Modern Concept Science and Technology 8 New

Modern Concept Science and Technology – 8 97 8. Fragmentation : Fragmentation is a method of asexual reproduction in which a new organism grows from the fragmented or broken part of the parent organism. 9. Regeneration : Regeneration is a method of asexual reproduction in which organism regains its lost parts or new organism is produced from the broken part of the parent organism. 10. Sporulation : Sporulation is a method of asexual reproduction which takes place by means of spores. 11. Vegetative propagation: Vegetative propagation is a method of asexual reproduction in which new plants are produced by means of vegetative parts of the plants like root, stem or leaf. 12. Sexual reproduction : The method of reproduction in which a male gamete and a female gamete fuse together to give a new offspring is called sexual reproduction. 13. Gametes : Gametes are the haploid sex cells which are involved in sexual reproduction. 14. Unisexual organism : Those organisms which have only one kind of reproductive system (either male or female) are called unisexual organisms. 15. Bisexual organisms : Those organisms which have both types of reproductive system (male and female) in the same body are called bisexual organisms. 16. Pollination : The process of transfer of pollen grains from the anther to the stigma of a flower is called pollination. 17. Self pollination : The process of transfer of pollen grains from anther to the stigma of the same flower or other flower of the same plant is called self pollination. 18. Cross pollination : The transfer of pollen grains from anther to the stigma of the flower from different plant is called cross pollination. 16. Fertilization : Fertilization is a process of union of a male gamete and a female gamete to form a zygote. 17. Internal fertilization : If the fusion of a male gamete and a female gamete takes place inside the body of female, it is called internal fertilization. 18. External fertilization : If the fusion of a male gamete and a female gamete takes place outside the body of female, it is called external fertilization. 19. Vegetative propagation by root: The method of asexual reproduction in which new plants grow from roots of plants is called vegetative propagation by roots. 20. Vegetative propagation by stem: The method of asexual reproduction in which new plants grow from stem is called vegetative propagation by stem. 21. Vegetative propagation by leaf: The method of asexual reproduction in which new plants grow from leaf is called vegetative propagation by leaf. 22. Seed : A ripened ovule of a flowering plant is called a seed. 23. Monocotyledons seeds : The seeds that contain only one cotyledon are called monocotyledon seeds. 24. Dicotyledonous seeds : The seeds that contain two cotyledons are called dicotyledonous seeds. 25. Testa : The tough and hard outer coat of the seed is called testa. 26. Endosperm : The tiny structure in the seed that stores nutrients is called endosperm. 27. Embryo : The baby plant inside the seed is called embryo. 28. Radicle : The part of an embryo which develops into the root of the plant is called radicle. 29. Plumule : The part of an embryo which develops into the shoot of the plant is called plumule. 30. Epicotyl : The part of the embryo above the point of attachment of cotyledons is called epicotyl. 31. Tegmen : The thin membrane under the testa of dictot seed is called tegmen. 32. Cotyledon : The cotyledon is the seed leaf present in the seed. 33. Hilium : The scar left by stalk on the seed is called hilium. 34. Micropyle : A tiny pore in the testa that can absorb water is called micropyle. 35. Endospermic seed : The seeds that store food in endosperm are called endospermic seed. 36. Non-endoseprmic seed :The seeds that do not have endosperms and stores food in cotyledon are called nonendospermic seeds.

98 Life Processes 37. Dispersal of seed : The process of distribution of seeds away from the mother plant is called dispersal of seed. 38. Germination of seed : The development of a seed into a young seedling is called germination of seed. 39. Epigeal germination : The type of germination where cotyledons emerge out of the soil is called epigeal germination. 40. Hypogeal germination: The type of germination where cotyledons remain inside the soil is called hypogeal germination. Introduction It is very easy to differentiate living beings and non-living beings. This is because living beings show various living activities such as respiration, nutrition, circulation, movement, excretion, reproduction, etc. These activities are very essential to survive for a living being. Plants do not show visible living activities as like that in animals but all life activities occurs in them. Those activities which are carried out by living organisms and essential to continue life on the earth are called life processes. Living beings cannot survive in absence of these life processes. 5.1 Reproduction No organism survives forever because each and every living organism is mortal. All species come to the nature, remain alive for a limited period of time and then die. But, why is the population of living organisms increasing day by day? Was the number of organisms in the present same as in the past? The simple answer of this question is no. Living organisms continue their generation by producing their own kind. This is called reproduction. Thus, the biological process in which living organisms produce their own kind by asexual or sexual method is called reproduction. Most of the living organisms have higher tendency of reproduction. Due to this reason, they grow in number increasing the population over a short period of time. FACTS WITH REASONS The number of organisms in the past was not same as the present. The number of organisms in the past was not the same as the present because the reproductive capacity of all organisms is higher in favourable environment condition. As a result, the population is increasing day by day. Importance of reproduction i. Reproduction helps to continue the generation of the species. ii. It protects species from being extinct. iii. It balances the population. iv. It balances the biodiversity in an ecosystem. v. It is the basis of evolution of new organism. Types of reproduction in organisms Reproduction in organisms occurs either through their vegetative parts or by involving male and female gametes. So, on the basis of above fact, reproduction in plants and animals occurs by two methods. They are:

Modern Concept Science and Technology – 8 99 a) Asexual reproduction b) Sexual reproduction Asexual Reproduction The type of reproduction which takes place without the fusion of a male gamete and a female gamete is called asexual reproduction. Asexual reproduction involves only one parent and mostly occurs in lower plants and animals. The offspring produced from asexual reproduction are completely identical to their parents. Organisms that undergo asexual reproduction are amoeba, hydra, planeria, mushroom, potato, onion, ginger, bryophyllum, spirogyra, rose, etc. In unicellular organisms, asexual reproduction occurs through the whole body whereas in multicellular organisms, the parts of the body like stem, roots, leaves, branches, etc. involve in reproduction. Characteristics of asexual reproduction i. The process of asexual reproduction does not involve the production and fusion of gametes. ii. It does not need male and female. iii. This reproduction can be carried out from the parts of whole body. iv. The offspring obtained from asexual reproduction do not have variation. Methods of asexual reproduction Some of the major methods of asexual reproduction in plants and animals are given below: a) Fission b) Budding c) Sporulation d) Fragmentation or Regeneration e) Vegetative propagation f) Parthenogenesis a) Fission In fission single organism divides into two or more individual organisms. Thus, fission is a method of asexual reproduction in which single parent body divides itself into two or more daughter organisms. It occurs in unicellular organisms like amoeba, paramecium, euglena, plasmodium, bacteria, etc. Depending on the number of resulting offspring, there are two kinds of fissions. They are binary fission and multiple fission. FACTS WITH REASONS An amoeba never gets old. An amoeba never gets old because it lives for sometimes and then itself divides by fission to form young amoeba again. MEMORY TIPS The word fission is derived from Latin word ‘fissio’ means to split. So, in fission single parent body divides into two or more daughter offspring.

100 Life Processes i) Binary fission : The method of asexual reproduction in which a unicellular organism divides into two daughter organisms is called binary fission. Binary fission generally occurs in the favourable conditions of food, habitat, temperature, pH value, etc. Binary fission is common in unicellular plants like bacteria, diatoms, etc. and animals like amoeba, paramecium, plasmodium, euglena, etc. Binary fission could be transverse or longitudinal. Transverse binary fission means the unicellular organism splits vertically (from the longer side). Transverse binary fission means the unicellular organism splits horizontally (from the shorter side). Parent cell Nucleus divides Daughter cells Cytoplasm divides Fig 5.1 : Binary fission of amoeba ii) Multiple fission : In this reproduction, the number of offspring produced is more than two. Thus, the method of asexual reproduction in which a unicellular organism divides into more than two daughter organisms is called multiple fission. During multiple fission, the resulting daughter cells are protected by a thick covering called the cyst. The cyst prevents the immature release of cells into the harsh environment. In multiple fission, the parent nucleus divides into many fragments. Each fragment is surrounded by cytoplasm followed by the formation of cell membrane to form multiple cells. When favourable conditions of food, habitat, temperature, pH value, etc. return, the cyst ruptures to release the cells into the environment. In this way many offspring from the single parent are formed. Examples: amoeba, paramecium, plasmodium, chlamydomonas, bacteria, etc. plasmodia Daughter nuclei Daughter Cyst Parent cell Fig 5.2 : Multiple fission in plasmodium MEMORY TIPS Plasmodium divides repeatedly in the blood by means of multiple fission causing malaria. Similarly amoeba divides by multiple fission causing dysentery.

Modern Concept Science and Technology – 8 101 b) Budding In some organisms like hydra, yeast, etc. a small bud like structure appears in the body of parent. This bud grows in size, collects the cellular materials and becomes matured. After the bud becomes matured, it detaches from the parent body to become a new individual. Thus, the method of asexual reproduction in which new offspring is reproduced by means of a small outgrowth or bud is called budding. During budding, the body of parent and the offspring are of unequal size. Examples: yeast, hydra, taenia, coral and jelly fish. Bud Bud grows Bud separates Fig 5.3 : Budding of hydra ACTIVITY 1 OBJECTIVE: To show that yeast converts glucose into ethyl alcohol and carbon dioxide. Take a packet of yeast, a small plastic water bottle, a cup, warm water, some sugar and a small balloon. Fill the cup with a small amount of warm water and add few spoons of sugar. Stir it to make a solution. Put water into the plastic bottle. Pour yeast and sugar solution into water bottle. Then, gently swirl the bottle about a couple of times. Finally, place the mouth of a highly stretchable balloon onto the neck of the bottle and leave it for about 20 to 30 minutes. You will observe that the balloon starts inflating. Why does it happen? Which gas is present in the balloon? The balloon inflates because the yeast present in the bottle feeds on sugar and converts sugar into ethyl alcohol and carbon dioxide. Due to the carbon dioxide gas, the balloon gets inflated. c) Sporulation Sporulation is a method of asexual reproduction which takes place by means of spores. Spores are the asexual microscopic structures. They are formed from sporogenesis. They are capable of germination into new organism under favourable conditions. The spores are present in the spore sac called sporangium. Spores sac bursts open on maturity and releases spores to germinate into new organisms. MEMORY TIPS 1. The word budding is derived from middle English budde means pod of seed. 2. Yeast is a unicellular fungi and hydra is a multicellular animal which show budding.

