Biology Mock Test - 5

The correct answer is Internal fertilization.

• Internal fertilization is the union of an egg cell with sperm during sexual reproduction inside the female body.
• Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction.
• For internal fertilization to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract.
• In mammals, reptiles, some birds, some fish and certain other groups of animals, this is done by copulation, the penis or other intromittent organ being introduced into the vagina or cloaca. In most birds, the cloacal kiss is used, the two animals pressing their cloacas together while transferring sperm.
• Salamanders, spiders, some insects and some molluscs undertake internal fertilization by transferring a spermatophore, a bundle of sperm, from the male to the female.
• Following fertilization, the embryos are laid as eggs in oviparous organisms, or in viviparous organisms, continue to develop inside the reproductive tract of the mother to be born later as live young.

The correct answer is Only I.
Key Points

• In asexual reproduction, only one parent is involved and sex cells are not involved. 
• It is observed in both multicellular and unicellular organisms.
• Types of asexual reproduction are:
  • Binary Fission
  • Budding
  • Fragmentation
  • Vegetative Propagation
  • Sporogenesis
• Spore formation comes under sporogenesis. Hence, statement 1 is correct.
• Spore formation is a kind of reproduction process in plants by producing tiny spores and propagates through them.
• Spore Formation is a method of asexual reproduction. 
• Spore formation can be seen in the bread mould / Rhizopus.
• The airborne spores land on bread under favourable conditions and they germinate and produce new bread mould plants.
• Each spore is covered with a protective coat to withstand unfavourable conditions.
• Plants like ferns, mucor, and mosses are also reproduced through spore formation
• Spores are present in a sac called sporangia.
• Fragmentation is a type of asexual reproduction. Hence, statement 2 is incorrect.

Additional Information

• In sexual reproduction, two parents are involved and the formation and fusion of gametes take place.

Important Points

Concept:

     Microsporogenesis is the formation of microspores in the form of tetrads, which later separate and are called pollen grains.

Explanation:

• During microsporogenesis, meiosis occurs in microspore mother cells.
• Microspore mother cell(2n) undergoes meiotic division for the formation of haploid pollen grains(n).

Additional Information

• Endothecium is the inner layer of a mature anther.
• Microspores are the structures that develop into a male gametophytes.
• Pollen grain is a single cell that contains a male gametophyte and is transferred to the stigma of the same flower or the adjacent flower of the same plant.

The Correct Answer is Removal of Anthers.

• Emasculation is achieved by the removal of Anther.

Key Points

• Emasculation can be achieved by the Removal of Anthers from a bisexual flower.
• Removal of anthers from the flower bud before the anther dehisces is called emasculation.
• Emasculation is essential to prevent self-pollination in bisexual flowers.
• It is to be done in the evening hours before the anthers are dehisced and stigma is likely to become fully receptive.

Additional Information

• Pollination is the transferring of pollen grains from the male anther of a flower to the female stigma.
• The two types of pollination found in flowering plants are:
  • Self-pollination: that occurs within the same plant.
  • Cross-pollination: that occurs between two flowers of two different plants but of the same kind.
    • In cross-pollinated flowers, more pollen grains are produced.
• The cross-pollination helps the flower to survive in a different climatic environment.

Concept: 

• Ploidy: It represents the total number of chromosome sets present in a cell.
• It is denoted by n
• For example n = haploid set (only one set of chromosomes) present
• 2n = Diploid (two sets of chromosomes) present
• Cells having 3 or more than 3 sets of chromosomes are said to be polyploid.

Explanation:

• A female gametophyte or embryo sac is the structure that carries the female gamete the ''egg cell'' along with other cells.
• A female gametophyte at maturity is 7-celled & 8-nucleate.
• Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus, in turn, consists of two synergids and one egg cell.
• Three cells are present at the chalazal end called the antipodals.
• A single large central cell is present at the centre having two polar nuclei (together called secondary nucleus).
• The egg cell, polar nucleus & synergids have haploid number of chromosomes. Whereas, Nucellus and secondary nucleus have a diploid number of chromosomes.
• Thus, the correct option is '3'

​

Mistake Points

• Polar nuclei are individually haploid (n) but when they fuse to form the secondary nucleus, it becomes diploid (2n)

Concept: 

• The endosperm is the food-laden tissue formed during the development of angiospermous seed which provides essential nutrients to the growing embryo and also to the young seedling at the time of seed germination. 
• In angiosperms, the endosperm develops from a triploid (3n) primary endosperm nucleus which is formed as a result of the fusion of a male gamete with the secondary nucleus of the central cell.
• Based on the first and subsequent divisions of the primary endosperm nucleus, the endosperm is of three types nuclear, cellular and helobial.

Explanation:

• In the nuclear type of endosperm development, the primary endosperm nucleus divides by repeated free nuclear divisions without the formation of walls.
• It results in the formation of a large number of free nuclei in the central cell of the embryosac. A big central vacuole develops in the embryosac pushing all the nuclei to the peripheral cytoplasm.
• The nuclear endosperm is the most common type of endosperm.

Additional Information

• Gametes are the reproductive cells. There are two types of gametes that are involved in reproduction, the male gamete, and the female gamete.
  Each gamete carries one copy of the chromosome from the respective parents and they combine together to form the fertilized egg called the zygote. 
• The flower is the reproductive organ of plants. It consists of sepals, petals, androecium, and gynoceium.
• Sepals and petals are the accessory appendages while androecium represents the male sex organ and gynoecium the female sex organ.
• The embryo is the result of the fertilization of male and female gamete. Embryo differentiates to form the complete organism

Concept:

• Menstrual cycle refers to the cyclical events that occur in a female primate, starting from puberty.
• The first menstruation is known as menarche and the end of it at the age of about 50 years is called menopause.
• The menstrual cycle in human females is about 28-30 days.
• Only one ovum is developed and released in each cycle.
• Each cycle can be divided into 4 phases:

1. Menstrual Phase -
   • It marks the beginning of each cycle.
   • The menstrual flow occurs and lasts for 4-5 days.
   • It is caused due to the breakdown of endometrium of uterus.
   • Blood along with clots come out of the vagina.
2. Follicular Phase -
   • It may last from 6th to 12th day.
   • Primary follicles develop into Graafian follicles in the ovary.
   • It is also called Proliferative phase because the endometrium is regenerated through proliferation.
   • The hormones LH and FSH stimulate follicular development and estrogen secretion from the ovary.
3. Ovulatory Phase -
   • It occurs mid-cycle around 13-15th day.
   • The Graafian follicle ruptures to release the ovum into the fallopian tube.
   • This process is called ovulation and is caused by a rapid increase in LH (LH surge).
4. Luteal Phase -
   • The ruptured Graafian follicle forms the corpus luteum, which secretes progesterone.
   • Progesterone maintains the endometrium in anticipation of pregnancy.
   • Absence of fertilization results in degeneration of corpus luteum.
   • This leads to breakdown of endometrium, that marks the beginning of the next cycle.

