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3. Plant Kingdom 

REVISION NOTES

 

CLASS 11 BIOLOGY

UNIT I – DIVERSITY IN THE LIVING WORLD

Chapter 1 – The Living World 

Chapter 2 – Biological Classification 

Chapter 3 – Plant Kingdom 

Chapter 4 – Animal Kingdom 

UNIT II – STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS

Chapter 5 – Morphology of Flowering Plants 

Chapter 6 – Anatomy of Flowering Plants 

Chapter 7 – Structural Organisation in Animals 

UNIT III – CELL : STRUCTURE AND FUNCTIONS

 

Chapter 8 – Cell: The Unit of Life 

Chapter 9 – Bio-Molecules 

Chapter 10 – Cell Cycle and Cell Division 

UNIT IV – PLANT PHYSIOLOGY 

Chapter 11 – Transport in Plants 

Chapter 12 – Mineral Nutrition 

Chapter 13 – Photosynthesis in higher plants 

Chapter 14 – Respiration in Plants 

Chapter 15 – Plant Growth and Development 

UNIT V – HUMAN PHYSIOLOGY 

Chapter 16 – Digestion And Absorption 

Chapter 17 – Breathing and Exchange of Gases 

Chapter 18 – Body fluids and circulation 

Chapter 19 – Excretory Products and their Elimination 

Chapter 20 – Locomotion and Movement 

Chapter 21 – Neural Control and Coordination 

Chapter 22 – Chemical Coordination and Integration 

CLASS 12 BIOLOGY

Unit-VI Reproduction
  

Chapter 1 : Reproduction in Organisms 

Chapter 2 : Sexual Reproduction in Flowering Plants 

Chapter 3 : Human Reproduction 

Chapter 4 : Reproductive Health 

Unit-VII Genetics and Evolution

Chapter 5 : Principles of Inheritance and Variation 

Chapter 6 : Molecular Basis of Inheritance 

Chapter 7 : Evolution 

Unit-VIII Biology and Human Welfare

Chapter 8 : Human Health and Disease 

Chapter 9 : Strategies for Enhancement in Food Production 

Chapter 10 : Microbes in Human Welfare 

Unit-IX Biotechnology  

Chapter 11 : Biotechnology Principles and Processes 

Chapter 12 : Biotechnology and its Applications 

Unit-X Ecology and Environment 

Chapter 13 : Organisms and Populations 

Chapter 14 : Ecosystem 

Chapter 15 : Biodiversity and Conservation 

Chapter 16 : Environmental Issues 

Phylogenetic Classification:

  1. At present phylogenetic classification systems based on evolutionary relationships between the various organisms are acceptable. This assumes that organisms belonging to the same taxa have a common ancestor. We now use information from many other sources too to help resolve difficulties in classification. These become more important when there is no supporting fossil evidence.

  2. Numerical Taxonomy: Numerical Taxonomy is based on all observable characteristics. Number and codes are assigned to all the characters and the data are then processed. In this way each character is given equal importance and at the same time hundreds of characters can be considered.

  1. Cytotaxonomy: Cytotaxonomy that is based on cytological information like chromosome number, structure, behaviour and chemotaxonomy that uses the chemical constituents of the plant to resolve confusions, are also used by taxonomists these days.

ALGAE

  1. Habit & Habitat: Algae are simple and thalloid organisms. They are mainly aquatic organisms and live in freshwater and marine habitats. They bear chlorophyll. Some of the algae also occur in association with fungi (as lichen) and animals (e.g. on sloth bear).

  2. Size: Some of them are unicellular, e.g. Chlamydomonas. Some algae live in colonies, e.g. Volvox. Some algae are in filamentous form, e.g. Ulothrix and Spirogyra. Some of the marine forms make massive plant bodies, e.g. kelps.

  3. Reproduction: Vegetative, asexual and sexual methods of reproduction are present in algae.

  4. Vegetative Reproduction: Vegetative reproduction takes place by fragmentation. During vegetative reproduction, a thallus divides into many fragments and each fragment develops into a thallus.

  5. Asexual Reproduction: Asexual reproduction takes place by different kinds of spores; in algae. Zoospores are the most common type of spore. The zoospores are flagellated and hence are motile. They give rise to new plants on germination.

  6. Sexual reproduction: Fusion of gametes is involved in sexual reproduction. There are following types of fusion of gametes in algae:

a. Isogamous Fusion: In this case, the gametes are similar in size, e.g. Spirogyra. The gametes can be flagellated or non-flagellated.

b. Anisogamous Fusion: In this case, the gametes are dissimilar in size, e.g. some species of Chlamydomonas.

c. Oogamous Fusion: In this case, the female gamete is large and non-motile, while the male gamete is small and motile, e.g. volvox and focus.

