What does alteration of generation mean?

Alteration of generation, is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages.

a symbiotic relationship with the mitochondria

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.