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Plants trap sunlight and make food, feeding almost every food chain and releasing the oxygen we breathe. Their kingdom spans simple algae to complex flowering trees.
- Plants are multicellular autotrophs that perform photosynthesis; their cells have rigid cellulose cell walls.
- They form the base of most food chains and release oxygen essential for life.
- Kingdom Plantae is divided into five classes — Thallophyta, Bryophyta, Pteridophyta, Gymnosperm and Angiosperm.
- Thallophyta (algae like Spirogyra ) — simplest plants, a thallus body, mostly aquatic.
- Bryophyta (mosses, Marchantia ) — ‘amphibians’ of the plant kingdom with rhizoids, needing water; Pteridophyta (ferns) — true roots, stems, leaves and vascular tissue, but no seeds.
- Gymnosperms (pines, cycads) — naked seeds on cones, no water needed for fertilisation; Angiosperms (flowering plants) — flowers and seeds enclosed in fruits.
Have you seen white-green patches on tree trunks or damp walls? These are lichens — symbiotic associations of an autotrophic alga and a heterotrophic fungus. They change colour with air pollutants, so they are natural bioindicators of air quality. Some, called patthar ke phool , are used as a spice, medicine or dye; some are poisonous, so correct identification matters.
- Thallophyta (algae) have an undifferentiated thallus body that directly exchanges gases, nutrients and water; they are well-adapted to water (e.g. Spirogyra , Fig. 12.9).
- Bryophytes (mosses, liverworts) have a more differentiated body with root-like rhizoids and simple stem- and leaf-like structures (e.g. Marchantia , moss).
- Bryophytes need water for reproduction, so they are called the ‘amphibians’ of the plant kingdom.
In this Activity, we will explore bryophytes under a dissecting microscope to see how they differ from ordinary leaves.
- Collect some bryophytes with a hand lens and place them in a watch glass.
- Put a drop of water on them and observe under a dissecting microscope.
- Note how their simple leaf-like structures differ from the leaves of the plants around you.
- Recall that bryophytes still depend on moisture and grow best in shady, damp places.
- Pteridophyta (ferns) have true roots, stems and leaves and vascular tissue (xylem and phloem, Fig. 12.11), but need water for reproduction and produce no seeds .
- Gymnosperms (pines, cycads) have needle-like leaves, produce seeds not enclosed in fruits (exposed on cones), and do not need water for fertilisation.
- Angiosperms (flowering plants) have the most complex bodies, producing flowers and fruits — the most diverse plant group on the Earth.
NCERT Question 11 — Both pteridophytes and bryophytes lack
In this Activity, we will compare the vascular tissue of a fern stem with that of a higher plant.
- Recall the cross section of the sunflower stem studied earlier (Chapter 3, Fig. 3.7).
- Compare it with the cross section of a fern stem, a pteridophyte (Fig. 12.11).
- Note the differences in the arrangement of vascular tissue in the two stems.
- Write and discuss your observations in class.
In this Activity, we will discuss how leaf shape and venation help us group flowering plants.
- Collect different leaves from your surroundings.
- Observe the shape and the venation (pattern of veins) of each leaf.
- Group the leaves as monocots or dicots based on these features.
- Discuss how these structures help the plants adapt and survive.
- 3. Features like rhizoids and simple structures reduce dependence on water but still need moist conditions — as in bryophytes and pteridophytes.
- 4. Taller plants need vascular (transport) tissues to carry water and food to all their parts.
- 5. Seeds and fruits protect the embryo and help spread it, letting plants survive in a wider range of places.
One of the earliest scientific books on Indian plants, Hortus Malabaricus , was compiled in the 17th century by Hendrik van Rheede with the help of Itty Achudan (an Indian herbalist, botanist and physician) and other local experts. It describes hundreds of plant species and their medicinal uses, showing how traditional knowledge and science can work together.
In this Activity, we will study the salient features of each plant group and note their survival advantages and challenges.
- Carefully study the salient features of each plant group.
- Note the advantages of each group for survival.
- Note the exceptions or challenges each group faces.
- Record your analysis in Table 12.3.
| Plant groups and salient features | Advantages of the group for survival | Exceptions/Challenges |
|---|---|---|
| Thallophyta — thallus body eases absorption of water, nutrients and gases. | Simple body aids survival and dispersal in water. | They cannot live on land. |
| Bryophyta — began to colonise land; slight body differentiation; no vascular tissue; need water for reproduction. | Plant amphibians; body adapted to live on moist land. | They always need moisture. |
| Pteridophyta — true roots, stems, leaves; vascular tissue (xylem, phloem); no seeds. | Live on land; transport food and water to all parts. | Reproduction does not take place without water. |
| Gymnosperm — needle-like leaves; water not needed for fertilisation; seeds on cones. | Leaves adapted for dry conditions; form seeds for continuity. | Seeds are not covered in the form of fruits. |
| Angiosperm — well-developed roots, stems, leaves; flowers; seeds enclosed in fruits. | Produce flowers, fruits and seeds; well-developed reproduction; covered seeds. | Reproduction depends on pollination by agents; complex processes need a well-developed tissue system. |
From algae to angiosperms, plant groups show a sequence of structural changes that help plants meet the challenges of life on land — early plants relied on water, then gradually evolved transport tissues, seeds and flowers.
