SO1BI Chapter 5 - Viruses and Living Things PDF

# Chapter Five: Viruses and Major Groups of Living Things ## Introduction There are many species of living organisms in the world. These organisms are placed in groups based on their common or shared characteristics. Each group has its own features that make it distinct from others. In this chapter...

# Chapter Five: Viruses and Major Groups of Living Things ## Introduction There are many species of living organisms in the world. These organisms are placed in groups based on their common or shared characteristics. Each group has its own features that make it distinct from others. In this chapter, you will learn about viruses and five kingdoms of organisms, namely, Monera, Protoctista, Fungi, Plantae and Animalia. The competencies developed will enable you to distinguish members of these groups, understand their interrelationships and explore their importance to human beings and other organisms. ## Think A world without the knowledge of cells. A virus is not a cell. ## Viruses ### 5.1 From the library and reliable internet sources, search for information about the characteristics, advantages and disadvantages of viruses. A virus is an extremely small fragment of nucleic acid (DNA or RNA) surrounded by a protein coat. It is smaller than a living cell. ### Characteristics of viruses - They do not have a nucleus, cytoplasm, or a cell organelle. - They have a simple structure consisting of a small piece of nucleic acid (DNA or RNA) surrounded by a protein coat called a capsid. Some viruses have viral envelopes. These are membranes enclosing the capsids. The envelopes are made up of proteins from the host cell. - They cannot reproduce on their own. They must attack a host cell and use the materials in that cell to reproduce. This is called obligate parasitism. The ability of a virus to reproduce inside the cell and crystallize in the absence of a living host places them between living and non-living things. - They do not show any symptoms of life (do not grow, feed, excrete, or respire). They exist in a dormant state. - They are host-specific. This means that a certain type of virus attacks only a specific host. For example, the rabies virus affects only mammals and HIV attacks only certain types of white blood cells in human beings. - They are infectious: This means they can cause diseases to their hosts. ### The structure of viruses Viruses are composed of strands of genetic material (DNA or RNA) which forms the core. The core is enclosed by a protein coat called capsid as in bacteriophage. DNA or RNA are of various shapes and sizes according to the type of the virus. ### Advantages of viruses - Viruses are important in the study of cell and molecular biology. - They are used by scientists to manipulate and investigate the functions of cells. - Some viruses are used to make vaccines. - Bacteriophages are viruses that attack bacteria. They help in controlling bacterial infections and diseases. - Some viruses are used in biological control to eradicate pests, such as insects. ### Disadvantages of viruses - Most viruses are pathogenic. - They can alter themselves often, and thus become difficult to cure viral infections. ## Kingdom Monera Kingdom Monera consists of bacteria and blue-green algae. The scientific study of bacteria is called Bacteriology. ### Characteristics of bacteria - They are prokaryotic as their cells lack a well-defined nucleus. - They are small unicellular organisms. - Some are free-living while others are parasites or saprophytes. - They have a slimy outer layer. - They reproduce asexually - They occur in various shapes. There are five known shapes of bacteria. - Spherical-shaped bacteria or cocci (singular is coccus) - Rod shaped bacteria or bacilli (singular is bacillus) - Spiral-shaped bacteria or spirilla (singular is spirillum) - Comma-shaped bacteria or vibrio (singular is vibrion) - Corkscrew bacteria or spirochaetes - ## Kingdom Protoctista Members of this kingdom include Amoeba sp., Euglena sp., Plasmodium sp., Paramecium sp., and Trypanosoma sp. ### Characteristics of protoctists - They are eukaryotic as they have nucleus and other membrane bound organelles. - Most of them are unicellular organisms. - Most of them live in or near water, or in moist places. - Some protoctists are autotrophs (manufacture their own food) while others are heterotrophs (obtain nutrients