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BIOLOGY FOR CLASS IX Class IX Chapter #15 Reproduction Content Types Of Reproduction Asexual Reproduction In Plants Vegetative Propagation Of Flowering Plants Advantages And Disadvantages Of Vegetative Propagation Uses Of Artificial Propagation By Cutting, Grafting And Cloning Sexual Reproduction In Flowering Plants Life Cycle Of A Flowering Plant(Angiosperm) Importance Of Pollination To Agriculture Dispersal Of Seeds And Fruits Seeds And Its Germination Reproduction And Development In Animals Reproduction And Development In Frog Reproduction The process by which plants and animals give rise to offspring and which fundamentally consists of the segregation of a portion of the parental body by a sexual or an asexual process and its subsequent growth and differentiation into a new individual. Asexual reproduction A form of reproduction that does not involve meiosis, ploidy reduction or fertilization, and the offspring is a clone of the parent organism;because of no exchange of genetic material. vegetative reproduction A form of asexual reproduction in plants, in which multicellular structures become detached from theparent plant and develop into new individuals that aregenetically identical to the parent plant. For exam ple,liverworts and mosses. Bulbs Bulbs, such as daffodils, form lateral buds from the base of the mother bulb, which produce new smaller bulbs or bulbels in subsequent years. Rhizomes . Rhizomes are root-like stems that grow horizontally under the ground. New roots and shoots form at the nodes with shoots growing upwards to form new plantlets. Lateral buds grow out to form new rhizomes. Examples include iris and root ginger. Stolons Stolons or runners are horizontal stems that grow above the ground, for example, strawberries. Tiny plantlets form along the stolon, and roots form where they touch the ground. When the connection with the parent plant breaks, the new plant becomes independent. Tubers Tubers are swollen portions of an underground stem that store food so a plant can lie dormant over the winter, for example, potatoes. Axillary buds, commonly known as ‘eyes’, form over the surface of the tuber and produce shoots that grow into a new plant the following year. Advantages of Vegetative The offsprings are genetically identical and therefore advantageous traits can be preserved. Only one parent is required which eliminates the need for special mechanisms such as pollination, etc. It is faster. For example, bacteria can multiply every 20 minutes. This helps the organisms to increase in number at a rapid rate that balances the loss in number due to various causes. Many plants are able to tide over unfavourable conditions. This is because of the presence of organs of asexual reproduction like the tubers, corm, bulbs, etc. Vegetative propagation is especially beneficial to the agriculturists and horticulturists. They can raise crops like bananas, sugarcane, potato, etc that do not produce viable seeds. The seedless varieties of fruits are also a result of vegetative propagation. The modern technique of tissue culture can be used to grow virus-free plants. Disadvantages of Vegetative Propagation The plants gradually lose their vigour as there is no genetic variation. Since many plants are produced, it results in overcrowding and lack of nutrients. Uses Of Artificial Propagation By Cutting, Grafting And Cloning Cutting Cutting involves removing a piece of the parent plant - stem, root or leaf, and planting it in a suitable medium. At first roots are produced and then the shoot with the leaves. If a stem is taken, it must contain the nodal region. In some cases, rooting hormone may be required to initiate root formation.For example: Stem cutting is commonly done for rose, sugarcane, banana, geranium, etc., Root cutting is done for dahlia Leaf cuttings are used for African violets. Layering Layering is the method of ind5ucing certain branches of the parent plant to produce roots by bending and pegging them to the ground around the parent plant leaving the tips exposed. Once the roots develop the branch is then cut off from the parent body. The branch that produces the roots is called the layer. It is a natural method in plants such as black raspberries. However, it is induced in plants like Jasminum, Rhododendron, strawberries, Magnolia, etc. Grafting It is the transfer of a part of one plant to the stump of another plant. The part taken from a plant is a portion of the stem with many buds. This portion is called scion and is selected for the quality of its fruit. The stump to which the scion is attached is called the stock. Stock is selected for qualities such as disease resistance and hardiness. The cut ends of both the scion and stock are shaped such that they complement each other and their cambial tissues are close to each other. The two cut ends are brought together and covered with grafting wax. After some time, the tissues of the scion and the stock become continuous. The plant bears flowers and fruits characteristic of the scion.It is commonly practised on apple trees and on such plants which either do not produce viable seeds or the seeds which have a lot of variation. Budding or Bud Grafting It is a variation of the grafting method explained above. In this method, the scion is a bud along with some bark. A 'T'-shaped cut is made on the stock into which the scion is inserted and bound with a tape. Three Stages of Bud Grafting - Method of Cleft Grafting The bud, once fixed, gives rise to new branches. For example, bud grafting is done on roses, plums, peaches, pears, citrus, etc. Sexual Reproduction in flowering plants The structure of a flower Petals: Brightly coloured structures used to attract insects by their bright colour and scent. Sepals: Green leaves around the outside of the flower. Sepals are usually smaller than the petals,. Used to protect the flower while it is still in bud. Stamens: Male part of the flower. Consist of two parts: the filament (a thin stalk) and the anther ( a swelling at the top of the stalk). Pollen, which contains the male gamete, is formed on the anther.