties, species, or genera for improving the crop.
• Crossing may be between two different varieties (intervarietal), between two different species (interspecific) and between different genera (intergeneric).
• Hybridization was first of all practically utilized in crop improvement by German botanist Joseph Koerauter in 1760.

Concept-

Microbes belong to diverse organisms – bacteria, fungi, protozoa, viruses.

Microbes influence man's life in several ways- they are found in clothes, jams, shoes, dead wood, food products, soil, etc.

• Yeast- it is used as a fermentation agent in the bakery (bread industry) and brewery (wine industry). So, Saccharomyces cerevisiae is also called “Baker’s yeast”.
• Agaricus- it is called “gill fungi” because gills like pores are present in its fruiting body. It is also called fairy rings because its fruiting body looks like rings.
• Mucor- it is called bread mold. It grows on bread. The tip of the mycelium is black colored. Therefore, this fungus looks black colored.
• Pythium- Causes “Damping-off’’ disease in tobacco and “vegetable crops”.

Explanation-

• Bread is made from grain usually wheat.
• The selected strain of yeast (Saccharomyces cerevisiae) grown on molasses are used as Baker’s yeast.
• Yeast is added to wheat flour. And is kneaded. The kneaded flour is kept at a warm temperature until it swells up. The phenomenon is called leavening.
• The process of leavening is done by secretion of 3 enzymes by yeast-
  • Amylase causes a breakdown.
  • Maltase convert maltose into glucose.
  • Glucose is acted upon by zymase.
  • Zymase is a complex of several enzymes of anaerobic respiration which brings about fermentation.
• Fermentation of glucose mainly forms ethyl alcohol and carbon dioxide. It leaves the dough.
• The leavened dough is baked. Both carbon dioxide and ethyl alcohol evaporate making the bread porous and soft.

Concept:

• This waste water needs to be treated in sewage treatment plants (STPs) before disposing it into water bodies.
• This treatment is carried out with the help of the heterotrophic microbes present in the sewage.
• The treatment takes place in 2 stages - primary and secondary treatments.

Important Points

Steps of Sewage Treatment - 

• Primary Treatment -
  • All the solid particulate matter are removed by primary treatment.
  • Floating debris is removed by sequential filtration.
  • The grit (soil and small pebbles) are removed by sedimentation.
  • The solids settle as primary sludge and the supernatant as effluent.
  • The effluent moves from primary settling tank to large aeration tanks for secondary treatment.​
• ​Secondary Treatment -
  • ​​The effluent is continuously agitated mechanically and air is pumped into it.
  • This allows vigorous growth of aerobic microbes into flocs.
  • These microbes use up most of the organic matter for their growth.
  • This reduces the BOD (biological oxygen demand) of the effluent.
  • Effluent is then passed into a settling tank, where the bacterial flocs sediment to form the activated sludge.
  • Most of the activated sludge is moved into large tanks called anaerobic sludge digesters, and the rest is used as inoculum in the aeration tanks.
  • Next, the anaerobic bacteria digest the other bacteria and fungi in the sludge.
  • The effluent is then discharged into water bodies.

Explanation:

• From the above steps we can see that the activated sludge is used as an inoculum in the aeration tanks.
• Thus it is recycled to the starting of the sewage treatment process.
• Hence, the sewage treatment process is also called activated sludge treatment.
• The activated sludge consists of decomposing bacteria which helps in reducing the BOD of the effluent.

Concept-

• The virus which infects the bacteria is called bacteriophage.
• A bacteriophage is generally a double-stranded DNA virus.
• In QB - bacteriophage - ss RNA is present.
• In ϕ X 174 - bacteriophage - ss DNA is present.
• A bacteriophage is of two types- Non-infective phages and infective phage.

Explanation-

• DNA is a long polymer of deoxyribonucleotides.
• The length of DNA is usually defined as a number of nucleotides (or a pair of nucleotides referred to as base pairs) present in it.
• This also is the characteristic of an organism.

A bacteriophage known as ϕ ×174 has 5386 bp.

