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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Looking at the sun may not only cause headache and distort your vision temporarily, but it can also cause permanent eye damage. Any exposure to sunlight adds to the cumulative effects of ultraviolet (UV) radiation on your eyes. UV exposure has been linked to eye disorders such as macular degeneration, solar retinitis, and corneal dystrophies.
About 600,000 particles of skin are shed every hour by each human. If you live to age 70 years, you have shed 105 pounds of dead skin.
All adults should have their cholesterol levels checked once every 5 years. During 2009–2010, 69.4% of Americans age 20 and older reported having their cholesterol checked within the last five years.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
![Bronfenbrenner’s model of the ecological-systems approach to studying development. He suggested that](https://biology-forums.com/gallery/47/medium_6_31_05_15_8_20_41_219701596.jpeg)
![Pin the skin and subcutaneous fascia on a spot on the back using the thumb of one hand; place the ...](https://biology-forums.com/gallery/32/medium_380798_22_08_17_12_32_35_328421547.jpeg)