Reaching the Age of Adolescence Class 8 Science Notes - Ch. 7

Chapter 7: Reaching the Age of Adolescence

Adolescence and Puberty

Adolescence is the period of life when the body undergoes changes, leading to reproductive maturity. It begins around the age of 11 and lasts up to 18 or 19 years of age. Adolescents are also called teenagers.

The onset of adolescence is marked by puberty, which is the time when humans become sexually mature and capable of reproduction.

Changes at Puberty

• Increase in Height: A sudden increase in height is one of the most noticeable changes.
• Change in Body Shape: In boys, shoulders broaden and muscles develop. In girls, the region below the waist becomes wider.
• Voice Change: In boys, the voice box or the larynx begins to grow, resulting in a deep, hoarse voice. This protruding part of the throat is called the Adam's apple.
• Increased Activity of Sweat and Sebaceous Glands: The secretion of sweat and oil glands increases, often leading to acne and pimples.
• Development of Sex Organs: In boys, the testes begin to produce sperm. In girls, the ovaries enlarge and eggs begin to mature.

Secondary Sexual Characters

These are features that distinguish males from females but are not directly part of the reproductive system.

In Boys

• Growth of facial hair (moustache and beard).
• Hair growth on the chest, under the arms, and in the pubic region.

In Girls

• Development of breasts.
• Hair growth under the arms and in the pubic region.

Role of Hormones in Initiating Reproductive Function

Hormones are chemical substances secreted by endocrine glands. The changes during puberty are controlled by hormones.

• Testosterone: The male hormone produced by the testes. It causes the secondary sexual characters in boys.
• Estrogen: The female hormone produced by the ovaries. It causes the development of breasts and other female secondary sexual characters.
• The production of these hormones is under the control of another hormone secreted from the pituitary gland.

Reproductive Phase and Sex Determination

Menstrual Cycle

In females, the reproductive phase begins at puberty (10 to 12 years of age) with the first menstruation, known as menarche. In this cycle, one mature egg is released by one of the ovaries every 28 to 30 days. During this period, the wall of the uterus becomes thick to receive the egg. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off, causing bleeding in women which is called menstruation. The stoppage of menstruation at around 45 to 50 years of age is termed menopause.

How the Sex of the Baby is Determined

The sex of a child is determined by the sex chromosomes inherited from the parents. Humans have 23 pairs of chromosomes. One pair is the sex chromosomes: X and Y.

• A female has two X chromosomes (XX).
• A male has one X and one Y chromosome (XY).
• If a sperm carrying an X chromosome fertilizes the egg (which always has an X), the child will be a girl (XX).
• If a sperm carrying a Y chromosome fertilizes the egg, the child will be a boy (XY).
• Therefore, the father is responsible for the sex of the child.

Reproductive Health

Maintaining good health, especially during adolescence, is crucial.

• Nutritional Needs: Adolescents need a balanced diet rich in carbohydrates, proteins, fats, vitamins, and minerals. Iron is particularly important for building blood, especially for girls.
• Personal Hygiene: Keeping the body clean is essential to prevent infections. Daily bathing and cleanliness during menstruation are very important.
• Physical Exercise: Regular exercise, walking, and playing outdoor games keep the body fit and healthy.

A Note on Drugs: Adolescence is a period of much activity in the body and mind, which may make a person feel insecure. It is important to say NO to drugs, as they are addictive and ruin health and happiness.

Frequently Asked Questions (FAQ)

What is the difference between adolescence and puberty?

Adolescence is the entire transitional period from childhood to adulthood (approx. 11-19 years), while puberty is the specific set of biological events within adolescence where a person becomes capable of reproduction.

What are hormones?

Hormones are chemical messengers produced by endocrine glands that travel through the bloodstream to target organs to regulate various bodily functions, including growth and reproduction.

Who determines the sex of a baby?

The father determines the sex of the baby. The type of sex chromosome (X or Y) in the sperm that fertilizes the egg determines whether the baby will be a girl (XX) or a boy (XY).