Geting to Know Plants: science class six
Magic of Plants
There are millions of plants on the earth. It is plants which makes our earth green. Plants are very useful and beneficial to us. Plants give us food, wood, oxygen, and many other things. Plant help in maintaining our environment by absorbing carbon dioxide from the air and released oxygen into the air. If we start making the list of benefits of plants, the list will become endless. Life exists on earth because of plants. Life cannot be imagined without existence of plants. As so far known, it is only earth where plant exists and consequently life.
There are millions of varieties of plants found. And it is not possible to study them without classification. Thus first of all, it is essential to classify them on the basis of their most common characteristics.
Classification of Plants
There are four types of plants on the basis of height, shape, size and structure.
Herbs, Shrubs, Trees, Climbers and Creepers.
Herbs
Herbs are small plant. Herbs are about 1m in height. Herbs have soft, flexible and green stem. Vegetables, grasses, wheat, paddy, spinach, mint, coriander and mustard and many flowering plants, etc. are the example of herbs.
Shrubs
Shrubs are medium sized plants. Shrubs are about 1 to 3 m height. Shrubs are bigger than herbs. Shrubs have woody stems. Shrubs have bushy look. For example, Rose, china rose, bougainvillea and jasmine, lemon tree, mehndi, hibiscus, etc.
Trees
Trees are taller than shrubs. Trees have short woody stems, which are called trunk. Trees are about 2 to 4 meter in height. Trees give out branches after a good height from the ground. Branches carry leaves, flowers and fruits. Neem, mango, eucalyptus, baniyan, coconut, etc are example of trees.
Climbers and creepers
Some plants have weak stems. They cannot stand upright of their own. These are called creepers and climbers. The climbers grow upwards but need support to stand above the ground. They attach themselves to sticks, walls and other support to climb above. Money-plant, pea-plant, etc, are examples of climbers and creepers. Creepers creep on the ground. Plants of pumpkin, cucumber, bottle gourd, etc. are the example of creepers.
Parts of plants
The body of a plant consists of many parts. Each parts of a plant have a specific function.
A group of two or more parts of plants is called a system.
The Root System
The underground part of the plant is called Root System. The root system anchors the plant to the soil and absorbs water and minerals.
The shoot system
The part which is above the ground of a plant is called Shoot System. Shoot system bears branches, leaves, flowers, fruits and seeds.
Root
There are two types of roots. Tap Root and Fibrous Root.
Tap Root
Tap root is the main root. Tap root generally grow vertically downwards. A tap root can have many lateral branches from the main root.
The main thick root of Tap root is called Primary Root. This primary root gives rise to many thin roots. These thin roots which are grown from primary root are called secondary roots. Root of neem, mango, pea, carrot, gram, mustered, turnip, radish etc. are the example of Tap root.
Fibrous root
The Fibrous Root generally grows in cluster of slender root from the base of the stem. In Fibrous root, there are no separated primary and secondary roots grow. Roots of Grass, money plant, maize, wheat, paddy, etc. are some example of Fibrous Root.
Functions of Root.
Roots have the following functions
(a) Root gives anchor to the plant. Roots go down into the soil, spread and hold the plant firmly to the ground. Root helps the plant to keep standing even in strong wind.
Root absorbs water and minerals from the soil. Root hair help in absorbing water and minerals from the soil. These absorbed water and mineral are then sent to the other part of the plant. Water and minerals are needed by the plants for growth and for photosynthesis.
Modified Roots
In many plants the structure of roots is changed in special way to perform additional functions. Such roots are called Modified Roots. For example radish, carrot, turnip, beet root, banyan, etc. have modified roots.
Modified Root to Store Food
Plants of radish, carrot, turnip, and beet root, etc. have swollen roots. Roots of these plants modified to store food produced by plants. To store food roots of these plants get swollen. Such plants use food energy stored in modified roots when needed. We eat roots of such plants as food.
Modified Root to give extra support
Roots of some plants get modified to provide additional support to the plant. In banyan tree, rope like roots grows from the main branches. These roots on reaching to the ground penetrate into the soil and provide extra support to the heavy branches. Such modified roots are called Prop roots.
Stem
The stem of a plant is a link between the roots and the leaves and flowers. The stem is the main support of a plant. The stem of a plant supports branches which bear buds, leaves, flowers, and fruits. The shape and size of stems differ from plants to plants.
The stem of a tree is called the trunk. The trunk in most of the tree is covered with an outer covering called bark. The bark protects the inner part of the trunk. Bark is similar to our skin. As our skin protects us, similarly bark protect stem of trees.
Node and Internode
The stem is divided into node and internode.
Node: The point from where a leaf grows is called the node.
Internode: The portion of the stem between two nodes is called internode.
Functions of the stem
(a) Stem carries water and minerals from the roots to different parts of the plants.
(b) Stem carries the food made by the leaves to the other part of the plant.
(c) Stem supports branches, leaves, flowers and fruits.
Modified stem
In some plants the structure of stem is changed in natural way to perform extra work. Such stems are called Modified Stems.
