Green Science 10 Final PDF (2076)

Functions of plasma 1. to transport digested food (nutrients) to Do You Know various body parts. Plasma contains anticoagulant 2. to transport waste materials like urea, substance called heparin which carbon dioxide, etc. for their removal prevents blood clotting inside the blood from the body. vessels. 3. to regulate body temperature The proteins (albumin, globulin and fibrinogen) help in clotting of blood. 4. to regulate the amount of water and minerals in the body. 5. to transport hormones to different parts of the body. 6. to transport urea produced by liver to kidneys. Blood corpuscles The blood corpuscles are solid particles that remain immersed in plasma. They occupy 45% of the blood volume. There are three types of blood corpuscles. They are: i. Red blood cells (Erythrocytes) ii. White blood cells (Leucocytes) and iii. Platelets (Thrombocytes) i. Red blood cells (RBCs) The red blood cells or erythrocyes are red- coloured blood cells having biconcave shape. They do not have nucleus. They appear red due to the presence of an iron- containing pigment called haemoglobin. Fig. Oxygen is absorbed by haemoglobin and supplied to various parts of the body. The haemoglobin rich in oxygen is called 16.2 oxyhaemoglobin and the haemoglobin Red Blood Cells rich in carbon dioxide is called carboxyhaemoglobin. RBCs are smaller than white blood cells and larger than platelets. The red blood cells are produced in bone marrow, live for about 90 to 120 days and are destroyed in liver and spleen. About 45 lakh to 50 lakh RBCs are found in 1 mm3 volume of blood. About 20 lakhs RBCs are formed in the bone marrow in one second and the same number is destroyed in liver and spleen per second. The iron present in old RBCs is reused to form new RBCs. The formation and destruction of RBCs continues throughout the life. GREEN Science (Biology) Book-10 301

Functions of RBCs i. RBCs absorb oxygen from lungs and transport to various tissues. ii. They transport carbon dioxide from various tissues to the lungs. ii. White blood cells (WBCs) The white blood cells (leucocytes) are colourless irregular blood cells having nucleus. They are the largest blood cells. They are produced in bone marrow and lymph nodes. They live for a few hours to few days. They are destroyed in liver, spleen and at the site of infection. Do You Know Eosinophil Basophil A person suffers from anaemia due to lack of RBCs or haemoglobin in Monocyte blood. Haemoglobin is absent in WBCs. Fig. A person suffers from blood cancer Lymphocytes Neutrophil leukaemia due to enormous increase in the number of WBCs in the blood. 16.3 White Blood Cells There are two types of white blood cells. They are granular and non-granular. Neutrophill, Eosinophyll and Basophyll are called granular WBCs whereas Lymphocytes and Monocytes are called non-granular leucocytes. The number of WBCs ranges from 6000 to 10,000 in 1 mm3 volume of blood. Functions of WBCs i. WBCs play a great role to form immune system in the body. ii. They help in formation of antibodies to neutralize the germs that enter the body. iii. WBCs fight against micro-organisms and protect us from various diseases. iii. Platelets The platelets or thrombocytes are colourless, oval or round blood cells without nucleus. They are the smallest blood cells. They are formed in bone marrow, live for 2 to 3 days and are destroyed in the spleen. The shape of platelets is irregular. 1mm3 volume of blood consists of 2-4 lakhs of platelets. Functions of Platelets i. The platelets play an important role in clotting of blood and prevent the loss of blood from cuts or wounds. 302 GREEN Science (Biology) Book-10

Functions of Blood In human body, blood performs three types of functions. They are: 1. Transportation 2. Regulation 3. Protection 1. Transportation i. Blood transports oxygen from the lungs to the different cells and tissues of the body. ii. It transports carbon dioxide from tissues to the lungs. iii. Blood transports nutrients absorbed by walls of intestine to different tissues of the body. iv. Blood transports hormones produced by endocrine glands to different parts of body. v. Blood transports various waste materials towards liver, lungs, kidney and skin for excretion. 2. Regulation i. Blood keeps our body warm by regulating body temperature. ii. Blood regulates the amount of water, minerals and other chemicals in the body. 3. Protection i. Blood fights against microbes that cause various diseases and protect our body from various diseases. ii. Blood transports WBCs in the infected area to fight against germs. iii. Blood helps to clot the blood in case of cuts or wound and prevents further loss of blood and infection. Differences between RBCs (Erythrocytes) and WBCs (Leucocytes) RBCs WBCs 1. RBCs don't have nucleus. 1. WBCs have nucleus. 2. Haemoglobin is present. 2. Haemoglobin is absent. 3. They are biconcave in shape. 3. They are irregular in shape. 4. They transport oxygen and carbon 4. They fight against microorganisms. dioxide. GREEN Science (Biology) Book-10 303

Activity Take a sterilized lancet and prick your fingertip under the supervision of your biology teacher. Put a drop of blood on a clean slide and spread the drop throughout the slide with the help of another glass slide. Put a drop of Leishman's stain on the blood film and leave it for 5 minutes. After 5 minutes, rinse the blood film with distilled water and let it to dry in the sunlight. Observe the blood film under the compound microscope. Draw neat figure and label the main parts. Heart The heart is a powerful Aorta and hollow organ made Superior Pulmonary of cardiac muscle. It is vena cava trunk conical in shape and is about the size of the fist Right Left of the individual. The artium atrium heart is located near the Pulmonary veins middle of the thoraic Right Left cavity between two ventricle ventricle Fig. lungs. About two-third ofFig. Inferior the heart is located on the 16.4 vena cava left side and one-third is External morphology of human heart located on the right side of the thoracic cavity. The average weight of the heart is about 300 grams in adults. Superior vena cava Aorta Pulmonary artery Pulmonary veins Right atriLuemft Pulmonary veins atrium Mitral valve Pulmonary valve Aortic valve Tricuspid valve Left ventricle Septum Right ventricle 16.5 Inferior vena cava Internal morphology of human heart 304 GREEN Science (Biology) Book-10

The human heart is surrounded by a double-layered membrane called the pericardium. The space between two layers of pericardium is filled with a slippery fluid called the pericardial fluid. This fluid enables the heart contract smoothly and also protects the heart from mechanical injury. The human heart consists of four complete chambers, viz. two upper chambers called auricles and two lower chambers called ventricles. The auricles are separated into right and left auricles by a muscular septum. Similarly, the ventricles are divided into right and left ventricle by a muscular septum. The auricles are thin-walled small chambers whereas ventricles are thick-walled large chambers. The wall of the right ventricle is thicker than that of the auricles as it pumps blood to a much farther distance to the lungs for purification. Similarly, the wall of left ventricle is the thickest of all as it pumps blood to different parts of the body. The various blood vessels enter and leave the heart. Superior vena cava and inferior vena cava are connected to the right ventricle whereas four pulmonary veins are connected to the left auricle. The pulmonary artery originates from the right ventricle and aorta is originated from the left ventricle. Four different types of valves are present in the human heart. They are aortic valve, pulmonary valve, tricuspid valve and bicuppid or mitral valve. The aortic valve is located at the base of aorta inside the heart. It regulates the flow of blood from left ventricle to different parts of the body and prevents the backflow of blood. The pulmonary valve is located at the base of pulmonary artery. It regulates the flow of blood from right ventricle to the lungs and prevents the back flow of blood. The tricuspid valve is located between the right auricle and the right ventricle. It has three muscular flaps or cusps. It regulates the flow of blood from the right auricle to the right ventricle and prevents the backflow of blood. Similarly, bicuspid or mitral valve is located between the left auricle and the left ventricle. It has two muscular flaps or cusps. It regulates the flow of blood from the left auricle to the left ventricle and prevents the backflow of blood. Blood vessels The muscular tubes or pipes through which blood flows are called blood vessels. There are three types of blood vessels. They are: i. Arteries ii. Veins iii. Capillaries i. Arteries Fig. External elastic membrane Smooth muscle The thick-walled blood vessels that carry 16.6 Internal elastic membrane blood away from the heart are called Lumen arteries. They are deep-seated inside the Endothelium muscles. All arteries carry pure blood except the pulmonary artery. Inside the Structure of an artery arteries, blood flows with a high speed and under high pressure. Therefore, their wall is GREEN Science (Biology) Book-10 305

thicker than that of venis. The branches of arteries are called the arterioles. An artery has a narrow lumen and a thick wall. Valves are absent in arteries. Examples: aorta, pulmonary artery. ii. Veins External elastic membrane Smooth muscle The thin-walled blood vessels that carry blood towards the heart are called veins. Internal elastic membrane They are situated on the surface of muscles. Lumen All veins carry impure blood except pulmonary veins. Inside the veins, blood Endothelium flows with a low speed and under low Valve pressure. Therefore, veins have a thin wall. The branches of veins are called venules. 16.7 A vein has a wide lumen and a thin wall. Structure of a vein Valves are present in veins to prevent the Fig. reverse flow of blood. Examples: vena cava, Fig. pulmonary veins. iii. Capillaries 16.8 Endothelium The capillaries are extremely narrow and microscopic Structure of a capillary blood vessels. They connect the arterioles to the venules and can penetrate every part of the body. The wall of the capillary consists of a single layer of cells. The capillaries help in exchange of materials between the blood and body cells. Differences between Arteries and Veins Arteries Veins 1. Arteries are thick-walled blood 1. Veins are thin-walled blood vessels. vessels. 2. They carry blood away from the heart. 2. They carry blood towards the heart. 3. Valves are absent. 3. Valves are present. 4. They have a narrow lumen. 4. They have a wide lumen. Process of Blood Circulation in the Human Body In human body, blood flows twice through the heart before the pure blood is supplied to various parts of the body. Superior vena cava and inferior vena cava collect impure blood from different body parts to the right auricle. The right auricle passes impure blood to the right ventricle. When the right ventricle contracts, impure blood is supplied to the lungs through the pulmonary artery. The impure blood combines with oxygen and becomes pure 306 GREEN Science (Biology) Book-10

