Refraction- The Unique Way Of Perceiving Light Rays By ‘Lenses’(Technique used- Ray diagrams)

At a glance, we may feel that lenses (example- magnifying glass) and plane mirrors (example- looking mirror) are more or less the same, as both are made of glass. But, the two are very different from each other, when we consider their properties as regards their behaviour towards light rays.

Outwardly, the basic difference between the two is that Plane mirrors are flat, shiny glasses, do not let any ray of light to pass through them, instead Reflect (send back) all the light rays falling on them.

Lenses, on the other hand, are spherical, transparent glasses through which the light rays can pass and while passing through the lens, they get Refracted (bent) to finally converge or diverge, at or from the Focus.

What is a lens?

A lens is made up of two spherical glasses joined together.

Lenses are of 2 types depending on their shape and properties:-

Two Types Of Lenses- CONVEX(Converging)above & CONCAVE (Diverging)below (Photo credit- Pixabay)

Convex lens

It is thickened (bulging out) in the middle and thinner towards the periphery. It converges all the light rays passing through it at the Focus. It is said to have a Positive Focus or Positive Focal length because the Incident ray and the refracted ray, both travel in the same direction.

Concave lens

It is thinner (bulging inwards) in the middle and thickened towards the periphery. It appears to diverge all the light rays passing through it from the Focus. It is said to have a Negative Focus or Negative Focal length because the refracted ray appear to diverge from the opposite direction of the Incident ray.

What is Focus, Focal length, Centre of curvature and Pole of the lens?


It is the point where all the light rays coming from Infinity converge (as in convex lens) or appear to diverge (as in concave lens) after passing through the lenses. The Focus lies on the right side of the lens as well as on the left side of the lens because the light rays can pass through the lens from any side. If light rays pass through the lens from the right side, image is formed on the left side and vice versa.

Focal length

It is the distance between the Focus and the Centre/ Pole of the lens. Focal length is half of the distance of Centre of curvature.

Centre of curvature

It is the centre of the Sphere of which the lens is part of. It is ‘Twice the distance of Focal length. It is also written as 2F. Any distance beyond 2F is called Infinity. A lens has 2 Centres of curvature because the lens is part of 2 Spheres. Centre of curvature for any spherical lens can be measured by measuring the Radius of the sphere of which the lens is a part (remember lens is made up of parts of 2 spheres joined together).

Pole of the lens

It is the point where the Principal axis meets the surface of the lens. The central vertical dotted line (shown in fig.) is taken as the Centre/ Pole of the Lens for ray diagram purposes.

Are the images formed by a lenses, real or virtual?

Generally speaking, the images formed by Convex lenses are REAL ie. they can be obtained on the screen while the images formed by Concave lenses are VIRTUAL.

How and where the images are formed in a Convex lens?

There can be 5 conditions (as shown in the above figure) of the different positions of the OBJECT. They are:-

1. Beyond 2F
2. At 2F
3. Between 2F and F
4. At F
5. Between F and Centre of the lens

By keeping the object at above positions, one by one, we can obtain images on the other side of the lens on the screen, by moving the screen closer or farther so as to obtain sharp images.

Let’s see what will be the positions of Images for the above 5 locations of the Object

Condition 1

When the object is beyond 2F, the image is formed between 2F1 and F1 on the other side of the lens. The image so formed is real, inverted and diminished.

Condition 2

When the object is at 2F, the image is formed at 2F1 on the other side of the lens. The image so formed is real, inverted and equal in size to Object.

Condition 3

When the object is between 2F and F, the image is formed beyond 2F1 on the other side of the lens. The image so formed is real, inverted and enlarged.

Condition 4

When the object is at F, No image is formed. After refracting, the light Rays are travelling parallel to each other and cannot produce an image.

Condition 5

When the object is between F and O, the image is formed somewhere behind the Object on the object side of the lens. The image so formed is virtual, erect and enlarged or magnified. Example- magnifying glass.

How and where the images are formed in a Concave lens?

Image Formed In A Concave Lens ; AB is the Object ( Photo credit- Pixabay)

By keeping the OBJECT at any of the 5 different positions (as described in conditions above) in front of the Concave lens, we always get Virtual (image that cannot be obtained on screen), Erect and Diminished images.

This can be verified in the same way as in Convex lens, by holding the Object (torch or candle) at different positions, one by one, on one side of the Concave lens and moving the screen on the other side of the lens at different positions till we get sharp images.

Uses of Convex lens

1. Used as a magnifying glass
2. Used in making spectacles, microscopes, telescopes, binoculars, cameras, projectors etc.

Uses of Concave lens

1. Used in making spectacles ie. convex lens to correct hypermetropia or farsightedness and concave lens to correct myopia or shortsightedness
2. Used in ‘Peep holes’ in the entrance doors
3. Used in TV dish antenna

Some FAQs

Q1.Why are Ray diagrams important?

Ans. Ray diagrams are valuable tools for determining the path of light from the object to our eyes.

Q2. Why do the light rays ‘bend’ when they pass through the lens?

Ans. Because while the light rays pass through the lens, the medium changes. So, when the light rays pass from rarer (air) medium to denser (glass) medium, they bend and vice versa.

Q3. How many incident rays do we take into consideration while making Ray diagrams for a convex lens?

Ans. 3

Q4. Where do these three incident rays are shown to pass from while making Ray diagrams to show the location of the image formed?

Ans. First incident ray travelling parallel to the Principal axis, passes through the focal point after refraction. Second incident ray travelling through the focus runs parallel to the principal axis after refraction. Third incident ray travelling through the centre of the lens continues to travel in the same direction after refraction.

