Did you know that you have seen cells many times? When a section ad an orange is broken open, the whole fibres that we see are cells. If the cell walls are broken, the juices will run out.
According to scientists, the cell is building block that makes up all living things. Everything that is alive is made up of one or more cells. Cells are also the units in which all life activities take place. Each cell in a plant or animal lives its own life and at the same time makes it possible for the living things as a whole to carry on its own life activities.
Living cells, both plant and animal, consists of a cell membrane, a mass of jelly-like colourless material called 'protoplasm', and a kernel-like part of the protoplasm called 'the nucleus'. It is the protoplasm which is the living matter.
In fact, this protoplasm is by far the most complicated chemical substances in existence. It carries on all processes necessary supplies to every one of their cells, the higher forms of living things have developed a circulatory system. This circulates food and oxygen to the cells and removes waste products,
Saturday, 3 March 2012
Saturday, 16 July 2011
How do Plants and Animal live in the Dessert?
To begin with, there are many kinds of dessert. Some are familiar deserts of bare rock and shifting sand, upon which the hot sun beats down. But some deserts, such as Gobi, have bitterly cols winters. So a desert is really a region where only special forms of life is the kind that has managed to adapt itself to the particular conditions of the particular deserts.
Fr example, cacti are well-known desert plants. They have thick, fleshy stems without true leaves. Desert shrubs that have leaves usually have small ones. Little or no leaf surface prevents too much evaporation of water from the plant.
Many desert plants have thorns, spines or a disagreeable taste or smell. This encourages animals that might eat them and so helps them survive. Desert plants usually lie dormant during the dry or cool season, or drop seeds that can survive such a period.
When the period for growth arrives, the seeds germinate and give rise to plants that rapidly flower and drop more seeds. Within a few weeks or months, the plants are ready again for the long season of dormancy.
When it comes to animals, they must be able to do without water for long periods, or be able to reach water holes at great distances. The camel, for example, is highly adapted to desert life. It has padded feet to walk on sand, a water-storing stomach, humps of fat as a reserve supply of energy, and nostrils that can be closed to keep out of sand during windstorms.
Many of the smaller desert creatures need to drink no water at all. They get what liquid they need from the sap of food plants and from night dew on leaves or stones.
Fr example, cacti are well-known desert plants. They have thick, fleshy stems without true leaves. Desert shrubs that have leaves usually have small ones. Little or no leaf surface prevents too much evaporation of water from the plant.
Many desert plants have thorns, spines or a disagreeable taste or smell. This encourages animals that might eat them and so helps them survive. Desert plants usually lie dormant during the dry or cool season, or drop seeds that can survive such a period.
When the period for growth arrives, the seeds germinate and give rise to plants that rapidly flower and drop more seeds. Within a few weeks or months, the plants are ready again for the long season of dormancy.
When it comes to animals, they must be able to do without water for long periods, or be able to reach water holes at great distances. The camel, for example, is highly adapted to desert life. It has padded feet to walk on sand, a water-storing stomach, humps of fat as a reserve supply of energy, and nostrils that can be closed to keep out of sand during windstorms.
Many of the smaller desert creatures need to drink no water at all. They get what liquid they need from the sap of food plants and from night dew on leaves or stones.
Friday, 15 July 2011
What is STONEHENGE?
When we try to learn to accomplishments of ancient man. we usually have to search or dig for evidence. But there is a case where ancient man has left all the evidence standing in a huge structure, and we still cannot understand what it is, what it was used for, and who built it !
This is Stonehenge. It consists of large, standing stones in a circular setting, surrounded by an earthwork, and located near Salisbury, England. As long as the year 1136, it was written that the stones were magically transported from Ireland by Merlin. Of course, this was only a legend. More recently, it was believed that Stonehenge was put up by the Druids, who were priests in ancient Britain. But there is actually no reason to believe that this is so.
Stonehenge has a somewhat complicated structure. On the outside is a circular ditch, with an entrance gasp. Then there is a bank of earth. Inside the bank is a ring of 56 pits. Between these and the stones in the centre, are two more rings of pits.
The stone setting consists of two circles and two horseshoes of upright stones. Then there are separate stones which have been given names, such as the Altar stone, the Slaughter stone, two Stations stones, and the Hele stone.
In most of the holes that have been excavated, cremated human bones have been found. By studying the pottery and objects found, and by making radioactive-carbon tests, it has been estimated that parts of Stonehenge date back to about 1848 B.C., and possibly 275 years earlier or later than this date.
Part of Stonehenge is aligned so that the rising sun in midsummer is seen at a certain point, but nobody is sure is this was intentional.
So this huge and remarkable structure, which may be 4,000 years old, still remains fascinating mystery !
