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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
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.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
A good example of polar molecules can be understood when trying to make a cake. If water and oil are required, they will not mix together. If you put them into a measuring cup, the oil will rise to the top while the water remains on the bottom.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.