Science Chapter 10 PDF

From the very birth of the Earth, there has been diversity in the biosphere or the living world. At present, there are approximately 87 lakh species of organisms living in the world. Not only that, new organisms are also being discovered almost every day. The diversity of the biosphere is due to...

From the very birth of the Earth, there has been diversity in the biosphere or the living world. At present, there are approximately 87 lakh species of organisms living in the world. Not only that, new organisms are also being discovered almost every day. The diversity of the biosphere is due to the different characteristics of the various types of organisms. All organisms depend on each other for their survival, so the contribution of this living world to maintain the balance of the environment is immense. These organisms have a variety of differences, their structures are different, their habitats are different, some are beneficial and some are harmful. Therefore, it is necessary to have a comprehensive idea about the classification of organisms in the biosphere. Scientists have been trying to classify this vast number of organisms for hundreds of years. With the help of classification, all the species of the world can be known easily in a scientific way, with less effort in less time. Classification is essential for identifying new species. Not only that, it provides various information and data on the inter-relationships among different organisms, and gives the idea about the gradual changes that have occurred or are occurring among them. Once upon a time, it was believed that the living organisms on Earth are divided into two kingdoms: plants and animals. However, with the scientific advancements, scientists gradually realized that this classification of living organisms into just plants and animals was not sufficient. For example, fungi are quite different from plants. They do not have chlorophyll and cannot produce their own food like plants. So, fungi are included in a separate kingdom. The discovery of the microscope led to the identification of a vast world of microorganisms, and scientists could learn about the structure of cells. Therefore, a separate kingdom is required for unicellular or single- celled organisms. But even among unicellular organisms, there are two clear divisions based on the structure of the cell: prokaryote (unorganized nucleus in the cell) and eukaryote (organized nucleus in the cell). Therefore, two different kingdoms are classified: Monera for prokaryote unicellular organisms and Protista for eukaryote unicellular organisms. With further advancements in science, scientists discovered that there are two distinct divisions called Archaebacteria and Eubacteria among prokaryote unicellular animals of the Monera kingdom, and they cannot be included in one kingdom. Consequently, at present, instead of Monera, Archaebacteria and Eubacteria are referred to as the two kingdoms. Therefore, if the living world is divided into six kingdoms: animals, plants, fungi, Protista, eubacteria and archaebacteria, it is possible to classify all organisms into specific categories. The following characteristics are considered for the classification of living organisms. 1) Number of cells (unicellular or multicellular) 2) Type of cells (prokaryotic or eukaryotic) 3) Type of nutrition (autotrophic or heterotrophic) At the same time, genetics continued progressing and organisms are divided into three domains: Eukarya, Bacteria, and Archaea, in a completely different way from the genetic structure of organisms. The related picture shows how the six kingdoms have evolved into three domains. A brief description of important characteristics the six kingdoms is presented below. It is worth mentioning that the living world is so diverse that many exceptions can be found among the characteristics mentioned above. For example, there are mammals called platypus that lay eggs, ghost plants that have no chloroplasts, protists called kelp that cover large areas, sea slugs that can photosynthesize, etc. Animal: This is the largest kingdom, with about 1 million species. They are multicellular, eukaryotic, motile, heterotrophic or parasitic, and reproduce sexually, contributing to population growth. Plant: There are about 2.5 lakh species of plants. They are also multicellular, eukaryotic, and autotrophic. Plant cells have chloroplasts and synthesize their own food through photosynthesis, and provide food for other animals in the biosphere. Apart from that, plants create oxygen and keep the biosphere alive. Fungi: There are about 1.5 lakh species of fungi. They are generally multicellular, eukaryotic, and heterotrophic or parasitic organisms. They create nutrient-rich food from perishable organic matter and play a vital role in maintaining the ecosystem. Protista: Most Protistans are unicellular, eukaryotic, and heterotrophic. Protistans can resemble animals, plants, or fungi in some aspects. Eubacteria: Eubacteria are prokaryotic, unicellular, and heterotrophic (parasitic). They reproduce through binary