The Mackay SchoolFifth Grade 2014

FROM A CELL TO AN ORGANISM

All living things on Earth are made of cells. Cells are the smallest unit of life. They eat, move, reproduce and expel waste substances.There are some cells able to have an independent life; they are called unicellular organisms because a single cell forms them. And, there are multicellular organisms that are made of two or more cells.

Unicellular OrganismsThey are formed by a single cell and do vital functions. The majority of organisms on Earth are unicellular. Among them we find bacteria, protozoa such as the paramecium and the amoeba, and certain fungi like yeast.Unicellular organisms interact with the environment using their membrane to protect them and to exchange substances with the environment.

Bacterial cell structure

Multicellular OrganismsMulticellular organisms can have from 2 to millions of cells. All of these cells are able to reproduce and absorb nutrients from the environment. This job is carried out in a very organized way so the organism can perform its vital functions.There are different types of cells and according to its type they perform specific functions. For example, red blood cells are in charge of carrying oxygen to the other cells and white blood cells are in charge of fighting infections. This is why we can say that they are specialized.Multicellular organisms begin their life as a single cell, which after multiplying many times makes the organism to be fully organized.All plants and animals are multicellular

Lions are an example of multicellular organisms. What other multicellular organism can you see in the picture?