As this topic is important for competitive examinations like SSC CGL, UPSC, etc. in this article, we will look into kingdom Plantae and its characteristics.
1. The current estimate of the total number of plant species is around 400,000. Though new species are being identified, calculating their accurate number is a complicated process as a single specie is often known in different regions by different names. In order to simplify their study, the kingdom plantae is divided into five major categories, namely algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
a. Cell type: Eukaryotic
b. Cell wall: Present (Cellulose)
c. Nuclear membrane: Present
d. Mode of nutrition: Autotrophic
2. A few members such as insectivorous plants or parasites are partially heterotrophic. Bladderwort and Venus flytrap are examples of insectivorous plants, while Cuscuta is a parasite.
3. Plants are the foundation of all terrestrial habitats and serve as the Earth’s primary autotrophs, producing organic molecules that will cycle through the food webs of most ecosystems.
4. Here, we will describe Plantae under Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.
a. Algae are chlorophyll-bearing (green pigment present in plants and cyanobacteria which helps to absorb light in order to provide energy for photosynthesis), simple, thalloid, autotrophic and largely aquatic (both freshwater and marine) organisms. They occur in a variety of other habitats, namely moist stones, soils, wood, etc.
b. Algae reproduce by vegetative, asexual and sexual methods. Fragmentation is a type of vegetative reproduction wherein a fragment develops into a thallus (undifferentiated body).
c. Asexual reproduction takes place by the production of spores, most commonly zoospores. They possess flagella (slender thread-like structure which aids mobility) and on germination give rise to new plants.
d. Sexual reproduction takes place through fusion of two gametes. Some gametes are flagellated and similar in size (as in Chlamydomonas) or non-flagellated (non-motile) but similar in size (as in Spirogyra). This is called the isogamous mode of reproduction, while fusion of two gametes dissimilar in size, as in the case of some species of Chlamydomonas, is termed as anisogamous.
e. The fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete is known as oogamous. For e.g., Volvox, Fucus.
f. Algae play a major role in carbon dioxide fixation (nearly 50% of it) by photosynthesis (process which utilises sunlight to convert light energy into chemical energy).
g. They are the primary producers of energy-rich compounds that form the basis for food cycles of all the aquatic animals. Porphyra, Laminaria and Sargassum are types of marine algae used as food.
h. Some brown and red marine algae produce huge amounts of hydrocolloids (water-retaining substances). Some examples include algin (brown algae) and carrageenan (red algae), which are used commercially.
i. Agar, one of the commercial products obtained from Gelidium and Gracilaria, is used to grow microbes and in preparation of ice-cream and jellies.
j. Chlorella, a unicellular alga rich in proteins is used as a food supplement by space travellers.
k. Algae are used for the purpose of bioremediation. Many pollutants present in water, especially heavy metals, are essential for the growth of algae. For e.g. iron (for photosynthesis), and chromium (for metabolism).
The use of algae for this purpose has several advantages over the normal bacteria-based bioremediation process, including the removal of pollutants without the requirement of oxygen i.e in the presence of light.
l. Algae can be used as an alternative to chemical dyes. For e.g. natural pigments like chlorophyll (green-coloured pigment) and carotenoids (yellow to orange-coloured) can be used instead of the chemical dyes.
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