Class 8 Science Reaching the Age of Adolescence

Reaching the Age of Adolescence

Adolescence:

Adolescence is the period during which several changes take place in the body; in order to attain reproductive maturity. The adolescence period usually begins at around 11 years of age and lasts till 18th year in girls and till 19th year in boys. Since these years are counted in ‘teens’ (as in thirteen and fourteen), hence the adolescence period is also called the teenage.
Puberty: The beginning of the adolescence period is called puberty. The puberty period ends when an adolescent reaches reproductive maturity.

Changes at Puberty:

The changes which take place during this period are as follows:
Change in Height: Change in height is the most conspicuous change during this period. The long bones, i.e. the bones of the limbs, suddenly grow during this period.
The following table shows percentage attainment of height in boys and girls at different years of the age. The percentages shown in this table can be utilized to calculate the approximate full height which a person is likely to attain in adulthood.
Change in Body Shape: The body of a boy becomes more muscular. Shoulders become wide and the hips become narrow. In girls, the shoulders become round and hips become wide.
Voice Change: The voice box becomes enlarged in the boys. Due to this, the voice of a boy becomes low pitched and deep. Sometimes the voice may become hoarse in a boy due to sudden growth in the vocal cords. This situation persists for a few days and then the voice becomes normal. The voice box does not grow in girls and their voice remains low pitched.
Increased Activity of Sweat and Sebaceous Glands: During adolescence period, the activity of sweat and sebaceous glands is increased. This results in secretion of more sweat and oil from the skin. This can result in problems of pimples and acne.
Development of Sex Organs: In boys, the testes become mature and begin the production of sperms. In girls, the ovaries and eggs become mature and ovaries begin to release ovules. Usually a single egg is produced during an ovulation cycle.
Attainment of Emotional, Mental and Intellectual Maturity: An adolescent person tends to become more independent. He/she may spend more time all alone. The thinking ability of the person also develops. Sudden changes in the body may also develop some sense of insecurity in the person, but this is a part and parcel of the growing up process.

Secondary Sexual Characters

Characters which mark segregation of the sexes are called secondary sexual characters. Secondary sexual characters are integral part of sexual dimorphism in animals. In most of the complex animals, the male of a species looks entirely different than the female of the species. This phenomenon is called sexual dimorphism. Some examples of sexual dimorphism are as follows:

• A human male appears physically stronger than a female and males are usually taller than the females.
• A male peacock has colourful feathers which are absent in the female peacock. Most of the male birds are more colourful than their female counterparts.
• A female spider is much bigger than the male spider.
• A male lion has a thick mane of hairs which are absent in female lion.

Secondary Sexual Characters in Male: Facial hairs develop in males and hairs also develop on the chest. The prominent protuberance in the neck is seen in males. This called the Adam’s apple.
Secondary Sexual Characters in Female: Mammary glands develop and breasts are formed in females.
Common Secondary Sexual Characters in Males and Females: Hairs under the armpit and in the pubic region are common in male and female.
Hormonal Control on Changes During Adolescence: The changes which take place during adolescence are under the control of certain hormones. The male hormone; testosterone is released by the testes. This hormone stimulates the production of sperms. This hormone also promotes various secondary sexual characters in males.
The female hormone; oestrogen is released by the ovaries. This promotes ovulation, i.e. release of a mature egg from the ovary. This hormone also promotes various secondary sexual characters in females.

Reproductive Phase of Life in Humans

The reproductive phase of life is the phase when a human being is able to produce gametes and is thus able to reproduce. The reproductive phase in females begins at around 10 to 12 years of age and lasts till 45 to 50 years of age. The reproductive phase in males begins at around 11 to 13 years of age and lasts beyond the 60th year.

