Well, it depends on what type of materials you are using. You should always consult your teacher because if you are doing chemisty, for example, then if you just throw everything in a trachcan, you never what elements or substances can react together.
Until more Oxygen accumulated in the atmosphere
That is called MUTUALISM, when both organisms benefit each other.
Cortex, in plants, tissue of unspecialized cells lying between the epidermis (surface cells) and the vascular, or conducting, tissues of stems and roots. Cortical cells may contain stored carbohydrates or other substances such as resins, latex, essential oils, and tannins.