Additional Information

• Escherichia coli has 4.6 × 10⁶ bp.
• The haploid content of human DNA is 3.3 × 10⁹ bp.
• Bacteriophage lambda has 48502 base pairs (bp).

Concept:

• In genetic engineering, a DNA molecule can be cut into desired fragments and inserted into DNA from another cell.
• The recombinant DNA thus formed needs to be screened out from the non-recombinant DNA.
• The cells with the recombinant DNA are called transformed cells.
• The 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.

Important Points

• Selectable markers -
  • These are specific gene sequences present in a cloning vector.
  • These genes have certain phenotypic expressions that help in selecting transformed cells.
  • Example - Ampicillin resistance (amp^R) gene and Tetracycline resistance (tet^R) gene in pBR322 plasmid.
• When a DNA fragment is inserted into any one of the selectable marker genes, it causes insertional inactivation of that gene.
• Thus, the transformed cells lose the expression of that inactivated gene.

Explanation:

• In pBR322, the BamHI site lies within the gene sequence of tet^R.
• If we insert the DNA fragment at the BamHI site, there will be insertional inactivation of the tetR gene.
• So, the transformed cell with the recombinant DNA will have only ampicillin resistance and not tetracycline resistance.
• To identify the transformed cells, 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.
• The transformed cells do not grow here due to lack of tetracycline resistance.
• Thus we can select the transformed colonies from the ampicillin medium.

Key Points

• Recombinant DNA technology helps us to produce our desired protein product.
• This is known as the recombinant protein.
• These proteins need to go through some industrial processes before marketing.

Downstream processing - 

• It is the process of separation and purification of biosynthetic products to make it market-ready.
• It involves formulating the products with suitable preservatives or other treatments.
• These formulations are then put to clinical trials. Example - For drugs.
• They also undergo strict quality control testing, which may vary for different products.

Additional InformationRecombinant DNA technology or biotechnology has the following applications:

• Production of pest-resistant crops - 
  • Bt-crops have been successfully produced for pest-resistance.
  • RNA interference method has also helped to produce disease-resistant plants.
• ​Production of medicines - 
  • Human insulin has been produced using E. coli bacteria.
  • These help in producing recombinant therapeutics that do not induce any unwanted immune response.
• Molecular diagnostics - 
  • Early detection of diseases has been made possible by processes like PCR which amplifies the pathogen DNA to detect it.
  • It helps in detection of HIV and cancer in suspected patients.
• Treatment Methods - 
  • Gene therapy allows the correction of gene defects in patients.
• Production of transgenic animals - 
  • Transgenic animals help in study of various physiological processes, diseases, etc.
  • They help in producing biological products for human welfare.
  • They are also used for vaccine and other chemical safety.

Key Points

• PCR - DNA polymerase : CORRECT
  • ​Polymerase chain reaction (PCR) is the process of amplifying or making multiple copies of a desired fragment of DNA.
  • It involves the use of a special thermostable DNA polymerase enzyme called Taq polymerase.
  • This enzyme acts to polymerize polynucleotide strands by being active at higher temperatures.
• DNA Isolation - Deoxyribonuclease : INCORRECT
  • Isolation of DNA from a cell requires the use of digestive enzymes like lysozyme, cellulase and chitinase to digest the bacterial, plant and fungal cell walls respectively.
  • Ribonuclease and protease are also required to remove RNA and proteins respectively.
  • Deoxyribonuclease digests DNA molecules and hence cannot be used in this process.
• Restriction Digestion - EcoRI - CORRECT
  • Restriction digestion refers to the process of cutting DNA molecules at specific sites with the help of restriction enzymes.
  • EcoRI is a restriction enzyme obtained from E. coli that is widely used in this process.
• Gel Electrophoresis - Ethidium bromide : CORRECT
  • ​Electrophoresis is a process by which negatively charged DNA fragments are separated according to size by running them on an agarose gel using electric field.
  • The smallest fragments move farthest towards the anode and hence a gradient of fragments are formed on the gel medium.
  • The desired fragment is then extracted and visualised under UV light.
  • Ethidium bromide is used to stain the DNA to view under UV light as unstained DNA is not visible to naked eye.​​

Additional Information

Steps of recombinant DNA technology - 

1. Isolation of DNA from the cell
2. Restriction digestion by restriction enzymes
3. isolation of desired fragment by gel electrophoresis
4. Ligation of fragment into cloning vector
5. Insertion of rDNA into host cell
6. Culturing of host cells in culture medium
7. Downstream processing for extraction and purification of desired product.