(oxygenated). Then the pure blood from the lungs is brought to the left auricle through the pulmonary veins. Capillary bed of lungs where gas exchange occurs Pulmonary Pulmonary circuit Pulmonary veins arteries Systemic circuit Aorta and branches Vena cavae Left atrium Right atrium Left ventricle Right ventricle Systemic arteries Systemic veins Capillary bed of all body tissuesFig. where gas exchange occurs 16.9 Schematic figure of blood circulation in human body The left auricle contracts and passes pure blood to the left ventricle. The left ventricle contracts and pumps pure blood to the aorta. The aorta supplies pure blood to various body parts through the arteries, arterioles and capillaries. In this way, the circulation of blood takes place in a human body. Types of Blood circulation The blood circulation in human body is of two types. They are as follows: 1. Systemic circulation 2. Pulmonary circulation 1. Systemic circulation The circulation of blood between the heart and various parts of body is called systemic circulation. It takes place with the help of arteries and veins. When left ventricle of the heart contracts, it pumps oxygenated blood to different parts of body through aorta, artery, arterioles and capillaries. Body cells absorb oxygen and digested food from blood. The carbon dioxide gas and waste products diffuse into blood. Then the deoxygenated blood is collected back to the heart through capillaries, venules, veins and vena cava. In short, the circulation of blood from the left ventricle to the right auricle of the heart is called systemic circulation. GREEN Science (Biology) Book-10 307

2. Pulmonary Circulation The circulation of blood between heart and lungs is called pulmonary circulation. It occurs with the help of pulmonary artery and pulmonary veins. When right ventricle contracts, it passes deoxygenated blood to the lungs through pulmonary artery. The deoxygenated blood becomes oxygenated in lungs. Then the oxygenated blood is collected to the left auricle of the heart through pulmonary circulation. Heart beat The heart beat is the rhythmic beat which is produced due to contraction and relaxation of the heart muscles. The average heart beat rate of a healthy young person is about 72 times per minute. The rate of heart beat increases with tension, physical exercise, emotion, fear, fever, etc. The rate of the heart beat may vary with age, sex and condition of the body. Blood Pressure The force exerted by blood which pushes the walls of arteries is called blood pressure. It depends on the amount of blood, speed of blood flow, shape of the blood vessel and the force exerted by the heart while pumping blood. Blood flows through blood vessels due to blood pressure. The normal blood pressure of a healthy young person is 120/80 mm of Hg. Blood pressure is measured in millimetre height of mercury column. Types of Blood Pressure Blood pressure is of two types, viz. systolic blood pressure and diastolic blood pressure. Systolic blood pressure The force exerted by blood per unit area of arterial walls when the ventricles of the heart contract is called systolic pressure. In adult human beings, the systolic blood pressure ranges between 90 mm of Hg to 120 mm of Hg. The average systolic blood pressure of a healthy adult is taken as 120 mm of Hg. Diastolic blood pressure Fig. The force exerted by blood per unit area of arterial Sphygmomanometer walls when ventricles of the heart relax is called diastolic blood pressure. In adult human beings, it ranges between 60 mm of Hg to 90 mm of Hg. The average diastolic pressure of healthy young person is taken as 70 mm of Hg. Systolic blood pressure is also called upper limit of arterial pressure and diastolic pressure is called lower limit of arterial pressure. The instrument which is used to measure the blood pressure is called 16.10 sphygmomanometer. 308 GREEN Science (Biology) Book-10

Now-a-days, many people suffer from high blood pressure. The major causes of high blood pressure(Hypertension) are given below. • Obesity • Unhealthy lifestyle • Over weight • Regular smoking • Consumption of more salt in food • Adrenal and thyroid disorder • Genetic cause • Lack of physical exercise • Drinking alcohol regularly • Regular consumption of fatty, oily and spicy foods • Regular consumption of cold drinks • Kidney disorder The symptoms of high blood pressure are as follows: • Headache • Dizziness • Chest pain • Blurred vision Following measures should be adopted to prevent high blood pressure. i We should adopt healthy lifestyle. ii. We should avoid smoking and drinking alcohol. iii. We should not consume fatty, oily and spicy foods regularly. iv. We should consume balanced diet. v. Physical exercise should be taken regularly. vi. Consumption of cold drinks should be avoided. vii. We should check the blood pressure regularly. Diabetes Diabetes is commonly known as sugar disease. This disease is caused due to lack of insulin hormone secreted by pancreas. In diabetes, the amount of sugar increases in blood. Insulin hormone regulates the amount of glucose or sugar in the blood. When there is lack of insulin, the excess glucose in blood cannot be changed into glycogen to GREEN Science (Biology) Book-10 309

store in the body. As a result, the amount of sugar increases in the blood and sugar passes out through urine. This disorder is called diabetes or sugar disease. Causes of diabetes i. Genetic cause ii. Insufficient insulin production iii. Stressful life style The major symptoms of diabetes are as follows: i. excessive thirst and hunger ii. frequent urination iii. blurred vision iv. weakness v. delay in wound healing vi. muscle cramping vii. unconsciousness, etc. Following measures should be adopted to prevent diabetes : • We should consume balanced diet. • We should reduce obesity. • We should take physical exercise regularly. • We should consume fruits and vegetables. • We should avoid smoking and drinking. • We should reduce hypertension. Uric acid The acid produced in the body as a byproduct due to decomposition of purine is called uric acid. Purine is an important chemical substance for our body because it provides protein to the body. Uric acid protects the inner part of blood vessels and helps to remove toxins from the body. In human body, uric acid is produced due to excess metabolism of purine. If the body produces too much uric acid and cannot be removed from the body through urine, a person suffers from uric acid. The condition of having high level of uric acid in blood is called hyperuricemia. Hyperuricemia occurs either due to failure to excrete uric acid from the body or increased production of uric acid in the body. The major causes of hyperuricemia or uric acid are as follows: i. Excessive consumption of meat products, pulses, beer, etc. ii. Excessive consumption of alcohol and caffeine. iii. Hypothyroidism iv. Obesity 310 GREEN Science (Biology) Book-10

v. Leukaemia The major symptoms of hyperuricemia are as follows: i. Joint ache ii. Deep pain in muscles iii. Difficulty in walking iv. Swelling and burning of skin v. Swelling of joints of leg with pain Following measures should be adopted to reduce uric acid in the blood: i. We should drink sufficient water. We should drink less water but many times in a day to wash away the excess uric acid through urine. ii. We should reduce the consumption of Do You Know pulses, sea foods and fatty red meat. Cherries contain anthocyanin which iii. We should consume baking soda. reduces burning sensation in skin and joints. iv. We should eat 10 - 40 cherries per day to reduce burning sensation in the body. Key Concepts 1. The system formed by heart, blood and blood vessels which transports various materials from one part of the body to another is called the blood circulatory system. 2. The human blood circulatory system consists of three main parts. They are: (i) Blood, (ii) Heart and (iii) Blood vessels. 3. The blood is a red fluid connective tissue. It consists of plasma (55%) and blood corpuscles (45%). 4. Plasma is a straw-coloured liquid which occupies 55% of the blood volume. 5. The blood corpuscles are solid particles that remain immersed in plasma. They occupy 45% of the blood volume. 6. The heart is a powerful and hollow organ made of cardiac muscle. 7. About two-third of the heart is located on the left side and one-third is located on the right side of the thoracic cavity. The average weight of the heart is about 300 grams in adults. 8. Four different types of valves are present in the human heart. They are aortic valve, pulmonary valve, tricuspid valve and bicusppid or mitral valve. 9. The muscular tubes or pipes through which blood flows are called blood vessels. There are three types of blood vessels. They are (i) Arteries, (ii) Veins and (iii) Capillaries. 10. The heart beat is the rhythmic beat which is produced due to contraction and relaxation of the heart muscles. GREEN Science (Biology) Book-10 311

11. The circulation of blood between the heart and various parts of body is called systemic circulation. It takes place with the help of arteries and veins. 12. The circulation of blood between heart and lungs is called pulmonary circulation. It occurs with the help of pulmonary artery and pulmonary veins. 13. The force exerted by blood which pushes the walls of arteries is called blood pressure. 14. The normal blood pressure of a healthy young person is 120/80 mm of Hg. Blood pressure is measured in millimetre height of mercury column. 15. The instrument which is used to measure the blood pressure is called sphygmomanometer. 16. Diabetes is commonly known as sugar disease. This disease is caused due to lack of insulin hormone secreted by pancreas. 17. The acid produced in the body as a byproduct due to decomposition of purine is called uric acid. 18. Joint ache, deep pain in muscles, difficulty in walking, swelling and burning of skin and swelling of joints of leg with pain are the major symptoms seen when the amount of uric acid increases in the blood. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. Haemoglobin is found in ........................... RBC WBC Platelets Plasma four b. Human heart consists of ................................ valves. brain one two three c. In human body, blood is purified in ............................ heart kidney lungs d. Which of the given diseases occurs due to lack of insulin? high blood pressure diabetes blood cancer anaemia e. The enormous increase in the number of WBC in blood causes ............................ uric acid diabetes high blood pressure blood cancer 312 GREEN Science (Biology) Book-10

