Plant kingdom | Algae |Pteridophytes | Bryophytes- plant amphibians |Gymnosperm | Angiosperm | HAPLO-DIPLONTIC life cycle
PLANT KINGDOM
1. Kingdom plantae of Whittaker’s classification has
o Algae,
o Bryophyta,
o Pteridophyta,
o Gymnosperm &
o Angiosperm.
2. PLANTS ARE
o Autotrophic (chlorophyll bearing),
o Eukaryotic,
o Having cellulosic cell wall,
o Tissue/organ level body organization.
3. ALGAE:
o Chlorophyll-bearing, autotrophic
o Simple, Thalloid Body
o Largely aquatic organisms.
o Thallus means plant body is not differentiated into root, stem and leaf.
o Lichen is symbiotic association of algae with fungi.
o Algae also show symbiotic relationship with sloth bear.
Algae provide camouflage & mineral nutrition to bear whereas sloth bear give shelter and water.
o Chlamydomos is microscopic unicellular. (now in Protista)
o Colonial form-volvox (green algae)
o Filamentous form-ulothrix and spirogyra (green algae).
o Kelp (brown algae) form massive plant body.
o Algae usually reproduce vegetative by fragmentation.
o Asexual reproduction by formation of different types of spores (mainly through zoospore i.e. having flagella).
o Sexual reproduction by formation of gametes
➤isogamy, anisogamy or oogamy.
➤Chlamydomonas (motile gametes), spirogyra (non-motile gametes) both show isogamy.
➤some species of chlamydomonas also show Anisogamy
➤Volvox and Fucus show oogamy
o Depending on the type of pigment possessed and the type of stored food, algae are classified into three main classes,
➤Chlorophyceae,
➤Phaeophyceae and
➤Rhodophyceae.
o Laminaria, sargassum (Brown algae) and porphyra (Red algae) are used as food.
o 70 species of marine algae are used as food.
o About 50% of the world’s photosynthesis is done by algae
➤Increase the level of dissolved O2 in their immediate environment.
o Important primary producers
➤form the basis of the food chain of all aquatic animals.
o Agar (commercial products) obtained from Gelidium and Gracilaria
➤Used to grow microbes
➤Used in preparations of ice-creams and jellies.
o Algin (from brown algae) and carrageen (from red algae) which are used commercially for their water holding capacity.
o Chlorella a unicellular alga rich in proteins is used as food supplement even by space travellers.
4. CHOLOROPHYCEAE (Green algae):
o Main pigment is chlorophyll a and b.
o Stored food is starch.
o Have one or more storage bodies –> pyrenoids
➤located in the chloroplasts.
➤Pyrenoids contain protein besides starch.
o Green algae usually have a rigid cell wall
➤made of an inner layer of cellulose and an outer layer of pectose
o Number of flagella in motile cell 2-8
➤they are equal in size and apical in position.
o Vegetative reproduction is by fragmentation.
o Asexual reproduction is flagellated zoospores
o Produced in zoosporangia.
o The sexual reproduction is isogamous, anisogamous or oogamous.
o Example of green algae is
➤Chlamydomonas,
➤Volvox,
➤Ulothrix,
➤Spirogyra and
➤Chara
o Volvox, spirogyra and some species of chlamydomonas show haplontic life (zygotic meiosis) cycle
➤main plant body is gametophyte
➤the only diploid cell in their life cycle is zygote.
5. PHAEOPHYCEAE (BROWN ALGAE):
o Main pigments chlorophyll a and c and fucoxanthin (brown colour).
o Food is stored as complex carbohydrates Laminarin or Mannitol.
o The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of ALGIN.
o The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the frond.
o Vegetative reproduction takes place by fragmentation.
o Asexual reproduction in most brown algae is by biflagellate zoospores.
o Motile cells (zoospores and gametes) are pyriform and have two unequal laterally inserted flagella.
o Sexual reproduction may be isogamous, anisogamous or oogamous.
o The common examples are :
➤Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
o Kelp belongs to brown algae.
o Most brown algae have haplontic life cycle but Brown algae Fucus shows DIPLONTIC LIFE CYCLE (sporic meiosis).
o main plant body is diploid.
