Fungi And Lichens

                                          Fungi And Lichens

FUNGI WERE ONCE THOUGHT OF AS PLANTS but are now classified as a separate kingdom. This kingdom includes not only the familiar mushrooms, puffballs, stinkhrons, and moulds, but also yeasts, smuts,rusts, and lichens. Most fungi are multicellular, consisting of a mass of thread - like hyphae that together from mycelium. However, the simpler fungi (e.g yeasts) are microscopic, single - celled organisms. Typically, fungi reproduce by means of spores. Most fungi obtain their food from plants or algae, with which they have symbiotic (mutually advantageous) relationship. Lichens are a symbiotic partnership between algae and fungi. Of the six types of lichens the three most common are crustose (flat and crusty), foliose (leafy), and fruticose (shrub-like). Some lichens (e.g Cladonia floerkeana) are a combination of types, Lichens reproduce by means of spores of soredia (powder vegetative fragments).

Early signs of life

                                      Early signs of life

FOR ALMOST A THOUSAND MILLION YEARS after its formation , there was no known life on Earth. The first simple , sea - dwelling organic structures appeared about 3,500 million years ago; they may have formed when certain chemical molecules join together.  Prokaryotes, single-celled micro-organisms such as blue-green algae, were able to photosynthesize and thus produce oxygen. A thousand million year later, sufficient oxygen had built up in the Earth atmosphere to allow multicellular orgeanisms to proliferate in the Precambrain seas (before 570 million years ago). Soft-bodies jellyfish, corals, and seaworms flourished with hard body frames, developed during the Cambrian period (570 million years ago). However,it was not until the beginning of the Devonian period (409-363 million years ago) that early land plants,such as Asteroxylon, formed a water retaining cuticle, which ended their dependence on aquatic environment. About 360 million years ago , the first amphibians crawled onto the land, although they probably still returned to the water to lay their soft eggs. By the time the first reptiles and synapsids appeared late in the Carboniferous, animals with backbones had become fully independent of water..

Earth's Physical features

                                     Earth's Physical features

MOST OF THE EARTH SURFACE (about 70 per cent) is covered with water. The largest single body of water, the Pacific Ocean, alone cover about 30 per cent of surface. Most of the land distributed as seven continents; these are (from largest to small) Asia, Africa, North America, South America , Antarctica, Europe, and Australasia. The physical feature of the land are remarkably varied. Among The most notable are mountain ranges , rivers , and desert. The largest mountain ranges the Himalayas in Asia and the Andes in South America extend for thousand of kilometers. The Himalayas included the world's highest mountain. Mount Everest  (8,848 meters). The longest rivers are Rivers Nile in Africa (6,695 Kilometers). Desert cover about 20 per cent of the total land area. The largest is the Sahara, which covers nearly a third of Africa. The Earth's surface feature can be represented in various ways. Only a globe can correctly represent areas , shape, size, and direction, because there is always distortion when a spherical surface the Earth's, for example is projected on the flat surface of the map. Each map projection is therefore compromise: it shows some features accurately but distorts others. Even satellite mapping does not produce completely accurate maps, although they can show physical features with great clarity.