The correct answer is Genetically Modified Organism.

• Genetically modified organisms (GMOs) can be defined as organisms (i.e. plants, animals or microorganisms) in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination.
  • Foods produced from or using GM organisms are often referred to as GM foods.

Additional Information

• Most GMOs have been engineered to withstand the direct application of herbicide and/or to produce an insecticide.
• However, new technologies are now being used to artificially develop other traits in plants, such as a resistance to browning in apples, and to create new organisms using synthetic biology.
• Grains, nuts, seeds, and legumes are largely free of GMO contamination, but you can buy Non-GMO Verified items to be safe. 
• In the United States, there are 11 commercially available genetically modified crops in the United States: soybeans, corn (field and sweet), canola, cotton, alfalfa, sugar beets, summer squash, papaya, apples and potatoes. 

The correct answer is E - Coli.

Key Points

• Genetically engineered human insulin: 
  • It is called humulin.
  • Humulin is the genetically engineered insulin produced by inserting a human insulin gene into a host cell (E. coli).
  • The inserted human DNA lead them to produce a synthetic version of human insulin.

Additional Information

•  E. Coli:
  • E. coli (Escherichia coli), is a type of bacteria that normally lives in our intestines.
  • It’s also found in the gut of some animals.
•  Rhizopus:
  • Rhizopus is a genus of common saprophytic fungi on plants and specialized parasites on animals.
• Pseudomonas:
  • Pseudomonas infections are diseases caused by a bacterium from the genus Pseudomonas.
  • The bacteria are found widely in the environment, such as in soil, water, and plants.
• Ashbya gossypii:
  • It is also known as Eremothecium.
  • It is a filamentous fungus or mold closely related to yeast.

The correct answer is Human alpha-Lactalbumin.

Key Points

• Organisms that have altered genomes through artificial means are known as transgenic.
• The first transgenic cow was Rosie and was produced in 1997.
• It consists of the human alpha-lactalbumin gene.
• This milk contained 2.4gms of human α-lactalbumin per liter of milk.
• It produces human protein-enriched milk, which was a nutritionally more balanced product for human babies than natural cow milk as it contains human alpha-lactalbumin.

Additional InformationReasons for production of transgenic animals - 

• 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.
• 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.
• 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.
• Vaccine Safety -
  • Transgenic mice can be used to test safety of vaccines before using for humans.
• 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.

Concept:

• Biosphere
  • Biosphere refers to the sum of all the ecosystems.
  • It is composed of all living on earth from deep in the soil, to oceans to land animals.
  • Biosphere is the largest system of interaction between all organisms with their respective physical environments.

Key Points

• An individual or an organism is a single living entity.
• Many organisms together form a population.
• Many such populations of different species who live in the same habitat come together to form a community.
• A community and its environment together constitute an ecosystem, e.g., lake ecosystem, forest ecosystem.
• Many ecosystems sharing similar climatic conditions form a biome, e.g., tropical ecosystem, desert.
• Biosphere is the sum of all the ecosystem on earth, regardless of climatic conditions.

Concept:

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

Important PointsLogistic Growth - 

• Resources are not available to any species population in unlimited amount.
• Thus, the species compete for the available resources to survive.
• This competition restricts the exponential or unlimited growth of any population.
• Any given habitat can only provide resources to support a maximum possible number, beyond which it further growth of population is not possible.
• This is known as the carrying capacity (K) for a particular species in a habitat.
• Such growth pattern is also known as the Verhulst-Pearl Logistic Growth.

