Final answer:
During tissue gas exchange, the PCO₂ in the tissue cell is 45 mm Hg, higher than in blood, allowing carbon dioxide to diffuse into systemic capillaries.
Step-by-step explanation:
The PCO₂ in the tissue cell during tissue gas exchange is 45 mm Hg. This is due to the pressure gradient created by cellular respiration, where carbon dioxide is produced within the tissue cells as a waste product.
The partial pressure of carbon dioxide (PCO₂) is higher in the tissue cells than in the blood, promoting diffusion of carbon dioxide from the cells into the systemic capillaries. Subsequently, the carbon dioxide is carried away in the blood and eventually exhaled through the lungs during external respiration.