Reaching Age of Adolescence Chapter Notes - Science Class 8

"Reaching Age of Adolescence" is a chapter in the Class 8 Science Curriculum that explores the significant changes that occur during adolescence. This phase of development marks the transition from childhood to adulthood, and the chapter delves into the physical and psychological changes that occur during this time. Let's see the notes for the chapter in this document. 

Adolescence & Puberty

• The period of life, when the body undergoes changes, leading to reproductive maturity.
• Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age.

• Adolescents are called teenagers as this period covers the teens (13-18 or 19 years of age).
• For females, adolescence begins a year or two earlier than boys. The period of adolescence varies from person to person.

Puberty

During adolescence, the human body experiences numerous transformations, signifying the beginning of puberty. The primary and significant change during this phase is the development of reproductive capabilities in both boys and girls. Puberty concludes once an adolescent attains reproductive maturity.

Changes at Puberty

Changes at Puberty

1. Increase in Height

• There is a sudden increase in height of a person during puberty due to the elongation of the bones of arms and legs. Even though the height of a person depends on an inherited gene, eating habits and exercise during adolescence also decides height.
• Initially, girls grow faster than boys. Both reach maximum height by the age of about 18 years.

Formula for calculating full height(cm) = Present height(cm)/ % of full height at this age X 100

2. Changes in Body Shape

• In boys, the shoulders broaden and muscles of the body grow more prominently than in girls. 
• For girls, there is the widening of the region below the waist and less growth of muscle.

3. Voice Change

During puberty, it is being noticed that the voice of boys starts cracking and their voice box or larynx starts to grow. 

Adam’s Apple:
The increase in the size of voice box in boys is seen as a prominent protrusion in the neck. This protrusion is called Adam’s apple.

4. Increased Activity of Sweat and Sebaceous Glands

During puberty, there is an increase in the secretion of sweat glands and sebaceous glands which may lead to the appearance of acne and pimples.

5. Development of Sex Organs

• At puberty, male sex organs like the testis and penis develop completely and begin to produce sperms. 
• In girls, the ovaries enlarge and start releasing eggs/ova.

6. Reaching Mental, Intellectual, and Emotional Maturity

• Adolescents are more independent and self-conscious than earlier. They tend to think more. Feeling insecure when while trying to adjust to the changes in mind and body is prominent. 
• During adolescence, a person’s brain has the greatest capacity for learning.

Secondary Sexual Characters

• Characters that develop prominently during adolescence which helps to distinguish between male and female are known as secondary sexual characters. 
• Some of these characters are listed below:

Role of Hormones in Initiating Reproductive Function:

• The endocrine glands release hormones into the bloodstream, which travel to specific target sites in the body. These target sites then respond to the hormones. 
• The body has several endocrine glands, also known as ductless glands. The testes and ovaries are examples of these glands, and they produce sex hormones. These hormones are responsible for the development of secondary sexual characteristics in males and females. 
• It is important to note that the production and regulation of sex hormones are influenced by hormones from the pituitary gland. 
• The pituitary gland produces various hormones, including one that stimulates the maturation of ova (eggs) in the ovaries and the formation of sperm in the testes.

The onset of puberty is controlled by hormones

Reproductive Phase of Life in Humans

• Adolescents become capable of reproduction when their testes and ovaries begin to produce gametes.
• In females, the reproductive phase of life begins at puberty (10-12 years of age and generally lasts till the age of approximately 45-50 years).
• Ova mature and is released by one of the ovaries once in about 28-30 days. During this period, the uterus becomes thick so as to receive the mature ova. A fertilized egg develops pregnancy.
• Unfertilized egg along with the thickened lining of the uterus and blood vessels are shed off in the form of bleeding in women once in about 28-30 days is termed Menstruation.
• Initial menstrual flow begins at puberty and is termed Menarche.
• Stoppage of the menstrual cycle at 45-50 years of age is called Menopause.
• Initially, the menstrual cycle may be irregular. It takes some time to become regular.

