Classification of Plants PDF

# CLASSIFICATION AND ITS NEED ## Introduction We know that the subject Biology deals with the study of living things - the plants and animals. Biologists have identified, named and grouped more than a million types of plants and animals living on this earth. In order to facilitate the study of thi...

# CLASSIFICATION AND ITS NEED ## Introduction We know that the subject Biology deals with the study of living things - the plants and animals. Biologists have identified, named and grouped more than a million types of plants and animals living on this earth. In order to facilitate the study of this vast variety of plants and animals, they have been classified into different groups. ## Classification and its need All living things are broadly classified into two main groups - **plants** and **animals**. Based on their similar characteristics, both plants and animals are further divided into various divisions or classes. On the basis of this grouping, the living organisms can be studying systematically. Thus, classification means grouping organisms together on the basis of certain common features. It is a system of putting organisms with similar characterstics into one group. In biology, classification is a system of arranging living organisms into groups based on their similarities and differences. ## Advantages of classification - It is not humanly possible to study all the plants and animals that exist in the world. Scientists have made this job simpler by classifying them on the basis of similarities. A few advantages of classification have been mentioned here: - The characteristics of all members of a group can be understood by studying only the characteristics of a few members. - Classification makes the study systematic. It highlights the relationship between different organisms. - It helps in identifying different organisms and placing them into particular groups. - It also gives us an idea about the evolution of organisms from simpler to more complex forms. ## Classification of living world Originally the living world was broadly classified into two main kingdoms - Kingdom Plantae (plants) and Kingdom Animalia (animals). But this classification presented certain anomalies. Bacteria in the original classification were classfied along with plants, but they possess characteristics of both plants and animals. Similarly, protozoans were initially put under the animal kingdom. For example, Euglena contains chlorophyll (like plants) but it is devoid of a cell wall made up of cellulose (unlike plants). At the same time it has an eye-spot like structure (like animals). Therefore, Robert Whittaker in 1969 suggested that bacteria should not be classified under plants, and protozoans should not be put under the animal kingdom. He proposed a five kingdom classification of the living world which is described below. **1. Kingdom Monera** - includes microscopic, unicellular or single-celled organisms with a cell wall, but no nucleus. They have a poorly developed nucleoid which contains the genetic material. For example, bacteria. **2. Kingdom Protista** - includes single-celled organims with a well-developed nucleus. For example, Amoeba, Paramecium, Chlamydomonas, Euglena. **3. Kingdom Fungi** - includes mostly multicellular or many-celled organisms. This group of organisms is characterised by the absence of chlorophyll. They can not synthesise their own food and depend on dead or decaying matter for their food. So, they are called saprotrophs. For example. mushrooms, yeasts, bread moulds. **4. Kingdom Plantae** - includes multicellular eukaryotes with cellulose cell wall, and chlorophyll present in their cells. They are autotrophs and conduct photosynthesis. **5. Kingdom Animalia** - includes all multicellular animals with hetrotrophic mode of nutrition. They depend on plants or other animals for food. They possess a nervous system with sense organs and unlike plants, can move from one place to another. Animals are classified into two groups, that is, invertebrates and vertebrates, based on the presence or absence of a backbone. Animals without a backbone are called invertebrates. Animals with backbone are called vertebrates. You will learn more about the classification of animals in the next chapter. ## Kingdom Monera This kingdom mainly contains bacteria. They are composed of a single cell but differ from other single-celled organisms because their nuclear material is not enclosed in a