Explanation:

It can be denoted by the equation:

\({dN \over dt} = rN ({K-N \over K})\)

where, N = Population Density,

K = Carrying Capacity,

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

• Here, 'r' represents the intrinsic rate of natural increase, which is the difference between the per capita birth and death (b-d).
• The environmental resistance is represented in the equation as \(({K-N \over K})\).
• When the population density (N) is plotted against time (t), it produces a S-shaped curve (sigmoid curve).
• Logistic growth shows 3 different phases:
  • Lag phase - This represents the initial lag time that a population shows before it starts growing.
  • Log phase - This is the phase of accelerated growth, which is itself an exponential growth.
  • Asymptote - This is the stationary phase where the population density reaches the carrying capacity.

The correct answer is ​Parasite.

Key Points

• Cuscuta:
  • ​Cuscuta are stem parasites.
  • Cuscuta is a genus of over 201 species of yellow, orange, or red (rarely green) parasitic plants also known as Amar bail in India.
  • The genus is found throughout the temperate and tropical regions of the world, with the greatest species diversity in subtropical and tropical regions; the genus becomes rare in cool temperate climates, with only four species native to northern Europe.
  • Cuscuta can be identified by its thin stems appearing leafless, with the leaves reduced to minute scales.

Concept:

• 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.

Important Points

• In a forest ecosystem, the lowermost trophic level is occupied by big trees followed by herbivorous or frugivorous birds and animals.
• The next levels are occupied by small carnivores, followed by the apex predator.
• If we represent the number of individuals of each trophic level in an ecological pyramid, we would get a variable shape of the pyramid.
• As given in the diagram above, the number of big trees will be very less compared to that of the primary consumers on the second trophic level.
• However, the pyramid then follows the upright shape or pattern from second to third and onto the fourth level.

Therefore, the given pyramid represents pyramid of the number in forest ecosystem.

Additional Information

Shapes of other ecological pyramids - 

• Pyramid of number:
  • Upright - Grassland ecosystem
  • Inverted - Parasitic food chain
• Pyramid of biomass:
  • Upright - Most of the food chains
  • Inverted - Pond/lake ecosystem
• Pyramid of energy:
  • Always upright

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.

Key Points

• Man is a part of nature and natural biodiversity.
• The future of humanity is at risk due to global warming, climate change, deforestation, overpopulation, and depletion of resources.
• Hence, efforts to conserve biodiversity and sustainable use of resources are in the best interest of man.
• Resource depletion is the consumption of resources faster than they can be replenished.
• Overuse of resources leads to an increased amount of waste generation which poses further risks to mankind.
• Reduction in the use of resources is the most feasible and effective way to help human survival.
• To prolong human survival we have to use available resources judiciously and conserve them for the future generation.
• We divide the reasons of conservation into 3 categories:

1. Narrowly utilitarian
   • Reduction and equitable consumption of natural resources is economically beneficial for human beings.
   • Humans derive resources for their use from the nature so we should protect them to benefit ourselves.
   • If resources are destroyed and depleted, human beings will have nothing to live off of and will perish.
2. Broadly utilitarian
   • Biodiversity plays a major role in many ecosystem services that nature provides.
   • We cannot put a price tag on nature services because she provides oxygen, food, and all our basic requirements.
   • We get many intangible benefits from nature like walking through thick woods, watching flowers, etc.
3. Ethical
   • Conserving resources and biodiversity is our moral duty.
   • We owe it to millions of plant, animal, and microbe species with whom we share this planet.

Explanation:

• Conservation of wildlife will help maintain species diversity and gene pool.
• It will help restore the ecosystem balance for it to function properly.
• Conservation is good for biodiversity but will not directly impact human survival.
• The planting of trees is known as afforestation.
• It will lead to greater oxygen levels, reduced carbon dioxide, will undo the effects of global warming, and help control climate change.
• This is very beneficial to human beings but planting in many areas is not possible, afforestation is a slow process.
• A ban on mining will reduce the pollution in the area.
• However, it will also lead to a reduced supply of the required minerals.

