Thursday, September 29, 2011

Top 10 Evolutionarily Unique Animals

Using a scientific framework to identify the world’s most Evolutionarily Distinct and Globally Endangered (EDGE) species, the EDGE of Existence programme highlights and protects some of the weirdest and most wonderful species on the planet. This is a list of the top 10.
10. Pygmy hippopotamus
Pygmyhippo
The pygmy hippo is a solitary animal that lives among dense vegetation along streams and swamps and in the rainforests of West Africa. It sometimes lives in cultivated areas, but the pygmy hippo is shy: it avoids people, as well as other hippos. Each hippo has its own territory. The male’s territory is larger than the female’s; both mark their territorial boundaries with their droppings. The pygmy hippo feeds mainly when it is dark. It spends most of the day resting within its territory. It changes resting places once or twice a week.
9. Attenborough’s long-beaked echidna
Echidna
This animal is one of three species from the genus Zaglossus to occur in New Guinea. It is named in honour of Sir David Attenborough. It was considered extinct until recent expeditions have discovered tracks and locals have reported seeing the creature.
8. Bactrian camel
Bactrian-Camel-Web
An imposing animal, the Bactrian camel can reach seven feet in height and weigh up to 1,500 pounds. The species’ thick, brown coat changes with the seasons. During winter, it thickens to provide added insulation against the cold while large chunks of fur are shed in the summer to keep the animal cool. Both male and female Bactrian camels have two large humps on their backs. The Bactarian camel is endangered due to loss of habitat.
7. Yangtze River dolphin
Baiji Dolphin 1Sfw
This dolphin, also called a Baiji, is a freshwater dolphin found only in the Yangtze River in China. Unfortunately it has already reached the conservation status of Critically endangered – possibly extinct. Fossil records suggest that the dolphin first appeared 25 million years ago and migrated from the Pacific Ocean to the Yangtze River 20 million years ago.
6. Slender loris
Slenderloris
The slender loris is a small, nocturnal primate found only in the tropical rainforests of Southern India and Sri Lanka. They are able to live in wet and dry forests, as well as lowland and highland forests. They prefer thick, thorny vegetation wherein they can easily escape predators and find the large assortment of insects that is the mainstay of their diet. The Indian government has laws protecting the slender loris, but its effect is difficult to gage.



5. Hirola antelope
Angelope
This antelope has recently become very rare, with current censuses reporting fewer than 400 individuals. Only one hirola exists in captivity: an aging female at the Gladys Porter Zoo in Brownsville, Texas. It is a relic species, and only exists today (barely) due to its unique habitat requirements. Another name for this antelope is the “four-eyed antelope”, due to its pronounced, dark-colored preorbital glands, which are enlarged when excited.
4. Bumblebee bat
Bat
The Bumblebee bat competes with the Etruscan pygmy shrew for the title of world’s smallest mammal. These bats are so-named since they’re about the size of a bumblebee, weigh about as much as a dime, and have the ability to hover like hummingbirds. Their roosting habitat consists of the hot upper chambers of caves in limestone hills. Bumblebee bats are are now considered one of the twelve most endangered species on the planet.
3. Golden-rumped elephant shrew
Golden Rumped3 New
The Golden-rumped elephant shrew is the largest of all the unique African family, the elephant shrews. It is the size of a small rabbit, and is only found in the coastal Arabuko Sokoke National Park north of Mombassa in Kenya. It is classified as endangered because of its highly restricted and fragmented environment; it is also hunted for food and by feral dogs.
2. Hispaniolan solenodon
Hispaniolan-Solenodon
Hispaniolan solenodon, also known as the Haitian Solenodon or Agouta, is a solenodon only found on the island of Hispaniola, shared by Haiti and the Dominican Republic, and was unknown to science until 1833. Currently, the solenodon may only be surviving in only two places in the Dominican Republic: Jaragua and Del Este National Parks and La Visite National Park in neighboring Haiti. Its presence in Los Haitises National Park in the Dominican Republic is inferred but unconfirmed.
1. Long-eared jerboa
 44284741 Jerboa 416203
The Long-eared Jerboa, is a nocturnal mouse-like rodent with a long tail, long hind legs for jumping, and exceptionally large ears. It is distinct enough that authorities consider it to be the only member of both its genus, Euchoreutes, and subfamily, Euchoreutinae. In 2007 Zoological Society of London sent a researcher to study human impact on its environment. The study returned with video footage that been noted as the “first time” the creature has been “recorded on camera”. This has helped to start a campaign to protect them.

