Keeping an eye on the sky-1

With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary—the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial. The search will continue. Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.
-Edwin Hubble

Few months ago Hubble completed its 20 years of space service. Through this blog post let me take you through some of my all time favorite snaps ( well, its actually difficult to say which one is not a favorite ), from the whole array of pictures that Hubble has taken. One must visit the Hubble site to get the complete story as to what Hubble has been doing.
Just in brief; this huge piece of mirrors, cameras, antennas and other stuff was put into orbit around Earth on 22nd April 1990. Since then it has been working tirelessly and increase our understanding of the universe. From new planets to dark energy Hubble has seen it all.
You can also read in details of Hubble’s history in Wikipedia


Into nothing:
This is what Hubble's WFPC2(Wide-Field Planetary Camera 2) camera came up with when it was made to stare at blank space(seemingly) for days:


From being just a blank sky to buzzing cluster of galaxies! Hubble made us realize how packed the space is!

Blast from the past:
This one is the image of a supernova(SN 1987a) that happened in 1987, one of the brightest in the last 400 years. Hubble has been monitoring the aftermaths.


Into the orion:
One of my favorites, the orion nebula. As in any Nebula action always happens here.New stars are formed , they spew out gases , hurricanes of stellar winds. From 1,500 light years away , here is what Hubble has for us:
Bit of explanation on what you are seeing:
Bowl is the radiation rich bright center made of the stellar winds and the star factory.
M43, the young star carving out its own space in the nebula.
Brown dwarfs are the failed stars which failed to kick start their nuclear fusion.
Arcs and bubbles are formed of charged particles from the stellar wind.

A peek into our future:
Billions of years hence our Sun is going blow its outer region and become a white dwarf. Hubble has brought us the image as to what may be our sun’s fate too. When stars around the size of our sun exhaust the hydrogen supply in their core, they start shrinking due to their gravity. But fusion still happens in the outer layers.The shrinking core heats up and causes the outer layers to expand. Finally outer layers burst and end up forming planetary nebula . A planetary nebula will exist till all the gases are dissipated into the space leaving behind the cool white dwarf. The best of the planetary nebula is the cat’s eye nebula.


The bright inner spot is the core of the star. The rings are the gases thrown out by the dying star.

There are still more to come , but in the subsequent posts.

In the Comfort Zone

The third planet from the sun, our Home; what made it so special? So ideal for the plethora of simple and complex organisms including us who can contemplate on “what makes Earth special”?


We have an atmosphere with right density, right pressure; the right temperature, and an ideal fluid to support life. But, is that all that makes Earth the right place for life to emerge? There is just one more essential parameter (which has made the other parameters possible). The distance from sun! A little nearer it would have been too hot, a little further too cold. Doesn’t that imply that for any given star if planets or moons happen to fall in this right place , then life might evolve on them? This region is called the Habitable zone or Goldilocks zone (after the same Goldilocks from “Goldilocks and three bears” who would have been part of your bedtime story as a kid) . But its not just the correct spot from a star that’s is essential for supporting life, but also the right location in the galaxy (galactic habitable zone). Near enough to the galactic center to have enough metals (to make it a rocky planet like ours) and far enough to remain protected from the high frequency radiations that is lethal to life forms similar to us (carbon based).

What makes such places hospitable? Simple! The perfect (or near perfect) temperature which can support liquid water, the one fluid that has changed or rather written the history of our planet. So when looking for earth-like life forms, it is such zones in the universe that should be the starting point for the search.
The above statement may be an oversimplification. For even on our own planet we have come across creatures called the extremophiles, living in deep hot sulphur filled vents, underneath ice sheaths in Antartica, in the darkest regions of ocean where no light penetrates; where one would have never imagined a possibility of existence of life. But even in these organisms survival has been possible because of liquid water( they have developed ways to keep water in liquid state within them).
Scientists studying the possibility of extraterrestrial life are trying to find and explore these comfort zones, where conditions seem to be like that on earth. Recently existence of a rocky planet in such a habitable zone has been observed for one of the close star (just 20 light years away) called Gliese 581.


