CBSE Class 8 Science Revision Notes Chapter 10

CBSE Class 8 Science Revision Notes Chapter 10 – Reaching the Age of Adolescence 

The period of transition in life, when the body undergoes certain changes, leading to reproductive maturity is known as adolescence. The World Health Organisation (WHO) mainly defines adolescence as a period between eleven years of age to eighteen or nineteen years of age. In other words, it is the period that occurs between childhood and adulthood. The several changes that a human body undergoes during adolescence mark the onset of puberty. 

The phase in which the reproductive organs of a human body become functionally active is called puberty. Puberty ends as soon as the adolescent reaches reproductive maturity. 

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Revision Notes for CBSE Class 8 Science Chapter 10 

Access Class 8 Science Chapter 10 – Reaching the age of Adolescence Notes in 30 Minutes 

Secondary Sexual Characters 

Sexual characteristics are traits in a living thing’s behaviour or physical makeup that reveal its biological sex. They fall into one of two categories:

1. Primary sexual features are the reproductive sex organs. Male testicles and female ovaries are two examples of these organs.
2. Secondary sexual characteristics are the physical traits that separate an organism’s two sexes and emerge throughout puberty.

Following are a few sexual features that both boys and girls experience during puberty:

• At the start of puberty, boys grow facial hair like beards and moustaches as well as hair on their chests, under their arms, and in the pubic area. They even grow muscles as their shoulders enlarge. Their weight rises and their voices get hoarse.
• In girls, breasts develop and enlarge at the onset of puberty. Their pelvic area widens and their hips become broader. Their voices become high-pitched and they start going through their menstrual cycle. They also develop hair under their armpit and the pubic area.

Hormones 

Hormones are the chemical compounds that the endocrine glands secrete into the bloodstream to reach the target location for control and coordination of the actions of many organs in the body. They are in charge of the alterations that take place during the adolescent stage. It is regulated by oestrogen and testosterone in females and males, respectively. 

Role of Hormones in Initiating Reproductive Function 

The abrupt rise in hormone production marks the start of puberty. The endocrine glands, such as the female ovary and the male testes, secrete sex hormones that cause puberty-related changes and activate the reproductive glands. Another hormone secreted by the pituitary gland also referred to as the body’s master gland regulates the production of oestrogen and testosterone.

The pituitary gland secrets all the growth hormones and hormones that cause other glands to secrete hormones, such as the thyroids, testes, ovaries and adrenals. While the pancreas produces insulin, the thyroid gland produces thyroxine and the adrenals produce adrenaline in our body. 

The male reproductive hormone is called testosterone, and the female reproductive hormone is called oestrogen. With the onset of puberty, the uterine wall prepares to receive the developing fertilised egg in females. If there is no fertilisation, the thicker lining of the uterine breaks down and is expelled along with the blood. This process is known as menstruation.

Reproductive Phase of Life in Humans 

Adolescents become capable of reproducing after they enter puberty because their testicles and ovaries start to create gametes.

The reproductive phase in a female’s life starts when she reaches puberty, which generally ranges between 10-12 years of age and continues till 45-50 years of age. The beginning of the reproductive life of a woman is termed menarche and when the menstrual cycle stops at 45-50 years of age, it is termed menopause. 

The ova begins to mature in the ovaries of a woman and a mature ovum is released once every 28-30 days with the onset of puberty. This process of the release of an egg by the ovary is known as ovulation. During this period, the uterus wall becomes thicker, preparing itself to receive the fertilised egg. When the fertilised egg gets implanted in the thick uterus wall, it results in pregnancy.

However, if fertilisation does not occur, then the released egg as well as the lining of the uterus wall gets discharged in the flow of blood, this process is called menstruation.

Determination of Sex of the Baby 

When a sperm and ovum fuse together, a zygote is formed. The gender of the child is determined by the sex chromosomes of the sperm. Each cell in the human body has 23 pairs of chromosomes and it is a pair of chromosomes that make up the sex chromosomes. While XX chromosomes are found in females, XY chromosomes are found in males. 

The type of the sex chromosomes in the fertilised egg, or how the fertilisation occurs, determines the sex of the child that will be born. There are 23 pairs of chromosomes in the nucleus of each human cell. The sex chromosomes make up one pair of them. X and Y chromosomes are two different types of sex chromosomes. Males have one X and one Y chromosome, whereas females have two X chromosomes.

When the sperm carrying X chromosomes fertilises with the egg containing X chromosomes, then a female child is born as the zygote formed will have two X chromosomes. If the sperm carrying Y chromosomes fertilises with the egg containing X chromosomes, a male child is born as the zygote formed and then will have XY chromosomes.

Endocrine Glands and Their Functions 

A group of ductless glands regulating the body processes and functioning of many systems is an endocrine system. They do so by secreting chemical substances known as hormones. The following are the main functions of endocrine glands:

• Release of their secretions directly into the bloodstream.
• The site and origin of action are distant usually for hormones.

Role of Hormones in Insects and Frogs

Hormones play an essential role in the life cycle of insects and frogs. For instance, to become a butterfly, a caterpillar goes through many stages. In a similar way, a tadpole goes through many stages of becoming a frog. These changes that take place for completing a full cycle are referred to as metamorphosis.

Reproductive Health 

Physical and mental well-being are considered to be components of health. Growing youngsters require extra attention during their growing stage since adolescents go through significant changes.

Nutritional Needs of the Adolescents 

Every individual needs to eat a balanced diet to stay healthy, but it is even more important for an adolescent to plan his/her diet carefully since they are growing. Their diet must include the right proportion of carbohydrates, vitamins, minerals, proteins, fibre, and water.

Personal Hygiene 

Besides eating a balanced diet, one must keep their body and surroundings clean to protect themselves from diseases and illness. Every adolescent needs to adopt proper habits such as washing hands before and after meals, bathing every day, not defecating in the open field, girls taking care of cleanliness during their menstrual cycle, etc. for maintaining their hygiene.

If boys and girls do not maintain hygiene, there will be higher chances of bacterial and fungal infections.

Physical Exercise 

Exercising regularly is necessary to become fit and fine. All adolescent girls and boys must be active and involve themselves in various physical activities such as walking, swimming, running, jogging, cycling, dancing, etc. in their daily routine to stay fit. 

‘NO’ to Drugs or Medicines 

Drugs are physically harmful in the long run and are highly addictive. Drug abuse can occasionally have an irreparable negative impact on one’s health and happiness. HIV infection is more likely to occur in drug addicts. HIV is a highly contagious illness that can spread to healthy individuals by sharing syringes, to infants from infected mothers through breast milk, etc. Sexual contact with an HIV-positive individual can also spread the virus.

Apart from this, many medicines have specific dosage levels and lead to adverse side effects, when not followed properly. Therefore, everyone must avoid taking medicines or any drugs unless prescribed by a doctor.