If a segment of DNA has 20% adenine in its base composition, what percent thymine is there? A. 20%B. 80%C. 60%D. 30%

A community of organisms along with their physical environment constitutes a(n)A) biosphere.B) ecosystem.C) population.D) habitat.E) community.

Choose the correct statement about proteins and their structure. A)Hydrogen bonding rarely occurs in proteins. B)Most proteins are made from a short chain of amino acids. C)A denatured protein is equally effective as the protein in its original shape .D)A protein’s conformation determines its function.

 All cells have these two characteristics: A. contain DNA in the nucleus and have a plasma membraneB. produce a cell wall outside of the plasma membraneC. contain mitochondria and chloroplastsD. have a plasma membrane and ribosomes in the cytoplasm

.Match the items below with their descriptions:

Which of the following elements is NOT one of the six most common in living organisms? A. carbonB. oxygenC. ironD. nitrogenE. hydrogen

The ______ of water molecules determines its chemistry and thus the chemistry of life. A.closeness B.cohesiveness C.wetness D.polarity

When one atom loses an electron to another atom, it results in the formation of A. a polar covalent bond and a new molecule.B. cations and anions that can form ionic bonds.C. a covalent bond between the two.D. many hydrogen bonds.E. a nonpolar covalent bond that is difficult to break.

What prevents stars greater than about 100 times the Sun’s mass from existing?

Which is the earliest stage of a star?