Stem modified to store food
In certain plants; the stem grows underground and store the food. Plants of ginger, potato, and onion, etc. have modified stem to store food. We eat the stem of ginger, potato and onion, etc.
Stem modified to make food
Stem of some plants get modified to make food. For example stems of plants like prickly pear, cactus, etc. The broader leaves like structures in the plants of prickly pear are actually modified stems.
Modified stem to give extra support
In some plants, the stem is modified in the form of tendrils. The tendrils are soft flexible, spring- like structures that arises from plants. Tendrils provide extra support to climbers which have weak stem. Cucumber, watermelon, and grapes vine have stem tendrils.
Some stems produce thorns for protection from the animals that feed on plant leaves. The stem thorns are commonly found in rose and orange.
Potato, onion and ginger are some modified stem that store food in them.
Leaves
The leaf is green coloured, thin, broad and flat part of a plant. The leaves of different plants differ in shape and size. The leaves of the most plant are green and few plants have other coloured leaves. The green colour of the leaves is due to the presence of a green pigment called chlorophyll. The leaves arise from the node of the stem.
Leaf blade or Lamina: The flat green portion of a leaf is called leaf blade or lamina.
Petiole: The leaf blade or lamina is attached to the stem by a short stalk called petiole.
Midrib: Petiole continues in the leaf as the midrib.
Veins: The midrib forms a network of veins.
Leaf Venatation: The design made by the veins in a leaf is called leaf venation.
Parallel Venatation: If the veins are parallel to each other, the venation is called parallel venation.
Reticulate: If this design is net-like on both the sides of midrib, the venation is called reticulate
The leaves and branches are joined to the stem at nodes.
Types of Leaves
There are two types of leaves
Simple leaves
A leaf with a single lamina is called simple leaf such as the leaf of peepal, mango, dahlia, sunflower, wheat, etc.
Compound leaf
A leaf with many small leaflets is called a compound leaf such as the leaf of rose, neem, touch me not, acacia, etc.
Functions of leaves
Leaves are important organs which perform various functions in plants.
The leaf is called the food factory of a plant. Green leaf makes food using carbon dioxide and water in the presence of sunlight. Chlorophyll present in green leaves absorbs sunlight and changes carbon dioxide and water into glucose and oxygen.
Carbon dioxide + water (in the presence of Chlorophyll and Sunlight)⇒ Food + Oxygen
Stomata: Leaves possess many minute holes called stomata on their lower surface. Plant can open and close these stomata to exchange gases.
Transpiration
Evaporation of water through the leaves is called Transpiration
Leaves help in transpiration. The excess of water absorbed by the root hairs is lost through the stomata. Transpiration helps in cooling the leaves.
Modified Leaves
In certain plants, the structure of leaves is changed in the natural way to perform extra work. Such leaves are called modified leaves. Spines in cactus and tendrils in climbers and creepers are modified leaves.
Leaves modified into spines in the plant of cactus, picley pear, etc. reduce loss of water. Because such plants are found in deserts. These spines protect plants from animals also.
Tendrils found in creepers and climbers are modified leaves. Tendrils help climbers to climb and creepers to creep.
Flowers and Fruits
Flowers are the most beautiful part of a plant. A flower is the reproductive organ of a plant. Flowers are of different sizes, shapes, colours and fragrance. Flowers of some plants change into fruits.
Structure of a flower
The basic part of a flower are,
Sepals or Calyx
The outermost green leafy structure in a flower is called SEPAL. Sepals protect the flower at bud stage. Sepals are the most important part in an open flower. Sepal is known as Calyx also.
Corolla or Petal
Corolla or Petal lies inside the calyx. Corolla or Petal consists of petals that are sweet scented and colourful. Corolla or Petal are meant to make the flower beautiful so as to attract insects for pollination. Pollination is the transfer of pollengrains from Anther to Stigma.
Stamen or Androcium
Stamen is the male reproductive part of a flower. Stamen consists of a thin green stalk called filament with a bag like top, called ANTHER. The anther carries several pollen grains. Pollen grains are dust like particles and take part in reproduction. Stamen is called Androcium also.
Carpel or Pistil
Carpel is the female reproductive part of a plant. A flask shaped structure in the centre of the flower is called pistil. Pistisl consists of stigma, style, ovule and ovary. The lower broader portion of the pistil is called ovary. The narrow upper portion of pistil is called the style. The sticky end at the top of the style is called stigma. Stigma receives pollen grains.
Functions of a Flower
The main function of a flower is reproduction. Pollen grains are transferred from the anther to the stigma by the process called pollination. After pollination, a male cell fuses with female cell in an ovule, called as fertilization. The fertilized ovules grow into seeds. Under favorable conditions, seeds germinate and give rise to seedlings, which develop into new plants.
Flowers are used for decoration in special occasions. Some flowers are used to make perfumes or scents. For example, rose, jasmine,, lavender, keora, etc.
Fruit
The fertilized ovary grows into a fruit. Thus fruit can be defined as a mature or ripened ovary. A fruit consists of two parts, the Pericarp and the Seed. The fruit stores food. Fruits protect seeds against injury and store them for longer period.
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