The fourth planet from the star lies in the outskirts of this region. Intially the planet Gliese 581 d was thought to be too cold for supporting life, but around April 2009 it was confirmed that it lies on the border of habitability. All it needs to do now is make some green house gases, raise its temperature to become suitable for supporting life.

So as Goldilocks famous line goes (and reason why the name was given):
"This porridge is too hot," Goldilocks exclaimed.
So she tasted the porridge from the second bowl.
"This porridge is too cold."
So she tasted the last bowl of porridge.
"Ahhh, this porridge is just right!" she said happily.
And she ate it all up.
It has to be ‘just right’ nothing less, nothing more.

On being the largest

I have no idea how it feels to be the largest flower on earth. You will have to ask that to Rafflesia arnoldii. But I definitely know how it smells: like rotting flesh. Yuk! Growing up to 3 ft, there are lots of things that are weird about this plant or should I say flower. For, all that this one seems to have is a flower. No sign whatsoever of stems, leaves (No photosynthesis! Wasn’t it a defining characteristic of being a plant? Got to go back to my 5th std book and make changes) or true roots.



This one belongs to a group of plants called Rafflesia, all of which are parasitic, an endoparasite (grow within the host) to be specific. They specifically parasitize on a member of grape family called Tetrastigma. Rafflesia grow inside the grape plant’s stem penetrating its tissue through a thread like thing called haustorium (Seen in parasitic fungi as well) and absorb all nutrient from it (its like… u make the food, I will put a pipe and suck it out and use it to grow 3ft. Too much of an extravaganza for a parasite).
Once in a while, they put out a bud and after months it flowers, which lasts for few days (~7days). The plant (Rafflesia arnoldii) is unisexual (some species of Rafflesia are bisexual too), so there is a male and female version of the big stinker. Ahh! Now I guess I understand why it stinks! To reproduce it has to pollinate and for that it requires pollinators like flies. And rotting flesh attracts flies. Off comes a fly expecting a feast and Rafflesia sticks its pollens onto its carrier, which unknowingly will transfer the pollen to a female flower. Ingenious! But means by which its seeds are distributed isn’t known for sure, but seems like some shrews eat its fruit (doesn’t that stink?) and thus disperse its seed.

For all this planning and parasitizing, the plant is highly endangered. Blame it on habitat encroachment by humans. That apart there are lots of stuff about Rafflesia that makes them more prone, starting from their requirement of specific host (habitat specificity, occur only in the rainforests of Sumatra and Borneo in the Indonesian Archipelago). Being unisexual, it’s important that the male and female flowers be close by and that they should open around the same time. And to add to it, they flower only for few days, a time constraint as well. What sort of conservation do you think will work out for this flowering giant? (Grow the grape and put some flies and Rafflesia seeds!). Of so many bizarre designs that nature has come up with, Rafflesia arnoldii, is definitely one.

References:
http://www.parasiticplants.siu.edu/Rafflesiaceae/Raff.arn.page.html
http://en.wikipedia.org/wiki/Rafflesia_arnoldii

Dance of light

Through the vast sky she flies, spreading her light ; green ,blue, red, yellow and pinkish hue and the night sky becomes a play of light . She is “Aurora” the Roman Goddess of dawn blessing and bringing the night sky to life.

Well its not some divine glow lighting up the sky around the polar regions although it was believed so, It is Aurora Borealis( Boreas greek for ‘north wind’) in northern hemisphere and Aurora Australis (latin for 'of the south’) in the southern hemisphere. They are brought about by the solar wind particles(more on solar winds in the next post on Coronal Mass Ejection) colliding with the particles in the earth’s upper atmosphere exciting them .The excited particles relax by transferring their energy to others and/ or emitting a photon. Check out these beautiful pictures taken from places like Alaska and North Canada

And Aurora Australis captured by NASA's IMAGE satellite:

Although its occurs everywhere, being a phenomenon of upper atmosphere, it is more clearly visible as one goes farther away from equator and during equinoxes ( guess the reason!)