Q5. How do we determine the location of the image?

Ans. The point of intersection of the three incident rays (explained above) determines the image location.

Home Assignment For Readers

Draw Ray diagrams to show the location of Images, individually, for all the 5 conditions for the positions of the Object in front of the convex lens.

Take help of the following fig. to draw the Ray diagrams:-

The Curious World Of Reflection (Technique used- Ray diagrams)

We, practically every day, see our reflection in the mirror and have always wondered how we get our reflection or image in the mirror. It almost looks like a magic, when we see our image doing exactly the same actions what we actually do in front of the mirror. In this blog, we will decipher, how we get an image in a plane mirror; Is that image real or virtual; How is it different from the image on a photograph and so on.

To know all the answers, we must first know that we can see reflection of an object only when there is a source of light illuminating the object.

We see our image or reflection in the mirror because our body is being illuminated, say by a bulb or a tube-light (our body itself has no light of its own and so are the many objects that we see around us).

Now, when we stand in front of the plane mirror, several parallel rays of light (called Incident Rays) strike the plane mirror surface and all these incident rays are sent back or reflected (called Reflected Rays) at various angles in accordance with their Angles Of Incidence.In a plane mirror, the ‘angle of incidence’ is always equal to the ‘angle of reflection’. This is the basic Law Of Reflection due to which images are formed. When the reflected ray reaches our eyes, we are able to see the image in the plane mirror.

Now, the question arises that if we are able to see the image due to the reflected ray of light, then why can’t we see our image in the wall or a paper or any other such surface, as all surfaces reflect lightsome more & some less?

RAY DIAGRAM Showing Incident Ray & Reflected Ray in PLANE MIRROR (Photo credit- Pinterest)

The surface of the plane mirror is smooth and there is a silver coating at the back to make the plane mirror shiny and this is protected by red paint to not allow the light to pass through the mirror. Very shiny surfaces like mirror reflect all the light. Here, the Incident Ray is sent back as Reflected Ray in a definite direction ( called Regular Reflection) & the angle of incidence is exactly equal to the angle of reflection, so image is formed on such a surface.

On the other hand, the surface of the wall or paper is rough, composed of several tiny particles. Each tiny particle disperses the Incident Ray in different directions (called Irregular or Diffuse Reflection), so no images are formed on such a surface.

Examples of smooth surfaces are- plane mirror, still water, polished metal surface etc.

Examples of rough surfaces are- paper, wall, stone, wood etc.

Is the image formed in a plane mirror- Real or Virtual (unreal)?

The image formed in a plane mirror is virtual (unreal) because it cannot be obtained on the screen. It appears to be formed behind the mirror. So, it’s just an illusion. If we extend the reflected rays backwards (shown by dotted lines) behind the mirror, they will meet at a point, that will mark the position/ location of the image so formed of the object.

RAY DIAGRAM showing REFLECTION in a PLANE MIRROR (Photo credit- Pinterest)

On the other hand a real image can be obtained on the screen. For example- the images on cinema screen shown by a projector are Real Images.

How is a Virtual image different from a Real image?

• A virtual image is unreal or an illusion and can’t be formed on the screen.

• A virtual image is ‘erect’ ie. top of the object is the top in the image and bottom of the object is the bottom in the image.

• A virtual image is at the same distance behind the mirror as the object is in front of the plane mirror.

• A virtual image shows ‘lateral inversion’ ie. the left side of the object becomes the right side of the image and vice-versa.

• A virtual image is exactly the same size as the object.

If several Incident Rays come out of an object, why do we take into consideration only 2 Incident Rays while making a ray diagram to show image formation?

This is done purely for the sake of convenience and clarity. We consider/take 2 Incident Rays from the two extremities of the object (top & bottom) and correspondingly show their 2 Reflected Rays.

What is ‘angle of incidence’ and ‘angle of reflection’?

If you draw a perpendicular (called Normal) to the surface of plane mirror, the angle formed between incident ray and the Normal is called the ‘angle of incidence’ and that formed between the reflected ray and the Normal is called the ‘angle of reflection’.

According to the law of reflection, these 2 angles should be equal ie. angle of incidence should be equal to angle of reflection.

Some FAQs

Q1. How are we able to see the image of another object in the plane mirror even when we are not standing in front of the mirror?

Ans. If the reflected rays from the mirror (originating from the object as incident ray) reach our eyes, we are able to see the image of that object in the mirror, even if we are not standing in front of the mirror or we are away or at an angle from the mirror.

Q2. How do we see objects in the universe?

• The object should either be luminous or be illuminated by a source of light (like sun, bulb, tube-light, candle etc.).

• The reflected ray from the object reaches our eyes and pass through the eye- lens and an image is formed on the retina (screen of the eye). This image is ‘inverted’ which is perceived and corrected by the brain by sending signals through the optic nerve.

Q3. Is the photograph a real or a virtual image?

Ans. The photograph is a real image as it is obtained on the screen- the photographic paper, in this case.

Q4. Does the photograph image show ‘lateral inversion’?

Ans. No

Q5. Will the movie (images) taken by a movie camera (Handy cam) be called real image or virtual image?

Ans. Real image

Q6. Why is an incident ray or a reflected ray shown as a straight line with an arrow?

Ans. Because light travels in a straight line and the arrows indicate the direction of the incident ray and the reflected ray respectively.

Applications Of Reflection In Plane Mirror

• We can see our image (same size and erect) in the mirror and so it helps us in viewing ourselves, doing make- up, combing hair etc.