Menstrual Cycle:

The menstrual cycle is usually of about 28 to 30 days. At the beginning of this cycle; ovulation starts and usually one egg is released from the ovary. The egg is transferred to the fallopian tube. The uterus gets ready in anticipation of a possible pregnancy. The uterine wall becomes thick so that it could be ready for the implantation of embryo. If fertilization does not take place, then the uterine thickening is shed off in small fragments. The fragments of the uterine lining and the egg are expelled out through the vagina; along with some blood. The flow of blood through the vagina is called menstruation. The menstrual flow last for about 4 to 7 days and marks the end of the menstrual cycle.
Menarche: The first menstrual flow is called menarche. It happens at the onset of puberty.
Menopause: The cessation of menstrual flow in the lifetime is called menopause. Menopause happens at around 45 to 50 years of age and marks the end of the reproductive phase in a female.
Various events during the menstrual cycle are controlled by different hormones.

eaching the Age of Adolescence

Sex Determination in Humans

The somatic cell in human beings has 23 pairs of chromosomes. The chromosomes in the last pair are called sex chromosomes and they are of two types, i.e. X and Y. In a male; the last pair of chromosomes contains an X and a Y chromosome. In a female; the last pair of chromosomes contains X chromosomes.
After gamete formation, each gamete has 23 chromosomes. Thus, a sperm can have either an X or a Y chromosome as the 23rd chromosome. On the other hand, an egg always has an X chromosome as the 23rd chromosome.
When a sperm with X chromosome fertilises an egg; the resulting zygote develops into a girl child. But when a sperm with Y chromosome fertilises an egg; the resulting zygote develops into a male child.

Role of Hormones in Life Cycle of Insects and Frogs:

In insects and frogs; the development is indirect. It means that there is an intermediate phase before the adult form of the animal. In an insect; a larva undergoes metamorphosis to become the adult. The process of metamorphosis in an insect is controlled by insect hormone.
In a frog; a tadpole undergoes metamorphosis. The process of metamorphosis in a frog is controlled by thyroxine. It is important to note that iodine is an important constituent of thyroxine. Hence, if a tadpole is growing in iodine deficient water; then the tadpole will fail to develop into a frog and would die at the tadpole stage itself.

Reproductive Health:

Diet: The adolescent phase is marked by rapid growth and rapid changes in the body. Hence, an adolescent needs a balanced diet to cope up with these changes. The diet should be rich in vitamins and minerals to promote proper development. Both boys and girls should take calcium rich diet so that proper development of bones can take place. Girls should take iron-rich diet to compensate for the loss of blood during each menstrual period. Iron is an important component of RBCs and hence is an important component of blood.
Personal Hygiene: An adolescent needs to take good care of personal hygiene. The increased activity of sweat and sebaceous glands can result in body odour and can also cause the problems of pimples and acne. These problems can be avoided by maintaining a good personal hygiene.
Girls should take special care of personal hygiene during menstruation. They should keep a track of their periods and should prepare in advance for the menstrual period.

Say NO to Drugs

The adolescents can have impressionable mind which could be swayed by various influences. People of this age group often run the risk of becoming drug addicts because of peer pressure and also because of a tendency to take risks. Drug addiction is a horrible thing which can spoil the life of a person. You should learn to say a big NO to the drugs and instead focus on more constructive things.

Teenage Pregnancy

Adolescents have an attitude to take risk and to experiment various things. Unsafe sex can result in teenage pregnancies during this age. While the body becomes ready for reproduction right from the beginning of the adolescence, it takes time to attain mental and emotional maturity. Moreover, bringing up a child is not only about procreation rather it is about taking the whole responsibility of basic needs of a new individual. Parents have to take care of food, cloth, shelter and education of the child.
As per the government laws the minimum age for marriage has been fixed at 18 years for the girls and 21 years for the boys. However, child marriage is still prevalent in many parts of the country; especially in rural areas. The government and various NGOs keep on carrying awareness programmes against child marriage. A person should only marry when he/she is mentally and emotionally mature to take up the responsibility of a family.

Reaching the Age of Adolescence

NCERT SOLUTION (Part - 1) class 8 science

Question – 1 - What is the term used for secretions of endocrine glands responsible for changes taking place in the body?

Answer: Hormone

Question – 2 - Define adolescence.

Answer: The period during which sexual maturity takes place is called adolescence.

Question – 3 - What is menstruation? Explain.

