- Biology Notes for UPSC IAS Prelims (Part I)
- Biology - Home
- Biology - Structure and Functions
- The Fundamental Unit of Life
- Biology - Tissues
- Biology - Animal Tissue
- Diversity in Living Organisms
- Biology - Plantae Kingdom
- Biology - Animalia Kingdom
- Biology - Vertebrata
- Biology - Transportation in Humans
- Biology - Transportation in Plants
- Biology - Excretion
- Biology - Control and Coordination
- Biology - Hormones in Animal
- How do Organisms Reproduce?
- Biology - Sexual Reproduction
- Biology - Reproduction in Animals
- Reaching the Age of Adolescence
- Biology - Heredity and Evolution
- Biology - Life Processes
- Biology - Respiration
- Microorganisms: Friend and Foe
- Biology - Why do We Fall Ill
- Biology - Natural Resources
- Biology - Our Environment
- Conservation of Plants and Animals
- Biology Useful Resources
- Biology Part 1 - Online Quiz
- Biology Part 1 - Online Test
- Biology Part 1 - Quick Guide
- Biology - Useful Resources
- Biology - Discussion
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Biology - Reaching the Age of Adolescence
The phase of life, when the body undergoes radical changes, leading to reproductive maturity, is known as adolescence.
Adolescence normally begins around the age of 11 and lasts up to 18 or 19 years of the age. However, the phase of adolescence varies from person to person.
Starting from thirteen (13) to nineteen (19), ‘teen’ is suffix and common in every number; therefore, adolescents are also known as ‘teenagers.’
In girls, adolescence phase may begin one year or two years earlier than the boys.
During the adolescence phase, the human body undergoes several changes, which are marked as the onset of puberty.
The most important change, which marks puberty, is that the boys and the girls become capable of reproduction.
Puberty, however, ends when an adolescent phase attains reproductive maturity.
Changes at Puberty
The most conspicuous change during the puberty is the swift increase in height.
In the beginning, girls grow faster than boys, but by reaching 18 years of the age, both attain their maximum height.
The rate of body growth (in terms of height) varies from person to person.
The changes occurring in adolescent boys and girls are also much different.
At puberty, especially the boys’ voice boxes or the larynxes begin to grow and develop larger voice boxes.
The growing larynxes in boys can be seen as a protruding part of the throat; it is known as Adam’s apple.
In girls, the larynx is small; hence, it is not visible from the outside.
Adolescence is also the phase of change in a person’s way of thinking.
Hormones, which are the chemical substances, are responsible for the changes in adolescence.
The testes (in boys), at the onset of puberty, release testosterone hormone.
Once puberty is reached in girls, ovaries begin to produce the hormone namely estrogen; it is responsible to the breasts develop.
Endocrine glands release hormones directly into the bloodstream.
In the body, there are many endocrine glands or ductless glands.
The sex hormones are under the control of hormones released by the pituitary gland.
Reproductive Phase of Life in Humans
At puberty, the released egg (in women), and the thickened lining of the uterus along with its blood vessels get shed off in the form of bleeding known as menstruation.
The first menstrual flow begins at puberty and is known as menarche.
Menstruation occurs once in about 28 to 30 days.
By the age of 45 to 50 years, the menstrual cycle stops, which is known as menopause.
The thread-like structures in the fertilized egg are known as chromosomes.
All human beings have 23 pairs or 46 chromosomes in the nuclei of their cells.
In boys, out of 23 pairs of chromosomes, two chromosomes named X and Y are the sex chromosomes.
In girls, out of 23 pairs of chromosomes, two chromosomes named X and X are the sex chromosomes.
When a sperm carrying X chromosome fertilizes with the egg, the zygote would have two X chromosomes that develop into a female child (as shown in the image given below).
When a sperm carrying Y chromosome fertilizes with the egg, the zygote would have two chromosomes i.e. X and Y and such zygote develops into a male child (as shown in the image given above).