Hence, reduced utilization of resources is required for better survival of human beings.

Concept :

Endangered animals :

• The animals that face extinction due to their diminishing numbers are known as endangered animals.
• Animals are becoming extinct because of disturbances in their natural habitat.
• To protect plants and animals strict rules are imposed in all National Parks.
• Human activities such as grazing, poaching, hunting, and capturing animals are restricted.
• Small animals are much more in danger of becoming extinct than the bigger animals

Explanation :

• Red Data Book is the sourcebook that keeps a record of all the endangered animals and plants.
• Red Data Book is maintained internationally by an organization.
• India also maintains Red Data Book for plants and animals found in India.

​So, the correct answer is a Red data book.

Important Points

• Snakes, frogs, lizards, bats, and owls are killed without realizing their importance in the ecosystem.
• By killing them we are harming ourselves.
• They might be small in size but their role in the ecosystem cannot be ignored.
• They form part of food chains and food webs.

Additional Information

• Some of the endangered species are the White-bellied heron, Great Indian bustard, Spoon-billed sandpiper, and White-rumped vulture.

Key Points

• BOD stands for Biochemical Oxygen Demand.
• It is the amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.

Explanation:

• Water with a lot of organic matter contains more microbes that decompose the organic matter.
• Such a water body with high organic matter will have high BOD.
• BOD is high because more dissolved O₂ is required by ​aerobic biological organisms to break down organic material.
• Water with high BOD will have less oxygen dissolved in it because most is being used by microorganisms.
• If the microorganism needs more oxygen for decomposing the organic material, then less of it is available for aquatic organisms.
• This decreases the number of aquatic animals in the water because less oxygen is left for them.

So, BOD is related to organic matter and microbes. Option 3) 'Both (1) and (2)' is correct.

Additional Information

• Sewage water from our homes contains a lot of organic matter in the form of fecal matter, kitchen waste, cloth and paper fibers, etc.
• These are first treated by microbes in sewage treatment plants before releasing in water bodies to reduce the BOD.

Key Points

• Adsorption
  • In adsorption, gaseous pollutants are removed from the air by adsorbing the pollutants on a solid surface
  • The porous solid comes selectively removes pollutants from the liquid or gaseous streams by adsorbing them.
  • The solid adsorbent usually used are activated carbon, polymers, zeolites.
• Electrostatic precipitators
  • It is most widely used for removing particulate matter.
  • Electrostatic precipitator has electrode wires that are maintained at several thousand volts, that release electron.
  • These electrons attach to SPM giving them a net negative charge that is attracted and collected by grounded plates.
• Pyrolysis
  • Pyrolysis is the process of heating organic material (biomass) in the absence of oxygen.
  • It converts biomass into hydrocarbon biofuels, oxygenated fuel additives, and petrochemical replacements.
• Incinerators
  • Incineration is a waste treatment process that involves the combustion of substances contained in waste materials.
  • This transforms the waste material into ash, gases, particles, and heat that are then stored in the electricity generation application.

Important Points

Key Points

• Particulate matter
  • Particulate matter is a mixture of a variety of microscopic particles of solid or liquid matter suspended in the air.
  • So, they are together called suspended particulate matter (SPM).
  • They lie in the size range of <0.1 µm and up to some 100 µm.
• Electrostatic precipitator
  • It is most widely used for removing particulate matter
  • It can remove over 99 percent of particulate matter present in the exhaust from a thermal power plant.
  • It has electrode wires that are maintained at several thousand volts.
  • The high voltage causes the corona which releases electrons.
  • These electrons attach to SPM giving them a net negative charge.
  • These negatively charged attracted and collected by grounded plates.
  • The velocity of air between the plates must be low enough to allow the dust to fall.

Additional Information

1. Cyclonic separators
   • Cyclonic separation is a method of removing particulates from an air, gas, or liquid stream through vortex separation.
2.  Incinerators
   • Incineration is a waste treatment process that involves the combustion of substances contained in waste materials.

