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O-level Biology: Growth and Development

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O-level Biology: Growth and Development
« on: September 08, 2014, 10:04:10 AM »
Growth and Development  A human being’s body is at continuous  growth state from the moment of the formation of the zygote until they are an  adult. Growth is a permanent increase in size and dry mass caused by an  increase in cell number or cell size or both. When a zygote starts forming  organs of the fetus like the brain for example, the organism is said to be developing. Development is an increase in complexity of an organism as it grows  to adulthood.
   Growth Patterns: Growth keeps on going after birth till  adolescence. Adolescence is the time at which a child’s growth rate increases  as the child becomes a teenager. A sudden rise in growth rate of an organism is called a growth spurt.  A human being experiences two growth spurts at his lifetime, the first is at his early years  from age 1-3, and then the child’s growth rate then decreases and stabilizes.  The second growth spurt is the adolescent one, which for girls, occurs at the  age of about 9-10 years old. And for boys, adolescent growth spurt occurs at an  age of about 12-13 years old. The adolescent growth spurt ends at an age of  around 17 years old.
During the adolescent growth spurt, some  changes occur on the body. One of these changes is their sex organs starting to  become mature, this is called puberty. Puberty takes place between ages of  11-17 but generally it is earlier in girls than boys. During puberty large  amounts of sex hormones are released by the body causing changes.
   Puberty in Boys:  The  main sex hormone of males is called testosterone. At puberty, the testicles  secrete large amounts of testosterone into the blood. The testicles now start  to become fully mature and start producing sperms. The chest and shoulders of  the boy become broader and muscles increase in size. Hairs start to grow around  his sex organ and under his armpits; facial hair may grow as well. Sweat glands  become more active and voice of the boy deepens.
   Puberty in girls: During  puberty for girls, the ovaries become mature and they start secreting estrogen  hormone. The changes that take place in the girls body is enlargement of  breasts and hip. The girl’s voice tone becomes sharper. The ovaries become  mature and start releasing eggs. Periods or the menstrual cycle also starts.


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