My Science School

A tree that loses its leaves in winter is called a deciduous tree. Trees that are about to lose their leaves in the autumn conserve their food supplies by withdrawing all the nutrients from the leaves. Chlorophyll is broken down in the leaves, causing their pigment to change. Eventually all the nutrients are moved from the leaves and they wither, turn brown and eventually fall from the tree.

Fact File: Every year a tree grows, it deposits a new layer of cells on the outside of its trunk, beneath the bark. This new layer is called an annual ring. By counting the annual rings it is simple to work out the exact age of a tree.

 

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Pollination is the process of transferring pollen from the stamen to stigma. It is possible for flowers to pollinate themselves, or other flowers on the same plant – this is called self-pollination. It is, however, much better for the health of the species if cross-pollination occurs, i.e. pollen is transferred from one plant to another. The most common method involves insects that are attracted to the flowers for their nectar. Pollen grains stick to the insects’ bodies and are effectively transferred from one plant to another as the insect moves from flower to flower. Other, less attractive types of flower, use wind to transport their pollen.

Fact File: The flowers of orchids are highly specialized for pollination by insects. When the insect pushes into the flower to reach the nectar, the pollinia stick onto its head.

 

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Seeds are the main means by which flowering plants reproduce and spread. After the plant has been fertilized the egg cells develop into a seed from which a new plant can develop. The seed contains an embryo from which the new plant will grow. It also contains a food store to nourish the embryo until it has developed roots and leaves. The seed is enclosed in a tough outer coating to protect it from drying out. Many seeds can be carried by the wind. Some even have a fluffy umbrella like the dandelion seed head, which enables them to be carried for very long distances.

Fact File: The biggest seed is the coco de mer, a kind of coconut that grows in the Seychelles, a group of islands in the Indian Ocean. The coco de mer seeds weigh 250 kg each.

 

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The simple answer to this question is that trees never stop growing. Trees are the largest tree of all is the Californian giant redwood which can grow nearly 100 m high and can have a trunk that is 11 metres thick. The oldest-known trees are bristle cone pine trees. They grow in the White Mountains in California, in the USA. Although they are quite small, some of these gnarled trees are more than 4,500 years old.

Environmental factors such as water availability, soil quality, and change in the weather can affect the growth of a tree. Water is pulled up from the roots to the top of the tree by their leaves.

Fact File: Bonsai trees are decorative miniature trees that were first developed in Japan. They grown in shallow dishes and the shoots and roots are carefully trimmed to stunt their growth. They can live for hundreds of years.

 

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Plants are organisms that use light as a source of energy and to produce the food they need in order to live and grow. The Earth’s original atmosphere contained poisonous gases. The lack of oxygen meant that no animals or plants could survive on the Earth. The earliest plants or plant-like bacteria began the process of photosynthesis, which releases oxygen as well as a waste product. This gas gradually built up in the atmosphere as the plant life spread, making it possible for oxygen-dependent animals to evolve.

Coral was formed by bacteria in much the same way as plants. It is made up of a variety of invertebrate marine organisms of a consistency. They live in colonies begun by just one polyp. Each polyp builds a hard skeleton around itself.

Fact File: Lichens are a mixture of algae and fungi. Many grow like a mat over rocks or tree trunks, while others look like a small branched plant.

 

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Although frogs and toads can live on land, they have to return to the water to breed. Common frogs can be found in many freshwater habitats. They often show up in garden ponds but are just as happy in lakes, canals and pools. Toads usually prefer wooded ponds and lakes and can sometimes be seen in boggy pools.

Frogs and toads are amphibians, which mean they are equally at home on land and water. Toads, however, generally spend more time away from water than most frogs. Their skin is leathery and watery and they do not lose water so easily on dry land. On land a frog hops to escape danger, whereas a toad will walk. The bodies of some frogs and toads have adapted to survive in very dry conditions, such as in deserts.

Fact File: A frog’s eyes are on top of its head so it can see above the water’s surface. This way he can keep a watch out for predators.

 

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According to the theory of evolution, some animal species become extinct because they are less successful than other species that gradually replace them.

These so-called ‘failed’ animals are also unable to adapt to changing circumstances. Humans have speeded up their extinction by changing the environment so rapidly that animals do not have the time to adapt. For example, the destruction of Indonesian rainforests has left nowhere for the orang-utan to live. It would take millions of years for the animal to evolve into a ground-living creature. Hunting is the main reason for the reduced numbers and probable extinction of animals such as the tiger, the blue whale, and the giant panda.

Fact File: The black rhino has been reduced down to about 2,250 due to poaching. Most of the ones that survive today live in protected game parks.

 

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Young swans, or cygnets, are hatched with a complete covering of down and can take to the water as soon as they leave the nest, within 24 to 48 hours. Right from the beginning they can forage for themselves, but at least one parent remains with them, guarding, guiding and, initially, brooding them at night. The dark downy plumage is retained for two to six weeks and it then replaced gradually by the juvenile feathers. The flight feathers are the last to develop, taking from five weeks to as many months. By the age of six months the cygnets are practically indistinguishable from adults in plumage and in size.

