No, although there are several theories with increasing evidence, there is still no way to know for sure how it occurred. The great mystery of the beginning of universe is way too vast and vague. Theories can only be proven by presenting a solid proof, but great creations such as universe itself doesn't have to be solved. Various possibilities must have happened or there must be a one conclusion leading to its existence; but moreover, it is not our problem to solve. The confirmation of beginning of its existence will only feed the curiosity of humans.
Answer:
I think it is a pure substance, not 100% though.
<span>Epidermal cells of a plant leaf have a similar function to the skin system of a human. Their common function is protection. The epidermal cells provide coverage of the plant parts and protect it from damage. Also, the epidermal layer of leaves allow the exchange of water through transpiration and thus, maintains the temperature of the plant body. The same does the human skin system.</span>
<span>Stomata of the plants are structures similar to the function of the human respiratory system (lungs). <span>Plants use stomata (tiny “holes”) which let the carbon dioxide and oxygen in and out in a process called diffusion.</span></span>