• Plane mirror (made slightly convex) is used as a rear view mirror in vehicles to view the vehicles coming from behind.

• You can view a person, who is in another adjoining room, if you have a mirror in your room and the connecting door is just open enough to let an incident ray from the person (object) come in.

• Plane mirror is used in jewellery shops and other showrooms to make the shop look bigger and glittering / loaded with stuff.

• A parallel arrangement of two plane mirrors can be used to make a Periscope. (Periscope is a device that gives a higher view than normal; used in submarines etc).

Home Assignment For Readers


Find the anomalies in the following ray diagrams:-

Answer 1
Answer 2
Answer 3
Answer 4

Cracking The “Periodic Table Of Elements” Using Mnemonic Technique

As a student, I found it very difficult to memorise the Periodic Table Of Elements in Chemistry course.

Periodic table has been very cautiously designed, considering or arranging all the elements, that exist on the earth, in the increasing order of their Atomic Numbers.

Elements have been recognised ROW-WISE which are called PERIODS (1 to 7). GROUPS 1 to18 have been marked COLUMN- WISE also. Among these, a few Groups show many common properties like the Boron family, Carbon family, Nitrogen family, Oxygen family, Fluorine family, Inert gases etc.

I have tried to figure out the easiest way of sequential remembering of the “names of elements” in the Periodic Table, which I found to be the “Mnemonic” technique.

The beauty of the Mnemonics that I have created is as follows :-

• They make minimal use of helping verbs, prepositions, articles, etc.
• They mostly include words (in Mnemonic) which follow the sound of the element (word) in consideration.
• Common names (wherever approved) of elements have been considered like iron, copper, gold, silver, etc.
• As far as possible, at least the first two letters of the words used in Mnemonics are the beginning letters of the elements ; somewhere even three letters match with the names of the elements.
• Use of names of ‘animals’ in Mnemonics make them interesting to read. At the same time, it aims at Multi- disciplinary approach by connecting Chemistry with Biology.
Periodic Table Of Elements (Photo credit – Pixabay)

Period 1 & 2

It includes the following elements :-

H He Li Be B C N O F Ne

They signify Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon respectively.

Mnemonic for Period 1 & 2

Hydra Heats Liver, Berries Both; Carries Nitrogen,Oxygen; Floats Nervously.

Period 3

It includes the following elements :-

Na Mg Al Si P S Cl Ar

They signify Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine, Argon respectively.

Mnemonic for Period 3

Soda Magically Alters Silicon-city’s Photo Shop’s Classic Arrangement.

Period 4

It includes the following elements:-

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

They signify Potassium, Calcium, Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Gallium, Germanium, Arsenic, Selenium, Bromine, Krypton respectively.

Mnemonic for Period 4

Potbellied Cat Scrubbed Till Vandy Cracked Mangoes. Irritated Cowboy Nipped Currants. Zika Gulped Germs As Selfish Brother Krafts.

Period 5

It includes the following elements:-

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

They signify Rubidium, Strontium, Yttrium, Zirconium, Niobium, Molybdenum, Technetium, Ruthenium, Rhodium, Palladium, Silver, Cadmium, Indium, Tin, Antimony, Tellurium, Iodine, Xenon respectively.

Mnemonic for Period 5

Ruby Straddled Yellow Zebra in Nairobi, Mopped Techie’s Rug in Rome. Plump, Silver- tongued Caddie’s Indecent Tinseltown Auntie Telecasted Idiot Xiang.

Period 6

It includes the following elements:-

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

They signify Caesium, Barium, Lanthanum, Hafnium, Tantalum, Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold, Mercury, Thallium, Lead, Bismuth, Polonium, Astatine, Radon respectively.

Mnemonic for Period 6

Case of Baboon’s Lantern, Handed-over to Tarantula, was Truly Resisted by Ostrich, Irrespective of Platinum, Gold Matters of Thefts in Leeds. Bills & Policies attracted Radio-news.

Home Assignment for Readers:-

Now, hope you got enough motivated to create your own Mnemonic for LANTHANIDES & ACTINIDES series & PERIOD 7.

Why children are not the exact copies of their parents? (Technique used- Simplified Definitions)

Conventionally, we feel that a child should look exactly like his parents since he inherits 50% of his genetic material from father and 50% from his mother. The siblings, too, should look alike. But the reality is that, you the child may look quite like his parents, somewhat similar, or totally different. The same holds true of siblings (except for monozygotic/ identical twins). This all happens, or depends on the mixing of genes, that is passed on to the child in case of sexual reproduction.

Now, before we move further we should know what genes are?

Genes are small parts of DNA that encode for a specific protein. (These Proteins carry out specific function as was described in the previous blogs). Genes are present on structures called Chromosomes which are present in the nucleus of the cell. There maybe 25,000 to 35,000 genes in a single human cell. These Genes make up the hereditary material where each gene is responsible for the expression of a particular trait. Genes are present in pairs, one each on the corresponding homologous chromosome pair. From the pair, one gene comes from the mother and the other from the father.

From this knowledge, an obvious question comes to our mind- what are chromosomes?

A chromosome is a thread like structure or a strand which bears the genes. It is composed of a single DNA double helix molecule (the double helix is held together by complimentary base pairs as was described in one of the previous blogs). Instead of having one long piece of DNA, our DNA is broken into 23 pairs of shorter pieces called chromosomes. Of the 23 pairs, 22 pairs of chromosomes look the same in both males and females and they are known as AUTOSOMES . The 23rd pair differs in male and female and so is known as the Sex Chromosome pair. The Sex Chromosome pair is XX in a female and XY in a male. In females, one X chromosome is inherited from the mother and the other X chromosome is inherited from the father. In males, the X chromosome is inherited from the mother and the Y chromosome is inherited from the father.