Important Points

The hormones responsible for menstruation are:

• LH -
  • Luteinizing hormone (LH) plays a vital role in causing ovulation.
  • It is secreted from the anterior pituitary gland.
• FSH -
  • Follicle stimulating hormone (FSH) is responsible for follicle development in the ovaries.
  • It may also stimulate estrogen secretion.
  • It is secreted from the anterior pituitary gland.
• Estrogen -
  • It is synthesized and secreted by the growing ovarian follicles.
  • It plays important role in controlling female sexual behaviour and organ development.
  • It stimulates mammary gland development and controls menstruation.
• Progesterone -
  • It is secreted by the corpus luteum in the ovaries.
  • It controls pregnancy by maintaining the uterine endometrium.
• Therefore, Hormones responsible for menstrual cycle are produced from both ovaries and anterior pituitary gland.

Concept:

Puberty:

• It represents the time period of adolescence when the rate of general body growth begins to slow down, and reproductive tissues begin to mature.
• The most important change which marks puberty is that boys and girls become capable of reproduction.
• Puberty ends when an adolescent reaches reproductive maturity.

Explanation:

• Testes are the primary sex organ in males, it performs two major functions on the onset of puberty - 

1. Testes begin the formation of germ cells or sperms. Sperms are the male gametes that fertilise the female gamete (ovum) to produce a zygote.
2. Secretion of the hormone testosterone. It brings about changes in appearance seen in boys at the time of puberty.

• The secretion of estrogen is not a function of the testes. It is a female sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. 

Thus, the correct option is both 1 & 2

The correct answer is option 2, i.e. Trophoblast.

Key Points

• After fertilization, the fertilized egg undergoes rapid mitotic divisions are called cleavage.
• Cleavage produces a solid ball of small blastomeres and the embryo now looks like a mulberry is known as a morula.
• The morula, later on, changes into a blastula. The blastula of mammals is called a blastocyst.
• The blastocyst of mammals consists of two types of cells - the outer trophoblast & inner cell mass.
• A cavity called blastocoel is also present.
• The inner cell mass differentiates to form the three germinal layers Ectoderm, Endoderm & Mesoderm.
• Trophoblast is the outer epithelium of the blastocyst.
• It forms the fetal part of the placenta.

Additional Information

• Placenta is a structure present in the uterus of a pregnant eutherian mammal that nourishes the foetus.
• Endometrium is the inner lining of the uterus which is richly supplied by blood vessels.
• Acrosome is a vesicle present at the tip of a sperm.
• Acrosome contains hydrolytic enzymes.

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:

• 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 the release of oxytocin from the maternal pituitary.
• Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates the further secretion of oxytocin.
• The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions.
• This leads to the expulsion of the baby out of the uterus through the birth canal
• Thus hormone Oxytocin helps in parturition in human beings.

Important Points 

• The hormone oxytocin is secreted by the posterior part of the pituitary gland also called Neurohypophysis (pars nervosa) 
• Due to its role in parturition, it is also called the birth hormone.

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. 
• Prolactin: It is also called lactotrophic hormone. It regulates the growth and milk formation of mammary glands.
• Progesterone: It is an ovarian hormone. It prepares the inner uterine lining called the endometrium for receiving the embryo and implantation. Progesterone inhibits uterine contraction so that the pregnancy can be maintained. For this reason, it is called the pregnancy hormone

Concept:

• Contraceptives are birth control devices that help in preventing unwanted pregnancies.
• Various contraceptive methods can be divided into:

1. 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.
2. Physical Methods/ Barriers -
   • This is the method by which physical barriers are used to prevent pregnancy.
   • Males can use condoms, while females can use diaphragm, cervical caps or vaults.
   • They block the entry of sperms through the cervix.
3. 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.
4. Oral Contraceptives -
   • This involves oral administration of contraceptives.
   • It is 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.
5. 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.

Important Points

• Intra-uterine devices or IUDs are inserted into the uterus through the vagina by any medical professional only.
• These can be of 3 basic types:

1. Non-medicated -
   • These devices increase phagocytosis of sperms within the uterus.
   • Examples - Lippes loop.
2. Copper-releasing -
   • They release Cu ions which suppress sperm motility and fertilizing capacity of sperms.
   • Examples - CuT, Cu7, Multiload 375.
3. Hormone-releasing -
   • These make the uterus hostile and unsuitable for implantation.
   • Examples - Progestasert, LNG-20.

Therefore, copper-releasing hormones are the contraceptives that prevent pregnancy by suppressing sperm motility.

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.

Therefore, GIFT cannot be used for females who cannot provide suitable environment for fertilization and also cannot retain the embryo inside 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.
• 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 heredity.

Hint

Heredity:

• It is the transmission of genetic characteristics (traits) from parents to offspring.
• As a result, the offspring look similar in some aspects to parents.
• Heredity takes place through reproduction.
• Traits may be - color, height, skin complexion, etc. 

Reproduction: 

• It is the process by which (parent) organisms give rise to new young ones (offspring).
• Reproduction is either asexual or asexual.
• In asexually reproducing organisms offspring looks identical to parents like plants and bacteria
• However, in sexually reproducing organisms variation (differences in traits) arise in offspring.

Inheritance:

• Process of transfer of genetic traits and their expression from one to another generation.
• Genetic information is stored in the DNA, which can be passed on to the next generation through reproduction..

Explanation

Mistake Points

• Please note that 'heredity' and 'hereditary' are words with different meanings.
• 'Heredity' refers to the process of transfer of characters from one generation to another.
• Whereas, 'hereditary' refers to the character that can be transferred from one generation to another.
• For example, haemophilia is a hereditary disease, meaning it can be transmitted by heredity.

Concept:

Aneuploidy is of two types:

1. Hypoaneuploidy (loss)

• 2n - 1 = monosomy (loss of one chromosome only) i.e. the presence of a single copy of a particular chromosome. Eg - Turner's syndrome.
• 2n - 2 = Nullisomy (loss of a pair of the homologous chromosome)

      2. Hyperaneuploidy (addition)

• 2n+1 = Trisomy: addition of one chromosome in one set. Eg - Down's syndrome
• 2n + 2 = Tetrasomy: addition of two chromosomes in one set.

Explanation:

• We know that in trisomy there is an addition of one chromosome in one set of the chromosomes (2n + 1 ).
• So if Drosophila is trisomic for one of the chromosomes A, B,C and D.
• The 4 possible genotypes could be - AAA BB CC DD, AA BBB CC DD,  AA BB CCC DD & AA BB CC DDD.
• Therefore by analysing the options the correct answer will be ''AA BB CCC DD''.

Concept-

• Every honey bee colony comprises a single queen, a few hundred drones, and several thousand worker castes of honey bees.
• A queen bee is the only female bee in the hive that gets to reproduce.
• Worker bees are all female and are all offspring of the queen​. 
• Queen is a fertile, functional female, the worker is a sterile female and the drone is a male insect.
• Queen and worker develop from the fertilized egg while drone develops from an unfertilized egg.
• Further differentiation of queen and worker depends on the quality and quantity of food that is fed to the queen or worker larvae.