Fact File: In captivity geese and swans have been known to live for more than 30 years; there are reports of geese exceeding 40 years of age. With luck and cunning a wild swan may survive for 15 to 20 years.

 

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Migration is the mass movement of groups of animals or birds. It is caused by the need to find food, by climatic changes during the year, and by the need to breed. Every autumn, for example, swallows gather in large flocks to rest before they begin their long migration to Africa. Swallows, and their relatives, swifts and martins, all migrate to Africa when the weather becomes too cold for them to catch their insect prey. They return in the spring when the weather in northern Europe begins to warm up. The Arctic tern makes the longest-known migration of any bird we know, by travelling from the Arctic to the Antarctic and then back again. On its flight it passes through Japan, Alaska, Canada and Fiji before returning home again to breed.

Fact File: Many fish migrate in both fresh water and the ocean. Tuna make some of the longest migrations. The need to migrate is due to sea temperature, as fish need the correct temperature in order to breed.

 

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An animal is classed as a vertebrate when it has a backbone to provide support for the muscles and protection for the spinal cord. Vertebrates include fish, amphibians, reptiles, birds and mammals. The backbone is actually a series of small bones called vertebrate. They are joined together and locked with rope-like ligaments to provide a flexible but extremely strong anchor for the back muscles. The spinal cord runs down a channel inside the vertebrate, providing protection from damage. Some primitive fish, such as sharks and rays, have a spine made of a rough rubbery material called cartilage. There are approximately 45,000 living species of vertebrates. In size, they range from minute fishes to elephants and whales (of up to 100 tons), the largest animals ever to have existed. They are adapted to life underground, on the surface, and in the air.

Fact File: The duck-billed platypus is a very unusual, small, semi aquatic mammal. It lives in lakes and streams of eastern Australia and Tasmania. It is notable in having abroad, flat, rubbery snout, webbed feet, and in that it lays eggs.

 

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Carl Linnaeus (1707-1778) was a Swedish botanist and explorer who was the first to create a uniform system for naming plants and animals. Most plants and animals have popular names that vary from place to place. Scientific names are given so that the same name is recognized everywhere. Latin is the language used for scientific names. The scientific names are in two parts. The first is the generic name, which describes a group of related living things, and the second name is the specific name, which applies only to that living thing.

Fact File: The Latin name of the White Water Lily is Nymphaea alba. They are one of a group of plants whose flowers close up for the night.

 

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Upon his return from the voyage, Darwin turned over all the specimens he had brought back to cataloguing experts in Cambridge and London. In South America he had found fossils of extinct armadillos that were similar but not identical to the living animals he had seen. On November 24, 1859 Darwin published his theories in a book called The Origin of the Species. It caused a great sensation, but it was some time before it was accepted by the scientific world. The first edition sold out immediately and by 1872 the work had run through six editions. It became generally accepted that evolution took place along the lines that Darwin suggested. His theory on evolution of species solved many puzzles.

Fact File: We can see how evolution has changed living things by examining fossils. Fossils preserve the body parts of living creatures from long ago so that we can see how they have changed over millions of years.

 

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In the year 1831 Charles Darwin (1809-1882) set out on an exploratory voyage in the ship Beagle, heading for South America. The voyage lasted five years and during this time Darwin kept careful notes of everything he saw, in particular the strange animal life on the Galapagos Islands, off the western coast of Ecuador. He was disturbed by the fact that the birds and tortoises of the Galapagos Islands tended to resemble species found on the nearby continent, while inhabits of similar adjoining islands to the Galapagos had quite different animal populations. In London Darwin later learned that the finches he had brought back belonged to a different species, not merely different varieties, as he had originally believed.

Fact File: When Charles Darwin first published his theories on evolution they created a sensation, but it took a while before they were accepted.

 

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We know the Mediterranean today as a huge sea off the coast of Europe. However, the Mediterranean was not always like that. Approximately 5 million years ago, the Mediterranean was a dry basin. Movements in the Earth’s crust opened up the Gibraltar Straits between the continental areas which are now Africa and Europe. The Atlantic Ocean would have poured through this new opening into the dry basin. The result would have been an enormous waterfall, nearly 800 metres high. So much water poured in from the Atlantic that the Mediterranean Sea was created in only a few years.

Fact File: Of course, through time the shape of the continents will continue to change, and new seas will form; some could even join together.

 

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No one knows for certain when the Earth was formed exactly. However, scientists have reasoned that it probably formed about 6,000 million years ago.

The most scientific reasoning for the creation of Earth is that it began as a huge ball of hot gases which cooled to form the planet. Seas of dissolved chemicals would have covered the land, and the air would have been an atmosphere of different gases. The atmosphere was thought to have consisted of swirling gaseous clouds which most likely caused huge electrical storms.

The poisonous gases in the atmosphere must have reacted to produce oxygen, which triggered off the first beginnings of life on Earth.

File Fact: As Earth cooled down, it gave off clouds of steam and gas. The moisture in these clouds eventually turned to rain, which formed the first seas.

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