Answer:
Humans are one of the important contributor for CO2 (Carbon Dioxide) Production. In our body, carbon dioxide is formed intracellularly as a byproduct of metabolism. Carbon Dioxide is transported in the bloodstream to the lungs where it is ultimately removed from the body through exhalation. This process is called Respiration generally Cellular Respiration.
And in Photosynthesis, the exhaled CO2 from human body ( or any other living organisms) are being used as the reactant (with the H2O) then produces Glucose (energy source of plants) and Oxygen (living organisms need to survive). This process takes place in chloroplasts, which contain the chlorophyll.
To sum up, carbon cycle is the process in which carbon travels from the atmosphere into organisms and the Earth and then back into the atmosphere. Plants take carbon dioxide from the air and use it to make food. Animals then eat the food and carbon is stored in their bodies or released as CO2 through respiration.
Therefore, without living organisms there are no carbon dioxide, oxygen and other gases will be produce same as without non-living organisms like gases, the sun, water and etc. human race and other organisms can't survive. And there will be no ecosystem.