So what exactly happens when there is collision of solar wind particles with the atmosphere? It either ionizes or excites the oxygen and nitrogen atoms in the atmosphere(the two most common elements in the atomsphere). So if a nitrogen atom is ionized, on getting back an electron it emits blue light.

If it had just got excited, it emits red light and comes to its normal ground state.

The colour of light when an excited oxygen atom comes back depends on its initial excitation and the time it takes to come back to ground state. Green light is given if it comes down within three quarters of a second; red if it takes more time. If it gets to collide some neighboring atom and transfer its energy then none at all.

Do u think the colour is going to be altitude dependent? ( No, not your altitude , I mean the atom’s)

Auroras aren’t restricted to Earth. Solar wind and the planet’s magnetic field brings about a similar recreation of what we observe on earth. This ones from Jupiter:

I leave you gaping with these youtube video. May be try living the moments that we , near the equator don’t get to see.

References:

http://en.wikipedia.org/wiki/Aurora_%28astronomy%29

Now you see it! Now you don't!

Driving through a highway on a hot afternoon, you would have seen water appear from nowhere on the road and then disappear as soon as you came close by.

Highway Mirage

You would have heard stories of how people traveling in deserts see water, when there is none in reality. Sometimes during sunrise or sunset you would have observed a flattened surface of sun near the horizon giving you an impression as if one more sun was coming from below like the following picture:

Inferior Mirage

All the above mentioned observations are due to an optical phenomenon called Mirage.
What is a mirage? Why do you see a mirage of water? Why not ice cream or chocolates? What are the types of mirages?

Let’s try finding out.

Mirage is the image of distant object which is displaced (formed away from where you would expect it, if it were simple reflection) by bending of light rays. The bending of rays is due to a phenomenon you would have heard of called refraction. Try doing this at home to figure out what refraction is: take a glass of water and put a straw in it , you see the straw appearing broken or thicker than the portions above water.

Similar to the bending that happens when light travels from one medium to another( from air to water in above example), changes in the density of a medium also causes light rays to bend.
On a hot day, when the air around the surface the road is hotter than air above it, refraction occurs. The water you see in the case of highway is actually the image of the sky .This is also why one sees water in deserts. Look at the picture below to see what happens to the light rays and what image forms on your eyes.

But why do we see water and not just the image of the sky? Why not ice cream or anything else. Well, because of the displacement of light rays the image of sky is formed on road. Now you can’t just see reflection of sky on a road (without water or mirror on the surface) , so it is your brain that perceives it as water to account for the appearance of sky on a road! So you will see only stuff whose presence you can logically account for.

This type of mirage is called inferior mirage. Inferior implies the image is below the actual object/sky. And this type is very much unstable as the hot and cold air keep mixing, the gradient keeps changing so the inferior mirage may keep moving its position or appear wavy or just vanish.

Another type of mirage is the superior mirage, and yes! As you would have figured out the image appears above the object! Extending the above funda to form a superior image the air below the line of sight must be cooler than above (a phenomenon called temperature inversion). So opposite to that of inferior mirage in this one the light ray is bent down and hence you get image above. So where would you find such temperature inversion frequently? In polar regions of course just above the ice sheets (and sometimes around the shorelines). And such mirages are stable! Cold air doesn’t rise up so the image stays longer.

Superior mirage come in different types depending on the density structure of the air: Towering(object appearing to be stretched as well as elevated), looming (objects appear to float above the horizon), inversion(inverted image and also the upright actual object is seen).The ray diagrams below explains the ways light bends creating the different superior mirages:

Towering superior mirage

Inverted superior mirage

Looming superior image

Superior mirage can make you see the sun before it has actually risen up (Novaya Zemlya effect) and far away ships appear at horizon or above the horizon. History has it that way back in 1596 the crew of an ill fated ship on an expedition to Polar Regions (where it got stuck at a place called Novaya Zemlya) saw a distorted sun rise in between a winter night weeks before it should! No one ever understood why it happened till late 20th century. Novaya Zemlya effect occurs when there is a huge temperature gradient (up to 400km ). The sunlight is bent to the earth’s curvature (to a minimum of 400km) that causes an elevation of 5 degrees of the sun disk. So sun appears in the sky long before it should.

