Cells can get rid of carbon dioxide because
A. capillaries contain many mitochondria for active transport of CO2 molecules
B. the enzyme carbonic anhydrase helps keep a low CO2 concentration in blood
C. hormones force CO2 into the blood
D. macrophages of the immune system also function to transport excess CO2
The correct answer is B. the enzyme carbonic anhydrase helps keep a low CO2 concentration in blood.
To understand why the enzyme carbonic anhydrase helps cells get rid of carbon dioxide, we need to break down the process. When cells produce energy through metabolism, one of the byproducts is carbon dioxide (CO2). Accumulation of CO2 is toxic to cells. Therefore, cells need a way to remove CO2 from their immediate surroundings.
In the human body, cells are in close proximity to blood vessels called capillaries. Capillaries allow for exchange of gases, including oxygen and carbon dioxide, between the cells and the bloodstream. Carbon dioxide moves from the cells into the blood.
Carbonic anhydrase is an enzyme found in red blood cells that plays an important role in this process. It catalyzes the conversion of carbon dioxide and water into a molecule called carbonic acid. This reaction occurs within red blood cells and is reversible. When carbonic acid dissociates, it forms bicarbonate ions (HCO3-) and hydrogen ions (H+).
The bicarbonate ions are transported out of the red blood cells into the blood plasma. This exchange is facilitated by special transporters in the cell membrane. As bicarbonate ions leave the red blood cells, chloride ions (Cl-) enter to maintain charge balance. This exchange is known as the chloride shift.
By converting carbon dioxide into bicarbonate ions, the enzyme carbonic anhydrase helps to maintain a low concentration of carbon dioxide in the blood. This allows for the continuous diffusion of carbon dioxide from the surrounding cells into the bloodstream. Eventually, as blood travels to the lungs, the reverse process occurs. Carbon dioxide is released from the blood into the alveoli of the lungs and exhaled.
Therefore, option B is the correct answer because the enzyme carbonic anhydrase plays a crucial role in converting carbon dioxide into bicarbonate ions to maintain the concentration gradient necessary for efficient removal of carbon dioxide from cells.