Explanation-

• ​The drones are male bees with no sting.
• They are much larger and stouter than either the queen or the workers.
• Their only function is to impregnate the young queen a task which they are unable to perform until they are about 10 days of age.
• They also help in the maintenance of hive temperature. 
• The drones are produced by unfertilized eggs of the queen, or by those workers which take up the reproductive function due to the absence of a queen in a colony.
• The normal life-span of a drone is 57 days. 

Thereby In the honeybee colony, the drones are produced by unfertilized egges.

Additional Information

• The queen
  • ​There is only one queen in a colony and considerably larger than the members of other castes.
  • Swarming is the natural method that honeybee colonies use for multiplying their colonies.
  • The old queen is killed as soon as the new queen is fertilized.
  • The phenomenon of raising a queen in the off-season is called supersedure.
  • The normal life-span of a queen is 3 years.
• ​​The worker
  • ​Smallest inhabitants of the beehive.
  • They are imperfect females incapable of laying eggs.
  • Worker bee's primary duties are cleaning, feeding developing larva once hypopharyngeal glands develop, ripening of honey, secreting/molding of wax into combs.
  • The life-span of a worker is about 4 weeks during the active season and 8 to 10 weeks during the less active season.
  • On certain occasions when the colony is in need of a queen, some of the workers start laying eggs from which only drones are produced.
  • These workers called laying workers.

The correct answer is Monohybrid cross.

Key Points

• Mendel gives the law of purity of gametes on the basis of monohybrid crosses.
  • To understand the idea of the purity of gametes, a monohybrid cross is taken.
  • A monohybrid cross between pea plant-bearing axial flowers (AA) and plant-bearing terminal flowers (aa). In hybrid F1, two types of male and female gametes are formed in equal quantity.
  • On separation, these factors are randomly united in pairs at the time of fertilization and transferred to offspring.
  • In pure homozygous forms both factors being alike, only one type of gametes is formed.
  • In F2 generation, two varieties appear in ratio 3:1.
  • That is why law can also be defined as allele pairs separate during gamete formation and the paired condition is restored by random fusion of gametes during fertilization.

Additional Information

• Backcrossing is the crossing of a hybrid with one of its parents, or an adult genetically identical to the parent, to obtain offspring with a genetic identity close to that of the parent.
  • It is used in horticulture, animal breeding and gene knockout organism development.
  • A dihybrid cross describes a mating experiment between two organisms that are equally hybrid for two traits.
  • A hybrid organism is one that is heterozygous, meaning that it carries two different alleles at a particular genetic position or locus.
  • In its simplest form, a test cross is an experimental cross of an individual organism of the dominant phenotype, but an organism with unknown genotype and a homozygous recessive genotype (and phenotype).

Concept-

• Mendel proposed two general rules to consolidate his understanding of inheritance in monohybrid crosses.
• Today these rules are called the Principles or Laws of Inheritance the First Law or Law of Dominance and the Second Law or Law of Segregation.
• According to the law of dominance.
  • Characters are controlled by discrete units called factors.
  • Factors occur in pairs.
  • In a dissimilar pair of factors, one member of the pair dominates the other.

Explanation-

• The dihybrid cross involves two characters in a single plant.
• The parent pea plants are of two types.
  • Tall plants with violet flowers.
  • Short plants with white flowers.
• So, the genotype of the parents could be-
  • Tall plants with violet flowers: TTWW or TtWw
  • Short plants with white flowers: ttww
• Since all the progeny bore violet flowers, it implies that the tall plant with violet flowers has genotype 'WW' for violet flower color. 
• Since the progeny acquired is both tall and short, the parent plant was not a pure tall plant and carry genes that determine the short height of the plant.
• Therefore, the genotype of the plant with respect to height would be 'Tt'.

So, if a cross is carried out between a tall parent with violet flowers (TtWW) and a short parent with white flowers (ttww), the progeny obtained is TtWw (8) : ttWw (8).

Mistake Points

• Please note that in pea plants violet colour of flowers is dominant over white colour.
• Also, the violet colour character has been denoted here by "W" and not "V" (which is the initial letter of the dominant character).
• It is important to remember which character is dominant over which, irrespective of the letters that are used to denote it in the cross.

Additional Information

• Law of Segregation 
  • This law is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the F2 generation though one of these is not seen at the F1 stage. 
  • Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors.
  • Of course, a homozygous parent produces all gametes that are similar while a heterozygous one produces two kinds of gametes each having one allele with equal proportion.

Concept-

• Genetic material is the substance that stores biological information, transfers this information from one generation to the next.
• Proteins because of their complexity and diversity were initially believed to be genetic material. But they are unable to replicate.
• DNA and RNA are the genetic material.
• DNA is the genetic material that came from the experiments of Alfred Hershey and Martha Chase.

Explanation-

• A molecule that can act as a genetic material must fulfill the following criteria:
  • It should be able to generate its replica (Replication).
  • It should chemically and structurally be stable.
  • It should provide the scope for slow changes (mutation) that are required for evolution.
  • It should be able to express itself in the form of 'Mendelian Characters’. 

Thereby the ability to replicate is one of the important properties of genetic material.

Important Points

DNA characteristic-

Concept:

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

Explanation:

• Replication of DNA occurs in the S phase of mitosis for this reason it is also called as synthesis phase.
• During the S phase, the amount of DNA present In each cell doubles i.e. if previously the cell had a 2C amount of DNA, now it has 4C.
• However, the chromosome number remains the same, if the cell had 2n or a diploid number of chromosomes at G1, even after the S phase number of chromosomes will remain the same i.e. 2n

Important Points

• Replication of Nuclear DNA occurs at the S phase, while replication of the cytoplasmic DNA may occur at any stage of the cell cycle.  

​Additional Information

• Interphase is divided into 3 phases:
• G1 phase/Post mitotic/Pre-DNA synthetic phase/Ist gap phase - Synthesis of different types of RNA and proteins.
• S-phase/Synthetic phase
• G2-phase/Pre mitotic/Post synthetic phase/IInd gap phase - Formation of tubulin protein required for the spindle fibre formation.
• Interphase is followed by M phase which is the division phase

The correct answer is All of the above.

Key Points

Characteristics features of genetic code:-

• It is always universal: CORRECT
  • Being universal means each codon codes for a specific amino acid in all organisms.
  • ​The genetic code is a set of codes by which a linear sequence of nucleotides specifies the linear sequence of a polypeptide.
  • That is, they specify how the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptide.
• It is a triplet of nucleotides bases corresponding to 20 amino acids: CORRECT
  • ​The nucleotide sequence is read as triplets called codons, each of which codes for a specific amino acid. 
  • There 20 non-essential amino acids that are produced in the body, but there are only 4 nucleotide bases.
  • Thus, a combination of bases is required.
  • Doublet codes are not adequate to code for 20 amino acids because it gives only 4² = 16 codons.
  • Triplet code gives 4³ = 64 codons.
  • Therefore, it was pointed out that the triplet code is the minimum required.
• It is non-overlapping, non-ambiguous, and commaless: CORRECT
  • ​Non-overlapping - It is read in a continuous manner without overlapping any codon.
  • Non-ambiguous - One codon codes for only one specific amino acid.
  • Commaless - It is comma-free and there is no other punctuation to indicate the end of one codon and the beginning of the next.
• It has a start and a stop codon: CORRECT
  • The codon AUG codes for Methionine as well as acts as a START codon.
  • It initiates the process of polypeptide chain formation.
  • The 3 codons UAA, UAG, UGA do not code for any amino acid, but act as STOP codons.
  • When any one of them occurs it causes the release of the polypeptide chain from the ribosome. 