Economic Importance of Algae:

 

  1. Almost 50% of carbon fixation on earth is carried out by algae. Thus, they are among the large producers on the earth; especially in aquatic habitat. About 70 species of marine algae are used as food, e.g. Porpyra, Laminaria and Sargassum.

  2. Some marine brown and red algae produce large amounts of hydrocolloids. Hydrocolloids are water holding substances and are used commercially.

  3. Agar; which is obtained from Gelidium and Gracilaria is used as culture medium in laboratories. It is also used in making ice-cream and jelly.

  4. Chlorella and Spirullaina are used as food supplements; even during space travel.

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

CHLOROPHYCEAE

  1. Characteristics: They are commonly called green algae. Plant body can be unicellular, colonial or filamentous. Dominance of chlorophyll a and b means that chlorophyceae are usually grass green. The chloroplasts may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped. Storage bodies; called pyrenoids are found in most of the members. Pyrenoids store protein and starch. Food is also stored in the form of oil droplets in some algae. Cell wall is usually rigid and is composed of an inner layer of cellulose and an outer layer of pectose.

  2. Reproduction: Vegetative reproduction happens by fragmentation or by formation of different types of spores.

  3. Asexual reproduction takes place by flagellated zoospores which are produced in zoosporangia.

  4. Sexual reproduction can be isogamous, anisogamous or oogamous.

  5. Common Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara

PHAEOPHYCEAE

 

  1. Characteristics: They are also called brown algae. They are found in marine habitats. The brown algae can range from simple branched, filamentous forms to profusely branched forms. Chlorophyll a, c, carotenoids and xanthophyll are the pigments found in phaeophyceae. Colour can vary from olive green to various shades of brown. The colour variation depends on the amount of xanthophyll and fucoxanthin.

  2. Food is stored as complex carbohydrates; in the form of laminarin or mannitol. The cell wall of vegetative cells is composed of cellulose and is covered by a gelatinous coating of algin. Protoplast contains plastids, centrally located vacuole and nucleus.

  3. Plant body is usually attached to the substratum by a holdfast. The plant body has a stalk, stipe and leaf-like fond.

  4. Reproduction: Vegetative reproduction is by fragmentation. Asexual reproduction takes place by biflagellate zoospores. Sexual reproduction can be isogamous, anisogamous or oogamous. Fusion of gametes can happen in water or within the oogonium. Gametes are pyriform (pear-shaped) and bear two laterally attached flagellum.

  5. Common Examples: Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus

RHODOPHYCEAE

 

  1. Characteristics: These are commonly called red algae. The red pigment, r-phycoerythrin is predominant in rhodopytes. Most of them are marine species and are mainly found in warm areas. They are found in well-lit regions close to the surface of water as well as at great depths. The thallus is multicellular in most of the cases. Food is stored as floridean starch.

  2. Reproduction: Vegetative reproduction is by fragmentation and it is the most prevalent method of reproduction. Asexual reproduction is by non-motile spores. Sexual reproduction is oogamous. Post-fertilisation development is complex.

  3. Common Examples: Polysiphonia, Porphyra, Gracilaria and Gelidium.

BRYOPHYTES

 

  1. Habits & Habitats: Bryophytes include the various mosses and liverworts which are usually found in moist shaded areas in the hills. Bryophytes are also called amphibians of the plant kingdom because they can live on soil but need water for sexual reproduction. They are usually found in damp, humid and shaded localities.

  2. Characteristics: The plant body is thallus-like and can be prostrate or erect. The plant body is attached to the substratum by unicellular or multicellular rhizoids. True roots, stem or leaves are absent. However, root-like, leaf-like or stem-like structures may be present.

  3. Reproduction: The main plant body is haploid in bryophytes. The main plant body is called gametophyte because it produces gametes. Sex organs are multicellular. Male sex organ is called antheridium and produces biflagellate antherozoids. The female sex organ is called archegonium and produces a single egg. Antherozoids are released into water for fertilization. After fertilization, zygote does not immediately divide meiotically. Zygote produces a multicellular body called sporophyte. Sporophyte is attached to the photosynthetic gametophyte so that it can get nourishment from the gametophyte. Some cells of the sporophyte undergo meiosis to produce haploid spores. The spores germinate to produce gametophyte.

