Question

What is the difference between unicellular and multi-cellular organisms in organisation of their cells?

Answer 1

In unicellular organisms, the body is made up of a single cell which can undergo cell division to regenerate. The cell has different organelles to carry out different functions. Being a single cell it is exposed to the environment on all sides. There is no division of labor. The cell body cannot attain large size due to a limited surface to volume ratio and injury to the cell can cause the death of an organism.

In multicellular organisms, the body is made up of numerous cells. These cells are specialized to perform different functions. Cells are organized in tissues which are a group of cells that have a similar function within an organism. Different tissues come together to form an organ to perform a specific function. The more complex organisms such as mammals, trees or flowers have organ system. An organ system is a group of organs that act together to carry out complex, related function, with each organ focusing on a part of a task. Thus, the division of labour is seen in multicellular organisms. For eg. human digestive system, in which food is chewed in the mouth, crushed in stomach, broken down into macromolecules by enzymes in pancreatic and gastric juices and absorbed by small intestines.