THE PLANT KINGDOM – Class XI Biology by TEACHING CARE online tuition and coaching classes
The Plant Kingdom
- Photosynthetic organisms are distributed in three kingdoms. But all the multicellular plants are in kingdom plantae. Plants were frequently classified on the basis of their use, form and structure. Earlier systems classified them on the basis of their habit, as trees, shrubs, undershrubs and herbs. Gradually, the natural affinities in addition to morphological features became the major consideration for grouping plants. Studies on evolution helped in understanding the phylogeny of organisms. Taxonomists started using the phylogenetic relationships for the purpose of classification.
- Plant classification is arrangement of plants into groups and subgroups on the basis of their affinities.
- In a majority of systems which recognized only two Kingdoms of organisms, the plants were included in the Plant Kingdom and animals were placed in the Animal Kingdom.
- For the classification of plants several systems were proposed from time to time by various botanists.
- Linnaeus (1735) using the number and position of stamens, divided flowering plants into 23 classes starting with the class Monandria with a single stamen (e.g., Canna) and plants with twenty or more stamens were assigned to class Icosandria.
- He also included all non-flowering plants such as algae, fungi, lichens, mosses and ferns in a separate 24th class called Cryptogamia.
- His system was based on a few characters. He himself stated that his system of classification did not consider relationships. Morever, his system places widely unrelated families of monocotyledons and dicotyledons in one class.
Types of Classification
- Artificial System of classification
- Natural System of classification
- Phylogenetic System of classification
- Artificial System of classification: Given by Carolous Linneus. This is based on the gross superficial morphological characters such as habit, colour, number and shape of leaves, etc.
- Natural System of classification: George Bentham and Josheph Dalton Hooker. These is based on natural affinities among the organisms and consider not only the external features, but also internal features, like ultra structure, anatomy, embryology and phytochemistry.
- Phylogenetic classification system: Given by Prantle and Englar. This is based on evolutionary relationships between the various organisms.
- Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms.
- Plant body is unicellular, colonial, filamentous, parenchymatous or pseudoparenchymatous.
- Vascular tissues are absent.
- A mechanical tissue is absent.
- Nutrition is autotrophic.
- A variety of pigments in algae provide different colours.
- Vegetative and asexual modes of reproduction are abundant.
- Sexual reproduction involves isogamy (Spirogyra), anisogamy (Chlamydomonas) and oogamy (Volvox, Fucus). Sex organs are unicellular and non-jacketed.
- An embryo stage is absent.
- Life cycle is various–haplontic, diplontic or diplohaplontic.
- CHLOROPHYCEAE: The green algae.
- The plant body may be unicellular, colonial or filamentous.
- They appears as grass green due to the dominance of pigments chlorophyll a and b.
- The pigments are located in definite chloroplasts. The shape of chloroplasts may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in different species.
- Pyrenoids located in the chloroplasts is the storing body that contains protein besides starch.
- A few algae may store food in the form of oil droplets.
- Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose.
- Reproduction is vegetative, asexual and sexual types. Vegetative by fragmentation of the main stem.
- Asexual reproduction by zoospore formation.
- Sexual reproduction isogamous, anisogamous and oogamous types.
PHEOPHYCEAE: Brown Algae
- Most of the brown algae are marine, except three-Pleurocladia, Heribaudiella and Bodanellia, which are found in fresh water.
- Unicellular forms are absent. The body consists of a branched filamentous structure in lower forms (g., Ectocarpus) and parenchymatous structure in higher forms (e.g., Sargassum, Laminaria, Fucus and Macrocystis).
- Brown algae include the largest algae. The giant brown algae are called kelps which may reach a height of 100 meters.
- The plant body is often differentiated into holdfast, stipe and lamina.
- They possess chlorophyll a, c, carotenoids and xanthophylls.
- Reproduction is vegetative, asexual and sexual type.
- The vegetative reproduction by fragmentation of the plant body.
- Asexual reproduction by biflagellated zoospores formation.
- Sexual reproduction may be isogamous, anisogamous and oogamous type.
RHODOPHYCEAE: Red algae
- They are marine except for a few fresh water species, e.g.