102 Life Processes sporangium mycelium (a) (b) columella spores sporangial wall Fig 5.4 : Sporulation of mucor FACTS WITH REASONS Spores are asexual structures. Spores are asexual structures because they are formed from the spore mother cell as a result of mitosis cell division without the fusion of a male gamete and a female gamete. ACTIVITY 2 OBJECTIVE : To observe sporulation in mucor. 1. Take a slice of bread and a small plastic container. 2. Sprinkle few drops of water on the bread and keep in the container. 3. Seal the container with the lid and tape it around. 4. After about 3-4 days observe the growth of mucor on the bread. 5. When mucor grows, it produces spores. These spores might be harmful to human beings. They might cause allergies, cough, skin rashes, respiratory problems, etc. So, do not expose them in air. Throw the plastic container after doing this activity. d) Fragmentation or regeneration Fragmentation and regeneration are similar terms but generally fragmentation is used for plants and regeneration is used for animals. i) Fragmentation : Fragmentation is a method of asexual reproduction in which a new organism grows from the fragmented or broken part of the parent organism. In fragmentation, a multicellular parent organism breaks down into two or more pieces. Later on, each piece of the organism develops into a complete organism. Spirogyra, marchantia, some mosses, fern, lichen etc. reproduce by means of fragmentation. MEMORY TIPS Sometimes, we get cut or wound. This cut or wound repairs after certain interval of time. So, it is a type of regeneration. Fragmentation of spirogyra

Modern Concept Science and Technology – 8 103 ii) Regeneration : Regeneration is a method of asexual reproduction in which organism regains its lost parts or new organism is produced from the broken part of the parent organism. For example, when a planarian is cut into pieces, after few weeks, these cut parts regenerate into fully living planarian. Other examples of animals which show regeneration are tapeworm, hydra, sponge, starfish, earthworm, etc. e) Parthenogenesis : Sometimes a female snake that has never met a male partner can hatch new snakes from its egg. The process in which new offspring comes from unfertilized egg is called parthenogenesis. It is common in ants, bees and grasshoppers. Plants such as apple, cucumber, jack fruit etc. also show parthenogenesis. FACTS WITH REASONS A planaria does not die on cutting into two halves. A planaria does not die on cutting into two halves because the cells of planeria are capable of regeneration. Therefore, these two halves grow fully into new planeria. Vegetative Propagation Vegetative propagation is a method of asexual reproduction in which new plants are produced by means of vegetative parts of the plants like root, stem or leaf. Vegetative propagation may be natural or artificial. In natural vegetative reproduction, a small bud grows on the vegetative parts of the plant like root, stem or leaf. On maturity, the bud detaches from the parent body and develops into a new plant. Similarly, the artificial method of vegetative propagation involves new techniques like cutting, grafting, layering, tissue culture, etc. to grow new plants. FACTS WITH REASONS Vegetative propagation cannot be done from all vegetative parts of the plant. Vegetative propagation cannot be done from all vegetative parts of the plant because all parts of plant cannot produce bud. So, only those parts of plants can do vegetative propagation which is capable of producing bud. A. Natural vegetative propagation i) Vegetative propagation by roots : The method of asexual reproduction in which new plants are produced by means of roots of plants is called vegetative propagation by roots. For examples: dahlia, sweet potato, mint, gladiolus, etc. Fig 5.5 : Regeneration of Planeria Fig 5.11 : Vegetative propagation by roots

104 Life Processes FACTS WITH REASONS The diseased part of the plant should not be used for vegetative propagation. The diseased part of the plant should not be used for vegetative propagation because the offspring produced through vegetative propagation are identical to their parent. They also carry the parental characters. If the diseased part of the plant is used in vegetative propagation, the new offspring may be affected by the same disease. ii) Vegetative propagation by stem : The method of asexual reproduction in which new plants are produced by means of stem of plants is called vegetative propagation by stem. Examples of some plants which grow by means of stem are given below: 1. Bulb of onion and tulip 2. Corm of ginger and gladiolus 3. Rhizome of sugarcane 4. Tuber of potato 5. Runner of airplane plant main root eye scale leaf root New plant Node Intermode Node disc bud scale leaf Fig 5.12 : Vegetative propagation by stem Vegetative propagation by underground stem: Some plants like onion, tulip, daffodil, arum, Colocasia, gladiolus, ginger, potato, etc. reproduce asexually using an underground stem. Stems of these plants contain buds on them. Each bud of the stem can grow into a new plant in favourable conditions. Vegetative propagation by sub-aerial stem: Some plants like water hyacinth, water lettuce, etc. reproduce by offset. Strawberry, raspberry, buttercup, blackberry, gooseberry, bamboo, pineapple, mint, chrysanthemum, banana, etc. reproduce asexually using a sub-aerial stem. FACTS WITH REASONS Planting the sugarcane by cutting the stem is an asexual reproduction. As no male and female gametes are involved during the cutting process, growing new sugarcane by cutting the stem is an asexual reproduction. ACTIVITY 3 OBJECTIVE : To observe vegetative propagation in sugarcane stem. 1. Take a mature sugarcane stem containing buds in the nodes. 2. Cut the stem into pieces in the way that each piece should have node. 3. Plant these pieces of sugarcane in the soil and supply water for about 12-15 days. 4. After about 12-15 days, the sugarcane nodes germinate into new sugarcane plants.

Modern Concept Science and Technology – 8 105 c) Vegetative propagation by leaf : The method of asexual reproduction in which new plants are produced by means of leaf of the plants is called vegetative propagation by leaf. The leaf on maturity produces buds from the notch at the end of leaf blade, lamina and veins. Examples: begonia, bryophyllum, etc. Leaf of Bryophyllum New plantlets New plantlet Leaf of Begonia Fig 5.13 : Vegetative propagation by leaf d) Vegetative propagation by bulbil: The group of buds at the apex of branches or stem is called bulbil. Certain plants such as jack fruit, agave, lily, onion, garlic, etc. can grow new plants from bulbil. FACTS WITH REASONS Vegetative propagation is beneficial for farmers. Vegetative propagation is beneficial for farmers because vegetative propagation produces flowers, fruits and seeds sooner than those from sexual reproduction. Vegetative propagation is very effective for the plants which do not produce viable seeds. Vegetative propagation is easier, cheaper and faster method of reproduction. B. Artificial vegetative propagation Besides natural methods of vegetative propagation, artificial methods of plant reproduction are also common among farmers, gardeners, horticulturists etc. Various methods like cutting, grafting, layering, tissue culture, etc. are used to reproduce plants asexually in gardens and nurseries. a. Cutting Cutting is a common artificial method of vegetative propagation in which new plants are obtained by planting the piece of stem, root or leaf of plants in favourable conditions. Each cutting piece should have buds for propagation. Some plants like sugarcane, rose, potato, pear, raspberry, black berry etc. are propagated by stem cutting. Lemon, tamarind, etc. are propagated by root cutting and Begonia, Bryophyllum, African violets, etc. are propagated asexually by leaf cutting. Fig: Reproduction by cutting

106 Life Processes b. Layering Layering is an artificial method of reproduction in which roots are developed on the stem while the stem is still attached to the parent plant. Layering is commonly used in jasmine, magnolia, strawberry, raspberry, etc. Many plantlets can be produced in a short period by this method. Layering is induced artificially by bending the branch to the ground and covering it with moist soil. The apical part of the stem produces leaves whereas the underground part produces roots. Later the layered branch is separated from the parent plant. c. Gootee (Air layering) Air layering is the most popular method of artificial vegetative propagation. In this method, the target region of the stem is wounded, or a strip of bark is removed and then encased in a moisture-retaining medium, such as moss or cloth, which is further surrounded by a moisture barrier such as a plastic film. Rooting hormone, i.e., I.B.A. hormone (Indole-3 butyric acid) is often applied to encourage the growth of roots. The wounded portion develops roots within 4-8 weeks. Then, the portion is separated from the parent plant and planted. Example: litchi, mango, guava, orange d. Grafting In this method, a plant of superior quality is obtained by combining the root system of a plant and shoot system of another plant. The plant whose root system is taken is called stock and whose shoot system is taken is called the scion. This technique is used in mango, rose, lemon, apple, peach, plum, etc. In grafting, the ends of a scion and stock to be grafted are cut obliquely and placed face to face in such a way that the cambia of both plants are in close contact. Then the scion and stock are bound firmly with tape (cloth) and covered with wax. After a few weeks, both the scion and stock combine firmly, resulting in a new plant. e. Tissue culture Tissue culture or micro-propagation is a modern technique of producing new plants from isolated plant cells or a small piece of plant tissue in a culture solution. The culture solution or medium is very important in tissue culture. The solution contains a special mixture of salts, vitamins and plant hormones. Fig: Layering Fig: Air layering Fig: Grafting Fig: Tissue culture

Modern Concept Science and Technology – 8 107 Ornamental plants like orchids, dahlia etc. are propagated artificially by this technique. In tissue culture, a few cells (or tissues) of the plant to be propagated are taken and kept in a culture solution under sterile conditions. In this solution, a shapeless lump, i.e., callus is produced by the rapid division of the plant cells. Then the callus is transferred into another culture solution containing suitable plant hormones, which stimulates the callus to develop roots. The callus with roots is again transferred into another culture solution having different hormones that stimulate the development of shoots. The callus has roots and shoots which can be separated into many tiny plantlets. The plantlets thus produced are transplanted into soil or pots to get natural plants. Advantages of artificial vegetative propagation i. By using artificial vegetative propagation we can improve generation of the plants. ii. By using this method, we can produce plants which give earlier flower and fruits. iii. We can use this method to produce many plants at a time. iv. We can produce new plants in those which cannot germinate seeds. Significance of asexual reproduction i) Asexual reproduction produces new individuals with exactly identical qualities as the parent. ii) It is a faster, easier and cheaper method of reproduction. iii) The plants produced by vegetative propagation bear flowers and fruits earlier than those produced from seeds. iv) The plants which do not produce viable seeds (like sugarcane, rose, potato, banana, bamboo, etc.) can easily be propagated by asexual reproduction. Sexual Reproduction The method of reproduction in which a male gamete and a female gamete fuse together to give a new offspring is called sexual reproduction. Sexual reproduction is a complex process. It needs both male and female parents. Generally, higher animals and plants involve sexual reproduction. In the life cycle of these higher animals and plants, the diploid phase (2n) is very long and represent by the main body. Similarly, the haploid phase (n) is very short and represents by the gametes. Characteristics of sexual reproduction i. The process of sexual reproduction involves the production and fusion of gametes. ii. It requires male and female. iii. This reproduction can be carried out from the sex organs of male and female. iv. The offspring obtained from sexual reproduction have variation. v. The offspring obtained from sexual reproduction have better adaptation to the environment. vi. This reproduction is responsible for the evolution of the organisms.

