Sponges, members of the Porifera, might be the simplest multicellular
animals on Earth. They do not have any tissues, organs, or organ systems. In
order for sponges to have evolved, what MUST have happened first?
the organization of cells into groups
symbiotic relationships among various cells
the evolution of cells with nuclei and organelles
the development of the cell wall as a protective mechanism
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Ces as a System

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

d) center of the mid-ocean ridge

give brainleysest

sinserly,

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