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CHAPTER 3
PLANT KINGDOM
The Kingdom Plantae includes plants which are multicellular, eukaryotic, photosynthetic and producers. 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 reproducing sporophytic generation. The two generations alternate. This is called alternation of generations.
3.1. ALGAE
Algae are mostly aquatic, autotrophic organisms. Their body is unicellular ( Chlamydomonas ), Colonial ( Volvox ) or filamentous ( Spirogyra ) or thalloid ( Sargassum ). They reproduce by vegetative (fragmentation), asexual (spore formation) and sexual methods. Sexual reproduction involves fusion of similar gametes ( isogamy ) eg:- Spirogyra or fusion between gametes of dissimilar in size ( anisogamy ) eg:- some species of Chlamydomonas or one large non-motile female gamete and a small motile male gamete ( oogamy ). eg:- Fucus, Volvox.
The algae are divided into three classes based on their main pigments– Chlorophyceae (Green algae) contain chlorophyll. e.g. Chlamydomonas, Volvox,Ulothrix,Spirogyra; Phaeophyceae (Brown algae) contain fucoxanthin e.g_. Ectocarpus, Dictyota, Fucus,Sargassum, Laminaria;_ Rhodophyceae (Red algae) contain phycoerythrin e.g. Polysiphonia, Porphyra, Gracilaria, Gelidium
Fig. 3.1. Algae: a) Chlamydomonas, b) Spirogyra , c) Laminaria ,d) Fucus, e) Porphyra , f) Polysiphonia.
3.2. BRYOPHYTES
The bryophytes include liverwort, hornwort and mosses. They are called amphibians of the Plant Kingdom because they live in soil but require water for sexual reproduction. They grow in moist shady places. 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
Pteridophyta
Tracheophyta
Embryophyta
Kingdom Plantae
Gymnospermae
Algae
- Chlorophyceae
- Phaeophyceae
- Rhodophyceae
Angiospermae
Bryophyta
(a) (b) (c) (d) (e) (f)
rhizoids. The gametophyte bears sex organs called antheridia (male) and archegonia (female) which produce gametes called antherozoids and eggs respectively. The antherozoid fuses with the egg to produce zygote. The zygote produces a multicellular sporophyte. The sporophyte is dependent on the gametophyte. The sporophyte reproduces asexually by producing spores. Meiosis takes place during spore formation , hence they are haploid. The spores germinate to produce the gametophyte.
The bryophytes are divided into three classes – Hepaticopsida (Liverworts) e.g. Riccia, Marchantia; Anthocerotopsida (Hornworts) e.g. Anthoceros, Notothylas,; Bryopsida (Mosses) – e.g. Funaria, Sphagnum, Polytrichum.
Fig. 3.2. Bryophytes: (a) Riccia ,(b) Marchantia , (c) Funaria.
3.3. PTERODOPHYTES
They are the first land plants which possess vascular tissues i.e. xylem and phloem. The plant body is a sporophyte which is differentiated into root, stem and leaves. Majority of the pteridophytes produce only one kind of spores in sporangia and the plants are called homosporous (e.g.:- Nephrolepis, Lycopodium ). Some produce two kinds of spores- megaspores (large) and microspores(small) .Such plants are called heterosporous (e.g.:- Selaginella, Salvinia ). The spore germinates to produce free- living, photosynthetic, haploid gametophyte called prothallus. The sex organs- antheridia and archegonia are produced on the prothallus. Fertilization results in the formation of zygote which develops into sporophyte.
The pteridophytes are divided into four classes- Psilopsida (Whisk ferns) e.g.: - Psilotum , Lycopsida (Club mosses) e.g.:- Lycopodium, Selaginella , Sphenopsida (Horse tails) e.g.:- Equisetum and Pteropsida (Ferns) e.g.:- Nephrolepis, Pteris, Adiantum, Dryopteris.
Fig.3.3. Pteridophytes: (a) Selaginella , (b) Equisetum , (c) Nephrolepis.
(a) (b) (c)
(a) (b) (c)
gametophyte bears male and female sex organs. The male and female gametes fuse to produce a zygote which produces sporophyte. Gymnosperms are naked seeded plants. The plant body is a sporophyte. The spores are of two types- megaspores and microspores. Megaspores produce female gametophyte and microspores produce male gametophyte. After fertilization the ovule develop into seed. Angiosperms are flowering plants bearing flowers having male parts (stamens) and female parts (carpels). The anther of the stamen produces haploid pollen grains. In the ovary of the carpel, ovules are present. The female gametophyte (embryo sac) develops within the ovule. The pollen grain produces a pollen tube which releases two male gametes. It fuses with two female gametes. Thus there is double fertilization and triple fusion. It is the unique feature of angiosperms.
EXERCISE
- Name the classes of algae based on the main pigment.
- Mention the types of sexual reproduction in algae?
- Name the sex organs of bryophytes.
- Why the bryophytes are called amphibians of plant kingdom?
- Which are the first terrestrial plants to possess vascular tissues?
- Name the gametophyte of ferns.
- Why gymnosperms are called naked-seeded plants?
- Match the following: a. Sargassum 1. Gymnosperm b. Pteris 2. Bryophyte c. Cycas 3. Brown alga d. Marchantia 4. Pteridophyte
- Name the female gametophyte of angiosperms.
- Name the two classes of angiosperms.
- In which group of plants double fertilization takes place?
Exercises – Answers
- Classes Chlorophyceae, Phaeophyceae and Rhodophyceae.
- Isogamy, anisogamy and oogamy.
- Antheridia (male) and archegonia (female) are the sex organs of bryophytes.
- Bryophytes require water to complete their sexual reproduction. So they are
called amphibians of the plant kingdom
- Pteridophytes
- Prothallus
- In gymnosperms, the seeds are not covered by fruit walls. So they are called
naked-seeded plants
- a – 1, b -4, c -1, d – 2
- Embryo sac
- Class Dicotyledonae and Class Monocotyledonae
Angiosperms (flowering plants)
