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Diversity of organisms. ~ Algae ~ Bryophytes ~ Ferns ~ Angiosperms ~ Gymnosperms. Evolution . Algae.
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Diversity of organisms ~ Algae ~ Bryophytes ~ Ferns ~ Angiosperms ~ Gymnosperms
Algae • This is a collective name for a varied group of phyla with no one diagnostic feature. They are normally aquatic or live in damp terrestrial habitats. Subdivisions are mainly associated with biochemical differences related to photosynthesis.
Algae are without roots, stems or leaves. • All contain chlorophyll and so can make their own food by photosynthesis. • The cells are long and their cellulose cell walls are covered by a layer of mucilage. • The major are green, but some are brown or red.
Type of algae Green algae Brown algae
analipus Example of algae egregia
Bryophytes • Bryophytes are small green plants with simple leaves, stems but no roots. • They grow close to ground, and usually do not grow more than 2cm in length. • They do not have vascular tissue which enables the plant to grow tall, and which they have no support to be stiff. • They are anchored in the ground by delicate structure called Rhizoid. • They live in damp places.
- The life cycle of Bryophytes begins with the release of haploid spores. Spores that geminate begin cell division, this produces the filament that will eventually form a gametophyte.
Ferns • Ferns consist of true stems, roots, leaves and vascular tissues. • Their roots grow horizontally underground • The preferred habitat of a fern is in the wetlands, or in moist woody areas; they also prefer damp shaded area. • They need water for fertilization. • As for reproduction, they reproduce by spores and vegetatively by rhizomes, which are horizontal underground stems.
Gymnosperms(conifers) • Gymnosperms are large evergreen trees with seeds growing inside cones for reproduction. • Most of them have needle-shaped leaves. • It does not have flowers but seeds. The seeds are naked. They are not enclosed in food and borne on structure called cones. Example is pine.
In conifers, the region of primary cell wall in the centre of the pit is thickened with a deposit of waxy material, forming a structure known as a torus. The phloem of conifers contains sieve cells, fibres, and parenchyma cells, but companion cells are absent.
Pine Examples of gymnosperms
Angiosperms • All angiosperms have flowers for reproduction. • Their seeds are produced inside the ovary. • Angiosperms form the dominant terrestrial vegetation today. • They are found in a wide range of habitats and have even re-established themselves in freshwater and the sea.
- They are extremely well suited to life on land both in their morphology. - They are divided into dicotyledons and monocotyledons.
Lily Morphology of herbaceous monocotyledon
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