8 Leaves change color

What is a plant? Plants are living things. They come in all shapes and sizes, from tiny waterweeds to towering trees. Plants are different from animals in one very important way—they can make food for themselves from sunlight. Animals can't do this. They depend on plants for their food. Where do plants grow? There are about 400,000 different kinds of plants on Earth, and they grow just about everywhere in fields and forests, deserts and mountains. Apart from air, the two things plants need are sunlight and water, so you won't find them in places that are completely dark or dry. Are plants really alive? Plants are just as alive as you are. They need air, food and water to grow, and they can make lots of new plants like themselves. This proves that they are alive. Things like stones and rocks don't feed, grow or have young because they are not alive. All the food in the world starts with plants. You may eat eggs, meat and cheese but, without plants, no chicken or cow could produce these foods! Corals and sea anemones may look like plants, but they are imposters, In fact, they are animals!

Why do trees have leaves? Like all plants, trees need their leaves to stay alive. Leaves are a tree's food factories. They contain a sticky green stuff called chlorophyll. The chlorophyll uses water, sunlight and carbon dioxide in the air to make a sugary food. The food is then carried to every part of the tree in a sweet and sticky juice called sap. Why do some trees lose their leaves in autumn? Big green leaves are useful in spring and summer. They make food while the Sun shines and the days are long. When the days get shorter, there's less time for making food and the tree must live off its food reserves. Rather than feed their leaves too, some trees shed their leaves in autumn. Why do leaves change colour? It's the chlorophyll in a plant's leaves that makes them look green. But in autumn, the chlorophyll breaks down. Once the green colouring has gone, the leaves' other colours show through beautiful shades of red, yellow and gold. If you have ever chewed a blade of grass you will know how sweet sap tastes. Hungry young caterpillars think so, too. That's why they eat leaves! The way plants make food in their leaves is called photosynthesis. During photosynthesis, plants take in carbon dioxide front the air. And they give out oxygen—the gas we all need to survive. We call plants that lose their leaves in the autumn deciduous. Evergreens have tough leaves that can survive the winter. The trees still lose their leaves, but not all at the same time.

why do roots grow so long? Long roots fix a plant firmly in the ground so that it won't fall over on windy days. But roots do another job, too. By spreading out far and wide, they can suck up water and goodness from all the soil around. Then the roots send the water up the stem or trunk and into the leaves. Why are stems so straight? A plant needs to hold its leaves up to the sunshine, which it uses to make its food. Many plants grow tall, straight stems, so that they can beat their neighbours to the sunlight. A wild fig tree in South Africa grew roots 120 metres down into the soil. If it was put on the roof of a 40-storey office block, its roots would reach down to the ground. In the strongest winds, a tree can sometimes be blown right over. Its roots are wrenched out of the ground as the tree falls down with a crash. At the ends of the roots are tiny hairs, which burrow into the spaces between the lumps of soil. Sunflowers not only grow up towards the light, but their flowers follow the Sun! As the Sun appears to move across the sky through the day, the flower-heads turn to face it. Not all plants have straight stems. Some have stems that bend and curl, clambering their way over nearby plants as they climb up to the light.

Which plants grow in water? The giant water lily grows in the lakes and rivers of South America. Its roots lie deep in the mud and its huge leaves float on the water's surface. This is the best place for catching the sun! Each leaf curls up at the rim so that it can push other leaves aside. Which are the smallest plants? Although some types of algae grow to be the most enormous plants, there are other algae so small you can only see them through a microscope. The very smallest float in lakes and oceans, and are called phytoplankton. They are so tiny that whales catch millions in every gulp! Which forests grow in the sea? Huge forests of kelp grow off the coast of California in the United States. Kelp is a kind of seaweed that grips on to rocks, and sends long, ribbon-like stems up through the water. Some of the stems can be 200 metres long-as long as eight swimming pools laid end to end. The giant water lily's leaves grow on long, strong stems. On the underside of each leaf is a web of supporting veins. This makes the leaves so strong that a toddler could sit on one without sinking! The leaves and roots of water plants give food and shelter to many animals. But they are also places where hunters can hide. Not all water plants are rooted in the mud. Some seaweeds float in the water, thanks to pockets of air in their leaves-rather like their very own rubber rings!

Which plant... traps a treat? When an insect lands on a Venus flytrap, it gets a nasty surprise! It only has to brush against one tiny hair on an open leaf tip, to make the leaf snap tightly shut. There's no escape for the poor insect. The flytrap changes it into a tasty soup, which it slowly soaks up. ...fools a fly? Pitcher plants have unusual vase-shaped leaves that tempt insects with a sugar-sweet smell. But the leaves are slippery traps. When a fly lands on them, it loses its footing, slips inside the 'vase', and drowns in a pool of juice. ...snares a snack? The sundew's leaves are covered in hairs, which sparkle with glue-like drops. When an insect lands on a leaf, it gets stuck fast. The more it struggles, the more it sticks. At last, the leaf folds over, traps the fly, and starts dissolving it into liquid food that it can drink up. The bladderwort is an underwater meat-eater. Along its leaves are bubble-shaped bags, which suck in tiny creatures as they paddle past. Did you know that flytraps can count? The first time an insect touches a hair on one of the leaf tips, the trap stays open. But if it touches it a second time, the trap snaps shut! Many meat-eating plants grow on wet. boggy ground where the soil is very poor. They need their juicy snacks for extra nourishment.

Why do plants have flowers? Many plants have colourful, perfumed flowers that attract insects and other animals. The visitors feed on drops of sweet nectar inside the flower. As they feed, they pick up a fine yellow dust called pollen, which they carry to another flower. When the pollen rubs off on the second flower, that flower can start to make seeds. Which flower fools a bee? A bee orchid's flowers look and smell just like female bees. Male bees zoom to the flowers wanting to mate with them but they have been tricked! The plant's just using them as postmen to deliver little packets of pollen to other orchids nearby. Which is the smelliest flower? The dead horse arum is well named it stinks of rotten meat! But blowflies love it. These plump flies usually lay their eggs inside the rotting bodies of dead animals. They are fooled by the plant's rotten smell, and crawl inside it to lay their eggs, picking up pollen on the way. This plant is called hotlips-and no wonder! The lipstick- red markings on its leaves are a wonderful way to attract visitors to its tiny flower. Many trees and grasses spread their pollen on the wind. They don't need animal visitors, so they don't grow bright flowers. Pollinators, such as this bat, don't mean to get pollen all over themselves. But a cactus flower is shaped in such a way that the bat just can't help it! During the summer, the air can be so full of pollen that it makes many people sneeze. Poor things they haven't got a cold, they've got hay fever.