1. The Mackay School
Fifth 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 Organisms
They 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 Organisms
Multicellular 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?