108 Life Processes Gametes Gametes are the haploid sex cells which are involved in sexual reproduction. The male gamete is called sperm for animals and pollen grain for plants. Similarly, the female gamete is called egg or ovum for both plants and animals. Sperms (male gametes) Eggs (female gametes) Fig 5.6 : Gametes Differences between male gamete and female gamete S.N. Male gamete S.N. Female gamete 1 The haploid male sex cell is called male gamete. It is also called sperm (for animals) and pollen grain (for plant). 1 The haploid female sex cell is called female gamete. It is also called egg or ovum for both plants and animals. 2 It is produced form the testes in animals and from anther in plants. 2 It is produced form the ovary in animals and from anther in plants. 3 Male gametes are smaller in size, more in number and motile in nature. 3 Female gametes are bigger in size, very less in number and non-motile in nature. Unisexual and bisexual organisms Most of the organisms have male and female reproductive system in the separate bodies. They are called unisexual or dioecious organisms. Examples: humans, birds, reptiles, etc. Thus, those organisms which have only one kind of reproductive system (either male or female) are called unisexual organism. Similarly, some organisms have both male and female reproductive systems in the same body. They are called bisexual, monoecious or hermaphrodite organisms. Examples: earthworm, tapeworm, starfish, leech, etc. Thus, those organisms which have both reproductive systems (male and female) in the same body are called bisexual organisms. MEMORY TIPS Sperm is called a male gamete and ovum or egg is called a female gamete. Male gametes are motile and more in number but female gametes are non-motile and very less in number. MEMORY TIPS Pumpkin, papaya, etc. are unisexual plants. Similarly, mustard, pea, mango, etc. are bisexual plants. stigma style ovary receptacle pistil pedicel sepal petal filament anther Fig 5.7 : Structure of flower

Modern Concept Science and Technology – 8 109 Process of Sexual Reproduction in Flowering Plants In flowering plants, the flower is a main reproductive organ. It is a colourful and the most attractive part of the plant. A complete flower has four whorls. They are calyx, corolla, androecium and gynoecium. Androecium is a male reproductive part whereas gynoecium is a female reproductive part. Pollination When a flower becomes mature, androecium releases pollen grains form its anther. These pollen grains reach to the stigma of the flower by various agents called pollination. Thus, pollination is a process of transfer of pollen grains (male gametes) from the anther to the stigma of a flower. It can be done by the various external agents like insects, wind, birds, animals, water, etc. Insects are the most common agents that help in pollination. There are two types of pollination. They are self-pollination and cross pollination. a) Self-pollination The process of transfer of pollen grains (male gametes) from the anther to the stigma of the same flower or different flower of the same plant is called self-pollination. This process is common in bisexual flowers where pollinating agents are not effective. Examples: pea, mustard, china rose, etc. Advantages of self-pollination i. As a result of self-pollination the offspring carry the parental characters. ii. Self-pollination makes sure of seed production. iii. It is an easy way of pollination. Disadvantages of self-pollination i. As a result of self-pollination the offspring do not carry the new characters. So, there is no evolution in the coming generation. ii. The continuous self-pollination declines the power of reproduction in coming generation. iii. We can not eliminate the bad characteristics of the parents in the coming generation. b) Cross pollination The process of transfer of pollen grains (male gametes) from the anther to the stigma of the different flower of the different plants is called cross-pollination. Cross pollination is common in bisexual as well as unisexual flowers where pollinating agents like air, water, insects, animals, etc. are effective. Examples: cucumber, pumpkin,etc. Self-pollination Cross-pollination Self-pollination Fig 5.8 : Pollination

110 Life Processes Advantages of cross-pollination i. As a result of cross-pollination the offspring of better characters are produced. ii. Offspring of cross-pollination are better suited in the changing environment. iii. It helps in evolution of the organisms. Disadvantages of cross-pollination i. Cross-pollination depends upon external agents. In absence of external agents, it does not occur. ii. As a result of cross-pollination, the offspring with unwanted characters may be produced. iii. As a result of cross-pollination, the beneficial characteristics of the offspring may disappear. iv. It does not make sure of seed production. Differences between self-pollination and cross-pollination. SN Self-pollination SN Cross-pollination 1 The process of transfer of pollen grains (male gametes) from the anther to the stigma of the same flower or different flower of the same plant is called selfpollination. 1 The process of transfer of pollen grains (male gametes) from the anther to the stigma of the different flower of the different plants is called crosspollination. 2 This pollination is common in bisexual flowers where pollinating agents are not effective. Examples: pea, mustard, china rose, etc. 2 This pollination is common in bisexual as well as unisexual flowers where pollinating agents like air, water, insects, animals, etc. are effective. Examples: cucumber, pumpkin, etc. FACTS WITH REASONS Some insects like the honey bee are the helpers of the farmers. Insects like honey bees help in pollination. As a result, crops are produced easily. So, some insects like the honeybee are the helpers of the farmers. Fertilization Fertilization is a process of union of a male gamete and a female gamete to form a zygote. The male and female gametes are haploid (n), so the zygote formed after their fusion is diploid (2n) in nature. After pollination, the pollen grain germinates forming a pollen tube. The nucleus of the pollen tube controls the growth of the pollen tube. The growth of pollen tube is an example of chemotropism since it is growing toward the chemicals produced from the ovule. The haploid male nucleus moves downwards through the pollen tube. In the course of its movement, it undergoes mitosis cell division and forms two haploid male nuclei. The pollen tube enters into the ovule through the micropyle and releases male gametes into the embryo sac. Now, the tube nucleus disintegrates. In the embryo sac, one male gamete fuses with egg cell (ovum) to form zygote (2n) while other male gamete fuses with secondary nucleus to form an endosperm nucleus (3n). Therefore, the fertilization in flowering plants is called double fertilization.

Modern Concept Science and Technology – 8 111 FACTS WITH REASONS The fertilization in flowering plants is called double fertilization. In the embryo sac of the flowering plants, one male gamete fuses with egg cell (ovum) to form zygote (2n). Similarly, another male gamete fuses with secondary nucleus to form an endosperm nucleus (3n). Therefore, the fertilization in the flowering plants is called double fertilization. Germinated pollen grain Anther at tip of stamen Pollen tube Ovary (base or carpel) Embryo sac Egg Sperm Germinating seed Seedling Mature plant with flowers Seed Seed (develops from ovule) Simple fruit (develops from ovary) Embryo Zygote Ovule Fig 5.9 : Fertilization Changes in the flower after fertilization After fertilization, the ovary turns into fruit and the fertilized ovule becomes a seed. The integument becomes the wall of the seed called testa. The micropyle closes. The endosperm nucleus divides and forms an endosperm which is a food tissue. The diploid zygote divides mitotically and develops into a baby plant called an embryo. The developing embryo draws nourishment from the endosperm. Now, the embryo stops developing and goes into dormancy. After getting favourable conditions the seed germinates into a new plant. In this way, the life cycle of a flowering plant completes. Differences between pollination and fertilization. SN Pollination SN Fertilization 1 Pollination is a process of transfer of pollen grains (male gametes) from the anther to the stigma of a flower. 1 Fertilization is a process of union of male gamete and female gamete to form a zygote. 2 It occurs before fertilization. 2 It occurs only after pollination.

112 Life Processes Process of Sexual Reproduction in Animals Sexual reproduction is an effective method of reproduction in most of the multicellular animals and in some unicellular animals. It is the most common method of reproduction in vertebrates and also found in lower invertebrates. In this type of reproduction, the fusion of a male gamete (sperm) with a female gamete (ovum) takes place inside or outside of the female body. In male, the testes produce sperms and in female, the ovaries produce eggs. Sperms are formed from the sperm mother cell through a process called spermatogenesis. Similarly, the eggs are formed from the egg mother cell through a process called oogenesis. During sexual reproduction, the haploid sperm and the haploid egg fuse together to form a diploid zygote called fertilization. The diploid zygote divides mitotically and forms an embryo. The embryo finally develops into a young animal. The duration in which an organism develops from a zygote into a young living organism is called embryonic period or pregnancy period. Internal fertilization and external fertilization On the basis of location, fertilization is of two types. They are internal fertilization and external fertilization. a) Internal fertilization For internal fertilization, the male has to introduce the male gametes into the female reproductive tracts. If fusion of a male gamete and a female gamete takes place inside the body of female, it is called internal fertilization. Internal fertilization is common in mammals, aves, reptiles, insects, etc. Usually, fertilization occurs in fallopian tube. b) External fertilization In external fertilization, male and female release their gametes out in open environment. If fusion of a male gamete and a female gamete takes place outside the body of female, it is called external fertilization. It is common in pisces and amphibian. External fertilization usually takes place in water. The female lays hundreds of eggs in water and male secretes millions of sperms over the eggs. Thus, the fusion of sperms and eggs takes place in water. Likewise, the eggs too hatch outside. MEMORY TIPS Formation of sperms is called spermatogenesis and formation of eggs is called oogenesis. The spermatogenesis and oogenesis together called gametogenesis. Haploid sperm Diploid zygote Haploid egg Fig 5.10 : Gamete and zygote

Modern Concept Science and Technology – 8 113 FACTS WITH REASONS In a pond, a female frog lays hundreds of eggs at a time but the rate of survival of frogs are very less. The eggs of frogs are not covered with the shell as in birds. So, they are very delicate. They dry due to sunlight and also eaten by others. It makes very difficult to survive. Therefore, in a pond, a female frog lays hundreds of eggs at a time but the rate of survival of frogs are very less. Significance of sexual reproduction i) Sexual reproduction helps to give continuity to the generation. ii) It brings out genetic variation and leads to evolution. iii) Sexual reproduction produces disease resistance offspring. iv) The offspring obtained from sexual reproduction have more adaptability. Differences between asexual and sexual reproduction. S.N. Asexual reproduction S.N. Sexual reproduction 1 Asexual reproduction takes place without the fusion of a male gamete and a female gamete. 1 Sexual reproduction takes place due to the fusion of a male gamete and a female gamete. 2 In asexual reproduction, only one parent is involved. 2 In sexual reproduction, both male and female parents are involved. 3 It is most common in primitive animals and plants. 3 It is most common in developed animals and plants. FACTS WITH REASONS The zygote is a diploid structure. Zygote is formed by the union of a haploid male gamete and a haploid female gamete. Combination of a male and female gametes finally forms a diploid zygote. Fertilization is only possible in sexual reproduction. The fusion of a male gamete and a female gamete takes place only in sexual reproduction. The gametes are not produced in asexual method. Planting of sugarcane by cutting the stem is an asexual reproduction. As no male and female gametes are involved during the cutting process, the planting of sugarcane by cutting the stem is an asexual reproduction. 5.2 Seed A seed is a ripened ovule of a flowering plant. The seeds of different plants have different shape, size, colour and number. Seeds of angiosperm are enclosed in the fruit while in gymnosperm seeds are exposed on the scales of the cones. Cotyledons are the germinating leaves inside seed. The seeds usually have three parts. They are seed coat, endosperm and embryo. Types of seeds (on the basis of cotyledons) On the basis of number of cotyledons, seed are of two types. They are: a) Monocotyledonous seeds b) Dicotyledonous seeds

114 Life Processes a) Monocotyledonous seed: The seeds having one cotyledon in them are called monocotyledonous seeds. Wheat, oats, rye, maize, paddy, grasses, etc. are some examples of monocotyledonous seeds. Maize seeds Wheat seeds Paddy seeds Fig 5.14 : monocot seeds Structure of a monocotyledonous seed A monocot seed consists three major parts. They are testa, endosperm and embryo. Testa: Testa is a tough and hard outer coat of the seed. It protects the seed from fungi, bacteria and insects. Endosperm: Below the testa there is a major part of the seed called endosperm which is filled with reserve food materials. Endosperm is a source of nutrients for the embryo. Inner starchy layer of the endosperm separates it from embryo. Embryo: Embryo is a baby plant that germinates in favourable condition. It contains a single cotyledon. It consists of three parts: radicle, plumule, and Epicotyl/hypocotyl. i) Radicle (young root): Radicle is the embryonic root. The part of an embryo which develops into the plants primary root is called radicle. It is present at the basal tip of hypocotyl. ii) Plumule (young shoot): Plumule is the embryonic shoot. The part of an embryo which develops into the shoot and first true leaves of a plant is called plumule. It is present at the tip of epicotyl. iii) Epicotyl/ hypocotyl: Epicotyl is the part of an embryo above the point of attachment of the cotyledon(s). The part of an embryo below the cotyledon attachment site is called the hypocotyl. Depending on the type of germination, one of these sections will be the first to emerge out of the soil. Micropyle, hilum and hypocotyl are not clearly visible in monocot seed. In case of maize seed, plumule faces towards the upper wider end of the seed while radicle faces towards the narrow end of the seed. During seed germination, radicle develops into root and plumule develops into shoot. Testa Cotyledon Plumule Radicle Fig 5.15 : Structure of a maize seed MEMORY TIPS There is one cotyledon in monocot, two cotyledons in dicot and one or more cotyledons in gymnosperms.

