The journey of a carbon atom It must move through at least 5 different living things (plants/animals) be sure that the plant / animal would actually interact with each other in nature
Plant- the step of photosynthesis (how it goes from being CO2 to glucose
In plants/animal either how it’s stored in the plant/ animal then the plant/animal being eaten or the step of cellular respiration

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

answer: 20 percent

the fish culture has become a developing commercial practice in developing countries which is already prominent in developed countries of the world. the major fish protein demand is being supplemented in developing countries is   fishing to meet the needs of the growing population. therefore, in some developing nations, the percentage of animal protein from fish in the diet can be as high as 20 percent.