Think about this: Had earth been flat, would you still see these mirages?

Another very complex type of mirage is the Fata Morgana. It is an ever changing mirage occurring as a combination of superior mirages and sometimes quickly fluctuating between superior and inferior types. The name Fata Morgan or Morgan le Fay is the name of a powerful sorceress and shape-shifting half sister of King Arthur, legendary British leader

This also commonly occurs in Polar Regions but may be seen in deserts and over ocean on a hot climate. For a Fata Morgana to occur, strong temperature inversions are required so that the light ray curve (within the inversion) more than the Earths curvature itself!

Fata Morgana :The arrow in the image on points the real boat. Apart from that you can see two more.

Mirages also occur for astronomical objects like the sun, moon, comets and planets. Below is the inferior image of Comet McNaught:

Thus, a simple play of light and perception of what is observed by the eye, gives rise to all the above mentioned optical phenomena called mirage.

References:

http://en.wikipedia.org/wiki/Mirage

http://mintaka.sdsu.edu/GF/mirages/mirintro.html

Combinatorics - 3

Combinatorics - 3

PREVIOUS

Kabani was making progress with her counting of how many possibilities are there in anything she did. Sometimes she found it easy like switching a light on or off, sometimes it became tougher like the possible lengths of a line she could draw with a 15cm scale. Her parents couldn't help her either on this. Her unsolved problem list was ever-increasing now. It was a big motivation to explore further...

Kabani observed that while calculating the number of possibilities sometimes she was adding and sometimes she was multiplying and she never did them together. Now this was strange! She wasn't told where to do what, then how did she know - when and what to do. Look at the following problems -

There are 5 apples and 3 oranges, the number of ways you can select an apple or an orange is ______.

There are 5 apples and 3 oranges, the number of ways you can select an apple and an orange is ______.

The two questions varied in just one word and that makes all the difference. When Kabani was given the choice to select an apple or an orange, she was selecting one object out of the 8 objects as there was no emphasis on what she should be selecting. So the number of ways she could have done that was 8. However, when she was told she had to select both an apple and an orange, the situation is very different. She can select any one of the 5 apples, so the selection is possible in 5 ways. Once she has selected the apple, she can select an orange in 3 ways. After every choice of an apple there are 3 further choices. So in all she can make a selection in 3 + 3 + 3 + 3 + 3 (=15) ways, i.e., 3*5 or 5*3 ways. (Do you remember the law which says 3*5 = 5*3?). What Kabani thought was multiplication was just repeated addition! But why repeated addition?

The reason lies in the fact that, in the first case Kabani was doing only one work but in the later she had two tasks. She could do the first in a few different ways and then later do the second in few more ways, thereby resulting in a huge number of ways she can complete both the tasks together.

Mathematicians call the first case as the law of sums and the second as the law of products. The names hardly matter... may be they should better be called as the law of addition and the law of repeated addition. It is for you to decide, what you would like to call them. How about Alpha Rule and Beta Rule? You are now one step ahead in your understanding of combinatorics, that is what matters. 

Until next time -

A "sign" is being assigned to every person in a village. Each "sign" consists of a geometrical figure (triangle, square, rectangle or circle), an alphabet and a single-digit number. How many unique signs can be made?

