What were oxygen levels in the atmosphere like when the first cells evolved?

Consider the diagram below, which represents components of the biosphere. what do the two arrows in the diagram most likely represent? a. radiation b. photosynthesis c. cellular respiration d. energy conversions will give to anyone who answers quickly

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

~fourth largest plate ~includes parts of the indian and atlantic oceans ~subducts below the eurasian plate on the west side ~ the arabian and somali plates form boundaries with it what is the name of the tectonic plate described above? a) african plate b) eurasian plate c) north american plate d) indo- australian plate