Modern Concept Science and Technology – 8 115 b) Dicotyledonous seeds The seeds having two cotyledons in them are called dicotyledonous seeds. Gram, pea, soayabean, mustard, mango, apple, orange, plum, etc. are few examples of dicotyledonous seeds. Seed of pea Seed of mango Seed of pumpkin Fig 5.16 : dicot seeds Structure of a dicotyledonous seed Some major parts of a dicotyledonous seed are described below: Testa: The seed is covered with a tough protective outer covering called testa. The testa is very thin in some plants like pea nut whereas it is hard and thick in coconut, walnut, peach, etc. Tegmen: In flowering plants, there is thin and membranous covering inside the testa called tegmen. Testa and tegmen make seed coat. Endosperm: Endosperm is absent in most of the dicotyledonous seeds. Cotyledons: A cotyledon is the seed leaf. It lies below the testa in non-endospermic seeds. In dicotyledons there are two cotyledons. Depending on the type of germination, the cotyledon may remain below the ground or be pulled above ground. Cotyledons often contain reserve food which is used during the early stage of the germination. In most of the plants the cotyledons are brought out of the testa above the ground. They become green and make food by photosynthesis. Hilum: The scar left by stalk which attaches the ovule with the wall of ovary is called hilum. Micropyle: A tiny pore in the testa opposite to the tip of the radicle is called micropyle. It allows water to enter into the embryo before active germination. Embryo: An embryo is the immature plant which will grow within the seed. The radicle is the embryonic root which grows and develops into the root system of the plant. The plumule is the embryonic shoot. It grows into the shoot system. Hypocotyl which is present between the plumule and radicle grows into stem. Testa Tegmen Plumule Epicotyl Hypocotyl Cotyledon Radicle Fig 5.17 : Structure of a gram seed

116 Life Processes Differences between monocotyledonous seed and dicotyledonous seed. SN Monocotyledonous seed SN Dicotyledonous seed 1 Monocotyledonous seed contains single cotyledon. 1 Dicotyledonous seed contains two cotyledons. 2 The cotyledon of this seed is thin and small which lacks food material. 2 The cotyledons of this seed are large and store food materials. 3 Seeds are endospermic. 3 Seeds are non-endospermic. 4 Micropyle and hilum are not visible. 4 Micropyle and hilum are visible. 5 Plumule is small in size. 5 Plumule is large in size. Types of seeds (on the basis of endosperm) On the basis of food storage tissues, there are two types of seeds. They are: a) Endospermic seeds b) Non-endospermic seeds a) Endospermic seeds : The seeds in which food is stored in endosperm are called endospermic seeds. All monocot seeds are called endospermic seeds. Examples: Seeds of wheat, maize, rice, bajra, barley, etc. b) Non-endospermic seeds : The seeds in which food is stored in cotyledons are called non-endospermic seeds. All dicot seeds (except castor) are called non-endospermic seeds. Examples: Seeds of pea, gram, orange, apple, soyabean, etc. ACTIVITY 4 1. Collect some seeds of plants from your home and surrounding. 2. Keep these seeds in water for about one day. 3. Try to separate out these seeds into equal parts. 4. On the basis of structure, classify these seeds into : a. Monocot seeds and dicot seeds. b. Endospermic seeds and non-endospermic seeds. Functions of seeds The major functions of the seed are given below: i) Seed protects embryo Seeds are covered with a tough outer covering called testa. Embryo is present inside the seed. Seed coat protects embryo from various injuries and microorganisms. Due to this reason seeds can remain dormant for a long time. ii) Seed provides nourishment to the embryo Seed contains endosperm and cotyledons in it. Endosperms and cotyledons store food materials for the development of embryo. iii) Seed helps in dispersal of seed itself Some seeds are modified for easy dispersal. Some seeds can float easily in air and water. Some seeds cannot be digested by animals. Some seeds are carried easily by animals, birds, insects, etc.

Modern Concept Science and Technology – 8 117 iv) Seed helps in germination Seed helps in germination of a plant. The germinated seed develops into a new plant and continue its life cycle. Dispersal of seeds Dispersal of seed means distribution or scattering of seeds away from the position of their origin. Seeds need favourable environmental condition to germinate. So, they have tendency to disperse in search of favourable conditions. Fruits or seeds are modified in various shapes and sizes to help in dispersion. Different modes of dispersion of seeds are given below: i) Dispersal of seeds by wind The seeds of pine, simal, orchids, grass, milkweeds cotton, dandelion, etc. have wings or hairy structures or dusty seeds. They disperse here and there by wind. ii) Dispersal of seeds by water Seeds of some plants like coconut, water lily, lotus, betel nut, mucuna, dioclea, etc. have buoyant seeds that float in water. Seeds of these plants do not decay in water for a long time. These seeds are dispersed by water to search favourable condition. iii) Dispersal of seeds by animals Some seeds are dispersed through animals and birds. They have hooks or sticky structures on their surface. Seeds of acaena, burdock, tomato, guava, apple, etc. attach to the fur of animal, clothes of human beings, feathers of birds and disperse from one place to another. Seeds of fleshy fruits are eaten by animals and dispersed from one place to another. Round seeds like acorns, hazelnuts, walnuts, etc. are rolled down by animals and reach far away from their origin. iv) Mechanical dispersal of seeds / Dispersal by explosion Some seeds are dispersed by their mechanical bursting. Examples: Seeds of mustard, peas, sesame, Tiuri, Aalas, etc. v) Dispersal of seeds by human beings Human beings transport different kinds of fruits and seeds from one place to another place and from one country to another country. It is a major method of dispersal of seeds in wide range of distance. vi) Dispersal by gravity The ripen fruits are broken from branches as they are pulled by gravity. They decay in the ground and germinate later. Usually hard fruits such as apple and mango disperse in this way. Fig 5.18 : Seeds of dandelion Fig 5.19 : Seeds of coconut Fig 5.20 : Dispersal by animal Fig 5.21 : Seeds of Pea

118 Life Processes Germination of seed After dispersal of seeds, if the environmental conditions are suitable then the embryo gets activated. It uses the stored food in the seed and begins to grow into a new seedling or young plant. The development of a seed into a young plant is called germination of seed. If a seed does not get suitable conditions for germination immediately, it will not die. It germinates only when the conditions become suitable. Seeds survive in a resting state. Such a resting period of seeds is called dormancy. Dormancy of a seed will continue if the embryo in the seed does not experience the suitable conditions. Conditions necessary for seed germination Water, air and suitable temperature are necessary for seed germination. 1. Water A dry seed does not germinate because respiration and other metabolic activities do not occur inside the seed. When the seed absorbs sufficient water from micropyle, enzymes are activated which starts chain bio-chemical reactions. It initiates the germination process. 2. Air The air contains oxygen. When a seed absorbs oxygen, respiration occurs in it. The energy produced from respiration increases metabolic activities in the embryo. As a result germination occurs. 3. Temperature Seeds are dormant at lower temperatures. If it gains temperature from 16 to 25 ⁰C, embryo becomes active for germination. 3. Light The sunlight helps to develop shoot from plumule and root from radicle. Process of seed germination The first step in the process of seed germination is absorption of water. When conditions are suitable the seed starts to take in water. As water is taken in, the seed swells bigger and bigger until the testa (coat) splits apart. Water and oxygen enter through gaps in the testa. Oxygen and glucose enable aerobic respiration, which releases energy. The embryo is able to grow as it receives raw materials and energy. Types of seed germination There are two types of seed germination: epigeal germination and hypogeal germination. a) Epigeal germination In this type of germination, the hypocotyl elongates rapidly upward pulling the cotyledons above the soil. The type of germination where cotyledons emerge out of the soil is called epigeal germination. The cotyledons turn green and act as the first leaves of the young plant. These leaves are called foliage leaves. Photosynthesis takes place in these leaves. They give the baby plant energy, until it gets its own leaves for photosynthesis. The energy for growth is primarily derived from cotyledon. For example, seed of bean, cotton, papaya, gourd, castor, etc. have epigeal germination.

Modern Concept Science and Technology – 8 119 b) Hypogeal germination In this type of germination, the epicotyl elongates and the cotyledons remain below the soil. The type of germination where cotyledons remain inside the soil is called hypogeal germination. In hypogeal germination, the cotyledons do not have any role in photosynthesis. The energy for growth is primarily derived from endosperm. For example, seeds of pea, mango, maize, rice, gram, groundnut, etc. have hypogeal germination. Epicotyl Epicotyl Hypocotyl Hypocotyl Hypocotyl Cotyledon Cotyledon Fig 5.22 : Epigeal germination Fig 5.23 : Hypogeal germination ACTIVITY 5 OBJECTIVE : To show the conditions necessary for germination of seeds. REQUIREMENT : Three bean seeds, glass slide, thread, beaker, water METHODS : 1. Tie three bean seeds at three different places on a glass slide with the help of a thread. 2. Keep that slide in a beaker with water in such a way that one seed is completely immersed in water, the middle one is half immersed in water and upper one is in air. 3. Leave this experiment for 3 to 4 days. OBSERVATION: After 3 to 4 days, we can observe that germination has occured in the middle seed only. RESULT: The middle seed has germinated because it got air, water and favourable temperature. CONCLUSION: This experiment shows that, air, water and temperature are the necessary conditions for the germination of a seed. Seed in air Water Seed inside water Seed partially in water Importance of seed germination i. Seed germination helps in the continuity of generation. ii. The germination of seeds helps in the production of flower, fruits and seeds. iii. Germinated seeds have more nutrients. Which is good for health. iv. Germination of seeds helps in the growth of plants and increase the biodiversity. FACTS WITH REASONS A seed enclosed in an air tight bottle or inside water does not germinate. Seeds need suitable amount of air, water and heat to germinate. A seed enclosed in a bottle does not get water and a seed inside water does not get air. So, a seed enclosed in an air tight bottle or inside water does not germinate.