This is Stonehenge. It consists of large, standing stones in a circular setting, surrounded by an earthwork, and located near Salisbury, England. As long as the year 1136, it was written that the stones were magically transported from Ireland by Merlin. Of course, this was only a legend. More recently, it was believed that Stonehenge was put up by the Druids, who were priests in ancient Britain. But there is actually no reason to believe that this is so.
Stonehenge has a somewhat complicated structure. On the outside is a circular ditch, with an entrance gasp. Then there is a bank of earth. Inside the bank is a ring of 56 pits. Between these and the stones in the centre, are two more rings of pits.
The stone setting consists of two circles and two horseshoes of upright stones. Then there are separate stones which have been given names, such as the Altar stone, the Slaughter stone, two Stations stones, and the Hele stone.
In most of the holes that have been excavated, cremated human bones have been found. By studying the pottery and objects found, and by making radioactive-carbon tests, it has been estimated that parts of Stonehenge date back to about 1848 B.C., and possibly 275 years earlier or later than this date.
Part of Stonehenge is aligned so that the rising sun in midsummer is seen at a certain point, but nobody is sure is this was intentional.
So this huge and remarkable structure, which may be 4,000 years old, still remains fascinating mystery !
Thursday, 14 July 2011
Whoa. Snow !
Snow is really nothing more than frozen water. Then why doesn't it look like ice?
There are a large number of ice crystals in each snowflake, and the reflection of light from all the surfaces of the crystals makes it look white.
Snow begins to be formed that are clear and transparent. Since there are currents in the air, these tiny crystals are carried up and down in the atmosphere. They fall and rise as different air currents move them along.
While this is happening, the crystals begin to gather around a nucleus, so that in time there may be hundred or more gathered together. When, this group of ice crystals is big enough, it floats down towards the ground. We call this collection of ice crystals a "snowflake". Some crystals are flat and some are like a column of needles. But regardless of shape, snow crystals are always have six sides or angles. The branches of any single snowflake are always identical, but the arrangement of the branches is different in every case. No two snowflakes are ever exactly very alike.
Did you know that snow is not always white ? In many parts of the world red, green, blue, and even black snow have been seen ! The reason for different colours is that sometimes there are tiny fungi in the air, or dust is floating about, and this is collected by the snow as it falls.
There are a large number of ice crystals in each snowflake, and the reflection of light from all the surfaces of the crystals makes it look white.
Snow begins to be formed that are clear and transparent. Since there are currents in the air, these tiny crystals are carried up and down in the atmosphere. They fall and rise as different air currents move them along.
While this is happening, the crystals begin to gather around a nucleus, so that in time there may be hundred or more gathered together. When, this group of ice crystals is big enough, it floats down towards the ground. We call this collection of ice crystals a "snowflake". Some crystals are flat and some are like a column of needles. But regardless of shape, snow crystals are always have six sides or angles. The branches of any single snowflake are always identical, but the arrangement of the branches is different in every case. No two snowflakes are ever exactly very alike.
Did you know that snow is not always white ? In many parts of the world red, green, blue, and even black snow have been seen ! The reason for different colours is that sometimes there are tiny fungi in the air, or dust is floating about, and this is collected by the snow as it falls.
MONSOON?
The word "monsoon" comes from an Arab word means "season". It has to do with a type of climate in which winds blows from the sea to land ( onshore ) during the warm season, and from land to sea ( offshore ) during the cool season. The warm season of onshore winds is often very rainy, while the cool season of offshore winds may be dry.
What cause this seasonal change in winds and rainfall ? It is due to the fact that large continents or land masses heat and cool more rapidly than the surrounding oceans. Central and Southern Asia grow warm rapidly in the spring, and during the summer they are much warmer than the Indian Ocean on the South, or the Pacific Ocean on the east.
The warmer temperatures inland create lower atmospheric pressure, and therefore the wind blows inland from the surrounding seas. This is the onshore or summer monsoon.
In the autumn, interior Asia cools rapidly and during the winter it has much lower temperatures than the surrounding oceans. These lower temperatures create high atmospheric pressure, and therefore the winter monsoon winds blow outward from the dry interior regions toward the sea.
What cause this seasonal change in winds and rainfall ? It is due to the fact that large continents or land masses heat and cool more rapidly than the surrounding oceans. Central and Southern Asia grow warm rapidly in the spring, and during the summer they are much warmer than the Indian Ocean on the South, or the Pacific Ocean on the east.
The warmer temperatures inland create lower atmospheric pressure, and therefore the wind blows inland from the surrounding seas. This is the onshore or summer monsoon.
In the autumn, interior Asia cools rapidly and during the winter it has much lower temperatures than the surrounding oceans. These lower temperatures create high atmospheric pressure, and therefore the winter monsoon winds blow outward from the dry interior regions toward the sea.
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