Basic Anatomy - Tissues & Organs

         There are many different types of cells in the human body.  None of these cells function well on there own, they are part of the larger organism that is called - you.
Tissues
Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function.  There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.
  1. Epithelial Tissue - The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body.  Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected.  Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.
  2. Connective Tissue - There are many types of connective tissue in the body.  Generally speaking, connective tissue adds support and structure to the body.  Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue.  Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue.  In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.
  3. Muscle Tissue - Muscle tissue is a specialized tissue that can contract.  Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement.  Examples of muscle tissue are contained in the muscles throughout your body.
  4. Nerve Tissue - Nerve tissue contains two types of cells: neurons and glial cells.  Nerve tissue has the ability to generate and conduct electrical signals in the body.  These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body.
Organs
Organs are the next level of organization in the body.  An organ is a structure that contains at least two different types of tissue functioning together for a common purpose.  There are many different organs in the body: the liver, kidneys, heart, even your skin is an organ.  In fact, the skin is the largest organ in the human body and provides us with an excellent example for explanation purposes.  The skin is composed of three layers: the epidermis, dermis and subcutaneous layer.  The epidermis is the outermost layer of skin.  It consists of epithelial tissue in which the cells are tightly packed together providing a barrier between the inside of the body and the outside world.  Below the epidermis lies a layer of connective tissue called the dermis.  In addition to providing support for the skin, the dermis has many other purposes.  The dermis contains blood vessels that nourish skin cells.  It contains nerve tissue that provides feeling in the skin.  And it contains muscle tissue that is responsible for giving you 'goosebumps' when you get cold or frightened.  The subcutaneous layer is beneath the dermis and consists mainly of a type of connective tissue called adipose tissue.  Adipose tissue is more commonly known as fat and it helps cushion the skin and provide protection from cold temperatures.
 A cross-section of skin

Epidermis

Dermis
Subcutaneous 
layer
Organ Systems
Organ systems are composed of two or more different organs that work together to provide a common function.  There are 10 major organ systems in the human body, they are the:
  • Skeletal System:
  • Image courtesy of A. McGann
    Major Role:
    The main role of the skeletal system is to provide support for the body, to protect delicate internal organs and to provide attachment sites for the organs.
    Major Organs:
    Bones, cartilage, tendons and ligaments.
  • Muscular System:

  • Image courtesy of G. Huang
    Major Role:
    The main role of the muscular system is to provide movement.  Muscles work in pairs to move limbs and provide the organism with mobility.  Muscles also control the movement of materials through some organs, such as the stomach and intestine, and the heart and circulatory system. 
    Major Organs:
    Skeletal muscles and smooth muscles throughout the body.
     
  •  Circulatory System:

  • Image courtesy of G. Huang
    Major Role:
    The main role of the circulatory system is to transport nutrients, gases (such as oxygen and CO2), hormones and wastes through the body. 
    Major Organs:
    Heart, blood vessels and blood.
  • Nervous System:

  • Image courtesy of G. Huang
    Major Role:
    The main role of the nervous system is to relay electrical signals through the body.  The nervous system directs behaviour and movement and, along with the endocrine system, controls physiological processes such as digestion, circulation, etc. 
    Major Organs:
    Brain, spinal cord and peripheral nerves.
  • Respiratory System:
  • Image courtesy of A. McGann
    Major Role:
    The main role of the respiratory system is to provide gas exchange between the blood and the environment.  Primarily, oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled from the body.
    Major Organs:
    Nose, trachea and lungs.
  • Digestive System:
  • Image courtesy of A. McGann
    Major Role:
    The main role of the digestive system is to breakdown and absorb nutrients that are necessary for growth and maintenance.
    Major Organs:
    Mouth, esophagus, stomach, small and large intestines.
  • Excretory System:

  • Image courtesy of G. Huang
    Major Role:
    The main role of the excretory system is to filter out cellular wastes, toxins and excess water or nutrients from the circulatory system. 
    Major Organs:
    Kidneys, ureters, bladder and urethra.
  • Endocrine System:

