Plant Kingdom Classification of Algae, Gymnosperms, Pteridophytes
INTRODUCTION OF PLANT KINGDOM CLASSIFICATION:
- Plant kingdom includes eukaryotic, autotrophic or photosynthetic and non-motile organisms.
- Plant kingdom includes five major plant groups i.e. Algae, Bryophyte, Pteridophyte, Gymnosperms and Angiosperms as proposed by R.H. Whittaker in 1969.
- Main characters of plant kingdom are–
- presence of cellulosic cell wall.
- non-motile, except some aquatic forms.
- reproduction is primarily sexual.
- photosynthetic mode of nutrition, e.g., different types of algae (green, brown, red algae), bryophytes, gymnosperms and angiosperms.
CLASSIFICATION OF ALGAE
Fritsch divided algae into 11 classes on the basis of type of pigments, nature of reserve food material and mode of reproduction. The three major classes are – Chlorophyceae, Phaeophyceae and Rhodophyceae.
CLASSIFICATION OF PTERIDOPHYTES
The pteridophytes are further classified into four classes:
- Psilopsida (Psilotum)
- Lycopsida (Selaginella, Lycopodium)
- Sphenopsida (Equisetum)
- Pteropsida (Dryopteris, Pteris, Ferns, Adiantum)
CLASSIFICATION OF GYMNOSPERMS
Gymnosperms are classified into three classes (Sporne, 1965). They are Cycadopsida (e.g. Cycas), Coniferopsida (e.g. Pinus, Ginkgo) and Gnetopsida (e.g. Gnetum)
PLANT LIFE CYCLES AND ALTERNATION OF GENERATIONS
- 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 fertilization the zygote also divides by mitosis to produce a diploid sporophytic plant body.
- Sexual reproduction : Plant of Cycas is sporophyte (2n) and dioecious. The sexual reproduction is of oogamous type, i.e., takes place by the fusion of distinct male and female gametes. The male and female gametes are formed by the germination of micro and megaspores which are born on microsporophylls and megasporophylls. The microsporophylls are grouped together to form a compact conical structure called male cone, whereas the megasporophylls are not aggregated to form a cone.
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