(1) The food chain refers to the relationship between consumers and producers. In this ecosystem, snakes occupy two food chains: green plants → cicadas → mantis → yellowbird → snakes; Green plants → cicada → yellowbird → snake, and the longest food chain is: green plants → cicada → mantis → yellowbird → snake. (2) The matter and energy in the ecosystem flow along the food chain and food web, and the yellowbird preys on mantis. If all the mantises in the food chain are removed, the number of yellowbirds will decrease first because of the disappearance of mantis. (3) Decomposition of ecosystem. The role of decomposers in the ecosystem is to decompose the remains of animals and plants, so that the organic matter in the ecosystem can be transformed into inorganic substances such as carbon dioxide, water and inorganic salts. Let the plants be reused. Therefore, such creatures play an important role in the energy flow and material circulation of ecosystems. The fundamental difference between bacteria and animal and plant cells in the picture is that bacterial cells have no real nucleus. (4) Photosynthesis of green plants is a process of synthesizing organic matter from carbon dioxide and water by using the light energy in chloroplasts, releasing oxygen, and at the same time converting the light energy into chemical energy and storing it in the synthesized organic matter. The formula of photosynthesis is as follows: carbon dioxide+water, light, chloroplast, organic matter (energy storage)+oxygen. It can be seen that the raw materials of photosynthesis are carbon dioxide and water, and the products are organic matter and oxygen. The conditions are light and the place is chloroplast. So the answer is: (1) green plant → cicada → mantis → yellowbird → snake; (2) reduce; Increase; Automatic regulation (3) bacterial cells have no real nucleus; (4) water; optical energy