How is the Sex of the Baby Determined?

Boy or Girl?

• Inside the fertilized egg or zygote, there are instructions that determine the sex of the baby.
• These instructions are found in thread-like structures called chromosomes in the fertilized egg.
• Chromosomes are present inside the nucleus of every cell.
• Humans have 23 pairs of chromosomes in their cells.
• Two of these chromosomes are called sex chromosomes, named X and Y.
• Females have two X chromosomes, while males have one X and one Y chromosome.
• The gametes (egg and sperm) have only one set of chromosomes.
• An unfertilized egg always has one X chromosome.
• Sperms come in two types, one with an X chromosome and the other with a Y chromosome.
• When an X chromosome sperm fertilizes the egg, the baby will be female (XX).
• When a Y chromosome sperm fertilizes the egg, the baby will be male (XY).
• The sex chromosomes from the father determine the sex of the unborn baby.
• It is incorrect and unfair to blame the mother for determining the sex of the baby.

Hormones other than Sex Hormones

• Hormones are chemical substances secreted by the endocrine system/ endocrine glands (Ductless glands, i.e. endocrine glands release hormone directly into the bloodstream to reach a particular body part/target site). 
• Hormones control the changes during adolescence. The pituitary gland (found attached to the brain) secretes hormones which in turn control the production of hormones from other endocrine glands.
• Some endocrine glands, their secretion, and effect are given in the table below:

Role of Hormones in Completing the Life History of Insects and Frogs

• The life span of insects can be categorized into four stages:
  (i) Egg
  (ii) Larva
  (iii) Pupa
  (iv) Adult
• Metamorphosis: It is the change of an insect from a larva to an adult.
• Hormones in insects control the metamorphosis under the action of thyroxine hormone produced by the thyroid.

Reproductive Health

The physical and mental well-being of an individual is regarded as healthy. To keep the body healthy, every human being at any age needs to have a balanced diet, must observe personal hygiene, and undertake adequate physical exercise.

1. Nutritional Needs of the Adolescents

• Adolescence is a stage of rapid growth and development. So a balanced diet comprising proteins, carbohydrates, fats, minerals, and vitamins in requisite quantity is essential. 
• Iron builds blood. Iron-rich food such as leafy vegetables, jaggery, meat, citrus, Indian gooseberry is good for adolescents.

Balanced Diet 

2. Personal Hygiene

Take bath once a day. It is more necessary for adolescents due to the increased activity of sweat glands which may lead to a smelly body. All parts of the body should be washed and cleaned every day.

3. Physical Exercise

Adolescents should take walk, exercise, and play outdoor games in fresh air to keep them fit and healthy.

Say No to Drugs

During teenage, anyone might get affected by the negative energies surrounding him. At such times, falling for drugs can ruin your life.

• Adolescence is a period of growth and changes in both the body and mind.
• It is normal to feel active during this time and there's no need to feel confused or insecure.
• If someone suggests that drugs can make you feel better, always say "No" unless prescribed by a doctor.
• Drugs can be addictive, meaning once you try them, you may want to keep using them, which is harmful.
• Using drugs can damage your body and ruin your health and happiness in the long run.
• AIDS is a dangerous disease caused by a virus called HIV.
• HIV can be transmitted from an infected person to a healthy person by sharing needles used for injecting drugs.
• It can also be passed from an infected mother to her baby through breastfeeding.
• HIV can also be transmitted through sexual contact with an infected person.
• It's important to stay away from drugs to protect yourself from harmful diseases like AIDS and to maintain good health.

