Revision: Kingdom Classification >> Kingdoms in Plants Biology ICSE ICSE Class 7 CISCE

Thallus refers to a plant body that is not differentiated into roots, stems, and leaves. Example: Algae.

1. Meaning - All single-celled eukaryotes act as a link between plants, animals and fungi; mostly aquatic; have a nucleus and membrane-bound organelles.

2. Chrysophytes - Includes diatoms and golden algae; cell wall has silica; deposits form Diatomaceous Earth (used in polishing and filtration); chief producers in oceans.

3. Dinoflagellates - Mostly marine, photosynthetic; cell wall of cellulosic plates; have two flagella (one longitudinal, one transverse); rapid multiplication of red dinoflagellates (e.g. Gonyaulax) causes red tides.

4. Euglenoids - Have a pellicle instead of a cell wall; photosynthetic in sunlight but become heterotrophs in its absence. e.g. Euglena.

5. Slime Moulds - Saprophytic; feed on decaying matter; undergo syngamy to form a plasmodium that spreads over several feet.

6. Protozoans - 4 types:

• Amoeboid - move by pseudopodia. e.g. Amoeba, Entamoeba
• Flagellated - have flagella; cause sleeping sickness. e.g. Trypanosoma
• Ciliated - have cilia; have a gullet for feeding. e.g. Paramecium
• Sporozoans - no locomotory organelle; all parasitic. e.g. Plasmodium

1. Meaning - Heterotrophic organisms; body made of thread-like hyphae; network of hyphae = mycelium; cell wall made of chitin; grow in warm and humid places; except yeasts, all are multicellular.

2. Nutrition - Can be saprophytic (feed on dead matter), parasitic or symbiotic (as lichens and mycorrhiza).

3. Reproduction - Asexual by spores (conidia, zoospores, aplanospores); sexual reproduction involves 3 steps - plasmogamy → karyogamy → meiosis; Ascomycetes and Basidiomycetes undergo a dikaryotic stage.

4. 4 Classes of Fungi:

• Phycomycetes - Mycelium aseptate, coenocytic; spores endogenous in sporangium. e.g. Rhizopus, Albugo
• Ascomycetes (Sac fungi) - Asexual spores = conidia; sexual spores = ascospores in ascus. e.g. Aspergillus, Neurospora
• Basidiomycetes - No asexual spores; sexual spores = basidiospores (exogenous). e.g. Agaricus, Ustilago, Puccinia
• Deuteromycetes (Imperfect Fungi) - Sexual form unknown; saprophytic/parasitic. e.g. Alternaria, Colletotrichum

5. Classification basis - Based on morphology, mode of spore formation and fruiting bodies.

6. Important examples - Puccinia (wheat rust), Penicillium (antibiotic), Agaricus (mushroom), Neurospora (genetic research).

1. Meaning- All eukaryotic, chlorophyll-containing organisms; cell wall made of cellulose; mostly autotrophic; some are insectivorous (e.g. Venus fly trap, Bladderwort) or parasitic (e.g. Cuscuta).

2. Members - Includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.

3. Alternation of generations - Life cycle has two phases - diploid sporophyte and haploid gametophyte - which alternate with each other.

4. Plant groups at a glance:

• Algae - Simple, aquatic, no true roots/stems/leaves. e.g. Seaweed, Green algae
• Bryophytes - Non-vascular, moist environments. e.g. Mosses, Liverworts
• Pteridophytes - Vascular, no seeds, reproduce by spores. e.g. Ferns
• Gymnosperms - Naked seeds in cones, no flowers/fruits. e.g. Pine, Fir
• Angiosperms - Seeds enclosed in fruits, the most diverse group. e.g. Rose, Lily

5. Key features - Have prominent chloroplasts for photosynthesis; membrane-bound organelles; the most diverse group among all kingdoms.

• Algae are simple, chlorophyll-containing, autotrophic organisms, mostly found in aquatic habitats.
• They have a thallus body without true roots, stems, and leaves.
• Algae show different forms, such as unicellular (Chlamydomonas), colonial (Volvox), and filamentous (Spirogyra).
• Reproduction occurs by vegetative, asexual, and sexual methods, including fragmentation and spore formation.
• Algae play an important role in CO₂ fixation and oxygen production, supporting aquatic ecosystems.
• They have economic importance, providing food, agar, algin, carrageenan, and protein-rich supplements like Spirulina.

