Plant Kingdom : A Comprehensive Study Notes for Class - 11, Chapter 3, Study notes of Biology

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Earliest systems of classification. They were based on vegetative characters or superficial morphological characters such as habit, colour, number and shape of leaves, etc. Linnaeus’s artificial system of classification was based on the androecium structure. Drawbacks: They separated the closely related species since they were based on a few characteristics. Equal weightage to vegetative & sexual characteristics. This is not acceptable since the vegetative characters are more easily affected by

environment. Carl Linnaeus

These are based on natural affinities among organisms. It considers external features and internal features (ultrastructure, anatomy, embryology & phytochemistry). E.g. Classification for flowering plants given by George Bentham & Joseph Dalton Hooker.

George Bentham^ Joseph Dalton Hooker

Simple, thalloid, autotrophic, chlorophyll-bearing and aquatic (fresh water & marine) organisms.

They also occur in moist stones, soils & wood.

Some occur in association with fungi (lichen) and animals (e.g. on sloth bear).

The form and size of algae is highly variable. Microscopic unicellular forms: E.g. Chlamydomonas. Colonial forms: E.g. Volvox. Filamentous forms: E.g. Ulothrix and Spirogyra.

Vegetative reproduction: By fragmentation. Each fragment develops into a thallus. Asexual reproduction: By the production of spores. E.g. zoospores (most common). They are flagellated (motile). They germinate to give rise to new plants. Sexual reproduction: Through fusion of two gametes.

Algae On Sloth hair

Lichens

Moss

Spirogyra Ulothrix

Chalmydomonas Volvox

Sexual reproduction is many types:

Isogamous: Fusion of gametes similar in size.

They may be flagellated (e.g. Chlamydomonas) or

non-flagellated (non-motile, e.g. Spirogyra).

Anisogamous: Fusion of two gametes dissimilar

in size.

E.g. Some species of Chlamydomonas.

Oogamous: Fusion between one large, non-motile

(static) female gamete and a smaller, motile male

gamete.

E.g. Volvox, Fucus.

Through photosynthesis, they fix half of the total CO2 on earth and increase the level of dissolved

oxygen.

They are primary producers and the basis of the food cycles of all aquatic animals

About 70 species of marine algae are used as food.

E.g. Porphyra, Laminaria &Sargassum.

Agar (from Gelidium & Gracilaria) is used to grow microbes and in ice-creams & jellies.

Some marine brown & red algae produce hydrocolloids (water holding substances). E.g. algin (brown algae) & carrageen (red algae). These are used commercially.

Protein-rich unicellular algae like Chlorella & Spirullina are used as food supplements by space travellers.

Most of them have one or more pyrenoids (storage bodies) located in chloroplasts. Pyrenoids contain protein besides starch. Some algae store food as oil droplets. They have rigid cell wall made of an inner cellulose layer and an outer pectose layer. E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara.

Chlamydomonas Volvox

Most of them have one or more pyrenoids (storage bodies) located in chloroplasts. Pyrenoids contain protein besides starch. Some algae store food as oil droplets. They have rigid cell wall made of an inner cellulose layer and an outer pectose layer. E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara.

Reproduction Vegetative reproduction: By fragmentation or by formation of different types of spores. Asexual reproduction: By flagellated zoospores produced in zoosporangia. Sexual reproduction: Isogamous, anisogamous or oogamous.

Ulothrix (^) Spirogyra Chara

They are mostly marine forms. They show great variation in size & form. They range from simple branched, filamentous forms (E.g. Ectocarpus) to profusely branched forms (e.g. kelps- 100 m in height). They have chlorophyll a, c, carotenoids & xanthophylls. They vary in colour from olive green to brown depending upon the amount of a xanthophyll pigment, fucoxanthin.

Food is stored as complex carbohydrates (laminarin or mannitol). The vegetative cells have a cellulosic wall covered by a gelatinous coating of algin. Protoplast contains plastids, central vacuole and nucleus. Plant body is attached to substratum by a holdfast, and has a stalk (stipe) and leaf like photosynthetic organ (frond). E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus.

Sargassum

Reproduction Vegetative reproduction: By fragmentation. Asexual reproduction: By pear- shaped biflagellate zoospores (have 2 unequal laterally attached flagella).

Sexual reproduction: Isogamous, anisogamous or oogamous. Union of gametes occurs in water or within the oogonium (oogamous species). Gametes are pear-shaped (pyriform) bearing 2 laterally attached flagella.

