std 11 biology

1. STD-11 BIOLOGY
CHAPTER- 3
PLANT
KINGDOM
Sanjay Siddhapura
M.Sc., B. Ed., GSET, GPSC.

2. CHARACTERISTICS FEATURE OF
KINGDOM PLANTAE
• The Kingdom Plantae includes plants which are multicellular eukaryotes.
• All plants contain plastids. Plastids are double membrane organelle that possess
photosynthetic pigments. They are called chloroplasts.
• They are usually autotrophic. Chloroplast contains a green colour pigment called chlorophyll
and prepares its own food by the process of photosynthesis.
• The cell walls possess mainly cellulose.
• The plant body may be thalloid or differentiated into root, stem and leaves.
• They may be non-vascular or vascular.
• They have two stages in their life cycle- a haploid, sexually reproducing gametophytic
generation and a diploid, asexually reproducings porophytic generation.
• The two generations alternate. This is called alternation of generations.

3. CLASSIFICATION WITHIN ANGIOSPERMS
• Artificial system of classification
• It was given by Linnaeus.
• They were based mainly on vegetative characters and androecium structures.
• This artificial system classification separated the closely related species since they were based
on a few characteristics.
• They gave equal importance to vegetative and sexual characteristics, which is not acceptable
since we know that often the vegetative characters are more easily affected by environment.
• Natural system of classification
• It was given by George Bentham and Joseph Dalton Hooker.
• It was based on natural affinities among the organisms and considers not only the external
features, but also internal features, like ultrastructure, anatomy, embryology and
phytochemistry.

4. CLASSIFICATION WITHIN ANGIOSPERMS
• Phylogenetic system of classification
• This is accepted system of classification as it is based on evolutionary relationship between the
organisms.
• This assumes that organisms belonging to the same taxa have a common ancestor.
• Numerical taxonomy
• It is based on all observable characteristics.
• Numbers and codes are assigned to all 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.
• Easily carried out using computers.
• Cytotaxonomy
• It is based on cytological information such as chromosome number, structure, behaviour.
• Chemotaxonomy
• It is based on chemical constituents of plant to resolve doubts and confusions.

5. KINGDOM PLANTAE
• Kingdom plantae shows a lot of diversity, because of which, it has been divided into four
divisions: Algae, Bryophyta, Pteridophyta, and Spermatophyta (Gymnosperms and
Angiosperms).

6. CRYPTAEGAMAE AND PHANEROGAMAE
• In 1883, Eichler divided the kingdom plante into two sub-kingdoms, Cryptogamae and Phanerogamae.
• Sub-kingdom Cryptagamae (Greek-cryptoshidden, gamos-marriage)
• (i) These include lower plants that do not bear flower or seed. They are known as seedless plants.
• (ii) The reproductive organs are inconspicuous.
• (iii) The embryo, if present, is naked and called spores.
• (iv) It includes three divisions: Thallophyta, Bryophyta and Pteridophyta.
• Sub-kingdom Phanerogamae (Greek-phanerosvisible, gamos-marriage)
• (i) These include plant that bears flowers and seeds.
• (ii) The plant body is well differentiated into true stem, leaves and roots.
• (iii) Main reproductive organ is seed. Seeds are formed as result of sexual reproduction. The male and
female gametes fuse together inside the ovary (female part of flower) and develop into seed. In some
plants seed is not produced inside an ovary.
• (iv) It includes a single division of spermatophyte.

7. DIVISION THALLOPHTA
(GREEK: THALLOS UNDIFFERENTIATED, PHYTON-PLANT)
• Plants of this division comprise the simplest plants that do not have well-differentiated body
design.
• The body design is simple i.e. not differentiated into stem, root and leaves. It is often called
thallus.
• They are unicellular.
• Thallophyta includes a single sub-division of algae.
• Sub-Division Algae
• Habit and habitat: Algae are largely aquatic either freshwater or marine organisms.
• Some members of algae occur in association with fungi (lichens) and animals (on sloth bear).

8. • Characteristic features of algae:
• Algae are chlorophyll-bearing, simple, thalloid,
autotrophic organisms.
• Their size ranges from microscopic unicellular forms
such as Chlamydomonas to colonial forms such as
Volvox and to filamentous forms such as Ulothrix and
Spirogyra.
• Massive plant-like bodies are seen in some marine
forms (such as kelps).
• Their body is unicellular (Chlamydomonas), Colonial
(Volvox) or filamentous (Spirogyra) or thalloid
• (Sargassum).
• Algae are covered over by mucilage, which protects
them from epiphytic growth and decaying effect of
water.

