(1), the aggravation of the greenhouse effect is mainly due to the excessive burning of coal, oil and natural gas in modern industrial society, which releases a large amount of carbon dioxide gas into the atmosphere after burning these fuels. Carbon dioxide is also called greenhouse gas. The greenhouse effect will lead to global warming and frequent natural disasters. Therefore, we

Advocate "low carbon life".

(2) Carbon dioxide is mainly consumed by plants for photosynthesis. As shown in the figure, process ① refers to that green plants absorb carbon dioxide in the air through photosynthesis, produce organic matter, store energy and release oxygen, which is conducive to maintaining the balance of carbon and oxygen in the atmosphere and is an automatic "air purifier".

(3) In the ecosystem, matter and energy are transferred along the food chain, so the energy flow is accompanied by the material cycle. The characteristics of energy flow are gradually decreasing along the food chain, unidirectional and non-circulating.

(4) As decomposers, saprophytic bacteria and fungi promote the material circulation in the biosphere. The main difference between them is that bacteria have not formed nuclei.

So the answer is: (1) CO2.

(2) photosynthesis?

(3) one-way flow and gradual decline

(4) No nucleus was formed.