Introduction
Plants are multi-multicellular, predominantly photosynthetic and eukaryotic organisms. They have well-defined body parts and their cell wall is composed of cellulose. They develop from embryos. Their stored carbohydrate is starch and they are non-motile. It is the second largest kingdom of living organisms comprising over 3,60,000 species.
The major groups of plants are bryophytes, seedless vascular plants, and seeded plants (gymnosperms and angiosperms). The angiosperms are very diverse and the largest group. Plants live in almost all sorts of habitats. i.e., deserts, mountains, tundra, tropical and subtropical regions as well as in water. The outline of the classification of the kingdom Plantae is given below.
8.1 The evolutionary origin of plants
The evolution of plants has resulted in widely varying levels of complexity. started from green algae through bryophytes, lycopods, and ferns to the complex gymnosperms and angiosperms.
8.1 The evolutionary origin of plants
The evolution of plants has resulted in widely varying levels of complexity. started from green algae through bryophytes, lycopods, and fers to the complex gymnosperms and angiosperms.
Evidence of the appearance of the first land plants is traced back to the Ordovician period about 450 million years ago. Land plans began to diversify in the late Silurian period about 430 million years ago. By the middle of Devonian, many of the features recognized in plants today were present, including roots and leaves.
Evolutionary innovation continued from more carboniferous and is still an ongoing process. Researchers have identified a lineage of green algae called charophytes as the closest relatives of land plants. Both groups i.e., land plants and charophytes share some common features like minimizing the loss of organic products as a
The high percentage of cellulose in their cell wall. The presence of peroxisome enzymes results in photorespiration Similar structure of flagellated sperms. Formation of phragmoplast during cell division
8.1.1 Diagnostic features of plants
Some of the diagnostic features of plants are as fo9981
The majority of plants are stationary and remain fixed in one place. Most plants are differentiated into roots, leaves, and tissues (except bryophytes). stems and mostly have vascular
Plants possess chlorophyll and hence have the ability of photosynthesis. Plants possess cuticles to prevent water loss by transpiration. The plant cells have cell walls chiefly composed of cellulose. The phenomenon of alteration of generation exists in plants.
Bryophytes (Non-Vascular plants)
The bryophytes are non-vascular planes having dominant gametophytes and dependent sporophytes attached to gametophytes. They are homosporous Bryophytes and possess the following characteristics. They are the first land plants that evolved from green algae.
They are poorly adapted for life on land so they are present mostly in damp shady places near water and need water for their fertilization called amphibious plants. They have no vascular tissues thus transport of minerals and food substances takes place by diffusion.
The gametophyte generation is dominant, green, and photosynthetic while sporophyte is non-photosynthetic and dependent on gametophyte.
8.2.1 Life cycle of Moss
Like other plants bryophytes (Mosses) also show alteration of generation. Alteration of generation is a phenomenon in which gametophyte and sporophyte generations regularly alternate with each other.
The bryophytes differ from other groups of plants in their life cycle. In bryophytes, gametophyte generation is dominant, photosynthetic, and independent while sporophyte is dependent and non-photosynthetic
Gametophyte Generation:
The gamete-producing generation is called gametophyte generation. It is haploid generation. The gametes are produced by mitosis. The male and female gametophyte generations are usually separated in the case of mosses. The male gametophyte produces sperm while the female gametophyte produces eggs.
The gamete-producing organs (sex organs) are the antheridium and archegonium. The sex organs are intermixed with some multicellular hair-like structures called paraphyses. The sperm is motile and needs water for reaching to the egg in the archegonium.
This fertilization occurs in archegonium. The egg is large and non-motile, containing a large amount of food for nourishment in the early stage of the embryo.
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