NEXT (coming up)

Dance for navigation

"The bees are buzzin' in the tree, to make some honey just for me…….If you act like that bee acts, uh uh you’re working too hard"- Baloo in the Jungle book

Bees are definitely one of the hardest workers on the planet, with ants being their only close competitors. Bees are social insects, having a hierarchical family group. At the top is the queen and the bottom most are workers who bring in honey to feed the ever growing family. Drones, whose only job is to fertilize the eggs that the queen lays (she actually lays a lot), and larvae in various stages of maturity are the other occupants of the beehive. But why do bees buzz and wiggle around so much, wasting their energy, as if the energy spent on finding and bringing honey wasn’t tiring enough? Well if you have keenly observed bees hard at work, you would realize that all that wiggling and buzzing is their way of communicating with each other. Yes they dance and buzz to convey to their fellow bees the location of a food source In case you never got to observe bees, then let’s do a bit of eavesdropping and find what they do. Make no noise! You don’t want to anger them and get stung.

Get down on the Dance floor



So lets follow the scout bee who is just entering the hive, he seems to be really happy and dancing in a particular way. Well the dance floor is usually near the entrance, but in winters it may move more inside the hive and in real hot climate they use the area outside the hive as dance floor. Since natural hives hang vertically, the dance is also on vertical plane and the bee has to tell a route that’s horizontal, that requires lots of sense of direction and distance (I am already wondering which plane is horizontal and which is vertical). When the dance is outside the hive (or in artificially constructed honey combs), it is generally done on a horizontal plane.

The Round dance

The bee that just entered is making vertical circles. Hey!!! See that he has suddenly reversed direction and is making a circle again. There are so many rapt observers (other bees I mean) besides us.

Let me translate it for you. Circles mean the food is nearby not more then 100 meters away. Having received the good news, the other bees, all fly away in all directions and search within 100 metres radius (hard work), but an experienced bee, using the odour given out by our scout, directly flies to the flower referred to by the scout’s odour (smart work).

The tail-waggle dance

Ohh, we have another arrival! The poor creature looks so tired, but excited nevertheless. So he is taking to the dance floor as well, meaning he too has found food. His moves are different though. Look! He is making a straight run and wagging and buzzing rhythmically (thought to be describing food quality and quantity);turning to left, making a semicircle, back to where he started; he is doing the straight run again, but look, now he is turning right and making a semicircle; making a near 8 figure each time. Some of them have joined in his dance. And the spectators have taken off, so sure of where they are headed. However strange this looks to you, it’s the most ingenious way of conveying the direction and the distance of the food (considering that they can’t speak as we do).
Well, tail waggling dance is performed when food is more than 100 meters away. It uses the angle of sunlight (or partially polarized light*- implies they can convey direction even when the sun isn’t directly visible, say as on a cloudy day or when sun is setting behind a mountain) to describe the direction and number of eights to describe the distance. Bees must be having the most accurate sense of time (since sun and its rays change position as the day progresses; also consider that he has to correct for its position from the time he found food to the time that has lapsed till his dance performance).With increase in distance the number of 8s per unit time decreases and the length and duration increases. So if for a food source 100 meters away the bee makes 10 eights in 15 seconds, for 3km it will make one stately 8 in the same time. Waggle part or the straight run is what conveys the direction. A straight vertical run upwards means the food is towards the direction of sun, downwards implies away from sun. If it is say 30 degrees to sun rays angle, then the run will be at an angle of 30 degrees to the vertical.


Courtesy: www.answersingenesis.org, www.theevidence.org

On days when the dance floor is shifted to the outside the sun itself may be used as reference. Sometimes even the onlookers join in the dance, learning the moves they are actually by-hearting the location.
This language of the bees was first deciphered and translated for us by Karl von Frisch when World War II was on in full swing (when people were decoding other stuff). He understood the bee language so well that he could tell his neighbors the exact distance and location of a flower from which the bees in his side were feasting upon. That’s some marvelous decoding Mr. Frisch! In fact he made artificial honey combs, exposed the bees to artificial polarized light and studied their dances out and out. But that’s not all to it, the dialect and the accent of the bees varies with regions. For e.g. An Austrian bee (von Frisch worked on these) does round dance for a distance up to 100meters, but an Italian bee shifts to tail-waggle after 80meters. So if you made an Italian honeybee talk to an Austrian one, you would most probably end up confusing the Austrian. The bee language is no less complicated than ours but nevertheless well structured to be precise every single time as if a GPS was inside their head.
* Tie a rope to a pole at one end, stretch it to its length and pluck it. It forms ripples in only one direction, the direction along which it was plucked. Similarly polarized light waves also vibrate only in one direction (light waves are polarized by polarizer and also by scattering). Sunrays get scattered by molecules in atmosphere and become partially polarized. Although the amount is going to vary with region and the sun’s location in the sky, the pattern is very much predictable. And it’s these patterns that the bees recognize and use for their communication.