  • Image courtesy of G. Huang
    Major Role:
    The main role of the endocrine system is to relay chemical messages through the body.  In conjunction with the nervous system, these chemical messages help control physiological processes such as nutrient absorption, growth, etc.
    Major Organs:
    Many glands exist in the body that secrete endocrine hormones.  Among these are the hypothalamus, pituitary, thyroid, pancreas and adrenal glands.
  • Reproductive System:
  •  Female: 


    Male: 
    Images courtesy of G. Huang
    Major Role:
    The main role of the reproductive system is to manufacture cells that allow reproduction.  In the male, sperm are created to inseminate egg cells produced in the female.
    Major Organs:
    Female (top): ovaries, oviducts, uterus, vagina and mammary glands. 
    Male (

Tuesday, September 27, 2011

Chemistry Quiz Questions-(Chemical and elements)

•H2O is liquid, but H2S is what?

Gas
• Which sulfur has needle shaped crystals?
Prismatic
• Gold paint made from:
Copper
• Name a reducing agent:
Hydrogen sulfide
• Name the dehydrating agent:
Sulfuric acid
• Name a bleaching agent:
Sulfur di oxide
• A rain coat is made up of what?
Polychloroethene
• Which element on adding to natural rubber makes it less sticky in hot weather and less hard in cold weather?
Sulfur
• Which chemical causes Minimata disease?
Mercury
• The absence of cobalt in minute quantities in human body causes what?
Pernicious anemia
• Which element can easily form chains?
Carbon
• Oxygen can accept electron from all elements except what?
Fluorine
• Which element is used as an antichlor?
SO2
• Which is the most reactive element in sixth group?
Oxygen
• Which is the smallest atom in sixth group element?
Oxygen
• All the oxide which contains two atoms of oxygen in a molecule is called what?
Di oxides
• Write example for slow chemical reaction:
Rusting of iron
Change of mill into curd
• Which catalyst used in the manufacture of ammonia from nitrogen and hydrogen?
Iron
• Which substance used as catalyst in the preparation of oxygen from potassium chlorate?
Manganese dioxide
• Which compound formed when hydrogen peroxide decomposes?
Water
• Which useable substance formed as a result of collision?
Active complexes
• Which element can toxic to plants growing in soils that are high acidity?
Aluminum
• Glass is made out of what?
Sand
• Which is considered to be an anomalous compound?
Water
• How would you know that a chemical is pure or not?
By checking its melting point
• Which drug is present in cola drinks?
Caffeine
• Which fuel produce maximum heat per gram burnt?
Hydrogen
• Which element in radioactive form is used for determining the age of artifacts, relics, bones etc. of the past?
Carbon
• Which product of living organisms was the first to be made under the laboratory conditions?
Urea
• Which drug is present in tobacco?
Nicotine
• What is the most common natural source for sulfur?
Volcanic region
• The first scientific definition of a chemical element was made in which book?
The Sceptical Chymist
• Which element is present in the least amount in a living body?
Manganese
• Which substance is produced when nitrogen react with hydrogen?
Ammonia
• Which metal has the density is less than that of water?
Sodium
• Which catalyst used in the manufacture of sulfuric acid?
Vanadium pent oxide
• Which metal react with water and forms an alkaline compound?
Sodium
• Which metal floats on water?
Sodium (potassium)
• Which theory is used for explaining the changes in reaction rate?
Collision theory