Key Points

• Spermatogenesis is the process of formation of haploid sperms from diploid spermatogonia in human males.
• Spermatogenesis starts at the age of puberty.
• This is caused by the increased secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus.
• This GnRH then acts on the pituitary gland to stimulate the secretion of two gonadotropins - LH and FSH.
• The LH and FSH play a major role in the spermatogenesis process by stimulating the secretion of androgens and other factors for sperm production.
• Spermatogenesis takes place in the seminiferous tubules of the testis in a male.

Therefore, the hormone X here represents GnRH.

Additional Information

• The male reproductive system consists of a pair of testes, some accessory ducts, glands and the external genitalia.
• The testes are present in a pouch-like structure called scrotum outside the abdominal body.
• The male gametes or sperms are produced inside the testes.
• In adult males, the testes contains about 250 compartments called testicular lobules.
• Each lobule contains 1-3 coiled structures called seminiferous tubules, where sperms are formed.

Key Points

• In the given question, hormone X represents gonadotropin-releasing hormone (GnRH).
• GnRH stimulates the secretion of 2 gonadotropins - LH and FSH.
• So, the hormones A and B represents LH and FSH.
• We know that LH surge is the cause for ovulation in women.
• Here, hormone A has been mentioned to cause ovulation.
• Therefore, Hormone A defines Luteinizing hormone or LH.

Additional Information

• The GnRH stimulates the anterior pituitary to secrete the gonadotropins.
• LH acts on the Leydig cells for the secretion of androgens.
• FSH acts on the Sertoli cells for the process of spermiogenesis.

Key Points

• In the given question, hormone X is identified as GnRH, which is released from the hypothalamus.
• GnRH stimulates the secretion of 2 gonadotropins - LH and FSH.
• So, the hormones A and B represents LH and FSH.
• LH and FSH are secreted from the anterior pituitary gland, which is stimulated by the GnRH.

Additional InformationLuteinizing hormone (LH) - 

• It acts on the Leydig cells in the seminiferous tubules of testis.
• It causes the secretion of androgens that are required for the process of spermatogenesis.

Follicle stimulating hormone (FSH) - 

• It stimulates the secretion of some factors from the Sertoli cells that help in the process of spermiogenesis.

Key Points

• In the given question, hormones A and B are identified as LH and FSH respectively.
• This is because hormone A is is mentioned to cause ovulation in a female and only LH is known to perform this function.
• Therefore, hormone B represents follicle stimulating hormone (FSH).
• FSH is secreted from the anterior pituitary gland on being stimulated by GnRH.
• FSH plays an important role in the spermatogenesis process.
• It stimulates the secretion of certain factors from the Sertoli cells.
• These factors help in the process of spermiogenesis in males.
• Spermiogenesis - is the process of transformation of spermatids into spermatozoa.

Explanation:

• The last step where the spermatids differentiate to form the spermatozoa is called as spermiogenesis.
• All the 4 spermatids develop into functional spermatozoa (or sperms).

Additional Information

• In females, FSH is responsible for follicle development in the ovaries.
• This takes place during the follicular phase of the menstrual cycle.
• It may also stimulate estrogen secretion.

Key Points

Spermatogenesis occurs in Seminiferous tubule : CORRECT

• Spermatogenesis is the process of formation of haploid sperms from diploid spermatogonia in human males.
• Spermatogenesis starts at the age of puberty.
• The seminiferous tubules are the coiled structures that comprises the testicular lobules inside the testis.
• The spermatogonia are present on the inside walls of the seminiferous tubules.
• Therefore, the process of spermatogenesis takes place in seminiferous tubules.

Four spermatids mature into four functional sperms : CORRECT

• The spermatogonia divide by mitosis to form primary spermatocytes.
• Primary spermatocytes undergo meiosis to form secondary spermatocytes and then spermatids.
• Thus 4 spermatids are formed by meiosis.
• All 4 spermatids differentiate to form 4 spermatozoa or sperms.