2. Answer the following questions. a. What is blood circulatory system? b. Write down the major functions of blood circulatory system. c. Write down the composition of blood. d. Draw a neat and labelled figure of blood film. e. Write down the structure and function of • RBC • WBC • platelets f. What are anaemia and leukaemia? g. Write down the major functions of blood. h. Where is heart located in human body? i. What is pericardium? Write down the function of pericardial fluid. j. Draw a neat and labelled figure of human heart and describe its structure. k. Name the four valves present in human heart. l. What are blood vessels? Write down the major functions of arteries, veins and capillaries. m. What is blood pressure? Name the instrument used for measuring blood pressure. n. What does it mean by the fact that the blood pressure of a person is 130/90 mm of Hg? o. Write down the causes and preventive measures of high blood pressure. p. Write down the cause, symptoms and preventive measures of diabetes. q. What is uric acid? Write down the causes and measures for reducing uric acid in blood. 3. Differentiate between: a. WBC and platelets b. Auricles and ventricles c. Arteries and veins d. Systolic pressure and diastolic pressure e. Systemic and pulmonary circulation f. Diabetes and uric acid g. Pulmonary vein and Pulmonary artery 4. Give reason. a. The wall of ventricle is thicker than that of auricles. b. Leucocytes are called the soldiers of the body. c. The wall of left ventricle is thicker than that of right ventricle. GREEN Science (Biology) Book-10 313

d. Valves are present in veins but not in arteries. e. We should not consume spicy, oily and fatty foods regularly. 5. Draw a schematic diagram showing blood circulation in human body. 6. What type of food should be consumed by the person suffering from: a. high blood pressure? b. uric acid? c. diabetes? 7. Write down the advantages of blood circulation in human body. Grid-based Exercise 2 Group’A’(Knowledge Type Questions) (1 Mark Each) 1. What is blood circulatory system ? 2. What is the life span of red blood cells and platelets? 3. Write the name of blood vessels that carry pure blood to the left auricle and impure blood to the right auricle of the heart. 4. What is systemic circulation ? 5. Define systolic blood pressure. 6. What is haemoglobin ? Write down its function. 7. Where are aortic valve and pulmonic valve located? 8. What is pulmonary circulation ? 9. What is the blood pressure of a healthy young adult ? Write. 10. Write the name of device which is used for measuring blood pressure. 11. Write the name of four valves of human heart. 12. Write one function of left ventricle and right ventricle of human heart. 13. Define heart beat. 14. Which blood cells’ number is less than average in a person suffering from anaemia ? 15. Write the use of sphygmonamometer. 314 GREEN Science (Biology) Book-10

Group ‘B’ (Understanding Type Questions) (2 Marks Each) 16. Write any two differences between erythrocytes and leucocytes. 17. Right auricle is larger than the left auricle, why? 18. Write any two differences between auricle and ventricle. 19. The wall of the left ventricle is thicker than that of the right ventricle, why? 20. Write two differences between systemic circulation and pulmonary circulation. 21. Write any two differences between white blood cells and thrombocytes. 22. The wall of arteries is thicker than that of the veins, why? 23. A person suffering from anaemia feels tired in short walk, why? 24. The blood pressure of a healthy man is 120/80 mm Hg. What does it mean ? 25. Bleeding from artery is more dangerous than that from vein, why? Group ’C’ (Application Type Questions) (3 Marks Each) 26. Draw a neat diagram showing the structure of blood. 27. Write any three functions of blood. 28. Name the valves present in between auricles and ventricles of human heart. Also, write down their structure and function. A 29. A small portion of blood film is shown in the figure. Identify the parts B A, B and C in the figure with major function of each. C 30. State one function of each of the following : i. Fibrinogen ii. ire (Pulmonary vein iii. Capillaries Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each) 31. Describe the structure of human heart with a labelled diagram. A B 32. What is shown in the given diagram? Name the parts A, B, C and C D. Also, mention the function of each. D 33. What are veins ? Describe the structure of veins in brief. 34. The blood circulating in the body does three functions. Explain transportation and control functions of blood. 35. Write short notes on: i. Uric acid ii. Diabetes 36. Describe the process of blood circulation in human body with a schematic diagram. GREEN Science (Biology) Book-10 315

UNIT Chromosomes and 17 Sex Determination Weighting Distribution Theory : 5 Practical: 1 Before You Begin The bodies of plants and animals are made up of numerous cells. Each cell consists of various cell organelles including nucleus. Each nucleus consists of a network of fine threads called chromatinreticulum. During cell division, chromatin reticulum condenses and forms thread-like structures which are commonly known as chromosomes. The thread- like structure present in the nucleus of a cell are called chromosomes. The word chromosome has been derived from two Greek words chrome-colour and soma-body. It means that chromosomes are colourful bodies present in the nucleus. Each chromosome is made of two strands called chromatids and a centromere. The point where two chromatids are attached is called centromere. Chromosomes contain DNA and genes. Chromosomes transmit parental characteristics to the offspring with the help of genes. In this unit, we will study about chromosomes and determination of sex in human beings. Similarly, we will study in brief about chromosome disorders with examples. Learning Objectives Syllabus After completing the study of this unit, students will be able to: i. introduce chromosomes with their types. • Introduction to chromosomes ii. describe determination of sex in human beings. • Types of chromosomes iii. introduce chromosome disorder with examples. • Sex determination • Chromosome disorder • Turner’s syndrome • Down’s syndrome • Klinefelter’s syndrome Glossary: A dictionary of scientific/technical terms chromosomes : the thread-like structures found in the nucleus centromere : the point where two chromatids are attached together autosomes : the chromosomes that carry genes for vegetative characters chromatid : the strand of a chromosome syndrome : a group of signs and symptoms that occur together and characterize a particular abnormality or condition 316 GREEN Science (Biology) Book-10

Chromosomes The bodies of plants and animals are made of numerous cells. These cells act as the basic, structural and functional units of life. A cell can perform various metabolic activities. Nucleus is the most important cell organelle which controls all the activities of the cell. It also takes part in Fig. Fig.reproduction. A nucleus consists of nuclear membrane, nucleus, nucleoplasm and a set of thread-like structures made of DNA and proteins 17.1 which are commonly known as chromosomes. Chromosome Chromosomes are the thread-like structures present in the nucleus of a cell which contain hereditary information of the cell. Chromosomes are made up of a DNA (deoxyribonucleic acid) and proteins. Thus, the components of chromosomes are DNA and proteins. The most important component of a chromosome is, however, DNA, each chromosome consists of two strands (or threads) called chromatids. The two chromatids of a chromosome are joined together at a point called centromere. It is calso called kinetochore. Each species has a fixed number of chromosomes in each of its cells. For example, the human beings have 46 chromosomes in every body cell. The chromosomes of each species occur in pair. In a pair of chromosomes, one chromosome comes from the father and the other from the mother. Thus, human beings have 23 pair of homologous chromosomes in each body cell. The two chromosomes in a pair of homologous chromosomes are of the same size and shape. But the chromosomes of one homologous pair differ in size and shape from the chromosomes of another pair. Each chromosome of a homologous pair has genes for the same characteristics in the same place. Secondary constriction Pellicle Matrix Satellite Secondary constriction Spindle fibre Primary constriction 17.2 Centromere Structure of a chromosome Chromosomes become shorter, thicker and distinct during cell division. When the cell is in resting stage, it consists of chromosomes in the form of long, thin and coiled structures which is commonly known as chromatin reticulum or chromatin network. GREEN Science (Biology) Book-10 317

Types of chromosomes Do You Know Depending on the position of centromere, a There are two types of chromosomes chromosome may have either equal arms or on the basis of their function. They are unequal arms. So, on the basis of the position autosomes and sex chromosomes. of the centromere, there are four types of chromosomes. They are: Autosomes determine the physical characteristics of the body whereas sex i. Metacentric chromosomes chromosomes determine the sex of an organism. ii. Submetacentric chromosomes iii. Acrocentric chromosomes iv. Telocentric chromosomes Satellite Chromatid Short arm Centromere Stalk Centromere Long armFig. 17.3 Telocentric Acrocentric Submetacentric Metacentric i. Metacentric chromosome The chromosome in which the centromere is located near the middle point is called a metacentric chromosome. In this chromosome, two arms are almost equal in length. ii. Sub-metacentric chromosome The chromosome in which the centromere is located a little away from the middle point is called a submetacentric chromosome. In this chromosome, one of its arm is slightly short and other arm is slightly long. iii. Acrocentric chromosome The chromosome in which the centromere is located near the end is called acrocentric chromosome. In this chromosome, one of its arm is very short and the other arm is very long. iv. Telocentric chromosome: The chromosome in which the centromere is located at its tip is called a telocentric chromosome. 318 GREEN Science (Biology) Book-10

Chromosomes are responsible for transmitting hereditary characteristics from one generation to another. So, they act as the vehicles of heredity. Sex chromosomes determine the sex of an organism. They bring out variation and hence help in organic evolution. They control protein synthesis and cell metabolism. Diploid and Haploid Number of Chromosomes Each species has a fixed number of chromosomes in its cells. For example, human beings have 46 chromosomes in every body cell. The 46 chromosomes in an ordinary human cells are of 23 different kinds. So, there are two chromosomes of each kind. The two chromosomes of each kind are called homologous chromosomes. A cell which has the full number of chromosomes, with two of each kind, is called a diploid cell. It is denoted by ‘2n’. In other words, a diploid cell has two sets of each type of chromosomes. We can now say that the ordinary body cells of human beings have a diploid number of chromosomes. The diploid number of chromosomes is specific for a species. The ordinary body cells of human beings contain the full number of 46 chromosomes, so they are the diploid cells or they contain the diploid number of chromosomes. The gametes (or sex cells) of human beings are different from their body cells because they contain only half the number of chromosomes. A cell which has half the number of chromosomes, with one of each kind, is called a haploid cell. It is denoted by ‘n’. In other words, a haploid cell has only one set of each type of chromosomes. Gametes (or sex cells) have haploid number of chromosomes. The human gametes (or sex cells) called sperm and egg have only 23 chromosomes each, which is half the number of chromosomes in other body cells. So, a gamete is a haploid cell. We can also say that gametes contain haploid number of chromosomes. Gametes have half the usual number of chromosomes so that when male and female gametes fuse together to form a zygote then their chromosomes will add up and the zygote they form will have the normal number of chromosomes. For example, the human sperm has 23 chromosomes and the human egg (or ovum) also has 23 chromosomes. So, when a sperm and an egg fuse together during fertilization, then the zygote formed will have 23+23=46 chromosomes, which is the normal number of chromosomes. Thus, the gametes (or sex cells) are always haploid. But when two gametes (sperm and egg) fuse together, they form a diploid zygote. All other chromosomes in a cell (except the sex chromosomes) are called autosomes. Thus, autosomes are non-sex chromosomes. Autosomes are of the same number and kind in both, the male and female of a species. In human beings there are 22 pairs of autosomes and one pair of sex chromosomes. GREEN Science (Biology) Book-10 319

