Oasis School Science and Technology 10 New

Oasis School Science and Technology - 10 51 14. Parrot Kingdom : Animalia Phylum : Chordata Sub-phylum : Vertebrata Class : Aves Type : Parrot 15. Bat Kingdom : Animalia Phylum : Chordata Sub-phylum : Vertebrata Class : Mammalia Type : Bat Relation of classification of organisms with evolution of life on the earth Classification means putting organisms into groups and sub-groups based on their similarities or differences. In the classification of organisms, the very simple and primitive organisms are kept ahead of the developed organisms. Kingdom Monera, for example, is a group of much simpler and primitive organisms than kingdom Protista. Similarly, kingdom Protista is simpler than kingdom Fungi, and so on. It demonstrates that the processes of evolution and classification of living beings on the earth is the same. Similarly, as one moves down each level of classification, the number of species in the group decreases. Two species within the same genus most likely share a recent common ancestor in their evolutionary history. It also demonstrates the evolution of life on Earth from simple and primitive to complex. Fig: evolutionary tree Fact File Horse is more developed than seahorse, whale is more developed than shark and bat is more developed than bird.

52 Oasis School Science and Technology - 10 Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Let’s suppose we saw a creature in the water, how can we tell if it is either a pisces or amphibian or a reptile. If we saw a creature in the water, we can tell if it is either pisces, amphibians or reptile by observing its physical features: i. If it has gills, scales and a streamlined body it is likely a fish. ii. If it has no neck, has four limbs, does not crawl, and can live in or out of the water, it is likely an amphibian. iii. If it has a streamlined body and rough scales on the body, it is likely a reptile. 2. Dolphins have fins, stream-lined bodies and live in water but they are not fish. Dolphins have fins, streamlined bodies and live in water but they are not fish because they do not have gills. They have lungs to breathe. 3. Fish, cow, cuttlefish, hydra and chicken are kept in the same kingdom. Fish, cows, cuttlefish and chicken are kept in the same kingdom because all of them are eukaryotic, multicellular, heterotrophic and possess no cell wall. 4. Name with function about the long projections growing from the mouth of hydra called. The long projections growing from the mouth of the hydra are called tentacles. They help in locomotion as well as hunting for food. 5. Compare between jelly fish and cuttle fish. The comparison between jelly fish and cuttle fish are: SN Jelly fish SN Cuttlefish 1. It has a coelenteron cavity called coelom. 1. It does not have a coelenteron cavity. 2. Jellyfish have tentacles. 2. Cuttlefish have 8 arms. 3. It belongs to the Coelenterata phylum. 3. It belongs to the Mollusca phylum. 6. Compare between moss and clubmoss. The comparison between moss and clubmoss are: SN Moss SN Clubmoss 1 It belongs to the division Bryophyta. 1 It belongs to the division Tracheophyta. 2 It is an amphibian plant. 2 It is a terrestrial plant. 3 It does not have a vascular bundle. 3 It has a vascular bundle.

Oasis School Science and Technology - 10 53 7. Fucus is similar in appearance to Marchantia but it is not a bryophyte. Fucus is similar in appearance to Marchantia but it is not a bryophyte because they do not have leaves and rhizomes. Fucus is thallus so it belongs to division algae. 8. Study the given diagram and answer the following questions. a. b. i. Write the subdivision of the given plants with reason. The figure (a) is cycas and figure (b) is banana. The subdivision of cycas is a gymnosperm. As it has naked seed. The subdivision of the banana plant is angiosperm. As it has closed seed. ii. Write any two similarities between these two plants. Similarities between cycas and banana plants are: i. The body of both plants are differentiated into root, stem and leaves. ii. Both of them have a vascular bundle. iii. Both of them have seeds. Dissimilarities between cycas and banana plants are: i. Cycas have cones but banana plants have flowers ii. Cycas do not have fruit but the banana plant bears fruit. iii. Which one is more developed? The banana plant is more developed than the cycas because the cycas plant cannot protect its seed but the banana plant has flowers and fruit to protect its seed. The banana plant also has a better way of pollination and fertilization than the cycas plant. 9. Bats and dolphins are different but kept in the same class. Bats and dolphins are much different but kept in the same class because both of them are viviparous and suckle milk to babies. 10. Discuss the relation between the classification of organisms and evolution. The classification of organisms and evolution are two branches of biology. These two branches of biology are closely related. They both deal with how living things came to be and how closely are they related. The classification of organisms is based on the similarities between the species. Similar species are kept in the same group whereas dissimilar species are kept in different groups. Whereas evolution studies how an organism slowly and gradually changes over time and develops into new species.

54 Oasis School Science and Technology - 10 Exercises 1. Choose the best answer from the given alternatives. a. What is the kingdom of non-green, eukaryotic organisms with cell wall called? i. monera ii. protista iii. fungi iv. plantae b. What is the class of plants with one cotyledon in the seed? i. angiosperm ii. gymnosperm iii. dicot iv. monocot c. Why does hydra belong to Coelenterata? i. it has tentacles ii. it has a non-porous body iii. it has coelom iv. it lives in water d. Which kingdom does euglena belong to? i. monera ii. protista iii. fungi iv. animalia e. Which of the following organism have cell wall? i. seahorse ii. euglena iii. horse iv. horse tail f. Why does mustard belong to the plant kingdom? i. eukaryotic, multicellular, no cell wall, heterotrophic, locomotion ii. prokaryotic, unicellular, cell wall, locomotion, heterotrophic iii. eukaryotic, multicellular, cell wall, autotrophic, no locomotion iv. eukaryotic, unicellular, no cell wall, heterotrophic, locomotion 2. Define the following terms with required examples. a. Classification h. Five kingdom system of classification b. Protista i. Plantae c. Algae j. Tracheophyta d. Porifera k. Nemathelminthes e. Chordata l. Pisces f. Amphibian m. Reptilia g. Aves n. Mammalia 3. Answer the following questions in very short. a. Who is called the father of taxonomy? b. Who and when introduced five-kingdom system of classification? c. Write down the scientific name of human beings, mustard plant, rose and frog. d. Where are spirogyra, mushroom, yeast, liverwort, fern and chlamydomonas found?

Oasis School Science and Technology - 10 55 e. Name any two animals that breathe through gills. f. Name any two plants having rhizoids. g. Name any two animals having a mouth but no anus. h. Name an animal which moves using tentacles. i. Where are sponges found? Can sponges locomote? j. Which kingdom does sycon belong to? k. Write the function of ostia and osculum. l. What is the mode of nutrition of sycon, liver fluke and earthworm? m. What helps arthropods to sense? n. What is the mantle? o. What helps molluscs in locomotion? p. What does it mean by bilaterally symmetrical? q. How do molluscs notice external threats and hide inside the mantle? r. Which of the five kingdoms have a cell wall? s. Which division of the plant kingdom do plants with vascular bundles belong to? t. Which class of plants have petals in 3 or multiples of 3 in the flower? u. How many chambers are there in the heart of each class of vertebrates? v. Which class of animals suckle milk to babies? w. Which class of aquatic animals have air bladders in them? 4. Give reasons. a. Two kingdom system of classification is replaced by five-kingdom system of classification. b. Carolus Linnaeus is called the father of taxonomy. c. Living beings are provided with scientific names. d. Rhizobium belongs to the Monera kingdom. e. Mushroom is not a plant. f. Platypus is oviparous. g. Bat is viviparous. h. Crocodile is called cold-blooded animal. i. Humans are called warm-blooded animals. j. Angiosperms have fruit but gymnosperms do not. k. Bryophyta are called amphibian plants. l. Potato plant is far too different from the banyan tree but kept in the same subdivision angiosperm. m. Crabs are arthropods. n. Dolphins and whales belong to mammals despite being similar to fish. o. Lycopodium is more developed than Marchantia. p. Horse tail and mucor are not kept in the same kingdom. q. Pine belongs to gymnosperm.

56 Oasis School Science and Technology - 10 5. Differentiate between the following. a. Plantae and Animalia b. Bryophyta and pteridophyte c. Gymnosperm and angiosperm d. Monocotyledon and dicotyledon e. Vertebrates and invertebrates f. Coelenterate and Platyhelminthes g. Annelida and Arthropoda h. Mollusca and Echinodermata i. Labeo and brittle star j. Bird and bat k. Mushroom and fern l. Shark and dolphin 6. Answer the following questions in short. a. What is the meaning of cold-blooded animals? Give examples. b. What are warm-blooded animals? Give examples. c. What are oviparous animals? Which classes of vertebrates are oviparous? d. What do you mean by viviparous animals? Which class of vertebrates are viviparous? e. Write two similarities between snake and frog. f. How do Porifera digest food and absorb nutrients? g. How do Coelenterata obtain food? h. How is euglena different from rhizobium? j. Write special features of the plant kingdom. k. Write the physical feature of the leaf of each subdivision of the plant kingdom. 7. Name the phylum and class of the animals having given features. Also, give an example of each. i. Breathe through gills, having scales ii. Having external ears, giving birth directly to young ones iii. Having webbed feet, living on both land and in water, three-chambered hearts iv. Fly in the air, lay eggs, vertebrates v. Aerial, having mammary glands vi. Oviparous, feathers, hollow bones vii. Viviparous, suckle milk, fur viii. Waterproof scales, oviparous, breathing through gills ix. Semiaquatic, oviparous, external fertilization x. Rough scales, oviparous, crawl 8. Name the group of the plants having the following features with one example of each. i. Having cones instead of flowers

Oasis School Science and Technology - 10 57 ii. Flowering, having primary roots and secondary roots iii. Having naked seeds and needle-shaped leaves iv. Having fibrous roots, flowering plants v. Flowering plants, leaves having reticulate venation vi. Having two cotyledons in seed, with broad leaves 9. Name the locomotory organs of the following animals. i. Amoeba ii. Starfish, iii. Slug iv. Butterfly v. Cockroach vi. Hydra vii. Leech viii. Paramecium 10. What is the meaning of the following terms? i. eukaryotic ii. prokaryotic iii. autotrophs iv. parasites v. unicellular vi. multicellular vii. saprophytes viii. thallus ix. sexual reproduction x. asexual reproduction xi. rhizoids xii. vascular tissue xiii. spores xiv. fibrous root xv. tap root xvi. hibernation xvii. parallel venation xviii. reticulate venation xix. diploblastic xx. triploblastic xxi. bilaterally symmetrical xxii. radially symmetrical xxiii. hermaphrodite xxiv. unisexual xxv. dorsoventrally flat xxvi. complete alimentary canal xxvii.closed circulatory system xxviii. locomotion xxx. terrestrial xxxi. aquatic xxxii.unsegmented body xxxiii. notochord xxxiv. external fertilization xxxv. internal fertilization 11. Observe the given diagram and write any three salient features of each of them. (i) (ii) (iii) (iv) 12. Answer the following long questions. a. Write any two differences between fish and frogs based on the habitat and structure of the heart.