One primary oocyte undergoes meiosis to form one ovum : CORRECT

• In oogenesis, primary oocytes are formed from oogonia by mitosis.
• A primary oocyte undergoes the 1st meiotic division to form 1 secondary oocyte and 1 polar body.
• The secondary oocyte then undergoes the 2nd meiotic division to form 1 ovum and another polar body.
• Therefore, one primary oocyte will form only one ovum.
• This is different from spermatogenesis where all one primary spermatocyte forms 4 sperms.

Oogonia are formed after puberty : INCORRECT

• In females, the diploid oogonia cells are formed during embryonic development in each fetal ovary.
• A few million oogonia are formed in each ovary.
• But oogonia are not formed or added after birth.
• The oogonia divide to form the primary oocyte and enter the prophase I stage of meiosis.
• The oocytes remain arrested at this stage till puberty.
• The division is completed only prior to ovulation.

Key Points

• A transcription unit is a segment of a DNA that comprises of 3 basic regions:
  • Promoter - It is the binding site for RNA polymerase and is located upstream of the structural gene.
  • Structural gene - This is the sequence of the DNA which actually codes for RNA.
  • Terminator - It is the DNA sequence downstream of structural gene, that defines the end of the transcription process.
• According to Watson-Crick's model, DNA has 2 complementary strands that run antiparallel to each other.
• This means that both the strands will have opposite polarity with respect to each other.
• If one is 5' → 3', the other will be 3' → 5'.
• In a transcription unit, the 2 strands are denoted as:

1. ​Template strand - 
   • ​​This acts as a template for RNA polymerase during transcription.
   • This has 3' → 5' polarity so that the RNA can be formed in 5' → 3' direction.
2. Coding strand - 
   • ​​This has the same polarity as the RNA that is to be formed i.e., 5' → 3'.
   • This strand is used as a reference point for denoting upstream and downstream of a gene.
   • The 5'-end of the coding strand is referred as upstream, whereas 3'-end is referred as downstream.
   • This shows that the promoter is towards the 5'-end of the coding strand.​​

​

​Explanation:

Given strand : 5’ - ATGGTAATCCTA - 3’

• The given DNA sequence of a strand that has 5' → 3' polarity.
• It is also mentioned that the promoter is located towards the 5'-end of this strand.
• The position of the promoter defines the coding and template strands.
• Hence, the given strand is the coding strand of a transcription unit.​

Confusion Points

• Please note that the template strand is sometimes called as the non-coding strand.
• This is done just to indicate the opposite strand of the coding strand.
• The coding strand, on the other hand, does not actually code for anything.
• The sequence of a coding strand is called so because it has the same sequence as the RNA with just T being replaced by U in RNA.
• Thus, this sequence shows the codons of the RNA and hence the name.

Key Points

According to Watson and Crick (1953), DNA is a double helical structure with the following features:

• It is made up of 2 polynucleotide strands.
• The two chains have anti-parallel polarity: one has 5'→3' and the other has 3'→5'.
• The two strands are known as complementary strands.
• The bases of two strands project inside and pair through H-bonds and form base pairs.
• Adenine pairs with Thymine by 2 H-bonds and Guanine with Cytosine by 3 H-bonds.
• Thus, purine is always paired with pyrimidine, creating uniform distance between both strands.

Explanation:

• The complementary bases always pair as:
  • A with T
  • G with C
• Here the given nucleotide sequence is: 5’ - ATGGTAATCCTA - 3’
• Therefore, the complementary strand sequence will be: 3’ - TACCATTAGGAT - 5’

Key Points

• The 2 strands of DNA in a transcription unit are referred to as:

1. Template strand - 
   • This acts as a template for RNA polymerase during transcription.
   • This has 3' → 5' polarity so that the RNA can be formed in 5' → 3' direction.
2. Coding strand - 
   • ​​This has the same polarity as the RNA that is to be formed i.e., 5' → 3'.
   • This strand is used as a reference point for denoting upstream and downstream of a gene.
   • The sequence of a coding strand is called so because it has the same sequence as the RNA with just T being replaced by U in RNA.

