Answer:
Theory: <u>A theory is a carefully thought-out explanation for observations of the natural world that has been constructed using the scientific method, and which brings together many facts and hypotheses.</u>
Answer: Hemoglobin is produced in bone marrow by erythrocytes and is circulated with them until their destruction. It is then broken down in the spleen, and some of its components, such as iron, are recycled to the bone marrow.
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In the heart, the valves are located between atria and ventricles and between ventricles and arteries (option D).
<h3>What are valves in the heart?</h3>
Valves are membranous partitions which permit the passage of the contents of a vessel or cavity in one direction, but stop or control the flow in the opposite direction.
Valves in the heart enforce a one-way blood flow through the heart and separate atria from ventricles, and ventricles from the large arteries that leave them.
The four valves in the heart and their location is as follows:
- tricuspid valve: located between the right atrium and the right ventricle
- pulmonary valve: located between the right ventricle and the pulmonary artery
- mitral valve: located between the left atrium and the left ventricle
- aortic valve: located between the left ventricle and the aorta.
The valves between the atria and ventricles are called atrioventricular valves or cuspid valves while those at the bases of the large vessels leaving the ventricles are called semilunar valves.
Therefore, it can be said that the valves of the heart are located between atria and ventricles and between ventricles and arteries.
Learn more about valves of the heart at: brainly.com/question/28266922
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They are ectotherms.
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