Friday, August 9. 2019What do we exactly understand about a Tree?
A tree is a large plant with a woody stem or trunk, covered with a layer of bark. There are two main groups of trees: broadleaves and the conifers. Broadleaved trees are flowering plants that produce fruits with seeds inside. Conifers produce cones, which carry seeds on the face of each of their scales. Many broadleaved trees are deciduous: their leaves drop in autumn, or, in hot countries, during the dry season. Some broadleaves and nearly all conifers are evergreen. Their leaves do fall, but not all at the same time. The palm tree, which grows in hot countries, is a different type of tree. It usually has no branches and only a few large leaves at its tip. Trees are a valuable resource. They give us fuel, timber, medicines, food, paper, rubber and even soap. Even more importantly, they take in carbon dioxide and give off oxygen, so maintaining the balance of gases in the atmosphere.
HOW A TREE LIVES Like all plants, a broadleaved tree has roots and a shoot. The shoot is made up of a trunk (its stem) and branches bearing leave buds and flowers. The trunk holds up the tree while the branches and twigs spread out the leaves so that they receive as much sunlight as possible. The leaves themselves grow in a spiral pattern to avoid shading. Water (blue arrow) is drawn up from the soil to the leaves through the sapwood. The leaves use the water and sunlight, as well as carbon dioxide in the air to make food by photosynthesis. This food (red arrow) passes from the leaves to all other parts of the tree through the inner bark. At the base of the tree, a network of roots spreads outwards, anchoring it into the ground. Behind the root tips lie the root hairs which soak up water and nutrients from the soil. A large tree may take up several hundreds of litres of water every day. A TREE’S YEAR As spring arrives, the buds of the horse chestnut tree open, the shoots lengthen and the leaves unfold. Flowers blossom, ready for pollination. In summer, the leaves are fully open. The fruits, made up of a spiny casing with a large seed or “conker” inside, ripen and fall to the ground. During autumn, the leaves turn brown as food drains from them into the trunk. A scar forms at the base of each stalk and the leaves fall off. In winter, the tree is protected by its waterproof bark. The buds, next year’s leaves and flowers, are covered by scales. Picture Credit : Google Friday, August 9. 2019Unfold the mystery of Seeds and Fruits?
SEEDS AND FRUITS After male pollen grains have been carried to the female parts of a flower, the male and female cells join and begin to develop into the baby plant. The flower parts are no longer needed and they shrivel away, to be replaced by the developing seeds in the seed-head. A seed is usually accompanied by a food store for its early growth, neatly packaged inside a casing. Some plants, like orchids, produce many thousands of tiny seeds. An ear of wheat is a head of wheat seeds or grains. We grind them up to make flour. Seeds have a better chance of growing if away from the parent plant. If they fall next to the parent, they would be in its shade and would also compete with it for soil nutrients. For these reasons, seeds have many ways of being spread far and wide.
FRUITS AND NUTS A fruit is the protective case around a seed. Some fruits are very light, like the feathery “parachutes” of the dandelion. They blow away in the wind. Some fall into water and float to a new place, like the coconut. A nut has an especially tough outer case. Animals may crack some nuts and eat the seeds within, but they also drop many as they feed. A squirrel buries nuts such as acorns, but may forget to dig them up, so in effect it has planted new oak trees! Some fruits have juicy, tasty flesh. These are known by the everyday name of “fruits”. The fruity part attracts animals to eat it. The seeds are spilled or pass through the animal’s guts to emerge unharmed and far away.
A seed germinates, or begins to grow, only when conditions are suitable. This usually requires moisture of some kind, the right temperature, and perhaps darkness, which means the seed, is buried in the soil. Some seeds like those of the ironwood tree do not germinate unless they have been scorched by fire. This usually means many plants have burned away so the ground is bare and ready for new life. Other seeds do not germinate until after they have been cracked by frost and then warmed slightly, that is, when winter is over and spring has arrived. When conditions are right, the baby plant begins to grow using its store of food in the seed-leaves, or cotyledons. It splits its case, sends roots down into the soil and grows its shoot up towards the light.
FUNGI Mushrooms, toadstools, brackets, yeasts, moulds and mildews are all fungi. They form one of the five great groups or kingdoms of living things. Fungi are rotters. They grow networks of thin, pale threads, called hyphae, into the bodies of dead and dying plants and animals. The threads cause the body to decompose. They then absorb the released nutrients through their surface. Like bacteria, fungi are nature’s recyclers. They return the nutrients in dead animal and plant matter or animal droppings back into the soil.
A fungus’s network of threads is known as the mycelium. It is usually hidden in the soil, inside a dead animal’s body or under a dying tree’s bark. So we rarely notice fungi at work. We are more likely to notice them when they reproduce. They do this by growing fruiting bodies. Many of these are shaped like umbrellas—we call them mushrooms and toadstools. The presence of a mushroom indicates a network of hyphae in the soil below, rotting down and absorbing nutrients. The mushroom’s top, or cap, releases millions of tiny fungal spores that blow away in the wind. Picture Credit : Google
Friday, August 9. 2019How do plants live?
A plant may not look lively and active. But inside its millions of microscopic cells, thousands of chemical changes take place as part of the plant’s life processes. Like an animal’s body, a plant’s body has many specialized parts for different jobs. The roots take in water, minerals, salts and other substances from the soil in which the plant grows. The stiff stem holds the main parts of the plant above the surface, away from animals on the ground that might eat it, and above other plants so that the leaves can catch more sunlight.
A plant’s leaves are “light-powered food factories”. They are broad and flat so that as much light as possible falls on them. A green substance called chlorophyll in the leaves catches or absorbs the energy in light. It uses this energy to make a chemical reaction. Water, taken up from the soil, and carbon dioxide, taken in from the air, join together to form sugar, which contains lots of energy in chemical form. The plant then uses the sugar to power its life activities. The process is called photosynthesis —a word meaning “making with light”. The carbon dioxide for photosynthesis comes from the air. It seeps into the leaf through tiny holes in its lower surface, known as stomata. In addition to sugar, photosynthesis also produces oxygen, which seeps out into the air. Living things including ourselves need oxygen to survive. Plants help to top up its level in the air.
FLOWERS AND POLLEN A plant’s flower is designed to reproduce—make seeds which grow into new plants. A typical flowering plant has both male and female parts. The male parts make tiny particles, pollen grains, which look like fine yellow powder. Each grain contains a male cell. Pollen is produced in bag-like anthers on stalks, called filaments. The female cells or ovules (eggs) are in the ovary, a fleshy part at the flower’s base. A taller part, called the style, sticks up from this, with the stigma at its top. Pollen must travel from the anthers of one flower to the stigma of another of the same kind, so the male and female cells can join and develop into seeds. The transfer of pollen is called pollination. Some pollen grains are light and balloon-like and are blown by the wind. Others are sticky and carried by animals. To attract animals, the flower has colourful petals and a strong scent and makes sugary liquid called nectar. When animals come to drink the nectar, the pollen sticks on them. It brushes off at the next flower on to the stigma. A tube grows from the pollen grain down the style to the ovary. The male cell moves down this to join the ovule. Picture Credit : Google |
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