- Red algae are autotropic with the exception of a few like It is colourless and parasitic on other red algae.
- A motile or flagellate stage is completely absent.
- The plant body varies from unicellular to multicellular forms.
- Cell wall possesses cellulose, pectic compounds and certain mucopolysaccharides called The latter are usually sulphated. The important phycocolloids (hydrocolloids) of red algae are agar, carrageenin and funori.
- The photosynthetic organelles are called They have single thylakoid.
- Photosynthetic pigments include chlorophyll a, carotenoids and phycobilins. Chlorophyll ‘d’ has been reported in some cases. Phycobilins are of two types, red coloured phycoerythrin and blue coloured phycocyanin.
- The term Bryophyta, (Gk. bryon : moss ; phyton : plant), is used as a collective name to represent a group of plants that includes liverworts, hornworts and mosses growing predominantly in amphibious environment.
- The group, therefore, goes well with the name of Amphibians of plant kingdom owing to the amphibious habitat of plants.
- The plants are characterized by the presence of conspicuous, green, well developed, nutritionally independent gametophytes to which are always attached physically and nutritionally dependent sporophytes.
- The gametophyte constitutes the dominant phase of life cycle that exhibits sharply defined alternation of generation.
- The plants show two morphologically distinct heteromorphic generations, i.e., gametophytic and sporophytic generations.
- Gametophytic generation is the dominant phase of life cycle and in general the term plant body is used to represent this phase.
- Bryophytes lack vascular tissues. The plant body consists of simple parenchymatous cells. Xylem, phloem and lignified cells are completely absent. The parenchymatous cells may be differentiated into several types g., chlorophyllous cells, storage cells, rhizoids, etc. to perform various functions, as in Riccia and Marchantia. Few thick walked cells called stereom are present in mosses. Mosses retain moisture like the sponges.
- Bryophytes reproduce by vegetative and sexual methods.
- Bryophytes largely multiply by means of vegetative reproduction which is accomplished by fragmentation, adventitious branches, tubers, buds, gemmae, rhizoids, primary protonema, secondary protonema etc.
- The sexual reproduction is invariably advanced Oogamous type.
- Sex organs are multicellular and jacketed with sterile jacket. They may be embedded type, g., Riccia, Anthoceros or projected type, e.g., Marchantia, mosses.
- The male reproductive organ is called It consists of a central mass of androcytes enclosed by a single layer of sterile jacket. Each androcyte produces a single biflagellate spermatozoid or antherozoid.
- The female reproductive organ is called Each archegonium is a multicellular and flask shaped structure. The basal swollen portion is called venter whereas slender and elongated upper portion is called neck.
- Hepatocopsida: Commonly called as Liver worts.
- Anthoceratopsida: Commonly called as horn worts.
- Bryopsida: Commonly known as mosses
- The liverworts grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, bark of trees and deep in the woods. The plant body of a liverwort is thalloid.
- The thallus is dorsiventral and closely appressed to the substrate.
- Asexual reproduction in liverworts takes place by fragmentation of main thalli, or by gemmae formation.
- The gemmae become detached from the parent body and germinate to form new individuals.
- During 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.
- After meiosis, spores are produced within the capsule. These spores germinate to form free-living gametophytes. g., Marchantia.
- The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages.
- Spore germinates to form a green filamentous primary protonema, which bear buds. Buds may develop into secondary protonema or directly into new gametophytic adult plant.
- The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud.
- Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema. In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots.
- After fertilization, the zygote develops into a sporophyte, consisting of a foot, seta and capsule. The sporophyte in mosses is more elaborate than that in liverworts.
- The capsule contains spores. Spores are formed after meiosis. The mosses have an elaborate mechanism of spore dispersal. e.g.; Funaria, Polytrichum and
- The Pteridophytes (Gk. petron = feather, phyton = plant, Haeckel, 1866) are the spore bearing most primitive vascular plants. They are commonly called Vascular Cryptogams.