58 Oasis School Science and Technology - 10 b. What types of animals are called mammals? Write down three characteristics. c. Humans belong to sub-phylum vertebrates. What are the features that make us vertebrates? d. How can we tell that the five-kingdom system is more appropriate than the two-kingdom system of classification? f. Classify Marchantia and write its three salient features. g. Dolphins live in water, have a stream-lined body and look like fish. But they are not classified as fish. Surprisingly they belong to Mammalia. What features might have placed them into the Mammalia? h. Write the classification of Ostrich and mention its three main features which keep them in that class. i. How is an angiosperm different from a gymnosperm? Write any three features that separate these two sub-divisions. j. Let’s suppose we saw a unique plant in a botanical garden. There is no label on it. How can we know if it is a gymnosperm or monocotyledon or dicotyledon? 13. Study the given diagram and answer the following questions. i. Write the phylum and class of the given organisms. ii. Write two differences and two similarities between these organisms. iii. How do these organisms support evolution? 14. Classify the following organisms and write their two main features. i. Sycon ii. Hydra iii. Liver fluke iv. Hookworm v. Earthworm vi. Crab vii. Octopus viii. Starfish ix. Shark x. Toad xi. Snake a. b.

Oasis School Science and Technology - 10 59 Key terms and terminologies 1. Honeybees : Honeybees are social insects, i.e., they live in colonies where all the individuals are of the same family, often the offspring of one mother. 2. Life cycle : A life cycle is the series of stages of life for an organism, beginning with life and ending with death. 3. Nectar : Nectar is a sugary liquid produced by plants in floral or extrafloral (on leaf or stem) nectar-secreting glandular organ. 4. Royal jelly : Royal jelly is a special type of secretion produced by the hypopharyngeal glands of the worker bees which contains water, proteins, sugars, amino acids, fatty acids and vitamins. 5. Apiology : Apiology is the branch of science which deals with the study of honey bees. 6. Queen bee : A bee colony has a single queen that runs the whole hive. It is the only egg laying female in a bee colony. 7. Drones : The drone bee is smaller than the queen bee and larger than the worker bee. Its body is black and hairy. It is fertile and haploid. 8. Worker bees : Worker bees are the smallest and sterile females that perform all the jobs in the hive. 9. Nuptial flight : After 3-5 days of maturity, the queen bee flies out of the hive to mate with the drones. This flight is called mating flight or nuptial flight. 10. Metamorphosis: The process which involves egg, larva, pupa and adult to complete life-cycle is called metamorphosis. 11. Spermathecae : After the mating, the sperms are stored in the special structure of queen bee called spermathecae or sperm sac. 12. Moulting : During larval stage, the larvae changes its skin 4-5. This process is called moulting. 13. Honeycomb : A honeycomb is a mass of hexagonal cells made by the worker bees using their wax. 14. Apiculture : The commercial rearing of bees is known as apiculture. UNIT 3 LIFE CYCLE OF HONEY BEE Estimated teaching periods Theory 3 Practical 1 • Life cycle of honey bee • Importance of honey bee The Sequence of Curriculum Issued by CDC Charles Darwin is synonymous with “evolution” for his contribution to evolutionary biology. He proposed that all species of life have descended from a common ancestor. He was born in England on 12th February 1809 and demised on 19th April 1882. He was a naturalist, geologist and biologist. He has contributed to the investigation of marine invertebrates and natural science. About the Scientist Charles Darwin

60 Oasis School Science and Technology - 10 Introduction to lifecycle An organism goes through a series of stages from birth to death. These stages are known as steps of life cycle. Thus, a life cycle is the sequence of stages that an organism goes through from birth to death. For example, a bird consists of four major stages in its life cycle. They are: egg, hatchling, young, and adult. The life cycle of many simple organisms, like bacteria and some Protista, is finished in one generation. The life cycle of these organisms starts with the splitting of an existing organism. When the new organism is fully grown, it splits into two or more new organisms. This completes the life cycle. The name for this kind of life cycle is called "haplontic." In the life cycle of higher animals, there is also only one generation. But in these organisms, the body cell is diploid. So, the lifecycle is called "dipolontic." But insects like silkworms, honeybees, etc. have a four-stage life cycle. There is an egg, a larva, a pupa, and an adult. The Honeybee (Apis mellifera) The branch of biology in which we study about honey bee is called apicology or melittology. Honeybees are social insects, i.e., they live in colonies where all the individuals are of the same family, often the offspring of one mother. There is a division of labor in which individuals carry out particular duties. Honeybees produce honey. Honeybees live in discipline, and their life is very busy. Structure The bodies of bees are divided into the head, thorax and abdomen. The thorax consists of three pairs of jointed legs and two pairs of wings. The head consists of a pair of antenna, a pair of compound eyes and mouth parts. Drone Queen Worker Fig. Honeybees The mouthparts consist of a tongue, or labium, which can be enclosed near the head by the labial palps and maxillae. Nectar can be drawn up the grooved surface of the labium in the head. When not in use, these elongated mouthparts are folded back under the head, leaving the shorter, stouter mandibles free in front. The abdomen is elongated and segmented. The ovipositor through which the queen lays her eggs in the wax cell is modified in the workers to form a sting. Organization of the Colony There are three morphologically different types of bees in a colony. They are: Fact File The drones are very lazy. They mate with the queen.

Oasis School Science and Technology - 10 61 1. The queen, or egg-laying female (one in a colony) 2. Drones, or males (a few hundred in a colony) 3. Workers, or sterile females (20 to 80 thousand in a colony) The Queen Generally, there is only one queen in a colony. The queen is larger than the drones and workers. The abdomen of the queen is large and slender. The head of the queen is smaller than that of the other types of bees, and its proboscis is shorter. The queen has a special smell in its body. All the drones and workers identify their colony on the basis of the smell of the queen. A queen bee may live from two to five years and, except for a short period at the end of her life, when one of her daughters takes over the colony. The queen is the only egg-laying female. All the members of the family, whether drones or workers, are her offspring. The queen spends all her time laying eggs, perhaps upto 3000 a day based on the species, each one being placed in a wax cell made by the workers. The queen can feed herself, but in the hive the nearest workers turn towards her, lick her body and feed her a special secretion of their salivary glands, called royal jelly. The queen usually mates only once in her life and stores the sperms received from the drone in a sperm sac in her abdomen. The stored sperms lasts for two or more years of egg-laying. When the store of sperms is used up, she may continue to lay eggs but they are all unfertilized and will become drones. By this time, one of her daughters has been reared as a queen and is ready to take over the egg-laying. Drones The drone bee is smaller than the queen bee and larger than the worker bee. Its body is black and hairy. It does not have a poison gland, nectar gland and pollen sac. The drones live for about four to five weeks and do not work inside the hive. They are fed by the workers. Their function is to fertilize the new queen. In the autumn, or when conditions are poor, they are turned out of the hive where, unable to find food for themselves, they die. It lives for about 2 months. Reasonable Fact The drones die after mating. The drones die after mating with the queen because their penis and abdominal tissues are expelled along with the sperm during the mating process. Fig. Queen Fact File Queen bee is female, diploid, largest, fertile, elongated and smooth. Fig: Drone bee Fact File Drone bee is male, haploid, medium sized, fertile, black, lazy and hairy.

62 Oasis School Science and Technology - 10 Workers Workers are the smallest bees in the colony. Their body can be divided into the head, thorax and abdomen. Their mouth is modified for chewing and lapping. The workers are female bees whose reproductive organs do not function. They collect food from outside the hive and store it, make the wax cells and feed the developing larvae. They are very laborious. Workers have pollen baskets to collect the nectar. It lives for 6 weeks to 6 months. Life Cycle of Honey bee The time taken to complete the life cycle depends upon the type of bee. Generally, there is a single queen for each hive. When the queen becomes old or the number of worker bees increases significantly, the old queen selects another place for building hives and many worker bees follow her. The worker bees build a new hive. In the old hive, the worker bees then select another queen. The life cycle of a honey bee is also completed into four stages. They are egg, larva, pupa and adult. The process which involves egg, larva, pupa and adult to complete life-cycle is called metamorphosis. i) Egg The queen usually stays inside the bee hive until maturity. The matured queen bee releases chemicals called pheromones to attract drones towards her. After 3-5 days of maturity, the queen bee flies out of the hive to mate with the drones. This flight is called mating flight or nuptial flight. Many drones follow the queen to get the opportunity to mate with her. She chooses to fly high and away from the drones to select the best and healthy drone male and mates with about 10-20 drones. After the mating process, the sperms are stored in the special structure called spermathecae or sperm sack in the body of the queen bee. These sperms can be utilized for few years to fertilize millions of eggs. After mating, drones die. After 2-3 days of mating, the queen lays eggs in brood cells inside the hive. She lays about 3000 eggs depending upon the species. These eggs are 1 mm to 1.5 mm in size and are lemon yellow in colour. The eggs are of two types. i) Fertilized eggs ii) Unfertilized eggs The fertilized eggs are formed after the fusion with sperms stored inside the female. Similarly, the unfertilized eggs are formed without fusion with the sperm. After laying, the fertilized eggs turn black while the unfertilized eggs turn white. The fertilized eggs develop into worker bees and queens. Similarly, the Fig: worker Fact File 1. Worker bee is female, diploid, smallest, nonfertile with hairy legs. 2. If pollen basket gets detached, workers cannot collect pollen grains. Fact File Fertilized eggs have 32 chromosomes and unfertilized eggs contain 16 chromosomes.

Oasis School Science and Technology - 10 63 unfertilized eggs develop into drones. It is called parthenogenesis. On the first day, the egg lies vertical inside the brood cell. Similarly, on the second day, it lies slightly slanted and on the third day, the egg lies horizontally in the cell. The brood cells for workers and drones are different, so the queen lays eggs in these cells differently. She lays fertilized eggs in the brood cells of the worker bees to develop them into workers in the future. Likewise, she lays unfertilized eggs in the brood cells of the drone bees to develop them into drones. The yolk present inside the egg acts as food. ii) Larva The eggs turn into larvae after three days. The larvae are continuously fed with large amount of pollen, honey and a special type of fluid called royal jelly. Not all the larvae are fed with the same type of feeding material. All types of larvae are fed with royal jelly for the first 3 days. But, after that, the feeding pattern changes. To make a queen, the worker bees feed the larva in the queen brood cell continuously with royal jelly till the end of this stage. But, after 3 days, the drones and the workers are fed with pollen and honey but no royal jelly. Due to this difference in the feeding pattern, the queen, workers and the drones grow and develop differently. The brood cells of larvae are covered with wax by the worker bees for their safety. The larvae then spin a cocoon around themselves for protection. They turn into pupa in 5-7 days depending on the type of bee. The larva stage is a period of 5 days in queen cells and 6 days in worker cells and 7 days in drone cells. During this stage, the larvae changes its skin 4-5 times called moulting. Reasonable Fact Why is the larva for queen bee continuously fed with royal jelly? The larva for queen is continuously fed with royal jelly because it activates to produce a fertile ovary that can bear eggs and turn her into a queen. The worker bees seal the brood cells after the development of larvae, why? The workers seal the cells after the development of larva to protect the larva, pupa and the adult during the metamorphosis. iii) Pupa After 5-7 days of larval stage, the larvae turn into pupae. The pupae slowly develop inside the brood cells and undergo active metamorphosis inside the cocoon. Finally, they turn into adults after about 7 to 14 days depending on the type of bee. In queen Fact File The process in which a haploid egg changes into drone bee is called parthenogenesis. Fact File Royal jelly is a special type of secretion produced by the hypopharyngeal glands of the worker bees which contains water, proteins, sugars, amino acids, fatty acids and vitamins. Fact File Honey bread is made from honey and pollen. The larvae for drone bee and worker bee are fed with pollen bread after 3 days.

