My Science School

FRUITS

All plants produce fruits that contain their seeds. Some fruits are dry husks, but others are juicy and tasty. These attract animals, which eat them and carry the seeds in their stomachs. The tough-skinned seeds are not digested, but are scattered far away from the parent plant in the animals’ droppings, and grow into new plants. The fruits are cultivated types that have been specially bred for their size and flavour.

1. ORANGE An orange has very soft juicy flesh contained in many segments, which are enclosed by a hard rind. Each segment usually contains a seed, or pip. An orange is technically a type of berry, which develops over the winter from the single ovary of an orange flower. Green at first, it turns orange as it swells to full size.


2. BANANA The bananas that are cultivated in the tropics have been bred to be seedless, but the wild bananas of Southeast Asia have small fruits containing many big, hard seeds. They grow in bunches on large plants with huge leaves that sprout straight from the ground.


3. NUTS All nuts are large seeds, which the plant has equipped with a store of concentrated plant food. This ensures that the seedlings get a good start in life. The nut is surrounded by a hard shell, which is technically a fruit, but tough and fibrous rather than soft and juicy.


4. DURIAN To attract fruit-eating mammals, many fruits are fragrant. The Southeast Asian durian fruit is famous for its strong aroma, which some people like and others hate. Animals such as forest pigs and orang-utans seem to love both its smell and taste.


5. GRAPES Some fruits such as grapes grow as clusters of soft, edible, thin-skinned berries. Each berry has several seeds embedded in its flesh, although many cultivated varieties of grapes are seedless. Berries are often vividly coloured to attract birds, which have excellent colour vision.


6. PEACH The juicy flesh of a peach, plum, or cherry encloses a hard “stone” that contains a single seed. This type of fruit is called a drupe. The fleshy part is meant to be eaten, so animals spread the seeds, but some animals such as parrots can crack the stones and eat the seeds, too.


7. BROAD BEAN The edible part of a broad bean plant is its seeds, and its fruit is the entire pod. The wild ancestors of such beans do not attract animals. Instead, their pods dry up and split open with explosive force, so the seeds shoot out and are scattered on the ground.


8. TOMATO Not all fruits are edible. Some of the wild relatives of tomatoes are extremely poisonous. They include deadly nightshade, which is lethal to humans, although some animals can eat the berries without coming to harm. Tomatoes are also related to chilli peppers.

TREES

Trees are the tallest, heaviest, and oldest of all living things. The Californian giant sequoia known as General Sherman weighs approximately 6,000 tonnes - 30 times as much as the biggest animal, the blue whale. The oldest living bristlecone pine tree, which also grows in California, is nearly 5,000 years old. Yet even these ancient giants can still produce tiny seeds that grow into new trees.

LEAVES Like all green plants, trees absorb sunlight through their leaves and use its energy to turn air and water into sugar. A tree’s leaves are its food factories.

COMPOUND LEAVES Most trees have simple leaves of various shapes, but some have compound leaves, made up of many leaflets. These either sprout from a long stalk (pinnate) or fan out from a single point (palmate).

NEEDLES AND SCALES Thin leaves make food efficiently, but they are easily damaged by hot sunshine or frost. So many trees that grow in very hot or cold places have thicker, tougher needles or scales.

FRUIT The flowers of some trees turn into juicy fruits that contain seeds. If birds eat the fruit, the seeds pass through them unharmed and are scattered far away.

TREE RINGS Every year a tree adds a layer of new wood to its trunk. If the tree is cut down, each year’s growth shows as a visible ring, so the number of rings gives its age.

FLOWERS All trees produce flowers, but some may not be obvious because they do not have colourful petals. Other trees, however, such as apples, have showy flowers that attract insects.

SEEDS AND NUTS Some trees have tiny seeds, but others produce the bigger seeds we call nuts. Animals eat them, but also bury and forget them, so they grow into new trees.

CONES Coniferous trees such as pines have woody cones that contain small papery seeds. When the cones open up in the sun, the seeds fall out and blow way.