Monday, September 26, 2011

Malaria deaths could vanish in ten years, claims report

Infant under bednet
Global malaria deaths could be reduced to near-zero, and cases of infection cut by 75 per cent, within the next decade, a report claims.
'A Decade of Partnerships and Results', published by the Roll Back Malaria (RBM) Partnership last week (12 September), says these goals can be met if the progress made fighting the disease over the last ten years is sustained.
The target has been adopted by the RBM's partners — more than 500 of them — including malaria endemic countries, the private sector, non-governmental organisations and academic institutions.
A ten-fold increase in funding to fight malaria over the last ten years has resulted in halving malaria cases and deaths in 43 countries. Eleven of these are in Sub-Saharan Africa, where an estimated 1.1 million infant malaria-related deaths have been avoided.
"We are light years ahead from where we were ten years ago," said Awa Marie Coll-Seck, executive director of the RBM Partnership. The report attributes this success to global collaboration — with African nations playing a major part — and availability of new tools to fight the disease.
It highlights artemisinin combination therapies (ACTs); better diagnostic techniques; and an increased use of insecticides for nets and indoor spraying. The prevalence of insecticide-treated nets, which are often given out for free, has jumped from around only two per cent of households to up to 80 per cent in some regions.
But the report comes amidst growing concern that the malarial parasite is growing resistant to artemisinin, and mosquitoes to insecticides.
A recent study linked a rise in cases of the disease in one locality to the decreased efficacy of insecticide-treated mosquito nets, while another found resistance to ACTs in South-East Asia. Meanwhile, the WHO has become so concerned about resistance to artemisinin, the cornerstone therapy, that it has issued a blueprint for urgent action to fight it.
Pierre Druilhe, from the Malaria Vaccine Development Laboratory, at the Pasteur Institute, France, said the report's claims may be unrealistic.
"Claiming that elimination will occur in ten years makes no sense with resistance on the rise," he told SciDev.Net.
"Altogether RBM is doing a good job, but making claims like this is dangerous in the long term."
The report acknowledges the spread of resistance, and says that the search for new drugs and insecticides is vital if the goals are to be met in time.
"It is a fight against time, but with enough resources I am confident that we will stay one step ahead, and the claims of the report are a real possibility," said Thomas Eisele, an associate professor at Tulane University's School of Public Health and Tropical Medicine, United States, and a contributor to the report.
Resistance to artemisinin has so far been contained within a small region in Cambodia and Thailand, and rigorous measures are in place to prevent it spreading, he said.
And insecticide resistance, although more worrying, is still very localised, he said.
The report was supported by the Bill & Melinda Gates Foundation, which has also been responsible for funding the Malaria Eradication Research Agenda (malERA)

indian scientists with date of births

 Scientists


Chandrasekhar Venkata Raman
Chandrasekhar Venkata Raman
Date of Birth : Nov 7, 1888
Date of Death : 1970
Place of Birth : Tamil Nadu

Dr. H. J. Bhabha
Dr. H. J. Bhabha
Date of Birth : Oct 30, 1909
Date of Death : 1966
Place of Birth : Mumbai


Dr. Hargobind Khorana
Dr. Hargobind Khorana
Date of Birth : Jan 9, 1922
Date of Death : -
Place of Birth : Raipur, Punjab

Jagadish  Chandra Bose
Jagadish Chandra Bose
Date of Birth : Nov 30, 1858
Date of Death : 1937
Place of Birth : Bengal


Meghnad Saha
Meghnad Saha
Date of Birth : 1894
Date of Death : 1956
Place of Birth : Dacca

Subramanyan Chandrasekhar
Subramanyan Chandrasekhar
Date of Birth : Oct 19, 1910
Date of Death : Aug 21, 1995
Place of Birth : Lahore


Dr.Shanti Swaroop Bhatnagar
Dr.Shanti Swaroop Bhatnagar
Date of Birth : 1895
Date of Death : 1955
Place of Birth : Punjab

Srinivasa Ramanujan
Srinivasa Ramanujan
Date of Birth : Dec 22, 1887
Date of Death : Apr 26, 1920
Place of Birth : Tamil Nadu


Vikram.A.Sarabhai
Vikram.A.Sarabhai
Date of Birth : 1919
Date of Death : 1971
Place of Birth : Ahmedabad

Professor Raj Reddy
Professor Raj Reddy
Date of Birth : -
Place of Birth : India


Prafulla Chandra Roy
Prafulla Chandra Roy
Date of Birth : Aug 2, 1861
Date of Death : Jun 16, 1944
Place of Birth : Khulna (now in Bangladesh)

Satyendra Nath Bose
Satyendra Nath Bose
Date of Birth : Jan 1, 1894
Date of Death : Feb 4, 1974
Place of Birth : Kolkata


Prasanta Chandra Mahalanobis
Prasanta Chandra Mahalanobis
Date of Birth : Jun 29, 1893
Date of Death : Jun 28, 1972
Place of Birth : India

Dr. Subhash Mukhopadhyay
Dr. Subhash Mukhopadhyay
Date of Birth : -
Date of Death : Jun 19, 1981
Place of Birth : Kolkata