64 Oasis School Science and Technology - 10 bees, the pupal stage lasts for 7 to 8 days. Similarly, in the worker bees, the pupal stage lasts for 11 to 12 days and in drones, it lasts for 14 days. The pupal stage is inactive stage because they do not move, eat and show any visible changes. The eyes, legs, wings and other parts are formed in pupal stage. iv) Adult The pupae finally turn into adults. They crawl out of the brood cells by cutting the cocoon and the cell cup with their mandible. Among the types of bees, the worker bees have very important function. So, they immediately join with other bees to perform various functions. Workers work inside the hive for about 3 weeks. In this period, they look after the brood cells, feed the larvae, guard the hive internally, etc. After 3 weeks, worker bees go out of the hive for doing outdoor works like collecting nectar, guarding the hive, etc. The function of the adult queen is only laying eggs after mating with the drones. If more than one queen hatches, the first queen that hatches kills the other queens and mates with the drone. Similarly, the function of drones is to mate with the queen and warm up the hive. Time taken by bees to complete their life cycle The time taken by the queen, drones and the workers to complete their life cycle is given in the table below. Bee Eggs Larva Pupa Duration required to be an adult Average life span Queen 3 days 5 days 7 to 8 days 15 to 16 days 2 to 5 years Worker 3 days 6 days 11 to 12 days 20 to 21 days 6 weeks to 6 months Drone 3 days 7 days 14 days 24 days about 2 months Fig: life cycle of honeybee Pupa Larva Adult Egg Fig. Different stages of honey bee

Oasis School Science and Technology - 10 65 Division of Labour in the Honeybee on the Basis of Their Type: S.N. Type and Age Functions / Duties 1. The Queen bee - To lay eggs - To control and guide the colony by releasing special odor 2. Drone - To fertilize the queen - To keep the hive warm 3. Worker (1 to 3 days) - To learn walking - To give warmth to egg, larva and pupa - To clean the cells 4. Worker (3 to 6 days) - To feed mature larva workers who also take a lot of food 5. Worker (6 to 12 days) - To feed royal jelly produced by the salivary glands to the larvae below 3 days and the queen bee. Workers also take a lot of food. 6. Worker (12-18 days) - To secrete wax from 4 pairs of wax glands in the abdomen - To build a honey comb using wax - To close the cells of the larvae and honey 7. Worker (18-20 days) - To protect the beehive from enemies with their poison glands and sting 8. Worker (21 days) - To be busy in outdoor works, i.e. to collect nectar from flowers, to collect pollen, water, etc. from crop fields and forests Activity 1 Draw a neat and labelled figure showing the life cycle of the Honeybee. Activity 2 Visit a nearby area having apiculture. Ask the owner to open a beehive and observe it. Identify the queen, drones and workers. Study their structure and draw a neat and labeled figure of each. Origin of the Three Types of Bees The wax combs are built hanging vertically with a gap of about half an inch separating each one. The cells in each comb thus lie horizontally. The workers prepare three types of cells. Worker cells are about 5mm across, drone cells are about 6mm across, and the queen cells are larger and made individually. Fact File If a 'one to three day old larva' is transferred from a worker to a queen cell, it will receive a diet of royal jelly and develop into a queen.

66 Oasis School Science and Technology - 10 Eggs are laid by a queen in a broad area. This is done where the temperature is about 320 C, kept so by the heat given out by the bees' bodies. The queen moves over a broad area, laying eggs in any of the three types of cells by placing her abdomen in the cell and depositing a single egg. The eggs placed in the larger, drone cells, are not fertilized, and this results in the eggs developing into a male bee or drone. In the queen and worker cells, fertilized eggs are laid. For the first three days after hatching, all the larvae are fed on a protein rich, milky secretion, called royal jelly, which comes from the salivary glands of the workers of certain age. The larvae in the queen cells continue to be fed on the royal jelly for the rest of their lives. The larvae in the drone and worker cell are fed on a mixture of dilute nectar and pollen. Swarming When the size of the colony reaches a certain stage, usually in spring or summer when the nectar flow is at its greatest, the queen and many workers leave the hive in a swarm. The swarm comes to rest in a great cluster on a tree branch. In the old hive, one new queen hatches out, mates and takes over the colony that is left. Comparison of the Queen, Drone and the Worker bees Basis of comparison Queen Drone Worker Size Largest Medium Smallest Stinger Present/ It can sting more than once Absent Present/ It can sting only once Life span 2 to 5 years About 2 months; dies after mating or in winter 6 weeks to 6 months Fertility Fertile Fertile Sterile Function Laying eggs and directing the worker bees Mating with the queen and keeping hive warm Constructing the hive, feeding larvae, collecting nectar, etc. Number Usually one Up to 500 20,000 to 80,000 Honey making process Honey is a sweet sugary liquid prepared by honey bees. It has food and medicinal values. It has about 80-85% carbohydrates, 15-17% water, 0.3% protein and 0.2% amino acids, vitamins, etc. The bees produce the honey by collecting the nectar of the flowers. In this process, the worker bees visit many types of flowers and collect different types of nectars. The nature and colour of honey depends on the nature of the flowers from which the nectar is collected. Fig. Swarming in honeybees Comb honey

Oasis School Science and Technology - 10 67 In the honey making process, the worker bees wander many kilometres around the bee hive and visit millions of flowers. After collecting nectar, worker bees store it in their abdomen where the nectar combines with several proteins and enzymes to form honey. The honey is then deposited and stored in the honeycomb in the bee hive. A honeycomb is a mass of hexagonal cells made by the worker bees using their wax. Till all the cells in a honeycomb are full, the worker bees keep on collecting the nectar and depositing the honey. To make the honey thick, the worker bees evaporate the water present in the honey juice by flapping their wings like a fan over the comb. Uses of honey i. It is used as a tonic. ii. Honey is used as a sweetening agent in foods, juices and beverages. iii. It is useful in the manufacturing of candies, cakes and breads. iv. It removes harmful substances from the body and acts as an antioxidant. v. Honey is used in manufacturing cosmetic products. vi. Honey has antibacterial properties and cures cuts and bruises. vii. It cures cough and throat infection. viii. It is beneficial for preventing or controlling diabetes as it does not raise blood sugar. ix. Honey lowers the risk of cancer, allergies, arthritis and heart diseases. Advantages of honey bees Honey bees are useful to both human beings and ecosystem. They are reared commercially near the crops which provide good nectar for honey. The commercial rearing of bees is known as apiculture. Apiculture provides us honey bee products. Some of the honey bee products are honey, wax, royal jelly, etc. Some advantages of honey bees are given below: i. Honey made by honey bees is consumed by human beings for food and medicinal purposes. ii. The systematic work division of honey bees is of great importance to anthropologists. iii. The wax that we get from bee hives is used for making candles, paints, shaving cream, cold creams etc. iv. Royal jelly produced from workers has several medicinal values. It is beneficial for reducing blood pressure and cholesterol levels in blood. It also helps to boost the immune system. v. Honey bees are good pollinators. They help in pollination while sucking the nectar. Thus, they increase the productivity and quality of the plants. vi. The rearing of honey bee generates income and also improves the national economy. Fact File The bees are the only insects which manufacture food that is directly consumed by human beings.

68 Oasis School Science and Technology - 10 Reasonable Fact Humans rear honey bee, why? Humans rear honey bees to get honey, royal jelly, wax and other bee products. Why does honeybee queen go out of the hive? Honeybee queen goes out of the hive to mate with the healthiest drones. If possible, mates with drones of other hives to collect new genes. Anthropologists have a keen interest in honey bees. Give reason. Anthropologists want to study about the systematic work division, dominance of certain castes and submissiveness of worker bees. The productivity of some crops increases in areas where honey bees are reared, why? Honeybees choose the best and healthy plants to collect pollen. It helps cross-pollination of the flowers easily and in a short period of time. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Scientists say that humans might go extinct if bees go extinct. Relate the extinction of bees to the extinction of humans. Scientists say that humans might go extinct if bees go extinct. Bees are insects that collect nectar from the flower and help in pollination. If the bees go extinct, the rate of pollination will drastically decrease. There will be no fruits and seeds. Most plants will go extinct. Food will be scarce. As a result, humans could go extinct. 2. Discuss the importance of nuptial flight for the colony of bees. Nuptial flight is the act in which queen bees fly out of the hive for a few durations and mate with drones. It is very important for the colony of bees because: i. It helps to prevent inbreeding. ii. It allows the queen to fly out and mate with bees of other hives. iii. It helps the queen bee to collect various genes. iv. It helps the queen to produce bees with better qualities. v. It helps queen to mate with the most healthiest drones. vi. Queen can collect and store sperms for future to fertilize eggs. 3. Apiculture can be a good source of income for Nepalese with low investment. Support the statement. Apiculture is the act of rearing honey bees. It can be a good source of income for Nepalese because of the following reasons: i. Nepal has lots of forests with varieties of flowering plants so bees can find food. ii. Nepal is an agricultural country so there are lots of crops where bees can collect nectar. iii. It does not cost much to start a bee farm.

Oasis School Science and Technology - 10 69 4. Harkaman sold all his bee hives and went abroad. His wife noticed that pumpkin production in her fields decreased by 90%. What could be the reason? Harkaman sold all his bee hives and went abroad. His wife noticed that pumpkin production in her fields decreased by 90%. It could be because of a decrease in the number of bees. Since there are lesser bees in his fields the pollination decreased. Hence, pumpkin production must have decreased by a lot. 5. Farmers should learn to distinguish between drone, queen and worker. Farmers should learn to distinguish between drone, queen and worker because it helps farmers to rear bees properly. If they can identify queen bees properly, they can kill the extra queen and prevent swarming. Sometimes they can transfer a new queen bee to another hive to make a new colony. If they can identify a drone, they can put it outside the hive and kill it if there are too many of them. 6. Name the form of bee that is formed if a female larva feeds upon royal jelly only. A queen bee is formed if a female larva feeds upon a royal jelly only. 7. Compare between nuptial flight and swarming. The comparison between nuptial flight and swarming are: SN Nuptial flight SN Swarming 1 Nuptial flight means the process in which matured queen bee flies out of the hive to mate with drones and collect sperm. 1 Swarming is a process in which a colony of bees splits into two or more separate colonies. 2 The queen bee and the drones take part in this flight. 2 Some queens, drones and workers take part in swarming to make a new hive. 8. What happens if worker bees lose their pollen basket? If worker bees lose their pollen basket, they cannot help in pollination and they cannot collect pollen to make food for the larva. 9. Who controls the hive if the queen bee dies? What happens if the queen bee dies in the hive? If the queen bee dies, either new queen bee takes control of hive or the colony will collapse. If the queen bees die following things can happen to the hive: i. The odour of the queen fades and the bees will go out of control. ii. No new eggs will be produced so the hive will end. iii. The worker bees will find multiple suitable female larvae and start feeding royal jelly to them. As a result, new queens are formed. If there are multiple queens, the stronger one will kill others. Then the new queen bee will spread her odour and take control of the hive. 10. If one farmer keeps bees, it is beneficial for other nearby farmers too. If one farmer keeps the bee it is beneficial for other nearby farmers too because the bees will pollinate the crops on their farms too. As a result, there will be more fruits and seeds in the plant. It will increase agricultural production.