6. RHODOPHYCEAE (red algae):
o Main pigments are chlorophyll a, d and r-phycoerythrin
o r-phycoerythrin –> reason of red colour
o Majority of the red algae are marine
➤greater concentrations found in the warmer areas.
➤They occur in both well-lighted regions close to the surface of water and also at great depths in oceans where relatively little light penetrates.
o Cell wall is made up of cellulose, pectin and polysulphate esters.
o The food is stored as Floridian starch
➤very similar to amylopectin and glycogen in structure.
o The red algae usually reproduce vegetatively by fragmentation.
o Motile cells are completely absent in their life cycle.
o Sexual reproduction is oogamous and accompanied by complex post fertilisation developments.
o The common members are:
➤Polysiphonia, Porphyra, Gracilaria and Gelidium.
o Red algae are mainly marine.
IMPORTANT COMPARISON
7. BRAYOPHYTA: PLANT AMPHIBIANS
o Plants which can live in soil but are dependent on water for sexual reproduction.
➤Therefore, their occurrence is limited to cool, damp and shady places.
o Their plant body is more differentiated than that of algae.
o It is thallus-like and prostrate or erect and attached to the substratum by rhizoids.
o Vascular tissue is absent.
o The main plant body of the bryophyte is GAMETOPHYTE (haploid).
➤It produces gametes.
o The sex organs in bryophytes are multicellular and jacketed.
o The male sex organ is called antheridium.
o They produce biflagellate anthrozoids.
o The female sex organ called archegonium
➤flask-shaped and produces a single egg.
o Sexual reproduction is oogamous.
o Fertilization requires water for anthrozoids movement.
o After fertilization, zygote divide mitotically and produce multicellular embryo which then differentiated as sporophyte.
o Sporophyte is the plant which produce haploid spores by meiosis (sporic meiosis).
o Haploid spores germinate to form gametophyte.
o Sporophyte is dependent upon gametophyte
➤for food and nourishment.
o Bryophyte shows alternation of generation
➤between gametophyte and sporophyte.
o LIFE-CYCLE IS HAPLO-DIPLONTIC (SPORIC MEIOSIS).
o Bryophyta is the first evolved group where embryo formed
o Species of Sphagnum, a moss, provide peat
➤that have long been used as fuel,
➤as packing material for trans-shipment of living material because of their capacity to hold water.
o Since mosses form dense mats on the soil, prevent soil erosion.
o They have great ECOLOGICAL IMPORTANCE as along with lichens they are pioneer of plant succession on bare rock/soil.
➤They decompose rocks making the substrate suitable for the growth of higher plants.
o The bryophytes are mainly divided into liverworts and mosses.
8. LIVERWORTS:
Plant body is dorsiventrally thalloid.
➤e.g. marchantia
o Leafy members have tiny leaf-like appendages in two rows on the stem-like structures.
o Asexual reproduction
➤takes place by fragmentation of thalli,
➤by the formation of specialised structures called gemmae.
o Gemmae
➤Green, multicellular, asexual buds
➤Develop in small receptacles called gemma cups
➤Gemmae cups located on the thalli.
➤Gemmae presents in gemmae cup
➤Become detached and germinate to form new individuals.
o In marchentia,
➤Antheridia (male sex organ)
➤Produce in receptacles called anthridiophore
➤Archegonia (female sex organ) -
➤Produce in receptacles called archigoniophore
o The sporophyte is differentiated into a foot, seta and capsule.
o After meiosis, spores are produced within the capsule.
o These spores germinate to form free-living gametophyte.
9. MOSSES:
o Mosses gametophyte has two stage.
o The first stage is the PRIMARY PROTONEMA STAGE, which develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage.
o The second stage is the LEAFY STAGE SECONDARY PROTONEMA which develops from the PRIMARY protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaf like structure.
o They are attached to the soil through multicellular and branched rhizoids.
o Secondary protonema bears sex organs.
o Vegetative reproduction
➤By fragmentation
➤Budding in the secondary protonema.
o In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots.
o After fertilisation, the zygote develops into a sporophyte,
➤consisting of a foot, seta and capsule.
o The sporophyte is more elaborate than that in liverworts.
o The capsule contains spores.
o Spores are formed after meiosis.
o The mosses have an elaborate mechanism of spore dispersal.
o Common examples of mosses are –
➤Funaria,
➤Polytrichum and
➤Sphagnum (peat moss).