120 Life Processes HOT SKILL HIGHER ORDER THINKING SKILL 1. Is it true that organisms can be born from single parent? How is it possible? If it is possible mention some ways. Yes! It is true that organisms can be born from single parent. It is called asexual reproduction. It does not involve gametes. So, male and female are not necessary. Organisms are born from other methods. Some of the major methods of asexual reproduction in plants and animals are given below: i) Fission ii) Budding iii) Sporulation iv) Fragmentation or Regeneration v) Vegetative propagation vi) Parthenogenesis 2. Let's say the oars break the long threads of spirogyra into multiple pieces. What will happen to the broken pieces? If we break the long threads of spirogyra into multiple pieces while rowing the boat, it does not kill them. These plants can regenerate from fragments and live separately as new plant. This asexual mode of reproduction is called fragmentation and regeneration. When ever the spirogyra is broken, each piece will continue to absorb essential materials from surrounding. They continue photosynthesis. Regenerate the body and continue living. 3. Is zygote formed during asexual reproduction? Why? Why not? No! zygote is not formed during asexual reproduction. The fusion of a male gamete with a female gamete forms zygote. During asexual reproduction gametes are not involved. Hence zygote is not formed. 4. How does a flowering plant reproduce? When flower becomes mature, androecium releases pollen grains form its anther. These pollen grains reach to the stigma of the flower by various agents called pollination. After pollination, the male gamete reaches to the ovary to fuse with ovum. It is called fertilization. Thus, fertilization is a process of union of a male gamete and a female gamete to form a zygote. The male and female gametes are haploid (n), so the zygote formed after their fusion is diploid (2n) in nature. After fertilization, the ovary turns into fruit and the fertilized ovule becomes a seed. The diploid zygote divides mitotically and develops into a baby plant called an embryo. After getting favourable conditions like heat, light, water, etc. the seed germinates into a new plant. In this way, sexual reproduction in a flowering plant takes place. 5. Bindiya is walking down the street. She saw a rose garden. She asked for seeds with the gardener but the gardener said that she has no seeds of rose. What options does she have to grow roses in her own fields? Bindiya asked for the seeds of roses but sadly they don't form viable seeds. So gardener could not give her the seeds. But she should not worry, there are other options to grow the rose plants. Beside seeds, plants can grow from other body parts too. It is called vegetative propagation.

Modern Concept Science and Technology – 8 121 She can ask for a twig of a rose plant from the gardener. She can plant the twig in her garden or flower vase. If she waters it properly and adds humus, the twig can grow roots. It can live in its own as a new plant. Later it can grow into a rose bush. It is called vegetative propagation by stem. 6. Plants cannot migrate. However plants are found everywhere. How can certain plants grow in different parts of the earth? Plants cannot migrate. However, as we can see, they are every where. I used to wonder how a particular plant is found in so many different places. Later I knew that, plants can grow in different places because their seeds are carried away by various agents into the various places. The rain can break fruits from trees and the stream, can carry it far away from the plant. The wind can break the fruits from trees and carry it far away from the mother plant. Sometimes animals such as monkey carry fruits and seeds to another place. Some plants know how to disperse seeds. They have evolved feathery seeds to fly or bursting pods to throw the seeds farther. Some seeds stick to the fur of animals and fall somewhere else. Humans can also help in dispersal of seeds. We transport fruits and seeds from one place to another for consumption and for agriculture. 7. Even though potato plant grows flower, fruits and seeds, farmers prefer using tubers to grow new potato plants. Potato is a flowering plant. It grows flowers and seeds. However it's fruits grow too late and its seeds are not viable. So it is not profitable for farmers to grow potatoes from seeds. So, they use alternative methods. The vegetative propagation by stem is popular method to grow potatoes. The best potatoes with one or more eyes are selected. They are stored for certain months. Later they are cut into pieces and planted into the soil. It grows into fine new potato plant. It is cheaper, faster and productive for farmers. 3 STEPS EXERCISE EXERCISE STEP1 1. Select the best answer from the given alternatives. a) Which of the following organism reproduces by binary fission? i) amoeba ii) hydra iii) spirogyra iv) moss b) Which mode of asexual reproduction is found in yeast? i) sporulation ii) budding iii) fission iv) regeneration c) A tapeworm breaks into multiple pieces and each piece develop into new organism. What mode of asexual reproduction is it? i) fission ii) fragmentation and regeneration ii) sporulation iv) vegetative propagation d) A new plant grew from the potato kept in the kitchen. What is this mode of reproduction?

122 Life Processes i. fragmentation and regeneration ii) sporulation iii. multiple fission iv) vegetative propagation e) What do you mean by fertilization? i. transfer of pollengrain from anther to stigma ii. cell division of zygote iii. transfer of pollengrain from stigma to anther iv. fusion of male gamete with female gamete 2. Write True for the correct and False for the incorrect statements. a) Multiple fission occurs in plasmodium parasite. b) Bread mould propagates through spores. c) Tuber of potato is an example of vegetation propagation by root. d) A sperm cell is diploid (2n). e) The development of a seed into a young plant is called germination of seed. 3. Fill in the blanks with appropriate words. a) The process of asexual reproduction in which a parent cell divides into two identical cells is called ……......... b) Yeast is reproduced by …………… c) The fertilization that takes place inside the body of female organism is called …………… fertilization. d) If fusion of a male gamete and a female gamete takes place inside the body of female, it is called ............ e) Endosperm is a source of nutrients for the ............ 4. Answer the following questions in very short. a) What is the male reproductive part of a flower? b) Which type of reproduction does not involve gametes? c) How do yeast and hydra generally reproduce? d) Which part of the stamen produces pollengrains? e) Write names of any two agents that help in pollination. STEP2 5. Give reasons. a) Farmers prefer vegetative propagation over seeds. b) Pumpkin flower is called a unisexual flower. c) Earthworm is called a hermaphrodite organism. d) Reproduction is necessarry for organisms and ecosystem. e) Cross pollination helps in evolution. 6. Write any two differences between: a) Sexual reproduction and asexual reproduction b) Binary fission and multiple fission c) Unisexual animals and bisexual animals d) Internal fertilization and external fertilization

Modern Concept Science and Technology – 8 123 e) Self pollination and cross pollination f) Monocotyledonous seeds and dicotyledonous seeds 7. Answer the following in short. a) What is life process? b) What is reproduction? c) Define fission, sporulation and vegetative propagation. d) Define asexual reproduction and list its types. e) What is pollination? f) Define fertilization. g) Identify the type of asexual reproduction shown in the given diagrams: plasmodia Daughter i) ii) iii) iv) v) vi) vii) viii) STEP3 8. Answer the following questions a) List three advantages of asexual reproduction. b) Name any two organisms that show the following mode of asexual reproduction: i) Binary fission ii) Multiple fission iii) Budding iv) Regeneration v) Fragmentation vi) Sporulation vii) Vegetative propagation by stem viii) Vegetative propagation by root. c) How do various organisms reproduce asexually? Describe each process briefly. d) How do flowering plants reproduce sexually? Explain. e) Explain vegetative propagation and its significances to a farmer. f) What are seeds? Mention their functions. g) What do you mean by dispersal of seeds? Discuss the modes of dispersal of seeds. h) What is germination of seeds? How does it occur? i) What do you mean by artificial vegetative propagation? Describe various techniques of artificial vegetative propagations.

124 Force and Motion Force and Motion Unit 6 Introduction Force is an external agent that can bring changes in the state of rest or motion of an object. A moving object covers distance as passing time. It gains velocity. The velocity of one object can be relative respective to another. The velocity of an object can either increase or decrease per unit time which is called acceleration. The force also can be used to operate machines. The simple machine can use force to do work. A lever can transfer force, multiply force or can change the rate of doing work. Door knobs, spoons, brooms and nail cutters are useful tools in our daily life. Friction decreases the mechanical advantages and efficiency of a simple machine but does not affect the velocity ratio. The force can create pressure too. Whenever force falls upon an area it produces pressure. Pressure can be exerted by solid, liquid and gas. The pressure exerted by a solid is directly proportional to the force applied and inversely proportional to the area. The pressure exerted by a liquid column is called liquid pressure. It is directly proportional to the density of the liquid, height of the liquid column and acceleration due to gravity. It is widely used in daily life. Hydraulic brakes and water supply systems in the house are based on liquid pressure. The weight of the air in the atmosphere also exerts pressure on the surface of the earth. Atmospheric pressure helps in drinking through a straw and filling medicine in a syringe. It also helps in the working of the water pump. The air stored in a container above the normal atmospheric pressure is called compressed air. It is widely used in industries to power machines. It is also used as a braking system in heavy trucks and trains. Fulcrum Crow bar Load Effort

Modern Concept Science and Technology – 8 125 Key terms and terminologies of the unit 1. Rest : A body is said to be at rest if it does not change its position with respect to a fixed point taken as a reference point in its surrounding. 2. Motion : A body is said to be in motion if it changes its position with respect to a fixed point taken as a reference point in its surrounding. 3. Reference point : The fixed point with respect to which rest and motion of an object can be studied is called a reference point. 4. Uniform motion : A body is said to have a uniform motion when it covers equal distance in equal interval of time. 5. Non-uniform motion: A body is said to have a non-uniform motion when it covers unequal distance in equal interval of time. 6. Scalar quantity : A physical quantity which has only magnitude but no direction is called a scalar quantity. 7. Vector quantity : A physical quantity which has both magnitude and direction is called a vector quantity. 8. Distance travelled :The actual length of the path travelled by a moving body, irrespective of its direction is called the distance travelled by the body. 9. Displacement : The shortest distance between the initial and final position of a moving body in a particular direction is called displacement. 10. Speed : The total distance travelled per unit time is called speed. 11. Velocity : The displacement of a body per unit time is called its velocity. Sequence of Curriculum Issued by CDC  Introduction to relative velocity  Introduction to average velocity and simple calculations  Introduction to acceleration and simple calculations UNIT Motion 6.1 Estimated teaching periods Theory Practical 4 1 Sir Isaac Newton Sir Isaac Newton is world famous for his contributions to universal gravitation and laws of motion. He was born in England on 4th January 1643 and died on 31st March 1727. He was a mathematician, physicist, astronomer, alchemist and philosopher. He is known for his works in classical mechanics and optics. He with his friend Gottfried Wilhelm Leibniz developed infinitesimal calculus. He was educated (M.A) at Trinity College, Cambridge. About the Scientist

126 Motion 12. Average velocity :The arithmetic mean of the initial velocity and final velocity over a given period of time is called average velocity. 13. Relative velocity : The velocity of a body with respect to a second body is called relative velocity. 14. Acceleration : The rate of change of velocity of a body is called acceleration. 15. Retardation : The rate of decrease in velocity is called negative acceleration or retardation. 16. Equation of motion:The relationship between initial velocity (u), final velocity (v), distance travelled (s), acceleration (a) and time taken (t) is called an equation of motion. Introduction Let us observe in our surrounding. We can see various things. Among them some can move and some cannot. A body is said to be at rest if it does not change its position with respect to its surrounding. For example, a book on the table does not change its position with respect to the table. So, the book is said to be in a state of rest. Similarly, school, house, bench, desk, chair, etc. are some examples of the resting objects. The fixed point with respect to which rest and motion of an object can be studied is called a reference point. Animals, human beings and other objects in our surrounding can move from one place to another. They are called moving objects. Thus, a body is said to be in motion if it can change its position with respect to its surrounding. For example, a football kicked by the player, falling apple, moving vehicle, rainfall, flying birds, walking animals, etc. We need to apply an external force to change the state of rest and state of motion. ACTIVITY 1 Observe your surrounding carefully and write down the name of any five objects which are in the state of motion and in the state of rest. Rest and motion are relative terms When we are on the seat of a moving bus, we are in the state motion with respect to the trees or buildings present along the road side. However, if we compare our position with respect to other passengers, we are at rest. Thus, an object can be at rest with respect to one reference point while it can be in motion with respect to another reference point at the same time. FACTS WITH REASONS Rest and motion are called relative terms. A body may be at rest with respect to one reference point and may in motion with respect to another reference point at the same time. So, rest and motion are the relative terms. Fig: Rest and motion MEMORY TIPS There is nothing at absolute rest. Everything in this world, from the smallest particle to the largest galaxies is in motion. An object at rest with respect to one reference point may be in motion with respect to another reference point.

