Answer: Organ
Step-by-step explanation:
An organ can be define as a group of different tissues that combine and work together so as to perform a particular function in the body of the organism. The example of organ includes the heart, lungs, kidneys, liver and others. When two or more organs grouped together to perform a specialized function in the body like respiration, digestion and circulation, then it is called as organ system.
A kidney is a organ which forms when several types of tissues combine to work together. It performs the function of filtration of blood and excretion of nitrogenous wastes, excess salts, water and other wastes from the body.