PTERIDOPHYTA:
o FIRST PLANT GROUP
➤Where sporophyte (2n) becomes the main plant body
➤Where main plant body (sporophyte) is truly differentiated into true root, stem and leaves. This content developed by Biomentors Classes Online
➤Possess well-differentiated vascular tissues.
➤The sporophyte bears sporangia which produces spores
➤ The spore germinates to form gametophyte which requires cool,damp places to grow.
o The gametophytes bear male and female sex organs called antheridia
and archegonia, respectively.
o Water is required for transfer of male gametes to archegonium (reason for limited restricted distribution) ; zygote is formed after fertilisation.
o The zygote gives rise to a sporophyte.
o Microphylls (small leaf) is found in selaginella
o Macrophylls or fronds (large leaf) are found in fern.
Cone or strobilus.
o Cones are found in Equisetum and selaginella.
o Sporangia either produce
➤Only one type of spores i.e. HOMOSPOROUS
➤Two types of spores i.e. HETEROSPOROUS.
o HETEROSPOROUS pteridophytes
➤Megaspore which germinate to form female gametophyte
➤Microspore germinate to form male gametophyte.
o Selaginella and Salvinia is example of heterospory.
o The female gametophyte in HETEROSPOROUS PTERIDOPHYTE are retained on the parent sporophytes for variable periods.
▪︎The development of the zygotes into young embryos take place within the female gametophytes.
GYMNOSPERM:
o Main plant body is sporophyte.
o Tap root system.
o Roots in some genera have fungal association in the form of mycorrhiza (Best example – Pinus)
o In some others (Cycas) small specialised roots called CORALLOID ROOTS are associated with N2- fixing cyanobacteria.
o CYCAS HAS UNBRANCHED STEM.
o PINUS & CEDRUS HAVE BRANCHED STEM.(
o The leaves in gymnosperms are well-adapted to withstand extremes of temperature, humidity and wind.
o In conifers (Pinus), the needle-like leaves reduce the surface area.
o In Gymnosperm, thick cuticle and sunken stomata also help to reduce water loss.
o All gymnosperms are heterosporous
➤they produce haploid microspores and megaspores.
o The two kinds of spores are produced within sporangia that are borne on Sporophylls
o These Sporophylls are compactly & spirally arranged in Cone or Strobilus.
o The strobili bearing microsporophylls and microsporangia are called
Male Strobili or Male Cone
o The microspores develop into a male gametophyte (gametophytic generation) which is highly reduced and is confined to only a limited number of cells.
o This reduced male gametophyte is called a pollen grain.
o The development of pollen grains take place within the microsporangia.
o The cones bearing megasporophylls with ovules(megasporangia) are called Female Strobili or Female Cone
o The megaspore mother cell is differentiated from one of the cells of the nucellus.
o The nucellus is protected by envelopes and the composite structure is called an OVULE (MEGASPORANGIUM) @ Ovule is integumented megasporangium
o The ovules are borne on megasporophylls
o Megasporophylls clustered to form the female cones.
o The megaspore mother cell divides meiotically to form four megaspores.
o One of the megaspores enclosed within the megasporangium develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs.
o The multicellular female gametophyte is also retained within megasporangium.
o Gametophytes are dependent on sporophyte and don’t have independent existence.
o Pollination by wind @ Anemophily
o Pollen grain come in contact with the opening of the ovules borne on megasporophylls.
o The pollen tube carrying the male gametes grows towards archegonia in the ovules and discharge their contents near the mouth of the archegonia. @ SIPHONOGAMY
o Water is not required for fertilization.
o Following fertilisation, zygote develops into an embryo and the ovules into seeds. @ Seeds are fertilised Ovule
o In Gymnosperm –> Endosperm is haploid and before fertilization structure. It represents female gametophyte.