• Bryophytes are called amphibians of the plant kingdom as they live on land but need water for reproduction.
• They are found in damp, humid, and shaded places and lack true roots, stems, and leaves.
• The plant body is thallus-like and attached to the substratum by rhizoids.
• The gametophyte is the dominant phase, which produces male (antheridia) and female (archegonia) gametes.
• Fertilisation requires water, forming a zygote that develops into a sporophyte (foot, seta, capsule).
• Reproduction occurs by vegetative (fragmentation), asexual (gemmae), and sexual methods.
• Economic importance: prevents soil erosion, acts as a pioneer species, provides peat (fuel), and has medicinal uses.

• Pteridophytes are vascular plants with true roots, stems, and leaves; the sporophyte is the dominant phase.
• They are the first terrestrial plants with vascular tissues (xylem and phloem).
• Leaves may be microphylls (small), as in Selaginella, or macrophylls (large), as in ferns.
• Sporangia produce spores and are present on sporophylls, often forming cones (strobili).
• Spores germinate into a haploid gametophyte (prothallus), which is small, independent, and photosynthetic.
• Fertilisation requires water, and the zygote develops into a new sporophyte.
• Some pteridophytes show heterospory (microspores and megaspores), which is an important step towards a seed habit.

• Naked seeds - Gymnosperms have ovules not enclosed by the ovary wall; seeds remain exposed before and after fertilisation.
• Vegetative features - Stem branched (Pinus) or unbranched (Cycas); leaves are needle-like with thick cuticle and sunken stomata to reduce water loss; roots are tap roots.
• Special roots - Pinus has mycorrhiza (fungal association); Cycas has coralloid roots with N₂-fixing cyanobacteria.
• Reproduction - Reproductive structures are strobili (cones); plants are heterosporous - male strobilus has microsporophylls (produce pollen); female strobilus has megasporophylls (bear ovules); pollination is by air (wind).
• Fertilisation - Pollen tube carries male gametes to archegonium → fuses with egg → zygote → embryo; ovule develops into seed; life cycle is diplontic (sporophyte dominant).
• 4 groups - Cycads (Cycas), Conifers (Pinus, Cedrus), Ginkgoales (Ginkgo biloba), Gnetales (Ephedra, Gnetum).
• Economic importance - Ephedrine (from Ephedra) for respiration; Taxol (from Taxus) for cancer; sago from Cycas; timber, resins, turpentine and paper pulp from conifers.

• Angiosperms are flowering plants with seeds enclosed in fruits.
• They show great variation in size, from small (Wolffia) to large trees (Eucalyptus).
• Classified into monocots and dicots.
• Double fertilisation occurs, forming a zygote and a triploid endosperm.
• After fertilisation, the ovary becomes a fruit, and the ovule becomes a seed.
• Life cycle is diplontic with a dominant sporophyte and a reduced gametophyte.

• Seed coat: Consists of two layers—testa (outer) and tegmen (inner).
• Hilum: A scar on the seed coat showing the point of attachment to the fruit.
• Micropyle: A small pore present above the hilum helps in water absorption.
• Cotyledons: Two fleshy cotyledons present, storing reserve food material.
• Embryo: Contains an embryonal axis with radicle and plumule at opposite ends.
• Endosperm: May be present (e.g., castor) or absent (e.g., bean, gram, pea) in mature seeds.

• Monocot seed: Usually endospermic, with endosperm storing food (except orchids).
• Endosperm: Large and bulky, separated from the embryo by a protein-rich aleurone layer.
• Embryo: Consists of a single cotyledon called the scutellum and a short embryonal axis.
• Cotyledon: Only one large, shield-shaped cotyledon present.
• Radicle and plumule: Radicle is enclosed in the coleorhiza, and plumule in the coleoptile.
• Seed structure: The seed coat is often fused with the fruit wall, and the embryo lies at one side of the endosperm.