Answer:
Circulatory and Respiratory Systems
Explanation:
Explanation: In the open water zone (or photic zone) sunlight supports photosynthetic algae and the species that feed upon them. In the deep water zone, sunlight is not available and the food web is based on detritus entering from the littoral and photic zones.
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The increase in size of the heart enables the left ventricle to stretch more and thus fill with more blood. The increase in muscle wall thickness also increases the contractility resulting in increased stroke volume at rest and during exercise, increasing blood supply to the body.
Intestinal gland secretes intestinal juice ,it contains enzymes and their role is to decompose food more and then conduct them into the large intestine or by intestinal absorption to the blood
D. radial symmetry evolved at least twice in unrelated invertebrates groups