from other organisms). - They include mobile and sessile species. - Some protoctists reproduce sexually and others asexually while others reproduce both sexually and asexually - Many protoctists have locomotory structures, such as cilia, flagella or pseudopodia. ### Phyla of kingdom Protoctista - **Phylum Rhizopoda** : Organisms in this phylum move and feed using structures known as pseudopodia. - **Phylum Euglenophyta** : This phylum consists of unicellular aquatic organisms most of which live in freshwater and possess flagella. - **Phylum Apicomplexa** : Organisms found in this phylum are unicellular and parasitic. - **Phylum Ciliophora** : Organisms found in this phylum are unicellular and are found in aquatic habitats. - **Phylum Zoomastigina** : Organisms found in this phylum are unicellular flagellate protoctists. ## Kingdom Fungi Members of the kingdom Fungi have the following general characteristics: - They are found in various places including air, water, soil, food, and in the bodies of animals and plants. - They are eukaryotic organisms with true nucleus which is enclosed in a nuclear membrane. - They can be either unicellular, example yeast or multicellular, examples mould and mushroom. - Their body is made up of a mycelium consisting of a network of fine, tube-like filaments called hyphae (except yeast). - They feed saprophytically, for example mushroom; but some of them are parasitic for example Candida albicans. - They reproduce both sexually by spores and asexually by budding. - They store carbohydrates in the form of glycogen. The members of kingdom Fungi are classified into different phyla. - **Phylum Ascomycota**: Members of this phylum are commonly called ascomycetes or sac fungi. -**Phylum Zygomycota**: The members of this group are known as zygomycetes. - **Phylum Basidiomycota**: Members of the phylum Basidiomycota are called basidiomycetes. ## Kingdom Plantae Kingdom Plantae is composed of a wide variety of plants. Members of this kingdom vary greatly in size, forms, habitat, means of reproduction, and morphology. Kingdom Plantae includes; moss, ferns, cone bearing plants, and flowering plants. Plants are found in various habitats, such as on land, in oceans, and in freshwater. ### General characteristics of members of the kingdom Plantae - They are multicellular and eukaryotic organisms. - They have cell organelles called chloroplasts that contain chlorophyll. - They are photoautotrophs. - Some plants reproduce sexually through flowers or cones while others reproduce asexually by means of spores or vegetative propagation. - Their cells are organised into tissues, organs, and organ systems. - They show limited movement. ### Divisions of Kingdom Plantae The kingdom Plantae is divided into four main divisions. These are: division Bryophyta; division Filicinophyta or Pteridophyta; division Coniferophyta; and division Angiospermophyta. ## Kingdom Animalia Kingdom Animalia comprises wide varieties of animals. Animals vary greatly in their structure, morphology and the way their bodies function. Kingdom Animalia includes worms, insects, and higher animals. They are found in various habitats, such as on land, in oceans, and in freshwater. ### General characteristics of animals - They are eukaryotes. - They are multicellular. - They depend on other organisms as a source of their food. - Most animals are mobile. - Most of the animals have bilateral symmetrical bodies. - Most of the animals have high level of tissue differentiation and specialised body organs. - Most of the animals have a well-developed nervous system. - Most of the animals have anterior and posterior ends. - The majority of the animals digest food internally. ### Phyla of the kingdom Animalia Kingdom Animalia comprises several phyla. However, only five phyla will be covered in this section. These are: - **Phylum Platyhelminthes**: includes pork tapeworm (Taenia solium), beef tapeworm (Taenia saginata), liver flukes (Fasciola species), blood flukes (Schistosoma species) and planaria. - **Phylum Nematoda**: includes ascaris, hookworms and filarial worms. - **Phylum Annelida**: includes earthworms, leeches and their marine relatives, such as ragworms and lugworms. - **Phylum Arthropoda**: includes prawns, crabs, ticks, spiders, butterflies and cockroaches. - **Phylum Chordata**: includes advanced organisms, such as human beings, cattle, fish, chicken, frogs and snakes. ## Revision Exercise 5 Choose the correct answer in questions 1- 7. 