70 Oasis School Science and Technology - 10 Exercises 1. Choose the best answer from the given alternatives. a. Why did Romans dip their food in honey? i. food will taste sweet because honey has sugar. ii. to make candy because it is sweet. iii. to prevent the decaying of food because it is antibacterial. iv. to store food because honey is thick b. Why do farmers kill old queen bees when there are multiple queen bees in the hive? i. to prevent swarming ii. to prevent honey from going sour iii. to prevent a fight between two queen bees iv. to prevent swarming and keep the young healthy queen in the colony c. What does a honey bee feed upon? i. blood ii. juice from the stem of herbs iii. nectar and pollen iv. insects d. How many morphologically different bees live in a hive? i. 2 ii. 3 iii. 1 iv. 4 e. How many chromosomes are present in a drone bee? i. 16 chromosomes ii. 16 pairs chromosomes ii. 32 chromosomes iv. 8 pairs f. What are the characteristics of worker bees? i. Haploid, sterile, furry, medium-sized ii. Diploid, sterile, small sized iii. Diploid fertile medium-sized iv. Diploid, fertile, large 2. Define the following terms with required examples. a. Honey bee b. Queen bee c. Drone bee d. Worker bee e. Swarming f. Nuptial flight g. Royal jelly h. Bee bread 3. Answer the following questions in very short. a. What is the scientific name of the honey bee? b. What is the food of the queen bee? c. Where is royal jelly produced? d. How many eggs queen lays per day? e. How many queens, drones and worker bees are usually present in a colony of bees?

Oasis School Science and Technology - 10 71 f. In how many days is, the life cycle of queen, drone and worker bee completed? g. Write the names of different morphological forms of bees in the hive. h. Where does the queen bee store sperm after the nuptial flight? i. What is the function of the pollen basket? j. At what age worker bee starts navigating surrounding for resources? 4. Give reasons. a. Queen bee has a very big abdomen. b. Queen bee lives for many years despite other bees live a few months only. c. Queen bees can control the entire hive. d. Bees are called social animals. f. Drone bees cannot collect nectar. g. Farmers kill the old queen bee when the new one is born. h. Queen bee flies up very fast during the nuptial flight. i. Swarming is observed in a bee colony. j. Archaeologists find pots of fine well-preserved honey in thousands of years old tombs. k. Apiculture needs bee pasture. l. Drones dies after copulation. m. Honey bees are useful in many ways. n. Drones come out of unfertilized eggs of bees. 5. Differentiate between the following. a. Queen and drone bee b. Worker bee and queen bee c. Pollen biscuit and honey d. Nuptial flight and swarming 6. Answer the following questions in short. a. What is the function of the queen bee? How does it control the hive? b. What is the role of drone bees? c. Discuss the labour division of bees. f. What is the role of honey bees in the ecosystem? g. Write a short note on the larva and pupa of a honey bee. h. What are the uses and advantages of honey? i. Show the development of different types of honeybees on a table. j. Why should we study the life cycle of the honeybee? k. Which bee live the longest and why?

72 Oasis School Science and Technology - 10 7. Answer the following questions on the basis of the given figure. i. Which bee is shown in the diagram? ii. What is its function in the colony? iii. How long does this bee live? 8. Answer the following long questions. a. Describe the structure of the queen bee, drone bee and worker bee with a diagram. b. The bee colony has three morphologically different bees. The queen, the drone and the worker bees. How are they formed? c. The drones are left outside the hive after the nuptial flight. Then all the drones die. What might be the reasons that all the drones die? Why are they not able to survive? d. What happens to the colony if the workers grow a new queen bee beside the old queen? What do farmers do if multiple queen bees are present in the hive? e. Ramesh has a cough and his mother gave him a spoon of honey. He is feeling better. Why? What could be the reason? f. Is bee keeping a suitable source of income for Nepalese farmers? Discuss. g. Arya has a mustard field. She is harvesting lots of mustard seeds after she started keeping bees on her roof. Is it related? h. Neharika has a bee farm and mustard farm nearby. She used chemical insecticides in her fields to kill bugs. She was expecting a huge harvest but the crops bear fewer fruits this year. There was very less honey in the hive too. What might be the reason? i. What different works do the worker bees do? Write their work according to their age. j. Describe the life cycle of a honeybee with a neat and clean diagram. 9. Answer the following questions on the basis of the given figure. Here A is a fertilized egg and B is an unfertilized egg. What are hatched out from the egg A and B? Larva from which egg will change into queen or worker. Mention the conditions.

Oasis School Science and Technology - 10 73 4 HEREDITY UNIT Parents → Genotype → Pure tall pea plant Pure dwarf pea plant Cross - pollination F1 - generation F2 - generation F3 - generation Gametes Self-pollination → Possible gametes → All hybrid tall→ Gametes → If the F1 - are bred together Tt T t TT Tt T TT t Tt T Tt t tt T TT Tt tt tt t T t Tt tt TT Tt

74 Oasis School Science and Technology - 10 Key terms and terminologies 1. Cell division : The biological process in which a pre-existing diploid cell divides into two or four daughter cells is called cell division. 2. Mitotic cell division: The cell division in which a diploid parent cell divides biologically into two diploid daughter cells is called mitotic cell division. 3. Meiosis cell division: The cell division in which a diploid (2n) parent cell divides into four haploid (n) daughter cells is called meiosis cell division. 4. Chromosomes : Chromosomes are thread-like microscopic structures present in the nucleus of a cell which contain genes. 5. Autosomes : The chromosomes which determine somatic body structure are called autosomes. 6. Sex chromosomes: The chromosomes which determine sex of the offspring are called sex chromosomes. 7. DNA : DNA (Deoxyribonucleic acid) is a genetic material which carries hereditary information from one generation to another. UNIT 4.1 CELL DIVISION AND CHROMOSOMES Estimated teaching periods Theory 4 Practical 1 • Concept of mitosis and meiosis cell division • Importance of mitosis and meiosis cell division • Differences between mitosis and meiosis cell division (based on numberof daughter cells, number of chromosomes and types of dividing cells) • Chromosomes,DNA and RNA (introduction and differences) • Role of sex chromosomes in sex determination of human beings The Sequence of Curriculum Issued by CDC Hugo Von Mohl is a botanist noted for his research on the anatomy and physiology of plant cells. He was born in Germany on 8th April1805 and died on 1st April 1872. He is renowned for discovering protoplasm. He pursued botany and mineralogy. He discovered many facts about cell walls, vacuoles and plastids. He discovered that all metabolic activities occur in protoplasm. Most importantly he discovered cell division in 1835. About the Scientist Hugo Von Mohl

Oasis School Science and Technology - 10 75 8. RNA : RNA (Ribonucleic acid ) is a single-stranded macromolecule which helps in protein synthesis. 9. Gametes : The haploid cells which take part in sexual reproduction are called gametes. 10. Sperms : Male gametes are called sperms which are represented by 22+Y and 22+X in humans. 11. Egg (ovum) : The female gametes are called eggs which are represented by 22+X in humans. 12. Sex determination: The biological cause for an organism developing into one sex or the other due to the genes in the fused gametes is called sex determination. Introduction to Cell Division A cell is defined as the fundamental, structural and functional unit of life. The bodies of living organisms are made up of microscopic units known as cells. Cells are made up of life giving substance called protoplasm, cell organelles and inclusions. A cell is capable of independent existence and performs essential functions of life. All organisms start their life as a single cell. New cells always arise from pre-existing cells. The biological process in which a pre-existing diploid cell divides into two or four daughter cells is called cell division. It is an important phenomenon which occurs in all living beings. New cells are formed by the process of cell division. Cell division is essential for continuity of a species. All of the structures of a parent cell are duplicated in cell division and they are distributed to each of the daughter cells. In unicellular organisms, cell division is a means of reproduction because cell division directly produces two daughter organisms. There are two types of cells in multicellular organisms, viz. somatic cells and reproductive cells. Somatic cells or body cells form the body of living organisms whereas reproductive cells form the gametes - eggs and sperms. The life of multicellular organisms begins from a single cell (i.e. zygote) which divides and redivides to form a complete organism. Types of Cell Division On the basis of mode of nuclear division, cells are divided by three different waysAmitosis, Mitosis and Meiosis. Mitosis: Somatic cell division Mitosis [Gr., mitos-thread, fibre] is an educational division in which a mother cell divides to form two identical daughter cells. This process was first observed by German Biologist Walter Flemming in 1877 AD. The two daughter cells formed as a result of mitosis are identical to the mother cell in all respects. Therefore, it is also called educational cell division. In mitotic cell division, the same (i.e. diploid) number of chromosomes of the parent cell is maintained in each division of the cell. The cell division in which a diploid parent cell divides biologically into two diploid daughter cells is called mitotic cell division. Mitosis takes place in vegetative or somatic cells. So, it is also called somatic cell division. Fact File The cells which contain two sets of chromosomes are called diploid cells. The cells which contain one set of chromosomes are called haploid cells.