Number of chromosomes The number of chromosomes present in the cells of an organism is fixed. Generally, the somatic cells of an organism contain diploid chromosomes and sex-cells or gametes contain haploid chromosomes. Diploid cells contain half chromosomes from the father and remaining half-chromosomes from the mother. The number of chromosomes present in somatic cells and gametic cells, i.e. sex-cells is tabulated below: S.N. Living beings No. of chromosomes in No. of chromosomes in somatic cells (2n) sex-cells (n) 1. Human beings 2. Housefly 23 pairs 23 3. Gorilla 12 pairs 12 4. Frog 24 pairs 24 5. Potato (Solanum) 13 pairs 13 6. Yeast 24 pairs 12 7. Pine 1 pair 1 8. Onion 12 pairs 12 9. Pea 8 pairs 8 10. Sugarcane 7 pairs 7 40 pairs 40 Importance of chromosomes i. Chromosomes contain genes and hence carry heredity characteristics. ii They play an important role in cell division, cell growth and cell repair. Activity Take a chromosome and draw a picture of different types of chromosomes. Demonstrate the chart paper in your classroom. Sex Determination Chromosomes are made up of genes, i.e. tiny units of heredity. The genes present in chromosomes of the male and female gametes determine the sex of an organism. In human somatic cell, there are 23 pairs of chromosomes. Out of 23 pairs, 22 pairs are called autosomes and 1 pair is called sex chromosomes. Autosomes control vegetative characteristics whereas sex-chromosomes determine the sex of an individual. A person can have a male sex or female sex. The process by which the sex of a person is determined is called sex determination. Genetics is involved in the determination of the sex of a person. This can be explained as follows: 320 GREEN Science (Biology) Book-10

Mother Father XX XY X Eggs X X Sperm Y XX XY XX XY Fig. Fig.17.4 Girl Boy Girl Boy Sex determination in human being The chromosomes which determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes, one is called X chromosome and other is called Y chromosome. i. A male gamete (sperm) of human being has one X chromosome and one Y chromosome. This means that half the male gametes or half the sperms will have X chromosome and the other half will have Y chromosome . ii. A female gamete (egg) of human being has two X chromosomes (but no Y chromosomes).This means that all the female gametes called ova (or eggs) will have only X chromosomes. The sex of a child depends on what happens at fertilization: (a)If a sperm carrying X chromosome fertilizes an ovum (or egg) which carries X chromosome, then the child born will be a girl (or female). This is because the child will have XX combination of sex chromosomes. iii. If a sperm carrying Y chromosome fertilizes an ovum (or egg) which carries X chromosome, then the child born will be a boy (male). This is because the child will have XY combination of sex chromosomes. 17.5 GREEN Science (Biology) Book-10 321

Please note that it is the sperm which determines the sex of the child. This is because half of the sperms have X chromosomes and the other half have Y chromosomes. Thus, there is a 50 percent chance of a boy and a 50 percent chance of a girl being born to the parents. This is why the human population is roughly half males and half females. In some of the animals, sex determination is also controlled by the environmental factors. For example, in some reptiles, the temperature at which the fertilized egg is incubated before hatching, plays a role in determining the sex of the offspring. It has been found that in a turtle (Chrysema picta), high incubation temperature leads to the development of female offspring (or female progeny). On the other hand, in the case of a lizard (Agama agama), high incubation temperature results in male offspring (or male progency). Chromosomal disorder Do You Know Genes, i.e. tiny units of heredity are located in Haemophilia is a sex-linked genetic chromosomes. They control the development disorder which leads continuous bleeding of various characteristics in the body. There is a through cut or wound. It transmits from fixed sequence of genes in a chromosome to parents to their offspring and is seen only develop a certain characteristic. When the in males. Females can transmit this disease sequence of genes or the number of but do not suffer. So, haemophilia is a sex- chromosomes in a body changes, a variety of linked disease. disorders are seen in the human body. These disorders are called chromosomal disorders. Do You Know Turner’s syndrome, Klinefelter's syndrome, Down’s syndrome, etc. are some examples of The diseases which occur only in males or chromosomal disorder. females are called sex-linked diseases. Examples: Chromosomal disorder can be defined as the 1. Haemophilia disorder caused in human body due to decrease 2. Male pattern baldness or increase in the number of chromosomes. 3. Uterine cancer Chromosomal disorder occurs when the 4. Colour blindness number of chromosomes changes during cell division. The number of chromosomes in cells may be more or less when centrosomes do not divide properly. This process is called aneuploidy. In this unit, we will discuss about chromosomal disorders like Turner’s syndrome, Down’s syndrome and Klinefelter’s syndrome. Turner’s syndrome (45 + XO) Do You Know Turner’s syndrome was described by Dr. Henry Girls and women suffer from Turner’s Turner. It occurs due to lack of X-chromosome. syndrome. In this condition, the number of chromosome becomes 45 + XO. The symptoms of this disorder are as follows: 1. Shorter body structure 322 GREEN Science (Biology) Book-10

2. Lack of secondary sexual characteristics 3. Poorly developed ovaries 4. Lack of menstrual periods Fig. Fig. 5. Sterility in females 6. Short neck 17.6 Turner’s syndrome Down’s syndrome (47, XY, + 21) or (47, XX, +21) Down’s syndrome is the chromosomal Do You Know disorder that occurs due to addition of extra chromosome in the 21 chromosome. It is also Down’s syndrome was first described called trisomy of chromosome 21. by John Langdon Down. The major symptoms of Down’s syndrome are It occurs in one in every 1000 live given below: births. 1. Flat face and small broad nose 2. Protruding tongue 3. Thick palm with creases 4. Lack of physical, mental and psychological development 5. Furrow in tongue 17.7 6. Dwarfism or short stature Down's syndrome 7. Small and round head 8. Half-opened mouth Do You Know 9. Upward slanting eyes Klinefelter’s syndrome (47, XXY) The person's having Down's syndrome are at increased risk of heart diseases, Klinefelter’s syndrome is the chromosomal leukaemia, respiratory infection, etc. disorder occurs due to addition of sex chromosome (X – chromosome). In this condition, the number of Tall stature Frontal baldness chromosome becomes 47, Slightly feminized absent XXY karyotype. This disorder physique Poor beard commonly occurs in males. In Mildly impaired growth 1942, Dr. Harry Klinefelter and IQ (15 points less his co-workers described this than average) Breast syndrome. Tendency to lose development (in chest hairs 30% of cases) The major symptoms of Osteoporosis Klinefelter’s syndrome are as Female-typeFig. Small testes follows: pubic hair pattern Klinefelter’s syndrome 1. Growth of breasts in males 17.8 2. Infertility or sterility in males GREEN Science (Biology) Book-10 323

3. Tall stature 4. Small genitals 5. Female type pubic hair pattern 6. Poor beard growth 7. Mildly impaired IQ 8. Wider hips, etc. Key Concepts 1. Chromosomes are the thread-like structures present in the nucleus of a cell which contain hereditary information of the cell. 2. The chromosomes of each species occur in pair. In a pair of chromosomes, one chromosome comes from the father and another comes from the mother. 3. Each chromosome of a homologous pair has genes for the same characteristics in the same place. 4. The chromosome in which the centromere is located near the middle point is called a metacentric chromosome. 5. The chromosome in which the centromere is located a little away from the middle point is called a submetacentric chromosome. 6. The chromosome in which the centromere is located near the end is called acrocentric chromosomes. 7. The chromosome in which the centromere is located at its tip is called a telocentric chromosomes. 8. A cell which has the full number of chromosomes, with two of each kind, is called a diploid cell (2n). 9. A cell which has half the number of chromosomes, with one of each kind, is called a haploid cell (n). 10. Gametes have half the usual number of chromosomes so that when male and female gametes fuse together to form a zygote then their chromosomes will add up and the zygote they form will have the normal number of chromosomes. 11. All other chromosomes in a cell (except the sex chromosomes) are called autosomes. Thus, autosomes are non-sex chromosomes. Autosomes are of the same number and kind in both, the male and female of a species. 12. The process by which the sex of a person is determined is called sex determination. 13. The sex of a child depends on what happens at fertilization: (a)If a sperm carrying X chromosome fertilizes an ovum (or egg) which carries X chromosome, then the child born will be a girl (or female). 14. If a sperm carrying Y chromosome fertilizes an ovum (or egg) which carries X chromosome, then the child born will be a boy (male). 15. There is a 50 percent chance of a boy and a 50 percent chance of a girl being born to the parents. This is why the human population is roughly half males and half females. 324 GREEN Science (Biology) Book-10