nuclear membrane but is organized in a region called a nucleoid. Since the nuclear membrane is absent, bacteria are called prokaryotes. Their cell-wall, although not made of cellulose, is a rigid structure. Many bacteria feed by absorption of externally digested food. Hence, they are called heterotrophs. Many others live on other living organisms and are called parasites. ## Structure of a Bacterium Cell - A bacterium cell has the most primitive nucleus not bound by nuclear membrane and has only chromatin material in the centre. Outermost cell wall is made up of largely protein-like material. The cell wall is surrounded by a gelatinous or proteinaceous 'capsule'. Nucleolus, mitochondria and plastids are absent. Reserve food is 'glycogen' (Fig. 2.2). ## How big are the bacteria? - The sketches below compare the sizes of our red blood cell (extreme left), a yeast cell and two kinds of bacteria - a rod-shaped and a spherical (extreme right). ## Useful Bacteria 1. **Medicines:** Antibiotics are medicines that can destroy disease causing germs in the body. Certain types of bacteria are used in the manufacture of antibiotics such as Streptomycin to treat various human diseases. These antibiotics are used in treating many plant and animal diseases also. Killed or weakened disease-causing bacteria are used in the preparation of vaccines. Vaccines are used in preventing diseases such as polio, tuberculosis, small pox, etc. 2. **Lactobacillus bacteria** is used for curdling of milk (formation of curd from milk). It converts the milk sugar (lactose) into lactic acid, giving the sour taste to the curd. 3. **Certain bacteria** like Acetobacter ferment fruit juices into vinegar (acetic acid). 4. **Tanning of leather:** Certain bacteria are used in curing of animal hides and skin. 5. **Retting of fibres:** Jute fibres are separated and made softer by the use of bacteria. 6. **Formation of compost and manure:** Cow dung, horse dung and agricultural wastes are subjected to bacterial action which causes their decay and produce very useful manure. 7. **Biogas and "gobar gas":** There are sewage plants in big cities (Delhi has one such unit) where the collected human excreta is decomposed by sewage bacteria. The inflammable gas produced in the process is collected for cooking, and the liquid and solid products are used as manure. 8. **Some bacteria** live in the large intestine of human beings (E. coli) and produce vitamins such as Vitamin B and K that are needed by the body. 9. **Bacteria** present in the intestines of herbivores, like cow and buffalo, help in the digestion of cellulose. 10. **Certain types of the Rhizobium bacteria** are found living in the root nodules (small swollen structures on roots) of leguminous plants like the pea, bean etc. These bacteria trap the nitrogen from the atmosphere and convert it into nitrates (mineral salts) which can be easily absorbed by the plants from the soil along with the water. It is observed here that the bacteria provide food to the host plant and the host plant in turn provides shelter to the bacteria. This kind of relationship wherein two organisms live in harmony, each benefitting from such a relationship is called symbiosis. The organisms are called symbionts. 11. **Certain bacteria** which are saprophytic, feed on dead organic remains. They act like scavengers, help in converting complex food material into agriculturally useful nutrients like nitrates, sulphates and phosphates. This way they increase the soil fertility, e.g. nitrifying bacteria. ## Harmful Bacteria 1. **Spoilage of food:** Food items such as milk, meat, fish and vegetables get spoiled quickly due to the presence of bacteria. Tinned and packaged foods should not be consumed after their expiry date as it can be infected by bacteria. 2. **Diseases:** Bacteria are responsible for a number of diseases, some of which are typhoid, leprosy, TB, pneumonia, cholera, etc. ## Kingdom Protista - This kingdom also consists of unicellular organisms. The nucleus here is bound by a nuclear membrane and hence, the organisms are called eukaryotes. Some are animal-like since they do not make their own food. Example, Amoeba and Paramecium. Some are plant-like since they have one or more chloroplasts and can make their own food using solar energy. Example, Euglena and diatoms. ## Amoeba - Amoeba is one of the simplest animals. It is made up of just one single cell. Being so small, it can be seen only under a microscope. ### Where is