76 Oasis School Science and Technology - 10 Fig: mitosis cell division Importance of mitosis i. It is a method of multiplication (i.e. asexual reproduction) in unicellular organisms. ii. In multicellular organisms, mitosis is responsible for growth and development from a zygote. iii. Since the daughter cells produced by mitosis contain equal number of chromosomes to the mother cell, genetic stability is maintained in living organisms. iv. It helps in replacement of damaged or lost body parts, healing of wounds, formation of body cells; and replacement of lost cells during normal wear and tear. v. The uncountrolled mitotic cell division may cause tumour or cancerous growth. Activity 1 To prepare a model of mitosis. • Take a white cardboard paper and draw all stages of mitosis and label them. • Put suitable colours to distinguish various parts of the cell. Meiosis: Gametic Cell Division Meiosis [Gk., meioum - to diminish] occurs only in the reproductive cells at the time of gametogenesis (i.e. the process of formation of male gamete and female gamete) in sexually reproducing organisms. Therefore, it is also called gametogenic division. Meiotic cell division is a modified mitosis in which chromosomes divide once and nucleus divides twice, after which the number of chromosomes in daughter cells is reduced to half. So meiosis is also called reduction division. The cell division in which a diploid (2n) parent cell divides into four haploid (n) daughter cells is called meiosis. The term 'meiosis' was coined by JB farmer and JE Morre in 1905 AD. Fact File No meiosis, no gametes and no sexual reproduction. Fig: meiosis cell division

Oasis School Science and Technology - 10 77 Importance of Meiosis 1. Meiosis is responsible for producing haploid gametes (i.e. sperms and ova), which after fertilization restores the original diploid number in the zygote. Thus, meiotic cell division helps to maintain genetic stability by keeping the fixed number of chromosomes in a species. 2. Crossing over provides new combination of chromosomes and hence new combination of characters is possible which brings out variation. 3. The four chromatids of a homologous pair of chromosomes are passed onto four different daughter cells, which brings out genetic variation in offsprings. 4. It helps in sexual reproduction and avoids the multiplication of chromosomes in offsprings by reduction division. Comparative study of Mitosis and Meiosis Mitosis Meiosis OCCURRENCE 1. It occurs in somatic cells or vegetative cells. 1. It occurs in gametic cells or reproductive cells at the time of gamete formation. RESULTANT CELLS 2. One diploid mother cell divides into two diploid daughter cells 2. One diploid mother cell divides into four haploid daughter cells. 3. The daughter cells resemble the mother cell in all respects. 3. The daughter cells do not resemble the mother cell in two basic characters (i) the contain haploid chromosomes and (ii) their chromosomes contain different combination of genes due to crossing over. Chromosomes: The Vehicles of Heredity Chromosomes (Gk., chrome–colour and soma–body) are thread-like microscopic structures present in the nucleus of a cell which contain genes (i.e. sub-microscopic units of heredity). Chromosomes are made up of the genetic material DNA and protein. Each chromosome consists of two identical strands called chromatids. Those chromatids are separate but firmly attached to each other at a constricted part called the centromere. The centromere is also called kinetochore. Each Fact File In meiosis, crossing over is a process of exchanging genetic materials between two nonsister chromatids. It brings variations in the gametes. So, offsprings are not exact to the parents. Chromatids Centromere Chromosome Fig. Chromosome

78 Oasis School Science and Technology - 10 cell of plants and animals contain a network of fine threads which is called chromatin reticulum. During cell division, the fine threads of chromatin reticulum become shorter and thicker. These shorter and thicker structures are called chromosomes. The number of chromosomes varies from species to species, however, it is constant for all individuals in a species. The number of chromosomes in the somatic cells of organisms is called diploid number and it is represented by '2n' whereas the number of chromosomes in gametes (sperm and ovum) is called haploid number and it is represented by 'n'. In human beings, each somatic cell contains 23 pairs of chromosomes and each gamete contains 23 chromosomes. Types of chromosomes: based on position of centromere Chromosomes vary greatly in their shape, size and position of the centromere. On the basis of the position of the centromere, chromosomes are of three types: metacentric, acrocentric and telocentric. In metacentric chromosome, the centromere is located at the middle. In acrocentric chromosome, the centromere is located away from the centre whereas the centromere is located very near the end in telocentric chromosome. Metacentric chromosome Sub-metacentric chromosome Acrocentric chromosome Telocentric chromosome Fig: various shapes of chromosomes Functions of Chromosomes 1. Chromosomes act as hereditary vehicles. They transmit characteristics of parents to their offspring with the help of genes. 2. Chromosomes control protein synthesis and thus induce cell division, cell growth and cell repair. 3. Sex chromosomes determine the sex of living organisms. 4. Chromosomes form a link (bridge) between parents and their offspring. 5. Chromosomes induce variation by crossing over and undergo mutation, which leads to evolution of life. 6. Chromosomes control cell metabolism by directing the synthesis of enzymatic proteins. Fact File Chromosome is made up of DNA and histon protein.

Oasis School Science and Technology - 10 79 Reasonable Fact Why are chromosomes called the blueprint of an organism? Chromosomes store information about every characteristic of the organism like body structure, height, skin complexion, behaviour, etc. So, chromosomes are called the blueprints of an organism. Number of chromosomes The number of chromosomes is generally different for different species of organisms. Even closely related organisms like humans and chimpanzees (46 and 48 respectively) or donkey and horse (62 and 64 respectively) have different numbers of chromosomes. But, some organisms have the same number of chromosomes. Generally, we write the chromosome number in pairs because one set comes from the father and the other set from the mother. For example, human cells have 46 chromosomes and we write 23 pairs. Among 46 chromosomes, we get 23 chromosomes from father and the rest 23 chromosomes from mother. Some of the organisms and their chromosome numbers are given in the table below. S.N. Organism Number of chromosomes S.N. Organism Number of chromosomes 1 Mucor 2 (1 pair) 8 Rat 40 (20 pairs) 2 Housefly 12 (6 pairs) 9 Monkey 42 (21 pairs) 3 Garden pea 14 (7 pairs) 10 Human, antelope 46 (23 pairs) 4 Onion 16 (8 pairs) 11 Chimpanzee, Orangutan, Gorilla, Potato, tobacco, water buffalo 48 (24 pairs) 5 Pine 24 (12 pairs) 12 Fox, goat, bull, cow 60 (30 pairs) 6 Frog 26 (13 pairs) 13 Dog 78 (39 pairs) 7 Tiger, lion, cat 38 (19 pairs) 14 Sugarcane 80 (40 pairs) Types of chromosomes in human body Human beings have 23 pairs of chromosomes in their cells. Out of them, 22 pairs of chromosomes determine the somatic body structure. So, they are called autosomes. The remaining one pair of chromosomes determines the sex of the offspring. So, they are called sex chromosomes. In males, the cells have 44+XY chromosomes and in females, the cells have 44+XX chromosomes. Fact File In human, there are 22 pairs (44) autosomes and one pair(2) sex chromosomes. Fact File The chromosomes which determine somatic body structure are called autosomes. Similarly, the chromosomes which determine sex of the offspring are called sex chromosomes.

80 Oasis School Science and Technology - 10 DNA DNA stands for Deoxyribonucleic acid. It is a double-stranded helically coiled macromolecule which is commonly found in chromosomes. It is the genetic material present in all living organisms. DNA is a genetic material which carries hereditary information from one generation to another. Location In eukaryotic cells, DNA is present in the nucleus which is the main component of chromosomes. However, a small amount of DNA is also found in mitochondria and plastids. In prokaryotic cells, DNA is found in the cytoplasm. Structure DNA is a helically twisted double-stranded polydeoxyribonucleotide macromolecule. It is a polymer made up of several hundred thousands of deoxyribonucleotides or monomers. A DNA molecule contains two unbranched complementary strands which are coiled around a common axis like a rope staircase with solid steps twisted into a spiral. The strands of DNA are antiparallel to each other. It means that two strands of DNA are parallel to each other but they run in opposite directions. DNA is formed by cross linking of three chemicals, viz. deoxyribose sugar (C5 H10 O4 ), phosporic acid (H3 PO4 ) and nitrogen bases. There are two types of nitrogen bases found in DNA. They are Purines and Pyrimidines. The purines are adenine (A) and guanine (G) whereas the pyrimidines are cytosine (C) and thymine (T). In DNA, adenine (A) of one chain is attached to thymine (T) of its complimentary chain by tow hydrogen bonds whereas cytosine (C) of one chain is attached to guanine (G) of its complimentary chain by three hydrogen bonds. Functions of DNA 1. DNA is responsible for passing genetic information from parents to their offspring. 2. DNA carries hereditary information in the form of codes arranged in nitrogen bases. 3. DNA gives rise to RNA by the process of transcription. 4. DNA controls metabolic activities of cells through RNA. Fig: Structure of DNA Fact File High intensity radiation may destroy DNA. It may bring genetic variation and infertility. Fact File No transcription of DNA, no RNA and no protein synthesis.

Oasis School Science and Technology - 10 81 RNA Ribonucleic acid (RNA) is a single-stranded macromolecule. It is mainly found in cytoplasm, some part in nucleolus and nucleoplasm, in association with chromosomes of a cell. It is made up phosporic acid, ribose sugar and four types of nitrogen bases (i.e. adenine, guanine, cytosine and urasil). The single strand of RNA is formed by the alternate bands of phosphoric acid and ribose sugar. RNA is formed by DNA and it cannot replicate itself. There are three types of RNA, viz. mRNA, rRNA and tRNA. mRNA stands for messenger RNA. It carries genetic information from DNA and helps in protein synthesis. rRNA stands for ribosomal RNA. It forms the basic component of ribosome. Similarly, tRNA stands for transfer RNA. It carries amino acid molecule to the ribosome for protein synthesis. Differences between DNA and RNA S.N. DNA S.N. RNA 1. DNA is mainly found in chromosomes in the nucleus. 1. RNA is mainly found in cytoplasm. 2. It contains deoxyribose sugar. 2. It contains ribose sugar. 3. DNA is responsible for transmitting hereditary characteristics from parents to their offspring. 3. RNA is responsible for protein synthesis. 4. DNA is a double-stranded helically coiled structure. 4. RNA is a single-stranded structure. 5. Thymine is present but urasil is absent 5. Urasil is present but thymine is absent. 6. DNA can replicate itself. 6. RNA cannot replicate itself. Gamete formation In the human body, the diploid cell undergoes meiosis cell division forming haploid cells. These haploid cells are called gametes. Gametes take part in sexual reproduction. Thus, the haploid cells which take part in sexual reproduction are called gametes. The male gametes are called sperms. Sperms are of two types. They are represented by 22+Y and 22+X. Similarly, in females, there is only one type of gametes. They are represented by 22+X. Determination of Sex Each cell of living beings contains two types of chromosomes. They are autosomes and sex chromosomes. Autosomes determine various characteristices of the body whereas sex chromosomes determine the sex of an individual. Thus, the biological cause for an Fig: Structure of RNA Fact File Male gametes are called sperms which are represented by 22+Y and 22+X. Similarly, female gametes are called eggs which are represented by 22+X.