16. Haemophilia is a chromosome disorder which leads continuous bleeding through cut or wound. It transmits from parents to their offspring and is seen only in males. 17. Chromosome disorder can be defined as the disorder caused in human body due to decrease or increase in the number of chromosomes. 18. Klinefelter’s syndrome occurs due to addition of sex chromosome (X – chromosome). In this condition, the number of chromosome becomes 47, XXY karyotype. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. ................... are the tiny units of heredity. cell chromosomes genes chromatids b. The strand of a chromosome is called ......................... centromere chromatid nucleus gene c. There are ..................... types of chromosomes on the basis of position of centromere. 1 2 3 4 d. The number of chromosomes in the somatic cells of human beings is ................... 23 46 40 12 e. The chromosome disorder that occurs due to addition of X-chromosome is called ................... Down’s syndrome Turner’s syndrome Haemophilia Klinefelter’s syndrome 2. Answer the following questions. a. What is chromosome? b. What are the components of a chromosome? c. Describe the different types of chromosomes. d. Define the following with the help of diagram i. Metacentric chromosomes ii. Submetacentric chromosomes iii. Acrocentric chromosomes iv. Telocentric chromosomes GREEN Science (Biology) Book-10 325

e. Write any three functions of chromosomes. f. Define chromosome disorder with one example. g. What are sex-linked diseases? Give any three examples. 3. What do you understand by the following? a. Diploid chromosomes b. Haploid chromosomes 4. What are sex chromosomes? 5. What are autosomes? 6. How is the sex of an individual determined? Explain with a chart. 7. Differentiate between: a. Haploid cell and diploid cell b. Autosomes and sex-chromosomes c. Metacentric chromosome and telocentric chromosome d. Down’s syndrome and Klinefelter’s syndrome 8. What is Turner’s syndrome? Write its symptoms. 9. What is Down’s syndrome? Write its symptoms. 10. What is Klinefelter’s syndrome? Write its symptoms. 11. What is meant by chromosome disorder? Explain with examples. Grid-based Exercise 2 Group ’A’ (Knowledge Type Questions) (1 Mark Each) 1. What is a chromosome? 2. What is chromosome made of? 3. What is chromatic reticulum? 4. What is kinetochore? 5. Define sub-metacentric chromosome. 6. Write down the number of chromosomes found in somatic cell and gametic cell of given organisms. (Ans: (i) 46,23 (ii) 26,13) i. Human ii. Frog 7. Where is chromosome found? 8. What is gene? 9. What is telocentric chromosome? 326 GREEN Science (Biology) Book-10

10. Write down the number of chromosomes found in somatic cell and gametic cell of given organisms. (Ans: (i) 24,12 (ii) 2,1) i. Pine ii. Yeast 11. What is sex determination? 12. Write any two characteristics of haemophilia. 13. Write any two characteristics of chromosome. 14. Write down the main cause of Down’s syndrome. 15. What is Turner’s syndrome? Group’B’(Understanding Type Questions) (2 Marks Each) 16. What is meant by chromosomal disorder? Write with one example. 17. Differentiate between metacentric chromosome and sub-metacentric chromosome. 18. What is sex-linked disease? Write one example. 19. Differentiate between autosome and sex chromosome. 20. What is meant by aneuploidy? Write with example. 21. What do you mean by somatic cell and gametic cell? 22. Why is haemophilia called a sex-linked disease? 23. How many chromosomes are there in human sperm and zygote? Why ? 24. How many chromosomes are there in ovum and zygote and why ? 25. Differentiate between diploid and haploid chromosome. Group ‘C’ (Application Type Questions) (3 Marks Each) 26. What is Down’s syndrome ? Write its two symptoms. 27. Define sex-linked disease with an example. Draw a figure showing metacentric chromosome. 28. How does chromosome disorder occur ? Write with an example. 29. Name the types of chromosomes on the basis of position of centromere. Draw figure of any one type of chromosome. 30. What is sex determination ? Write down the function of autosome and sex chromosome. Group ’D’ (Higher Abilities Type Questions) (4 Marks Each) 31. Describe the structure of chromosome with a labelled figure. 32. How is sex determined ? Explain with figure. 33. Write short note on: i. Turner’s syndrome ii. Klinefelter’s syndrome 34. How is sex of a boy and girl determined ? Describe. i. Explain the role of chromosomes for living beings. ii. Write a short note on chromosome disorder. GREEN Science (Biology) Book-10 327

UNIT Asexual and Sexual 18 Reproduction Weighting Distribution Theory : 10 Practical: 2 Before You Begin Reproduction is the basic characteristic of living beings. All plants and animal produce offspring similar to them. Reproduction is the process of creation of new organisms by asexual or sexual method. Living beings reproduce to continue their races on the earth. Primitive plants and animals reproduce by asexual method whereas advanced animals and plants reproduce by sexual method. The reproduction which takes place without the fusion of a male gamete and a female gamete is called reproduction. It is common in primitive plants and animals. The reproduction which takes place by the fusion of a male gamete and a female gamete is called sexual reproduction. It is common in higher plants and animals. In this unit, we will study asexual and sexual reproduction that occurs in plants and animals. Learning Objectives Syllabus After completing the study of this unit, students will be able to: • Introduction to reproduction i. explain asexual and sexual reproduction that occurs • Asexual reproduction and its in plants and animals with examples. characteristics ii. explain artificial vegetative propagation in animals • Sexual reproduction and its with examples. characteristics iii. describe the significance of asexual and sexual • Artificial vegetative propaga- reproduction. tion in plants Glossary: A dictionary of scientific/technical terms reproduction : the biological process by which plants and animals produce their offspring asexual : without involvement of gametes sexual : by the involvement of gametes fission : the process in which a unicellular organism splits into two or more gamete daughter organisms zygote : the male or female sex cell : the cell formed by the fusion of a male gamete and a female gamete 328 GREEN Science (Biology) Book-10

A. Reproduction Reproduction is the basic characteristic of living beings, i.e. plants and animals. Living organisms on the earth have a certain life span. They cannot survive forever and die after a certain period of time. Therefore, living beings reproduce Fig. their own kinds to continue their races on the earth. This process is called reproduction. So, reproduction is a 18.1 biological process in which living beings Tiger with cubs produce their own kinds asexually or sexually. Some living beings reproduce from their single body. Some animals and plants reproduce with the help of gametes. Different animals and plants reproduce by different methods. Types of Reproduction 2. Sexual reproduction 1. Asexual reproduction 1. Asexual reproduction The reproduction which takes place without the fusion of a male gamete and a female gamete is called asexual reproduction. This process is common in primitive plants and animals. In asexual reproduction, only one organism can reproduce and the offspring produced are exactly identical to their parent. It is an easy and fast method of reproduction. Examples: budding in yeast, budding in hydra, fission in amoeba, sporulation in mucor, vegetative propagation in potato, etc. Characteristics of asexual reproduction 1. Only one organism can reproduce by this method. 2. In this type of reproduction, gametes are not produced. 3. Fertilization does not occur in this reproduction. 4. All offspring produced by this method are exactly identical to their parent. 5. It is a fast and easy method of reproduction. 6. Mitosis takes place in this reproduction. Types of Asexual reproduction i. Fission ii. Budding iii. Sporulation vi. Vegetative propagation iv. Fragmentation v. Regeneration i. Fission It is the most common method of reproduction in unicellular organisms. A fission is the method of asexual reproduction in which a unicellular organism divides into two or GREEN Science (Biology) Book-10 329

more daughter organisms. This method is common in amoeba, paramecium, bacteria, plasmodium, euglena, etc. A fission is of two types, viz. binary fission and multiple fission. Binary fission Daughter amoeba Mother amoeba The method of asexual reproduction in which one unicellular organism divides into two daughter organisms is called a binary fission. Plants like bacteria, chlamydomonas, diatoms, etc. and animals like amoeba, paramecium, euglena , etc. reproduce by this method. Fig. Fig.18.2 Fig.Multiple fission Binary fission on amoeba The method of asexual reproduction in which one unicellular organism divides into more than two daughter organisms is called a multiple fission. It is common in plasmodium, chlamydomonas, amoeba, etc. It generally occurs during unfavourable condition. Cytoplasm Nucleus Many daughter cells produced Daughter cells by multiple fission Cell Cyst Cyst breaks 18.3 Multiple fission in plasmodium During unfavourable condition, unicellular organisms like amoeba, plasmodium, etc. from a thick cover called cyst in the outer surface of the body. Inside the cyst, nucleus divides repeatedly and forms numerous daughter nuclei. When conditions are suitable, the cyst breaks and each nucleus is surrounded by cell-membrane and cytoplasm forming numerous daughter organisms. ii. Budding 18.4 The method of asexual reproduction which Budding in yeast takes place with the help of a bud is called budding. Plants like yeast and animals like hydra reproduce asexually by this method. In this method, a small bud develops in the body which separates as a new organism after its growth. Activity 1 Take a test tube and add 20 ml water and dissolve 5 gram of sugar into it. Add some yeasts into the test tube and keep it in a warm place for a few hours. Observe the test tube carefully. What did you observe? 330 GREEN Science (Biology) Book-10

iii. Sporulation The method of asexual reproduction which takes place by means of spores is called sporulation. This method is common in mucor, marchantia, moss, mushroom, fern, etc. In sporulation, spores are formed inside sporangia. At maturity, sporangia burst and release spores on soil. These spores germinate and form new plants on favourable condition. Sporangium Female gametophyte Gemma cup Stolon Fig. Fig. Thallus RhizoidFig. Rhizoids 18.5 Sporulation in mucor Sporulation in liverwort iv. Fragmentation 18.6 Nucleus A fragmentation is the method of asexual Spiral reproduction in which a multicellular organism chloroplast splits into two or more fragments and each fragment develops into a new organism. Fragmentation in spirogyra Spirogyra reproduces by this method. In fragmentation a multicellular organism splits into two or more fragments and each fragment regains its lost body parts and develops into a complete organism. v. Regeneration 18.7 A regeneration is the method of asexual Regeneration in Planaria reproduction in which each fragment of an organism regains its lost body parts and develops into a complete organism. This method is common in planaria, hydra, tapeworm, starfish, sponge, etc. vi. Vegetative propagation A vegetative propagation is the method of asexual reproduction in which new plants are produced by vegetative parts like roots, stem and leaf. This process occurs in some flowering plants which do not produce viable seeds. Flowering plants like sweet potato, dahlia, mint, etc. reproduce asexually by means of roots. GREEN Science (Biology) Book-10 331

