I'm pretty sure it is the Krebs cycle
Attached is the image to which model 1 refers to. I found the exercise on the internet.
The phospho part of the the structure is the one with the phosphate group (

³⁻): one atom of phosphorous (P) with four atoms of oxygen (O) attached. It has various functions depending on which biological molecule is present.
Life and death are complex things. Life is the existence of something and death is the end. They go hand in hand. Without one you cannot have the other. To live means to die and to die means you have lived.
Hopes this helps. Add a comment if not and I will try to assist.
Enzymes act as a catalyst in digestion process. It fastens the reaction and lowers it time. Like, if it will absent, digestion process which normally takes 1 hour, will take approx. few weeks. So, enzymes are so important.
B ecosystem. They include abiotic factors and biotic factors.