There are three circles the innermost circle indicated the cells middle circle is the tissues and the outermost circle indicated the organs. Multicellular organisms are made up of thousands of different types of cells .Different cells constitute together forma a tissues and different tissues form a organ and different organs together form an organ system. Hence the X labeled circle denotes the tissues.
The type of food chain that exists in a pond is called the grazing food chain. In a pond, the producers are phytoplankton like some algae and submerged plants found at the edges. The consumers have included zooplankton and the last decomposers are some bacteria, fungi, etc found at the bottom of the pond.