Full Set Of Human Chromosomes (23 pairs)
Including The Sex Chromosome Pair (circled) (either XX or XY will be present)
(Photo credit- Shutterstock)
The Chromosomes including the sex chromosomes are present in all the cells, be it somatic or reproductive cell.

How the sex cells are different from the other cells of the body in the type of cell division methods?

The somatic cells other than the sex cells undergo a cell division called MITOSIS (equational cell division) by which new cells are formed (each daughter cell receives a full set of chromosomes from the parent cell ie. diploid condition) from the old cells which have a fixed lifespan. Due to Mitosis, damaged body cells are constantly repaired and replaced. So, in Mitosis, the chromosome number is maintained at 46.

The sex sells undergo another type of cell division called MEIOSIS (reductional cell division) apart from Mitosis. In males, MEIOSIS I followed by MEIOSIS II, occurs at the time of Puberty and as a result of this, 4 haploid Sperms (having half the number of chromosomes from parents cell) are produced from each germ cell.

In females, MEIOSIS I occurs during the embryonic stage, during which a fixed number of germs cells are produced. MEIOSIS II occurs on maturation, when 1 haploid Egg (and 3 Polar bodies which are discarded) is released during each Menstrual cycle.

What are homologous chromosomes?

  • Homologous chromosomes occur in pairs.
  • A pair of homologous chromosome contains one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization (ie. zygote formation).
  • A pair of homologous chromosomes carry the same genes, one from each parent.
  • The two X chromosomes are considered homologous, whereas the X and Y chromosomes are not considered homologous.
  • The following diagram explains well about the homologous chromosomes and the sister chromatids :-
Homologous Chromosomes (Yellow & Orange colours show chromosomes, one each from mother & father)
(Photo credit- Shutterstock)

What are non- sister chromatids?

Following the DNA replication, now each chromosome is composed of two DNA molecules. The two identical copies of chromosomes are called chromatids. So, now each homologous chromosomes pair contains four chromatids.

Non-sister chromatids are the chromatids of the homologous chromosomes pair.

Where does mixing of genes occur?

Mixing of Genes occurs in Prophase I Stage of MEIOSIS I in both males and females through a process of Crossing Over and Recombination between non-sister chromatids of homologous chromosomes.

How Crossing Over occurs?

  • Crossing over is basically a phenomenon of breaking, transposition and fusion of chromosomal segments.
  • The non-sister chromatids first break at certain points due to the activity of enzymes called endonucleases.
  • Then the broken segments get exchanged and finally get fused with the other chromatid due to the action of the enzyme called ligase.
  • A little amount (3%) of DNA synthesis occurs during the time of crossing over to repair the broken chromosomes.
  • The resultant cross after crossing over is called Chiasma or Chiasmata.
Homologous Chromosomes Showing Crossing Over & Recombinants Formed
(Photo credit- Shutterstock)

Result of Mixing of Genes/ Random chance splitting of genetic material :-

• The spermatozoa (sperms) so formed (after Meiosis II), contain haploid number of chromosomes ie. only one set of chromosomes, and are comprised of Recombinant Chromosomes (due to mixing of genes or crossing over). So,this set of chromosomes/ genes is unique to that particular sperm.
• Similarly, the ova (eggs) so formed (after Meiosis II), contain haploid number of chromosomes ie. single set of chromosomes, which are comprised of Recombinant Chromosomes (due to crossing over). So, this set of chromosomes/ genes is unique to this particular egg.
• Here, it’s worth mentioning that the different sperms and different ova produced by individuals, have different genes due to random chance separation of genetic material. So, siblings who share the same parents, may have little similarities or a lot of dissimilarities. If the siblings look alike, the mix of genes they inherited is similar.

When this ‘unique sperm’ (haploid) fertilizes the ‘unique egg’ (also haploid), a ‘zygote’ is formed which is diploid with two sets of chromosomes- one from sperm and the other from egg. So, this zygote gives rise to a ‘unique individual’.

Significance of Crossing over and Recombination

Meiosis cell division, involving Crossing over and Recombination of chromosomes, lead to segregation of chromosomes and accounts for Genetic Variations, which is the most important evolutionary benefit of sexual reproduction.

Search, explore and find out, the many interesting mysteries, heredity and genetics unfold…

Easy-Way-To-Understand Science Concepts Using Controlled Experiment Technique

The most tangible way to comprehend science concepts is ‘learning by doing’.

It has been very well said by Confucius

I hear and I forget. I see and I remember. I do and I understand.

The pragmatic approach for learning science rudiments is by conducting experiments, starting from simpler Hands-on to Lab. experiments.

So, the Motto of science learning becomes –

Experimentation, Experimentation and Experimentation“.

Experiments are a part and parcel of science learning. Many so-called difficult concepts can be subdivided into simpler rules, derived from previous knowledge, observations and logic. Then, based on previous knowledge/ observations, a chain of experiments can be developed to arrive at the BIG, FINAL Concept/ Rule.

Experiments are hands-on activities every child enjoys and performs with great delight and interest.Even the weakest child feels enthused and motivated when he experiments with his own hands. Here, he uses his own intellect and creativity and sees things happening in the way written in the text books. Such a hands-on activity has an indelible mark on his cognition.
Science concepts which are dependent on a number of factors or conditions can be easily taught and explained by CONTROLLED EXPERIMENTS technique.
In Controlled Experiments, all conditions are kept CONSTANT except for the one which you want to test/ verify.
The ADVANTAGE of a Controlled Experiment is that you can eliminate much of the Uncertainty about your Results.If you couldn’t control each factor, you might end up with a confusing outcome.

