Whats a pure substance that cant be broken down into simpler substances by chemical or physical means

Which of the following is True for valence electrons? A) Valence electrons are always located in the innermost energy level B) Each element in the periodic table has a different number of valence electrons.

This is the copying process by which a cell duplicates its dna.

If you observe a cell nucleus under a compound microscope, you will not see a molecule of dna. why will you be able to see the dna you extract?

Scientists have successfully cloned animals, including mammals such as sheep. Which statement provides the most likely reason that a human has not yet been cloned?

The drought alone did not cause the dust bowl. It was combination of several things, the drought and

A sedimentary rock containing a fern fossil was found. What does this tell about the area at the time the rock was formed? The area was hot. The area was covered by an ocean. The area was on land. The area was cold.

1. Which of the following statements best describe the difference between angiosperms and gymnosperms? A. Angiosperms produce cones to protect their seeds; gymnosperm seeds are surrounded by fruit. B.

If DNA polymerase is observed to pause as it is synthesizing genetic material from a template strand, this is likely the result of: (A) DNA polymerase encountering a "bulky lesion" on the template strand.

Do all social hazards result from an individuals lifestyle choice? Explain

Some species of wasps are social. The queen starts a colony from scratch each spring. She builds a small nest, and lays and raises a group of female workers. The workers enlarge the nest while the queen continues to lay eggs.