Sunday, April 24, 2011

The Kingdom Protoctista

This kingdom contains all single celled organisms in which there is a distinct nucleus enclosed in a membrane, and in which there are also other discrete organelles, such as mitochondria and endoplasmic reticula. It includes all those microscopic organisms, such as amoeba and paramecium that were once regarded as single celled animals and placed in the phylum Protozoa. It also includes the slime moulds. The large sea weeds that is also included in the Protoctista because, although they are multi cellular organisms, their cells are all alike and not easily differentiable from single celled algae.

The sea weeds include species with fronds many meters long and made up of millions of cells, but they are included with the single celled organisms in the Protoctita because their cells are all more or less alike. Some biologists regard the seaweeds as assemblages of cells rather than true multi cellular organisms. There are three major groups or phyla- the green sea weeds (Chlorophyta), the brown sea weeds (phaeophyta) and the red sea weeds (Rhodophyta). All contains chlorophyll and make their food by photosynthesis, but the brown and red seaweeds contain other pigments that mask the chlorophyll. They have a variety of reproductive strategies.

Thursday, April 21, 2011

The Five Kingdom of Life and The Characteristics Of Living Things

Until fair recently, all living things were classified as either plants or animals this simple division is perfectly adequate for non scientific purposes, but most biologists now recognize five separate kingdoms of life, based largely on microscopic structure and bio chemical activity, these are the bacterial kingdom, or Prokaryote; the Protoctista; the Fungal kingdom; the Plant kingdom and the Animal kingdom.
Although we cannot give a simple definition of life, there are seven distinctive features that are shared by all living things and distinguish them from inanimate objects.

These characteristics are:
The initial letters of these features form the word MERRING, a convenient mnemonic for keeping them in mind.
The Kingdom of Prokaryote:
This kingdom contains the bacteria. These are all microscopic, single celled organisms, but their structure is very different from that of other single celled organisms, with no obvious nuclei or other well defined structures – organelles- within the cell division, sometimes as often as once every 15 minutes. Some bacteria can carry out photosynthesis, using the energy of sunlight just as plants do, but most of them rely on other chemical reactions to provide their energy. Bacteria play a major role in the natural world, where they are heavily involved in the breakdown of dead plants and animals and return back to the soil.

Tuesday, April 19, 2011

Origin of Life

The earliest traces of the life on earth have been found in the rocks about 3.5 billion years old. They are layered structures similar to those formed by some of today’s marine bacteria, and it is generally accepted that the first forms of life were some kind of bacteria. We do not know exactly how these first living things or organisms were produced, and probably never will, but laboratory experiments suggest that energy from lightning or from ultra violet radiation could have caused gases, like methane and ammonia to combine with simple minerals to produce proteins and other building blocks of life such reactions would probably have taken place in shallow water.
As more and more life’s building blocks were formed, they inevitably mingled and reacted with each other to form new compounds. Eventually, a chance combination gave rise to a molecule of DNA, a self replicating material that is the basis of all living matter. Here, perhaps, was the “spark of life” and the scene was then set for the appearance of the first cells and the subsequent evolution of all life on Earth. Since the beginning of life, millions of different kinds of organisms have come and gone. It is estimated that there are about 300,000 different kinds of plants in the world at the present time, and there may be over five million kinds of animals- or some estimates, nearer ten million – although only a little over a million of these have so far been described.

Thursday, April 14, 2011

Map Projections

Representing a globe on a flat plane requires the use of projections. Cylindrical projections are created by wrapping a piece of paper around the equator to form a cylinder. This was the principle used by the Flemish geographer Geradus Mercator to draw up one of the first reasonably accurate maps of the world in 1569. A Mercator projection shows equatorial regions very accurately and has the advantage that the shape of the landmasses o the map are the same as on the ground, which is useful for navigators. However, away from the equator, the actual areas of the landmasses become more and more distorted so that Greenland seems bigger than Africa. Mercator’s projection is most distorted at the poles because the point of each pole is stretched out into a line as long as the equator.

Arno Peter, a German historian, devised an alternative in 1973. Peter’s projection is also cylindrical but it differs in that the north south scale is adjusted so that the actual areas of the landmasses are accurately represented at all latitudes, although Peters’ projections shows the correct areas of all landmasses, it distorts their shapes. For example Africa appears to have been stretched while Greenland seems squashed.

Another form projection is the Zenithal or Azimuthal projection. The paper remains flat and touches the globe at the north or South Pole. Lines of longitude show their correct angles. For this reason they are often used to represent polar region.

A conical projection , in which the paper is rolled into come and placed over the globe to touch it along the line of latitude, shows countries with the minimum of distortion.

Google’s projection is not strictly a projection but a series of manipulations of the curved surface of the sphere. Such maps look rather like the skin of an orange after it has been removed in one piece and rolled out flat. The continents are shown accurately but the oceans are opened up to stretch the segments on to the paper.