CLASS 8 SCIENCE NOTES
Chapter: Reaching the Age of Adolescence
Target Exam & Curriculum: CBSE / NCERT Class 8 Science | Subject: Biology | Format: Quick Revision & Summary
Notes
1. Important Definitions
Adolescence: The period of life when the body undergoes structural and physiological changes leading to
reproductive maturity. It typically begins around age 11 and lasts until age 18 or 19.
Puberty: The phase during which adolescent boys and girls reach sexual maturity and become physically capable
of reproduction.
Target Site: The specific organ, tissue, or cell group on which a particular hormone acts inside the human body.
2. Key Changes During Puberty
• Increase in Height: Sudden rapid growth in the long bones of the arms and legs.
• Body Shape Changes:
◦ Boys: Shoulders broaden, chest becomes wider, and muscle mass increases.
◦ Girls: The region below the waist widens as hips develop.
• Voice Change:
◦ Boys: The voice box (Larynx) grows substantially, forming a visible protrusion in the throat known as Adam's
Apple. Voice turns deep or hoarse temporarily.
◦ Girls: The larynx stays relatively small; voice is high-pitched and clear.
• Increased Sweat & Sebaceous Gland Activity: Secretion increases dramatically, often causing acne and pimples
on the face.
• Development of Sex Organs: Male organs (testes and penis) mature fully; female ovaries enlarge and start
releasing mature ova (eggs).
3. Endocrine Glands and Hormones
Hormones are chemical messengers produced by ductless endocrine glands and secreted directly into the
bloodstream.
Page 1 of 2
Chapter: Reaching the Age of Adolescence
Target Exam & Curriculum: CBSE / NCERT Class 8 Science | Subject: Biology | Format: Quick Revision & Summary
Notes
1. Important Definitions
Adolescence: The period of life when the body undergoes structural and physiological changes leading to
reproductive maturity. It typically begins around age 11 and lasts until age 18 or 19.
Puberty: The phase during which adolescent boys and girls reach sexual maturity and become physically capable
of reproduction.
Target Site: The specific organ, tissue, or cell group on which a particular hormone acts inside the human body.
2. Key Changes During Puberty
• Increase in Height: Sudden rapid growth in the long bones of the arms and legs.
• Body Shape Changes:
◦ Boys: Shoulders broaden, chest becomes wider, and muscle mass increases.
◦ Girls: The region below the waist widens as hips develop.
• Voice Change:
◦ Boys: The voice box (Larynx) grows substantially, forming a visible protrusion in the throat known as Adam's
Apple. Voice turns deep or hoarse temporarily.
◦ Girls: The larynx stays relatively small; voice is high-pitched and clear.
• Increased Sweat & Sebaceous Gland Activity: Secretion increases dramatically, often causing acne and pimples
on the face.
• Development of Sex Organs: Male organs (testes and penis) mature fully; female ovaries enlarge and start
releasing mature ova (eggs).
3. Endocrine Glands and Hormones
Hormones are chemical messengers produced by ductless endocrine glands and secreted directly into the
bloodstream.
Page 1 of 2