  4. Economic Importance of Bryophytes:

  • Peat is obtained from species of Sphagnum which is a moss. Peat has been in use as fuel. Peat is also used as packing material for shipment of living materials; because peat has good capacity to hold water.

  • Mosses are among the first organisms to colonise rocks and thus play an important role in soil formation. Some mosses also prevent soil erosion which may happen because of rains; as they form dense mats on soil.

  • The bryophytes are divided into two classes, viz. liverworts and mosses.

LIVERWORTS

 

  1. Characteristics: They usually grow in moist and shady habitats. The plant body is thalloid. Thallus is dorsiventral and closely appressed to the substrate. Some members have tiny leaf-like appandages in two rows on the stem-like structures.

  2. Reproduction: Asexual reproduction takes place by fragmentation, or by formation of specialized structures called gemmae. A gemma is a green, multicellular, asexual bud. A gemma develops in small receptacles called gemma cup. The gemma gets detached from the parent body and germinates to form a new individual.

  3. In case of sexual reproduction; male and female sex organs are produced either on the same or on different thalli. The sporophyte is differentiated into a foot, seta and capsule. Spores are produced after meiosis. These spores germinate to produce free-living gametophytes.

MOSSES

 

  1. Characteristics: Gametophyte is the predominant stage of the life cycle of moss. The gametophyte consists of two stages, viz. protonema stage and leafy stage.

  2. Protonema develops from the spore. It is creeping, branched and usually filamentous.

  3. The leafy stage develops from the protonema as a lateral bud. The leafy stage consists of upright, slender axes bearing spirally arranged leaves. It is attached to the soil through multicellular and branched rhizoids. The leafy stage bears the sex organs.

  4. Reproduction: Vegetative reproduction takes place by fragmentation and budding in the secondary protonema.

  5. In case of sexual reproduction, antheridia and archegonia are produced at the apex of the leafy shoots. After fertilization, the zygote develops into a sporophyte. The sporophyte consists of a foot, seta and capsule. The capsule contains spores. Spores are formed after meiosis. There is an elaborate mechanism of spore dispersal in mosses.

  6. Common Examples: Funaria, Polytrichum and Sphagnum

PTERIDOPHYTES

 

  1. Characteristics: Pteridophytes are found in cool, damp and shady places. Some of them may also proliferate in sandy soil. The main plant body is a sporophyte. It is differentiated into true root, stem and leaves. Well-differentiated vascular tissues are present. Small leaves called microphylls are found in some pteridophytes, e.g. Selaginella. Large leaves called megaphylls are found in some others, e.g. ferns. Sporophyte bears sporangia which are subtended by leaf-like appendages called sporophylls. In some cases, the sporophylls may form distinct compact structures called strobili or cones, e.g. Selaginella, Equisetum.

  2. Reproduction: Spores are produced by the mother cells in sporangia; through meiosis. The spores germinate and produce thalloid gametophyte called prothallus. The prothallus is inconspicuous, small but multicellular. The prothallus is free-living and usually photosynthetic.

  3. The gametophytes need cool, damp and shady places to grow. Due to this specific requirement, pteridophytes are spread to limited areas to narrow geographical regions.

  4. The gametophyte bears antheridia and archegonia. Transfer of antheroizoids is facilitated by water. The zygote produces a multicellular well-differentiated sporophyte.

  5. Most of the pteridophytes are homosporous, i.e. they produce spores of similar type. Some pteriophytes are heterosporous, e.g. Selaginella and Salvinia. In heterospory, the megaspore germinates to produce female gametophyte, while the microspore germinates to produce the male gametophyte. This event is a precursor of the seed habit in higher plants.

  6. The pteridophytes are divided into four classes, viz. Psilopsida, Lycopsida, Sphenopsida and Pteropsida.

GYMNOSPERMS

Characteristics of Gymnosperms

 

  1. The ovules in gymnosperms are not enclosed by an ovary wall. The seeds too are not covered, i.e. naked. Gymnosperms include medium-sized or tall trees and shrubs.

  2. These plants usually have tap roots. Roots of some plants have fungal association in the form of mycorrhiza, e.g. Pinus. In some other plants, small specialized roots; called coralloid roots; are associated with nitrogen-fixing cyanobacteria, e.g. Cycas.

  3. The stems are unbranched (Cycas) or branched (Pinus, cedrus). Leaves can be simple or compound. The pinnate leaves in Cycas persist for a few years. The leaves are well adapted to withstand extremes of temperature, humidity and wind. Needle-like leaves of conifer reduce surface area and thus reduce transpiration. Thick cuticle and sunken stomata also help in preventing water loss.