Modern Concept Science and Technology – 8 127 Uniform Motion and Non-uniform Motion Uniform motion A body is said to be in a uniform motion when it covers equal distance in equal interval of time. For example, a car moving in a straight line with a constant speed has uniform velocity. 12m 12m 12m 12m 0s 1s 2s 3s 4s Fig: A uniform motion Non-uniform motion or variable motion A body is said to be in a non-uniform motion when it covers unequal distance in equal interval of time. For example, the motion of a freely falling object is in non- uniform. 8m 20m 10m 22m 0s 1s 2s 3s 4s Fig: A non-uniform motion FACTS WITH REASONS Motion of a falling object towards the earth is a variable motion (neglecting the air resistance). Gravity of the earth accelerates the falling body towards the earth's surface. In average, the acceleration due to gravity of the earth is 9.8 m/s2 . So, every second a falling body moves 9.8 m/s faster. So motion of a falling object towards the earth is a variable motion. ACTIVITY 2 Observe your surrounding carefully and write down the name of objects which are in the state of uniform motion and in non-uniform motion. Scalar Quantities and Vector Quantities Scalar quantity Those physical quantities which have only magnitude are called scalars or scalar quantities. For example, distance, speed, mass, work, energy, etc. A scalar quantity does not need a direction to express it. Vector quantity Those physical quantities which have both magnitude and direction are called vectors or vector quantities. A vector quantity requires both magnitude and direction for its complete description. For example, displacement, force, weight, velocity, etc.

128 Motion Differences between vectors and scalars SN Vectors SN Scalars 1 Vector quantities have both magnitude and direction. 1 Scalar quantities have only magnitude. 2 The sum of vectors may be positive or zero or negative. 2 The sum of scalars is always positive. 3 Addition and subtraction of the vectors can be done by vector algebra. 3 Addition and subtraction of the scalars can be done by simple algebra. Distance and Displacement Distance The actual length of the path travelled by a body is called distance. The SI unit of distance is meter (m). It is a scalar quantity. In distance we measure actual length of the path covered by a moving body. We do not account direction. For example, If a man travels 8 m from point B to point C, 4 m from point C to point D and then 8 m from point D to point A, then the total length of the path travelled by the man = BC + CD + DA Or, Distance = 8 m + 4 m +8 m = 20 m. Displacement The shortest distance between the initial position and the final position of a moving body in a particular direction is called its displacement. It is a vector quantity. Its value may be positive, negative or zero. For example, when a man travels from a point B to another point A towards the north, then the displacement (BA) of the man is 4 m towards north. FACTS WITH REASONS Is it possible to have a zero displacement but non-zero distance? In case of a body moving in a circular track, after one complete revolution, the distance travelled by the body is equal to the circumference of the track i.e.,2πr, where r is radius of the track. But the displacement is zero. Differences between distance and displacement. SN Distance SN Displacement 1 The actual length of the path travelled by a body is called distance. 1 The shortest distance between the initial position and the final position of a moving body in a particular direction is called its displacement. 2 It is a scalar quantity. 2 It is a vector quantity. 3 It is always positive. 3 It may be positive, zero or negative. A B 4 m 4 m 8 m 8 m D C Fig: Distance

Modern Concept Science and Technology – 8 129 Speed and Velocity Speed The speed of a body gives an idea of how fast a body is moving. With the help of speed we can compare the distance travelled by the two bodies in a given interval of time. For example, if a car covers 1 km distance in one minute and another car covers the same distance in 2 minutes, then the first car has more speed than the second car. Thus, the rate of change of distance is called speed. Speed = Distance travelled (s) Time taken (t) You might have seen a meter fitted on the dashboard of cars, buses and other vehicles, which records the speed. It is called speedometer. Its SI unit is m/s and CGS unit is cm/s. The speed of the fast moving bodies like cars, bus, trains, aeroplanes, etc. is expressed in kilometer per hour written as km/h. When the speedometer in a car indicates 72 km/h, it indicates that the car covers a distance of 72 kilometer in one hour. FACTS WITH REASONS Speed is a scalar quantity. Speed has only magnitude but it does not have direction. So,speed is a scalar quantity. Velocity Velocity is same as speed except direction of motion. Velocity is a physical quantity which has both direction of motion and the distance covered. Thus, the rate of change of displacement is called velocity. Velocity (v)= Displacement (s) Time taken (t) It is a vector quantity. The unit of velocity is same as that of speed, i.e. In SI system, unit of velocity is m/s. FACTS WITH REASONS Velocity is a vector quantity. Velocity has both magnitude and direction. So, it is a vector quantity. Differences between speed and velocity SN Speed SN Velocity 1 Speed is the rate of change of distance. 1 Velocity is the rate of change of displacement. 2 It is a scalar quantity. 2 It is a vector quantity. 3 It cannot be zero. 3 It can be zero.

130 Motion Solved Numerical 2.1 Find the speed of a car which covers 800 m distance in 40 seconds. Solution: Distance covered by the car (s) = 800 m Time taken = 40 s Speed = ? We know, speed = distance travelled (s) time taken (t) = 800 40 = 20 m/s ∴ The speed of car is 20 m/s. 6.1.1 Relative Velocity The calculated value of a velocity depends upon the observer when one is moving with respect to another. For example, when two cars are moving in the same direction at a high speed on the highway, then the observer along the road side observes that both the cars are moving with high velocity. But relative to one another, the two cars hardly move at all. Thus, the velocity of one body with respect to another body is called relative velocity. Fig: Relative velocity a) Relative velocity for the bodies moving in the same direction When two bodies A and B are moving along a straight line in the same direction, the magnitude of the relative velocity of A with respect to (w.r.t.) B is given by VAB = VA – VB VAB is the relative velocity of the object A as seen from the object B. In the given figure, the velocity of the police car with respect to the sport car is given by VPS = VP – VS VPS = 80 – 70 = 10 kmh–1 Thus, the velocity of the police car as seen from the sport car is 10 kmh–1. FACTS WITH REASONS When two buses are moving in the same direction with the same velocity then a passenger in one bus finds another bus at rest. When two buses are moving in the same direction with the same velocity then the relative velocity is zero. In this condition, one bus does not change its position with respect to another. So, a passenger in one bus finds another bus at rest. If the bodies are moving with the same velocity (i.e. VA = VB , their relative velocity will be zero. i.e. VAB = VA – VB = VA – VA = 0 Memory Tips 80km/hr 70km/hr Fig: Bodies moving in the same direction

Modern Concept Science and Technology – 8 131 b) For the bodies moving in the opposite direction When two bodies A and B are moving along a straight line in the opposite direction, the magnitude of the relative velocity of A w.r.t. B is equal to the sum of the magnitude of their velocities. i.e. VAB = VA – (–VB) = VA + VB In the given figure, the velocity of polish car (80km/h) with respect to the sport car(70km/h) is given by VP = VP + VS VPS= 80 + 70 = 150 kmh–1 Thus, the velocity of the polish car as seen from the sport car is 150 kmh–1. Solved Numerical 2.3 The velocity of car A is 10 m/s towards north and the velocity of the car B is 15 m/s towards south. If both the cars start from the same line, calculate: i) the distance travelled by each of them in 2 minutes ii) the relative velocity iii) the distance between them after 1 minute Solution: Velocity of car A (VA) = 10 m/s Velocity of car B (VB) = 15 m/s i) Time (t) = 2 minutes = 2× 60 = 120 s Distance travelled by the car A in 2 minutes = VA × t = 10 × 120 = 1200 m Distance travelled by the car B in 2 minutes = VB × t = 15 × 120 = 1800 m ii) Relative velocity VAB = VA + VB = 10 + 15 = 25 m/s iii) Time (t) = 1 minute = 60 s The distance between two cars after 1 minutes = Relative velocity × time = 25 × 60 = 1500 m 6.1.2 Average velocity If the velocity of a body in a particular direction changes continuously at a uniform rate, then the arithmetic mean of the initial velocity and final velocity over a given period of time is called average velocity. Thus, the mean of the initial velocity and final velocity over a given period of time is called average velocity. Velocity (vav) = Initial velocity (u) + Final velocity (v) 2 Bodies moving in the opposite direction A 10 m/s 15 m/s B

132 Motion But if the velocity of a body in a particular direction does not change continuously at a uniform rate the average velocity is given by Average velocity (v) = Total displacement Total time taken 3m 4m 2m 4m 0s 1s 1s 1s 1s In the given figure, total displacement (s) = 3 m + 4 m + 2 m + 4 m = 13 m Total time (t) = 4 s ∴ The average velocity = Total displacement (s) Total time taken (t) = 13 4 = 3.25 m/s Solved Numerical 2.2 Calculate the average velocity of a bus which covers 7500 m distance towards east in 5 minutes. Solution: Total displacement = 7500 m Total time taken = 5 minutes = 5 × 60 second = 300 s We know, average velocity (v) = Total displacement (s) Total time taken (t) = 7500 300 = 25 m/s ∴ The average velocity of the bus is 25 m/s. 6.1.3Acceleration A moving object may not have uniform velocity all the time. Sometimes, its velocity increases and sometimes decreases. For example, a bus starts from the rest and after a certain interval of time it attains a constant velocity. If a person comes on the road in front of the bus, then the driver applies brakes and the velocity gradually decreases. Finally, the velocity of the bus becomes zero and the bus stops. In this example, the bus is under acceleration. That is, the velocity of the bus changes with time. Thus, the rate of change in velocity is called acceleration. Acceleration = Change in velocity Time taken Acceleration (a) = Final velocity (v) – Initial velocity (u) Time taken (t) or, a = v – u t The SI unit of acceleration is m/s2 and it is a vector quantity. Meaning of positive acceleration An object has acceleration of 2 m/s2 means the velocity of the object increases by 2 m/s in every second. MEMORY TIPS When the velocity of an object increases (i.e., v > u), it is under positive acceleration.

Modern Concept Science and Technology – 8 133 FACTS WITH REASONS A body in a uniform linear motion is not under acceleration but that in a uniform circular motion is under acceleration. In a uniform linear motion, the change in velocity is zero and the direction of motion is fixed. But, in case of a uniform circular motion, the direction of motion changes continuously. So, a body in a uniform linear motion is not under acceleration but that in a uniform circular motion is under acceleration. The motion of an athlete running in a circular track with a constant speed is an accelerated motion. When an athlete runs in a circular track with a constant speed, then the direction of athlete in the track changes continuously. Such motion is called an accelerated circular motion. Solved Numerical 2.4 A car moving with a speed of 15 m/s speeds up to 30 m/s in 5 seconds. Calculate its acceleration. Solution: Initial velocity of the car (u) = 15 m/s Final velocity of the car (v) = 30 m/s Total time taken = 5 s Acceleration (a) = ? From the formula, acceleration (a) = v – u t = 30 – 15 5 = 3 m/s2 ∴ Acceleration of the car is 3 m/s2 . Negative acceleration or Retardation If final velocity (v) of a moving body is less than the initial velocity (u), then the acceleration comes in negative. It can be expressed as: Acceleration (a) = Final velocity (v) – Initial velocity (u) Time taken (t) = Negative quantity Time taken = Negative quantity The decrease in velocity of a body in motion with time causes negative acceleration. Thus, the rate of decrease in velocity is called negative acceleration, or retardation. For example, a ball thrown vertically upward from the earth has a negative acceleration; a football rolling on the plane football ground also has a negative acceleration. Meaning of negative acceleration An acceleration of – 7 m/s2 means that the velocity of the body decreases by 7 m/s in every second. Solved Numerical 2.5 A car has an initial speed of 45 m/s at a point A. When brakes are applied then after 4 seconds its speedometer records a speed of 15 m/s. Find acceleration of the car. Solution: Initial velocity of the car (u) = 45 m/s Final velocity of the car (v) = 15 m/s MEMORY TIPS When the velocity of an object decreases (i.e., v < u), it is under negative acceleration, or retardation.