Tuesday, September 20, 2011

Deep oceans can mask global warming for decade-long periods

The planet's deep oceans at times may absorb enough heat to flatten the rate of global warming for periods of as long as a decade even in the midst of longer-term warming, according to a new analysis led by the National Center for Atmospheric Research (NCAR). The study, based on computer simulations of global climate, points to ocean layers deeper than 1,000 feet (300 meters) as the main location of the "missing heat" during periods such as the past decade when global air temperatures showed little trend. The findings also suggest that several more intervals like this can be expected over the next century, even as the trend toward overall warming continues.
"We will see global warming go through hiatus periods in the future," says NCAR's Gerald Meehl, lead author of the study. "However, these periods would likely last only about a decade or so, and warming would then resume. This study illustrates one reason why global temperatures do not simply rise in a straight line."
The research, by scientists at NCAR and the Bureau of Meteorology in Australia, is published online in Nature Climate Change. Funding for the study came from the National Science Foundation, NCAR's sponsor, and the Department of Energy.
Where the missing heat goes
The 2000s were Earth's warmest decade in more than a century of weather records. However, the single-year mark for warmest global temperature, which had been set in 1998, remained unmatched until 2010.
Yet emissions of greenhouse gases continued to climb during the 2000s, and satellite measurements showed that the discrepancy between incoming sunshine and outgoing radiation from Earth actually increased. This implied that heat was building up somewhere on Earth, according to a 2010 study published in Science by NCAR researchers Kevin Trenberth and John Fasullo.
The two scientists, who are coauthors on the new study, suggested that the oceans might be storing some of the heat that would otherwise go toward other processes, such as warming the atmosphere or land, or melting more ice and snow. Observations from a global network of buoys showed some warming in the upper ocean, but not enough to account for the global build-up of heat. Although scientists suspected the deep oceans were playing a role, few measurements were available to confirm that hypothesis.
To track where the heat was going, Meehl and colleagues used a powerful software tool known as the Community Climate System Model, which was developed by scientists at NCAR and the Department of Energy with colleagues at other organizations. Using the model's ability to portray complex interactions between the atmosphere, land, oceans, and sea ice, they performed five simulations of global temperatures.
The simulations, which were based on projections of future greenhouse gas emissions from human activities, indicated that temperatures would rise by several degrees during this century. But each simulation also showed periods in which temperatures would stabilize for about a decade before climbing again. For example, one simulation showed the global average rising by about 2.5 degrees Fahrenheit (1.4 degrees Celsius) between 2000 and 2100, but with two decade-long hiatus periods during the century.
During these hiatus periods, simulations showed that extra energy entered the oceans, with deeper layers absorbing a disproportionate amount of heat due to changes in oceanic circulation. The vast area of ocean below about 1,000 feet (300 meters) warmed by 18% to 19% more during hiatus periods than at other times. In contrast, the shallower global ocean above 1,000 feet warmed by 60% less than during non-hiatus periods in the simulation.
"This study suggests the missing energy has indeed been buried in the ocean," Trenberth says. "The heat has not disappeared, and so it cannot be ignored. It must have consequences."
A pattern like La Niña
The simulations also indicated that the oceanic warming during hiatus periods has a regional signature. During a hiatus, average sea-surface temperatures decrease across the tropical Pacific, while they tend to increase at higher latitudes, especially around 30°S and 30°N in the Pacific and between 35°N and 40°N in the Atlantic, where surface waters converge to push heat into deeper oceanic layers.
These patterns are similar to those observed during a La Niña event, according to Meehl. He adds that El Niño and La Niña events can be overlaid on top of a hiatus-related pattern. Global temperatures tend to drop slightly during La Niña, as cooler waters reach the surface of the tropical Pacific, and they rise slightly during El Niño, when those waters are warmer.
"The main hiatus in observed warming has corresponded with La Niña conditions, which is consistent with the simulations," Trenberth says.
The simulations were part of NCAR's contribution to the Coupled Model Intercomparison Project Phase 5 (CMIP5). They were run on supercomputers at NCAR's National Science Foundation-supported Climate Simulation Laboratory, and on supercomputers at Oak Ridge Leadership Computing Facility and the National Energy Research Scientific Computing Center, both supported by the Office of Science of the U.S. Department of Energy.