Concept

• Lactose is used as an energy source in E. coli in absence of glucose.
• The presence of lactose induces a polycistronic lac operon.
• This is a set of genes regulated by a common promoter and regulatory genes.
• The lac operon after being induced produces β-galactosidase.
• β-galactosidase hydrolyses lactose into monomeric units that can be further used as an energy source.

Important Points 

• E. coli does not produce β-galactosidase in absence of lactose.
• The operon uses lactose as an inducer to produce β-galactosidase only in presence of lactose.
• The operon is inhibited from transcribing by a repressor. 
• The i gene constitutively (all the time) produces the repressor protein. 
• In the absence of lactose as an inducer, the repressor binds to the operator and discourages transcription.
• In presence of lactose, lactose binds to the repressor, which then gets inactivated.
• Lactose binds to the repressor and frees the operator site.
• ​RNA polymerase can then slide along the operator site.
• Transcription begins for genes z, y, a.
• The gene z codes for β-galactosidase, y codes for permease and gene codes for transacetylase.

​Therefore, if E. coli is grown in the absence of lactose, it will stop the synthesis of β-galactosidase.

The correct answer is Alec Jeffreys.

• DNA fingerprinting is a technique that shows the genetic makeup of living things.
• Father of DNA fingerprinting in the world is Sir Alec John Jeffreys.
• Father of DNA fingerprinting in India is Dr Lalji Singh.

Additional Information

Some other important names:

The correct answer is A, B and C.

Key Points

• The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859.
• It is the process by which organisms change over time as a result of changes in heritable physical or behavioural traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.
• Hugo de Vries (1901) put forward a theory of evolution, called mutation theory.
• The theory states that evolution is a jerky process where new varieties and species are formed by mutations (discontinuous variations) that function as the raw material of evolution.
  • Mutations or discontinuous variations are the raw material of evolution.
  • Mutations appear all of a sudden. They become operational immediately.
  • Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.
  • The same type of mutations can appear in a number of individuals of a species.
  • All mutations are inheritable.
  • Mutations appear in all conceivable directions.
• Lamarck is best known for his Theory of Inheritance of Acquired Characteristics, first presented in 1801 (Darwin's first book dealing with natural selection was published in 1859)
• If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring.
• Lamarck also said that body parts that are not being used, such as the human appendix and little toes are gradually disappearing. Eventually, people will be born without these parts.
• Lamarck also believed that evolution happens according to a predetermined plan and that the results have already been decided.
• The theory of segregation deals with the meiosis (cell division) of human and does not deal with the evolution of life. This theory is given by Mendel.

The correct answer is to perform the same function in both animals but is anatomically very different.

Concept:

Evidence for evolution:​

• Fossils
• Analogous and homologous organs 
• Embryological evidence 

Anatomy: It refers to the internal structure of an organism. 

Explanation:

Homologous organs:

• These organs are similar in origin and structure but perform different functions.
• For example, the Forelimbs of frogs, lizards, bats, and humans have the same basic structural plan but different functions.
• The wings help in flight whereas the human forearm helps in various activities.

Analogous organs:

• These organs have similar functions but are different in structure and origin.
• For instance, the wings of a bat and a bird are similar in function, but this similarity does not mean that these animals are more closely related.
•  The wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are modified forearms covered in feathers. 

Thus, we can say that analogous organs perform the same function in both animals but are anatomically very different.

Concept:

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

Key Points

• One of the theories regarding the origin of life was given by Oparin and Haldane.
• They suggested the following:
  • The first forms of life originated from pre-existing non-living organic molecules.
  • This meant that chemical evolution preceded biological evolution or formation of life.
  • Chemical evolution - refers to the formation of diverse organic molecules from the existing inorganic molecules.
• This theory of chemical evolution was first established by Miller's experiment in 1953.

Explanation:

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

Additional Information

• Louis Pasteur - He suggested that life originates from pre-existing life only.
• S. L. Miller - He performed an experiment to establish the theory of chemical evolution.
• Darwin and Wallace - They both worked on the theory of natural selection.
• Hugo de Vries - He proposed the mutation theory of evolution.

Concept:

• The duration of the earth's history has been divided into smaller spans called the eras.
• The five eras are Archeozoic era, Proterozoic era, paleozoic era, Mesozoic era & Cenozoic era 
• Out of these, the three more recent eras are further divided into smaller spans known as the periods. which in turn are split up into epoches.

Explanation:

• The most recent era is considered to be the Cenozoic era. It is also called the era of Modern life
• The correct order of eras from beginning to present is
• Archeozoic era → Proterozoic era → paleozoic era → Mesozoic era → Cenozoic era

Key Points

• Ascaris is an intestinal parasite that causes ascariasis.
• Symptoms - internal bleeding, muscular pain, fever, anemia, blockage of the intestinal passage.
• The worms reside in the intestine and eggs are excreted along with the feces.
• A healthy person can acquire infection through water, vegetables, fruits, etc. contaminated by the feces of an infected person.
• These worms can reside, reproduce and grow in large numbers inside the human intestine.

Additional Information

Diseases spread by imperfectly cooked pork - Trichinosis diseases

• Pigs and cows can accidentally ingest eggs of tape-worms. 
• These tapeworm eggs hatch and the larval stages settle in the muscle of pigs.
• Thorough cooking kills the tape-worm, its eggs and larval stages.
• Undercooked pork and beef may still have the tape-worm which can enter our intestine and cause infection.

Diseases spread by Tse-tse fly - African Trypanosomiasis or Sleeping sickness

• It is caused by microscopic parasites Trypanosoma brucei.
• Trypanosoma brucei is transmitted by the tsetse fly (Glossina species)
• The fly is found only in sub-Saharan Africa.

Diseases spread by Mosquito bite - Malaria, Dengue, Chikunguniya, Filariasis, Yellow fever, Encephalitis, etc.

Diseases spread by contaminated food and water - Typhoid, Ascariasis, Amoebiasis, Cholera, Botulism, etc.

Key Points

​Auto-immune disease -

• Due to genetic abnormalities in the immune system sometimes the body attacks its own cells, tissues and organs.
• This occurrence is called auto-immunity.
• This might cause certain disorders or disease that are known as auto-immune disease.
• In this disorder, the body cannot distinguish its own cells (self cells) and foreign cells (non-self cells) and hence attacks particular cells of its own body
• Example: Rheumatoid arthritis.