- The Pteridophytes grow under varied habitats, most of them are terrestrial plants and thrive well under damp and shady conditions while some flourish well in open grasslands or even under xeric conditions (e.g., Selaginella lepidophylla). A few pteridophytes grow as aquatic (e.g., Marsilea, Azolla and Salvinia) while still other are epiphytes (e.g., Lycopodium phlegmaria).
- The primary root is short lived. It is replaced by adventitious roots which generally arise endogenously.
- The stem bears leaves which may be small microphyllous (e.g., Lycopodium, Equisetum) or very large macrophyllous (Pteridium, Pteris and other ferns).
- Evolutionarily this was the first land plant that possess vascular tissue- Xylem and phloem All the vegetative parts possess vascular tissues, organized in definite groups or stele.
- The xylem mainly consists of tracheids and xylem parenchyma. The vessels are generally absent but primitive type of vessels has been reported in Selaginella, Equisetum, Pteridium,
- The phloem consists of sieve-tube and phloem parenchyma. The companion cells are absent.
- The main plant body is sporophytic which is differentiated into root, stem and leaves.
- The sporophytic plant reproduces by means of spores that are produced by
- Leaves bearing the sporangia are called
- The sporophylls may be widely scattered on a plant or may be clustered in definite areas and structures called cones or strobili (g., Selaginella and Equisetum).
- In aquatic Pteridophytes, the sporangia are produced within the specialized structures called the sporocarps (e.g., Marsiliea, Salvinia and Azolla).
- The spores, on germination give rise to the haploid gametophytes or prothalli that are usually small, multicellular, free-living and with insignificant structures. The gametophytes are inconspicuous as compared to the sporophytes. One of the most characteristic features of the pteridophytes is that the sporophyte has become the dominant morphological part of the life cycle while the gametophyte has been much reduced.
- Antheridia: The antheridia may be embedded either wholly or partially in the tissue of gametophyte or they may project from it. It consists large number of Androcytes that give rise to single motile antherozoids.
- Archegonia: The archegonium is a flask shaped structure, consisting of a basal swollen, embedded portion the venter and a short neck. It produces female gamete.
- In majority of the pteridophytes all the spores are of similar kinds; such plants are called homosporous.
- Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively.
- Fertilization : Fertilization in all cases is accomplished by the agency of water. The fusion of a male gamete and an egg restores the diploid chromosome (2n) number and results in the formation of the zygote. e.g.; Selaginella, Equisetum
- The living Gymnosperms are widely distributed in the cold climates where snow, rather than rain, is the source of water. Cycads occur in tropical and subtropical areas.
- In India, mostly the conifers thrive well in hilly areas. Very few Gymnosperms grown in plains.
- The main plant body is sporophyte (2n) and is well differentiated into root, stem and leaves.
- Plants possess tap root. In some cases roots show symbiosis with certain algal cells, g., coralloid roots of Cycas or with fungus, e.g., mycorrhizal roots of Pinus, Araucaria, etc.
- Stems are erect, branched (unbranched in most species of Cycas) and woody. Leaf scars show their characteristic presence on the stem.
- Leaves may be of one kind, e., monomorphic; or of two kinds, i.e., dimorphic :
Foliage leaves that are all invariably evergreen may be simple or compound, and Scale leaves that are minute and deciduous.
- The leaves may be few, large and pinnately compound as in Cycas, numerous small, simple and needle shaped as in Pinus or reduced and scaly as in
- Stems are characterized by the presence of collateral and open vascular bundles arranged in a ring, with endarch xylem.
- The vessels are absent in the xylem (except in Gnetales) and the companion cells are absent in phloem. However, albuminous cells are present. Sieve tubes are also not organized as the sieve cells are not placed end to end in rows. Vessels have bordered pits.
- In most of the living Gymnosperms (except ovulate structures of Cycas) reproductive organs are aggregated in the form of compact cones. Cones may either be male (microsporangiate) or female (megasporangiate), rarely they are bisporangiate.
- Male cones are usually short lived and smaller than female cones.
- Female cones are usually long lived. They sometimes remain on the plants for several years for the maturity and repening of the seeds. Megasporophylls may be foliar and are loosely arranged to form female strobilus (g., Cycas) or cauline and compactly aggregated to form female cone.
