All living organisms are classified into five kingdoms. The kingdom Monera, Protista, Fungi, Plantae and the Animalia. In this section, let discuss in brief about kingdoms Animalia and Plantae, and viruses, viroids, and lichens.
Kingdom Animalia occupies the level belonging to the eukaryotic, multicellular and heterotrophic organisms in the hierarchy of classification. The organisms in this kingdom lack cell walls. They show all levels of organization in structure i.e. they range from primitive organization to proper organ system level of organization. Most of the members of kingdom Animalia are capable of locomotion. They show growth and differentiation during their lifetime and most of them are capable of the sexual mode of reproduction.
Kingdom Plantae consists of all the plants that we see around us. They belong to that level in the organization in which the organisms are classified to be multicellular, with cell wall and follow the autotrophic mode of nutrition. However, we do have a few exceptions like the pitcher plant, which is a heterotroph as it feeds on insects. There also exist a few parasitic plants like Cuscuta. The members of kingdom Plantae have a unique life cycle which follows alternation of generation between two phases – diploid sporophytic phase and haploid gametophytic phase.
Viruses, Viroids, and Lichens
Even after the establishment of the five kingdom classification, some organisms could not be placed in any of the five kingdoms. These included the viruses, viroids, and lichens. Viruses are not included in this five kingdoms as they are said to belong to their own kingdom, the kingdom Virus. Viruses could not be placed in any of the kingdoms because they are practically neither alive nor dead. Viruses basically consist of genetic material i.e. nucleic acid (DNA or RNA) surrounded by a protein capsule. Viruses take shelter on other living organisms and use the host’s machinery to replicate and produce multiple copies of them thus, resulting in a number of viruses to spread the infection.
Viruses are usually smaller than bacteria in size. The first virus to be discovered was Tobacco mosaic virus (TMV). They infect the tobacco plant.
Viroids are smaller than viruses and unlike viruses, they lack any protein coating. Thus, they are basically free living RNA.
Lichens are the symbiotic association of fungi and algae. They help each other survive – the fungi provide shelter to the algae and the algae provide food to the fungi in return. Lichens are very good indicators of pollution. They cease to grow in areas which become polluted.
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