I really think that its the second one; Nihilist
The answer is <span> an endothermic reaction. </span>Photosynthesis is a type of endothermic reaction because it needs the energy from light (sun) to convert water and carbon dioxide into oxygen and glucose needed by other organisms.
The answer is diffusion.
The most important mechanism that enables oxygen and carbon dioxide (but as well other small molecules such as glucose, amino acids, wastes) across capillary walls is diffusion. Diffusion is a net movement of molecules through some barrier from an area of high concentration to the area of low concentration. When blood rich in oxygen reaches capillaries close to the cell, now there <span>is </span>more oxygen in the capillaries than in the cells and by diffusion, oxygen will pass capillary walls and enter the cell. Since blood in capillaries lacks in carbon dioxide, it will easily leave the cells and enter the blood. It should be taken into consideration that capillary walls may be fenestrated, continuous, and discontinuous which can affect movement through them.