- Microsporangia (pollen sacs) are borne on the abaxial surface of microsporophylls. They may be numerous and grouped in sori as in ferns, (g., Cycas) or reduced to two (e.g., Pinus).
- Megasporangia (ovules) are borne naked on the sporophyllous scales. They are generally orthotropous and covered by a single integument. Integument that surrounds nucellus may be differentiated into an outer fleshy, inner fleshy and middle stony
- The plants are heterosporous, e., they bear two types of spores.
- The male gameteophyte bears only one or two prothallial cells.
- The female gametophyte possesses archegonia. Each archegonium possesses single egg and a ventral canal cell. Neck canal cells are lacking.
- Fertilization takes place by the fusion of male and female nuclei resulting in the formation of zygote.
- Medicinally most important Gymnosperms are Taxus and
- In the angiosperms or flowering plants, the pollen grains and ovules are developed in specialised structures called flowers. In angiosperms, the seeds are enclosed by fruits.
- This is classified into Dicotyledonous and Monocotyledonous plant group.
Table : Comparision of Dicotyledons and Monocotyledons
Character Dicotyledons Monocotyledons
Morphology Tap roots Adventitious roots
Recticulate venation Parallel venation
Tetra-or pentamerous flowers Trimerous flowers
Anatomy Vascular bundles of stem Vascular bundles of stem are cattered
arranged in a ring in the ground tissue
2-6 vascular bundles in root Many vascular bundles in root
In stem, each vascular bundle is open In stem, each vascular bundle is closed
Secondary growth occurs Secondary growth does not occur
- Monocotyledonous: These types of plants have single cotyledons in their seeds.
- Dicotyledonous: These types of plants have two cotyledons in their seeds.
- In angiosperms, the male sex organs (stamen) and female sex organs (pistil) are borne in a flower.
- Each stamen consists of a filament and an anther.
- The anther produces pollen grains (male gametophyte) after meiosis.
- The pistil consists of an ovary enclosing one to many ovules.
- Inside the ovule is the female gametophyte or embryo sac which contains the egg cell.
- The pollen tube enters the embryo-sac where two male gametes are discharged. One male gamete fuses with egg cell (syngamy) and other fuses with diploid secondary nucleus (triple fusion). This phenomenon of two fusions (i.e. Triple fusion and Syngamy) is called double fertilisation and is unique to angiosperms.
- During the life cycle of any sexually reproducing plant, there is alternation of generations between gamete producing haploid gametophyte and spore producing diploid sporophyte. However, different plant groups as well as individuals may show different patterns of life cycles – haplontic, diplontic or intermediate.
|VERY SHORT ANSWER QUESTIONS (1 mARK)|
- Define the term hydrocolloids.
- Why bryophytes are called as amphibious plant?
- Give one economic importance of Sphagnum.
- What do you mean by haplo-diplontic life cycle?
- What is triple fusion?
|SHORT ANSWER QUESTIONS (2 mARKS)|
- What is double fertilization?
- Differentiate between liverworts and mosses.
- Describe the important characteristics of gymnosperm.
- How would you distinguish monocots from dicots?
- Both gymnosperm and angiosperm bear seeds, then why are they classified separately?
|LONG ANSWER QUESTIONS (5 mARKS)|
- What is the basis of classification of algae?
- When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
- Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
- Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
- Explain briefly the following terms with suitable examples:-
- Differentiate between the following:-
(i) red algae and brown algae
(ii) liverworts and moss
(iii) homosporous and heterosporous pteridophyte
(iv) syngamy and triple fusion
|MULTIPLE CHOICE QUESTIONS|
Pick (Ö) the correct option :
- Which of the following statements concerning the algae is wrong ?
(1) Most algae are photosynthetic
(2) Algae can be classified according to their pigments
(3) All algae are filamentous
(4) Some algae are parasitic
- Red colour of red algae is due to
(1) r-phycoerythrin (2) r-phycocyanin
(3) Carotenoids (4) Xanthophylls
- Floridian starch as a stored photosynthate is present in
(1) Red algae (2) Green algae
(3) Blue green algae (4) Brown algae
- Which of the following is a colourless parasitic red alga ?