Reference:

Bionics,Vincent Marteka;Lippincot, 1965

Decode the bar code

Ever wondered what differentiates a can of diet coke from a jar of peanut butter? If yes then welcome to the club. For answer, one has to look into the ubiquitous black and white stripes on these products, the barcode.

History of barcode dates back to about six decades, when it was invented by Bernard Silver in 1948. (Twenty five years gone by, before it was first used to read a price on a juicy fruit gum on June 26th 1974).Today it act as both a mundane fingerprint of modern life and a cultural icon of retail shops across the world.

Anatomy of a Bar Code is composed of a series of parallel black and white lines. When a scanner's laser beam hits the bar code, the black modules absorb the light, while the white modules reflect light. A photo diode in the scanner decodes the reflected light into an electrical signal, which is amplified and translated into digital code by the scanner's microprocessor (Fig1). That code is then fed into the store's main computer, which finds the price.



Fig 1

Different bar-code languages are used to identify different types of products, like groceries, clothing and electronics. Although many bar-code languages have been developed by the retail and manufacturing industries since they were first adopted in the early 1970's.The most widely used type is the Universal Product Code (U.P.C), found in most groceries and retail stores.
The U.P.C. is a 12-digit code: the first digit identifies the general category of the product; the next five, the product's manufacturer; the next five, the individual item (like Coke, Diet Coke or Caffeine Free Coke), and finally a ''check digit'' that is used to make sure that the code is scanned correctly in the right orientation.

A typical U.P.C., read from left to right (Fig 2), starts with a quiet zone Next comes the left guard pattern, which alerts the scanner and computer system that information is coming. The next modules identify the number of the product category. That number is printed at the lower left margin of the U.P.C. manufacturer. The next five digits identify the manufacturer. Centre guard pattern divides the left and right halves of the bar code. The next five digits on the right side identify the particular product -- e.g., whether it is a 12-ounce jar of Brand X crispy peanut butter or an 8-ounce jar of a smooth one. The check digit (the last digit on the right) is used to make sure that a U.P.C. has been scanned correctly. The computer does the following calculations; if it comes out with the check digit, the scanning was correct. For a U.P.C. that starts with 0 12345 67890: Add the digits in odd positions: 0 + 2 + 4 + 6 + 8 + 0 = 20 Multiply the results by 3: 20 X 3 = 60 Add the digits in even positions: 1 + 3 + 5 + 7 + 9 = 25 Add the last two results: 60 + 25 = 85 Subtracting that answer from the next-highest multiple of 10 should produce the Check Digit: 90 - 85 = 5.




Fig 2

Next time, when u go to a supermarket figure out what these lines implies. Now you know what it means!

μίτος (Mitos)

Every one of us starts our life’s journey as a single cell. How do we grow up to become what we are? (Of course several other processes go into making a human being but just consider the sheer increase in the number of cells in your body from 1 to billions). You fall down playing football injure your knee, but after few days the knee looks as it was before. How does mould grow on your bread to such huge amount when you had left it just for few days? Let’s do a bit of time traveling and try finding out.