9. • Reproduction: The algae reproduce vegetatively, asexually and sexually.
• Vegetative Reproduction: Vegetative reproduction is by fragmentation. Each fragment develops into a thallus.
• Asexual Reproduction: It takes place by means of different kinds of spores like zoospores, aplanospores and
akinetes. Zoospores are naked, flagellated and motile. (E.g. Chlamydomonas). Aplanospores are thin walled and
non-motile (E.g. Chlorella).
• Akinetes are thick walled and non-motile spores (E.g. Pithophora).
• Sexual reproduction: Sexual reproduction involves fusion of two gametes. If fusing gametes belong to the
same thallus it is called homothallic and if they belong to different thalli it is heterothallic. Fusing gametes may
be isogametes or heterogametes.

10. • Isogamy: It is the fusion of two morphologically and physiologically similar gametes.
• E.g. Spirogyra and some species of Chlamydomonas.
• Anisogamy: It is the fusion of two gametes which are morphologically dissimilar but
physiologically similar (both motile or both non-motile). E.g. some species of Chlamydomonas.
• Oogamy: It refers to the fusion of gametes which are both morphologically and physiologically
dissimilar.
• In this type of fusion the male gamete is usually referred to as antherozoid which is usually
motile and smaller in size and the female gamete which is usually non- motile and bigger in size
is referred to as egg.
• The sex organ which produces the antherozoids is called antheridium and the egg is produced
in oogonium.
• The fusion product of antherozoid and egg is called zygote.
• The zygote may germinate directly after meiosis or may produce meiospores which in turn will
germinate. E.g., Volvox, Fucus.

11. (a) Class I– Chlorophyceae (Green algae)
• The members of chlorophyceae are commonly called green algae.
• The plant body may be unicellular, colonial or filamentous.
• The major pigments are Chlorophyll a and b. The pigments are localised in definite chloroplasts.
• Most of the members have one or more storage bodies called pyrenoids located in the
chloroplasts. Pyrenoids contain protein besides starch.
• Stored food : They store their food in the form of starch. Some algae may store food in the
form of oil droplets.
• Cell wall composition : Green algae usually have a rigid cell wall made of an inner layer of
cellulose and an outer layer of pectose.

12. (a) Class I– Chlorophyceae (Green algae)
• Reproduction:
• Vegetative reproduction usually takes place by fragmentation or by formation of different types
of spores.
• Asexual reproduction is by spores. The common asexual spores are flagellated zoospores
produced in zoosporangia, aplanospores, hypnospores, akinetes etc.
• The sexual reproduction may be isogamous, anisogamous or oogamous.
• E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara, etc.

13. (b) Class II– Phaeophyceae (Brown algae)
• The members of Phaeophyceae are commonly called brown algae.
• Habit and habitat: Brown algae are found primarily in marine habitats.
• Size and Form: They show great variation in size and form. Body consists of branched,
filamentous structures (e.g. Ectocarpus) to profusely branched forms as represented by kelps,
which may reach a height of 100 metres.
• The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and
leaf like photosynthetic organ called the frond.
• Major pigments: They possess chlorophyll a, c, carotenoids and xanthophyll pigment, called
fucoxanthin. The brown colour of algae is due to the presence of large amount of xanthophyll
pigment.
• Stored Food : Food is stored as complex carbohydrates, which may be in the form of laminarin
or mannitol.
• Cell wall composition: The cells have a cellulosic wall usually covered on the outside by a
gelatinous coating of algin.

14. (b) Class II– Phaeophyceae (Brown algae)
• Reproduction
• Vegetative reproduction takes place by fragmentation.
• Asexual reproduction is by biflagellate zoospores that are pear-shaped and
have two unequal laterally attached flagella.
• Sexual reproduction may be isogamous, anisogamous or oogamous. In
isogamy and anisogamy both the gametes are motile while in oogamy, only
the male gametes are motile or flagellate.
• The female gametes are non-motile.
• The union of gametes may take place in water or within the oogonium
(oogamous species).
• The gametes are pyriform (pear-shaped) and bear two laterally attached
flagella.
• E.g. Ectocarpus, Dictyota, Fucus, Sargassum, Laminaria,

