Chapter 4 - Reproduction | PDF

Okay, I will convert the content of the images into a structured markdown format as best as I can. ## 4 Reproduction Reproduction, as you have studied in your class, is the process by which living beings produce copies of themselves. In many simple organisms reproduction takes place asexually. In...

Okay, I will convert the content of the images into a structured markdown format as best as I can. ## 4 Reproduction Reproduction, as you have studied in your class, is the process by which living beings produce copies of themselves. In many simple organisms reproduction takes place asexually. In higher organisms (plants and animals) it takes place sexually. In asexual reproduction, an individual produces offspring without the help of another individual. In sexual reproduction, on the other hand, two individuals - a male and a female - are required. ### SEXUAL REPRODUCTION IN ANIMALS Sexual reproduction involves the fusion of a male (reproductive) cell with a female (reproductive) cell to produce a single cell, called the zygote. The process of fusion of the two cells is known as fertilization. In animals, the male cell, or male gamete, is called the sperm. The female cell, or female gamete, is called the ovum (plural: ova), or egg. #### Types of fertilisation In some animals, like fish and frogs, fertilisation takes place outside the body. This is called external fertilisation. The females discharge many eggs into the water and the males discharge sperms close to the eggs. The sperms swim to the eggs and fertilise them. In higher animals, like lizards, crocodiles, birds and mammals, fertilisation takes place inside the female's body. This is called internal fertilisation. Mammals are animals that have babies, which are nursed by their mothers. Other animals, like birds, crocodiles, snakes and lizards lay eggs. There are some exceptional mammals, like the platypus and the spiny anteater) or (echidna, which lay eggs. However, these too nurse their young. ### REPRODUCTION IN MAN To understand how reproduction takes place in man and how a baby develops and is born, you must first know about the male and female reproductive systems. #### The male reproductive system The male reproductive organs are called testes (singular: testis). They start producing sperms at puberty Puberty is the stage at which a person attains (sexual maturity or becomes capable of reproduction) We will discuss this in greater detail later in the chapter. Fig. 4.1 The echidna is an exceptional mammal which lays eggs. Fig. 4.2 (a) The male reproductive system (b) A sperm The testes lie in a sac, called the scrotal sac, which is located outside the abdominal cavity They produce sperms. The sperms collect and mature in a tube called the epididymis. From here, they travel through a muscular tube, called the vas deferens, into the urethra, which lies inside the penis. As the sperms travel through the vas deferens, secretions from various glands pour in. The mixture of secretions and sperms is called semen. The semen (containing sperms) is transferred into the vagina, or the opening of the female reproductive system, by the penis. Sperms have a head and a long tail. The tail helps them swim towards the ovum. #### The female reproductive system The ovaries, or the female reproductive organs, lie in the lower part of the abdominal cavity. They start producing ova when a girl reaches puberty. Usually, either of the ovaries produces one ovum every month. Over each ovary is a muscular tube, which ends in a funnel with fingerlike projections. This tube carries the ovum from the ovary to the uterus, or womb, and is called the Fallopian tube, or oviduct. The uterus is a muscular organ. Its lower portion, called the cervix, is connected to the vagina, which opens to the outside. The ovaries are attached to the uterus by ligaments. Fig. 4.3 The female reproductive system #### Fertilisation, pregnancy and childbirth The sperms introduced into the vagina, during intercourse, travel up the vagina and uterus into the Fallopian tube. It is here that one (usually) of the sperms fuses with the ovum, or fertilisation takes place. The zygote, thus formed, divides repeatedly and travels to the uterus. It gets attached to the wall of the uterus and forms the embryo, or the tiny baby. The cells of the embryo divide and differentiate into different types to form tissues. The tissues form organs, and the embryo slowly takes the familiar form of a baby. This is when it is called a foetus. The process of pregnancy to birth of a baby within nine months is known as Gestation Period. Fig. 4.4 (a) After fertilisation, the zygote divides. (b) The embryo attaches itself to the uterine wall and grows until the baby is ready to be born. The wall of the uterus has a rich supply of blood vessels from which the growing embryo draws nutrition. Nutrients and oxygen pass into the embryo through a structure called the placenta. The placenta also carries waste material from the embryo into the mother's blood. It is connected to the embryo by the umbilical cord. The baby (embryo/foetus) grows in the mother's uterus for about nine months. This period is called pregnancy. Inside the uterus, it is protected by a sac called the amniotic sac. This sac contains amniotic fluid, which acts like a cushion. When the baby is ready to be born, the sac bursts, and the wall of the uterus goes through contractions to push the baby out through the vagina. Usually, only one ovum is produced at a time, so only one baby is born. Sometimes, however, two ova happen to mature and are released at the same time. They are fertilised by two sperms, which results in the birth of twins. Twins born this way are called nonidentical