MODULE - 5 Reproduction The Living World 24 Notes REPRODUCTION You are well aware that a family continues generation after generation and also that organisms produce their own kind. This process of reproducing one’s own kind ensures the continuance of the variety of organisms that inhabit the earth. Reproduction is a characteristic feature of every living being and has its own role to play in the body just like the other biological processes such as respiration, circulation, nutrition and others. In this lesson, you shall learn how new organisms gain life, grow and become ready to give rise to another generation of similar individuals. You shall also learn the importance of reproductive health and hygiene so as to prevent the spread of sexually transmitted diseases. This will enable you to make correct choices at the appropriate time. OBJECTIVES After completing this lesson you will be able to: • appreciate that reproduction is a characteristic feature of organisms for the continuance of their species and that asexual and sexual reproduction are the two different modes of reproduction; • identify the different types of asexual reproduction in organisms; • identify the sex organs and describe in brief the process of reproduction in flowering plants; • state facts about reproduction in animals with special emphasis on human reproduction; • identify the changes in the human body upon reaching puberty and emphasize importance of reproductive health and hygiene; • identify the major organs of reproduction in humans (both male and female), state their location in the body and relate each organ with its function; 116 SCIENCE AND TECHNOLOGY Reproduction MODULE - 5 The Living World • mention the reproductive events leading to pregnancy and parturition, and express concern regarding negative consequences of adolescent pregnancy; • demonstrate awareness regarding the prevention and transmission of Sexually Transmitted Diseases (STDs) and Reproductive Tract Infections (RTIs) Notes caused by microbes; • express awareness of increase in population growth and suggest methods of Species: a group into population control. which animals, plants etc. that are able to • understand modes of transmission and prevention of Human Immuno Deficieny breed with each other Virus (HIV)/Acquired Immuno Deficiency Syndrome (AIDS) and utilize this are place and information in making safe informed choices. identified by a Latin name. The members 24.1 REPRODUCTION of the group look similar and behave in You must have heard from your parents what a joyful event it was when you were the same way because they possess born! Your parents, elder relatives or family friends might have told you how the same genes e.g. happy they were to see you take your first steps! And then, as an infant, how you The Asians, the got frightened when a dog barked! Ask your parents about your infancy and Europeans, the childhood. They would certainly remember many anecdotes of the past while you Africans are all as a teenager are now busy understanding changes within yourself as you grow human beings into an adult. Note the changes as you progressed from infancy to childhood and belonging to the species scientifically thence to adolescence. named Homo sapiens. ACTIVITY 24.1 As you do so, make an album of your photographs from infancy to date. If there are no photographs, collect pictures of infants and growing children to get an idea of how changes take place in the body as one grows up. As you read this lesson, you shall begin to realize that a naturally occurring feature of all organisms is to grow up. Microbes, plants, animals all need to grow up to an extent when they are able to perpetuate their own species. Thus, the species lives on from one generation to the next. The biological process involved in the perpetuation of species is called reproduction. Reproduction may be defined as the biological process by which organisms give rise to their own kind. Reproduction may occur in two ways: — Asexual reproduction SCIENCE AND TECHNOLOGY 117 MODULE - 5 Reproduction The Living World — Sexual reproduction Bacterial and protozoan offspring may be produced by single individuals. This is termed asexual reproduction. Certain animals and many plants reproduce asexually as shown in figures 24.1 to 24.3. When two individuals are involved in Notes reproduction, it is termed sexual reproduction. In sexual reproduction, male gamete fuses with female gamete to mark the beginning of a new individual. This Offspring: is a more common mode of reproduction in plants and animals. The young ones of living organisms 24.2 ASEXUAL REPRODUCTION Reproduction by single individuals takes place in many ways in lower organisms like bacteria and protozoa and some algae. In plants, asexual reproduction is by vegetative propagation. Animals like sponges and hydra reproduce both asexually and sexually. (i) Asexual