Class 8 Science Reaching at the Age of Adolescence Exam Notes

Read and download free pdf of Class 8 Science Reaching at the Age of Adolescence Exam Notes. Students and teachers of Class 8 Science can get free advanced study material, revision notes, sure shot questions and answers for Class 8 Science prepared as per the latest syllabus and examination guidelines in your school. Standard 8 students should download this study material which will give them more knowledge for all chapters in Science and all important topics which are scoring and can get you more marks. Students should also download free pdf of Chapter wise Notes for Class 8 Science prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this year and also download free worksheets and question papers available here to get higher scores in school exams and tests, also click here for more Study Material for Class 8 Science

Class 8 Science Reaching at the Age of Adolescence Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Covers the following topics:

1.Adolescence

2.Puberty

3.Changes at puberty

4.Secondary sexual characters

5.Endocrine system & hormones

6.Menstrual cycle

7.Sex determination in human    

Adolescence  

The period of transition from childhood to adulthood is called adolescence.

Puberty

The age at which the sex hormones and gamets begin to be produced and the boy and the girl become sexually matured, is called puberty. Generally boys

Change In Puberty

(1)Increase in Height : There is a sudden increase in the height of both boys and girls during puberty. This occurs due to increase in the length of bones of arms and legs.

(2)Change in body shape : In girls hips become broader and the pelvic region widens. Deposition of fat takes place around the hips.In boys shoulders broaden and the body muscles grow more than that of the girls.

(3)Change in voice : At puberty the voice box or the larynx begins to grow. The larynx in boys is larger than that in girls. In boys, the voice becomes deep and harsh whereas girls have high pitched voice.

(4)Increased activity of sweat and sebaceous glands : The secretion of sweat glands and sebaceous glands (oil glands) increases during puberty. This causes acne and pimples on the face of boys and girls at this time.

(5)Development of sex organs : In boys, the male sex organs like the testes and penis develop completely. In girls, the ovary enlarges and eggs begin to mature. Ovaries start releasing matured eggs. Only one egg is released per month.

(6) Production of hormones : The testes produce the male sex hormone called testosterone. The ovaries produce the female sex hormone called estrogen.

SECONDARY SEXUAL CHARACTERS

Some of the secondary sexual characteristics that develop in girls and boys are as follows :

 In Males (boys) :

(1) Facial hairs such as beard and moustaches develop.

(2) Hairs develop under the arm pit, under chest and in the pubic regions.

(3) Voice becomes deeper (low pitches voice).

(4) Muscles develop and shoulder becomes broad.

(5) Increase in weight.

In Females (girls) :

(1) Development and enlargement of breast (mammary glands).

(2) Hairs develop under arm pit and in the pubic regions.

(3) Hips broaden and pelvic region widens.

(4) Initiation of menstrual cycle.

(5) Deposition of fat around hips

(6) Have high pitched voice (shrill voice).

These changes which occur at adolescence are controlled by hormones.

ENDOCRINE SYSTEM & HORMONES

A group of endocrine glands which produces various hormones constitutes the endocrine system.

 Hormones :

Hormones are chemical substances secreted by ductless glands in the body. These glands release hormones directly into the blood of person, and with the circulation of blood these hormones are carried to target sites.

◊ Example of Some Endocrines Glands Are :

Some Endocrine Glands and their functions

Class 8 Science Reaching at the Age of Adolescence Exam Notes

(1) Pituitary Gland : The pituitary gland is located just below the brain. It secretes growth hormone. Growth hormone controls the development of bones and muscles.

(2) Thyroid Gland : The thyroid glands is located in the throat region. It makes a hormone called thyroxine which contains iodine. The function of thyroxine hormone is to control the rate of metabolism, growth and respiration.

(3) Pancreas : It secretes insulin along with some other hormones. The function of insulin hormone is to control sugar metabolism in the body. Deficiency of insulin in the body causes a disease known as diabetes.

(4) Adrenal Gland : The adrenal gland secretes adrenalin hormone. This hormone is produced under stress. It regulates heartbeat, breathing rate, blood pressure, carbohydrate metabolism and mineral balance.

MENSTRUAL CYCLE

The beginning of the menstrual cycle (menarche) marks the onset of puberty (at the age of 12–13 years) in human females and it lasts upto 40–50 years (menopause) when the reproductive capacity of the female is arrested.

  Menstrual phase (Bleeding phase) : This phase is also called the stage of menstrual flow and lasts about 4 days. During this phase, uterus endometrial lining is sloughed off and bleeding also takes place due to rupture of blood vessels.

Proliferactive phase : This phase is also called follicular phase or stage of repair and proliferation. This is mainly influenced by estrogens.

 Ovulatory phase : During this phase, no conspicuous changes occur in the uterus endometrium. It occurs midway between two menstrual periods.

•Secretory phase : This phase is under the control of progesterone and estrogens. If pregancy does not retain it is followed by menstruation and so it is called premenstrual phase. This phase lests for about 13
to 14 days.

SEX DETERMINATION

The body cells of every human individual, whether male or female, possess 23 pair of chromosomes. Of these 23 pairs of chromosomes are similar in all respects. However 23rd pair is different. The chromosomes of 23rd pair are called sex chromosomes. In females these chromosomes are 22 + XX pairs of chromosomes and in males they are 22 + XY pairs of chromosomes. When female gametes (eggs) are produced, each egg contains 22 + X and 22 + X chromosomes. The males on the other hand produce male gametes (sperms) having 22 + X and other having 22 + Y chromosomes. During fertilization, the sex of the unborn gets decided as shown in the figure

Class 8 Science Reaching at the Age of Adolescence Exam Notes

 

From the above it is clear that all children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus the sex of the children will be determined by what they inherit from their father. A child inheriting an X chromosome from the father will be a girl and the one who inherits Y from the father will be a boy. In our society it is often the mother who is blamed for giving birth to a girl child which is incorrect scientifically and medically.


Please click on below link to download pdf file for Class 8 Science Reaching at the Age of Adolescence Exam Notes.

Tags: 

 


Click to View or Download pdf file
Click for more Science Study Material

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

FAQs on Policy for Tabulation of Marks for Class 10 Board Exams

ON POLICY Question.1 How CBSE will declare the result of Class-X? Answer. Results of Class X Board will be declared on the basis of an objective criterion developed by the Board vide Notification no.CBSE/CE/2021 dated 01.05.2021. Question.2. If any candidate is not...

ICSE Board Exams Cancelled

The ICSE (Class X) 2021 Examination: Given the present worsening situation of the Covid- 19 Pandemic in the country, the CISCE has decided to CANCEL the ICSE (Class X) 2021 Examination. The options given in the earlier Circular dated 16th April 2021, now stands...

Time management for CBSE students

The first thing to learn about Time Management is that time is theoretical so you can’t really manage it. What you do when you get into time management, is that you manage yourself. You decide what has to be done, when it must be done and how to do it in the stipulated...

Class 10 Boards Cancelled Class 12 postponed

Looking to the present situation of the pandemic and school closures, and also taking in account the safety and well-being of the students, it is decided as follows:   1. The Board Exams for Class XIIth to be held from May 4th to June, 14th, 2021 are hereby postponed....

CBSE asks schools to load Class 12 Internal Assessment Marks

This has a reference to the letter no CBSE/COORD/2021 dated 11.02.2021 regarding conduct of the School-Based Assessment (Internal Assessment/Practical/ Project) of Class-XII and uploading the marks by 11.06.2021. It has been observed that some schools have not been...

×
Studies Today