134 Motion Total time taken = 4 s Acceleration (a) = ? From the formula, acceleration (a) = v – u t = 15 – 45 4 = – 30 4 = – 7.5 m/s2 ∴ Retardation of the car is 7.5 m/s2 . HOT SKILL HIGHER ORDER THINKING SKILL 1. How can we tell if an object is in either rest or motion? We can tell if any object is either at motion or at rest by comparing it with another object taken as a reference point. 2. Write any two differences between acceleration and retardation. : Differences between acceleration and retardation are: S.N. Acceleration S.N. Retardation 1 The rate of change in velocity is called acceleration. 1 The negative acceleration, or the rate of decrease in velocity is called retardation. 2 It is represented by ‘a’. 2 It is represented by‘-a’. 3. Write any two differences between average velocity and relative velocity. Differences between average velocity and relative velocity are: S.N. Average velocity S.N. Relative velocity 1 The mean of the initial velocity and final velocity over a given period of time is called average velocity. 1 The velocity of one body with respect to another body is called relative velocity. 2 Average velocity depends upon the initial and final velocity of the body. 2 Relative velocity depends upon the velocity and direction of the moving bodies. 4. Distance, speed, mass, time, work, etc. are called scalar quantities. Distance, speed, mass, time, work, etc. are called scalar quantities because they have magnitude but no direction. 5. What are constant and variable velocities? If a body covers equal displacement in equal interval of time, the velocity of the body is called constant velocity. It is also called a uniform velocity. If a body does not cover equal displacement in equal interval of time, the velocity of the body is called variable velocity. 6. Under what condition the acceleration of a moving object becomes zero? Acceleration of a moving object becomes zero if it is moving with a uniform velocity.

Modern Concept Science and Technology – 8 135 7. Acceleration of an object with uniform velocity is zero. If an object is moving with a uniform velocity, then there is no change in velocity. It means that initial velocity is equal to the final velocity of the body. Hence, acceleration becomes zero. 8. A running horse covers a distance of 1200 m in 3 minutes. What is the speed of the horse? Solution: Total distance travelled(s) = 1200 m Total time taken (t) = 3 minutes = 3 × 60 second = 180 s Speed of the horse = ? From the formula, speed = Total distance Total time taken = 1200 180 = 6.667 m/s ∴ The speed of the horse is 6.667 m/s. 9. A bus starts from rest and attains a velocity of 20 m/s after 5 seconds. Find its acceleration. Solution: Total time taken = 5 s Initial velocity of the bus (u) = 0 m/s Final velocity of the bus (v) = 20 m/s Acceleration of the bus (a) = ? From the formula, Acceleration (a) = v – u t = 20 – 0 5 = 4 ∴ Acceleration of the bus is 4 m/s2 . 10. A ‘car A’ is moving towards east with a velocity of 70 km/h and another ‘car B’ is moving towards west with a velocity of 50 km/h. Find their relative velocity. Also, find their relative velocity if they move in the same direction. Solution: Velocity of car A (VA) = 70 km/h Velocity of car B (VB) = 50 km/h Relative velocity (VAB) = ? When both the cars are moving in the opposite direction Relative velocity (VAB) = VA + VB = 70 + 50 = 120 km/h When both the cars are moving in the same direction Relative velocity (VAB) = VA – VB = 70 – 50 = 20 km/h

136 Motion 3 STEPS EXERCISE EXERCISE STEP1 1. Select the best answer from the given alternatives. a) What is true for a body moving with a uniform velocity of 2 m s-1 ? i) uniform acceleration ii) non-uniform acceleration iii) zero acceleration iv) variable acceleration b) What is true for a body moving with a constant velocity ? i) constant acceleration ii) zero acceleration iii) variable acceleration iv) deceleration c) What kind of velocity does a freely falling apple have? i) increasing velocity ii) decreasing velocity iii) uniform velocity iv) acceleration d) What is the SI unit of velocity? i) ms-1 ii) ms-2 iii) cms-1 iv) cm-2 e) What is the SI unit of acceleration? i) ms-1 ii) ms-2 iii) cms-1 iv) cm-2 f) When two bodies A and B are moving along a straight line in the same direction, What equation will give the magnitude of relative velocity of A w.r.t B? i) VBA = VB – VA ii) VAB = VA + VB ii) VAB = VA – VB iv) VBA = VB + VA 2. Write True for the correct and False for the incorrect statements. a) A freely falling stone towards the earth has a uniform velocity. b) Two cars A and B are moving with the same speed in the same direction. A passenger in the car A finds that the car B is at rest. c) In SI system the acceleration due to gravity is 8.9 m /s2 . d) When a body starts from rest, its final velocity is zero. e) The SI unit of speed is m/s. f) A ball thrown vertically upward is under retardation. g) Acceleration is a scalar quantity. 3. Fill in the blanks with appropriate words. a) Velocity………… in freely falling body. b) The distance covered by a body in unit time in a specified direction is called……. c) The........................ is produced in an object if there is change in its velocity? The SI unit of acceleration is …….....

Modern Concept Science and Technology – 8 137 d) If a body is moving with a constant velocity then it has ……. acceleration. e) The negative acceleration is called ……..... f) The velocity of a body A with respect to another body B in motion is denoted by......... . 4. Answer the following questions in one word. a) How much is the relative velocity of two cars moving along a straight path with same velocity? b) What is called to the total distance travelled by a body per unit time? c) What is called to the rate of change of velocity? d) What is the rate of decrease of velocity of a body called? e) How much is the initial velocity of a body which is dropped from a certain height from the earth surface? STEP2 5. Give reasons. a) Rest and motion are relative terms. b) Motion of a falling object towards the earth is a variable motion (neglecting the air resistance). c) It is possible to have a zero displacement but non-zero distance travelled. d) Speed is a scalar quantity. e) Velocity is a vector quantity. f) When two buses are moving in the same direction with the same velocity then a passenger in one bus finds another bus at rest. g) Motion of an athlete running in a circular track with a constant speed is an accelerated motion. 6. Write any two differences between: a) Scalar quantities and vector quantities b) Distance travelled and displacement c) Speed and velocity d) Uniform velocity and variable velocity e) Positive acceleration and negative acceleration 7. Answer the following questions. a) What are rest and motion? b) What do you mean by a reference point? c) Write down SI unit of the followings: i) Distance ii) Displacement

138 Motion iii) Velocity iv) Acceleration d) Define the following terms with required examples. i) uniform velocity ii) average velocity iii) relative velocity iv) retardation e) When does a body have: i) positive acceleration ii) negative acceleration iii) zero acceleration STEP3 8. Answer the following questions. a) How is the relative velocity calculated when: i) the two bodies A and B are moving in a straight line in the same direction. ii) the two bodies A and B are moving in a straight line in the opposite direction. b) In which condition the relative velocity of the two bodies moving in the same direction becomes zero? c) Find the relative velocity of the jeep with respect to the cyclist shown in the figure below. [Ans: 15 m/s] 10 m/s 25 m/s 9. Numerical Problems a) A tiger covers a distance of 600 m in 1.5 minutes. What is the speed of the tiger? [Ans: 6.67 m/s] b) A motor bike covers a distance of 1.5 km on a straight road in 2 minutes. Find average velocity of the motor bike. [Ans: 12.5 m/s] c) A car is moving with a speed of 15 ms-1. How long does it take to cover a distance of 1.2 km? [Ans: 80 seconds] d) A car starts from rest and gains a velocity of 20 m/s in 10 s. Calculate acceleration and average velocity. [Ans: 2m/s2 , 10 m/s] e) A vehicle accelerates with 0.4 m/s2 . Calculate the time taken by the vehicle to increase its speed from 20 m/s to 40 m/s. [Ans: 50 s] f) A bike is moving with a velocity of 10 m/s. If its acceleration is 1.2 m/s2 for 10 s, calculate the final velocity of the bike. [Ans: 22 m/s] g) A bus starts from rest and attains an acceleration of 2 m/s2 after 10 seconds. Find the distance covered by the bus in that time. [Ans: 100 m]

Modern Concept Science and Technology – 8 139 h) A train is moving with the velocity 10 m/s. It attains an acceleration of 4 m/s2 after 5 seconds. Find the distance covered by the train in that time. [Ans: 10 m] i) A car moving along a straight highway at a speed of 144 km/h is brought to rest within a distance of 200 m. i) What is the retardation of the car? [Ans: 4m/s2 ] ii) How long does it take for the car to stop? [Ans: 10 s] j) A bus ‘A’ is moving towards east with a velocity of 170 km/h and another bus ‘B’ is moving towards west with a velocity of 70 km/h. Find their relative velocity. Also, find their velocity if both are moving in the same direction. [Ans: 240 km/h, 100 km/h.] k) A motorcycle ‘A’ and another motorcycle ‘B’ are moving in the same direction with the velocities 60 km/h and 80 km/h respectively. Find the relative velocity of the motorcycle B with respect to car A. Also, find their velocity if both motorcycles move in the opposite direction. [Ans: 20 km/h, 140 km/h.] l) A body moves in the east with the velocity of 25 m/s. Another body B moves in the same direction with a velocity of 10 m/s. If both of them had started from the same point then find: i) the velocity of A w.r.t. B. [Ans: 15 m/s] ii) the distance covered by each in 30 seconds. [Ans: 750m, 300m] ii) the distance between them after 1 minute. [Ans: 900 m] Project Work Project Work 1. Mark a line on your school ground. Then measure a length of 50 m from the mark with the help of a measuring tape. Put another mark there. Now, tell your two friends to run from one mark to another mark and measure the time taken to cross the length. Find their average velocity. 2. Make two running tracks each of 50 m on your school ground. Tell two friends to run once in the same direction and next time in the opposite direction. Measure the time taken by them to complete the distance of 50 m. Find their average velocity. Use these values to find their relative velocity.