82 Oasis School Science and Technology - 10 organism developing into one sex or the other due to the genes in the fused gametes is called sex determination. In human beings, sex is determined by genetic inheritance. Genes inherited from the parents determine whether an offspring will be a boy or girl. Genes for all the characteristics are linear on chromosomes. These include the genes for sexual characteristics. Generally, characters related to the reproductive system are called sexual characters and those that are not are called vegetative characters. The chromosomes that carry genes for sexual characters are called sex chromosomes and those that carry genes for the vegetative characters are called autosomes. A sex chromosome that carries the genes for male characters is called Y-chromosome and one which carries the genes for female characters is called X-chromosome. Each cell of human has a total of 46 chromosomes. Half of them come from the mother and the rest, from the father. Out of these 46 chromosomes, 44 are autosomes and 2 are sex chromosomes. The sex chromosomes are not always a perfect pair. In females, there are 44 autosomes and two X-chromosomes. Similarly, in males, there are 44 autosomes, one X-chromosome and one Y-chromosome. So, the chromosomes in a woman are 44+XX, while the chromosomes in man are 44+XY. Let us see the inheritance pattern of X and Y chromosomes. During gamete formation, the normal diploid chromosome number is havled. This is called the haploid condition. All the eggs of a female have 22+X chromosome. A male produces two types of sperms–one type bears the 22+X composition and the other, 22+Y. Therefore, in 100 sperms 50 have Y chromosome and 50 have X-chromosome. Parents → Result in F1 -generation Father Mother Sperm Sperm Ovum Ovum (female) Sperms (male) Girl (daughter) Girl (daughter) Boy (son) Boy (son) Ovum Gametes → 44+XY 44+XX 44+XY 44+XX 44+XX 44+XY 22+X 22+X 22+X 22+X 22+X 22+Y 22+Y 22+X

Oasis School Science and Technology - 10 83 Any one of the two types of sperms can fertilize the egg. If a Y-bearing sperm fertilizes the egg, the zygote has the 44+XY composition, and the resulting embryo grows to be a boy or son. When an X-bearing sperm fertilizes the egg, the resulting zygote has the 44+XX composition. This embryo develops into a girl or daughter. All the children inherit one X-chromosome from the mother. Therefore, sex is always determined by the other sex chromosome that they inherit from the father. One who inherits X-chromosome of the father is a girl, while one who inherits Y-chromosome of the father is a boy. Reasonable Fact A mother has no role in sex determination of the offspring, why? A mother has only X chromosomes in her egg cells but father has either X or Y chromosomes in his sperm cells. The sex is determined by the X or Y chromosomes of the sperm of the father that combines with the X chromosomes of the mother. Since both the sex chromosomes of the mother are the same ( XX), the offspring’s sex does not change due to the mother’s sex chromosomes. Why is there an equal probability of a boy and girl in the new born baby, though there are 3 girls already? There is equal chance of fusion of sperms having X-chromosomes and Y-chromosomes with the egg of female having X-chromosomes. So, there is an equal probability of a boy and girl in the new born baby. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. The meiosis cell division helps in evolution. The meiosis cell division forms the haploid gametes. Male gametes are produced in males and female gametes are produced in females. The male and female gamete fuses to form a zygote. The zygote has two different sets of chromosomes. So, the new offspring can select better traits from either of the chromosomes of the pair. As a result, there will be variation in offsprings. After multiple generations, the offspring will be far too different from their ancestors and form new species. Hence meiosis helps in evolution. 2. Compare between haploid cells and diploid cells. The comparision between haploid cells and diploid cells are: Father XY XX Daughter Son Daughter Son XY XX XY Mother XX Fig. X-Y system of sex determination in humans

84 Oasis School Science and Technology - 10 SN Haploid cells SN Diploid cells 1 The haploid cells contain a single set of chromosomes. 1 The diploid cells contain two sets of chromosomes. 2 The haploid cells are formed from meiosis. 2 The diploid cells are born from mitosis. 3. The cell division is necessary for living things. The cell division is very necessary for living things because it helps in growth, healing of wounds, formation of new blood cells and production of gametes. 4. What kind of cell division occurs in the zygote of the flowering plants? Why? The mitosis cell division occurs in the zygote of the flowering plants. It happens to multiply the zygotic cell and form the embryo. 5. Describe the structure of the chromosomes. Chromosomes are vehicles of heredity. They are thread-like structures. They are made of genes and histone protein. Histones bind the genes to form chromatin. The long thread-like structure that extends throughout the nucleus is called chromatin. During cell division, it shrinks and becomes thicker, called chromosomes. The chromosomes split vertically to form chromatids. 6. How is the gender of a human foetus determined? Humans reproduce sexually. The male gamete comes from the father that brings either X or Y chromosomes. The female gamete comes from the mother that brings X chromosomes. The male gamete swims toward the egg and fuses to form a zygote. Based on the fusion of gametes, gender of a human foetus is determined. It can be simplified in the picture below. XY X XX XX XX XY XY X Y X X Father Sperms Eggs Mother Gametes Offspring Daughters Sons Parents i. If a sperm containing X chromosome fuses with egg, a daughter is born. ii. If a sperm containing Y chromosome fuses with egg, a son is born. 7. Children are similar to parent. Children are similar to parents because they have genes from their parents. The genes are responsible for physical development.

Oasis School Science and Technology - 10 85 8. Which part of the cell is usually damaged by high-intensity radiation? DNA of the cell is usually damaged by high-intensity radiation. 9. If the ovum contains X chromosome, what does sperm contain? If the ovum contains X chromosome, then the sperm contains either X or Y chromosomes. 10. How do wounds heal? Where do the new cells to fill the wounds come from? The wounds heal by generating new cells. The new cells come from mitosis cell division. Exercises 1. Choose the best answer from the given alternatives. a. What is the living fluid inside the cell called? i. soul ii. water iii. protoplasm iv. cell sap b. Which types of cell division help in the healing of the wounds? i. amitosis ii. mitosis iii. meiosis iv. multiple fission c. Why is meiosis cell division called reductional cell division? i. number of cells decreases during meiosis ii. number of chromosomes decreases in the cell during meiosis iii. size of cells decreases during meiosis iv. number of chromosomes increases in the daughter cells d. Which one of the following is DNA? i. ATGC ii. AUGC iii. ACDC iv. AURC e. How do the characteristics of parents transfer to the children? i. through the blood ii. through the food iii. through the genes iv. through the environment f. Which are the male gametes in human being? i. 22+X and 22+X ii. 22+Y and 22+Y iii. 22+X and 22+Y iv. 44+X and 44+Y 2. Define the following terms with required examples. a. Cell b. Cell division c. Mitosis d. Meiosis e. Chromosomes f. Sex chromosomes g. Autosomes h. Genes i. DNA j. RNA 3. Answer the following questions in very short. a. What is it called if one mother cell divides into four? b. Which cell division helps in asexual reproduction? c. When does meiosis occur? d. What is the region where chromatids are still attached called? e. What is the long thin network of fine threads of chromosomes called?

86 Oasis School Science and Technology - 10 f. Where do the new cells come from? g. What are chromosomes made up of? h. Where are chromosomes found? i. How many chromosomes are there in a human body? How many of them are autosomes and how many of them are sex chromosomes? j. What is the primary function of autosomes? k. What is the function of sex chromosomes? l. What happens if the transcription of DNA is malfunctioning? m. Write the karyotype of man and woman. n. If a couple has 4 sons in a row, does that mean the sperm contained Y chromosomes only? Discuss. o. What is the basic structural and functional unit of heredity? p. What are called vehicles of heredity? 4. Give reasons. a. Mitosis is important for growth. b. Meiosis is important for sexual reproduction. c. Mitosis is called somatic cell division. d. Meiosis is called reductional cell division. e. Mitosis is called equational cell division. f. Pollen grain is haploid. g. Zygote is diploid. h. Woman is not responsible for the gender of the foetus. i. Even though sperm could have either X or Y chromosomes, some couples have children of the same gender, either all boys or all girls. Why? j. Meiosis cell division brings variation but mitosis does not. k. Mitosis helps in the reproduction of underdeveloped unicellular organisms. 5. Differentiate between the following. a. Mitosis and meiosis b. Sex chromosome and autosome c. DNA and RNA d. Gamete and somatic cells e. Diploid cells and haploid cells 6. Answer the following questions in short. a. Write any four properties of mitosis cell division. b. What is the importance of mitosis cell division? c. How do meiosis cell division help in sexual reproduction? d. What is the importance of meiosis cell division? e. Write any four properties of meiosis cell division. f. What is the function of DNA and RNA? g. Discuss the role of genes in an organism. h. What are the functions of chromosomes? i. What happens if there is no meiosis in germ cells of gonads?

Oasis School Science and Technology - 10 87 7. Answer the following questions on the basis of the given figure. B A i. What is shown in the diagram? ii. Write the name of A and B. 8. Answer the following long questions. a. Draw the labelled diagram of a chromosome. b. Let’s suppose there is a cut on your hand. What kind of cell division should occur there to heal wounds and why? Discuss. c. Draw the diagram of each type of chromosome based on the location of the centromere. d. What are the functions of chromosomes? e. Where is DNA located? Describe its structure with a suitable diagram. f. Where is RNA located? Describe its location with a suitable diagram. g. Pollen grains are formed in the anther of the flower. What type of cell division occurs in the anther? Is pollen grain haploid or diploid? How does this cell division bring variation? h. Discuss the importance of cell division in the human body. i. Describe sex-determination in human beings. 9. Answer the following questions on the basis of the given figure. i. What is the function of the structure shown in the diagram? ii. What chemicals form this structure? iii. What are the purines found in it?

88 Oasis School Science and Technology - 10 Key terms and terminologies 1. Heredity : The phenomenon by which living organisms transmit parental characteristics to their offspring is called heredity. 2. Hereditary characteristics: The characteristics of the parents which are transmitted to their offspring are called hereditary characteristics. 3. Variation : Variation can be defined as the differences in the characteristics, or traits, among the individuals of a species. 4. Genetics : The branch of biological science which deals with the study of heredity and variation is called genetics. 5. Gene : A gene is a segment of DNA which contains genetic information. 6. Allele : An alternative form of matching genes is called allele. Examples, TT, Tt, RR, Rr, etc. 7. Homozygous : When both alleles of a particular gene are identical, it is called homozygous. Examples, TT, RR, etc. 8. Heterozygous : When two alleles of a gene are not identical, it is called heterozygous. Examples, Tt, Rr, etc. UNIT 4.2 HEREDITY AND MENDELISM Estimated teaching periods Theory 5 Practical 1 • Introduction to gene • Reason to select pea plant in Mendel experiment • Dominant and recessive characters: introduction and examples • Mendel’s law: related to monohybrid cross only The Sequence of Curriculum Issued by CDC Gregor Johann Mendel is well known as the father of genetics for discovering fundamental laws of inheritance. He was born in Austria (now the Czech Republic) on 20th July 1822 and died on 6th January 1884. He was a biologist, mathematician and meteorologist. He is well known for his pea plant experiments that established many rules of heredity. He has also experimented on bees. About the Scientist Gregor Johann Mendel

Oasis School Science and Technology - 10 89 9. Dominant characteristics: The characteristics which are prominent and appear in successive generations are called dominant characteristics. 10. Recessive characteristics: The suppressed characteristics, which remain unexpressed in successive generations, are called recessive characteristics. 11. Phenotype : The external appearance of an organism for a contrasting characteristic is called phenotype. 12. Genotype : The genetic make up or genetic constitution of an organism is called genotype. 13. Hybrids : Hybrids are the organisms produced after cross fertilization between two genetically different organisms. 14. Monohybrid cross : The cross involving only one pair of contrasting characteristics or allelomorphs is called monohybrid cross. 15. Dihybrid cross : The cross involving two pairs of contrasting characteristics is called dihybrid cross. 16. Law of dominance : "In crossing between pure (homozygous) organisms for contrasting characteristics of a pair, only one characteristic of the pair appears in the first filial generation." 17. Law of segregation : The dominant and recessive characters of the hybrids separate during the gamete formation in such a way that each gamete receives only one character at a time. Introduction Asexual or sexual reproduction is used by living organisms to produce offspring. Reproduction is a fundamental feature of all living organisms that involves the transmission of genetic material from one generation to the next. Living beings are capable of producing offspring of their own kind. Cats, for example, have kittens, dogs have puppies, and orange seeds grow into orange plants. Reproduction ensures the survival of a race or species. Offspring produces by asexual reproduction are identical to their parents as well as to one another because all offspring and parents have identical genes in asexual reproduction. On the other hand, in sexual reproduction, although the offspring are similar to their parents they are not completely identical to them or one another. It is because, in sexual reproduction, offspring receive some genes from the father and some from the mother. Identical twins look almost alike as they have the same genetic material or hereditary material. Actually, the hereditary material is present in the gametes, or sex cells. Thus sex cells constitute the link from one generation to the next. The relation that continues to exist between successive generations is referred to as heredity. The phenomenon by which living organisms transmit parental characteristics to their offspring is called heredity, and the characteristics of the parents which are transmitted to their offspring are called hereditary characteristics. Heredity is also known as inheritance. Fact File Those characteristics which are transferred from one generation to the next generation are called hereditary characteristics.