Additional Information

Allergic Response

• Allergy is the exaggerated response of the immune system to certain antigens present in the environment 
• The substances to which produce allergic immune responses are called allergens.
• IgE antibody is produced against allergens. 
• Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
• Symptoms are sneezing, watery eyes, running nose and difficulty in breathing.
• Drugs against allergy - anti-histamine, adrenalin and steroids.
• Examples of allergens - mites in dust, pollens, animal dander, etc. 

​Graft Rejection

• Graft rejection is the event of rejection of the organ received from the donor by the recipient of an organ transplant.
•  This happens because the immune system has the ability to differentiate self and non-self cells/tissues/organs.
• The cell-mediated immune response is responsible for graft rejection.

Active Immunity

• It results from the direct exposure to the disease-causing organism
• The immune system of the organism itself is responsible for providing protection
• Active immunity is provided due to the production of antibodies by the organism after the attack of disease-causing organism
• It is long-term or in most cases permanent immunity
• This immunity takes a longer time (a few weeks) to develop and no immediate immunity is observed
• Active immunity has immunological memory, i.e., in case of the event of the disease infecting a second time the organism recognizes the pathogen and activates defense against it and is able to fight it.
• Examples:

1. Injecting weakened or dead microbes for vaccination
2. Natural Infection

Key Points

Oncogenes -

• Oncogene = Onco + genes
• 'Onco' means 'relating to tumors' and genes are 'units of heredity that give characteristics to an organism'.
• Oncogenes are genes that are related to tumor or the genes that cause cancer.
• They can be 

1. viral oncogene - genes present in virus that on infection cause cancer.
2. cellular oncogenes/ proto oncogenes - genes present in normal cells which when activated under certain conditions can cause cancer.

Additional Information

• Carcinomas - it is a type of cancer that starts in cells of skin or tissue that make up the lining of organs such as the liver or kidneys
• Cancer -
  • Normal cells stop diving after coming in contact with other cell
  • This property is called 'contact inhibition'.
  • Cancer cells lose this property and produce tumors.
  • Tumors are of two types 1. benign 2. malignant
  • Benign tumor remain confined to their original place of growth
  • Malignant tumors grow very rapidly and starve neighbouring cells.
  • They show the property of metastasis.
  • In metastasis, cells slough off from cancerous growth and reach distant sites via blood and form a new tumor wherever they lodge.
  • Cancer can be cause by oncogenic viruses, radiation, carcinogens, etc.
  • Interferons, chemotherapy, and radiation therapy are some of the treatments for cancer.

The correct answer is option 2, i.e. Pusa Komal.

• Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant. 
• Some crop varieties bred by hybridization and selection, for disease resistance to fungi, bacteria and viral diseases are as follows:

Concept-

• A virus is a small parasite that cannot reproduce by itself.
• Viruses contain a nucleic acid core, enclosed with a protein capsid.
• After infection of a susceptible cell, a virus can direct the cell machinery to produce more viruses.
• The virus was discovered by Russian scientist Ivanovsky.
• In nature, there are ultra-microscopic particles known as viruses.
• Viruses are a connecting link between the living and nonliving organisms.

Explanation-

• Several wild relatives of different cultivated species of plants have been shown to have certain resistant characters but have very low yields.
• Hence, there is a need to introduce resistant genes into the high-yielding cultivated varieties.
• Resistance to the yellow mosaic virus in bhindi (Abelmoschus esculentus) was transferred from a wild species.
• And resulted in a new variety of A. esculentus called Parbhani Kranti.

Therefore Yellow mosaic in ladyfinger is a viral disease.

Additional InformationBacteria

• Bacteria are the sole members of the kingdom Monera.
• They are the most abundant micro-organisms.
• Bacteria occur almost everywhere.
• Hundreds of bacteria are present in a handful of soil.

Fungi

• The fungi constitute a unique kingdom of heterotrophic organisms.
• They show a great diversity in morphology and habitat.
• Fungi are cosmopolitan and occur in air, water, soil, and on animals and plants.
• Reproduction in fungi can take place by vegetative means fragmentation, fission, and budding.

Protozoa

• All protozoans are heterotrophs and live as predators or parasites.
• They are believed to be primitive relatives of animals.

Concept:

• Plant breeding is the intentional manipulation of plant species to create desirable varieties that are better suited for cultivation, can give better yield and are disease resistant.
• Breeding can be achieved by conventional methods or mutation breeding.

Important PointsSteps of conventional Plant Breeding Technique -

1. Collection of Germplasm -
   • Germplasm - is the entire collection of plants or seeds that have all the diverse alleles for all the genes in a given crop, i.e., the entire variability of a crop.
   • Germplasm is collected for the preservation of all the different wild varieties, species and relatives of the cultivated species for exploitation of natural genes present in population.
2. Selection of Parents -
   • The germplasm collection is screened for identifying parents with the desirable combination of characters.
   • The selected parents may be multiplied to obtain a pure-line variety, if required.
3. Crossing of Selected Parents -
   • Cross-hybridization of the parents are done to obtain 2 different characters from 2 different plants.
   • Thus the parent plants produce hybrid plants.
4. Selection of Hybrids -
   • All the crosses do not produce the desirable hybrid plants.
   • Therefore, the hybrids need to be selected according to the desired combination of characters.
   • The hybrids are then self-pollinated for several generations to obtain homozygosity and prevent segregation of characters in the progeny.
5. Testing & Release of New Cultivars -
   • The selected varieties are tested for yield and other agronomic values.
   • They are grown in testing fields under ideal conditions of fertilizers, irrigation, etc. and the results are recorded.
   • After that the cultivars are grown in the farmer's field for at least 3 growing seasons at different agroclimatic zones across the country.
   • The evaluation is then compared with the best local cultivars for reference.
   • The hybrid cultivars are then released into the market for commercialization.

Therefore, the correct sequence for the steps of plant breeding technique is C → B → D → A → E.

• Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa, and some algae.
• Microorganisms may be single-celled like bacteria, some algae, and protozoa, or multicellular, such as algae and fungi.
• They can survive under all types of environments, ranging from ice-cold climates to hot springs and deserts to marshy lands.
• They are also found inside the bodies of animals including humans.
• Microorganisms play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases
• Microorganisms are used for various purposes. They are used in the preparation of curd, bread, and cake.

• Curd contains several microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
• Lactobacillus is a gram-negative bacteria
• It is rod-shaped and a beneficial bacteria that can be found in fermented foods and supplements.

Important Points

• Conversion of milk into curd is done by the process called fermentation.  

Additional Information

• Yeast: It is used in the fermentation of bread & alcohol  
• Paramecium is a genus of Protozoa. They belong to the Protista kingdom.
• It has a stiff outer covering which gives it a shape of a slipper. It has the ability to swim very fast.
• Amoebae are eukaryotes whose bodies most often consist of a single cell.  It can be found on decaying bottom vegetation of freshwater streams and ponds.

