it has one atric and one ventrical. it is a 2 chambered heart
When relaxed, the atria expand, and then the ventricles contract.
Yes, atria contracts before the ventricles.
the difference between the ventricles and the atria is that the ventricles are thicker
2, the atria is the upper chamber of the heart. since there is alower and upper chamber in the heart, and the upper part is the atria, do the math: four chamber divided in half (two lower and two upper and 2+2=4) equals two which gives the the number of atria!
ventricles
The Atria and Ventricles are parts of the heart not the blood. The Atria is the upper chambers of the heart and the Ventricles are the lower chambers of the heart.
One atria
to force blood to the ventricles
There are no valves between the atria. The valves between the atria and ventricles close when the ventricles contract.
atria are just the receiving chambers, it is the ventricles that actually pump the blood into the pulmonary and systemic circuits
I believe this would be your heart because that is the only time ventricles and atria are brought up.
Assuming you mean the atria and ventricles by "the two heart chambers", the fact that in all species the atria are smaller than the ventricles reflects the fact that the atria receive blood from either the body or the lungs and then pump it into the larger and much stronger ventricles. One-way valves between the atria and ventricles prevent backflow of blood from the ventricles to the atria. The ventricles then pump the blood received from the atria to either the oxygenating organ (i.e. gills or lungs) or the body. The much thicker walls of the ventricles reflect the fact that much greater force is needed to pump the blood throughout the body or to the lungs than is needed to pump the blood from the atria to the ventricles.