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CBSE Class 6 Science: Structure and Functions of Parts of Plants

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There are various types of plants classified into different categories based on certain charateristcis

Types of Plants

Plants are broadly classified into:
  1. Flowering Plants
  2. Non-flowering Plants
Flowering plants are classified into 3 types:

Types of Flowering Plants

  1. Trees
  2. Shrubs
  3. Herbs

Parts of Plants (Parts of Flowering Plants)

Flowering plants consist of two main parts (systems). These are:
  1. Root system
  2. Shoot system

1. Parts of Root System and Their Functions

Root system / roots are:
  • the parts of plants that grows under the ground (soil).
  • They consist of roots and root hairs.

2. Shoot System

Shoots system / shoots are:
  • the parts of the plants that grows above the ground (soil).
  • they consist of stem, branches, leaves, flowers and fruits.
Parts of a Plant

Types of Root System

There are 2 types of root systems:
  1. Tap Root
  2. Fibrous Root

1. Tap Root: Definition and Function

Tap Root
  • Tap root consists of one thick main root called the primary root.
  • The primary root grows vertically downward into the soil.
  • Many branches called the secondary root grow from the primary root.
  • E.g. tulasi, neem etc.

2. Fibrous Root: Definition and Functions

Fibrous Root
  • Fibrous roots consist of a number of fibre-like roots.
  • These fibre-like roots grow in cluster from the bottom of the stem and spread out into the soil.
  • All the plants of grass family like paddy (rice) and wheat have fibrous roots.

Main Functions of a Root

  • Roots fix the plant to the soil and enables it to stand erect above the soil.
  • It absorbs water and minerals from the soil and conduct it to the stem.
  • It binds the soil particles and prevent the soil from erosion i.e. from being blown away or washed away by wind / water.

In some plants, roots modify to perform additional functions. Such roots are called modified roots.

Root Modifications

In some plants roots are modified for performing additional functions like:

  • Storage of food
  • Give mechanical support to plant
  • Give additional support for respiration.

1. Root Modification for Food Storage

  • In some plants roots store the food prepared by the plant.
  • These roots are swollen as they store food.
  • Such swollen roots are called tuberous roots.
  • E.g. radish, beet root, carrot, turnip, sweet potato

2. Root Modification for Additional Support

There are two types of supporting roots. These are:
  1. Prop Roots
  2. Stilt Roots

1. Prop Roots: Their Functions

  • Big trees like the banyan have heavy branches that bend down.
  • Roots from these branches grow downwards and fix in the soil.
  • And they give additional support to the plant.
  • Such supporting roots are called Prop Roots.
  • They give additional (mechanical) support to the plant.

2. Stilt Roots: Their Functions

  • The thin stem of the plants like sugarcane and bamboo cannot stand erect.
  • Such plants grow roots from the stem nodes and fix in the soil.
  • Thus they give additional (mechanical) support to the stem to stand erect.
  • Such supporting roots are called stilt roots.

3. Root Modification for Respiration

  • Mangrove plants grow in marshy areas where the soil is sticky and is covered with water.
  • The roots of these plants do not get air as they remain in water.
  • So, the roots grow vertically upward above the soil / water for breathing (respiration).
  • Such roots are called breathing roots.

2. Parts of Shoot system and Their Functions

Following are the parts of shoot system of plants:
  1. Stem
  2. Branches
  3. Leaves
  4. Flowers
  5. Fruits

1. Stem: Definition and Functions

Stem: The part of the plant that forms the main axis of the plant body and contains the following parts:
  1. Node: The point on the stem from where a leaf and / or a branch grows.
  2. Internode: The place in between two nodes.
  3. Apical or Terminal Bud:
    • Present at the tip of the stem or a branch.
    • It helps the plant to grow taller.
  4. Axillary Bud:
    • Present in the axiles of leaves.
    • They grow into branches
  5. Trunk:
    • The hard woody part of the stem as it grows.
    • The trunk is protected by a outer covering called bark.

Functions of a Stem

The functions of a stem are:
  • It bears leaves, flowers and fruits.
  • Stem and branches hold the leaves in such a way that the leaves get maximum sunlight for photosynthesis.
  • In baby plants / saplings, the green stem makes food for the baby plant.
  • It carries (conducts) water and minerals from the roots to different parts of the plant.
  • It carries (conducts) the prepared food from the leaves to the different parts of the plant.
In some plants, the stem modifies to perform additional functions like storage of food, preparing food and giving additional support to the plant.

Types of Stem Modification

Following are the various types of stem modification:
  1. Underground modification
  2. Stem tendrils
  3. Modification for protection
  4. Modification for photosynthesis

1. Underground Modified Stem and Its Functions

In some plants the stem grows under the ground and modifies to perform additional functios.
  • In plants like ginger, potato and turmeric, the stem grows under the ground.
  • It modifies to store food.
  • The underground modified stem helps the plant to survive in harsh (unfavourable) conditions.

Types of Underground Modified Stems

There are 3 types of underground modified stems. These are:

  1. Tubers

    • A tuber is an underground modified stem which is swollen as it stores food in the form of starch.
    • It is small, thick and fleshy and has buds called 'eyes'.
    • New plants grow from the eyes.
    • It has prominently visible nodes and internodes.
    • Ex: potatoes

  2. Bulbs

    • A bulb-like short and thick underground stem.
    • The bulb bears fibrous roots at the base and leaves above the base.
    • The outer leaves are dry and scaly while the inner leaves are fleshy and store food.
    • Ex: onion, garlic.

  3. Rhizomes

    • An underground modified stem that grows horizontally is called a rhizome.
    • It is modified to store food
    • Ex: ginger and turmeric.

2.Stem Tendrils

  • Tendril: These are the axillary buds grow into thin and coiled thread-like structures
  • Tendrils coil around the nearby objects and help the plants to climb.
  • They give support to the weak stem.
  • Ex: climbers like grapevine.

3. Stem Modification for Protection

In plants like rose and lemon, the axillary bud is modified into sharp, hard and pointed structures called thorns which protect the plants from grazing animals.

4. Stem Modification for Photosynthesis

  • In plants like cactus, the stem is green and fleshy.
  • It contains chlorophyll and prepares food for the plant as the leaves in these plants are modified into spines.
  • The stem also stores water for a long period due to scarcity of water in desert xerophytes.
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