Friday, December 12, 2008


These are the mosses and liverworts. Liverworts are plants requiring damp conditions and they are often found in shade by water or near ditches, where they make green growths on the surface of the soil or on rocks. The flattish visible part of the plant is called the thallus and from its underside are produced simple root-like growths which anchor it to the ground. Most liverworts can increase by sending out branches which eventually become detached from the main plant. They can also reproduce sexually and after the fertilization of egg a stalk is produced from the upper surface of the thallus. At the top of the stalk is a capsule containing spores which when released to fall on a suitable place for growth, will produce a new generation of liverworts

Antibiotics and Viruses

Some tiny plant organisms produce substances which are capable of killing bacteria, and penicillin and streptomycin are two examples of these. The organisms producing these useful antibiotics are in fact fungi, and are cultivated by man in order to obtain large quantities for treating diseases. Viruses are organisms which are very much smaller even than bacteria and very little is known about them. They seem to be on the borderline between the living and non-living although they do have the ability to increase and spread. They cause many diseases to plants and animals and in man are thought to be responsible for such things as colds, influenza and measles. In plants they produce disorders such as wrinkling and yellowing of leaves. They seldom kill plants, but completely upset their normal way of life, and because they can ruin crops are a problem to man. Unlike a lot of bacterial and fungal diseases in plants, they cannot be killed by chemical sprays


Bacteria also come within the division of thallophytes that are dependent on green plants, for they are a group of minute organisms without any cholorophyll. They are parasites or saprophytes and are usually single celled often with the power of movement in the same way as chlamydomonas. They increase by straightforward division of an old cell into two new ones, or they can also form resting spores. These consist of cells which have specially tough cell walls, and in this stage the bacteria is very resistant, in some cases even to boiling water. These spores are very numerous and are present in the soil, the air and water. In fact they are present virtually everywhere unless special precautions are taken to kill them. During the resting stage they are not increasing at all but when conditions are suitable for their growth the cell wall breaks down and the bacteria become active again. Parasitic bacteria are often harmful such as anthrax in animals tetanus in man and soft roots in plants but quite a number do exist on other living organisms without doing them any harm. Saprophytic bacteria are often useful for they help in rooting down dead material. They are very active in for example a compost heap. Some are used to covert alcohol into vinegar. One group of bacteria (nitrogen fixing bacteria) are especially important as they live in swellings in the roots of plants of the legume family (peas and beans) and have the power of extracting nitrogen from the surrounding air in the soil and making it into a form that can be used by plants. This is why plants of this family, especially clover, are often grown in fields and then ploughed in to improve the soil. Other bacteria in the soil (nitrifying bacteria) can covert plant and animal remains into a form that plants can use. So by the very valuable action of these tiny life forms a continuous process is set up of turning waste and dead materials back into food for other plants. This called the nitrogen cycle.


Fungi represent a very important part of the thallophytes and are separated from the rest by many definite characteristics. They have no chlorophyll and no starch is present in their cells and it is easy to see from the example of a few familiar toadstools that they are quite different in actual make-up from all other plants. They do not live on their own manufactured food, but rely either on the decaying remains of other plants and animal life(these types are called saprophytes)or on living plants or animals(parasites). The fungi may be single celled plants such as yeast, which is used for baking bread and brewing beer, or multi-celled plants such as the mushroom. In these more advanced forms the main part of the plant is an intricate web of threads known as hyphae, the whole web being called the mycelium. This often lives underground or inside the host plant on which the fungus is living. The hyphae threads run about either in or between the cells of the plant and have the power of dissolving the cellulose of the cell walls and living on the contents. The saprophytic ones act in a similar way on dead organic material and are not generally harmful to plants or animals. These parasites on the other hand cause man a great deal of trouble and expense in trying to get rid of them. Some fungi attack animals, including man, an example being the fungal disease athlete's foot. With the larger fungi, the hyphae sometimes come above ground and form a special structure which can produce spores. This is the fruiting stage of the plant and the mushroom and toadstool are examples of this. The hyphae have another property which is important to the fungus and this is the formation of a hard tuber like body called sclerotium(again a resting stage) which is capable of existing for a long time without actually growing, or doing damage in the case of harmful fungi. This stage makes it difficult to get rid of some fungal diseases for they can withstand a lot of adverse treatment, and then germinate when conditions are suitable. As fungi lack chlorophyll they cannot make their own food by photosynthesis. They must therefore absorb carbohydrates from the plant or animal matter on which they live. Having got s source of supply of carbohydrates they can themselves convert these substances into the more complicated ones needed to make cellulose for cell walls, and for proteins and protoplasm. The last two can only be formed if the fungus has a source of nitrogen and other more complex chemicals from an outside source, so for this reason a lot of fungi are rather specialized in their choice of where to grow. Like the animals, fungi are dependent upon green plants for their food and could not live without them. So it is that the first living matter to colonise a new piece of ground will be something which can manufacture its own food, without depending on any other life form and it must therefore be a green plant whether one celled or multi celled. When this is established, fungi and animals will appear either to grow on or eat the plant or live on the organic matter which occurs when it dies.


