As of 2010, there are 118 known elements. of those, how many are believed to be essential to human biology?

From the 118 known elements, 25 elements are believed to be essential to human biology.

Out of 25 elements , 6 elements namely  – carbon, oxygen, hydrogen, nitrogen, calcium and phosphorus , they make up about 99% of the human body. Some other elements like - potassium, sulfur, sodium, chlorine, and magnesium, they are also found in the human biology.

humans are now responsible for causing changes in the environment that hurt animals and plant species. we take up more space on earth for our homes and cities. we pollute habitats. human activity often changes or destroys the habitats that plants and animals need to survive.

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."