Answer:
Once the oxygen diffuses across the alveoli, it enters the bloodstream and is transported to the tissues where it is unloaded, and carbon dioxide diffuses out of the blood and into the alveoli to be expelled from the body. Although gas exchange is a continuous process, the oxygen and carbon dioxide are transported by different mechanisms.
Transport of Oxygen in the Blood
Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself. Most oxygen—98.5 percent—is bound to a protein called hemoglobin and carried to the tissues.
Hemoglobin
Hemoglobin, or Hb, is a protein molecule found in red blood cells (erythrocytes) made of four subunits: two alpha subunits and two beta subunits (Figure 20.19). Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules. Molecules with more oxygen bound to the heme groups are brighter red. As a result, oxygenated arterial blood where the Hb is carrying four oxygen molecules is bright red, while venous blood that is deoxygenated is darker red.
Answer:
"Scientists are not close to knowing the exact processes that took place on the earth which led to the origins of life. They may never know the exact answer because the evidence for this very primitive life has probably been destroyed by the more efficient life which evolved from it.
Explanation:
Answer:They hypothesized that the transitional fossils were in sedimentary rocks older than 365 million years ago, when the first tetrapods appear in the fossil record.
Explanation:
Answer:
Coma
Explanation:
Such a cloud, termed a coma, is a distinguishing feature of comets and consists of gases and entrained dust escaping from the cometary nucleus when sunlight causes its ices to sublimate.
Without a nucleus, multicellular life forms, called eukaryotes, would not exist. According to the Molecular Expressions , the nucleus acts as the administrative center and information processor for the cell by storing its genetic material and coordinating its activities.