Key Points

• Carbon monoxide is NOT a constituent of biogas.
• Biogas is the mixture of different gases produced by the breakdown of organic matter in the absence of oxygen.
• Biogas consists of Methane (CH₄) which is about 60 to 65 per cent and Carbon Dioxide (CO₂) which is about 30 to 35 per cent.
• Biogas also consists of 4 to 5 per cent of water vapour and traces of Hydrogen Sulphide (H₂S) and oxidised sulphur compounds.

Additional Information

• Biogas is a renewable source of energy that can used for heat or electricity generation.
• It can be produced from agricultural wastes, cattle dung, etc. by the action of methanogenic bacteria.

Concept:

• Biotechnology uses the living organism, its machinery or parts to develop, create and produce different products.
• Many enzymes naturally found in living systems are used in biotechnology.
• Some of such enzymes are restriction enzymes, DNA ligase, DNA polymerase, reverse transcriptase and many more.
• These enzymes have different functions and are used for different purposes.

Key Points

• Restriction enzyme - production of RFLPs : CORRECT
  • Restriction enzyme is a protein that cleaves DNA strands at sequence-specific sites.
  • It recognizes a certain DNA sequence and cuts DNA at those sites.
  • Restriction Fragment Length Polymorphism (RFLP) works on the principle that different individuals have variations in DNA sequence at sites recognized by restriction enzymes.
  • This variation leads to the production of different length fragments when cut by restriction enzymes.
  • Different individual DNA, when cut by the same restriction enzyme, can produce DNA fragments of different lengths.
  • Therefore, Restriction enzymes are used in RFLP.
• DNA ligase - enzyme that cuts DNA, creating the sticky ends of restriction fragments : INCORRECT
  • DNA ligase is a specific type of enzyme that facilitates the joining of DNA strands.
  • Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.
  • DNA ligases are able to catalyze the formation of such 3'-5' phosphodiester linkage.
  • Sticky ends of restriction fragments are formed by the use of restriction endonucleases.
  • Restriction enzymes cut DNA, DNA ligases join them.
  • Therefore, DNA ligase is not involved in cutting DNA and producing sticky ends.
• DNA polymerase - used in a polymerase chain reaction to amplify sections of DNA : CORRECT
  • DNA polymerase adds nucleotides to the 3'-end of a DNA strand, one nucleotide at a time.
  • The polymerization is in 5'→3' direction.
  • The polymerase chain reaction is a laboratory method used to multiply a specific region of DNA and produce millions of copies.
  • The PCR requires a DNA template, primer, DNA polymerase, and dNTPs to function.
  • DNA polymerase is required to catalyze the polymerization step of PCR. 
• Reverse transcriptase - production of cDNA from mRNA : CORRECT
  • Reverse transcriptase is an RNA-dependent DNA polymerase.
  • It transcribes a single-stranded RNA into DNA.
  • mRNA is used as a template for a cDNA product.
  • Mature mRNA does not contain introns. 
  • Because of the removal of introns, the DNA produced is not an exact copy of genetic DNA and hence called complementary DNA or cDNA.
  • Therefore reverse transcriptase helps in the production of cDNA.

Therefore only option 2 is an incorrectly paired option.

Concept:

• Recombinant DNA using a bacterial cell is prepared by joining a gene of interest from the source with a bacterial plasmid.
• The plasmid acts as a vector carrying the gene of interest.
• The plasmid carrying the gene of interest is called recombinant DNA.
• Recombinant DNA can then be transferred into the host cell.
• In this case, the gene of interest is a human gene and the host cell is a bacterial cell.
• The host cell then uses its own machinery to produce the desired gene product.

Explanation:

• Eukaryotic mRNA has introns that prokaryotes do not have.
• The eukaryote mRNA needs post-transcriptional modification like splicing, capping, and tailing to act as a mature functional mRNA.
• Splicing is the removal of introns, capping is the addition of 7-methylguanosine to the 5' end of mRNA and tailing is the polyadenylation of 3' end of mRNA.
• These processes are not required in prokaryotes.
• A directly inserted human gene is NOT processed in prokaryotes because eukaryotic genes require post-transcriptional modification to be able to translate.
• The machinery for post transcriptional modification is inside eukaryotes and the bacterial cell does not contain it.

Therefore, in the given case, the human gene might have had introns, which the transformed bacterial cells could not process and thus the desired protein was not produced.

 Additional Information

Correct Method that would yield the desired protein:

• Instead of direct insertion of DNA of interest, its mRNA product is isolated from a human cell.
• An mRNA product of the desired gene will be modified post-transcription in the human cell.
• The mature mRNA DOES NOT have any introns.
• This mature mRNA is then extracted and transformed into a cDNA using reverse transcription.
• Reverse transcription will use the mRNA template to produce a DNA product, called cDNA.
• cDNA will NOT contain intron sequences because the mature mRNA did not have intron sequence after splicing inside human cell.
• This cDNA can be inserted into a bacterial cell.
• cDNA CAN BE processed by the prokaryotic cellular machinery to produce the desired protein.

Concept:

• In recombinant DNA (rDNA) technology, the aim is to produce a desirable protein product.
• In order to obtain the protein, the rDNA needs to be expressed.
• The host cells must be induced to express the foreign gene by providing appropriate conditions.
• This would provide us with the recombinant protein, produced by a heterologous host.
• Heterologous host refers to the host cell that produces the protein in a cell line where it is not supposed to be.
• The recombinant proteins can be extracted and purified using various separation techniques in the laboratory.
• But this would only give a small-scale production.
• Large scale productions are done in bioreactors.

Important Points

• Bioreactor - is a vessel where substances can be biologically converted to specific protein products.
• They use a continuous culture system, where used medium is removed from one side while fresh medium is added from other side.
• This helps in maintaining the cells in the exponential phase of growth.
• This gives us a higher yield of the desired protein due to the larger biomass produced.
• In a bioreactor, 100-1000L of cultures can be processed.

Therefore, a continuous culture system should be chosen for producing recombinant proteins in large amounts.

Additional Information

Stirred-type Bioreactor -

• It is usually cylindrical or with a curved base that helps in mixing of the contents.
  • A simple stirred-tank bioreactor comes with a stirrer that mixes the contents evenly and facilitates oxygen availability throughout the reactor.
  • A sparged stirred-tank bioreactor uses sterile air bubbles that increase the surface area for oxygen transfer.
• These bioreactors typically consist of:
  • Agitator system
  • Oxygen delivery system
  • Foam control system
  • Temperature control system
  • pH control system
  • Sampling ports.

Concept:

• Plant genomes are often modified genetically to obtain pest-resistant or stress-tolerant varieties that give higher yield.
• These are referred to as genetically modified organisms (GMOs).
• One such example is the Bt-cotton that carries the gene for Bt-toxin.

Key Points

• Bt-toxin is obtained from the bacterium Bacillus thuringiensis.
• This toxin is effective in killing insects like -
  • Lepidopterans - Tobacco budworm, armyworm.
  • Coleopterans - Beetles.
  • Dipterans - Flies, mosquitoes.
• The gene encoding this toxin is named as 'cry' gene and so Bt-toxin is also known as Cry protein.
• These genes produce insect-group specific toxins and thus can be introduced into crop plant genomes to make them pest-resistant.
• The genes cryIAc and cryIIAb are effective against cotton bollworms, while the gene cryIAb is effective against corn borers.
• Thus, Bt-cotton is resistant against cotton bollworms and Bt-corn is resistant against corn borers.