90 Oasis School Science and Technology - 10 How do all organisms produce same kind of offspring? Hereditary information is present in the gametes. When a male gamete fuses with a female gamete, a zygote is formed, which finally develops into a new organism of the same kind. It is possible due to the presence of hereditary information in the gametes. Therefore, a crow always hatches crows and not parrots, a cat gives birth to kittens, not puppies, a seed of a mango always grows into a mango tree and not an orange tree. Variation Though the offspring inherit the traits, or characteristics, of their parents and resemble them very closely, they are not identical to their parents in all aspects. The offspring are never a true copy of their parents. Even though twins show resemblance in many aspects, they also show differences in many characteristics. There may be morphological, physiological and behavioristic differences among the individuals of a species. Those differences are known as variations. So, variation can be defined as the differences in the characteristics, or traits, among the individuals of a species. For example, the height of a human being is a trait which shows variations because some people are very tall, some have medium height whereas some are dwarfs. Similarly, the complexion of a human being, type of hair, color of the eyes, shape of the nose, etc. are the traits of human beings. These traits bring out variation. The difference in the traits, or variation, is necessary for organic evolution. Genetics Heredity and variation are two fundamental factors in the process of organic evolution and formation of new species. The branch of biological science which deals with the study of heredity and variation is called genetics. It can also be defined as the biological science of inheritance. Genetics is the modern experimental study of the laws of inheritance (variation and heredity). It deals with the mechanisms responsible for similarities and differences among closely related species. The term genetics was first coined by W. Batesman in 1905 AD [Gk., genesis – grow into or to become). The first scientific study of genetics was carried out by an Austrian monk Gregor Johann Mendel (1822 – 1884 AD). He introduced the concept of genes as the basic unit of heredity. Mendel's work Mendel carried out his scientific investigation on hybridization of pea plants. He established the laws of inheritance of characteristics. The results of his eight-year breeding experiments were read before the Natural History of Society of Brunn (Austria) in 1865 AD. However, his work remained unnoticed until 1900 AD, when three scientists Hugo De Vries in Holland, Tschermak in Austria and Correns in Germany discovered its significance. Since then Mendel's work has formed the basis of the study of genetics. Mendel died in 1884 AD before he could see his work accepted and appreciated. Genes and Gene Concept Genes are tiny units of heredity located in the chromosomes. The concept of gene was introduced by Sutten, and the term 'gene' was introduced by Johannson. The essential

Oasis School Science and Technology - 10 91 features of the modern gene concept are given below: Genes are located in chromosomes, and they are arranged in a linear fashion. Each gene occupies a fixed position in a fixed chromosome. The position of a gene in a chromosome is called locus (pl.–loci). Genes determine the physical, anatomical and physiological characteristics of organisms. These characteristics are transmitted from one generation to another. Each chromosome contains a large number of genes. It is estimated that about 60000 genes are present in 23 pairs of chromosomes of human beings. A single gene may occur in several forms and a gene may undergo a sudden change in expression. This phenomenon is called mutation. A gene is a segment of DNA which can form exact copies by the process of replication. Reasonable Fact The offspring of the organisms look like their parents but are not exactly identical. The offspring gets half of its characteristics from mother and half from father. So, they look similar to their parents. Since variation occurs in every gene that is passed to the offsprings, they do not look exactly identical. Chemically, a gene is a segment of a large polynucleotide molecule called DNA (deoxyribonucleic acid), which forms the most important constituent of a chromosome. Functions of genes 1. Genes are responsible for the inheritance of characteristics from one generation to another. 2. They code for proteins to control phenotype and metabolism. 3. Genes help in evolution by mutation and genetic recombination. 4. Genes code for different types of RNAs for protein synthesis. Reasonable Fact Why are genes called hereditary vehicles? Genes are called hereditary vehicles because they carry and transfer the genetic characteristics from the parents to the offsprings. Terminology Related to Genetics a. Allele: An allele is one form of a gene or pair of matching genes. There may be two or more alleles of a gene. Diploid organisms contain two alleles, one on each pair of chromosomes. For example, in pea plants, the gene for the height of the plant may have a tall allele and a dwarf allele. In genetics, different alleles are denoted by letters, e.g., TT, Tt, Rr, etc. b. Homozygous: When both alleles of a particular gene are identical, it is called homozygous. Such an individual is called pure breeding because this type of individual always produces the same phenotype of offspring as it does not hide a recessive allele. For example, TT (pure tall), RR (pure red), rr (pure white), etc. Fact File An alternative form of matching genes is called allele. Examples, TT, Tt, RR, Rr, etc.

92 Oasis School Science and Technology - 10 c. Heterozygous: When two alleles of a gene are not identical, it is called heterozygous. A heterozygous individual contains one dominant allele and another recessive allele. It is also called a hybrid. For example, Rr (hybrid red). It contains one dominant allele, i.e. R and another recessive allele, i.e., r, where R = Red and r = white. Generally, the capital letter stands for a dominant allele, and the small letter stands for a recessive allele in a set of allele. d. Dominant characteristics: The characteristics which are prominent and appear in successive generations are called dominant characteristics, e.g., in the crosspollination between a tall pea plant and a dwarf pea plant, tall is a dominant characteristic as it appears in F1 –generation. Reasonable Fact The cross fertilization between a tall and a dwarf pea plant produces only tall pea plants in the first generation. The cross fertilization between a tall and a dwarf pea plant produces only tall pea plants in the first generation because in a cross between pure tall and pure dwarf, the tall character is dominant and expresses itself over the dwarf character which is recessive and remains hidden in the first generation. e. Recessive characteristics:The suppressed characteristics, which remain unexpressed in successive generations, are called recessive characteristics, e.g. in the crosspollination between a tall pea plant and a dwarf pea plant, dwarf is a recessive characteristic as it remains hidden in F1 –generation. f. Phenotype: The external appearance of an organism for a contrasting characteristic is called phenotype. It is expressed in words, e.g., tall, dwarf, etc. Parental characteristics of an organism cannot be known from the phenotype of an organism. g. Genotype: The genetic make up or genetic constitution of an organism is called genotype. It is expressed in letters, e.g., TT (pure tall), Tt (hybrid tall), tt (dwarf), etc. Parental characteristics of an organism can be found from the genotype of an organism. h. Hybrids: Hybrids are the organisms produced after cross fertilization between two genetically different organisms. The process by which hybrids are formed is called hybridization (i.e., the process of crossing between organisms having two contrasting characteristics). Hybrids are of various types, e.g., monohybrids, dihybrids, polyhybrids, etc. i. Monohybrid cross: The cross involving only one pair of contrasting characteristics or allelomorphs is called monohybrid cross. As a result of monohybrid cross, offspring having phenotypic ratio of 3:1 are produced in F2 - generation, e.g., cross between a tall plant with a dwarf plant. j. Dihybrid cross: The cross involving two pairs of contrasting characteristics is called dihybrid cross. As a result of dihybrid cross, offspring having phenotypic ratio of

Oasis School Science and Technology - 10 93 9:3:3:1 are produced in F2 - generation, e.g., cross between a red - flowered tall pea plant with a white - flowered dwarf pea plant. k. F1 –generation: The generation obtained by crossing two parental stocks is called F1 – generation. It is also called the first filial generation. l. F2 –generation: The generation obtained by crossing two parental stocks of F1 - generation is called F2 - generation. It is also called the second filial generation. Mendel's Material for His Experiment Gregor Mendel conducted his experiments over a period of eight years on the common edible garden pea plant (Pisum sativum) in his Monastery garden at Brunn, Austria. Mendel chose garden pea plant for his experiment because of the following reasons: 1. Pea plants have several distinct varieties having a large number of contrasting characteristics in pairs, such as tall (T) and dwarf (t), round (R) and wrinkled (r) seeds, smooth (I) and constricted (i) pea pods, etc. Mendel observed seven pairs of contrasting characteristics in pea plants. The seven pairs of traits present in pea plants are given in a table. 2. Pea plants can be cultivated easily, and they have a short life cycle. So it is possible to study several generations within a few years. 3. Breeding can be controlled easily in pea plants because of the structure of the flowers. 4. They produce a large number of offspring after fertilization, and the hybrids produced after cross– pollination are also fertile. 5. In pea plants, it is easy to obtain pure lines for several generations due to selfpollination. 6. The flowers of a pea plant are adequate in size and are easy to handle. 7. In pea plants, petals of flowers completely enclose the male and female reproductive organs until fertilization which ensures self-pollination. Table 19.1: Seven pairs of contrasting traits in pea plants studied by Mendel Traits Contrasting forms Dominant Recessive 1. Height of the plant Tall Dwarf 2. Color of flower Purple (Red) White 3. Shape of seeds Round Wrinkled 4. Color of pods Green Yellow 5. Shape of pods Inflated Constricted 6. Position of flowers Axial Terminal 7. Color of seeds Yellow Green

94 Oasis School Science and Technology - 10 Fig. Mendel's material for his experiment with its traits Recessive trait Dominant trait Height Seed shape Seed colour Seed coat Pod shape Pod colour Flower position Short (Dwarf) Wrinkled Green White Constricted (flat) Yellow Terminal Tall Round Yellow Green Inflated (full) Green Axial Mendel's Experiment Mendel had an idea that a plant inherits two genes of information for a single characteristic, one from each parent in every generation. So he selected seven pairs of contrasting characteristics in the garden pea. He concentrated his attention on only one pair of characteristics at a time, and traced them carefully through many successive generations. Mendel controlled his experimental conditions carefully, ensuring that pea plants were pollinated only by the pollen grains he transferred. He made careful observations and performed his experiments repeatedly keeping meticulous records. Mendel crossed homozygous (pure) tall pea plant (2 m tall) and a homozygous dwarf pea plant (0.5 m tall). He carried out his experiment by transferring pollen grains of the tall plant to the stigma of the dwarf plant. He prevented self–pollination by removing all stamens of the dwarf plant. The seeds produced by the dwarf plant were collected and sown. The plants obtained in this generation were called F1 –generation. He found that all plants obtained in F1 –generation were tall. Reasonable Fact Only one character is expressed in the first filial generation. In a cross between contrasting characters, only one allele of the gene is expressed as a dominant character while the other remains hidden as recessive character. The dominance of one character over the other causes only one character to appear in the first filial generation. These tall plants of F1 –generation were allowed to self–pollinate. The seeds were collected and sown. The plants obtained were called F2 –generation. In this generation, some plants were tall and a few were dwarfs in the ratio of 3 : 1.

