The main responsible for the delay among the atrial and
ventricular contractions is the action potential conduction velocity of the AV
node cells. If the atria and ventricles contract simultaneously, atria cannot
give any help in filling the ventricles, which is needed, especially in those
with stiff ventricles as in the elderly. Hence atria have to contract first and
then the ventricles.
I think it's option four because as far as I know, red/green color blindness is an example of a recessive, sex-linked trait (encoded on the X chromosome), which results in much more men to suffer from it than women.
Hope that helps!
1. tetrapods are ( four-limbed animals ) . examples of tetrapods include (extanct and extinct amphibians , reptiles , and mammals )
2. Tetrapods first appear in the fossil record ( 367.5 ) million years ago .
3. Charles Darwin predicted that tetrapods evolved from ( a finned organism that lived in the water) . What observation leads do that hypothesis?( they have “fleshy fins” and “lobe fins”) .
5. Fish use ( gills ) to breathe underwater .
