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Male Reproductive System

The male reproductive system consists of the following:

  • Primary sex organ: testes.

  • Secondary or accessory sex organs:

  1. Accessory ducts: rete testis, vasa efferentia, epididymis, and vas deferens.

  2. Accessory glands: seminal vesicle, prostate, and bulbourethral glands (Cowper's gland).

  • External genitalia: penis.

Female Reproductive System

The female reproductive system consists of the following:

  • Primary sex organ: ovary

  • Secondary sex organs:

  1. Accessory ducts: pair of oviducts (fallopian tubes), uterus, cervix, and vagina.

  2. Accessory gland: mammary gland.

  • External genitalia: vulva.

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Mammary gland

  • The human female has a pair of mammary glands (breasts) that contain glandular tissues and fatty tissues.

  • Each glandular tissue is divided into 15-20 mammary lobes and each lobe consists of a group of alveoli.

  • The alveoli open into mammary tubules.

  • The mammary tubules of each lobe open into small mammary duct.

  • Several mammary ducts join to form a wider mammary ampulla that is connected to lactiferous duct just before the nipple through which milk is released.

Human Sperm

  • The sperm consists of four parts — head, neck, middle piece, and tail.

  • A plasma membrane envelops the whole body of the sperm.

  • The Head is the enlarged end of a sperm, contains an elongated haploid nucleus, the anterior portion of the nucleus capped by the acrosome.

  • The neck contains proximal centriole which is necessary for the first cleavage division of the zygote and the distal centriole that is connected to the tail filament.

  • Middle piece contains a number of mitochondria that provide energy for the movement of the tail.

  • The tail consists of axial filaments surrounded by the plasma membrane. It helps the sperms to swim in a fluid medium.

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Section of Young Anther

A typical microsporangium appears circular in outline and is surrounded by four walls:

  1. Epidermis: It is the outermost single layer of cell which is protective in nature.

  2. Endothecium: It is the second layer with thick cells, helps in dehiscence, and is protective in nature.

  3. Middle layer: It is the third layer composed of 1-3 layers of cells, helps in dehiscence, and is protective in nature.

  4. Tapetum: It is the fourth and innermost layer of cell with dense cytoplasm and many nuclei. It provides nourishment to the developing pollen grains.

Anatropous ovule 

  • The ovule is a small structure attached to the placenta by means of a stalk called a funicle.

  • The junction between an ovule and a funicle is called the hilum.

  • The ovule is surrounded by one or two protective envelopes called integuments.

  • Integument encircles the ovule entirely except at the tip, resulting in a small opening called the micropyle.

  • The basal part of an ovule opposite to micropyle is called chalaza.

  • The cells with high or abundant reserve food material enclosed within the integument is called nucellus.

  • The female gametophyte located within the nucellus is called an embryo sac.

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An Embryo Sac

  • The female gametophyte (embryo sac) develops from a single functional megaspore.​

  • This megaspore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.

  • At the micropylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus.

  • Similarly, at the chalazal end, three out of four nuclei differentiate as antipodal cells.

  • The remaining two cells (of the micropylar and the chalazal end) move towards the centre and are known as the polar nuclei, which are situated in a large central cell.

  • Hence, at maturity, the female gametophyte appears as a 7-celled structure, though it has 8 nucleate.

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Spermatogenesis is a process in which diploid spermatogonia undergo meiosis to produce haploid spermatids.

  • Each spermatogonium (2n) present within the seminiferous tubules undergoes mitotic division, resultant cells are called primary spermatocytes (2n).

  • These primary spermatocytes periodically undergo meiosis and produce two equal, haploid cells called secondary spermatocytes (n), which have only 23 chromosomes each.

  • The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids (n).

  • The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.


The process of formation of a mature haploid female gamete from the diploid oogonium is called oogenesis.

  • Oogonia undergo meiosis and enters prophase-I, and get temporarily arrested at the stage called primary oocytes.

  • Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle.

  • The primary follicles get surrounded by more layers of granulosa cells and a new theca and called secondary follicles.

  • The primary oocyte within the tertiary follicle undergoes first meiotic division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.

  • Secondary oocyte undergoes second meiotic division to produce a haploid ovum (n) with a second polar body.

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Dihybrid Cross

The cross between two homozygous individuals differing in two characters is called dihybrid cross.

  • Mendel crossed true-breeding round yellow-coloured seeds (RRYY) with wrinkle green coloured seeds (rryy).

  • The gametes RY and ry unite on fertilisation to produce the F1 hybrid RrYy.

  • Mendel found that the seeds resulting from the crossing of the parents had round shaped yellow coloured seeds (RrYy) in the F1 generation.

  • In the next step, F1 hybrids were self-pollinated.

  • In the F2 generation 9 Round, yellow: 3 Wrinkled, yellow: 3 Round, green: 1 Wrinkle, green seeds are produced.

  • The phenotypic ratio of the dihybrid cross is 9:3:3:1.

Incomplete Dominance

It’s a phenomenon in which the F1 hybrid exhibits intermediate characters of the parental gene.

  • It is seen in flower colours of Mirabilis jalapa (4 O'clock plant and Antirrhinus majus (Snapdragon).

  • In a cross between true breeding red flowered (RR) and true breeding white flowered plants (rr), the F1 (Rr) was pink.

  • When the F1 was selfpollinated the F2 resulted in the following ratio 1 Red (RR) : 2 Pink (Rr) : 1 White (rr).

