Final answer:
Cells in body organs are generally within 100 µm of a blood capillary to decrease mean diffusion time. This proximity ensures a short path for efficient nutrient and waste exchange, which is critical for cellular health and function.
Step-by-step explanation:
The cells in body organs are generally within 100 micrometers (100 µm) of a blood capillary to decrease mean diffusion time for substances. Diffusion is a key mechanism by which nutrients and waste products are exchanged between blood and tissue, and this process is faster over shorter distances. Given that larger organisms cannot rely solely on net diffusion due to the increased distances involved, circulatory systems have developed to facilitate efficient transport. Cells being close to capillaries ensures that there is a short diffusion path for oxygen, nutrients, and waste products to travel, maintaining cell survival and function.
The distance that a substance must travel greatly affects the diffusion rate; the greater the distance, the slower the rate. This necessity for a short diffusion path places a limitation on cell size and organizes the cellular environment for optimal exchange conditions. Therefore, being near to blood capillaries allows for efficient and timely diffusion, critical for cell health and activity.