Fig. Fig.18.8 Roots of sweet potato Roots of dahlia Flowering plants like potato, onion, rose, sugarcane, garlic, bamboo, banana, ginger, colocasia, etc. reproduce asexually by stem. 18.9 Buds in ginger Buds in potato Activity 2 Take a matured potato and observe its surface. You will see small scars called eyes. Cut the potato into 3-4 pieces keeping 2-3 eyes in each piece. Plant those pieces in moist soil. Observe those pieces after 8-10 days. What do you observe? Flowering plants like Bryophyllum, Begonia, etc. reproduce asexually by leaf. Fig. 18.9 Reproduction in Begonia by leaf Reproduction in Bryophyllum by leaf 332 GREEN Science (Biology) Book-10

Activity 3 Take a matured Bryophyllum plant and observe the plantlets developed on its leaf. Draw neat and labelled figure. Advantages of asexual reproduction or vegetative propagation 1. It is an easy and fast method of reproduction. 2. Only one organism can reproduce by this method. 3. The offspring produced by this method are genetically identical to their parents. 4. Some flowering plants like potato, rose, sugarcane, banana, bamboo, etc. do not produce viable seeds. These plants can easily be propagated by this method. 5. The flowering plants produced by this method start bearing flowers and fruits earlier than those reproduced from their seeds. 6. Farmers can produce a large number of flower and fruit trees by this method. 7. The species of rare and endangered plants can be reproduced by this method. 2. Sexual Reproduction The method of reproduction which takes place by the fusion of a male gamete and a female gamete is called sexual reproduction. Both male and female organisms are involved in sexual reproduction. Flowering plants and developed animals reproduce by sexual reproduction. Some animals produce only one types of gametes (either male or female). These animals are called unisexual animals. Examples: human beings, birds, reptiles, amphibians, fishes, etc. Some animals produce both male and female gametes in the same body. These animals are called bisexual or hermaphrodite animals. Examples: hydra, tapeworm, liverfluke, earthworm, etc. Similarly, flowering plants also have unisexual and bisexual flowers. Pumpkin, cucumber, papaya, gourd, etc. produce unisexual flowers whereas mustard, pea, tomato, orange, etc. produce bisexual flowers. Sexual Reproduction in Plants Petal Most flowering plants Stigma Anther reproduce sexually by Style Filament means of seeds. A flower is the colourful, attractive and sexually reproductive part of flowering plants. A bisexual flower consists of four whorls. They are: calyx, corolla, androecium and gynoecium. Fig. Sepal Ovary Receptacle 18.11 Bisexual flower GREEN Science (Biology) Book-10 333

A brief description of each whorl of a flower is given below: i. Calyx It is the outermost whorl of a flower. It consists of green leaf like structures called sepals. Calyx protects a flower in the bud stage and helps in photosynthesis. ii. Corolla It forms the second whorl of a flower. It consists of colourful and attractive structures called petals. Petals protect the reproductive organs of a flower and attract insects for pollination. iii. Androecium It forms the third inner whorl Anther of a flower. It consists of a group of male reproductive organs called stamens. Each stamen consists of a filament, connective and a Fig. Filament Fig. anther. Each anther consists 18.12 of four pollen sacs where A typical androecium microspore mother cells are present. Each microspore mother cell undergoes meiosis cell division and forms four haploid pollen grains. Each pollen grain contains male gametes. Anthers produce pollen grains at maturity. Pollen grains are fine powdery structures having male gametes. iv. Gynoecium It forms the fourth innermost whorl of a flower. It consists of one or more female reproductive organs called carpels or pistils. Each carpel or pistil consists of three distinct parts. They are stigma, style and ovary. Stigma Stigma Style Style Ovary Ovary 18.13 Gynoecium of mustard Typical carpel (gynoecium) The uppermost spreading part of a pistil is called a stigma, the middle cylindrical part is called a style and the lowermost swollen part is called a ovary. At maturity, an ovary produces ovules containing female gametes or egg cells. 334 GREEN Science (Biology) Book-10

Pollination The transfer of pollen grains from anther to the stigma of the same flower or different flower is called pollination. Various external agents like air, water, insects, birds, animals, etc. help in pollination. Cross-pollination Self-pollination Fig.18.14 Fig. Pollination Pollination is of two types, viz. self-pollination and cross-pollination. i. Self-pollination It is the transfer of pollen grains from the anther to the stigma of the same flower. This process is common in bisexual flowers like pea, chinarose, tomato, wheat, cotton, etc. ii. Cross-pollination It is the transfer of pollen grains from the anther of a flower of one plant to the stigma of a flower of another plant of the same species. This process is common in unisexual flowers like pumpkin, cucumber, gourd, maize, coconut, oak, etc. and bisexual flowers. In flowering plants, pollination is followed by fertilization. Fertilization Pollination Pollen The process of fusion of a male gamete and a female gamete Stigma Anther to form a zygote is called fertilization. After pollination, Filament pollen grains germinate and form pollen tubes which Style grow towards ovary through Pollen tube style and finally reaches the ovule in the ovary through Ovule micropyle. After entering into Embryo sac Polar nuclei ovule, the pollen tube enters Synergids Sperm cells into the embryo sac. In the Petal embryo sac three antipodal Sepal cells, two synergids, a female 18.15 gamete or egg cell and a Fertilization in flowering plants GREEN Science (Biology) Book-10 335

diploid secondary nucleus are found. When Do You Know the pollen tube enters embryo sac, the apex of the tube dissolves and two male gametes are The fertilization in flowering plants is released. One of the male gamete fuses with called double fertilization because the the female gamete and forms a diploid zygote. fertilization involves the fusion of two This process is called fertilization. The second male gametes separately, i.e. one male male gamete (n) fuses with secondary nucleus gamete with the egg cell and another (2n) and forms endosperm nucleus (3n). This male gamete with the secondary nucleus. process is called triple fusion. Later on the zygote develops into embryo and endosperm nucleus develops into endosperm of the seed. After fertilization, ovule develops into seeds and ovary develops into fruit. In this way, flowering plants reproduce sexually. Activity 4 Collect different types of flowers from the school garden. Identify calyx, corolla, androecium and gynoecium in these flowers. Also, separate unisexual and bisexual flowers. Draw a neat figure showing each whorl of the flower and label the main parts. Differences between self-pollination and cross-pollination Self-pollination Cross-pollination 1. In this method, pollen grains transfer 1. In this method, pollen grains transfer from anther to the stigma of the same from anther of one plant to the stigma flower. of another plant of the same species. 2. It occurs in the same plant. 2. It occurs in between the plants of the same species. 3. It occurs in bisexual flowers. 3. It occurs in both unisexual as well as bisexual flowers. 4. Agents of pollination are not essential. 4. Agents of pollination are essential. Sexual Reproduction in Animals Do You Know Vertebrate animals reproduce sexually by The fusion of a male gamete and a means of gametes. However, invertebrates female gamete to form a zygote is like arthropods, molluscs, annelids, round called fertilization. It is of two types, worms, flatworms, etc. reproduce by sexual viz. external fertilization and internal method. Male organisms produce male fertilization. gametes and female organisms produce female gametes. On favourable condition, The process by which gamete are fusion of a male gamete and female gamete formed is called gametogenesis. takes place to form a zygote. This process 336 GREEN Science (Biology) Book-10

is called fertilization. In animals, fertilization is of two types, i.e. external fertilization and internal fertilization. If the fusion of a male gamete and a female gamete takes place outside the body of a female organism, it is called external fertilization. It occurs in fishes and frogs. If the fusion of a male gamete and female gamete takes place inside the body of a female organism, it is called internal fertilization. It occurs in insects, reptiles, birds and mammals. After formation of a zygote, it divides repeatedly and forms embryo which finally develops into a new organism. In this way, animals reproduce by sexual method. Difference between Asexual reproduction and Sexual reproduction Asexual reproduction Sexual reproduction 1. Gametes are not involved. 1. Gametes are involved. 2. It occurs in lower organisms. 2. It occurs in higher organisms. 3. A single organism can reproduce by 3. A single organism cannot reproduce this method. by this method. 4. It does not help in evolution of 4. It helps in evolution of organisms. organisms. 5. All offspring are identical to their 5. All offspring are not exactly identical parents. to their parents. Differences between external fertilization and internal fertilization External fertilization Internal fertilization 1. Fusion of a male gamete and a female 1. Fusion of a male gamete and a female gamete takes place outside the body gamete takes place inside the body of of a female. a female. 2. This method is common in fishes and 2. This method is common in insects, amphibians. reptiles, birds and mammals. Advantages of Sexual Reproduction 1. It gives continuity to the generations of a species. 2. It brings out variation among the members of the same species. 3. It helps in evolution of organisms. Difference between gamete and zygote Gamete (male/female) Zygote 1. Gamete is a haploid sex cell. 1. Zygote is a diploid sex cell. 2. It is produced by male or female sex 2. It is produced by the fusion of a male organ. sex cell with a female sex cell. GREEN Science (Biology) Book-10 337