Fig. 4.5 The menstrual cycle fraternal or nonidentical twins, it can also happen that the fertilised egg divides into two. This leads to the birth of identical twins. Identical twins look almost like copies of each other and are of the same sex. Fraternal twins are as similar as any other siblings and need not be of the same sex. When a girl reaches puberty, either of the ovaries releases an ovum into the Fallopian tube once in every 28 days (or so). This is called ovulation. When this happens, the uterus starts preparing to receive and nourish the embryo. Its wall gets thickened with an increased supply of blood. If the ovum does not get fertilised, it is expelled through the vagina. And together with it is expelled the lining of the uterus and blood. This is called menstruation. The entire process of ovulation, thickening of the uterine wall and menstruation is called the menstrual cycle. This is usually a 28-day cycle. #### Secondary sexual characters Many physical and emotional changes occur in boys and girls around the age when they attain puberty. This period of life, referred to as adolescence is associated with a great deal of physical and mental growth. Generally, girls attain puberty between 11 and 14 years and boys, between 13 and 16 years. Puberty is marked by the onset of menstruation in girls and the production of sperms in boys. It is also associated with several external physical changes known as secondary sexual characters In the case of girls, the secondary sexual characters are enlargement of the breasts, widening of the pelvic girdle, and growth of hair in the pubic region and armpits. In the case of boys, the characters are deepening of the voice caused by enlargement of the larynx; growth of hair on the face, pubic region and armpits; enlargement of the penis and scrotum; and increase in muscle mass. ### THE ENDOCRINE SYSTEM This system consists of several glands scattered over the body. These glands, called endocrine glands are different from other glands. They discharge the chemicals they produce directly into the blood, unlike other glands, which discharge their secretions through vessels or ducts. The chemicals produced by the endocrine glands are called hormones. Hormones act like chemical messengers. They are carried by the blood to specific organs or tissues with messages for them to function in particular ways. Thus, the endocrine system controls and coordinates the functioning of many organs of the body. The endocrine glands, their location and functions are mentioned in Table 4.1. The ones that are of interest to us in this chapter are the testes and ovaries. Apart from being reproductive organs, they also function as endocrine glands. The testes produce the male sex hormone called testosterone. This hormone causes the development of the secondary sexual characters in males. The ovaries produce estrogen, which is responsible for the development of the secondary sexual characters in females. Oestrogen also prepares the uterus for pregnancy. Another hormone released by the ovaries is called progesterone. It brings about changes in the body during pregnancy. Fig. 4.6 The endocrine glands Table 4.1 The endocrine glands | Glands | Location | Functions | | -------------- | -------------------------- | ------------------------------------------------------------------------------------------------ | | Pituitary | Base of the brain | Regulates growth and the functioning of the other endocrine glands | | Thyroid | Near the larynx | Controls many activities of the body including the rate at which energy is produced | | Parathyroids | Behind the thyroid | Control the balance of calcium in the body | | Adrenals | Attached to each kidney | Regulate heartbeat, respiration rate and blood pressure | | Pancreas | Below the stomach | Controls glucose level in blood | | Testes | Outside abdominal cavity | Promote development of secondary sexual characters | | Ovaries | Lower part of abdominal cavity | Control secondary sexual characters and changes related to pregnancy | Though the words 'sex' and 'gender' are sometimes used interchangeably, sex is determined by nature, while gender is a social or cultural concept. When we refer to sex, we mean the biological characteristics that make one male or female. On the other hand, when we speak of gender, we mean the characteristics people associate with being male or female. Since gender differences are a social or cultural concept, they vary from one society to another. They also change with time. For example, way back in the 1840s and '50s when Florence Nightingale wanted to serve the sick, her family was horrified. At that time, no 'decent' woman became a nurse. And now nursing, by and large, is seen as a feminine profession. Similarly, Elizabeth Blackwell (the first woman doctor) had to overcome a great deal of resistance in order to study medicine. Gender roles are functions that society sees as feminine or masculine. These roles are encouraged in children from a very early age. There is no law that binds a girl to behave in a particular way or compels a boy to perform certain functions. However, since most people in a society have certain ideas of what is feminine and what is masculine, boys and girls grow up performing these roles. example, an Indian girl may be encouraged by her parents to learn cooking, while a boy may automatically help his father mend a fuse or fix a leaking tap. Fig. 4.7 A poster issued by Rajasthan Patrika to change gender bias in primary education The idea of the roles men and women should perform is often reflected in their choice of profession. For example, women are associated with nurturing, caring, looking after the old and the young. Thus, quite often, women become nurses, dietitians, counsellors or primary school teachers. Men are associated with protection, valour, physical stamina and the ability to put up with physical hardships. Thus, young boys often dream of joining the army, navy or air force. Prepare a set of questions to test people on their ideas of gender roles. Each of you can interview five or more people (from different families) and then collate the answers to get a general idea of gender roles in our society. Here are some examples of the questions you can ask. 1. Who looks after the children and the elderly in your family? 