1. The following are diseases caused by fungi in plants and animals EXCEPT - wheat rust and maize rust - candidiasis - influenza - powdery mildew 2. Which of the following is the advantage of bryophytes? - They cause fungal diseases in human beings - They help to retain water in the soil - They reproduced resins - **They are goof sources of timber** 3. One of the following plants is an example of conifers. - Mango tree - Orange tree - Coconut tree - **Pine tree** 4. Which of the following groups of organisms belong to the same Phylum? - Liver fluke, hook worm, earthworm, and spider - **Tapeworm, earth worm, grasshopper, and rat** - Butterfly, grasshopper, frog, and elephant - Crabs, grasshopper, spider, and centipede 5. Which of the following is among the distinctive features of annelids? - Their bodies have similar body segments - They have a cylindrical, elongated and unsegmented body - They are dorso-ventrally flattened - **They have suckers, hooks or both** 6. Which animals is not a distinctive feature of animals? - They depend on other organisms as source of food - Most of animals are capable of locomotion - They have well developed nervous system - **They have exoskeleton** 7. Which of the following is correctly matched? - Platyhelminthes - segmented worms - Nematoda - round worms - Annelida - jointed appendages - **Arthropoda -flatworms** ## Write TRUE for a correct statements and FALSE for an incorrect statements in the spaces provided. 8. **TRUE** A virus is an extremely small organism. 9. **FALSE** Kingdom Monera includes Amoeba sp. 10. **FALSE** Plasmodium sp. is a parasite that causes sleeping sickness. 11. **TRUE** Rhizoids are found in moulds and mosses. 12. **TRUE** Coniferophyta is one of the divisions of the Kingdom Plantae. ### Explain the effects of the following organisms to humans. - **Entamoeba sp.** can cause amoebic dysentery. - **Plasmodium sp.** can cause malaria. - **Trypanosoma sp.** can cause sleeping sickness. ### List characteristics of phylum to which Euglena sp. belongs. - Phylum Euglenophyta - They are unicellular. - They possess both plant and animal characteristics. - They can move using a flagellum ### A bread was put in a moist cupboard. After a few days black thread-like structures which ended up in club-like structure appeared on the bread. **(a) Write the common name of the organism that grew on the bread surface.** - Bread mould **(b) Name the kingdom to which the observed organism belongs.** - Kingdom Fungi **(c) Name the phylum or division in which the observed organism belongs.** - Phylum Zygomycota **(d) Outline the advantages of the members of the kingdom you mentioned in (b)** - They feed saprophytically, for example mushroom; but some of them are parasitic for example Candida albicans. - They are used in food manufacturing industries - They are used in making lactic acid, citric acid, cheese, and commercial enzymes. - They are used in production of drugs - Most species of fungi are used in genetic engineering and biological researches. - They are very important in the decomposition of dead organisms and waste materials. ### What features make cockroach and human being to belong in the same kingdom? - They are both eukaryotes - They are multicellular ### Classify each of the following organisms to phylum level; (a) tape worm, (b) housefly and (c) monkey. - **Phylum Platyhelminthes** - **Phylum Arthropoda** - **Phylum Chordata** ### Mtakuja villagers believe that all insects are dangerous. They decided to kill them by spraying insecticide. As a biologist, convince them that insects are beneficial to their lives. Insects play a vital role in maintaining a healthy ecosystem. They are essential for pollination, pest control, decomposition, and food sources for many animals. - **Pollination:** Insects help to pollinate flowers, which is essential for the production of fruits and vegetables. - **Pest control:** Some insects eat other insects that can harm crops. - **Decomposition:** Insects break down dead plant and animal matter, which helps to recycle nutrients back into the soil. - **Food source:** Insects are an important food source for birds, amphibians, and reptiles. Instead of killing all insects, we should focus on understanding the vital role they play in our ecosystem and find ways to co-exist peacefully with them.