Keywords from NCERT

• ADAM'S APPLE: The Adam's apple is a noticeable bump in the throat that is more prominent in boys during puberty. It is actually the thyroid cartilage of the larynx, which grows larger and more visible as the voice deepens.
• ADOLESCENCE: Adolescence is the stage of life between childhood and adulthood. It is a time of significant physical, emotional, and social changes as individuals transition into adulthood.
• ADRENALIN: Adrenalin, also known as adrenaline, is a hormone released by the adrenal glands in response to stress or excitement. It prepares the body for "fight or flight" responses by increasing heart rate, boosting energy, and improving alertness.
• BALANCED DIET: A balanced diet refers to eating a variety of foods that provide all the necessary nutrients in the right proportions. It includes foods from different food groups, such as fruits, vegetables, grains, proteins, and dairy, to ensure proper growth, development, and overall health.
• ENDOCRINE GLANDS: Endocrine glands are special glands in the body that produce and release hormones directly into the bloodstream. These hormones regulate various bodily functions and maintain balance in the body.
• ESTROGEN: Estrogen is a hormone found predominantly in females. It plays a crucial role in the development of secondary sexual characteristics, such as breast development and the menstrual cycle.
• HORMONES: Hormones are chemical messengers produced by the endocrine glands. They travel through the bloodstream and regulate various body functions, including growth, metabolism, reproduction, and mood.
• INSULIN: Insulin is a hormone produced by the pancreas that helps regulate blood sugar levels. It allows cells to take in glucose from the bloodstream and use it for energy.
• LARYNX: The larynx, also known as the voice box, is a part of the throat that contains the vocal cords. It is responsible for producing sound and controlling the pitch and volume of our voices.
• PITUITARY GLAND: The pituitary gland is a small gland located at the base of the brain. It is often referred to as the "master gland" because it releases several hormones that control the functions of other endocrine glands and regulate growth, metabolism, and reproduction.
• PUBERTY: Puberty is the stage of development when a child's body undergoes physical and hormonal changes to reach sexual maturity. It involves the development of secondary sexual characteristics and the ability to reproduce.
• REPRODUCTIVE HEALTH: Reproductive health refers to the overall well-being and proper functioning of the reproductive system. It includes the ability to have safe and satisfying sexual relationships, access to healthcare for reproductive concerns, and the freedom to make informed choices about reproduction.
• SECONDARY SEXUAL CHARACTERISTICS: Secondary sexual characteristics are physical changes that occur during puberty and distinguish males from females. Examples include breast development and widened hips in females, and deepened voice and facial hair growth in males.
• SEX CHROMOSOMES: Sex chromosomes are a pair of chromosomes that determine an individual's biological sex. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
• TARGET SITE: A target site is a specific part of the body that is affected by a particular hormone. Hormones travel through the bloodstream and bind to specific receptors at the target site, triggering specific responses.
• TESTOSTERONE: Testosterone is the primary male sex hormone. It plays a crucial role in the development of male reproductive organs, secondary sexual characteristics, and sperm production.
• THYROXINE: Thyroxine is a hormone produced by the thyroid gland. It helps regulate metabolism, growth, and development in the body.
• VOICE BOX: The voice box, also known as the larynx, is a part of the throat that contains the vocal cords. It is responsible for producing sound and enabling us to speak.

(FAQs) Frequently Asked Questions 

Q.1. What is adolescence?

Ans: Adolescence is a phase of development that marks the transition from childhood to adulthood. It is a period of significant physical, emotional, and psychological changes.

Q2: What physical changes occur during adolescence?

Ans: During adolescence, the body undergoes several physical changes, including growth spurts, changes in body shape, and the development of secondary sexual characteristics like facial hair, breast development, and voice changes.

Q3: What are the hormonal changes that occur during puberty?

Ans: The hormonal changes during puberty lead to sexual maturation, such as the release of sex hormones like estrogen and testosterone. These hormones are responsible for the development of secondary sexual characteristics.

Q4: How can one maintain good reproductive health during adolescence?

Ans: Maintaining good reproductive health during adolescence involves practicing safe sex, seeking medical help in case of any issues, and taking care of personal hygiene.

Q5: What are the psychological changes that occur during adolescence?

Ans: Adolescence is a time of significant psychological changes, including mood swings, the development of self-identity, and increased peer pressure.