How long do various cells in humans live? Cerebral cortex cells endure from birth to death.
Epithelial cells lining the gut last about 5 days. Red blood cells last about 120 days. Adult liver Cells live around 300-500 days. www.supercentenarian.com/archive/cells.html

What web sites with geometric problems are available for 4 th -8 th grades? See 'Polygon Capture' at www.shodor.org/interactive/lessons/angles-elem

Can you suggest activities addressing pollution for middle elementary students? See NatureScope Pollution Problems & Solutions , also see Hands On Earth Science K-8.

What is the total number of orchid species in the world? There are more than 20,000 species of orchids worldwide. www.theorchidsite.com
- How do oil spills in the ocean affect sea birds? Oil clumps in feathers, weighing the birds down, thus preventing them from flying and moving about easily.(Australian Maritime Safety Authority- www.amsa.gov.au/marine_environment_protection/......).

Is there a mathematical term for a pentagon with two sets of parallel lines? UNC Mathematics Instructor Lane Andrews explains that there is no common term for a pentagon with two sets of parallel lines.

I'm looking for solar system lessons appropriate for third grade-suggestions? See McGraw-Hill- National Geographic Society Science V. 2 , for grade 3.  

In performing a transpiration activity on two flower stalks with warm and cold colored water, why did the cold water have the quickest movement? You shared that the activity was performed twice on the flower stalks. In such an investigation, the activity needs to occur numerous times on several flower stalks in order to find the average transpiration rates for the two water temperatures. Careful measurements need to be made. This way your activity should produce more accurate results, explains Dr. Chhandak Basu, UNC Biology.

With a Celestron telescope and a 35 mm camera, what kind of film and speed do I need to film Mercury moving across the sun? The camera needs an automatic metering system, or you need to take lots of different exposures, notes Dr. Dick Dietz, UNC Physics.