(Anther + filament = stamen) Carpel: Female part of the flower. Contains the ovary, stigma and style. The ovules, which contain the female gamete, are found in the ovary.(Stigma + style + ovary = carpel) Angiosperm Life Cycle The Stages of the Flower Life Cycle The plant life cycle starts when a seed falls on the ground. There are many different kinds of plant life, but the flowering plants, or angiosperms, are the most advanced and widespread due to their amazing ability to attract pollinators and spread seeds. Flowers are more than beautiful objects to look at or decorate with; they serve a very Important purpose in the reproduction of plants. The major stages of the flower life cycle are the seed, germination, growth, reproduction, pollination, and seed spreading stages. Seed Stage The plant life cycle starts with a seed; every seed holds a miniature plant called the embryo. There are two types of flowering plant seeds: dicots and monocots. An example of a dicot is a bean seed. It has two parts called cotyledons in addition to the embryo. The cotyledons store food for the plant. Cotyledons are also the first leaves that a plant hasthey emerge from the ground during germination. Monocots have only one cotyledon-the corn seed is an example. Both kinds of seeds have the beginnings of a root system as well. The hard outside of the seed is called the seed coat and it protects the embryo. Some seeds are capable of growing even after many years if they are kept cool and dry. Seed Stage Germination When a seed falls on the ground, it needs warmth and water in order to germinate; some seeds also need light. Dicots have seed coats that soften with moisture. After being planted in the soil for a few days, the seed absorbs water and swells until the seed coat splits. Monocots have harder seed coats that do not split, but stay in one piece. The stem, called the hypocotyl, pushes through the soil along with the ,or seed leaves; this is called germination, or sprouting. The tiny root pushes down and grows, looking for water and nutrients. Soon the cotyledons fall off and the firsttrue leaves emerge. It is important that the seed is planted in the right place at the right time in order for it to germinate. Some seeds need to go through a fire in order to sprout, such as prairie grasses. Some need to go through the stomachs ofanimals, or be scraped. Different seedhave different needs! Growth In order to complete the flower life cycle stage of growth, plants have to produce their own food. This process is called photosynthesis. As soon as the leaves emerge, they start the process of photosynthesis. Plants contain chloroplasts in the leaves which convert the energy from sunlight, carbon dioxide, and water into sugars, which they use as food. The plants store the sugars in the roots and stem. The root system continues to develop, anchoring the plant into the ground and growing root hairs which help the plant to better absorb water and nutrients. The stem grows longer towards the sun and transports water and food between the roots and leaves. Sugars and starches are changed into energy used to make new plant growth. New leaves grow from the top of thestem, or meristem. After a while, flower buds develop. Some plants flower within days while it takes others months or even years. Reproduction The female part of the flower is called the pistil and it has four parts-- the stigma, style, ovary, and ovules. The male part of the flower is called the stamen and it consists of the long filament and the anther, where pollen is made. In the center of the flower, there is a long slender tube that ends in a rounded oval. The tube is called the style. On the top of the style is the stigma-its job is to catch pollen. It may be sticky, hairy, or shaped in a way that helps it to better trap pollen. Sometimes several stamens surround the pistil. Once the pollen is trapped it travels down the style to the rounded part at the end, called the ovary, where eggs are waiting to be fertilized. The fertilized eggs become seeds in this stage of the flower life cycle. In fruit producing plants, the ovary ripens and becomes fruit. Pollination Some flowers have only male parts, and some have only female parts. In others, the male and female structures are far apart. These plants depend on insects, birds, animals, wind, water, or other pollinators to carry pollen from the male flowers or male parts to the female flowers or female parts. Without pollinators, there would be no seeds or new plants in these plant species. . Even flowers that can self-pollinate benefit from being fertilized by pollen from a different plant, which is called cross pollination, because cross pollination results in stronger plants. Brightly