Important Points

• Assertion : TRUE
  • The cry gene from Bacillus thuringiensis is inserted into the plant genome to get pest-resistance.
  • This protects the plants from harmful insects, which leads to an increase in crop yield.
• Reason : TRUE & CORRECT Explanation
  • The Bt-toxin exists in the inactive protoxin crystal form in the bacteria.
  • The Bt-toxin gets activated in the alkaline gut of insects, where the crystals get solubilized.
  • This releases the active toxin, which binds to the midgut epithelial cells of insects.
  • This creates pores causing cell swelling and lysis.
  • This leads to the death of the insect or insect larvae.

Therefore, both the assertion and the reason are true and the reason is a correct explanation of the assertion.

Concept:

• Transgenic plants refer to those that have had their genomes modified to possess and express a foreign gene.
• This is achieved by genetic engineering techniques.

Key Points

• The tumour-inducing plasmid that is used in the production of transgenic plants is also known as the Ti plasmid.
• The Ti plasmid is obtained from the bacterium Agrobacterium tumefaciens.
• This bacterium is a pathogen for several dicot plants.
• The plasmid is responsible for converting normal cells into tumor cells in the plant.
• The bacteria can naturally deliver the pathogenic DNA called T-DNA with the help of this Ti-plasmid.
• The T-DNA induces the formation of tumor or crown gall, which then secretes the chemicals required by the pathogen.
• Thus, this Ti-plasmid has been modified to be a non-pathogenic cloning vector that can efficiently deliver our desired gene fragment.
• The modified Ti plasmid does not cause any tumour, but effectively transfer the foreign DNA by acting as a vector.
• These plasmid vectors were also used for RNA interference (RNAi), to prevent infestation of tobacco roots by the nematode Meloidegyne incognita.

Additional Information

• Escherichia coli
  • ​It is widely used in biotechnological processes for various purposes.
  • EcoRI is a restriction enzyme obtained from this bacteria.
  • The cloning vector pBR322 is also obtained from E. coli.
• Bacillus thuringiensis
  • ​It is a bacterium that produces the Bt-toxin, which is insecticidal in nature.
  • The genes producing this toxin is used to produce transgenic plants that are resistant to certain insects.
  • Example - Bt-cotton is resistant to cotton bollworms.
• Staphylococcus aureus
  • ​It is Gram-positive bacterium that can cause a number of infections in the human body.

Concept:

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

Important Points

• The first clinical gene therapy was done in 1990 to a 4 years old girl for the treatment of SCID caused by ADA deficiency.
• ADA stands for adenosine deaminase, an enzyme crucial for the immune system.
• The deficiency of ADA results in severe combined immunodeficiency (SCID) disorder.
• It is caused by the deletion of the gene encoding ADA.
• If not treated properly, the disease can even be fatal because of the weak immune system.

Additional Information

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

Concept:

• The environmental conditions or abiotic factors varies from from one habitat to another.
• Some habitats even have some extreme conditions for life to survive.
• Thus, organisms evolve responses towards these conditions that would give them better survivability.
• Adaptation refers to such attributes of an organism that enables it to survive and reproduce in its habitat.

Important PointsTypes of Adaptations -

• Morphological - These are morphological changes in an organism that helps them survive harsh climates.
  • Desert plants minimize transpiration by having thick cuticle on leaves, reduced leaves in form of spines, sunken and reduced stomata on lower epidermis.
  • Aquatic mammals of polar seas have a thick layer of fat called blubber that insulates and reduces heat loss.
  • Mammals from colder climates have shorter ears and limbs, which helps in reducing heat loss.
• Physiological -
  • The CAM pathway in desert plants allows the stomata to be closed during day and open for respiration only at night, when transpiration can be minimum.
  • Kangaroo rat in North American deserts use internal fat oxidation to obtain water as a byproduct and thus meet its water requirement.
  • Humans compensate the low O2 availability at higher altitudes by increasing the rate of breathing and RBC production.
• Biochemical -
  • Microbes survive in hot springs and hydrothermal vents by producing enzymes that are thermostable i.e., the enzymes remain active even in high temperatures. 
• Behavioural -
  • Organisms like desert lizards bask in the sun to absorb maximum heat and move into the shade to avoid the heat.

Explanation:

• According to Allen's rule, mammals from the colder climates have shorter ears and shorter limbs.
• This reduces the surface area to volume ratio and thus help in minimizing heat loss.
• It was shown with the example of hare species that lived at different climatic conditions.
• For example, jackrabbits that live in North American grasslands have longer ears and limbs.
• Whereas, the arctic hare that lives in the arctic tundra region have shorter ears and shorter limbs.

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 PointsExponential Growth -

• Growth of a population depends on the resources available.
• Therefore, ideally if the resources in a habitat are unlimited, the growth in also unlimited.
• Such cases where the population keeps growing exponentially is known as exponential growth.
• As observed by Darwin, with unlimited resources the species are able to realize their full growth potential.
• This results in an increased reproductive ability leading to exponential growth of the population.

It can be denoted by the equation:

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

where, N = Population Density,

\(dN \over dt\) = 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 'r' value varies from population to population:
  • Norway rat - 0.015
  • Flour beetle - 0.12
  • Human population in India (1981) - 0.0205
• When the population density (N) is plotted against time (t), it produces a J-shaped curve for exponential or geometric growth.

Additional InformationThe integral form of the above equation is:

\(N_t = N_0 e^{rt}\)

where, \(N_t\) = Population density after time 't'

\(N_0\) = Population density at time 0 (zero)

\(e\) = Base of natural log (2.71828)

\(r\) = Intrinsic rate of natural increase

Concept:

• Symbios is is the interaction between two different organisms living in a close physical association. Members of the different population (species) often interact with each other, in various ways in their environment. Their interactions are based on three factors:-

1. Nature of food and mode of obtaining it.
2. Kind of space needed as a shelter.
3. Habits such as aggregation, breeding etc.

• 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:

• The term symbiosis means "living together'' (G. syn = together, bios = life).
• Symbiosis includes all interactions in which two species actually live together without regard to benefit or harm to the participants (de Bary, 1879).
• It thus includes commensalism, protocooperation, mutualism, ammensalism and parasitism.
• Hence, symbiosis may be defined as short or life - long intimate association of two different species as a means of obtaining food by one or both the partners but may also provide protection to one member from enemies, thus in general both the species gets benefited. The species participating in symbiosis are termed as symbionts.

Additional Information

• Replacement of one organism by another more adapted to its environment is called Natural Selection.
• In this phenomena, nature selects the individual with high reproductive fitness i.e. survival of the fittest.
• For example - Excessive use of herbicides and pesticides results in resistant varieties of microbes in a much lesser time scale.
• When one organism being host to a parasite that causes it to become ill. This state is called parasitism in which the parasite is benefited while the host is harmed.
• Example - Louse (pediculus) living on the human scalp. It sucks blood, cause irritation and spread diseases like typhus, replasing fever.

