Unit 3: The Structure and Functions of Plants

Learning Objectives

Description of flowering parts

Two main systems of a flowering plant in root system and shoot system

Different modified roots, stems and leaves

Parts of a flower and their functions

Pollination and the description of cross-pollination and self-pollination

Various agencies of pollination

Structure of a seed and its dispersal

Structure of a simple fruit

A Flowering Plant

If you look around, you will find various kinds of plants. Some are big, others are small. They may differ in size but they have some structural similarities. All flowering plants have root system and shoot system. The root, stem and leaves are vegetative parts whereas flower is a reproductive part.

Take out a balsam or a mustard plant from the soil and study it. A flowering plant can be divided into two parts:

(i) An underground part called the root system and

(ii) The part above the ground called shoot system.

The root system consists of branches of roots, root hairs, etc. while the shoot system consists of branches, leaves, flowers, fruits, etc.

Teacher's Note

When we observe plants in our garden or schoolyard, we can easily identify the root system underground and the shoot system above ground, helping students connect abstract concepts to their immediate natural surroundings.

The Root System

The root fixes the plant with soil. In certain plants like balsam, mustard, pea, neem, etc. the root system consists of a main root called tap root. The tap root grows down the soil and gives out lateral branches.

In grasses and a few other plants like wheat, maize, rice, sugarcane, etc. the roots arise as a cluster from the base of the stem; there is no main root. This type of root is called fibrous root.

Functions of the Root

Primary Functions

1. Fixation: The root fixes the plant firmly in the soil.

2. Absorption: The root hairs help in the absorption of water and minerals from the soil.

Secondary Functions

1. Storage: In plants like carrot, turnip, radish and sweet potato, the roots are modified for the storage of food.

2. Mechanical support: In plants like banyan and maize, the roots support heavy horizontal branches like a pillar.

Teacher's Note

Students can observe the difference between tap and fibrous roots by examining actual root systems or comparing vegetables like carrots (tap root) with grass or wheat (fibrous root) from their kitchen or garden.

Modifications of the Root

For Storage of Food

Plants likes radish, carrot, turnip and sweet potato store food in their roots. These roots swell-up and become thick due to accumulation of food. This food is utilized whenever required. Such roots are called tuberous roots.

For Additional Support

In banyan tree and screw pine the roots grow downward from the branches of the tree. These roots penetrate the ground and tree become pillar like for additional support. These roots are called prop roots.

For Respiration

In plants growing in marshy habitat, the root system produces vertically upward branches. These roots come out of the soil and help in breathing. These special roots are called as pneumatophores or breathing roots.

For Absorption of Nutrients and Water

A plant like a money plant develops long, fibrous roots called feeder roots. These roots reach the soil and absorb more nutrients and water from the soil.

Teacher's Note

Visiting a local botanical garden or examining vegetables at the market (carrots, radishes, sweet potatoes) helps students recognize how roots have adapted to different functions beyond simple water absorption.

The Shoot System

The Stem

The portion of the plant above the ground, called shoot system consists of stem, leaves, flowers, etc. Small plants have soft and green stem. Some plants have weak stem. They cannot stand erect. They creep on the ground. Still few stems climb with some support. They swing around a support (pole or wire, etc). Trees have woody and hard stem. It is called trunk. The portion of stem from where leaves arise is called node. The portion of stem between two nodes is called internode.

The stem bears various types of buds. The tip of the stem bears a bud which is called terminal bud or apical bud. It consists of young tender leaves and leads to increase in length. Buds are also present in the axil of leaves. These buds are called as axillary bud. These buds grow into lateral branches. The stem also bears flowering buds. On maturity flowering buds give rise to flowers.

Functions of the Stem

1. The stem conducts water to various parts of the plant.

2. The food prepared by leaves reaches various parts of the plant through stem.

3. The stem bears leaves, flowers, fruits, etc.

4. A few stems are modified to manufacture food and store food.

Teacher's Note

Observing the nodes and internodes on bamboo stems or examining the growth rings on a tree stump makes the abstract concepts of stem structure concrete and memorable for students.

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