colored petals, strong smell, nectar, and pollen attract pollinators. Flowers are specially adapted to attract their specific pollinators. For example, the corpse flower smells like rotting flesh in order to attract flies. Pollen sticks to the legs and wings of insects that go from flower to flower for nectar and pollen, which they use as a food. Pollen sticks to the fur of animals and even to the clothes of humans. Wind blows pollen which lands on other flowers. Spreading Seeds Seed spreading, or dispersal, is the final stage of the flower life cycle. Seeds are spread in many ways. Some, like dandelion seeds, are scattered by the wind. Others rely on animals-an example of this is the cockleburs that get stuck in the fur of animals and hitchhike to new locations. Water lilies depend on water to spread their seeds. Humans spread many seeds intentionally by planting gardens. Once the seeds fall to the ground, the plant life cycle starts all over again. Importance Of Pollination To Agriculture Pollinators are vital to creating and maintaining the habitats and ecosystems that many animals rely on for food and shelter. Worldwide, over half the diet of fats and oils comes from crops pollinated by animals. They facilitate the reproduction in 90% of the world’s flowering plants. Pollinators are vital to creating and maintaining the habitats and ecosystems that many animals rely on for food and shelter. Worldwide, over half the diet of fats and oils comes from crops pollinated by animals. They facilitate the reproduction in 90% of the world’s flowering plants. Foods and beverages produced with the help of pollinators include: apples, bananas, blueberries, chocolate, coffee, melons, peaches, potatoes, pumpkins, vanilla, almonds, and tequila. (Imagine a world without some of these things!) In the United States, pollination by honeybees and other insects produces $40 billion worth of products annually! Fruit and seed dispersal Poricidal fruit Triodanis perfoliata(clasping Venus' looking-glass) When ripe, pores in the side of the fruit open, allowing the tiny seeds to shake out. Winged fruit Acer rubrum (red maple) - Maple fruits are winged, two seeded samaras. They spin like helicopters as they fall from the tree, providing a longer time for dispersal by wind. "Parachutes" Carduus nutans (nodding plumeless thistle) - The dry, one-seeded fruits are carried on the wind by plumose "parachutes". Fleshy fruits The seeds of many plants are dispersed after passing through the digestive system of animals that have eaten the fleshy fruits. Diospyros virginiana (persimmon) - The sweet fruits are enjoyed by many animals including humans Reproduction And Development In Animals Animals reproductive by asexual and sexual methods: • Asexual is the production of offspring with genes all from one individual, without the fusion of gametes. • Sexual involves formation of gametes and fertilization, genetic variation sexual reproduction, which is when two parents produce offspring with unique combinations of genes from both parents. Some multicellular animals, like corals, use both asexual and sexual reproduction, while others, like mammals, only reproduce sexually. A sexual reproduction Budding in Hydra Gemmules in Sponges Starfish Regeneration PARTHENOGENESIS parthenogenesis, like reproduction without the need of male gametes, there are costs, such as a decrease in genetic variation. In the intricate eusocial organization of honeybees, there are three social classes –queen bee, worker bees and drone bees. The queen bee, as the name entails, holds the superior position in the colony. The queen bee lays all the eggs in the colony, being the only bee with a set of completely developed ovaries and having life-long fertility (Back Yard Beekeepers Association n.d.). After only one mating flight were the queen mates with a couple male drone bees, she stores the sperm to later fertilizes some of the eggs. The eggs that get fertilized develop into female worker bees and the eggs that develop without fertilization produce male drone bees. Due to the high maintenance of both the colony and its products, i.e. honey, most of the bees in a hive are female worker bees. These worker bees carry on a magnitude of different tasks, not including reproduction, which is reserved only for the queen. The male drone bees are reserved for mating with the queen bee. Queen Worker (female) Drone (male) Binary Fission Binary Fission Binary fission involves mitosis only and hence the resultant individuals are genetically identical to each other and to the parent.It is the simplest and most common method of asexual reproduction. The whole parental body acts as the reproductive unit. The nucleus of the unicellular parent organism divides into two. This is followed by the division of the cytoplasm and 2 daughter cells of almost equal size are formed. The daughter cells grow in size and then divide again. Examples: Seen in euglena, amoeba, paramoecium.Based on the plane of cytoplasmic division binary fission is of 3 types, namely: a) Simple binary fission b) Transverse binary fission c) Longitudinal binary fission Simple binary fission When the cytoplasmic division passes through any plane, the fission is called simple binary fission.Example: Amoeba b) Transverse binary fission When the plane of cytoplasmic division coincides with the transverse axis of the individual, the fission is called transverse binary fission.Example: Paramoecium, Planaria Longitudinal binary fission When the plane of cytoplasmic division coincides with the longitudinal axis of the individual, the fission is called longitudinal binary fission.Example: Euglena Multiple Fission In some organismsthe nucleus of the parent divides into many daughter nuclei by repeated divisions (amitosis). This is followed by the division of the cytoplasm into several parts with each part enclosing one nucleus. So a number of daughter cells are formed from a single parent at the same time. This kind of fission is known as multiple fission.Example: Seen in Plasmodium (malarial parasite) where it is known as schizogony or sporulation, amoeba. BUDDING During the process of bud formation or budding an outgrowth or bud appears on the parent body. The bud may be unicellular as in some protozoans (suctoria) or multicellular as in certain lower metazoans like, Sycon (sponge), Hydra (Goelenterate), Planaria (flatworm), Syllis (annelid) etc. One or more such buds may be produced from a single parent body. The bud, which is much smaller than the parent develops to its full size either after detachment from the parent or prior to detachment being attached to its parent body. Budding may be external or exogenous as in Hydra or internal or endogenous as in Acinata. In Hydra the external bud develops as a conical outgrowth from the body wall by the accumulation of intcrsitial cells. The bud gradually develops tentacles around the mouth, coelenteron and later separated lion) its parent by developing a constriction at its base. When the body of Hydra or Planaria is cut into several fragments, each fragment develops into a new individual. This process is known as fragmentation. Regeneration is a process by which organisms develop or regenerate their lost or worn-out parts. Regeneration is highly developed in lower animals like protozoans, sponges, coelenterates, planarians, echinoderms etc. Regeneration Many animals can regenerate—that is, regrow or grow new parts of their bodies to replace those that have been damaged. Here are a few of these amazing creatures. Lizards who lose all or part of their tails can grow new ones. This is a good escape technique. A lost tail will continue to wiggle, which might distract the predator and give the lizard a chance to escape. Most lizards will have regrown their tail within nine months. Planarians are flat worms. If cut into pieces, each piece can grow into a new worm. Sharks continually replace lost teeth. A shark may grow 24,000 teeth in a lifetime. Spiders can regrow missing legs or parts of legs. Sponges can be divided. In that case, the cells of the sponge will regrow and combine exactly as before. Starfish that lose arms can grow new ones; sometimes an entire animal can grow from a single lost arm Sexual Reproduction: Sexual reproduction is commonly found in the complex, multicellular organisms. It involves the union of male and female sex cells or gametes to form the zygote which grow into a new individual. Two different sexes (male and female) take part in the process. The testes in male produce male gametes or sperms and the ovaries in female produce female gametes or ova. Both these sex organs may be present in the same body. Such animals are known as bisexual or hermaphrodite animals, e.g. earthworm. Formation of sperms and ova involves meiosis or reduction division during which haploid gametes are formed from the diploid cells. Gametes vary in shapes and sizes in different animals. Fusion of male and female gamete is known as fertilization. During fertilization a haploid (n), motile male gamete or sperm fuses with a non- motile, haploid (n) female gamete or ovum to form a diploid (2n) zygote which gives rise to a new individual Advantages of Sexual Reproduction: 1. The offspring’s produced due to sexual reproduction adapt themselves successfully to the changing environmental conditions. 2. Formation of gametes by meiosis and their fusion during fertilization produce reshuffling of genes and variation in the offspring’s. Variations in the offspring’s help them in natural selection and evolution. Disadvantages of Sexual Reproduction Since two parents of opposite sexes are needed i.e., biparental reproduction (except hermaphrodite forms) it is not as easy or as frequent as asexual or uni parental reproduction. major differences between asexual and sexual reproduction Asexual reproduction sexual reproduction 1. It occurs in lower 1. It occurs almost in all invertebrates and lower types of animals and mostly chordates and plants in higher plants. with simple organisations. 2. It is always uni-parental. 2. It is usually bi-parental. 3. Gametes are not formed. 3. Gametes formed. are always 4. No fertilization. 5. It involves only mitosis. 4. Fertilization takes place. 5. It involves both meiosis and mitosis. 6. Daughter organisms 6. Daughter organisms are genetically identical to the genetically differ from the parents. parent. 7. Multiplication is not as 7. Multiplication occurs rapid as in asexual rapidly. reproduction. 