B. Artificial Vegetative Propagation in Plants Most flowering plants reproduce sexually through seeds. However, some flowering plants like apple, pear, rose, potato, plum, etc. do not produce viable seeds. Such type of plants can be propagated artificially by using their vegetative parts (root, stem or leaves). This process is called artificial vegetative propagation. Now-a-days, farmers, gardeners, horticulturists and botanists produce a large number of plantlets artificially by vegetative propagation. This method of propagation of plants is mainly applied in fruits, vegetables and flowers. Some of the common artificial methods of vegetative propagation are as follows: 1. Layering 2. Grafting 3. Tissue culture 1. Layering Layering is the artificial vegetative propagation in which new plants are obtained in the stem of parent plants. Different types of fruit plants like strawberry, raspberry, lemon, citrus, apple, pear, etc. are propagated by this method. Types of Layering i. Simple layering Parent plant Vigorous shoot Simple layering is applied in lemon, citrus, etc. to propagate new plants. In simple layering, a long and flexible stem more than one year age Stem is bent down and the stem is buried Fig. Fig. in the soil about 20cm away from its tip. After 2-3 months, the buried portion develops roots. Then the 18.16 plant is separated from the parent Simple layering plant. Generally, new plants are separated from the parent plant at the end of rainy season and planted in a new place. ii. Compound layering Parent plant New plant Soil cover Roots This type of layering is commonly applied in walnut, apple, pear, etc. 18.17 to propagate new plants. In this method, the entire flexible stem is Compound layering burried in the soil leaving its tip outside the soil. The nodes in the stem produce new plantlets within 2-3 months when watered regularly. Then the plantlets are separated from the parent plant. 338 GREEN Science (Biology) Book-10

iii. Air layering Flowering plants like lemon, orange, peach, plum, etc. are propagated artificially by air layering. In air layering, the bark of the stem of about 2 year age is removed in the shape of a ring. Then the portion of Fig. Fig. the stem is covered with moist soil and cloth. We can give IBA hormone to enhance the growth of roots in the 18.18 stem. The portion of the stem can Air layering also be covered with moss and plastic to make it airproof. The covered portion develops roots within 1-2 months. Then the plantlets can be separated from the parent plant. iv. Tip layering Plants like raspberry, blackberry, etc. are propagated artificially by tip layering. The tip of the plant is bent and burried in the soil to grow roots. The tip develops roots within 3-4 months. Then the plant is separated from the parent plant and cultivated. 18.19 Tip layering v. Stool layering or mound layering Flowering plants like mango, guava, apple, peach, plum, etc. are propagated artificially by stool layering. In this method, the selected plant is cut at the height of 5-10cm from the ground. Then the plant produces many branches. When these branches grow to a certain height (20-25cm), stem is covered with soil or saw dust upto height of 10-15cm and watered regularly. These branches develop roots within 3-4 months. Then these plants can be separated from the parent plant. Fig. 18.20 Mound layering Stool layering GREEN Science (Biology) Book-10 339

2. Grafting Grafting is the method of artificial vegetative propagation in which shoot system of one plant is combined with root system of another plant. Most of the fruit plants like peach, apple, mango, plum, guava, lemon, orange, etc. are propagated by this method. The plant whose root system is used is called stock. Similarly, the plant whose shoot system is used is called scion. Generally, scion of plant of superior quality is grafted on the stock of closely related plant. Types of grafting i. Whip grafting In this method, the scion and stock of closely related plants are cut obliquely. The length of the cut portion should be 3-5cm. Then both stock and scion are combined together and sealed with a tape. After 3-4 months, both stems combine together. This method should be done before spring season. Whip grafting is a simple and very common method of grafting which is generally done in commercial fruit trees. Fig. Fig. 18.21 Whip grafting ii. Cleft grafting Cleft grafting is the most common method of grafting. In this method, the stock is cut and split down the middle making a cleft about 5-8 cm deep. The end of scion should be cut slanted in the shape of wedge and inserted into the cleft. The portion is sealed with a tape making air tight. If the stock and scion are not disturbed, they combine within 2-3 months. Cleft grafting is generally done in spring season. 18.22 Cleft grafting 340 GREEN Science (Biology) Book-10

iii. Tongue grafting Fig. Tongue grafting is the popular method of grafting in 18.23 hilly and Himalayan region. In this method, a tongue like deep structure (about 3 to 5 cm) is cut into scion and stock. Then they are joined together. The joint is sealed with a tape or a plastic until they combine firmly. If remain undistributed and air tight, both scion and stock combine within 2-3 months. Tongue grafting Activity 5 Visit the school garden with your science teacher. Select some suitable plants and apply layering and grafting in some plants. Observe these plants after 2 months. What do you find? 3. Tissue culture The scientific method of propagation of new plants from cell, tissue or organ of a parent plant keeping them in a culture solution is called tissue culture. The plants with exactly identical characteristics to the parent can be produced by tissue culture. Now-a-days, tissue culture is very common among botanists because of the following reasons: 1. Exactly identical plants to the parents can be produced by this method. 2. A large number of new plants can be produced within a short time. 3. The plants which do not produce viable seeds can be propagated by this method. 4. Disease free plants can be produced. 5. Hybrid plants of desired quality can be produced. 6. Endangered plants can be protected. Method of tissue culture In laboratory, an artificial medium is prepared for tissue culture. The artificial medium is called culture solution. The culture solution consists of nutrients and plant hormones. In this method, a small lump is tissue is taken and kept in the culture solution under sterile conditions. This lump is called callus. When the callus gets nutrients and hormones (auxin and cytokinin), it grows and develops roots and shoot. Please note that auxin enhances the growth of roots and cytokinin enhances the growth of the shoot. When the callus develops roots and shoot, it is cut into several tiny plantlets. The plantlets with root and shoot are planted into soil. In this way, new plantlets are propagated by tissue culture. GREEN Science (Biology) Book-10 341

Tissue sample scraped Tissue samples placed in Agar from parent plant growth medium containing nutrients and auxins Samples develop into tiny plantlets Fig. 18.24 Plantlets planted into compost Tissue culture Key Concepts 1. Reproduction is a biological process in which living beings produce their own kinds asexually or sexually. 2. The reproduction which takes place without the fusion of a male gamete and a female gamete is called asexual reproduction. 3. A fission is the method of asexual reproduction in which a unicellular organism divides into two or more daughter organisms. 4. The method of asexual reproduction in which one unicellular organism divides into more than two daughter organisms is called a multiple fission. 5. The method of asexual reproduction which takes place with the help of a bud is called budding. 6. The method of asexual reproduction which takes place by means of spores is called sporulation. 7. A fragmentation is the method of asexual reproduction in which a multicellular organism splits into two or more fragments and each fragment develops into a new organism. 8. A regeneration is the method of asexual reproduction in which each fragment of an organism regains its lost body parts and develops into a complete organism. 9. A vegetative propagation is the method of asexual reproduction in which new plants are produced by vegetative parts like roots, stem and leaf. This process occurs in some flowering plants which do not produce viable seeds. 10. The method of reproduction which takes place by the fusion of a male gamete and a female gamete is called sexual reproduction. 11. A bisexual flower consists of four whorls. They are: calyx, corolla, androecium and gynoecium. 12. The transfer of pollen grains from anther to the stigma of the same flower or different flower is called pollination. 13. Pollination is of two types, viz. self-pollination and cross-pollination. 342 GREEN Science (Biology) Book-10

14. The process of fusion of a male gamete and a female gamete to form a zygote is called fertilization. 15. The fusion of a male gamete and a female gamete to form a zygote is called fertilization. 16. The process by which gametes are formed is called gametogenesis. 17. Layering is the artificial vegetative propagation in which new plants are obtained in the stem of parent plants. 18. Grafting is the method of artificial vegetative propagation in which shoot system of one plant is combined with root system of another plant. 19. The plant whose root system is used is called stock. Similarly, the plant whose shoot system is used is called scion. 20. Whip grafting is a simple and very common method of grafting which is generally done in commercial fruit trees. 21. Tongue grafting is the popular method of grafting in hilly and Himalayan region. 22. The scientific method of propagation of new plants from cell, tissue or organ of a parent plant keeping them in a culture solution is called tissue culture. Sequential General Exercise 1 1. Choose the best answer from the given alternatives. a. Which of the given asexual methods is common in amoeba? fission budding sporulation fragmentation b. Planaria reproduces asexually by ........... regeneration fragmentation sporulation vegetative propagation c. Which of the given part of a flower produces female gametes? sepal stamen petal pistil d. Which of the given organisms cannot reproduce by asexual method? hydra rose cow starfish e. Which method of artificial vegetative propagation requires culture solution? air layering whip grafting tissue culture tip layering GREEN Science (Biology) Book-10 343

2. Answer the following questions. a. Define reproduction. b. What is asexual reproduction? Name any five organisms that reproduce asexually. c. Define: - fission - budding - sporulation - fragmentation - regeneration d. Write down the advantages of asexual reproduction. e. What is vegetative propagation? Write its types. f. Define sexual reproduction. g. What is meant by a complete flower? Explain with a neat figure. h. Define pollination and write its types. i. What is fertilization? How is zygote formed? Describe. j. What is artificial vegetative propagation? k. Define layering and write its types. l. What is grafting? How is grafting done. m. Define tissue culture and write its advantages. 3. Differentiate between: a. Asexual and sexual reproduction b. Budding and sporulation c. Self-pollination and cross-pollination d. Layering and grafting e. External and internal fertilization f. Ovum and sperm g. Simple layering and compound layering h. Stock and scion 4. How does amoeba reproduce by fission? Describe. 5. Draw a neat and labelled figure showing: a. Budding in hydra b. Complete flower c. Cross-pollination d. Whip grafting 6. How is simple layering done? Explain with figure. 7. What is cleft grafting? Explain with figure. 8. Artificial vegetative propagation is beneficial for farmers. Justify this statement. 9. Write down the technique of tissue culture in brief. 10. The existence of variety of plants and animals would be impossible in the absence of sexual reproduction. Justify this statement. 11. Out of layering, grafting and tissue culture, which method of artificial propagation is suitable in the context of Nepal? Why? 344 GREEN Science (Biology) Book-10