15. (c) Class III– Rhodophyceae (Red algae)
• Common name: Rhodophyta are commonly called red algae because of the predominance of
the red pigment, r-phycoerythrin in their body.
• Habit and habitat: Majority of the red algae are marine except for a few fresh water species.
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.
• Major pigments: They possess chlorophyll a and b, and phycoerythrin. The red colour of the
red algae is due to abundant formation of phycoerythrin.
• Stored food: The food is stored as floridean starch. Its constituent is very similar to amylopectin
and glycogen in structure.
• Cell wall: It is made of cellulose, pectin, and polysulphate esters. Some red algae have an
incrustation of calcium carbonate over their walls. They appear coral like and are called coralline.
Corallina algae produce limestone and are important component of reef formations along with
corals.
• Flagella is absent in members of this class.

16. (c) Class III– Rhodophyceae (Red algae)
• Reproduction:
• The red algae usually reproduce vegetatively by fragmentation.
• They reproduce asexually by non-motile spores.
• They reproduce sexually by non-motile gametes.
• Sexual reproduction is oogamous.
• The male sex organ is called antheridium.
• It produces non flagellate male gametes called spermatium.
• The female sex organ is flask shaped and is termed carpogonium.
• It possesses an elongated receptive organ called trichogyne.
• Male gamete is carried by water currents to trichogyne for effective fertilization.
• E.g. Polysiphonia, Porphyra, Gracilaria, Gelidium

17. Divisions of Algae and their Main Characteristics

18. BRYOPHYTES
• Habit and habitat: They usually occur in cool, damp, and shady areas. They are known as
amphibians of plant kingdom since they live on land, but depend on water for sexual
reproduction.
• Characteristics:
• Bryophyte is a division of non-vascular plants having an embryo stage in their developmental
process.
• Plant body is more differentiated than algae.
• The plant body is thallus-like and is attached to substratum by rhizoids.
• Rhizoids may be unicellular or multicellular. Roots are absent.
• Bryophytes lack true roots, stem and leaves; They may possesses root-like, stem-like, and leaf-
like structures
• They have no specialized tissue for the conduction of water and other substances from one
part of the body to another.

19. BRYOPHYTES
• The dominant phase in the life cycle is haploid gametophyte. It may be a flattened thallus or
differentiated into stem-like, root-like and leaf-like structures. The root-like structures are called
rhizoids.
• The gametophyte bears sex organs. Sex organs are multicellular and jacketed.
• They are of two types:
• The male sex organ is called antheridium, which produces biflagellate antherozoids or sperms.
• The female sex organ is called archegonium. Archegonium is flask-shaped and produces a fertile egg or oosphere.
• The antherozoid fuses with the egg to produce zygote.
• The zygote produces a multicellular body called a sporophyte.
• The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives
nourishment from it. That means, the sporophyte is dependent on the gametophyte.
• The sporophyte reproduces asexually by producing spores. Meiosis takes place during spore formation,
hence they are haploid. These spores germinate to produce the gametophyte.
• Bryophytes show distinct alternation of gametophytic generation with sporophytic generation.

20. BRYOPHYTES
• Gametophyte (Greek-gametos-spouse, phyton-plant): Gametophyte is a haploid plant structure that produces
gametes directly.
• Sporophyte (Greek-Sporos-seed, phyton-plant): Sporophyte is diploid (2n) plant structure that produces
haploid spores. Sporophyte is formed form diploid zygote or fusion of gametes.
• Economic Importance of Bryophytes
• Food: Some mosses are good source of food for herbaceous mammals, birds and other animals.
• Peat: Sphagnum in form of peat is used as fuel and also used for trans-shipment of living material as it has water
holding capacity, prevent soil erosion, along with lichens are first colonisers on barren rocks.
• Soil formation: Mosses along with lichens are the first organisms to colonise rocks and hence, are of great
ecological importance. They decompose rocks making the substrate suitable for the growth of higher plants.
• Prevention of soil erosion: Bryophytes especially mosses form dense mats on the soil, reduce the impact of
falling rain and prevent soil erosion.
• The bryophytes are divided into three classes:
• Hepaticopsida (Liverworts): e.g. Riccia, Marchantia, Pellia, Sphaerocarpos.
• Anthocerotopsida (Hornworts): e.g. Anthoceros, Notothylas.
• Bryopsida (Mosses): e.g.Funaria, Sphagnum, Polytrichum.