Although there are freshwater species the majority of algae live in the sea and the various seaweeds found at low tide are familiar examples. A lot of the most primitive of these plants are single-celled and invisible to the naked eye, whereas the large, more advanced seaweeds are made up of countless cells which may be divided into groups or tissues performing different tasks. Such plants may have primitive roots. These algae are very similar to other plants in the way they obtain their food, for they contain chlorophyll and photosynthesis takes place in the same way as it does in the advanced forms of plant life. Although many are green, quite a number have pigments in their cells which are stronger colours than green, giving the algae red, brown or even bluish colours. Their method of increase can be either by simple division of the original plant or sexual reproduction. There are thousands of different species of algae and it would be impossible here to describe even a small proportion of them, but one or two examples can be taken to show what life-forms exist in this group. Some of the tiny single-celled species are capable of movement and such a plant is Chlamydomonas, which is found in ponds and ditches. It is roundish in shape and is built up in the same basic way as other cells. At one end are two thread-like arms which project through the cell wall. These are called flagella, and by waving them around the cell can move in the water. The cell contains a nucleus and chloroplasts for manufacturing food, and in addition an orange-coloured object known as the eye-spot. This helps the chlamydomonas find its way towards brighter light, and in doing so gives the chloroplast a better chance to produce food. Other single celled algae do not go through life individually, but group themselves into a calony and hundreds or thousands together may just be visible without a microscope. These types are interesting in that they all use their flagella together and move as a whole colony towards light. Sometimes in bright weather the rate of reproduction is so fast that the water in ponds may be coloured green by their presence, and can easily be seen. The hard green covering often seen on older wooden fences is formed by large numbers of a small land alga known as Pleurococcus. It can withstand long periods of drought but like those which live in water it only becomes very active when there is plenty of moisture and it is warm. Many of the other algae in water can also form what are called resting stages so they can withstand adverse conditions such as the drying out of the pond in which they live. One of the commonest alga in ponds and slow steams is the plant which sometimes forms the slimy green masses familiar to all who spend some time near the water. This is called Spirogyra and is a long thread like plant formed from short cylindrical cells joined end to end. Among the most advanced of the algae are the common forms of seaweed called wracks which inhabit rocky costs all over Europe. Fucus vesiculosus commonly called bladder wrack, has a portion as its base which is adapted to clasp on to rocks and prevent the plant being washed away. This part of the plant has no powers of absorbing foods and is entirely an anchor. The stem is cylindrical at first then higher up it is flattened out and has built in bladders of air which act like water wings and keep the plant upright in the water. The whole plant is very slippery, being covered with a jelly like substance and it is rubbery to withstand the buffeting of waves. Reproduction is either by the simple breaking off of sections of the stem which in these plants is called the thallus, or by the formation of two kinds of special cells, one of which is capable of movement like chlamydomonas plants.These special cells are set free when the tide is in and the mobile ones swim to the others and they fuse together forming a spore. This can germinate and develop into another plant.

Friday, December 05, 2008


Woodpeckers are real tree- dwellers, where they dig for insects and grubs. The loud drumming made by the beak is a male's warning to other males, and also an invitation to a female. A hole is bored in a tree for a nest. Common in Europe are the Lesser Spotted (no larger than a sparrow) the Great Spotted and the Green Woodpeckers. The largest European species is the Black Woodpecker, as big as a crow. Largest of all is the Ivory – billed Woodpecker of Mexico, fifty centimeters long.

Some gaudily coloured birds related to woodpeckers are the toucans of South America, which have enormous beaks and look top-heavy. In fact the beak is quite light, and a toucan can hold and play with a grape or an egg without damaging it.