Answer: At the end of ovulation cycle, unfertilized egg and the thickened lining of the uterine wall are shed in fragments; along with blood; through vagina. This event is called menstruation. Menstruation happens once in every 28 to 30 days and lasts for about 4 to 7 days.

Question – 4 - List changes in the body that take place at puberty.

Answer: Changes which takes place at puberty are as follows:

In Boys and Girls: Sudden increase in height, growth of hair under armpit and in pubic area, excess secretion of sweat and oil on skin.

In Boys: Development of muscular body, protrusion of Adam’s apple, voice becomes deep, facial hairs grow, testis begin producing sperms.

In Girls: Development of a rounded body, fat deposition near hip, enlargement of breasts, voice becomes thin, menstrual cycle begins.

Question – 5 - Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Answer:

Question – 6 - What are sex hormones? Why are they named so? State their function.

Answer: The hormones which stimulate the production of gametes and are responsible for development of secondary sexual characters are called sex hormones.

Testosterone is the sex hormone in males, while oestrogen is the sex hormone in females. Testosterone stimulates production of sperms and is responsible for secondary sexual characters in males. Oestrogen stimulates ovulation and is responsible for secondary sexual characters in females.

Question – 7 - Choose the correct option.
(a) Adolescents should be careful about what they eat, because

1. Proper diet develops their brains.
2. Proper diet is needed for the rapid growth taking place in their body.
3. Adolescents feel hungry all the time.
4. Taste buds are well developed in teenagers.

Answer: (2) Proper diet is needed for the rapid growth taking place in their body

(b) Reproductive age in women starts when their

1. Menstruation starts.
2. Breasts start developing.
3. Body weight increases.
4. Height increases.

Answer: (1) Menstruation starts

(c) The right meal for adolescents consists of

1. Chips, noodles, coke.
2. Chapatti, dal, vegetables.
3. Rice, noodles and burger.
4. Vegetable cutlets, chips and lemon drink.

Answer: (2) Chapatti, dal, vegetables 

Reaching the Age of Adolescence

NCERT SOLUTION (Part - 2)class 8 science

Question – 8 - Write notes on—
(a) Adam’s apple.

Answer: The prominent protrusion seen in the neck of adult male is called Adam’s apple. At the onset of puberty, the voice box grows in size. This is manifested by protrusion in the neck; called Adam’s apple. It is one of the secondary sexual characters in males.

(b) Secondary sexual characters.

Answer: The characters which have no role to play in sexual reproduction but which mark sexual dimporphism in an animal are called secondary sexual characters. Sexual dimorphism is a phenomenon in which male and female of a species can be clearly segregated on the basis of certain external physical characters. Some animals; like humans, gorilla, peacock, lion, etc. show a high level of sexual dimorphism.

(c) Sex determination in the unborn baby.

Answer: The somatic cell in human body has 23 pairs of chromosomes. Out of them the 23rd pair contains the sex chromosomes. The 23rd pair can have two types of chromosomes, i.e. X and Y chromosomes in males but just X chromosomes in females. When sperm or egg are formed; they get half the number of chromosomes, i.e. 23 chromosomes each. As a result, the 23rd chromosome in an egg shall be X chromosome, while it can be either an X or a Y chromosome in a sperm. If a sperm; with X chromosome fertilizes the egg then the zygote will develop into a female child. If a sperm; with Y chromosome fertilizes the egg then the zygote will develop into a male child.

Question – 9 - Word game : Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone

Answer: 3: Adam’s Apple, 4: Endocrine, 7: Pituitary, 8: Hormone, 9: Insulin, 10: Oestrogen

Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through blood stream
6 . Voice box
7. Term for changes at adolescence

Answer: 1: Testosterone, 2: Thyroid, 3: Adolesscent, 5: Action Site, 6: Larynx, 7: Puberty

Question – 10 - The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs showing height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Answer: From the given graph, following conclusions can be made:

• Growth in height is fastest till 4 years of age.
• Height grows at the same rate in boys and girls till about 16 years of age.
• Height of boys grows much faster than that of girls; between 16th and 20th years of age.