Learning Controlled Experiment Method With An Example

We want to find out which conditions are required for seed germination.

We know from our previous knowledge/ observations that when we sow a seed in the soil, we give it the following things or conditions:-

• Water
• Air

Now we need to devise an experiment in which we keep controlling one condition at a time which we want to verify, and keep all the other conditions Constant.

STAGE 1 : Seed Germination (bean seeds) On Moist Cotton
(Photo credit- seeds grown at home)
STAGE 2 : Emergence of Hypocotyl (embryonic stem)
(Photo credit- seeds grown at home)
STAGE 3 : Emergence of Plumule
(embryonic shoot)
(Photo credit- seeds grown at home)
STAGE 4 : Emergence of First Leaves
(Seedling developed)
(Photo credit- seeds grown at home)
Let’s verify each condition one by one

BOWL 1: We control the factor ‘soil’ by eliminating it and germinating seeds on moist cotton(to provide water). Other conditions ie. air, water and warmth are kept constant.

BOWL 2 : We control the factor ‘water’ by germinating seeds on dry cotton (to eliminate water). Other conditions ie. air and warmth are kept constant.

BOWL 3 : We control the factor ‘air’ by keeping the cotton containing seeds immersed in water (to cut off the air supply). Other conditions ie. water and warmth are kept constant.

BOWL 4 : We control the factor ‘warmth’ by putting the seeds on moist cotton in a refrigerator.So, other conditions ie.air and water are kept constant.

After a few days we observe the following results :-

BOWL 1 : Seedlings develop; so soil is not necessary for seed germination.

BOWL 2 : No seedlings develop; so ‘water’ is an essential requirement for seed germination.

BOWL 3 : No seedlings develop; so ‘air’ is an essential requirement for seed germination.

BOWL 4 : No seedlings develop; so ‘warmth’ is an essential requirement for seed germination.

Conclusion- Since no seedings develop in Bowl -2, 3 & 4, so we infer that water, air and warmth are the three essential factors/conditions for Seed Germination.
Extrapolation – Since seedlings develop in Bowl 1, we infer that soil is not required for seed germination. This means that seeds can germinate without soil also.This is because, in the initial stages of growth/germination, the embryo utilises the food/ nourishment stored in seed cotyledons/ endosperms to give rise to the baby root (radicle) and the baby shoot (plumule).By the time, the first few leaves appear, the food stored in the cotyledons/endosperms gets exhausted and now the leaves make food for the plant. Also, by this time the seedlings should have been planted in the soil for further growth.

Some examples of science concepts which can be better understood by Controlled Experiment technique

1) ‘Buoyancy’ which depends on factors like volume of the object and density of the liquid
2) ‘Evaporation’ which depends on factors like surface area and temperature
3) ‘Photosynthesis’ which depends on factors like presence or absence of chlorophyll, carbon dioxide, and sunlight
4) ‘Rate of a chemical reaction ‘ which depends on factors like amount of reactants, temperature, presence or absence of catalyst

Ponder a while and get going …it’s simple & fun!


Home grown Pinto bean seeds (on moist cotton in a bowl ) showing Stage 4 of Seed Germination. It shows Developing Seedling with coming out of First leaves and Epicotyl leaving Dried Cotyledons below........(.images for Stages 1, 2 & 3 also available immediately )


Knowing The ‘Virus’ To Understand The Ongoing Pandemic Better (technique used- diagrams)

Viruses have always been the focal point of concern for man because of their great infectivity, great numbers in which they exist, ultramicroscopic size, ever-changing genetic nature due to mutations etc and their status /existence (living or nonliving).

In this blog, we will try to shed some light on various aspects of virus viz. structure, infectivity, virulency, genetic changes or mutations, and nature of Coronavirus.

Structure of virus

Structure Of A DNA Virus(Icosahedral) & A Bacteriophage(Icosahedral head & Helical tail) (Photo credit- Pinterest)

All viruses contain two components

1) A nucleic acid genome – DNA or RNA and not both

2) A protein coat or capsid – that covers the genome

Together they are called Nucleocapsid.

3) In addition, many animal viruses contain a lipid envelope

The entire intact infectious virus particle is called VIRION. So, a Virion consists of an RNA or DNA core, with a protein coat, sometimes with external envelopes.

The core confers infectivity and the capsid provides specificity to the virus.

The Protein capsid is 2 types

1) ICOSAHEDRAL– (a) Identical protein subunits form an icosahedron (made up of equilateral triangles fused together in a spherical shape) coat or capsid.

(b) Such viruses are released into the environment when the host cell dies, breaks down or lyses, thus releasing the virion.

(c) Ex- polio rhinovirus

2) HELICAL– (a) The proteins are arranged in a circular fashion, creating a disc like shape. The disc shapes are attached helically creating a tube, with room for nucleic acid in the middle.

(b) Ex- tobacco mosaic virus

Two types of virus based on structure

1) ENVELOPED Virus- (a) in these viruses, the nucleocapsid is surrounded by a lipid bilayer called envelope, which is derived from the host cell membrane during replication after infection.

(b) The envelope is formed when the virus is exiting the host cell via budding. (Non-enveloped viruses kill the host cell in order to escape).

