Class 8 Science Chapter 7 MCQ

For metamorphosis of tadpoles, iodine should be present in water. This is because metamorphosis is brought about by thyroxine hormone that required the presence of iodine for its production by thyroid gland.

The most visible change during puberty in boys is sudden increase in height. At this time, the long bones elongate and make a person tall.

The sex of baby is determined by the type of sex chromosomes present in the fertilised egg from which the baby develops. There are two types of sex chromosomes-X and Y. A female has only two X-chromosomes, i.e., XX, whereas a male has one X and one Y-chromosome, i.e., XY combination.

Adrenaline is called stress hormone which is secreted from adrenal glands at the time of stress. It helps the body to face the emergency situation or flight away from it.

The sex hormones, testosterone and oestrogen are responsible for the development of sexual characters. Secondary sexual characters are visible characters which help us to differentiate between two sexes i.e., male and female. The growth of secondary sexual characters is controlled by sex hormones i.e., testosterone in males produced by testes and oestrogen in females produced by ovaries.

Menarche is the beginning of the reproductive life of a girl or woman. The first menstruation or menstrual flow begins at puberty when the girl or woman is around 10 to 12 years of age. The first occurrence of menstruation at puberty is called “Menarche”. In other words, menarche is the time from which a girl or woman become capable of having a baby.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

A female (women or mother) has only X-chromosomes in all her gametes called “eggs or ova”. A male (man or father) has X-chromosomes as well as Y-chromosomes in male gametes called “sperms”.

Here, all the statements are correct. Hence, your answer will be option [D].

We know that a female has only X-chromosome in all her gametes and a male has X- chromosome as well as Y-chromosomes in male gametes. If a sperm carrying X-chromosome fertilises an egg cell which carries X-chromosome, then the zygote formed will have XX combination of sex chromosome due to which the child born will be a girl. If sperm carrying Y-chromosome fertilises an egg cell which carries X-chromosome, in the zygote formed will have XY combination of sex chromosome due to which the child born will be a boy or male.

The diet which contains the correct amount of each constituent (such as carbohydrates, fats, proteins, vitamins and minerals) sufficient for the normal growth and development of the body and keep a person healthy is called a balanced diet. Our Indian meal of roti (or rice), pulses (or dal), and vegetables is a balanced diet. Remember, for infants (or small babies) mother’s milk provides all the necessary nourishment which they need.

Adrenals are endocrine glands. The adrenal glands produce adrenaline hormone. Pituitary is endocrine glands. The pituitary gland secretes a number of hormones such as testes, ovaries, thyroid gland and adrenal gland to secrete their hormones. Rest of all are correctly match.

Drugs are very powerful chemical substances and should be used only under a doctor’s supervision. Adolescent boys and girls should avoid drugs to maintain physical, mental and social well-being which are necessary to live a purposeful, fruitful and satisfying life in this world. There are many harmful effects of taking drugs so we should avoid these.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

The hormones play an important role in initiating the reproductive function of adolescence at the time of puberty. The rise in the level of sex hormones is responsible for the changes in the bodies of adolescent boys and girls at puberty. The testes make male sex hormone called “testosterone” and the ovaries make female sex hormone called “estrogen”. The production of these sex hormones is under the control of another hormone called “gonadotropic hormone” secreted by pituitary gland.

The main secondary sexual characteristics in females or girls are: i)Development of breasts in girls. ii)Hips broaden and become more curved and prominent in girls. iii)A shrill voice or high-pitched voice in girls. The secondary sexual characteristics in girls are produced by the female sex hormone called “estrogen” made in ovaries.

Many young boys and girls get pimples and acne on the face during puberty. The pimples and acne are formed due to the increased activity of sebaceous glands and sweat glands present in the skin. The level of hormones in boys and girls rises too much at puberty. These hormones stimulate the glands and sweat glands present in skin and secrete more oil and sweat. The accumulation of oil, sweat and dead skin cells blocked the tiny pore in the skin of the face. Bacteria grows in the mixture of oils, sweat and dead skin cells in the blocked skin pores causing the swelling and redness of skin which leads to the formation of pimples.

All the changes which occur in boys and girls at puberty are brought about by various hormones. When a boy or girl reaches puberty, he or she becomes an adolescent. Adolescence continues until the age of about 18 or 19 years when the growth stops and the person becomes an adult. Puberty marks the beginning of the reproductive period when one becomes capable of reproduction.