21. BRYOPHYTES

22. Liverworts
• Characteristics:
• Habit and habitat: 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.
• Body features: The plant body of a liverwort is thalloid, e.g., Marchantia. The thallus is dorsi-
ventral and closely appressed to the substrate.

23. • Reproduction:
• Asexual reproduction: It takes place by
fragmentation of thalli, or by the formation of
gemmae. Gemmae are small green, multicellular,
asexual buds, which are borne dorsally inside gemma
cups located on the thalli. The mature gemmae
separatefrom the parent body and germinate to form
new individuals.
• Sexual reproduction: The male and female sex
organs are produced either on the same or on different
thalli. Fertilization produces zygote which grows to
form diploid sporophyte. Each 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.
• Common examples: Riccia, Marchantia etc.

24. Mosses
• Characteristics:
• The predominant stage of the life cycle of a moss is
the gametophyte which consists of two stages.
• Protonema stage: It is the first stage and develops
directly from a spore.
• It is a creeping, green, branched and frequently
filamentous stage.
• Leafy stage: It is the second stage, which develops
from the secondary protonema as a lateral bud.
• They consist of upright, slender axis bearing spirally
arranged leaves.
• They are attached to the soil through multicellular
and branched rhizoids.
• This stage bears the sex organs.

25. • Reproduction
• Vegetative reproduction: It is by fragmentation and budding in the
secondary protonema.
• Sexual reproduction:
• In mosses, the primary protonema (developed in the first stage) developsinto the secondary
protonema.
• Both these stages are haploid or gametophytic.
• The secondary protonema bears the sex organs antheridia and archegonia, which produce gametes.
• These gametes fuse to form a zygote.
• The zygote develops into a sporophyte, consisting of foot, seta and capsule.
• The capsule contains spores.
• Many spores are formed as a result of the reduction division taking place in the capsule of this
sporophyte.
• Common Examples: Funaria, Polytrichum and Sphagnum etc.

26. BRYOPHYTES

27. PTERIDOPHYTA (Greek. Pteris-fern, phyton-plant)
• Habit and habitat: The pteridophytes are found in cool, damp, shady places though
some may flourish well in sandy-soil conditions.
• Characteristic features:
• They are first terrestrial plants which possess vascular tissue i.e. xylem and phloem.
• It is a division of seedless vascular plants. Hence commonly known as vascular
cryptogams.
• They have well developed vascular system (sylem and phloem).
• The dominant plant body is sporophyte, which is differentiated into true root, stem
and leaves. These organs possess well-differentiated vascular tissues.
• The leaves in pteridophyta are small (microphylls) as in Selaginella or large
(macrophylls) as in ferns.
• The sporophytes bear sporangia that develop in association with leaf-like appendages
called sporophylls.
• In some pteridophytes, sporophylls form distinct, compact structures called strobili
or cones (Selaginella, Equisetum).

28. • Seeds are absent. They produce naked embryos called spores.
• Homosporous pteridophytes: They bear spores that are of same type. They produce bisexual
gametophytes. E.g. Pteris, Adiantum,Nephrolepis, Lycopodium.
• Heterosporous pteridophytes: They bear two kinds of spores-microspores (small) and
megaspores (large). They produce unisexual gametophytes. E.g. Selaginella, Salvinia, Marsilea.
• The sporangia produce spores by meiosis in spore mother cells.
• The spores germinate to give rise to inconspicuous, small but multicellular, free-living, mostly
photosynthetic thalloid gametophytes called prothallus.
• The gametophyte, prothallus bear male and female sex organs called antheridia and archegonia,
respectively.
• Antheridia are small and sessile. Archegonia are partially embedded. Archegonial neck is four-
rowed.
• Sperms are motile and require an external supply of water to reach archegonia.

29. • Fusion of male gamete with the egg present in the
archegonium result in the formation of zygote.
• Zygote thereafter produces a multicellular
welldifferentiated sporophyte which is the dominant
phase of the pteridophytes.
• Spores may be similar (homosporous) as in majority
of pteridophytes.
• However, few plants are heterosporous.
• They produce two types of spores-microspores and
megaspores.
• The megaspores and microspores germinate and give
rise to female and male gametophytes, respectively.
• The female gametophytes in these plants are retained
on the parent sporophytes for variable periods.
• The development of the zygotes into young embryos
takes place within the female gametophytes.