The animals we know best for man is one of them-are called vertebrates, or animals with a backbone (vertebra, Latin for a twisting joint) there are five classes: mammals, birds, reptiles, amphibians and fishes. Some zoologists give this group another name, the Chordata, so as to include a few very primitive sea- creatures like sea- squirts and lampreys which also have a kind of simple backbone, called notochord. In the true vertebrates this is found in the embryos only(when the animal is in its earliest stage of development and is slowly replaced by a bony, jointed vertebral column down the back.

Tortoises and Turtles

Tortoises and Turtles are unique among animals, having their whole bodies enclosed in a bony box. This is built from the rib cage which grows and joins up outside the limbs. The earliest tortoise show separate ribs but even these are already flattened as if about to join together. This peculiarity goes back even before the dinosaurs, so that chelonians (the name of the order to which tortoises and turtles belong are the oldest group of reptiles. They even have the oldest individuals on earth today- the giant tortoises which can live to a hundred and fifty years or more. Chelonians are of three kinds-tortoises, turtles and terrapins. Tortoises are land reptiles with domed shells and stumpy legs. They move about clumsily and feed mostly on plants and fruit. The largest are the giant tortoises of the Galapagos Islands in the Pacific, and the Aldabra Islands in the Indian Ocean. They can weigh up to 550 kilograms and measure almost two meters in length. Tortoises sold in shops as pets come from the Mediterranean countries, and have been known to live up to a hundred years. Eggs are laid in the ground and left to hatch in the sun.

Turtles are sea-going chelonians, with flatter shells than tortoises and more paddle – like feet for swimming. At night the females come ashore on some lonely tropical beach where there is sand. They dig pits in which up to 150 eggs may be laid. These are covered up and the mother then returns to the sea. Later the babies hatch out, struggle to the surface, then make as fast as they can for the water. On the way many are caught by the waiting sea-birds. Because turtles are also caught for food and their eggs dug up, some are now becoming rare. One or two countries do protect turtles by fencing off some of the beaches where they lay their eggs, later collecting the young and taking them out to sea where they will be safe to grow up. The largest turtles, up to 400 kilograms and one and a half meters long, is the Leathery Turtle. The Green Turtle is the species usually caught for making turtle soup, and the Hawksbill Turtle for its shell, called tortoiseshell.

Terrapin is an American Indian name for freshwater tortoises which swim in rivers and marshes, catching fish and water animals. They spend hours basking in the sun at the waterside, but dive in at any sign of danger.


One of the most interesting stories of plant life is the history of the rubber tree(Hevea brasiliensis). From the very early days of its discovery in South America, when the conquering Spanish saw children playing with rubber balls it was realized that rubber had water proofing and other properties which made it valuable. The real boom for the rubber industry came when rubber tyres were made. Whole books have been written about it and the way in which world history has been changed by this indispensable substance.

Although originally from South America, rubber trees are now grown throughout the tropics, especially in South-East Aisa. The rubber begins life as a white latex which is obtained by cutting grooves in the bark of the trees. First it goes through a chemical process which results in a sheet of crepe rubber and in this form it can be transported. Further processing is necessary before it is made into such items as tyres. Nowadays synthetic materials are generally mixed with natural rubber.

A few other plants have been used to produce rubber, particularly in war-time when the transport of tropical rubber was difficult. A species of dandelion was used for this purpose in the Second World War, the white sticky latex producing a rather inferior grade of rubber. Another form of latex, from trees of the Sapotaceae family, is used for chewing gum.

Parasitic Worms

Most annelid worms live freely in the soil or water, but some worm-like groups live inside other animals, even man. One of these is the group called Nematoda, or roundworms, containg some 10,000 species. They are pale in colour, without segments, and have pointed ends. They move about in a curious figure – of-eight fashion. Some of these nematodes, can be up to fifteen centimeters long, but many kinds are microscopic. All told there are vast numbers of these nematodes living in all sorts of animals, also plants, and a great number n the soil.

Each animal victim of a parasite is called a host. The human is host to another kind of worm, called a tapeworm. This belongs to the group of 6,000 species called Platyhelminthes or flatworms. In this case here are two hosts, the human and another animals which he may eat as meat, such as pork or beef. The pig or bull may pick up a tapeworm egg and swallow it. This hatches into a larva and bores into the flesh.

Another type of flatworm, called a fluke, has the shape of a small leaf. One example is the liver-flike which attacks sheep.


This is one of the most widespread divisions of the animal kingdom, certainly the largest. Arthropod means jointed legs but whereas vertebrates have only four legs, some of these invertebrates have many more. The main classes of arthropods are insects, arachnids(spiders, scorpions and mites), millipedes and centipedes, and crustaceans(crabs, lobsters and shrimps)