DECIDUOUS LEAVES Many trees lose their leaves in winter, and grow new ones in spring. Before they fall, the old leaves lose their green colour and turn yellow, brown or even red.

Picture Credit : Google

FLOWERS

Many plants produce beautiful flowers, often vividly coloured and fragrant. These intricate structures form the reproductive parts of plants and have evolved so that they attract insects and birds to sip the sugary nectar at the flower’s centre. While feeding, the insect or bird is dusted with pollen, which is produced by the stamens and contains the male sex cells. The pollen is deposited on the sticky stigma of another flower. This is pollination. A pollen tube then grows down the style to the ovary and fertilizes an ovule. This is fertilization. Some plants, such as grasses and many types of trees, rely on the wind to carry their pollen and their flowers do not need showy petals or fragrant nectar to attract animals. Since this is a less efficient system, they must produce far more pollen, which can fill the air and cause hay fever.

1. Flower Structure A typical flower develops inside a bud at the end of a stalk. When the bud opens, it reveals a ring of petals, each of which secretes nectar from its base. At the centre of the flower lie the male structures that produce pollen. These surround the female structures that hold the ovules, or egg cells. An outer ring of green sepals may protect the flower when it is in bud.


2. Carpel An ovary, a style, and a stigma form the main parts of a carpel. At the heart of the flower lie the ovules, enclosed in a case called an ovary. The top of each ovary extends into a style that carries a sticky pad called a stigma. The flowers of some plants have man carpels, each with their own stigma, but this lily has just one.


3. Stamen The tiny, dust-like pollen grains that contain the male cells are produced by stamens. These usually form a ring around the central carpel or carpels. Each stamen has a long filament, which supports a club-like anther that produces the pollen.


4. Transferring Pollen Insects such as butterflies often drink nectar from one type of flower. Hummingbirds do the same, because their bills are the right shape to reach the nectar. The bird and the insect get dusted with pollen in the process, and carry it directly to another flower of the same type.


5. Fertilization If a hummingbird sips nectar from this lily, it will pickup pollen on its breast feathers. If the bird visits another lily, the sticky central stigma may pick up the pollen. Each pollen grain then sprouts a long tube that grows down through the carpel to reach an ovule. The male cell moves down the tube to fertilize the ovule so it can develop into a seed.

Picture Credit : Google

PLANTS

All green plants use the energy of sunlight to make sugary carbohydrate food from water and carbon dioxide in the air. This is why they grow well only in sunlit, moist places. The food fuels growth and is used to make cellulose — the tough, fibrous tissue that helps support all the various parts of the plant, from its stems and leaves to its flowers.

1. GERMINATION A bean plant begins life as a seed with two halves, called cotyledons. In spring when the weather is mild, the seed starts to absorb water through a minute hole in its outer coating (the testa). The seed swells and about three days later a root grows to hold the plant in place, and a shoot appears above the ground. This process is called germination.


2. ROOTS The plant’s roots absorb water from the soil. The water is used by the leaves to make food. The water also contains dissolved mineral salts, such as nitrates and phosphates, which are essential for growth.


3. STEM The strong stem of the plant supports its leaves in the sunlight. It also contains bundles of tubes or veins. These allow water containing dissolved nutrients to flow up from the roots to the leaves, and also carry sugary food from the leaves to other parts of the plant.


4. LEAVES The leaves are the plant’s food factories. They act like solar panels, as the green chlorophyll enables the plant to absorb the energy of sunlight and use it for photosynthesis - the process in which the plant takes carbon dioxide from the air, and combines it with water drawn up by the roots to make sugar. Oxygen is also produced in the process and released into the air.


5. TRANSPIRATION As sunlight warms a plant; water in the leaves is lost as water vapour, through pores called stomata. The leaves then take in water from the stem, which in turn draws more water up into the plant from the roots. The water carries nutrients from the soil with it.

Picture Credit : Google