Answer:
ORGAN
Step-by-step explanation:
The liver is a very important organ in the system of multicellular organisms e.g humans. It performs various functions in the body e.g. detoxification, metabolism etc. As rightly said in this question, multicellular organisms are made up of five levels of organization.
Firstly, all living organisms are made up of CELLS, which are the basic unit of life. Cells come together to form the TISSUE. Tissues that perform similar functions come together to form the ORGAN, the organ that specifically play a similar role in the body are collectively called ORGAN SYSTEM. The various organ systems make up the whole ORGANISM.
In this five level of organization, the liver falls under the ORGAN category because it is made up of cells called Hepatocytes, which come together to form tissues. The tissues collectively make up the LIVER.