Chlorophyceae Phaeophyceae Rhodophyceae

Common name Green algae Brown algae Red algae

Major

pigments

Chlorophyll a, b

Chlorophyll a, c, Fucoxanthin

Chlorophyll a, d, Phycoerythrin

Stored food Starch Mannitol, laminarin Floridean Starch

Cell wall Cellulose Cellulose and algin Cellulose

Flagellar

number &

position of

insertion

2-8, equal, apical 2, unequal, lateral Absent

Habitat

Fresh water, salt water & brackish water

Fresh water (rare), salt water & brackish water

Fresh water (some), salt water (most) & brackish water

They are called amphibians of the plant kingdom because they can live in soil but need water for sexual reproduction. They occur in damp, humid and shaded localities.

Body is more differentiated than that of algae. It is thallus- like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids. They lack true roots, stem or leaves. They may possess root- like, leaf-like or stem- like structures. The main plant body is haploid. It produces gametes, hence is called a gametophyte.

The sex organs in bryophytes are multicellular. Male sex organ (antheridium) produces biflagellate antherozoids. Female sex organ (archegonium) is flask-shaped and produces a single egg.

Antherozoids are released to water and meet archegonium. An antherozoid fuses with the egg to form zygote.

They grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, bark of trees and deep in the woods. Their plant body is thalloid. E.g. Marchantia. Thallus is dorsi-ventral and closely appressed to the substrate. The leafy members have tiny leaf-like appendages in two rows on the stem-like structures.

Asexual reproduction By fragmentation of thalli, or by the formation of gemmae (sing. gemma). Gemmae are green, multicellular, asexual buds that develop in small receptacles (gemma cups) on the thalli. The gemmae are detached from the parent body and germinate to form new individuals.

Sexual reproduction Male and female sex organs are produced on the same or different thalli. Sporophyte is differentiated into a foot, seta and capsule. After meiosis, spores are produced within the capsule. These spores germinate to form free- living gametophytes

The predominant stage of the life cycle of a moss is the gametophyte. It consists of two stages: First stage: Protonema stage Second stage: Leafy stage

Protonema stage: It develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage. Leafy stage: It develops from the secondary protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaves. They are attached to soil through multicellular and branched rhizoids. This stage bears the sex organs.

Vegetative reproduction By fragmentation and budding in the secondary protonema Sexual reproduction The antheridia & archegonia are produced at the apex of leafy shoots. After fertilisation, zygote develops to a sporophyte having a foot, seta & capsule. The sporophyte in mosses is more elaborate than that in liverworts. The capsule contains spores. Spores are formed after meiosis. Mosses have an elaborate mechanism of spore dispersal.

Sporophyte

Sporophylls

Sporangium

The sporophytes bear sporangia that are subtended by leaf-like appendages called sporophylls

In some cases, sporophylls form distinct compact structures called strobili or cones (E.g. Selaginella, Equisetum).

Sporangia produce spores by meiosis in spore mother cells.

The spores germinate to give inconspicuous, small, multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus

Prothallus requires cool, damp, shady places to grow. Also, it needs water for fertilization. So, the spread of pteridophytes is limited and restricted to narrow geographical regions. The gametophytes (prothallus) bear male and female sex organs called antheridia and archegonia, respectively

Water is needed for transfer of antherozoids (male gametes from antheridia) to the mouth of archegonium. Antherozoid fuses with the egg in the archegonium to form zygote. Zygote develops to a multicellular well- differentiated sporophyte.

Most of the pteridophytes produce similar kinds of spores (homosporous plants). Others produce two kinds of spores, macro (mega) & micro spores. They are heterosporous. E.g. Selaginella & Salvinia.

The megaspores & microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes are retained on the parent sporophytes for variable periods.

Within female gametophytes, zygotes develop into young embryos. This event is a precursor to the seed habit. It is considered as an important step in evolution.

Gymnosperms (gymnos: naked, sperma: seeds) are plants in which the ovules are not enclosed by ovary wall and remain exposed before and after fertilization.

Seeds that develop post-fertilization are not covered (naked).

Gymnosperm ovule Angiosperm ovule

The gymnosperm, Sequoia (giant redwood) is the tallest tree species.

They include medium- sized trees or tall trees and shrubs.

Pinus roots with mycorrhiza

The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (E.g. Pinus).

In plants like Cycas, small specialized roots (coralloid roots) are associated with N2- fixing cyanobacteria.

Stems are unbranched (Cycas) or branched (Pinus, Cedrus).

Leaves are simple or compound. They are well-adapted to withstand extreme temperature, humidity and wind.

In Cycas, the pinnate leaves persist for a few years.

In conifers (Pinus, Cedrus etc.), the needle-like leaves reduce the surface area. Their thick cuticle & sunken stomata also help to reduce water loss.

Gymnosperms are heterosporous. They produce haploid microspores and megaspores. Some leaves are modified into sporophylls. They are compactly and spirally arranged along an axis to form lax or strobili or cones.