It’s late 1870s (somewhere around 1876-77). Enter the University of Kiel, Germany; into the lab of Prof. Walther Flemming. He pioneered the use of aniline dyes to stain and observe the nucleus. His discovery – the chromosomes (Greek for colored bodies) would become one of the 10 most important discoveries in cell biology. He seems to be busy observing something under the microscope and making some drawings. Come closer let’s have a look at what he is up to. Can you see the red colored thread (figure below are sketches made by Prof. Flemming, with black ink though) like structures at different locations in different cells? They are nothing but the chromosomes, the packaged form of DNA. Walther Flemming is observing and recording various stages of cell division for the 1st time.

Courtesy: Wikipedia

What he had seen in the 17th century is mitosis (From Greek word Mitos- for thread). Mitosis is the process of multiplying a cell’s chromosome into two sets which is generally followed by division of the cell into two daughter cells (cytokinesis), each one getting one set of the chromosome.
To embark on the journey of mitosis (cell division) the cell has to equip itself. This is what it does in the interphase (or the in between phase-in between two mitosis). The entire cell’s machinery starts to work in full swing. Lets have a 1st hand information from the cell himself as to what he is upto.

“Hello there! Oh don’t get intimidated by the hurry burry happening around. Lots of work going on…. got to prepare for the big event you see. So I am taking in the nutrients, making proteins and lots and lots of energy, soon I will have to start duplicating my DNA. By the way, I am currently in G1 phase of interphase (that’s what you humans call it). Sometimes some of my brother cells decide to take a break at this phase (may be because of lack of nourishment or bad conditions around) and do not go ahead to synthesis DNA. But no breaks for me now, so I am going ahead with DNA synthesis such that there are two copies of my DNA (S phase). I got to distribute the DNA equally to my daughters. That’s a tiring process, takes up huge energy to do that, since I have to ensure no mistakes are made else my progeny will pay heavily for it. But since everything till now has gone well I can’t afford to rest now, have to keep synthesizing proteins (G2 phase) that will help in the mitosis. For successful occurrence of interphase and mitosis (that is yet to occur), the credits go to two groups of proteins that are mainly responsible for it, which together are called the cyclin-CDK complexes.

Now I am all set to start off mitosis. The 1st step in the process of mitosis is the prophase (the before stage). As you might have already noticed, the DNA, which was present as loose coil (chromatin) till now, has started to condense, forming the chromosome (dividing/distributing is easier when things are compact). The two copies of each region of the chromosomes also appear in doublets (sister chromatids) attached at a region called centromere. The architect who helps maintains shape and structure - the centrosome - jumps into action (centrioles making up the centrosome have also replicated during the interphase) and you can see the centrioles going to the two poles of the nucleus, as things proceed centrioles are going to be doing the chromosome separating job.Whoosh goes the nuclear membrane!!! I have broken it down so that for the 1st time ever, in my existence, the nuclear contents are going to mingle with the rest of the regions that make me up. It is now prometaphase. Can you see centrioles and the chromosome playing search and capture game? Well that’s actually a serious business. Some of the microtubules (now also called the mitotic spindles) bind (with the help of motor proteins) at the centromere (kinetochore microtubules), few at the arms of the sister chromatids (astral microtubules) and still others with the spindles arising from the opposite poles (nonkinetochore microtubules).

Into the metaphase, which is exactly half way through the process you can notice that my chromosomes are getting aligned one by one along my centre plane. They are all set to be separated into two, once the check proteins finish their last minute testing to ensure everything has been fine till now (similar to the checking before a rocket launch that you people do). As I had told you before, I cannot afford any mistakes. The final GO is yet to arrive from the kinetochore (which is the centromere bound by various proteins). Ahh!! There…. got it.

Now my next task is to separate out the sister chromatids (named Anaphase, Ana in Greek means up. Weird how humans come up with such names!) and bring them to the two poles. Any guesses how I am going to manage that? Well I have got a simple old strategy which I learnt from my mom. Make one set of the microtubules, which is holding the chromosomes at the centre, short and the others to elongate. Yes creating a pull and a push force, ripping the sister chromatids to two (Its now daughter chromatids) and stretching the cell as well. I will be handing down each of the pair of chromatids to my daughter cells.