140 Simple Machine Key terms and terminologies of the unit 1. Simple machine : The device which makes our work easier, faster and more convenient is called a simple machine. 2. Compound machine : The machine which has a complex structure and made from two or more simple machines working together is called a compound machine. 3. Load : Load is the weight which has to be lifted by a simple machine. 4. Load distance : The distance moved by the load in a simple machine is called load distance. 5. Effort : Effort is the force applied directly to a simple machine to move the load or to do work. 6. Effort distance : The distance moved by effort in a simple machine is called effort distance. 7. Mechanical advantage : The ratio of the load lifted to the effort applied in a simple machine is called mechanical advantage. 8. Velocity ratio (V.R.) : The ratio of the distance moved by effort to the distance moved by load in a simple machine is called velocity ratio. 9. Input work : The work done on a simple machine by a given effort is called input work. 10. Output work : The work done by a simple machine on the load is called output work. 11. Efficiency : The percentage ratio of output work to input work is called efficiency of a machine. 12. Practical machine : The machine which is useful in our daily life is called a real or practical machine. 13. Perfect simple machine : A hypothetical frictionless machine in which total input work is converted into output work without wastage of energy is called an ideal or a perfect simple machine. 14. Lever : A lever is a rigid bar which is capable of rotating about a fixed axis called fulcrum. Sequence of Curriculum Issued by CDC  Introduction to lever and its types  Working principles of the lever  Introduction to mechanical advantage, velocity ratio and efficiency and simple calculations UNIT Simple Machine 6.2 Estimated teaching periods Theory Practical 4 1 Archimedes of Syracuse is well known for Archimedes principle developed to find the volume of irregular solids which could be used to find the purity of metals. He was born in Ancient Greece, the ancient city of Syracuse in Sicily in 287 BC and died in 212 BC. He was a Greek mathematician, physicist, engineer, astronomer and inventor. He discovered the centre of gravity, the law of lever and Archimedes’ screw. Archimedes of Syracuse About the Scientist

Modern Concept Science and Technology – 8 141 15. Principle of lever : The principle of lever states that, “at an equilibrium condition the product of effort and effort arm is equal to the product of load and load arm.” 16. First class lever : The lever in which fulcrum lies in between load and effort is called first class lever. 17. Second class lever : The lever in which load lies in between fulcrum and effort is called a second class lever. 18. Third class lever : The lever in which effort lies in between load and fulcrum is called third class lever. Introduction Present age is the age of tools and machines. They make our work easier and faster. Varieties of tools are used in our daily life. Among them some machines are simple in structure while others are complex. Those machines which are simple in structure are called simple machines. For example, sharp knife is used for cutting things, pulley is used to lift loads, wheel and axle is used to multiply effort, slanted surface is used to load and unload the things easily, etc. Thus, those devices which make our work easier, faster and more convenient are called simple machines. Examples: scissors, knife, nut cracker, bottle opener, spoon, pulley, screw. These machines need muscular energy to work. Scissors Beam balance Wheelbarrow Pulley Screw Axe Fig: Some simple machines Most of the modern machines are compound in their structure. They are made by the combination of two or more simple machines. So, the machine which has complex structure and made from two or more simple machines working together is called a compound machine. For example, bicycle, motor bike, sewing machine, etc. Compound machines use different types of energy like electrical energy, chemical energy, etc. In this unit, we will describe about the lever. 6.2.1 Advantages of Simple Machines Simple machines make our work easier, faster and more convenient by the following ways: i) Simple machines help to multiply effort. ii) They help to change the direction of effort. iii) They help to increase the speed of work. iv) They transfer the applied force. v) They help to do work safely.

142 Simple Machine 6.2.2 General Terms Used in the Study of Simple Machines 1. Load and Load Distance Load is the weight which has to be lifted by a simple machine. The SI unit of load is newton (N). It is represented by ‘L’. The distance moved by the load in a simple machine is called load distance. Its SI unit is meter (m). It is represented by ‘Ld’. 2. Effort and effort distance Effort is the force applied directly to a simple machine to move the load or to do work. The SI unit of effort is newton (N). It is represented by ‘E’. The distance moved by the effort applied in a simple machine is called effort distance. Its SI unit is meter (m). It is represented by ‘Ed’. 3. Mechanical advantage The ratio of the load to the effort is called mechanical advantage, i.e. MA = Load (L) Effort (E) MA does not have unit as it is a simple ratio of two forces. If the load lifted by a machine is greater than the effort applied, the mechanical advantage becomes greater than 1. Similarly, if the load lifted by the simple machine is less than the effort applied, the mechanical advantage becomes less than 1. FACTS WITH REASONS Mechanical advantage of a simple machine is 2. What does it mean? Mechanical advantage of a simple machine is 2 means that this simple machine multiplies the effort applied by 2 times. 4. Velocity ratio Velocity ratio is a measure that shows how many times the effort distance is longer than the load distance. Thus, the ratio of the distance travelled by effort to the distance travelled by load in a simple machine is called velocity ratio. VR = Distance moved by effort (Ed) Distance moved by load (Ld) VR does not have unit as it is a simple ratio of two distances. FACTS WITH REASONS Velocity ratio of a simple machine is 4. What does it mean? Velocity ratio of a simple machine is 4 means that the effort applied moves 4 times longer distance than the distance moved by the load. MEMORY TIPS MA is affected by friction and weight of the machine. If friction increases, MA decreases and viceversa. In the world, no machine is frictionless. So, large amount of input work is lost to overcome friction and weight of the machine.

Modern Concept Science and Technology – 8 143 i) Velocity ratio of a simple machine is independent of friction Velocity ratio is the simple ratio of effort distance to the load distance. So, friction does not affect velocity ratio. ii) Velocity ratio of a simple machine is always greater than its mechanical advantage Mechanical advantage of a simple machine is affected by the friction and weight of the simple machine but the velocity ratio is not affected by friction and weight of the simple machine. So, velocity ratio of a simple machine is always greater than mechanical advantage. FACTS WITH REASONS M.A. and V.R. of simple machines do not have unit. MA = Load (L) Effort (E), it is a simple ratio of two forces. Similarly, VR =Effort distance Load distance, it is a simple ratio of two distances. So, M.A. and V.R. of a simple machines do not have unit. 5. Input work The work done on a simple machine is called input work. It is the energy supplied to the machine. Input work is calculated by : Input work = Effort (E) × Effort distance (Ed) The SI unit of input work is joule (J). 6. Output work The work done by a simple machine on the load is called output work. It is calculated by Output work = Load (L) × Load distance (Ld) The SI unit of output work is joule (J). 7. Efficiency The percentage ratio of output work to input work is called efficiency of a machine, i.e. Efficiency (η) = Output work Input work × 100% Efficiency doesn’t have unit as it is a simple ratio of two works. FACTS WITH REASONS Efficiency of a simple machine is 80%. What does it mean? Efficiency of a simple machine is 80% means that, only 80% of the input work is utilized to do useful work and the remaining 20% input work is changed into other forms of energy while overcoming frictional force. a) Effect of friction in efficiency of a machine Frictional force converts the energy supplied to a machine into other forms of energy like heat. So, the efficiency of a machine decreases as the frictional force increases. Frication should be reduced to increase efficiency of a machine.

144 Simple Machine b) Methods of reducing friction in a machine i) Use of grease or lubricants: Proper greasing or lubrication between sliding parts of a simple machine reduces friction. ii) Use of ball bearing: Sliding friction can be reduced by rolling friction with the help of ball bearings. iii) Designing smooth surfaces: There is less frictional force between two smooth surfaces. So, surfaces are made smooth to reduce friction. c) Real or practical machine The machine which is used in our daily life is called a real machine or a practical machine. A real simple machine is never 100 % efficient because of the following reasons: i) The real machine is affected by friction. In a real machine, total input work does not change into output work. Some of the input energy is changed into other forms of energy like heat, sound, etc. ii) The real machine has weight. No machine is weightless. So, weight of the simple machine affects its efficiency. FACTS WITH REASONS A real simple machine is never 100 % efficient. No machine is weightless and frictionless. The total input work in a real machine does not change into output work. Some of the input work changes into other forms of energy like heat, sound etc. Therefore, output work becomes less than input work in a real simple machine. Hence, a real simple machine is never 100 % efficient. d) Ideal or perfect simple machine A hypothetical weightless and frictionless machine in which total input work is converted into output work without wastage of energy is called an ideal or a perfect simple machine. Efficiency (η) = Output work Input work × 100% In case of an ideal simple machine, Input work = Output work, Efficiency (η) = 1 × 100% = 100% So an ideal simple machine has 100 % efficiency. FACTS WITH REASONS It is impossible to have an ideal machine. An ideal machine has 100% efficiency. A machine can have 100% efficiency if it does not have friction and weight. Since it is impossible to make a weightless and frictionless machine, it is impossible to make an ideal machine.

Modern Concept Science and Technology – 8 145 Differences between Real simple machines and Ideal simple machines S.N. Real simple machines S.N. Ideal simple machines 1 The efficiency of a real simple machine is always less than 100%. 1 The efficiency of an ideal simple machine is always equal to 100%. 2 In real simple machines, output work is less than input work. 2 In ideal simple machines, output work is equal to input work. 3 In a practical machine, MA is less than VR. 3 In an ideal machine, MA is equal to VR. 6.2.3 Relation between MA, VR and Efficiency Efficiency of a simple machine is given by: Efficiency (η) = Output work Input work × 100% or, Efficiency (η) = Load × Load distance Effort × Effort distance × 100% or, Efficiency (η) = Load Effort Effort distance Load distance × 100% or, Efficiency (η) = MA VR × 100% From the above relation, efficiency of a machine can also be defined as the percentage ratio of mechanical advantage (MA) to the velocity ratio (VR) of the machine. 6.2.4Types of Simple Machines 1. Lever 2. Pulley 3. Wheel and axle 4. Inclined plane 5. Wedge 6. Screw All six types of simple machines are basically from two types of simple machines. They are : i) Lever ii) Inclined plane The modified forms of lever are pulley and wheel and axle. Whereas the modified form of inclined planes are wedge and screw. MACHINE LEVER PULLEY WHEEL AND WEDGE SCREW AXLE INCLINED PLANE Memory Tips 6.2.5Lever A lever is a rigid bar which is capable of rotating about a fixed axis called fulcrum. Lever was invented around 240 BC. The weight to be lifted by using a lever is called load (L) and the force applied on the lever to lift a load is called effort(E). The distance of effort from the fulcrum is called Effort distance (Ed) and the distance of load from the fulcrum is called load distance (Ld).

146 Simple Machine Principle of lever The principle of lever states that, “when a lever is in equilibrium condition then the product of effort and effort arm is equal to the product of load and load arm.”i.e. In an equilibrium condition, Effort (E) × Effort arm (Ed) = Load (L) × Load arm (Ld) Types of lever a) First class lever The lever in which fulcrum lies in between load and effort is called first class lever. Examples: crow bar, see-saw, scissors, dhiki, pliers, nail cutter, etc. Crowbar See-saw Scissors Pliers Nail cutter Fig: First class lever Mechanical advantage of first class lever From the principle of lever, Effort (E) × Effort arm (Ed) = Load (L) × Load arm (Ld) or, L E = Ed Ld ∴ MA = Ed Ld Thus, the mechanical advantage of the first class lever depends upon the position of fulcrum in between load and effort. On the basis of length of effort distance and load distance, we can summarize the following conditions: i) When Ed >Ld, M.A. > 1 ii) When Ed <Ld, M.A. < 1 iii) When Ed = Ld, M.A. = 1 Application of first class lever to multiply effort From the principle of lever, Input work = Output work or, E × Ed = L × Ld Thus, when effort distance (Ed) is greater than the load distance (Ld), then effort gets multiplied. Less effort (E) can lift a heavy load (L) as shown in the given figure. Load arm Load Effort arm Effort Fulcrum Fulcrum Crow bar Load Effort