(c) Ex- herpes simplex, chickenpox, influenza virus, hepatitis C virus

(d) Some viruses have projections from the envelope known as ‘SPIKES’ which help in attachment of virus to the host cell. Ex- HIV, coronavirus

2) COMPLEX Virus – (a) These virus structures have a combination of icosahedral and helical shape and may have head- tail morphology.

(b) This head- tail morphology is unique to viruses that only infect bacteria and are known as bacteriophages.

(c) Here, the head is icosahedral with the helical tail. The tail is used to attach to the bacterium.

(d) Ex – poxvirus

Different Types Of Viruses (Photo credit- Pinterest)

Classification of Viruses

The virus may contain RNA ( so called RNA viruses)or DNA (so called DNA viruses) in their genome. RNA viruses comprise about 70% of all viruses on earth.

The RNA single strand may be –

(1) a sense strand ( plus strand) which can function as a mRNA or

(2) an anti-sense strand (minus strand) which cannot function as mRNA for protein translation.

So, RNA & DNA viruses can be classified as –

1)Plus strand RNA viruses
2) Minus strand RNA viruses
3) Double- stranded RNA viruses
4) Single-stranded DNA viruses
5) double-stranded DNA viruses

Genetic changes in viruses (Mutations)

Viruses are continuously changing as a result of genetic selection. They undergo subtle genetic changes through Mutation and major genetic changes through Recombination.

Mutation occurs when an ERROR is incorporated in the viral genome. Recombination occurs when two related viruses exchange genetic material during co-infection of a host cell creating a NOVEL virus.

Alterations in the genetic material of a virus may lead to change in the function of viral proteins. Such changes may result in the creation of new viral serotypes or viruses of altered virulence.

Mutations arise when the virus replicates inside host cells and mistakes are made in copying its genetic code.

Mutations in virus happen by chance all the time. Most have little effect, and some hamper the virus, but over time, single or multiple mutations can potentially buildup, that make the virus more successful by enabling it to spread more easily.

Mutations can also make the virus more dangerous, for example, by making it more efficient at infecting cells.

Mutations can make a virus either more or less virulent.

A virus that is less virulent could infect far more hosts because the hosts are well enough to come in contact with many other potential hosts.

Seasonal influenza virus mutates so rapidly that we need a different vaccine each year.

The faster a virus mutates, the quicker it changes its behaviour.

Mutations may cause the virus’s outer surface to appear different to a host previously infected with the ancestor viral strain. So, antibodies produced by previous infection cannot effectively fight the mutated virus and disease results.

Significance Of Proteins –

Proteins are large molecules made up by 20 small molecules called amino acids. All living organisms have the same 20 amino acids ( as described in the previous blog), but they are arranged in different ways and this determines the different function for each protein.

7 types of proteins are:-

• antibodies

• contractile proteins

• enzymes

• hormonal proteins

• structural proteins

• storage proteins

• transport proteins

Characteristics of Coronavirus

Structure Of Coronavirus (Photo credit- Pinterest)

• family of Plus strand RNA viruses

• encode a complex RNA- dependent RNA polymerase

• coronavirus is a non-reverse transcribing RNA virus

• coronavirus is an ENVELOPED Virus

• coronavirus has large genomes

• coronavirus is a plus strand single-stranded RNA virus with helical nucleocapsid

• coronavirus is a recombinant virus

• it causes diseases in mammals and birds

RNA virus versus DNA virus –

DNA viruses are able to attack both human cellular and metabolic processes simultaneously.

RNA viruses interact with human PROTEINS functioning in specific cellular processes and intra cellular transport.

Single Nucleotide Variation (Substitution) in human gene/DNAcaused by viral infection (Photo credit- Pinterest)
How do viruses multiply?

Viruses multiply in the host cell, where they find the machinery, the PROTEINS with which they can copy their genetic material before infecting other cells.

Which Viruses show higher mutation rate?

• RNA viruses mutate faster than the DNA viruses as RNA nucleotides are more unstable than DNA nucleotides.

• Single-stranded viruses mutate faster than double- stranded viruses.

• The lesser the genome size, the higher is the mutation rate.

Decoding the Genetic code and viewing Gene Expression (protein synthesis) through its lens (using Flow Chart technique)

This early morning, when I took the Morning Daily in my hand, I was awestruck and pained by the most haunted news about the pandemic – the steeply rising global tally of Covid-19 cases and death toll. This aching health issue anguished me and urged me to take a call, and share with readers, the biology of this one entity- the VIRUS,which is playing havoc in the lives of a great chunk of world’s populations. In my last blog, I had given a fair idea about the different types of WBCs which fight against the foreign invaders – bacteria and viruses, which are the causative agents of so many diseases/ infections in our body. As we all know that these foreign intruders viz. virus and bacteria cannot be seen with naked eye. Viruses are ultramicroscopic, even smaller than bacteria, ranging in size from 30 nm to 300 nm.

To know the structure & functioning of virus, we must first broadly understand the set of rules (Genetic code) by which information encoded in the genetic material viz. Nucleic acid (DNA or RNA) is translated into proteins (amino acid sequences). Biological decoding is accomplished by the ribosome using tRNA to read mRNA three nucleotides at a time. Most viruses have either RNA or DNA as genetic material (or genome). The nucleic acid may be single or double stranded. The simplest viruses contain only enough RNA or DNA to encode 4 proteins. Most complex can encode 100- 200 proteins. The portion of the genome that codes for a protein or an RNA is referred to as a GENE. (Significance of Proteins – Autism is linked to egg cells’ difficulty creating large proteins.) The Genetic code is highly similar among all organisms with the exception of some RNA viruses. They all use the same 4 bases ie. Guanine(G), Adenine(A), Cytosine(C) & Thymine(T) – or Uracil(U) in case of RNA and make the same amino acids.Because of Genetic code, many different species have same genes.