Grid-based Exercise 2 Group ‘A’ (Knowledge Type Questions) (1 Mark Each) 1. What is asexual reproduction? 2. What is fission? What are the types of fission? 3. Write the name of any two organisms that reproduce by binary fission. 4. Write the name of a plant and one animal that reproduce by multiple fission. 5. What is budding? 6. What is regeneration? 7. Write the name of a plant each that reproduce asexually by root and stem. 8. What is artificial vegetative propagation? 9. Name an organism which reproduces by either of the given methods: i. Binary fission ii. Sporulation 10. What is vegetative propagation? 11. What is sexual reproduction? 12. What is internal fertilization? 13. What is simple layering? 14. What is air layering? 15. What is tissue culture? Group ’B’ (Understanding Type Questions) (2 Marks Each) 16. Write any two differences between asexual reproduction and sexual reproduction. 17. Write any two differences between fission and budding. 18. What does it mean by the saying that spirogyra reproduces by fragmentation? 19. Write any two differences between self-pollination and cross-pollination. 20. Why is layering done in plants? Give any two reasons. 21. Which method is widely used in Nepal out of grafting, layering and tissue culture? Why? 22. The number of chromosome is different in gametes and zygote, why? 23. Write any two differences between pollination and fertilization. 24. The number of chromosome in gametes is haploid, why? 25. Write two differences between external and internal fertilization. Group ‘C’ (Application Type Questions) (3 Marks Each) 26. How does amoeba reproduce by binary fission? Describe in brief. 27. Draw a diagram showing various parts of a bisexual flower. 28. How does hydra reproduce by budding? Describe in brief. 29. Write any three advantages of asexual reproduction. 30. Write any three reasons for reproducing plants by artificial vegetative propagation. Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each) 31. Describe in brief the importance of artificial reproduction in plants. 32. How is compound layering done? Explain with figure. 33. Draw a chart showing the process of sexual reproduction in developed organisms. 34. How do flowering plants reproduce? Describe in brief. 35. How is cleft grafting done? Describe with figure. GREEN Science (Biology) Book-10 345

UNIT Heredity 19 Weighting Distribution Theory : 5 Practical: 0 Before You Begin A variety of plants and animals are found in our surroundings. These organisms differ from each other in many aspects. Though many organisms look similar, they differ in many characteristics. The offspring produced by asexual reproduction look identical to each other but there are many dissimilarities in the offspring produced by sexual reproduction. It is because, offspring get some genes from father and some genes from mother. The characteristics of parents are transmitted to their offspring through genes. The process of transmission of parental heredity. Genes are the tiny units of heredity present in chromosomes. In this unit, we will study about heredity, Mendel’s laws of heredity, variation and mutation. Learning Objectives Syllabus After completing the study of this unit, students will be able to: i. introduce heredity and state Mendel's laws of • Introduction to heredity • Mendel's experiment heredity. • - Law of dominance • - Law of segregation ii. explain Mendel's experiment with figures and charts. • Genetic characteristics in iii. list the causes of heredity. human beings • Variation and mutation iv. differentiate between mutation and variation. Glossary: A dictionary of scientific/technical terms heredity : the phenomenon by which parental characteristics are transmitted to their offspring genes hybrid : the tiny units of heredity located in chromosomes variation : the offspring produced by two genetically different parents mutation : the differences among the members of the same species : the sudden heritable change in the genetic material of an organism 346 GREEN Science (Biology) Book-10

Heredity Heredity is the phenomenon by which living beings transmit parental characteristics to their offspring. Living beings transmit their characteristics with the help of genes. The nucleus of a cell contains thread like structures called chromosomes. Genes are located in chromosomes in the nucleus. They are arranged in a linear fashion in a chromosome. Genes determine physical, anatomical and physiological characteristics of organisms. These characteristics are transmitted from one generation to another. Each chromosome consists of a large number of genes. It is estimated that about 60,000 genes are found in 23 pairs of chromosomes of human beings. A gene is a segment of DNA (deoxyribo nucleic acid) which can form exact copies by the process of replication. Genes are responsible for inheritance of characteristics from one generation to another. The characteristics of the parents which are transmitted to their offspring are called hereditary characteristics. For example, colour of eyes, colour of skin, shape of face, colour of hair, etc. Genes also help in evolution of organisms by mutation and genetic recombination. Terminology related to heredity 1. Allele: An allele is one form of a gene or pair of matching gene. There may be two or more alleles of a gene. Alleles are denoted by letters, e.g. BB, Bb, Tt, tt, etc. 2. Homozygous or pure organism: The organism having two identical alleles for a particular characteristics is called homozygous or pure organism, e.g. TT (tall) BB (black), rr (white), etc. 3. Heterozygous organism: The organism having two different alleles for a particular characteristics is called heterozygous organism, e.g. Tt (hybrid tall, Bb (hybrid black), Rr (hybrid red), etc. 4. Phenotype: The external appearance of an organism is called phenotype. 5. Genotype: The genetic make up of an organism is called genotype. 6. Dominant characteristic: The characteristic which is prominent and appears in successive generation is called dominant characteristics. 7. Recessive characteristic: The characteristics which remains hidden in successive generation is called recessive characteristic. For example, in cross between a pure tall pea plant and a dwarf pea plant, tall characteristic and dwarf is the recessive one. 8. First filial generation: The generation produced by crossing two pure parents is called first filial or F1 generation. 9. Second filial generation: The generation obtained by crossing two parents of F1- generation is called second filial generation. GREEN Science (Biology) Book-10 347

10. Monohybrid cross: The cross made between two pure organisms or considering only one pair of contrasting characteristics is called monohybrid cross, e.g. cross between a pure tall pea plant with a dwarf pea plant. 11. Dihybrid cross: The cross made by considering two pairs of contrasting characteristics is called dihybrid cross. e.g. the cross between a pure tall pea plant with pure red flowers and a dwarf pea plant with pure white flowers. Symbols given to the genes Genes are symbolized by letters of English alphabet. The alphabet used is the first letter of the character, .e.g. T for tall, R for red, etc. The dominant gene is symbolized with capital letter and recessive gene is symbolized with small letter. For example, in genotype Tt, 'T' represents tall character and 't' represents dwarf character. Mendel's experiment The branch of biology in which we study about genes and heredity is called genetics. The first scientific study of genes was done by an Austrian scientist Gregor Mendel (1822 - 1884 AD). He established the concept of genes as the basic unit of heredity. Therefore, Gregor Mendel is considered as the father of genetics. Fig. Fig. Gregor Johann Mendel conducted experiment on hybridization of garden pea plants. On the basis of his research, he formulated the laws of inheritance. These 19.1 laws are popularly known as Mendel's laws of inheritance. Gregor Mendel Gregor Mendel selected common edible garden pea plants (Pisum sativum). He cross-pollinated pea plants having different traits in his Monastery garden at Brunn, Austria. He found seven pairs of contrasting characteristics (traits) in pea plants which are as follows: 1. Height of plant : Tall (Dominant) and dwarf (recessive) 19.2 Dwarf pea plant Tall pea plant 348 GREEN Science (Biology) Book-10

2. Colour of flower: Red (purple) (Dominant) and white (Recessive) Fig. Fig. Fig.19.3 White flowers of pea Purple flowers of pea 3. Colour of seed: Yellow (Dominant) and green (Recessive) 19.4 Green seeds Yellow seeds 4. Colour of pod: Green (Dominant) and yellow (Recessive) 19.5 Yellow pods of pea Green pods of pea 5. Shape of seed: Round (Dominant) and wrinkled (Recessive) Fig. 19.6 Wrinkled seeds of pea Round seeds of pea GREEN Science (Biology) Book-10 349

6. Shape of pod: Smooth (Dominant) and constricted (Recessive) Fig. Fig.19.7 Constricted pods of pea Smooth pods of pea 7. Position of flower: Axial (Dominant) and terminal (Recessive) 19.8 Terminal flowers of pea Axial flowers of pea Mendel selected pea plants for his experiment because of the following reasons: 1. Pea plants contain a large number of contrasting characteristics in pairs. 2. They are easy to cultivate. 3. They have a short life cycle. So it is possible to study several generations of pea plants within a few years. 4. In pea plants, cross-pollination can be done easily. 5. The flowers of pea plants are closed and bisexual. So they can reproduce naturally. 6. The flowers of pea plants are easy to handle. 7. In pea plants, breeding can be controlled easily due to structure of flowers. 8. Pea plants produce a large number of offspring after pollination. 9. The offspring of pea plants produced after cross-pollination are also fertile. While conducting experiment on pea plants, Mendel concentrated his attention on only one pair of contrasting characteristics at a time and observed the offspring produced by cross-pollination and self-pollination for several generations. He controlled the experimental conditions ensuring that all pea plants were pollinated only by the pollen grains that he transferred. Mendel cross-pollinated pure (homozygous) red-flowered pea with a pure white-flowered pea plants. He transferred pollen grains from the stamen of red-flower to the stigma of white-flower preventing self-pollination. 350 GREEN Science (Biology) Book-10