  • Here the phenotypic ratio deviates from the Mendel's monohybrid cross.

  • Both phenotypic and genotypic ratio will be the same 1:2:1.

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  • The negatively charged DNA is wrapped around the positively charged histone octomere to form a structure called a nucleosome.

  • A typical nucleosome contains 200 bp of DNA helix.

  • Nucleosomes constitute the repeating unit of a structure in the nucleus called chromatin, a thread-like stained bodies seen in the nucleus.

  • The nucleosomes in chromatin are seen as ‘beads-on-string’ structure under electron microscope.

  • Histones are organised to form a unit of eight molecules called histone octomere.

Replicating Fork

  • The unique and fixed point where the DNA replication originate is called ‘origin of replication’ or ‘ori’.

  • The complementary strands of DNA double helix are separated by DNA helicase and DNA gyrase. This process is called unwinding of double stranded DNA.

  • The unwinding of double-stranded DNA forms a ‘Y-shaped’ configuration in the DNA duplex, which is called the replication fork.

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Transcriptional Unit

The transcription unit of DNA contains three regions in the DNA:

  1. The promoter: It is the binding site for RNA polymerase for initiation of transcription.

  2. The structural gene: It codes for enzymes or protein for structural functions.

  3. The terminator: It is the region where transcription ends.​

lac Operon Concept

  • In the absence of inducer (Lactose): The regulator gene i regulates and produces repressor protein. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. Hence, no enzymes are formed. This type of operon is said to be “Switched off”.

  • In the presence of inducer: Lactose as an inducer, binds to the repressor and repressor becomes inactive. Now the repressor fails to bind to the operator region. This allows RNA polymerase binds to the operator and transcribes lac mRNA. Lac mRNA is polycistronic, produces all three enzymes called β-galactosidase, permease, and transacetylase. Now the operon is termed as “Switched on”.

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Miller's Experiment

S L Miller and H C Urey performed an experiment in 1953 for chemical evolution.

He created electric discharge in a closed flask containing CH4, H2, NH3 and water vapours at 800 oC.

After few weeks he observed the formation of amino acids and complex molecules like sugars, nitrogen bases, pigments and fats in the flask.


  • It provides experimental evidence for the theory of chemical origin.

  • It showed that the first non-cellular form of life was created about 3 billion years ago.

  • It showed that non-cellular biomolecules exist in the form of DNA, RNA, polysaccharides and proteins. Formation of first cell first non-cellular.

An Antibody Molecule

Antibodies are protein molecules called immunoglobulins (Ig) and are of five typesIgA, IgM, IgE, IgG, and IgD.

An antibody has a Y-shaped structure.

Each antibody molecule consists of four polypeptide chains, two are long called heavy (H) chains while the other two are short called light (L) chains. Hence, an antibody is represented as H2L2.

IgG is the most prevalent antibody in the blood followed by IgA and IgM.

IgA is present in breast milk (colostrum).

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Biogas Plant

  • The raw material for biogas production is the excreta (dung) of cattle.

  • The biogas plant has a concrete tank (10-15 feet deep) in which bio-wastes and slurry of dung are collected.

  • The tank has a floating cover, which keeps on rising on the production of gas in the tank.

  • Methanobacterium in the dung act on the bio-wastes to produce biogas.

  • The gas produced is supplied to nearby houses by an outlet.

  • Through another outlet, the spent slurry is removed to be used as fertiliser.

  • Biogas is used as fuel for cooking and lighting.


Bioreactors are vessels of large volumes (100-1000 liters) in which raw materials are biologically converted into specific products.

  • It provides all the optimal conditions for achieving the desired product by providing optimal growth conditions like temperature, pH, substrate, salt, vitamins, and oxygen.

  • Stirred-tank bioreactors are commonly used bioreactors.

  • These are cylindrical with a curved base to facilitate proper mixing of the contents.

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Agarose Gel Electrophoresis

Gel electrophoresis is a technique for separating DNA fragments based on their size and net electric charges.


pBR322 is the first artificial cloning vector developed in 1977 by Boliver and Rodriguez from E. coli plasmid.

A cloning vector ha the following features;

  • Origin of replication (ori)

  • Selectable markers

  • Cloning site


Life-cyle of Retrovirus (HIV)

  • After getting into the body of a person, the virus enters the macrophages.

  • Here, RNA is replicated to form viral DNA by enzyme reverse transcriptase.

  • The viral DNA now gets incorporated into the host cell's DNA and directs the infected cells to produce viruses.

  • The virus particles enter helper T-lymphocytes (TH cells) in the blood, where they continue to replicate and produce viral progenies.

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Life-cyle of Plasmodium vivax

  • Plasmodium requires two hosts to complete its cycle – Mosquito and human.

  • The infected female Anopheles mosquito transfers the infectious form of Plasmodium, i.e., sporozoites to the human body by biting.

  • The sporozoites reach the liver cells, where they multiply.

  • This is followed by their attack on red blood cells resulting in their rupture.

  • ​The ruptured RBCs release a toxin called haemozoin, which is responsible for high recurring fever, chills, and shivering.

  • These parasites enter the female Anopheles mosquitoes when they bite an infected person.

  • In the body of mosquitoes, they fertilize and multiply in the stomach wall.

  • Sporozoites are now stored in the salivary gland of mosquito till it is again transferred to the human body by a mosquito bite. After entering the human body, all the events are repeated.​

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