amoeba found? - Amoeba is found in ponds, ditches and other places with stagnating water. When seen under the microscope, it looks like as shown in the Fig. 2.4. ### The body of Amoeba - The body of Amoeba is irregular in shape. The outer covering of the body is the cell membrane. A prominent nucleus lies in the centre surrounded by cytoplasm. ### How an Amoeba moves - The organ of locomotion in an amoeba is the pseudopodium (meaning false foot, plural: pseudopodia). It is a finger-like projection formed temporarily by the extension of cytoplasm along with the cell membrane in a particular direction. Many pseudopodia may be seen projecting out from the body of an amoeba at a time. But only one of them extends longer than the others towards the direction it wants to move in. This type of movement is often termed as the "amoeboid movement". ### How an amoeba feeds - When the amoeba senses food in its immediate surroundings, it quickly puts out its pseudopodia and moves towards it. On reaching the food particle, it extends two of its pseudopodia and surrounds the food particle. The tips of the two pseudopodia fuse together to form a small space with the food inside it. A food vacuole is thus formed (Fig. 2.6). ### How amoeba "Excretes" - Ammonia is the main waste product that is formed in the body of an amoeba. This is eliminated from the body through the general body surface by the simple process of diffusion. ### How amoeba respires - In amoeba, exchange of gases occurs through the cell membrane. Oxygen from the surrounding water diffuses into the cytoplasm and carbon dioxide from the body of the amoeba diffuses out into the surrounding water. ### How amoeba reproduces - Amoeba reproduces by splitting into two. In a full-grown Amoeba, first the nucleus divides into two, and then the rest of the cell divides in a way that each half gets one daughter nucleus. This process is called binary fission (binary = two; fission = division). The two daughter amoebae live independently, grow to full size and divide again (Fig. 2.8). ## Kingdom Fungi - The fungi may be unicellular (e.g. Yeast), multicellular or filamentous. Their nuclei are distributed throughout the cytoplasm. Since, they do not have chlorophyll, as such they can not prepare their own food. They mostly live on dead decaying organic matter, so they are called saprophytes. ### What are some examples of Fungi? - The fungi include fairly familiar organisms such as mushrooms, toadstools, and the bracket fungi that grow on tree-trunks. There are also the less obvious, but very important, mould fungi which grow on stale bread, cheese, fruit or other food items. ### Bread Mould - The bread mould is a type of fungi commonly seen growing on stale bread. Its body is made of thread like structures called hyphae (sing: hypha). A network of hyphae is called mycelium. Mature, erect structures bearing rounded bodies at its tip start developing from the hyphae. The erect hyphae are called the sporangiophores and the rounded bodies are the sporangium. These are the spore containing bodies. When the sporangium bursts open, the spores are dispersed into the air. When they land on a suitable substratum, each can grow to form a new mycelium (Fig. 2.9). ### Respiration in bread mould - Respiration in the bread mould is mainly aerobic. They respire in the presence of oxygen, that is why they are seen growing on the top layer of the bread, and not in the lower layer. - Saprophytic mode of nutrition is seen in the bread mould. Saprophytes obtain their nourishment from dead and decaying organic matter. - The hyphae of the bread mould secrete digestive juices into the bread. These enzymes convert the starch present in the bread into a simple sugar glucose. This is then absorbed through the body surface and stored as glycogen. Thus we see that digestion occurs outside the body of the mould and the nutrients are absorbed directly into the hyphae. ## Useful Fungi 1. Fungi are an important source of food. Some mushrooms such as Morchella and Agaricus are edible. 2. Yeast, a unicellular fungus, is important in bakeries as it is used in the making of bread. It is also important in the breweries for making alcohol. 3. Yeast slso produces vitamin B. 4. Fungi, like bacteria, are also good decomposers. They decompose dead organic matter and return the nutrients back into the soil. 5. Penicillin an important antibiotic is obtained from a fungus called Penicillium notatum. 