reproduction in lower organisms Asexual reproduction is of various types: (a) Binary fission: A cell may divide to give rise to two individuals and lose its own identity as in binary fission that takes place in amoeba and bacteria (figure 24.1). (b) Budding: In budding, a bud forms Fig. 24.1 Binary Fission in Amoeba from the body of the mother cell and remains attached to it. The parental nucleus elongates and then divides into two, one of which moves into the bud. Example: yeast (figure 24.2). In animals like sponges and hydra which are multicellular; a bud arises from some part of the body, Fig. 24.2: Budding in Yeast enlarges and then detaches from the parent Multicellular: body after all its body parts have organism made up of been formed (figure 24.3). many cells. (c) Spore formation: The cytoplasm and nucleus of algae such as Chlamydomonas divide Fig. 24.3: Budding in Hydra 118 SCIENCE AND TECHNOLOGY Reproduction MODULE - 5 The Living World successively to form 4 to 8 spores. Spores are also formed for reproduction in fungus, moss and fern. Spores are single cells which upon their release from the parent plant develop into new individuals Notes (figure 24.4). (ii) Asexual reproduction in plants Fig. 24.4 Spore formation in Chlamydomonas Vegetative Propagation: In nature, new plants may arise from root, stem or leaves that is from the vegetative parts of the plant as shown in fig. 24.5 (a to h). This form of asexual reproduction in plants is termed vegetative propagation. Table 24.1: Modes of vegetative propagation with examples Mode of reproduction Specialised plant part Examples (A) Natural Methods Adventitious roots Sweet potato, Dahlia (a) Roots (fig. 24.5 a&b) (b) Stem (a) Runner (fig. 24.5g) Lawn grass, (b) Sucker(fig. 24.5h) Chrysanthemum (c) Bulb (fig24.5c) Onion (d) Tuber (fig.24.5d) Potato, Canna (e) Rhizome (fig. 24.5e) Ginger (c) Leaves (f) Adventitious buds (fig. 24.5f ) Bryophyllum (B) Artificial Methods Rose, Money Plant (fig. 24.6 a to c) Jasmine, (a) Cutting Grapevine (b) Layering Citrus, Mango (c) Grafting Orchid, Chrysanthemum, Asparagus. New plants may be formed from roots (fig. 24.5 a,b) or stem (24.5 c,d,e) or leaves (fig.24.5f) or when a stem grows to a distance and then enters soil and strikes roots to form a new plant (fig. 24.5 g,h) SCIENCE AND TECHNOLOGY 119 MODULE - 5 Reproduction The Living World Notes Fig. 24.5 (a to h) Natural vegetative propagation in plants (iii) Artificial propagation in plants Humans have taken hints from natural methods of vegetative propagation to grow many plants through artificial propagation. Fig. 24.6 shows the various methods by which farmers and nursery owners multiply desired plants using the method of artificial propagation. (a): Cutting: A piece of branch is (b): Layering: A branch of the plant is laid on the cut and embedded in the soil. Roots ground and a portion is embedded in the soil. form and a new plant results. This part strikes root and gives rise to new plant. (d):(a) The lower part of the stem or scion is cut in a wedge, (b) The shoot of the plant to be used as a stock is cut off. The stem (c): Vegetative reproduction is slit vertically and the scion is inserted into the stock and tied by gootee with a tape (c) The graft union occurs within a short time Fig. 24.6 (a to d): Artificial vegetative propagation in plants 120 SCIENCE AND TECHNOLOGY Reproduction MODULE - 5 The Living World ACTIVITY 24.2 1. Take a branch from a champa tree or a money plant. Grow it. Observe how the branch produces a full fledged plant. Notes ___________________________________________________________ ___________________________________________________________ 2. You may even try to grow some grass picked up from the wild. What do you find? Under which conditions does the grass reproduce to form a carpet of grass? Write your observations in the space provided below: ___________________________________________________________ ___________________________________________________________ (iv) Other methods of asexual propagation In the laboratories, researchers have raised offspring from single parent through tissue culture. Dolly was a sheep, an exact copy of her mother, raised through cloning. (a) Micro propagation Researchers have standardized the methods of tissue culture. Every living cell or every part of a plant has been found to be totipotent, that is, it has the potential to give rise to more plants. Can you explain why? Try and answer after you have finished reading this lesson and can understand that all the cells of an individual arise from a single cell, the zygote and hence all cells have the same genes. Genes control growth, development and all the life processes. From a piece of plant, say root of carrot, or a leaf, cells can now be cultured in adequate nutrient solution to form an undifferentiated mass of cells called callus which can then give rise to new plantlets.