Class 8 Science
Boy or Girl?
Gender of a child is determined by the combination of chromosomes in the zygote. A normal cell in human beings has 46 chromosomes, i.e. 23 pairs of chromosomes. Out of them, chromosomes in 22 pairs are identical. But chromosomes in the 23rd pair may be identical or different.
There are two types of chromosomes in 23rd pair. They are called X and Y chromosomes. The 23rd pair in a male has XY combination, while that in a female has XX combination.
Gametes in humans have 23 chromosomes, i.e. half the number in somatic cells. So, a sperm may have X or Y chromosome as 23rd chromosome. But, an ovum has X chromosome as 23rd chromosome.
- If a sperm with X chromosome fertilizes the egg, the zygote thus formed will lead to birth of a girl child.
- If a sperm with Y chromosome fertilizes the egg, the zygote thus formed will lead to birth of a male child.
Hormone other than Sex Hormones
|Pituitary||Growth hormone||Normal growth of body|
|Adrenal||Adrenalin||Prepares the body for a fight or flight like situation.|
Goiter: This disease happens due to iodine deficiency. Iodine deficiency results in less production of thyroxin. This may result in a disease called goiter which is manifested by a permanent swelling in the neck.
Diabetes: Less insulin secretion results in a disease called diabetes. In common language, this disease is called blood sugar. There are two types of diabetes, viz. insulin dependent and non-insulin dependent. As the name suggest, a person suffering from insulin dependent diabetes needs to regularly take insulin injections.
Role of Hormone in Completing the Life Cycle of insects and frogs
- Insect hormones control the metamorphosis of larva into adult.
- Thyroxin controls the metamorphosis of tadpole into frog. If a frog lays eggs in iodine deficient water, the tadpoles will not develop into frogs and will perish.
Balanced Diet: Rapid growth during adolescence necessitates balanced diet. A teenager should take adequate amount of carbohydrates, protein, fat, vitamins and minerals in food. One should avoid eating fried food and junk food. Girls need to take lot of iron-rich food because iron is necessary for formation of RBCs.
Personal Hygiene: You have read that sweat and sebaceous glands show increased activity during this period. If proper hygiene is not maintained, it can lead to many skin diseases in adolescents. Girls need to take special care of hygiene during menstrual period.
Physical Exercise: Physical exercise is helpful not only in making a strong body but also in properly utilizing your energy. A good workout ensures all your systems are working in perfect condition.
Say ‘NO’ to Drugs: The menace of drugs is spoiling many a life. During this period, one can easily get influenced and carried away by negative stimulations. You need to have a strong will power to say NO to drugs. Addiction to drugs will destroy your career and life.
HIV (Human Immunodeficiency Virus): This is a virus which causes AIDS (Acquired Immunodeficiency Disease). Till date, there is no cure for this disease. Hence, prevention is the only way to keep away from this dangerous disease. AIDS can spread through sexual contact, through infected needles and from a mother to her unborn child. This can also be transmitted to an infant through mother’s milk.