fission or amitosis, an asexual process. They can infect humans. Archaebacteria: Archaebacteria are prokaryotic, unicellular, and ancient bacteria. Archaebacteria have been found in adverse environments such as hot springs, deep-sea hydrothermal vents, and hypersaline places. They cannot infect humans. Because they are much different from bacteria, they are often simply called Archaea. You all know that there is another large world of acellular (noncellular) microorganisms. in addition to the six kingdoms mentioned above. An example of such microorganism, which is outside the living world, and between living and non-living matter, is the virus. In the previous class, you learnt in detail about bacteria, fungi, and Protista. In this chapter you will learn about the plant and animal kingdoms. 10.2 The Basis of the Classification of Plant Kingdom An attempt has been made to classify the plant kingdom based on various characteristics of plants. For example, various species of plants are seen around us, whose life span is one year. Again, perennial plants are also seen alongside. Some plants bear flowers, while many are flowerless. Again, there is a lot of variation in shape and size. There are various types of plants based on food preparation and food intake. For this reason, two English botanists named George Bentham (1800-1884) and Sir Joseph Dalton Hooker (1817-1911) proposed a classification system based on different characteristics of plants. This natural system of classification of plants was first published in their book Genera Plantarum written in Latin and published in three volumes. The classification of plants proposed by Bentham and Hooker is described here. They have divided the entire plant kingdom into two sub-kingdoms namely Cryptogamiae or non-flowering plants and Phanerogamae or flowering plants. 10.2.1 Cryptogamae Plants that never produce flowers are known as non-flowering plants or Cryptogamae. They reproduce by spores. Non-flowering plants are again divided into three groups in the natural system of classification: 1) Thallophyta 2) Bryophyta 3) Ptreidophyta 1। Thallophyta: All plants whose body cannot be divided into roots, stems, and leaves are included in this category. They do not have a vascular system. The reproductive organs are usually unicellular. There are about 1 lakh 10 thousand species of Thallophyta. 2। Bryophyta: Plants in this order have soft stems and leaves. Instead of roots, their bodies have filaments like rhizoids, through which they absorb essential water and mineral salts from the soil. No vascular system is seen in their body. There are about 23,000 species of Bryophyta 3। Pteridophyte: The body of pteridophytes can be divided into roots, stems and leaves. There is a vascular system in their body. The total number of pteridophytes is ten thousand. 10.2.2 Phanerogamae Plants that produce flowers (and seeds) are included in this sub-kingdom. They reproduce through seeds. Pine, mango, java plum, jackfruit etc. are examples of seed plants. This sub-kingdom is divided into two categories: 1) Gymnospermae 2) Angiospermae 1) Gymnospermae : The plants of this category do not have ovary in its gynoecium. So, they do not produce fruits. Since they do not have ovary, their seeds remain naked. That is why, they are called gymnosperms. Cycas, Pinus etc. are examples of Gymnospermae. 2) Angiospermae: These plants have ovary in their flowers, so they produce fruits, and the seeds are enclosed within the fruits. Angiosperms can be divided into two classes based on the number of cotyledons in the seed: a) Monocotyledons b) Dicotyledons a) Monocotyledons: Plants that have only one cotyledon are called monocotyledons. Their leaves have parallel venation and the roots are clustered. The vascular tissues in the stem are sparsely arranged without cambium. The number of species of monocotyledonous plants is more than 18000. Rice, wheat, banana, taro, coconut etc. are some examples of monocotyledons. b) Dicotyledons:Plants that have two cotyledons in their seeds are dicotyledons. The leaves of dicotyledonous plants are usually reticulate venation, and the root form the main root system. The trunk of these plants consists of bundles of vascular tissue with cambium and arranged in circular form. Examples of dicotyledonous plants are jackfruit, litchi, rye mustard, dhutura etc. The number of species of dicotyledonous plants is about 80 thousand. Based on the presence, absence and attachment of petals, this category is divided into three subcategories- a) Polypetalae b) Gamopetalae c) Monochlamydae a) Polypetalae: The flower petals of such plants are separate, or not connected. For example: mustard. b) Gamopetalae: Such plants have flower petals joined together, such as dhutura. c) Monochlamydae: All these plants do not have petals in their flowers. For example: jackfruit. It is to be noted here that with the advancement of modern science and a clearer understanding of the biochemical composition of plants, the work of classifying new types of plants in combination with genetics and evolution has begun.