Plant Kingdom | Chapter 3 Notes 2024

Last updated on July 14th, 2024 at 05:48 pm

Plant Kingdom chapter 3 cbse, class 11 Biology notes. This cbse Biology class 11 notes has a brief explanation of every topic that NCERT Biology syllabus has.

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Plant Kingdom

Plant kingdom includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms. Algae are classified into three classes, namely Chlorophyceae, Phaeophyceae and Rhodophyceae. 

Algae

Algae are a diverse group of aquatic organisms capable of producing oxygen through photosynthesis (the process of harvesting light energy from the sun to generate carbohydrates).

These are simple, chlorophyll-bearing, thalloid, autotrophic and largely aquatic (both freshwater and marine) organisms. 

Algae exist in oceans, rivers, and lakes to ponds, brackish waters and even snow. They are usually green, but they can be found in a variety of different colours.

Certain algae are familiar to us, such as seaweeds (such as kelp or phytoplankton), pond scum or the algal blooms in lakes. Algae are not only helpful to us, but are critical to our existence. 

Some examples of algae are Volvox, Spirogyra, Ulothrix, Fucus

Characteristic of Algae

• They are photosynthetic organisms
• It can be either uni or multicellular organisms
• Algae don’t have a well-defined body, so, structures like roots, stems or leaves are absent
• Algaes are found in moist areas
• Reproduction occurs in both asexual and sexual forms. Asexual reproduction occurs by spore formation.
• Algae are free-living, some can form a relationship with other organisms.
• Algae don’t have Vascular tissues and mechanical tissues 
• Life cycle is various- haplontic, diplontic or diplohaplontic.

The algae are divided into three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae.

Chlorophyceae (Green Algae) 

It is an informal grouping of algae having the primary photosynthetic pigments chlorophyll a and b, along with auxiliary pigments such as xanthophylls and beta carotene.

They are unicellular, colonial or filamentous. Most of the members of algae have one or more storage bodies called pyrenoids(contain protein-based starch) found in the chloroplasts. 

Other organisms use green algae to conduct photosynthesis for them. Members of these algae are unicellular, multicellular, colonial and flagellates. Examples of green algae include Spirogyra, Ulothrix, Volvox, etc. 

Phaeophyceae (Brown Algae)

Brown Algae are found in marine habitats. They range from simple branched, filamentous forms to profusely branched forms.

Brown algae possesses chlorophyll a, c, xanthophylls, carotenoids. Food is stored as complex carbohydrates, which may be in the form of laminarin or mannitol. 

Sexual reproduction may be isogamous, anisogamous or oogamous. Examples – Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus

Rhodophyceae (Red Algae)

Red Algae is also called Rhodophyta, it is found in marine as well as freshwater ecosystems. They are red due to the predominance of the red pigment, r-phycoerythrin in their body. 

Most of these algae are marine with greater concentrations found in the warmer areas. 

Red Algae are found in both well-lighted regions close to the surface of water and also at great depths in oceans where relatively little light seeps in. 

Sexual reproduction is oogamous following complex post fertilisation developments. Examples : Gelidium, Porphyra, Polysiphonia, Gracilaria

Bryophytes

Bryophytes are non-vascular mosses and liverworts that commonly grow in moist shady region in the hills. They are amphibians of the plant kingdom because they live on soil but depend on water for sexual reproduction.

Their plant body is more differentiated. They are thallus-like and erect attached to the substratum by multicellular or unicellular rhizoids.

Characteristic features

• They live in damp and shady habitats, grow during the rainy season on damp soil, rocks, walls, etc.
• The dominant phase or plant body is free living gametophyte.
• Roots and stems are absent but contain rhizoids
• Vegetative reproduction is by fragmentation, tubers, gemmae, buds etc. sex organs are multicellular and jacketed. 
• The male sex organ is called antheridium. They produce biflagellate antherozoids. 
• The female sex organ called archegonium is flask-shaped and produces a single egg.
• Sporophyte is dependent on gametophyte for nourishment.
• Plant body is haploid, producing gametes hence they are called gametophytes
• Give rise to a multicellular body known as sporophytes that are attached to the photosynthetic gametophytes, deriving its nourishment from them.

The Bryophytes are divided into liverworts and mosses.

Liverworts (Hepaticopsida)

Liverworts are found in moist, shady regions such as marshy ground, banks of streams, damp soil, bark trees and deep in the woods

Plant body of liverworts is thalloid. The thallus is dorsiventral. The leafy members of them have small leaf-like appendages on steam-like structures

Their sexual reproduction is through fragmentation or formation of gemma. During sexual reproduction both female and male sex organs are produced on the same or different thalli

Their sporophyte is differentiated into foot, seta and capsule. Post meiosis the spores are produced within the capsule. These spores germinate for the formation of free-living gametophytes

Moses (Bryopsida)

Gametophyte has 2 stages, the first one is the protonema stage and the second one is the leafy stage. 

Protonema develops directly from spores and the leafy stage develops from secondary protonema as lateral buds having upright, slender axes bearing spirally arranged leaves.