30. Pteridophytes : (a) Selaginella (b) Equisetum (c) Fern (d) Salvinia
• The pteridophytes are divided into four classes:
• Psilopsida (Whisk ferns): E.g.Psilotum, Rhynia.
• Lycopsida (Club mosses): E.g. Lycopodium, Selaginella.
• Sphenopsida (Horse tails): E.g. Equisetum, Hyenia
• Pteropsida (Ferns): E.g. Pteris, Adiantum, Dryopteris.
Pteridophytes : (a) Selaginella
(b) Equisetum (c) Fern (d) Salvinia

31. GYMNOSPERMS
• The gymnosperms (gymnos : naked, sperma : seeds) are plants in which the
ovules are not enclosed by any ovary wall and remain exposed, both before
and after fertilisation.
• The seeds that develop post-fertilisation, are not covered, i.e., are naked.
• Gymnosperms include medium-sized trees or tall trees and shrubs.
• One of the gymnosperms, the giant redwood tree Sequoia is one of the tallest
tree species.
• The roots are generally tap roots.
• Roots in some genera have fungal association in the form of mycorrhiza
(Pinus), while in some others (Cycas) small specialized roots called coralloid
roots are associated with N2- fixing cyanobacteria.

32. • The stems are unbranched (Cycas) or branched (Pinus, Cedrus).
• The leaves may be simple or compound.
• In Cycas the pinnate leaves persist for a few years.
• The leaves in gymnosperms are well-adapted to withstand extremes of temperature, humidity
and wind.
• In conifers, the needle-like leaves reduce the surface area.
• Their thick cuticle and sunken stomata also help to reduce water loss.

33. • The gymnosperms are heterosporous;
• They produce haploid microspores and megaspores.
• The two kinds of spores are produced within sporangia that are
borne on sporophylls which are arranged spirally along an axis
to form lax or compact strobili or cones.
• The strobili bearing microsporophylls and microsporangia are called
microsporangiate or male strobili or male cone.
• The microspores develop into a male gametophytic generation which is
highly reduced and is confined to only a limited number of cells.
• This reduced gametophyte is called a pollen grain.
• The development of pollen grains take place within the
microsporangia.

34. • The cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate
or female strobili.
• The male or female cones or strobili may be borne on the same tree (Pinus).
• However, in cycas male cones and megasporophylls are borne on different trees.

35. • The megaspore mother cell is differentiated from one of the cells of the nucellus.
• The nucellus is protected by envelopes and the composite structure is called an ovule.
• The ovules are borne on megasporophylls which may be clustered to form the female cones.
• The megaspore mother cell divides meiotically to form four megaspores.
• One of the megaspores enclosed within the megasporangium develops into a multicellular
female gametophyte that bears two or more archegonia or female sex organs.
• The multicellular female gametophyte is also retained within megasporangium.

36. • In gymnosperms the male and the female gametophytes do not have an independent free-living
existence.
• They remain within the sporangia retained on the sporophytes.
• The pollen grain is released from the microsporangium.
• They are carried in air currents and come in contact with the opening of the ovules borne on
megasporophylls.
• The pollen tube carrying the male gametes grows towards archegonia in the ovules and
discharge their contents near the mouth of the archegonia.
• Following fertilisation, zygote develops into an embryo and the ovules into seeds.
• These seeds are not covered.

38. • Habit and habitat: The angiosperms are an exceptionally large group of plants occurring in
wide range of habitats.
• Size: They range in size from tiny, almost microscopic Wolfia to tall trees of Eucalyptus, which is
over 100 metres.
• Characteristic features:
• Angiosperms are also known as flowering plants which bear flowers and produce fruit enclosing
the seeds.
• They are the most recently and highly evolved plants.
• The plant body is a sporophyte which differentiated into underground root system and aerial
shoot system.
• They have sporophyll that aggregate to form flowers with the perianth.
• Both microsporophylls and megasporophylls are specialised.
Angiosperms

39. • In angiosperms or flowering plants, the pollen grains and ovules are developed in specialised
structures called flowers.
• In angiosperms, the seeds are enclosed in fruits.
• The angiosperms are an exceptionally large group of plants occurring in wide range of habitats.
• They range in size from the smallest Wolffia to tall trees of Eucalyptus (over 100 metres).
• They provide us with food, fodder, fuel, medicines and several other commercially important
products.
• They are divided into two classes : the dicotyledons and the monocotyledons.
• The dicotyledons arecharacterised by seeds having two cotyledons, reticulate venations in leaves,
and tetramerous or pentamerous flowers, i.e., having four or five members in each floral whorls.
• The monocotyledons on the other hand are characterised by single cotyledonous seeds, parallel
venation in leaves, and trimerous flowers having three members in each floral whorls.