Oh boy! Oh boy! I can’t contain my excitement. I have finally reached the final leg (Telophase) of my journey and all set to give the finishing touch to this long and tedious but well planned and executed journey of mine by first forming a nuclear membrane around the two segregated set of chromosomes.”

Well what happened next to our cell is anybody’s guess. He distributed his contents equally to two daughter cells in a process called cytokinesis (considered to be separate from that of the phases making the process of mitosis). A kind of constriction (cleavage furrow) occurred around the region where the chromosomes were present during the metaphase, to bring about the separation. (Cytokinesis usually starts off along with telophase and by the time the nuclear membrane forms completely the cell has also divided into two with all the organelles and the constituents in a parent cell, divided equally among the daughter cell).

There you go, the cell just showed you a way it has learnt and perfected through the course of evolution to increase in number, a means of replacing the dying cells, a process employed in making you (development of all multicellular organisms) and repairing you.

Reference :
Molecular biology of the cell. Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. Garland science 4th edition.

A quick story of quicksand!!!

Many years ago, when I had been to my ancestral village as a kid, the people there excitedly showed us around places, telling us the history behind each and every place-from the temple to the fort. Near one of the cannons located on the edge of a hillock was a big sign that read: “DANGER! QUICKSAND AHEAD”. The guide accompanying us saw my eyes moving in that direction and started describing how dangerous that place was. Apparently a monster that had been living inside for ages, pulls in any animal or people going that way and eats them.

Lots of myths surround the very idea of a quicksand. Many movies also showcase quicksand, where the villain slowly sinks and dies. What is this quicksand? Why does it pull things in? Can people sink in a quicksand and die?

Firstly how does quicksand come into existence? A quicksand is composed of water, clay, salt and of course, as the name suggests lots of sand. You would have seen a house made of cards. A quicksand also has a similar structure, with sand for cards, water in the gaps and clay gluing the cards. When water saturates a region with loose sand and this sand gets agitated (due to flowing underground water or due to earthquakes, wherein shaking ground increases the pressure in the ground water, which then liquefies the sand) the water gets trapped between the agitated sand and liquefies the sand. That’s why one finds quicksand mainly near the river beds and marshy places.


What happens when you disturb a house of card? It collapses of course. That’s exactly what happens to a quicksand into which, say, the hero of our movie falls. So what happens next? Nope….he is not going to sink and die (heroes don’t die in our Indian films). In a series of events, rapidly following the collapse of the structure called the liquefaction of the quicksand, the water and sand separate out into different layers. And the clay particles come together and get packed nicely due to the salts. The densely packed (nearly double of what it was in the undisturbed quicksand) wet sand and the clay is what traps the hero in. Would he sink further? No he can’t, because the sand below and around him is a lot denser than his body weight. So he is just trapped in and can rest assured that he won’t die by sinking.



How do we get our hero out? Definitely not by throwing a rope to him and pulling him out. That would be nearly impossible. The researchers who have studied quicksand behavior have estimated that a force equivalent to lifting a mid sized family car is what is required to pull just a leg out of the quicksand. So if you try pulling him out with that force you will get our hero back…..but minus his limbs.

The only way out is to rebuild the house-of-cards structure again around the trapped hero. All that needs to be done is to reintroduce the water (now in a separate layer) into the sand and the clay and decrease their viscosity. It is easier said than done. This again needs lots of force estimated around to introduce water at a speed of 1 cm s-1, say, a pressure of 106 pascals (Pa) is needed (Ref 2). But persistently making small circles around his trapped body parts, our hero can help rebuild the house of cards and then someone can pull him out.

Now you know for sure that, as shown in the movies, people cant die in quicksand by sinking in. Nor are there any quicksand monsters (by the way I had brushed off that story even as a kid ).


References:
1. http://science.howstuffworks.com/quicksand1.htm (How Quicksand Works )
2. Khaldoun, Bonn et al., Nature 437; pp 635