Plants require gas exchange to intake carbon dioxide and make glucose via photosynthesis, and to release oxygen as a byproduct. Animal whose cells respire aerobically require oxygen to produce energy for their metabolism, while releasing carbon dioxide which is the byproduct (yes, photosynthesis and respiration are converse processes; bear in mind plants do carry out both).
The factors which affect the diffusion rate of these gases through the organism are surface area, diffusion path, moist exchange surface and concentration gradients.
A large surface area with a short diffusion path length, moist exchange surface and steep concentration gradient of gases favours the fastest rate of diffusion. More space, quicker exchange, moist environment for gases dissolving better and a steeper gradient increase the rate of diffusion.
On the other hand, a small surface area that is dry, with a long diffusion path and a shallow concentration gradient results in little to no diffusion taking…