o These seeds are not covered i.e. naked seed (seeds are not enclosed in fruit because ovary is absent in gymnosperm).
o Pinus is a monoecious
➤Microsporangia and megasporangia born on same plant.
o Cycas is dioceous plant
➤Microsporangia and megasporangia born on different plants.
o Life cycle is DIPLONTIC. Editing by Sciencegajab
ANGIOSPERM
o The pollen grains and ovules are developed in specialised structures called FLOWERS.
o The seeds are enclosed by fruits.
o The angiosperms are an exceptionally large group of plants occurring in wide range of habitats.
o They provide us with food, fodder, fuel, medicines and several other commercially important products.
o Wolfia is smallest angiosperm plant.
o Eucalyptus is the tallest angiospermic plant.
o In angiosperms, the male sex organs (stamen) and female sex organs (Pistil or Carpel) are borne in a flower.
o The pollen tube carry two male gametes; One male gamete fuses with egg cell (syngamy) and other fuses with diploid secondary nucleus (triple fusion). This phenomenon of two fusions is called double fertilisation and is unique to angiosperms.
o Endosperm is triploid & post fertilization structure.
o The angiosperms are divided into two classes – the dicotyledons and the monocotyledons.
ALTERNATION OF GENERATIONS:
o Alternate occurrence of gametes producing gametophyte and spore producing sporophyte in LIFE-CYCLE is called ALTERNATION OF GENERATIONS.
HAPLONTIC life cycle
o the main plant body is gametophyte(n),
o zygote is the only diploid in its life cycle
o characterised by ZYGOTIC MEIOSIS.
o EXAMPLES: volvox, spirogyra and chlamydomonas.
DIPLONTIC LIFE-CYCLE:
o Main plant body is diploid sporophyte.
o Sporic meiosis.
o Haploid gametophytes are very reduced type(one to few celled).
o Examples: Gymnosperm, Angiosperm and fucus (brown algae).
HAPLO-DIPLONTIC LIFE CYCLE:
o In this type of life cycle, plants exhibit an intermediate condition both phases are multicellular.
o Bryophytes and pteridophyte are the examples.
o In bryophyte, gametophyte is dominant whereas in Pteridophyta, sporophyte is dominant.
o Sporic meiosis takes place in sporophyte
➤Pteridophyte is the group where gametophyte and sporophyte both are independent and free living.
➤Ectocarpus, kelp (brown algae), polysiphonia (red algae) show haplo- diplontic life cycle.
➤Algae is the group in plant kingdom which show all three type of alternation of generations.
READ for knowledge
1. The term PTERIDOPHYTA was first introduced by Haeckel in (1866).
2. Pteridophytes flourished well during devonian, mississipian and pensylvanian periods of late paleozoic age. This period can be well recognised as “age of pteridophyta”.
3. Salvinia is Root less pteridophyte
4. In ferns the sporangia are borne in sori on the sporophylls.
5. In fern -The sporangia are generally stalked structures. Each sporangium is distinguishable into a jacket enclosing a mass of sporogenous tissue. The sporangial jacket may be 2-4 layered. The innermost wall layer is the tapetum. It is a nutritive layer which degenerates at maturity of the sporangium.
6. The spores germinate to produce haploid gametophyte, called PROTHALLUS.
7. The homosporous pteridophytes produce bisexual (monoecious) gametophytes whereas heterosporous one produce unisexual (dioecious) gametophytes.
8. The archegonia and antheridia are generally of embedded type.
9. Fertilization is affected by water medium (zooidogamous). The antherozoids are attracted towards the egg by a chemotactic stimulus provided by the degeneration of neck canal cell and venter canal cell, in the form of malic acid.
10. The stellar theory was proposed by Van Tiegham and Douliot .
11. Protostele : Solid core of xylem surrounded by phloem, pericycle and endodermis.
12. The terms apogamy was coined by de Bary (1878). It is defined as formation of sporophyte from a gametophytic cell other than egg without fertilization.
o it was observed in Lycopodium, Selaginella, Marsilea etc.
