During which portion of the electrocardiogram do the atria contract

Answer;

- P-R interval

Explanation;

-P-R interval is the period of time from the onset of the P wave to the beginning of the QRS complex . This period normally ranges from 0.12 to 0.20 seconds in duration.

-The P-R interval represents the time between the onset of atrial depolarization and the onset of ventricular depolarization. A prolonged PR interval indicates delayed conduction of the sino-atrial, or SA, nodal impulse to the ventricles and is called first-degree AV block. A short PR interval can be seen when the AV node delay is bypassed.

thymine. in rna, thymine is replace by uracil

the answer is yes, they are born/created, then they grow to their limit then produce offspring, then die.