ICSE Class 6 Biology Chapter 2 Classification of Plants

Classification of Plants

Syllabus

Plants may be classified into groups:

Herbs, shrubs and trees.

Annuals, biennials and perennials.

Flowering and non-flowering plants.

Common examples of these categories.

Practical observation (in garden/park) of different groups of plants (E). (This is an opportunity to train students not to break twigs/branches, or pluck more than one specimen of each kind).

Drawing leaves. (Drawing from specimens is an essential skill in which students need practice)

Identification/labelling of trees/plants in the school garden (E).

Introduction

You have learnt that the subject Biology is concerned with living things - plants and animals. In this and the next lesson, you will study about the systematic classification of plants and animals.

Classification and Its Need

There are numerous varieties of living organisms on this earth. It is not possible to remember all of them and their characteristics individually. To make their study systematic, they are classified into various groups based on certain similar characteristics. Thus, all living things are classified into plants and animals. Both plants and animals are further divided into various groups and classes. On the basis of this grouping, the living organisms can be studied easily and systematically. Thus, classification means grouping things together on the basis of certain common features. It is actually the method of putting similar things into one group.

Classification helps us to identify the living organisms and to study them more easily and systematically.

Classification of Plants

Plants show a great variety.

Some plants are very large, some are small and some are tiny.

Many plants produce flowers and others do not.

Some plants produce fruits containing seeds, while others may neither produce fruits nor seeds.

Some plants show distinct parts such as stem, leaves and roots whereas in others, there is no such differentiation of parts at all.

Considering the above characteristics, plants can be categorised by their size and their nature of producing flowers, fruits, etc., into different groups that have been discussed below.

On the Basis of Size and Shape

On the basis of their size and shape, plants are divided into the following three categories:

(i) Herbs, (ii) Shrubs, and (iii) Trees

Herbs

Plants which have soft, green and perishable stems are called herbs. They are generally small in size, not more than one metre in height and may live for 1-2 seasons. Examples: grass, maize, rice, mint, coriander, etc.

Shrubs

Plants with woody stems, with branches of almost equal size arising from the stem immediately above the soil are called shrubs. They look like bushes and are medium-sized plants. They survive for many years, though less than trees. Examples: China rose, lemon, pomegranate, jasmine, nerium, etc.

Trees

Trees are tall and big plants and have one hard, woody stem called trunk. It bears woody branches, twigs and leaves at some distance above the ground. Coconut and palm are also trees, though they do not have branches. Trees generally survive for many years. Examples: Mango, neem, palm, banyan, etc.

Note: This is the simple classification of plants as you see in your surroundings. These plants are further classified into many types on the basis of several other characteristics as discussed ahead.

Teacher's Note

When you visit a park or garden, you can observe the different sizes of plants around you - from tiny herbs in the ground cover to massive trees overhead - and understand why plants are grouped this way.

Activity 1

Visit a garden park with your teacher or parents and take along with you, a notebook and a pencil. In the park, you would see a large variety of plants - some very small, some with average height and some very tall. These plants differ in their features like shape, size (small/medium/tall) and life span. Observe these features carefully (you may even take help from the gardener) and note down in the table given below. Classify these plants in their respective appearance and categories:

Plants are classified mainly into two categories

1. Non-flowering plants, and

2. Flowering plants

A. Non-Flowering Plants

The non-flowering plants neither bear flowers nor seeds. They are further classified under three groups:

1. Bacteria, Fungi and Algae (Thallophyta)

2. Mosses (Bryophyta)

3. Ferns (Pteridophyta)

Let us study each of these groups one by one.

Bacteria, Fungi and Algae (Thallophyta)

The term Thallophyta is used to describe undivided bodies called thalli. They are sometimes also called 'thalloid plants'.

These are mostly microscopic. They do not bear roots, stems or leaves. They are further divided into three groups:

(a) Bacteria (b) Fungi (c) Algae

Bacteria (sing. "bacterium")

Bacteria are microscopic single-celled organisms. They occur everywhere - in air, soil and water, and sometimes, even in the food we eat. Besides these common habitats, bacteria are also found inside our bodies particularly the intestines. Bacteria have mainly three shapes - Spherical (cocci), rod like (bacilli), spiral-shaped (spirilla).

Some bacteria live naturally in our intestine causing no harm. But sometimes, harmful bacteria enter our body and cause diseases.

Fungi (sing. Fungus)

They may be single-celled or multi-celled. Fungi do not have chlorophyll and thus cannot have chlorophyll and thus cannot prepare their own food. Most fungi live on dead and decaying organic matter. That is why, they are also called saprophytes (sapro: rotten). The blackish cottony growth on a stale bread is a type of fungus called bread mould. Another common fungus is the white umbrella-like mushroom, that generally grows on decaying wood or on garbage.

Activity 2

Take a few slices of bread and moisten them by sprinkling some water. Keep them for 2-3 days in open and observe. You will see bluish fur-like outgrowth on these bread pieces. This is a fungus called Rhizopus, commonly known as bread mould.

Algae (sing. Alga)

Algae are found in stagnant water of ponds, growing as green scum. These may be single-celled or multi-celled. They are usually green, having chlorophyll. Spirogyra is a filamentous alga most commonly found in ponds. Some algae have different colours such as brown or bluish-green.

Mosses (Bryophyta)

Mosses grow as green, velvety layers but only at moist places such as on damp soil, on the bark of trees, and on damp walls. Such plants have stems and leaves, but no roots. Instead, they have thread-like structures called rhizoids by which they stick to the surface and absorb water. They are also called 'amphibians of the plant group' as they need water to reproduce.

Ferns (Pteridophyta)

Ferns are grown in most of the gardens for their beautiful leaves. They bear well-formed leaves, stems and roots but do not produce flowers and seeds. Their leaves produce small rounded bodies on their undersurface. These bodies contain tiny spores which get scattered to produce new plants. Spores are not seeds. Remember, seeds are produced in flowers, through the union of male and female gametes.

Spores are tiny structures capable of producing new plants.

B. Flowering Plants (Phanerogams)

The word phanerogams (literally means "visible marriage", referring to "pollination") is a biological term for the flowering plants.

The flowering plants bear flowers and seeds. They are further grouped into two categories:

(i) Gymnosperms, (ii) Angiosperms

Teacher's Note

When you observe a flowering plant in your garden and see how bees visit its flowers, you are watching the first step in seed production - pollination - which nature designed to create the next generation of plants.

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