(1) Batrachospermum (2) Chlorella
(3) Porphyra (4) Harveyella
- Which is not a character of Bryophytes?
(1) Presence of archegonia
(2) Independent sporophyte
(3) Motile sperms
(4) Water is essential for fertilization
- In the five-kingdom system of classification developed by Robert Whittaker, members of the kingdom Plantae are : autotrophic, eukaryotic and
(3) Either unicellular or multicellular
(4) Have sexual reproduction
- Prothallus of fern is
(3) Dioceious and protogynous
(4) Monoceous and protoandrous
- Gymnosperms do not possess
(1) Sexual reproduction
(3) Vegetative reproduction
(4) All of these
- Gymnosperms are connecting link between
(1) Bryophytes & pteridophytes
(2) Angiosperm & gymnosperm
(3) Pteridophytes & angiosperms
(4) Bryophytes & angiosperms
- The positive evidence of aquatic ancestry of bryophytes is indicated by
(1) Thread like protonema
(2) Ciliated sperms
(3) Some forms are still aquatic
(4) Their green colour
- Bryophytes are popularly called amphibian plants because
(1) They grow on land
(2) They require external free water sexual reproduction
(3) Anteroids swim through water
(4) All of these
- The gymnosperms resemble angiosperms in having
(1) Ciliated sperms
(2) Presence of archegonia
(3) Presence of ovules
(4) Presence of monoxylic wood
- Which of the following characters can be used to distinguish gymnosperms from angiosperms?
(1) Presence of pollen sacs in gymnosperms
(2) Presence of stomata in angiosperms
(3) Presence of naked ovules in gymnosperms
(4) None of these
- Phloem of gymnosperms differ from that of angiosperms in having
(1) Parenchyma (2) No companion cells
(3) No sieve cells (4) No sclerenchyma fibres
- In angiosperm, the endosperm is
(1) Gametophytic (2) Sporophytic
(3) Triploid (4) Deprived of reserve food
- A plant having vascular supply, producing spores but lacking seeds can be grouped under
(1) Bryophyta (2) Pteridophyta
(3) Gymnosperms (4) Angiosperms
- Match the following (column I with column II)
Column I Column II
(a) Chlamydomonas (i) Moss
(b) Cycas (ii) Pteridophyte
(c) Selaginella (iii) Algae
(d) Sphagnum (iv) Gymnosperm
- Match the following (column I with column II)
Column I Column II
(a) Carrageen (i) Peat Moss
(b) Cycas (ii) Triploid
(c) PEN (iii) Hydrocolloids
(d) Sphagnum (iv) N2 fixing Cynobacteria
WORKSHEET – 1
- Why is the plant body of an algae called a thallus?
- Most algae genera show haplontic life cycle. Name the alga which is
- Write the economic importance of red algae.
- Give the major difference between dicotyledons and monocotyledons.
- Why bryophytes are called amphibians of plant kingdom?
- Describe the general character of seedless vascular plants.
WORKSHEET – 2
- Assign the following organism in their respective plant group. Chlamydomonas, Focus, Ectocarpous, Gracilaria, Gelidium, Chara, Polytrichum, Sphagnum, Equisetum, Lectrus, Cycas etc.
- Why presence of water is must for fertilization in Bryophytes?
- Explain following terms :
(i) Mycorrhiza (ii) Coralloid roots
(iii) Megasporangium (iv) PEN
- Explain the difference between syngamy and triple fusion.
- Differentiate between the following terms :
(i) Antheridium and Archaegonium
(ii) Protonema and Prothallus
(iii) Gametophytes and Sporophytes
WORKSHEET – 3
- Write the differences between gymnosperm and angiosperm.
- Differentiate the following terms :
(i) Roots and Rhizoids
(ii) Holdfast and Frond
(iii) Xanthophyll and g-phytoerythrin
- Write the pigments and stored food materials in phaeophyceae.
- Differentiate between chlorophyceae and rhodophyceae.
- Write the economic importance of pteridophytes.