6. Some species of Mucor and Penicillium are used in the ripening of cheese. ## Harmful fungi 1. Some moulds are responsible for the spoilage of food, leather goods and textiles. 2. Many of the crops are susceptible to fungal attacks. This causes huge losses to farmers. 3. Fungi cause serious skin and lung infection in human beings. Athlete's foot and ringworm are some common fungal infections that are seen in humans. ## Kingdom Plantae - It is the second largest kingdom of organisms after the animal kingdom There are over 250,000 species that make up this kingdom. The constituent organisms of this kingdom are multicellular and eukaryotic. They are characterized by the presence of a green pigment called chlorophyll. Because of this pigment, plants are capable of producing their own food via photosynthesis. Hence, plants are autotrophic organisms which provide food and oxygen to other living organisms for their survial. Life on earth, in other words, is possible because of plants. The plant kingdom can further be divided into algae, mosses, ferns and flowering plants. ### Algae (sing. Alga) - Algae are aquatic in habitat. These may be unicellular or multicellular. They are usually green, having chlorophyll. e.g. Spirogyra (Fig. 2.10). Some algae, however, have colours like red and brown also. ## Table: Differences between algae and fungi | Algae | Fungi | |---|---| | 1. Chlorophyll present. | 1. Chlorophyll absent. | | 2. Photosynthetic organisms synthesizing their own food. | 2. Heterotrophic organisms usually living on dead and decaying organic matter and are called saprotrophs. | | 3. Are mostly aquatic, found in fresh as well as marine water. | 3. Are mostly terrestrial i.e. growing on land. | | 4. Body not differentiated into root, stem and leaves, and is known as a thallus. | 4. Body is composed of thread-like structures called hyphae, and is known as a mycelium. | | Example: Spirogyra, Ulothrix, etc. | Example: Agaricus, Penicillium, etc. | ## Mosses (Bryophyta) - Mosses grow as green, velvety layers in moist places such as damp soil, on the bark of trees, and on damp walls. These plants have stems and leaves, but no roots. Instead, they have thread-like structures called rhizoids which stick to the surface and absorb water. They are also called 'amphibians of the plant group' as they need water to reproduce. ## Ferns (Pteridophyta) - Ferns are grown in most of the gardens for their beautiful leaves. They bear well-formed leaves, stems and roots, but do not produce flowers and seeds. ## Gymnosperms - The group of plants that bear seeds but no fruits are called gymnosperms. Their seeds are thin and naked, not enclosed in fruits (gymno means naked; sperm means seed). ### Gymnosperm characteristics - Most gymnosperms are evergreen i.e. they do not shed all their leaves at one time. Some examples are pine, fir, cedar (Fig. 2.14) and spruce trees that grow in mountainous areas. Pine and fir are usually big trees. They do not bear true flowers, but they bear seeds inside the cones (Fig. 2.14). Some cones are male while others are female. ## Angiosperms - The group of plants which bear flowers, fruits and seeds are known as angiosperms ("angios" means "case", referring to the fruit, and "sperm" means "seed"). Their seeds are enclosed in a fruit. Some common examples are cashewnut, mango, peas, etc. In angiosperms, the seeds develop within the female part of the flower, called ovary. The ovary grows into a fruit containing the seeds inside. ### Types of Angiosperms - Angiosperms are characterised by the presence of "seed-leaves" or cotyledons that store food and form the bulk of the seed (Fig. 2.17). On the basis of their number, angiosperms are divide into the following two categories: 1. **Monocotyledons:** Plants containing only one cotyledon or one seed leaf in their seeds. Examples: rice, grass, maize, etc. (Fig. 2.18). 2. **Dicotyledons:** Plants containing two cotyledons or two seed leaves in their seeds. Examples: rose, balsam, mango, sunflower, pea, brinjal, etc. (Fig. 2.19). ## Table: Differences between monoctyledonous and dicotyledonous plants | Monocotyledonous plant | Dicotyledonous plant | |---|---| | 1. Seeds have a single cotyledon. | 1. Seeds contain two cotyledons. | | 2. Leaves have parallel venation. | 2. Leaves with reticulate venation. | | 3. Fibrous root system is present. | 3. Tap root system is present. | | 4. Stem usually hollow. | 4. Stem mostly solid. | | Example: Rice, grass, etc. | Example: Pea, rose, etc. |