What is Genetic code ?

RNA or DNA is a long polymer made from repeating units called nucleotides. A Nucleotide has three components viz. (1) a nitrogenous base, which are two types- Purines (A,G) and Pyrimidines (C,T). Purines pair with Pyrimidines. So, Adenine(A) pairs with Thymine (T) (in RNA, Thymine is replaced with Uracil (U) ) & Guanine (G) pairs with Cytosine (C). This is called Complementary Base Pairing. (2) a pentose sugar (5-carbon sugar)– ribose in case of RNA and 2-deoxyribose for DNA. (3) a phosphate group The Genetic code is the sequence of the nucleotide bases in nucleic acids (RNA & DNA), that code for 20 different amino acids, by triplets formed from combinations of the above 4 nucleotide bases. A triplet is called a CODON. The Genetic code is the set of rules by which information encoded within DNA or (mRNA sequences) is translated into Proteins by living cells. The Genetic code can be expressed in 64 entries. Of the 64 codons, 61 codons specify 20 different amino acids and 3 codons (UAA, UAG, UGA) serve as Stop Codons to end Protein Synthesis. The codon AUG (codes for amino acid – Methionine) serve as Start Codon for beginning of Protein Synthesis (Translation).

Multiple codons may specify the same amino acid. For example – the codons UCU, UCC, UCA, UCG, AGU, and AGC all specify the amino acid – Serine. See the table below :-

Amino Acid Sequencing Table (Photo credit- Shutterstock)

The Genetic code has redundancy but no ambiguity.

Types of RNA – 3 types:-

(1) messenger RNA (mRNA):

mRNA plays important roles in Transcription process. Transcription is the first step of Gene Expression. It is the process that involves copying the genetic information contained in DNA into an RNA message. During transcription, the DNA strand unwinds and allows the enzyme RNA polymerase to transcribe only a single strand of DNA. When RNA polymerase transcribes the DNA into a mRNA molecule, Adenine pairs with Uracil and Cytosine pairs with Guanine.

(2) transfer RNA (tRNA):

The job of tRNA is to translate the nucleotide sequences of mRNA into specific amino acid sequences. The amino acid sequences are joined together to form a Protein.

(3) ribosomal RNA (rRNA):

The cell organelle called Ribosome consists of ribosomal proteins and rRNA. A ribosome consists of 2 subunits – a large subunit and a small subunit.

Process of Protein Synthesis (Translation):

During translation, a small ribosomal subunit attaches to a mRNA molecule. At the same time an initiator tRNA molecule recognises and binds to a specific codon sequence on the same mRNA. A large ribosomal subunit then joins the newly formed complex. Both ribosomal subunits travel along the mRNA translating the codons on mRNA into a polypeptide chain as they go. When a termination codon is reached on mRNA, the translation process ends. The polypeptide chain is released from the tRNA and the ribosome splits back into large and small sub units. The new formed polypeptide chain undergoes several modifications before becoming a fully functional protein. These proteins are used in the membrane of the cell, others remain in cytoplasm or transported out of the cell.

Process of Protein Synthesis (Translation) (Photo credit- Shutterstock)

Tips for following’Flow Chart’ methodology:

(1) Divide the matter into brief, small, all- inclusive key points .
(2) Step-wise/ sequential jotting down of these points.
(3) Separating each step by a downward arrow.

Quick Recap of Transcription & Translation through FLOW CHART teaching methodology:


Enzyme RNA polymerase binds to ⬇️ DNA transcription unit at PROMOTOR Site ⬇️ Sigma unit of RNA polymerase target START site to align polymerase onto Promotor ⬇️ Unwinding of one helix turn of DNA ⬇️ Tight binding of Polymerase with initiation of RNA Synthesis (first base added is usually a Purine) ⬇️ RNA polymerases use nucleoside triphosphate as substrate & polymerises in a template dependent fashion following the rule of Base Complementarity ⬇️ Elongation continues at a rate between 30 & 50 nucleotides per second ⬇️ Cessation of Elongation ⬇️ Release of Transcript ⬇️ Dissociation of Polymerase & mRNA chain from Template ⬇️ Post- transcriptional modifications of mRNAs (removal of INTRONS etc) ⬇️ Poly-A tail (Adenine bases) added to one end & a Guanosine triphosphate Cap added to the other end of mRNA for its protection


mRNA binds to smaller subunit of Ribosome ⬇️ Anticodon arm of tRNA binds to a specific codon sequence on same mRNA ⬇️ A large ribosomal subunit joins this complex ⬇️ Initiator tRNA in the P site of ribosome is released & tRNA in A site of ribosome is translocated to P site ⬇️ ‘A’ binding site becomes vacant ⬇️ Another tRNA recognising new mRNA codon attaches to this site ⬇️ Pattern continues ie. old tRNAs are released from the complex, new tRNAs attach and amino acid chain grows ⬇️ Ribosome reaches a termination codon on mRNA ⬇️ Polypeptide chain formed and released from tRNA ⬇️ Ribosome splits back into large and small subunits ⬇️ Newly formed polypeptide chain undergoes modifications ⬇️ Fully functional PROTEIN is formed

About next blog:

In the wake of the knowledge on Genetic code and Protein Synthesis shared in this blog, we’ll apply this information to know the ‘Genetic change in Viruses’ causing serious diseases, Structure of Virus, with a mention of Coronavirus also, in my next blog.

