PLANTS

A living organism of the kind exemplified by trees, shrubs, herbs, grasses, ferns, and mosses, typically growing in a permanent site, absorbing water and inorganic substances through its roots, and synthesizing nutrients in its leaves by photosynthesis using the green pigment chlorophyll.

Parts of a plant

A typical plant has different parts in its body. Different parts of the plant are the roots, stem, leaves, flowers and fruits. The parts which are present underground are the roots. Parts which are present above the ground are stem, leaves, buds, flowers, fruits and seeds.

                                                                                                        

Root

The roots of a plant are mostly seen underground and look brown in color. The tiny thread-like structures over the roots are the root hairs. The tip of the root is covered by root cap which is preventive in function. Root and the root hairs form the root system.

Features of root

Root grows towards the soil and away from the light. Hence, it is called as geotropic structure.
Root does not possess green color pigment, the chlorophyll. It cannot produce food.
Root does not bear leaves, buds or flowers.
Roots along with their root hairs absorb water and minerals from the soil.

Functions of root

They hold the plant firmly in the soil, thereby serving as an anchor to the plant.
They absorb water and nutrients from the soil required for the growth of the plan
Some roots also store starch and sugars in them
Some roots also help in respiration. They possess special structures called as pneumatophores.
Some roots have useful bacteria in them to increase the soil fertility with nitrogen content.

Types of roots

Roots are of two types - tap root and fibrous roots.
Tap root is a primary root that grows more or less straight down into the soil, and is tapered towards the end. It is found in many of the plants. It is also called as true root. Smaller roots that branch out from the tap root are called as lateral roots. Examples of plants with tap roots are hibiscus, carrot, turnip and sunflower.
Fibrous roots are a group of lateral roots arising at the base of the stem. In the plants bearing fibrous roots, tap root slowly weakens and replaced by bunch of roots arising from the base of the stem. These bunch of roots form the fibrous roots. Examples of plants with fibrous roots are banana, grass and onion.

Modifications of roots

Roots in many plants are modified to perform additional functions by some modifications.
Storage roots are the roots modified to store food in them. e.g. Carrot, turnip, radish, sweet potato etc.
Respiratory roots are the roots modified for respiration. The plants in mangroves have roots with special structures called as pneumatothodes to obtain more oxygen.
Parasitic roots are the roots which arise from the stem and absorb nourishment from the host plant. e.g. Cuscuta.

Climbing roots are the roots which help the plant to climb and cling on to the support. e.g. Money plant, betel.
Reproductive roots are the roots which help in the process of producing the offspring.
Prop roots are the roots which offer support to huge structure of the tree. e.g. Banyan tree

Stem

The stem is the part of the plant seen above the ground. It bears the leaves, flowers and fruits of a plant. It is almost green or woody. It grows towards the sunlight. It moves away from the ground.

Features of stem

They support the entire plant to stand as a whole.
They are always phototropic. i.e. they grow towards light.
Stem has nodes separated by inter nodes. Stem bears branches, leaves, flowers and fruits.





Functions of stem

Stem helps in transportation of absorbed water and nutrients through vascular tissue from roots to leaves

Stem also transports food from the leaves to different storage organs.

Stem exposes leaves to light and help them in performing the process of photosynthesis.

The stem bearing leaves helps in the process of transpiration. Transpiration is the process by which plants release excess water in the form of water vapor through minute openings in the leaves called as stomata.

Sometimes stem can store food which is mostly underground.

Stem can store water by becoming fleshy as in desert plants.

Stem can perform photosynthesis when leaves are reduced or absent as in desert plants.

Modifications of stem

Stems in many plants are modified to perform additional functions by some modifications.

Storage of food: In some plants, underground stem is modified to store food in the form of starch. Three types of underground modifications of stem are tubers (e.g. Potato), rhizome (e.g.Ginger) and bulb (e.g.Onion).

Photosynthesis: In some desert plants, leaves are absent or reduced to spines. Here, the stem performs photosynthesis to synthesis food.

Protective structures: In some plants like rose, stems are modified into thorns to protect the plant from being eaten by animals.

Supportive structures: In climbing plants, stems are modified sometimes into structures which twine around the support.

Storage of water: In some plants like cactus and jade, stems become fleshy and succulent to store water.

Leaves

Leaves are the structures which develop on branches. These are green coloured structures rich in chloroplasts. As they have chlorophyll in them, they are considered to be food factories of the plant. Photosynthesis occurs in the leaves. Each leaf bears a bud in its axil.

                                                                                                  Parts of leaf

The point of attachment of the leaf to the node on the stem is called as leaf base.

Leaf bears a stalk with which it is attached to the stem. It is called as petiole.

The flat part of the leaf exposed to light is called as lamina.

A thin structure which extends from the leaf base to the tip on the lamina is called as mid-vein. Many small thread like structures extend from the mid rib to the leaf margin. These are called as vein lets. Arrangement of veins on the lamina of the leaf is called as venation. Veins help in transportation of food and water.

Two types of arrangement of veins on the leaf are parallel venation and reticulate venation.

Types of leaves

Leaves can be simple leaf or compound leaves.
Simple leaf is a single leaf with undivided lamina.
Compound leaf is a leaf which has divided lamina into a number of leaflets. The central structure called rachis bears all the leaflets.

Arrangement of leaves

Leaves are arranged in different patterns at the node on the stem. Arrangement can be alternate, opposite, whorl etc.
Alternate leaves are the ones which arise one at a node.

Opposite leaves are the leaves which arise as two at a node.
Whorl type of arrangement includes three or more leaves arise at a node.

Structure and surface of the leaf

Leaf has two surfaces namely, dorsal surface and ventral surface. Dorsal surface is the upper surface which is exposed to sunlight. It has number of chloroplasts having lot of chlorophyll in them. Upper surface of the leaf is dark green in colour.
Leaf has many pores called as stomata on both of its sides. These stomata help in exchange of gases like oxygen and carbon dioxide. Stomata also help in loss of excess water by the process of transpiration.

Functions of leaf

Leaves are the food factories of the plant which help in the process of photosynthesis to synthesise their food. They make use of raw materials like carbon dioxide and water in the presence of chlorophyll and sunlight.
Leaves lose excess water by the process of transpiration. Transpiration cools the body of the plant by regulating the temperature.

Modifications of leaf

In weak stemmed plants, leaves are modified into special structures which twine around a support. These are tendrils. These offer support to the plant while climbing up.
In some plants like onion, leaves are modified to store food. These are termed to be scaly leaves.
In some desert plants like cactus, leaves are reduced to spines so as to reduce loss of water through transpiration. These spines are also called as thorns. Thorns protect these plants from grazing animals.
In some insectivorous plants, leaves are modified into pitchers where they are used to trap insects. These insects can be digested inside the body of the plant. In this way, plants obtain nitrogen from animals.

Flower

Flower is a reproductive structure of the plant. The different parts of a flower include sepals, petals, stamens and pistil. Flower helps the plant to give rise to new plants by the process of sexual reproduction.

Parts of a flower

The green leaf-like structures surrounding the bud are called as sepals.
The colored parts of a flower are called as petals. These help in attracting insects.
The male reproductive part of a flower is called as stamen. It carries pollen grains.
The female reproductive part of a flower is called the pistil. It carries ovules.

Fruits

Fertilization is the union of male and female cells in a flower to produce a fruit. Fruit is basically the fertilized ovary. This grows in size to store sugars. Ovules develop into seeds. So, fruits enclose seeds.

Posted by: Rea Ritchel J.de Arao