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| Sunday, 22 January 2006 |
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Junior Observer |  |
| News Business Features Editorial
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The fascinating world of plants What is the difference between an animal and a plant? Both live, feed, and reproduce, but it is how they do this that varies. Plants cannot move in the same way as animals can. This means that they have to get their food in one place. They do this by using their roots and their green leaves, through a process called photosynthesis.
During the daytime, the leaves make food for the plant. They use water that comes up from the soil, together with a part of the air called carbon dioxide, which is taken into the plant through tiny pores on the surface of the leaf. With the help of energy trapped by the leaves from sunlight, the plant uses the water and carbon dioxide to make a kind of sugar, which is the basic food for plants. After the sugar has been made, the plant gives off another gas - oxygen. Both plants and animals need oxygen in order to breathe, so without plants, no form of life could survive, on this planet.
Plants have a network of roots under the ground. These help to anchor the plant in the ground, but they are also used for taking up water, salt and nutrients from the soil. All these pass through tubes from the roots, up the stem and to the leaves. Other tubes carry the sugars from the leaves to the roots. Some plants such as mosses and liverworts, are very small and simple, while flowering plants can often grow to a great size.
The coastal redwood trees of California are the largest plants in the world.The famous giant redwood, also known as the giant sequoia, is a conifer that grows to over 80 metres in height. The tallest in the world is 82 metres tall, with a circumference of 24 metres. Plants without flowers Mosses and liverworts are primitive plants that grow very slowly. Some mosses are feathery while others grow in cushions. Mosses can often be seen in woods, making soft, green cushions on the ground. But they also grow on old walls and roofs, where it is much drier.
Mosses never have flowers or make seeds, so they have to reproduce in other ways. Often, pieces are broken off and moved away, perhaps by the wind or rain, or animals brushing against them. If they end up in a suitable place, they will begin to grow again. This is one way how mosses reproduce. At certain times of the year, very thin stalks may grow up from some moss plants. At the end of the stalks are tiny spore boxes. When the spores are ripe, a little lid falls off and the spores come out. They are so light that every puff of wind blows them away. When they land, they can begin to grow into new moss plants.
Liverworts are also plants that have no flowers. They grow very slowly and like damp and shady places. They are often found on riverbanks or on rock faces dripping with water. Ferns reproduce by spores, too. They usually lie in special places on the undersides of the leaves. When it first lands, a spore grows into a small heart-shaped plant before eventually becoming a large fern. Ferns are taller than mosses and have larger leaves, called fronds. Some have leaves like straps, some are like huge feathers. There are tree ferns more than four metres tall that grow in tropical countries. There have been ferns on Earth for many, many years. The coal that is dug out of the ground today was formed from ferns and other plants that grew in marshy places millions of years ago.Ferns like to grow where the soil and air are damp. You can find them on shady walls, on riverbanks and in wet woodland.Lichens do not like pollution, so many types occur by the sea. Flowering plants For flowering plants to reproduce, the plants must get the pollen from one flower to another. Plants have developed many ways to get the pollen across to other flowers.
In grasses and many types of trees, the pollen, which is like yellow dust, is distributed with the help of the wind. However, most plants that have brightly coloured petals depend on various types of insects such as butterflies and bees to distribute the pollen which is called pollination. The insects, you may have learnt at school, are usually attracted to a flower by the colour and the sweet nectar in it. When an insect crawls into the flower to gather the nectar, the pollen from the flower rubs off onto its body. Then, when it flies to another flower, the pollen rubs off onto that flower and pollination takes place. The pollen goes through a process of fertilisation, and seeds are formed.Plants try to spread their seeds as far as possible. There are many different kinds of seed and many different ways of making them spread as far away as possible. Dandelion seeds are blown by the wind, poppy seeds are shaken out of their seed box like pepper from a pepper pot and burdock seeds stick to the fur of animals. Some seeds, such as sycamore, have wings which keep them in the air. Seeds are often encased in berries which are eaten by birds or other small animals. The seeds inside pass through the gut unharmed and are later deposited far away.Coconut seeds can float and are carried by the sea. Unusual plants There are at least 250,000 kinds of flowering plants. The plants and their flowers come in all shapes and sizes. The flower of duckweed, which floats on ponds, is so small that it is hard to see. But the flower of a plant called rafflesia, which grows in the jungles of Asia, may measure as much as one metre across. Plants grow in all kinds of places. Cacti are plants that can grow in very dry places, such as deserts. When it does rain, they store water in their stems, to be used whenever they need it. Their flowers are very lovely, but very rare - some kinds of cacti do not flower very often. Most plants have green leaves which help them make their food. A few kinds of plants do not make their own food, but instead eat decaying matter. They are called saprophytes. The bird's-nest orchid, for example, lives in the deep shade of beechwoods and feeds on rotten leaves. Some plants feed on other living plants. They are called parasites. Mistletoe attacks apple trees and feeds on their sap. There are even a few carnivorous plants. Certain leaves on pitcher plants are shaped like pots, and have water in the bottom. Sometimes an insect will land on the rim of the pot, slip and fall into the pitcher, where it stays until it dies and rots. The plant produces a liquid that helps dissolve the soft parts of the insect, releasing nutrients that the plant can use for food. Sundew also traps insects on its sticky leaves and the Venus' fly-trap has leaves which close around any prey that lands on them. Some plants live to a great age. Bristlecone pines grow in the White Mountains of California. Many of the trees are more than a thousand years old, and are the oldest living things in the world. The cuckoo pint attracts small flies to its strange flower. Trapped inside, the flies become covered in pollen. Eventually they escape and take the pollen to the flower of another cuckoo pint. The next time you step out into the garden, or outside take time to
observe the plants around you and learn as much as you can about the
different species... Remember, if not for them, life will not continue on
planet Earth because plants give us valuable oxygen to breathe. |
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