Explanation:

Given sequence: 5’ - ATGGTAATCCTA - 3’

• This denotes the coding strand as the promoter is towards the 5'-end of this sequence.
• Thus, we can get the mRNA transcript by simply replacing the thymine (T) bases with Uracil (U) in the above sequence.
• Therefore, the mRNA transcript will have the sequence: 5’ - AUGGUAUCCUA - 3’​

Alternate Method

• We can also find the template strand sequence first and then the mRNA transcript sequence from there.
• This method will be based on the complementarity of the bases in DNA and RNA.
• The template strand is the complementary DNA strand of the coding sequence.
• Hence, the template strand will be 3’ - TACCATTAGGAT - 5’
• Again the complementarity of the template strand for RNA will give us the mRNA sequence as: 5’ - AUGGUAUCCUA - 3’

Concept:

• Transcription is the process of copying the genetic information from one strand of DNA onto the RNA.
• It takes place with the help of the enzyme RNA polymerase (RNA pol).
• It takes place at a defined region of DNA that is known as the transcription unit.
• A transcriptional unit can be recognized by the following:
  • Template strand - It acts as the template for RNA pol to act on and has 3'→5' polarity.
  • Coding strand - It has 5'→3' polarity and is used as a reference strand for denoting upstream or downstream of a gene.
  • Structural gene - It contains the nucleotide sequence that actually codes for the required RNA.
  • Promoter - It is the nucleotide sequence that acts as a binding site for RNA pol enzyme.
  • Terminator - It is the nucleotide sequence that defines the end of transcription.
• The promoter is located upstream of the gene, while the terminator is located downstream of the gene.
• Upstream and downstream indicate towards the 5'-end and the 3'-end of coding strand respectively.

Key Points

Steps of Prokaryotic Transcription - 

1. Initiation -
   • RNA pol enzyme binds at the promoter site of DNA with the help of sigma (σ) factor and initiates transcription.
2. Elongation -
   • The sigma factor is released and RNA pol moves along the DNA to untwist the DNA double helix.
   • RNA pol uses nucleoside triphosphates for polymerization of RNA that remains bound to the DNA in the transcription bubble.
   • Some of the newly synthesized RNA is released from the enzyme as a single strand.
   • Only a part of the RNA remains bound as DNA-RNA hybrid.
3. Termination -
   • It is carried out by the Rho protein (ρ) that binds to the terminator site.
   • When the Rho protein comes across the RNA pol enzyme, the RNA is unwound from the DNA.
   • The nascent RNA is released along with the enzyme.
   • The DNA double helix reforms and Rho protein dissociates, terminating the transcription process.

Therefore, Sigma - Initiation, Rho - Termination is the correct answer.

Key Points

• Polyadenylation is a process for post-transcriptional modification of mRNA in eukaryotes.
• In eukaryotes, the mRNA is formed is the form of heterogenous RNA (hnRNA).
• This hnRNA needs to go through some post-transcriptional modification processes to form the mature mRNA that can be translated into polypeptide.
• Transcription in eukaryotes takes place inside the nucleus whereas the translation takes place in the cytoplasm.
• Thus, the mRNA needs to be transported to the cytoplasm for translation to proceed.

Polyadenylation - 

• It is the process of adding about 200-300 adenylate residues to the 3'-end of the newly formed RNA.
• These residues form a poly-A tail at the 3'-end of the mRNA and thus, this process is also known as tailing.
• This process takes place in a template independent manner.
• The RNA molecules have the risk of being degraded by cytoplasmic enzymes when the RNA is transported from nucleus to cytoplasm.
• Polyadenylation helps in protecting the 3'-end of the coding sequence of the RNA from digestive enzymes.

Therefore, none of the given options define polyadenylation.

Additional Information

• Splicing - Removal of introns from the mRNA
• Capping - Addition of methyl guanosine triphosphate at 5’-end of mRNA