2. Who cooks the meals? 3. Who arranges for the maid? 4. Who calls the plumber/electrician and carries out minor repairs? 5. Who books the tickets when the family goes for a holiday? 6. Who decides which car/TV/computer/motorcycle to buy? 7. Who decides which doctor to consult? 8. Who decides what to do with the family's savings? 9. Who drops/picks up children from school? 10. Who decides the colour/type of curtains and other furnishings? A taboo is a social (or religious) custom that prohibits or restricts a certain behaviour or practice. For example, widow remarriage was considered taboo in India until the Widow Remarriage Act was passed in 1856. In fact, it was frowned upon even after that. Fig. 4.8 Sign outside a hospital Though sex determination is punishable, female foeticide is a part of life in may parts of India (and elsewhere). So much so that the female to male ratio in our country has fallen to 933:1000. Normally, the number of females should be the same as or more than the number of males. **Points to Remember:** * Sexual reproduction requires two individuals a male and a female. It involves the fusion of a male gamete with a female gamete to form a zygote, which develops into a new individual. The process of fusion of the gametes is called fertilisation. * When fertilisation occurs outside the body, as in fish and frogs, it is called external fertilisation. When it occurs inside the body of the female, it is called internal fertilisation. * In humans, the male reproductive system consists of the testes, vas deferens, epididymis, penis and some glands. * The female reproductive system consists of the ovaries, fallopian tubes, uterus and vagina. * Sperms produced by the testes are transferred into the vagina of the female by the penis during intercourse. They travel to the fallopian tube, where one of them fertilises the ovum. * The zygote produced after fertilisation divides and redivides to form the embryo. The embryo attaches itself to the wall of the uterus and derives nutrition through the placenta. The placenta is attached to the embryo by the umbilical cord. * The embryo is protected by the amniotic sac containing amniotic fluid. When the baby is ready to be born, the sac bursts and the uterine wall undergoes contractions to push the baby out through the vagina * If the ovum does not get fertilised, it is expelled through the vagina along with the disintegrated wall of the uterus and blood. This is called menstruation. * Puberty is the state of attaining sexual maturity. In girls, it is marked by the onset of menstruation. In boys, it is marked by the production of sperms. * The external physical changes that occur at puberty are called secondary sexual characters. For girls, these changes are growth of hair in the pubic region and armpits; enlargement of the breasts and widening of the pelvic girdle. For boys, the changes are growth of hair on the face, pubic region and armpits; deepening of the voice; enlargement of the penis and scrotum; and increase in muscle mass. * The endocrine glands produce hormones, which control the functioning of specific organs and tissues in the body. The reproductive system and secondary sexual characters are controlled by the testes and ovaries. The testes produce testosterone, while the ovaries produce oestrogen and progesterone. * The pituitary gland regulates growth and other endocrine glands. The thyroid is associated with the rate at which energy is produced. The parathyroids control the balance of calcium. The adrenals regulate heart beat, respiration rate and blood pressure. The pancreas regulates the sugar level in the blood. * Gender refers to the characteristics people associate with being male or female. It is a social or cultural concept. * The determination of the sex of a foetus is prohibited by law. It is done by testing the amniotic fluid, the mother's urine or ultrasonography. ### Exercises **A. Answer the following in not more than 20 words.** 1. What is asexual reproduction? 2. What are the male and female gametes known as in human beings? 3. Name one animal in which reproduction takes place outside the body. 4. Name the organs that form the male reproductive system. 5. Where does fertilisation take place in human beings? 6. How does the embryo receive nutrition in the mother's womb? 7. Name the organs of the female reproductive system in human beings. 8. What happens to the zygote formed after the fertilisation of the ovum? 9. Name the hormone that regulates secondary sexual characters in males. **B. Answer the following in not more than 40 words.** 1. What is the menstrual cycle? 2. How are twins born? 3. What are endocrine glands? What do they do? 4. What is a taboo? Give an example to illustrate how the idea of what is taboo changes with time. **C. Answer the following in not more than 100 words.** 1. What are secondary sexual characters? Mention the male and female secondary sexual characters in human beings. 2. What do you understand by 'gender roles'? 3. How is the sex of a foetus determined? Why is it prohibited by law? I hope this is helpful! Let me know if you have any other questions.