New technologies altering healthcare landscape, says UN report - SciDev.Net

New technologies altering healthcare landscape, says UN report - SciDev.Net

Sunday, September 18, 2011

EYE STRUCTURE

Structure

    The eye is a very complex organ that sends a huge amount of information to the brain. It has a very specific design to capture and analyze light. In its simplest description, the eye is a box, with a lens to focus the light that enters it, and cells to process the light.
    Almost the entire exterior of the eye is a"light-tight" box. Its outer walls are formed by a hard, white substance called sclera. The outside of the eye is light-tight so that light can only enter through a small opening. This produces clearer vision, because a smaller opening, or aperture, creates a sharper image.
Prove it to yourself: Take an index card and puncture it using a pin. Be careful not to allow the hole to be too large! Look at something just far enough away that you cannot focus clearly on it. Hold your index card up to your eye and look through the tiny hole. While the aperture, the hole, blocks most of the light hitting your eye, it makes the far away object look clearer!
    The eye is filled with two liquids. These provide nourishment to the other cells in the eye, just as blood vessels provide nourishment to most cells in the body. The difference between these liquids and blood is that they are nearly transparent, so they can nourish the cells of the eye without interfering with the light that enters. The two liquids in the eye are called the vitreous humorand aqueous humor.Eye Diagram
Prove it to yourself: Rapidly move your eyes (NOT YOUR HEAD!) back and forth. Suddenly stop moving your eyes, close them, and look at a bright light. You should see what appears to be little bubbles or chains floating across your closed eyes. These are dead cells floating in your vitreous and aqueous humors. The older you are the better this experiment will work. If you are young or have healthy eyes, try moving your eyes for a longer period of time.

 Focusing

    Light entering the eye is focused by two lenses: the cornea and the eye lens. The lenses hold their shape due to pressure from the vitreous humor and aqueous humor, as well as a muscle group called the ciliary muscles. Light is bent by the lenses to focus at the back of the eye. You can learn more about the bending of light in refraction.  As objects get further away from the eye the ciliary muscles relax, allowing the eye lens to become flatter and bend the light differently. Sometimes, due to age or genetics, the ciliary muscles will not bend the eye lens correctly, causing a blurred image. This condition is called either myopia (nearsightedness) or hyperopia (farsightedness).
As an object moves closer to or further from the eye, the ciliary muscles adjust the shape of the eye lens so that the light is always focused to the same point on the back of the eye.

The Image

    The image created by the eye is real and inverted. Many people are surprised to learn that the images we always see are inverted. The reason we do not notice this is that we know no other reality. Studies have been performed where subjects have worn special goggles that distort their vision in certain ways. After along period of time, the brain accommodates for the goggles, and the subjects are able to do everyday tasks without difficulty!
Don't Believe Us? Very carefully, place your finger on the side of your nose, next to your eye. Very lightly (be careful, extreme or prolonged pressure may cause eye damage) press on the inside of your eye. Notice a black spot appears on the outside of your vision! Because the image is inverted, what appears to be a sensation on the outside of your eye is actually a sensation on the inside!
Still don't Believe us? Go into a dark room with a friend, and have him or her look at a small light-emitting object, like a candle. If the room is dark enough, you will be able to see up to three images in his or her pupil. The first image (upright and brighter than the other images) is a reflection off the cornea. The second image (upright and very dim) is a reflection off the eye lens. The third image (dim and inverted) is a reflection off the retina. This third image is the image that is sent to the brain!

Light Control

    One of the wonders of the human eye is that it can respondto a wider range of light than any artificial device ever created. In otherwords, it is possible to see not only in very low light levels (such as a darkroom) but also in very high light levels (such as a sunny day). In fact, thebrightest conditions under which an eye can operate are around 1013times as bright as the dimmest conditions.
    How does the eye do this? One way is by using the iris.The iris changes in size to allow different amounts of light to enter your eye.When there is more light, the iris shrinks. This blocks out much of the light,and as is demonstrated by the first activity, thisincreases the sharpness of your vision. If there is less light, the irisincreases in size, allowing more light to enter the eye to be processed.
Prove it to yourself: There is a very simple way to see the iris at work. Stand in a dark room and look at a mirror. Suddenly turn on a light. You will see the iris, the black circle in your eye, quickly shrink as it adjusts to a greater level of light.