Reproduction in Gymnosperms

  1. Gymnosperms are heterosporous. Haploid microspores and megaspores are produced. Spores are produced within sporangia. Sporangia are borne on sporophylls which are arranged spirally along an axis. The Sporophylls form lax or compact strobili or cones.
    The male strobili are called microsporangiate. Microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells. This small-sized gametophyte is called pollen grain.
    The female strobili are called megasporangiate. The male or female cones can be found on the same tree (Pinus) or on different trees (Cycas). The megaspore mother cell is differentiated from one of the cells of the nucellus. Nucellus is protected by envelopes and the composite structure and is called an ovule. Meiotic division in the megaspore mother cell produces four megaspores. One of the megaspores develops into a multicellular female gametophyte. The female gametophyte bears two or more archegonia or female sex organs. The female gametophyte is retained within the megasporangium.

  2. Fertilization:

  3. The pollen grains are released from the microsporangium and carried by air currents. They come in contact with the opening of the ovules on the female cone. A pollen tube develops in the pollen grain. The male gamete travels through the pollen tube to reach near the mouth of archegonia. After fertilization, zygote develops into an embryo. The ovule develops into seed.

ANGIOSPERMS

Characteristics of Angiosperms

 

  1. These are also called the “Flowering Plants”. Male and female gametes are developed in specialized structures called flowers. The seeds are enclosed by fruits. They are a very large group of plants and are found in a wide range of habitats. The angiosperms can be microscopic (Wolfia) to over 100 metre tall trees. They are highly important for us because we get food, fodder, fuel, medicines, and many other useful products from them.

  2. Angiosperms are divided into two classes, viz. dicotyledon and monocotyledon.

Reproduction In Angiosperms

 

  1. Male Sex Organ: Stamen is the male sex organ in the flower. A stamen is composed of a slender filament and an anther at the top. The anthers produce pollen grains through meiosis.

  2. Female Sex Organs: Pistil or carpel is the female sex organ in a flower. The pistil consists of an ovary. The ovary may enclose one or many ovules. The embryo sac is formed by meiosis. Each embryo sac has a three-celled egg apparatus, three antipodal cells and two polar nuclei. The egg apparatus has one egg cell and two synergids. The polar nuclei finally fuse to produce a diploid secondary nucleus.

  3. Pollination: Transfer of pollen grains to stigma is called pollination. Pollination is facilitated by various agents; like wind, water, animals, insects, etc.

  4. Fertilization: Pollen grain germinates on the stigma and produces a pollen tube. The pollen tube pierces through the stigma and style and reaches the ovule. The male gametes are discharged near the embryo sac. One of the male gametes fuses with the egg cell and forms a zygote. The other male gamete fuses with the diploid secondary nucleus to produce the triploid Primary Endosperm Nucleus (PEN). This event is called Double Fertilisation because of the involvement of two fusions. Double fertilization is unique to angiosperms.

  5. Embryo: The zygote develops into an embryo and the PEN develops into endosperm. Endosperm provides nutrition to the developing embryo. Synergids and antipodals degenerate after fertilization. Ovules develop into seeds and ovaries develop into fruits.

Alteration of generations

 

  1. Both haploid and diploid cells in plants can undergo mitosis. Due to this, formation of haploid and diploid plant bodies becomes possible. The haploid plant body produces gametes and it represents a gametophyte. After fertilization, the zygote undergoes mitosis and produces a diploid sporophytic plant body. The diploid sporophytic plant produces haploid spores by meiosis. The spores then undergo mitosis and form a haploid plant body once again.

  2. Thus, during the life cycle of any sexually reproducing plant, there is an alternation of generations between gametophyte and sporophyte. This phenomenon is called alternation of generations.

  3. But different groups of plants differ in relative length and size of haploid or diploid generations. Such variations are as follows:

  • Haplontic: In such plants, a free-living gametophyte is the dominant photosynthetic phase. In this case, the sporophytic generation is represented only by the one-celled zygote. There is no free-living sporophyte. The zygote undergoes meiosis to form haploid spores. The spores then undergo mitosis to form the gametophyte. Examples: Volvox, Spirogyra and some species of Chlamydomonas.

  • Diplontic: In this case, the diploid sporophyte is the dominant photosynthetic phase of the plant. The gametophyte is represented by the single to few-celled haploid gametophyte. Gymnosperms and angiosperms show this pattern.

  • Haplo-diplontic: In this case, both phases are multicellular and free-living. Bryophytes and pteridophytes follow this pattern.

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