• Moses consists of slender axes, upright arranged leaves spirally. When they are attached to the soil through branched and multicellular rhizoids, the stage bears the sex organs
• Fragmentation and budding of vegetative reproduction is observed in secondary protonema while in sexual reproduction, the sex organs are produced at the apex of leafy shoots
• Sporophytes in mosses are more elaborate than liverworts. Capsules are spores formed after meiosis. Some examples – Funaria, Sphagnum

Pteridophytes

Pteridophytes are seedless vascular plants that have a sporophytic plant body and inconspicuous gametophyte.

They are found in damp, cool, shady places and sandy-soil conditions.

Sporophytic plant body is differentiated into true stem, roots and leaves.

They include ferns and have medicinal purposes and soil-binders, also frequently grown as ornaments. 

Vascular tissue- xylem and phloem, are present but vessels are absent from xylem and companion cells and sieve tube are absent.

Sporophytes bear sporangia subtended by leaf like appendages called sporophylls. 

Sporangia produce spores in spore mother cells by meiosis which germinate to produce the prothallus.

Most of Pteridophytes produce spores (homosporous), some others may be heterosporous (macro and microspores)

The pteridophytes are further classified into four classes: Psilopsida (Psilotum); Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum) and Pteropsida (Dryopteris, Pteris, Adiantum).

Gymnosperms

Gymnosperms include medium-sized trees or tall trees & shrubs. 

In these plants the ovules are not enclosed inside the ovary wall and remain exposed before and after fertilisation.

The roots are tap roots. Stems may be unbranched(Cycas) or branched(Pinus). Leaves may be simple or compound.

The leaves are well-adapted to withstand extremes of temperature, humidity and wind

Gametophytes are heterosporous, strobili bear two kinds of spores microsporophylls and microsporangia

Male and female of them don’t have independent free-living existence. Pollination occurs through air and zygote develops into embryos and ovules into seeds. These seeds are naked.

Example- Pines, Cycus, Cedrus, Ginkgo, etc

Angiosperms

Angiosperms occur in a wide range of habitats. In angiosperms, the pollen grains and ovules are developed in specialized structures known as flowers while seeds are enclosed in fruits.

They render us with fuel, food, medicines and several more commercially important products

Male sex organ is stamen consisting of the anther at the tip while female sex organ is the pistil consisting of a swollen ovary at its base consisting of a long slender style and stigma. Ovules are present inside the ovary.

Pollen grain and ovules are developed in specialized structures called flowers. Seeds are enclosed inside the fruits.

Each ovule of angiosperms has a megaspore mother cell which undergoes meiosis to form four haploid megaspores. 

Embryo-sac has a three-celled egg apparatus, one egg cell and two synergids, three antipodal cells and two polar nuclei. 

The male sex organs in a flower called stamen. It contains pollen grains.

The female sex organs in a flower is the pistil. Pistil consists of an ovary enclosing one or many ovules. Within ovules female gametophytes termed embryo-sacs are present.

Each of their embryo-sacs has a three-celled egg apparatus – one egg cell and two synergids, three antipodal cells and two polar nuclei. The polar nuclei eventually fuse to produce a diploid secondary nucleus.

They can be divided into two classes – dicotyledons and monocotyledons. 

Dicotyledons have two cotyledons with reticulate venation in leaves, tetramerous or pentamerous flowers

Monocotyledons have a single cotyledons seed, parallel venation in leaves, trimerous flowers, with three members in each floral whorls 

Plant Life Cycles and Alternation of Generations

Plant Life Cycle

There are many variations observed in the plant life cycle. Different plants exhibit different levels of complexity. That is why different generations are dominant in different plants. 

In case of algae, the haplontic life cycle is observed where the sporophyte generation is depicted by only one-celled zygote where there are no free-living sporophytes and the dominant phase is marked by the gametophyte.

Plants diplontic life cycle is observed with a few variations in angiosperms and gymnosperms. The diploid sporophyte in this life cycle is dominant, photosynthetic and marks the independent stage of plants. 

Pteridophytes and bryophytes of plants exhibit an intermediate stage known as the haplo-diplontic life cycle where in the stage is multicellular. 

The dominant phase in Bryophytes is the gametophyte and it is the sporophyte stage in Pteridophytes.

Alternation Of Generations

There are two systems of reproduction in plants where each is called generation and are related.

One complete life cycle of a plant has two generations which alternate with each other. Thus, it is called alternation of generations. 

Two generations are sporophyte and the gametophyte generation which is a rotation in between the haploid and diploid stages associated with chromosomes in the cells of plants.

Haploid cell has one set of chromosomes, and two sets of chromosomes in a diploid cell. The haploid generation produces plants with diploid cells which creates another generation of haploid plants that in turn gives rise to a generation of diploid plants and the cycle goes on.

Bad genes are removed in the haploid cell whereas the diploid stage enables greater genetic diversity.

Also Read Chapter 2 : Biological Classification

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