ICSE Class 6 Biology Chapter 3 Classification of Plants

Classification of Plants

Learning Objectives

After completing this chapter you will be able to

classify plants as non-flowering and flowering.

differentiate between gymnosperms and angiosperms.

classify plants as annuals, biennials and perennials on the basis of time taken to complete their life cycle.

classify plants as herbs, shrubs and trees on the basis of their size.

classify plants into mesophytes, hydrophytes and xerophytes on the basis of their habitats.

give characteristic features of major categories of plants.

Introduction

The plant kingdom can be classified into two broad categories, that is, non-flowering plants or cryptogams and flowering plants or phanerogams. Flowering plants bear flowers and seeds. However, non-flowering plants do not produce flowers and seeds.

Cryptogams

Non-flowering plants or cryptogams are divided into three groups - Thallophyta, Bryophyta and Pteridophyta.

Thallophyta (Algae, Bacteria, Fungi)

Thallophyta do not bear roots, stems or leaves. They rather have an undifferentiated body. They are further divided into three categories - algae, bacteria and fungi.

Algae

Algae may be unicellular or multicellular. Algae mostly grow in stagnant water, may be in puddles, streams or pond. The green layer seen on the surface of water in a pond is algae (Singular: alga). As all algae contain the green pigment chlorophyll, they make food on their own. In addition to chlorophyll, algae may also possess pigments of other colours like green, brown and red. Both red and brown algae are found in sea water. Brown algae called kelp are among the largest known plants and may grow up to a length of 60 metres. Some examples of algae are Spirogyra, Chlamydomonas and Volvox.

Teacher's Note

You can observe algae in your local pond or aquarium, and discuss how these simple organisms are essential for aquatic ecosystems and oxygen production.

Bacteria

Bacteria are unicellular microscopic organisms. They are mainly found in three different shapes, that is, cocci (spherical), bacilli (rod-like) and spirilla (spiral-shaped). They are present almost everywhere, even inside our bodies. Some bacteria cause many harmful diseases.

Fungi

Have you ever seen a cotton-like growth on bread, chapatti or cheese? This cotton-like growth is fungus (plural: fungi). They lack chlorophyll and cannot prepare food on their own, and therefore, feed on organic matter. Fungi include moulds, yeast, mushrooms and toadstools. They may be parasitic, that is, derive their food from other living organisms, or saprophytic, that is, derive food from dead or decaying organisms. Fungi reproduce by spore formation, budding and fragmentation. Fungi may be single-celled or many-celled. They can sometimes be seen in your shoes, be seen in your food and skin also. They grow best where warmth and moisture are available.

Teacher's Note

Show students examples of mold on old bread or fruit to illustrate how fungi decompose organic matter in everyday life.

Bryophyta (Mosses)

These plants grow at moist places and need water to reproduce. Since they grow on land but need water for reproduction they are called the 'amphibians of the plant kingdom'. Bryophytes mostly include mosses and liverworts. These plants do not have true roots. Instead of roots, they have thread-like structures called rhizoids. Rhizoids help plant to anchor with the soil and absorb water and minerals. Commonly mosses can be seen on damp soil and on the bark of trees.

Pteridophyta (Ferns)

These plants grow in damp and shady areas. Ferns have well-developed leaves, stems and roots but no flowers and seeds are produced. The plants either have underground stems called rhizome or stems above the ground. The leaves are called fronds and are divided into leaflets. The lower side of the leaves bear small rounded brown structures called sori which contain spores for reproduction.

Teacher's Note

Take students to see ferns growing in shaded, damp areas like near water fountains or under dense trees to understand their natural habitat.

Phanerogams

Flowering plants are further divided into two categories - gymnosperms and angiosperms.

Gymnosperms

They are either tall trees or bushes. Instead of flowers, gymnosperms produce cones. Cones are woody reproductive structures that produce thin and naked seeds, that is, the seeds are not enclosed in fruits. Due to presence of naked seeds, these plants are called gymnosperms (gymno-naked, sperm-seed). Some cones are male and produce pollen, while some are female.

Gymnosperms have well-developed roots, thick and woody stems and long and needle-shaped (pointed) leaves. Pointed leaves do not allow snow to stick to them, thus, the plants are not affected. Water is also conserved as there is less transpiration. Most gymnosperms do not shed all their leaves at one time and remain green throughout the year. So, they are called evergreen plants. Cedar, pine, Ginkgo, juniper, spruce and Cycas are some examples of gymnosperms.

Teacher's Note

Visit a local botanical garden or park where gymnosperms like pine or cedar trees grow, and examine their needle-like leaves and cones up close.

Angiosperms

Most plants on the earth are angiosperms or flowering plants. They bear true flowers. Angiosperms are also called closed-seeded plants because their seeds are enclosed in fruits. All crop plants, sunflower, Petunia, sugar cane and pea are some examples of angiosperms.

Angiosperms are further divided into two groups depending on the kind of seeds they have.

Dicotyledons

These plants bear seeds which are divided into two parts or cotyledons. For example, gram, pea, bean and so on.

Monocotyledons

These plants bear seeds which have only one part or cotyledon. For example, wheat, maize, rice and so on.

This is a preview of the first 3 pages. To get the complete book, click below.