Oasis School Science and Technology - 10 95 The seeds of F2 –generation were sown again and allowed to self-pollinate. This gave the F3 - generation. In this generation, Mendel found that the dwarf plants of F2 -generation produced dwarf plants. Out of tall plants of F2 -generation, one third were pure tall, and the remaining two thirds were hybrid tall. Pure tall plant of F2 - generation produced pure tall plant in F3 - generation. Mendel's experiment can be demonstrated as follows: Where, TT – pure tall Tt – hybrid tall tt – pure dwarf Law of Dominance: Mendel's First Law According to Mendel's experiments, the law of dominance states, "In crossing between pure (homozygous) organisms for contrasting characteristics of a pair, only one characteristic of the pair appears in the first filial generation." This law can be explained as follows: Let's consider a pure tall pea plant (TT) and a pure dwarf pea plant (tt). When a pure tall pea plant is cross - pollinated with a pure dwarf plant, all pea plants become tall (genetically hybrid tall) in the first filial generation. Here, tallness appears by suppressing the dwarfness. In this cross, tall is the dominant characteristic Parents → Genotype → Pure tall pea plant Pure dwarf pea plant Cross - pollination F1 - generation F2 - generation F3 - generation Gametes Self-pollination → Possible gametes → All hybrid tall→ Gametes → If the F1 - are bred together Tt T t TT Tt T TT t Tt T Tt t tt T TT Tt tt tt t T t Tt tt TT Tt T T t t Parents → Genotype → Pure tall Gametes Cross-pollination Offspring in F1 -generation Tall Tall Tall Tall Pure dwarf Tt Tt Tt Tt TT tt

96 Oasis School Science and Technology - 10 as it appears in F1 –generation whereas dwarf is the recessive characteristic as it remains hidden in F1 –generation. Law of Segregation: Mendel's Second Law Mendel's second law of inheritance, i.e., law of segregation states, "The hybrids obtained in F1 –generation contain two contrasting characteristics of dominant and recessive nature. Those characteristics remain together for a long period of time in hybrids but do not mix with each other and separate or segregate at the time of gamete formation so that each gamete gets only one characteristic, either dominant characteristic or recessive characteristic." This law is also called law of purity of gametes. Mendel's second law can be explained by the monohybrid cross between a pure redflowered pea plant (RR) and a pure white flowered pea plant (rr) upto the second filial generation. Parents - Pure red flowered pea plant Pure white flowered pea plant RR rr RR Rr Rr rr R r R r Rr Rr Rr Rr R R r r Genotypes Gametes Cross-pollination Gametes Pure red Hybrid red Pure white F2 - generation Self - pollination F1 - generation Phenotypic ratio of Red : White is 3 : 1. Genotypic ratio of Pure red : Hybrid red : Pure white is 1 : 2 : 1. In F1 –generation, all pea plants produce hybrid red (Rr) with dominant (R) and recessive characteristic (r). Both characteristics remain together for a long period of time without mixing and finally separate into two different pure gametes, either red (R) or white (r). Those hybrids, after interbreeding, produce three different types of offspring, i.e., pure red, hybrid red and pure white in the ratio of 1 : 2 : 1 in the second filial generation. It is possible due to the segregation or purity of the gametes. Mendel also experimented on other pairs of alternative characteristics, and he found that, in every case, the characteristics followed the same scheme of inheritance. Thus in the garden pea, he found that purple (red) flower was dominant over white flower, yellow seed over green seed, tall plant over dwarf plant, and smooth seed over wrinkled seed. Fact File Hybrid black father and hybrid black mother may give pure white baby.

Oasis School Science and Technology - 10 97 Reasonable Fact We can see all characters in the F2 generation, why? The probability of separation of allele from their pair is 50-50 at the time of gamete formation. During gamete formation in the F1 generation, each gamete contains only one allele due to meiosis cell division. So, we can see all characters in the F2 generation. Crossing in Some Organisms i) Fruit-fly (Drosophila melanogaster) Even in the 1900s, Mendelian genetics was regarded as doubtful. Thomas Hunt Morgan, an American geneticist, experimented on fruit flies at Columbia University to test the law of dominance. Fruit-flies (Drosophila) have two types of wings: long wings and short wings. Out of these wings, long wing character is a dominant character while the short wing character is a recessive character. When a long wing fruit-fly (LL) is crossed with a short wing fruit-fly (ll), all fruit-flies in the F1 generation have long wings. But, in the F2 generation, 75% of the flies were long winged and the remaining 25% were short-winged. This experiment proves Mendelian law of dominance. ii) Guinea pig The black colour of a guinea pig is dominant over the white colour. If we cross a black-coloured guinea pig with genotype BB with a white-coloured guinea pig with genotype bb, all guinea pig in the F1 generation are black. But, in F2 generation, the ratio of black to white guinea pigs is 3:1( three blackcolour guinea pig and one white-colour guinea pig). Guinea pigs are generally chosen for the genetic experiments because they are small, have short life cycle, easy to handle, to look after and show a wide range of pair of contrasting characters. Genetic characteristics in human beings Humans have several dominant and recessive characters that are inherited from one generation to another. Dominant characters are common in human population while the recessive characters are rare. Some of the human characters are given below: Drosophila with short wings Drosophila with long wings Drosophila with long wings (Sibling crosses) Drosophila with long wings Drosophila with long wings Drosophila with long wings Drosophila with short wings BB B B B B B B b b b b b b BB Bb Bb Bb Bb Bb Bb bb bb

98 Oasis School Science and Technology - 10 S.N. Characteristics Contrasting pairs Dominant Recessive 1 Earlobes Free earlobes Attached earlobes 2 Rolling of tongue Tongue rolling Non-tongue rolling 3 Dimple Dimpled cheek Non-dimpled cheek 4 Thumbs Hitchhiker's thumb Straight thumb 5 Hairline Widow's peak Straight hairline 6 Chin Cleft chin Normal chin 7 Handedness Right handed Left handed 8 Hairstyle Curly hair Straight hair Eearlobe trait Tongue-rolling trait Chin dimple trait Thick and thin lips trait Cheek dimple trait Curly and straight hair trait Hitchhiker's thumb trait Genetic characteristics in human beings Activity 1 Human beings contain a number of dominant and recessive characteristics. Study five types of dominant and recessive characteristics present in your body. Compare the hereditary characteristics of your own family members and prepare a list of those characteristics. Certain characteristics found in human beings depend on the sex of an individual. Due to this, certain diseases are found only in males and others are found only in females. Such diseases are called sex-linked diseases. For example, baldness and color blindness are found only in males whereas breast cancer and uterine cancer are found only in females.

Oasis School Science and Technology - 10 99 Significance of Mendelism Mendel's laws can be used for solving many problems of genetics. The significance of Mendelism is stated below: 1. Disease resistant and high yielding varieties of plants and animals can be produced by the application of Mendelism. 2. Hybrids with desired characteristics can be produced. 3. The genotypes and phenotypes likely to be produced in successive generations can be predicted before the cross is made. 4. Dominant and recessive characteristics of the organisms can be known. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Genes determine our physical traits. Genes contain codes that directly determine the physical traits. Our body structure, physical traits, disease resistance and adaptation are all determined by genes. 2. Both parents are tall but Himani is short. What might be the reasons? Explain with the help of a phylogenetic chart. Both parents of Himani are tall but she is not. The only reason might be her parents are hybrid tall. There is a 25 % chance that a child will be born with a recessive character. Phylogenetic chart of a cross between hybrid parents: Let the father be hybrid tall ‘Tt’ and let the mother be hybrid tall ‘Tt’. In the above scenario, allele tt would represent Himani. 3. Gregor Mendel is called the father of genetics. Gregor Mendel is called the father of genetics because he discovered that: i. Certain factors transfer from parents to children. ii. Factors exist in pairs. One comes from the father and another comes from the mother. iii. Only one factor is expressed in children whereas the other remains hidden without blending. Based on it he proposed three laws of genetics. Therefore, he is called the father of genetics. 4. Rama Kumari has a black goat. She bred it with a white goat and all kids were born white. What could be the reason? Did the genes of the black goat got lost forever or blended? Will it ever appear again? Explain. Were the parent goats pure or hybrid? Answer with reason. Rama Kumari has a black goat which was bred with a white goat. All kids were born white. The only reason could be the black goats and white goats were purebreds. And white goat was dominant. Therefore, only white kids were born in first filial generation. No! the genes of the black goat are not lost for ever. It will appear again in the second filial generation. It is because it has not blended. The probability of a black goat being O O T t TT T Tt Tt t tt +

100 Oasis School Science and Technology - 10 born in the second filial generation is 25%. The parent goats were pure organisms because only pure organisms can produce 100% hybrid offspring. 5. Do Mendel's laws apply to human beings too? What difficulties would Mendel have faced if hehad carried out his experiment on human beings instead of pea plants? Yes! Mendel’s laws apply to human beings too. If Mendel had carried out his experiment on humans instead of pea plants, he would have faced problems. Some of them are: i. Human experiment is illegal. ii. Human beings have a very long-life span, so it would require a very long time for the experiment. iii. One cannot own and keep humans like pets or plants. iv. Inbreeding is not good for anyone's health. v. Inbreeding among siblings is unethical. 6. Clarify the law of dominance and purity of gamete with the help of an example. Let's take an example of a monohybrid cross of a pea plant with pure red flowers and pure white flowers. Let the gamete of pure red flowered pea plant be RR and the gamete of pure white flowered pea plant be rr. Parents - Pure red flowered pea plant Pure white flowered pea plant RR rr RR Rr Rr rr R r R r Rr Rr Rr Rr R R r r Genotypes Gametes Cross-pollination Gametes Pure red Hybrid red Pure white F2 - generation Self - pollination F1 - generation Here, in the first filial generation, all of the offspring are hybrid red. Only red flowers are available in the first filial generation. It must have happened because the red was a dominant character and the white was recessive. Such appearance of only one character in the first filial generation is called the law of dominance. Here, the hybrid organisms were self-pollinated. The hybrid organisms had different genes (Rr). Those genes did not mix or blend. They separate into different gametes (r) and (R). It means the gamete does not blende, they stay pure. 7. No dwarf pea plants were observed in the first filial generation when the pure tall pea plant and pure dwarf pea plant were crossed. No dwarf pea plants were observed in the first filial generation when pure tall pea