The valve prevents backward flow of blood into the left ventricle.

What are chlorofluorocarbons made of

Which statement is true about the cell theory? a) it is well-supported by evidence. b) it is unchangeable and permanent.

Which of the following statements about c4 carbon fixation is not true? a c4 carbon fixation is an adaptation for plants exposed to high light intensityb. c4 carbon fixation occurs in more plants than c3 carbon fixation. c c4 carbon fixation is more common in areas of high temperatures than c3 carbon fixation. d. c4 carbon fixation occurs in the inner cells of a leaf rather than the entire leaf.