13. The formation of gametophyte from a sporophytic cell without meiosis is called as apospory. This phenomenon was first observed by Druery in Athyrium filix-femina.
14. Formation of sporophyte from egg without fertilization is called as parthenogenesis.
15. Medicines :
o An anthelmintic drug is obtained from fern Dryopteris.
o Lycopodium is used in skin diseases.
o Equisetum has diuretic properties.
16. Selaginella is commonly called the little club moss or spike moss.
17. In Selaginella
o Leaves are ligulate, i.e., a flap-like outgrowth is present at the base on adaxial side called ligule.
o At the base of ligule, there is present a sheath of elongated cells called glossopodium.
o At the place of bifuraction of stem, a leafless, colourless, positively geotropic, elongated, cylindrical structure grows downwards. This is called the rhizophore (ORGAN SUI GENERIS)
o The stele is suspended by unicelled trabaculae (modified endodermis).
o The microspore on germination forms the male gametophyte. Usually the male gametophytes are shed from the microsporangium on the ground at 13-celled stage. Water is necessary for fertilization and sperms are attracted due to malic acid.
18. Ferns live in moist, cool and shady places. They are perennial and evergreen.
19. Fern Dryopteris filix-mas is commonly known as Beech fern or Male shield fern or Hay scented fern.
20. Fern plant is sporophytic (2n) with an underground rhizomatous stem, large aerial leaves or fronds & adventitious roots.
21. Adiantum commonly called walking fern because it propagates vegetatively by its leaf tips)
22. Younger parts of leaves and rhizome are surrounded by brown hairy structures called scales or RAMENTA.
23. Leaves which bear groups of sori on the under surface of fertile pinnae. Such fronds are called sporophylls.
24. Each sorus is surrounded by a kidney-shaped covering called indusium.
25. Prothallus : Fern prothallus is monoecious but protandrous (antheridia mature first). Antheridia are present in between the rhizoids while archegonia are present near the apical notch.
26. The term gymnosperm was introduced by Theophrastus.
27. Gymnosperms are called fruitless phanerogames or flowering plants without ovary Robert Brown (1827) separated them from angiosperms This content developed by Biomentors Classes Online
28. Plants of gymnosperms occur throughout the world. The group is presently represented by only 900 living species. Of these, about 500 species belong to ‘Conifers’ or cone bearing plants.
29. The smallest gymnospermous tree is Zamia pygmia.
30. In gymnosperm xylem is generally made up of tracheids but vessels have been observed in Gnetum, Ephedra and Welwitschia.
31. In gymnosperm ➤The ovules are orthotropous and remain exposed on the megasporophyll. Each ovule is surrounded by integuments. It encloses the nucellus and a female gametophyte formed from the haploid megaspore. The female gametophyte contains archegonia.
32. Cleavage polyembryony is seen in Pinus.
33. The seeds of gymnosperms comprise tissue of three generations namely parent sporophytic (integument and nucellus), gametophytic (endosperm) and second sporophytic (embryo).
34. When a group of plants is represented by a single genus or species while rest of the other representatives of the group have become extinct and fossilized the long surviving individual is called a LIVING FOSSIL e.g., Ginkgo biloba. However, Cycas is also regarded as a living fossil because most of the cycad species are confined to tropical and subtropical regions and the group is becoming endangered.
35. The wood of Cedrus deodara is used for making railway sleepers. The wood of Pinus is used for making furniture. Juniperus virginiana wood is used for making pencils.
36. The gymnosperm Agathis australis is perhaps the largest timber producing tree of the world.
37. Several conifers yield resin which is obtained by tapping. By distilling the oleoresin is obtained from pines.
38. An important source of turpentine is Pinus The oil obtained from Juniperus virginiana (cedar wood oil) is also used in microscopic work.
39. The seeds of Pinus gerardiana (chilgoza) and P. roxburghii are edible.
40. Sago is obtained from Cycas revoluta.
41. Species of Ephedra yield an alkaloid called ephedrine. It is used in the preparation of medicines for the treatment of cough, asthma and bronchitis.
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