Plant Kingdom

Algae are classified into three main classes (Chlorophyceae, Phaeophyceae, and Rhodophyceae) based on the following criteria:

• Pigmentation: The type of major pigment present (Chlorophylls, Fucoxanthin, Phycoerythrin).
• Stored Food: The form in which food is stored (Starch, Mannitol/Laminarin, Floridean starch).
• Cell Wall Composition: The chemical nature of the cell wall (Cellulose, Algin, Pectin/Polysulphate esters).
• Flagellar Number/Position: The number and insertion of flagella (2-8 equal/apical, 2 unequal/lateral, or Absent).

Plant Group	When	Where
Liverwort	After zygote formation, during capsule development.	In the capsule of the Sporophyte (Spore mother cells).
Moss	After zygote formation, during spore formation.	In the capsule of the Sporophyte (Spore mother cells).
Fern	During spore formation.	In the Sporangia on sporophylls (Spore mother cells).
Gymnosperm	During micro/megaspore formation.	In Microsporangia and Megasporangia (Nucellus).
Angiosperm	During gamete formation.	In Anthers (Microsporangia) and Ovules (Megasporangia).

Three Groups: Bryophytes, Pteridophytes, and Gymnosperms.

Life Cycle of a Bryophyte (Moss):

• Gametophyte Phase (Dominant): The haploid gametophyte is the dominant, photosynthetic stage. It develops from a protonema into a leafy stage bearing sex organs (Antheridia and Archegonia).
• Fertilization: Antherozoids (male gametes) swim in water to reach the Archegonium (female) and fuse with the egg to form a diploid Zygote.
• Sporophyte Phase: The zygote develops into a multicellular sporophyte (Foot, Seta, Capsule) which remains attached to the gametophyte for nutrition.
• Meiosis: Cells in the capsule undergo meiosis to produce haploid spores.
• Germination: Spores germinate to form the new gametophyte (protonema).

• Protonemal cell of a moss: Haploid (n)
• Primary endosperm nucleus in dicot: Triploid (3n)
• Leaf cell of a moss: Haploid (n)
• Prothallus cell of a fern: Haploid (n)
• Gemma cell in Marchantia: Haploid (n)
• Meristem cell of monocot: Diploid (2n)
• Ovum of a liverwort: Haploid (n)
• Zygote of a fern: Diploid (2n)

Economic Importance of Algae:

• Food Source: Many marine algae like Porphyra, Laminaria, Sargassum are used as food. Chlorella is used by space travellers.
• Hydrocolloids: Algin (Brown algae) and Carrageen (Red algae) are water-holding substances used commercially.
• Laboratory Use: Agar (from Gelidium, Gracilaria) is used to grow microbes and in ice-creams.
• Oxygen Production: They fix half of the total CO₂ on earth and increase dissolved oxygen.

Economic Importance of Gymnosperms:

• Timber: Conifers provide soft wood for construction, packing boxes, and plywood.
• Paper Industry: Wood pulp is used for making paper.
• Food: Seeds of Pinus gerardiana (Chilgoza) are edible.
• Resins & Turpentine: Extracted from Pinus species, used in paints and polishes.
• Medicinal: Taxol (anti-cancer drug) is obtained from Taxus.

They are classified separately mainly due to the nature of their seeds:

• Gymnosperms (Naked Seeds): The ovules are not enclosed by any ovary wall and remain exposed before and after fertilization. The seeds develop exposed on megasporophylls.
• Angiosperms (Enclosed Seeds): The ovules are enclosed inside the ovary. After fertilization, the ovary ripens into a fruit containing the seeds.

Heterospory: The phenomenon of producing two different kinds of spores—Macro (large) and Micro (small) spores—by a single plant.

Significance:

• It is a precursor to the seed habit.
• The female gametophyte remains retained on the parent sporophyte for variable periods.
• The development of the zygote into young embryos takes place within the female gametophyte, ensuring better protection and nutrition.

Examples: Selaginella and Salvinia.

• (i) Protonema: The juvenile, creeping, green, branched, and filamentous stage in the life cycle of mosses, developing directly from a spore.
• (ii) Antheridium: The male sex organ in bryophytes and pteridophytes that produces antherozoids.
• (iii) Archegonium: The flask-shaped female sex organ producing a single egg.
• (iv) Diplontic: A life cycle pattern where the diploid sporophyte is the dominant, photosynthetic, independent phase (e.g., Fucus, Gymnosperms, Angiosperms).
• (v) Sporophyll: A leaf that bears sporangia (spore-producing structures).
• (vi) Isogamy: Fusion of two gametes which are similar in size and structure (morphologically indistinguishable).

Feature	Red Algae (Rhodophyceae)	Brown Algae (Phaeophyceae)
Pigment	Chlorophyll a, d, Phycoerythrin	Chlorophyll a, c, Fucoxanthin
Stored Food	Floridean Starch	Mannitol, Laminarin
Cell Wall	Cellulose, Pectin, Polysulphate esters	Cellulose, Algin

Feature	Liverworts	Moss
Plant Body	Thalloid (flat), dorsiventral	Leafy (upright), radial symmetry
Protonema	Absent	Present (juvenile stage)
Rhizoids	Unicellular	Multicellular, branched

Feature	Homosporous	Heterosporous
Spores	One kind of spore	Two kinds (Macro & Micro)
Gametophyte	Monoecious (bisexual)	Dioecious (unisexual)
Example	Dryopteris, Lycopodium	Selaginella, Salvinia

Column I	Column II
(a) Chlamydomonas	(iii) Algae
(b) Cycas	(iv) Gymnosperm
(c) Selaginella	(ii) Pteridophyte
(d) Sphagnum	(i) Moss

[Image of Gymnosperm life cycle]

• Naked Seeds: Ovules are not enclosed by an ovary wall and remain exposed.
• Plant Body: Medium to tall trees or shrubs. The sporophyte is differentiated into root, stem, and leaves.
• Roots: Generally tap roots. Some have fungal association (Mycorrhiza in Pinus) or Coralloid roots (Cycas) with N₂-fixing cyanobacteria.
• Stem: Can be unbranched (Cycas) or branched (Pinus, Cedrus).
• Leaves: Adapted to withstand extremes (needle-like, thick cuticle, sunken stomata).
• Heterospory: They produce haploid microspores and megaspores.
• Cones: Spores are produced within sporangia arranged on sporophylls which form compact strobili or cones (Male and Female cones).