8. Since there are variations, 8. Since there is no variation, so it does not contribute to so it contributes to evolution of the species. evolution of the species. Frog Embryology The Egg The frog egg is a huge cell; its volume is over 1.6 million times larger than a normal frog cell. During embryonic development, the egg will be converted into a tadpole containing millions of cells but containing the same volume of material. The upper hemisphere of the egg - the animal pole - is dark. The lower hemisphere - the vegetal pole - is light. When deposited in the water and ready for fertilization, the haploid egg is at metaphase of meiosis II. Fertilization Entrance of the sperm initiates a sequence of events:Meiosis II is completed the cytoplasm of the egg rotates about 30 degrees relative to the poles In some amphibians (including Xenopus), this is revealed by the appearance of a light-colored band, the gray crescent. The gray crescent forms opposite the point where the sperm entered. It foretells the future pattern of the animal: its dorsal (D) and ventral (V) surfaces; its anterior (A) and posterior (P); its left and right sides. The haploid sperm and egg nuclei fuse to form the diploid zygote nucleus. Cleavage The zygote nucleus undergoes a series of mitoses, with the resulting daughter nuclei becoming partitioned off, by cytokinesis, in separate, and ever-smaller, cells. Thefirst cleavage occurs shortly after the zygote nucleus forms.A furrow appears that runs longitudinally through the poles of the egg, passing through the point at which the sperm entered and bisecting the gray crescent. This divides the egg into two halves forming the 2-cell stage The second cleavage forms the 4-cell stage. The cleavage furrow again runs through the poles but at right angles to the first furrow. The furrow in the third cleavage runs horizontally but in a plane closer to the animal than to the vegetal pole. It produces the 8-cell stage. The next few cleavages also proceed in synchrony, producing a 16-cell and then a 32-cell embryo.However, as cleavage continues, the cells in the animal pole begin dividing more rapidly than those in the vegetal pole and thus become smaller and more numerous. By the next day, continued cleavage has produced a hollow ball of thousands of cells called the blastula. A fluid-filled cavity, the blastocoel, forms within it. During this entire process there has been no growth of the embryo. In fact, because the cells of the blastula are so small, the blastula looks just like the original egg to the unaided eye. there has been no transcription and translation of zygote genes. All of the activities up to now have been run by gene products (mRNA and proteins) deposited by the mother when she formed the egg. Gastrulation The start of gastrulation is marked by the pushing inward ("invagination") of cells in the region of the embryo once occupied by the middle of the gray crescent. This produces:an opening (the blastopore) that will be the future anus a cluster of cells that develops into the Spemann organizer (named after one of the German embryologists who discovered its remarkable inductive properties). Summary As gastrulation continues, three distinct "germ layers" are formed:ectoderm mesoderm endoderm Each of which will have special roles to play in building the complete animal. Some of these are listed in the table. A single-celled zygote will undergo multiple rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula, with a fluid-filled cavity in its center, called a blastocoel. In animals with little yolk in the egg, the zygote undergoes holoblastic cleavage, in which the entire zygote is cleaved repeatedly; in animals with a lot of yolk in the egg, the zygote undergoes meroblastic cleavage, in which only part of the zygote is cleaved. The blastula eventually organizes itself into two layers: the inner cell mass (which will become the embryo) and the outer layer or trophoblast (which will become the placenta); the structure is now called a blastocyst. During gastrulation, the blastula folds in on itself to form three germ layers, the ectoderm, the mesoderm, and the endoderm, that will give rise to the internal structures of the organism. gastrulationthe stage of embryo development at which a gastrula is formed from the blastula by the inward migration of cells Blastomere any cell that results from division of a fertilized egg Meroblasticundergoing only partial cleavage trophoblast the membrane of cells that forms the wall of a blastocyst during early pregnancy, providing nutrients to the embryo and later developing into part of the placenta blastula a 6-32-celled hollow structure that is formed after a zygote undergoes cell division inner cell mass a mass of cells within a primordial embryo that will eventually develop into the distinct form of a fetus in most eutherian mammals holoblastic cleaving, and separating into separate blastomeres Neurulation is the development of the nervous system in the vertebrates, at the thickened area above the notochord in ectoderms. METAMORPHOSIS: The Lifecycle of a Frog Metamorphosis is the change of shape during an animal’s life. During metamorphosis the tadpole will develop back legs first, then front legs. Around 6 weeks of life the mouth starts to widen. Sometime around 10 weeks the froglet’s, as it is now called, eyes start to swell out and the tail begins to shrink and eventually disappear. When the lungs finish developing the froglet makes it’s way onto the land. Frog eggs floating in a pond: these clusters of floating eggs are called "egg masses". Frogs lay up to 4,000 eggs at one time! Tadpoles hatch from the eggs and live in the pond. The tadpoles turn into Froglets. The body shrinks and legs form. The Froglet's tail shrinks, the lungs develop and the back legs grow and then we have a Frog.