Till then, Happy Reading…

Teaching/Learning Science Concepts Through Storytelling Coupled With Analogy

Here, in this blog I’ll throw some light on an innovative teaching technology/ method of learning Science concepts(which I’ll also be taking up in next few of my upcoming blogs).

Science learning seems difficult, boring and scary, if done through textbook reading. One of the methods, which I found very interesting and effective during the course of my profound teaching, is learning science concepts through Storytelling coupled with Analogy.

As is a worldwide established fact that stories always are welcomed and listened with great enthusiasm. Stories arouse immense interest in students and so, can be used as an effective tool for teaching-learning process.The concepts learned through this method will remain etched in the minds of students forever.

Another objective of this blog is to touch simple methods of learning difficult scientific terms with ease.

Our Storytelling Tool. Let’s practice it with the science concept –Knowing the types of white blood cells(WBCs).

Let’s begin our story – The title of the story is the “WBC Brigades”. Once there was a country called ‘Human body’. It was a very peaceful country until it was once invaded by some foreign intruders called bacteria. (The foreign intruders can be virus, bacteria, fungi or parasites). The intruders soon captured the entire country ( body). The country‘s peace was disrupted (infection/bacteria spread all through the body). Immediately, the country‘s head (brain) sent a message to the country’s Army

(body’s immune system/ body’s defence mechanism comprising of WBCs) (via lymphoid organs) to fight against the intruders and defuse the situation (get rid of infection/ bacteria). The Country’s Army had 5 Brigades (5 types of WBCs). They are – 1. Eosinophils 2. Basophils 3. Neutrophils. 4. Lymphocytes 5. Monocytes.

5 Types Of WBCs (Photo credit- Shutterstock)

Comparative analysis of the 5 Brigades (5 types of WBCs):- Brigade 1(Eosinophils):-Uniform (structure)- granular cytoplasm ; lobed nucleus Duty (function) – to bring about destruction of toxins of protein origin Strength (number)-2 to 3% of TLC. Brigade 2 (Basophils):- Uniform (structure)- cytoplasm contain coarse granules ; lobed nucleus Duty (function)- fight allergens by releasing Histamine Strength (number)- 0 to 4% of TLC Brigade 3 (Neutrophils):-Uniform (structure)- cytoplasm contains fine granules ; many shaped nucleus (polymorphonuclear) Duty (function)- engulf the bacteria and digest Strength (number)- 65 to 70% of TLC Brigade 4 (Lymphocytes):- Uniform (structure)- agranular cytoplasm which is much less ; large spherical nucleus Duty (function)- to produce antibodies Strength (number)- 20 to 30% of TLC Brigade 5 (Monocytes):- Uniform (structure)- agranular cytoplasm which is more ; bean shaped or oval nucleus Duty (function)- motile in nature and engulf the bacteria. Strength (number)- 4 to 8% of TLC

Simple methods to spell & pronounce the difficult Scientific terms/ names correctly:-

1. Break the word and then spell and pronounce Eosinophils = eo- si- no- phils Lymphocytes = lym- pho- cytes

2. Memorising the endings (-phils, -cytes) which are common to the terms/names

Some ideas to get you going with storytelling & analogy technique:-

1. Germination of Seed- using development of an egg into an adult analogy…… 2. Monocot & Dicot seeds- using objects like sun ☀️,moon 🌔(Monocots); sandwich 🥪, burger 🍔 (Dicots) for analogy…… 3. Cycles in nature (water, nitrogen etc)- using cyclic movement in a clock analogy……

A Holistic module for science learning

Science, invariably called as the systematised knowledge, has always fascinated people because of its multitude inventions and applications.What incites me to write this blog is the craving to share and capture a few Takeaways of Science, which make it a fun way to learn.

Over the long long years of my study and teaching, my greatest Takeaway from Science is that, a keen observer comprehends rules fuller and faster. So, the keyword to learning/getting insight into Science is OBSERVATION. The more you observe (your surroundings-be them the man-made wonders like home, park, shopping mall, airport, seaport, factory on the one hand or the mother nature on the other hand) the better learning unfolds.

Let’s extrapolate it further. Will simply observing things- living or non-living, help you understand Science concepts or extract the laws of Science? The answer is’NO’. As introduced earlier that science is a systematised knowledge, so one needs to arrange/organise his/her observations.

I have devised a Six-Step Module, which I call ‘TOPPIC’ to understand any Science concept by experiencing.

T – Task that fascinates you

O – Observation

P– Point wise Penning down

P – see the Patterns like similarities, differences etc

I – Interpretation

C – Conclusion

Seed Dispersal By Wind (Photo credit- WordPress photo library)

Let’s show up with an example:-

Task– I see fluffy clusters flying freely in the air in front of my house all the time.

Observation – The fluffy clusters are breaking off from Alstonia tree in front of my house and flying everywhere.

Point wise penning down– 1.The fluffy clusters are seen in my backyard, driveway, on road in front of my house, under the tree, near the Colony Main Gate (which is about 30 metres away).

2. I took them in my hand and found them to be soft, light and hairy.

3. When I opened the cluster, they all separated out into individual units, each having a bead-like thing in the centre with hair all around.

Patterns– 1. The hairy clusters are all coming out of pod-like structures hanging from the tree.

2. All hairy units are alike.

3. They are moving to far and near places.

Interpretation– 1. Since, the hairy units are coming out of a pod-like structure (which is tree’s fruit),so these hairy units should be seeds.

2. Because these seeds are light and hairy, they are able to move to far off distances.
3. Seeds, when grown in soil, give rise to a new plant.

ConclusionSeeds are dispersed by wind.