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.

Key Points

• Trophic system refers to the system in which energy flows from one trophic level to another.
• Trophic level is the specific place in the food chain that is occupied by an organism based on their source of food.
• In an ecosystem, we find unidirectional flow of energy from Sun to producers to consumers.
• Ecosystems need a constant supply of energy to synthesize the molecules required in order to counteract the universal tendency of increasing disorderliness.
• In a grazing food chain, the energy trapped by the producer is passed on to the consumer or leads to death, which starts the detritus food chain and the energy is passed on to the decomposer.
• According to Lindeman's 10% Law, only 10% of the energy in a trophic level is transferred to the next, so that there can only be a limited number of trophic levels in each ecological pyramid.

Explanation:

• The pyramid of energy is always upright because of the 10% Law, meaning energy keeps decreasing at successive trophic levels.
• The unidirectional flow of energy gives stability to the ecosystem.
• Therefore, the pyramid of energy can never be inverted in a stable ecosystem.

Additional Information

• The pyramid of number is upright in grassland ecosystem, while inverted in parasitic ecosystem and variable in forest ecosystem.
• The pyramid of biomass is usually upright, but can be inverted in pond ecosystem.

Explanation:

• An ecosystem is the basic ecological unit in which living organisms interact among themselves and with their surrounding physical environment.
• Except for the deep sea hydro-thermal ecosystem, the sun (sunlight) is the only source of energy for all ecosystems on earth.
• Out of the total incident solar radiation, only 50% of it is photosynthetically active radiation (PAR).
• Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. So, there is the unidirectional flow of energy from the sun to producers and then to consumers.
• The energy is transferred in an ecosystem in the form of food which is degraded and lose a major part of food energy as heat during metabolic activities, this can be explained by Lindeman’s 10 per cent law which says only 10% of energy is transferred from one trophic level to the next higher trophic level. 

Additional Information

• Glucose is a simple sugar with the molecular formula C₆H₁₂O₆. Glucose is the most abundant monosaccharide.
• Proteins are long chains of amino acids that are interconnected by peptide bonds.
• A.T.P is the energy currency of cells produced in mitochondria, these are required for various biochemical processes.

Key Points

• Food chain - is a linear sequence of flow of energy takes place between different organisms that are related to each other by the food they consume.
• Food chains outline who eats whom in an ecosystem.
• The organisms are classified into different categories according to their feeding order.
  • Producers - synthesize food from solar energy. This covers all photosynthesizing plants and algae.
  • Primary consumers - come immediately after producers and comprise herbivores that feed on the producers directly.
  • Secondary consumers - feed on primary consumers and hence comprise of carnivores.
  • Tertiary consumers - feed on secondary consumers and are also carnivores.
  • Decomposers - break down dead, decaying organisms into simpler inorganic substances. E.g. - Fungi.

Explanation:

• In the given food chain: Green plants → Insects → Snakes → Peacock
• Therefore, this food chain follows as:
  • Starting from the green plants which are the producers
  • Insects are the primary consumers
  • Snakes are the secondary consumers
  • Peacock is the tertiary or apex consumer.
• ​The apex of a food pyramid comprises of such a consumer which is not eaten by any other animal in that food chain.

Additional Information

• There are two main types of food chains:
  • Grazing - These food chains start with the producers and are the major system of energy flow in aquatic ecosystems.
  • Detritus - The starting point is dead organic matter from other food chains and is the major energy flow system in terrestrial ecosystems.

The correct answer is 1, 2, and 3.

Key Points

There are four major causes 

• Habitat loss and fragmentation:
  • This is the most important cause of driving animals and plants to extinction.
  • The most dramatic examples of habitat loss come from tropical rainforests.
  • Once covering more than 14 percent of the earth’s land surface, these rain forests now cover no more than 6 percent.
    • They are being destroyed fast.
  • Besides total loss, the degradation of many habitats by pollution also threatens the survival of many species.
  • When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories, and certain animals with migratory habits are badly affected, leading to population declines.
• Over-exploitation:
  • Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources.
  • Many species extinctions in the last 500 years were due to overexploitation by humans.
  • Presently many marine fish populations around the world are over-harvested, endangering the continued existence of some commercially important species.
• Alien species invasions:
  • When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive and cause the decline or extinction of indigenous species.
  • The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.
  • The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.
• Co-extinctions:
  • When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.
  • When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate.
  • Another example is the case of a coevolved plant-pollinator mutualism where the extinction of one invariably leads to the extinction of the other. 

Key Points

• Biodiversity has been defined by Edward Wilson as the combined diversity of all the levels of biological organization.
• It has taken millions of years to accumulate the current biodiversity that we observe on Earth today.
• This biodiversity can be categorized in 3 different levels:

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

Explanation:

• Rauwolfia vomitoria is a medicinal plant that yields an alkaloid drug called reserpine.
• Species of R. vomitoria growing in different Himalayan regions show variations in their potency and reserpine concentrations.
• This variation in the same species represents genetic diversity.

The correct option is 1.

Key Points

• Eichhornia crassipes is also called as water hyacinth.
• Eichhornia crassipes, the world’s most problematic aquatic weed, is also called the ‘Terror of Bengal’.
• Because they grow faster than our ability to remove them.
• It grows abundantly in eutrophic water bodies and leads to an imbalance in the ecosystem dynamics of the water body.
• It is a beautiful mauve-colored flower.
• These plants which were introduced into India for their lovely flowers have caused havoc by their excessive growth by causing blocks in our waterways. 

Important Points 

• Eutrophication is the gradual increase in the biomass of phytoplankton resulting in 'algal blooms' due to an increase in the concentration of phosphorus, nitrogen, and other plant nutrients in an ageing aquatic ecosystem such as a lake.

Additional Information

• Lantana Camara is a flower-bearing shrub.
• Parthenium hysterophorus is a flowering plant species.

Concept:

Greenhouse effect

• It occurs due to the increase in the percentage of carbon dioxide in the atmosphere
• It absorbs the solar rays and energy of the sun due to which the temperature on the earth increases and natural balance gets disturbed
• Our vehicles and industries are continuously increasing the amount of carbon dioxide in the atmosphere

Global Warming

• An increase in the average temperature of the earth surface due to the greenhouse effect is called global warming
• It also refers to the increase in the average temperature of the air and sea at the earth's surface which causes climate change

​Explanation:

• It is clear from the above-given concept that the greenhouse effect increases the earth's temperature by trapping the reflected Sunlight, and in turn become a major cause of Global Warming
• Thereby, the correct option is ''Global Warming''

Important Points

Green House Gases (GHG):

• Water vapour - causes about 36% - 70% of the greenhouse effect
• Carbon dioxide (CO2) causes 9 - 26%
• Methane (CH4) causes 4 - 9% and ozone (O3)