40. • The male sex organ in a flower is the stamen.
• Each stamen consists of a slender filament with an anther at the tip.
• Within the anthers, the pollen mother cell divide by meiosis to produce
microspores which matures into pollen grains.
• The female sex organ in a flower is the pistil.
• Pistil consists of a swollen ovary at its base, a long slender style and
stigma.
• Inside the ovary, ovules are present.
• Generally each ovule has a megaspore mother cell that undergoes meiosis
to form four haploid megaspores.
• Three of them degenerate and one divide to form the embryo sac.
• Each embryo-sac 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.

41. • Pollen grain, after dispersal from the anthers, are carried by wind or
various other agencies to the stigma of a pistil. This is termed as
pollination.
• The pollen grains germinate on the stigma and the resulting pollen
tubes grow through the tissues of stigma and style and reach the
ovule.
• The pollen tubes enter the embryo-sac where two male gametes are
discharged.
• One of the male gametes fuses with the egg cell (syngamy) to form a
zygote.
• The other male gamete fuses with the diploid secondary nucleus to
produce the triploid primary endosperm nucleus (PEN).
• Because of the occurrence of two fusions i.e., syngamy and triple
fusion, this event is termed as double fertilisation, an event unique to
angiosperms.
• The zygote develops into an embryo (with one or two cotyledons)
and the PEN develops into endosperm which provides nourishment
to the developing embryo.
• The synergids and antipodals degenerate after fertilisation.
• During these events the ovules develop into seeds and the ovaries
develop into fruit.

42. • In plants, both haploid and diploid cells can divide by mitosis.
• This ability leads to the formation of different plant bodies - haploid and diploid.
• The haploid plant body produces gametes by mitosis.
• This plant body represents a gametophyte.
• Following fertilisation the zygote also divides by mitosis to produce a diploid sporophytic plant
body.
• Haploid spores are produced by this plant body by meiosis.
• These in turn, divide by mitosis to form a haploid plant body once again.
• Thus, during the life cycle of any sexually reproducing plant, there is an alternation of
generations between gamete producing haploid gametophyte and spore producing diploid
sporophyte.
PLANT LIFE CYCLES AND
ALTERNATION ON GENERATIONS

43. • Sporophytic generation is represented only by
the one-celled zygote.
• There are no free-living sporophytes.
• Meiosis in the zygote results in the formation of
haploid spores.
• The haploid spores divide mitotically and form
the gametophyte.
• The dominant, photosynthetic phase in such
plants is the free-living gametophyte.
• This kind of life cycle is termed as haplontic.
• Many algae such as Volvox, Spirogyra and some
species of Chlamydomonas represent this pattern.
HAPLONTIC LIFE CYCLES

44. • The type wherein the diploid sporophyte is
the dominant, photosynthetic, independent
phase of the plant.
• The gametophytic phase is represented by
the single to few-celled haploid
gametophyte.
• This kind of life cycle is termed as diplontic.
• An alga, Fucus sp., represents this pattern.
• In addition, all seed bearing plants i.e.,
gymnosperms and angiosperms, follow this
pattern with some variations, wherein, the
gametophytic phase is few to multi-celled.
DIPLONTIC LIFE CYCLES

45. • Bryophytes and pteridophytes, interestingly, exhibit an intermediate
condition (Haplo-diplontic); both phases are multicellular.
• They differ in their dominant phases.
• A dominant, independent, photosynthetic, thalloid or erect phase is
represented by a haploid gametophyte and it alternates with the
shortlived multicelluler sporophyte totally or partially dependent on
the gametophyte for its anchorage and nutrition. All bryophytes
represent this pattern.
• The diploid sporophyte is represented by a dominant, independent,
photosynthetic, vascular plant body. It alternates with multicellular,
saprophytic/autotrophic, independent but short-lived haploid
gametophyte. Such a pattern is known as haplo-diplontic life cycle.
All pteridophytes exhibit this pattern.
• Interestingly, while most algal genera are haplontic, some of them
such as Ectocarpus, Polysiphonia, kelps are haplo-diplontic. Fucus, an
alga is diplontic.
HAPLO-DIPLONTIC LIFE CYCLES