Structure and Function of
Multi-celled Organisms
Single-Celled vs. Multicellular Organisms
Learning Target
The student will distinguish between single cell and
multicellular organisms.
Single-Celled and Multicellular
Organisms
one cell.
Some organisms are made up of only ________
Multicellular organisms are made up of ______
many
cells. Often, cells in multicellular organisms are
specialized to perform one task. These specialized
cells must work together to keep the organisms
healthy.
What does specialized mean?
Single-Celled Organisms
Single-celled organisms are organisms that are made
up of only one cell. Examples include bacteria,
paramecia, and amoebas. Even though single-celled
organisms are simple life forms, they still perform
life functions. They move, find food, grow, and
reproduce.
Single-Celled Organisms
Look at the amoebas below.
Single-Celled Movement
Amoebas move in the direction that their cytoplasm
flows. These single-celled organisms eat by
surrounding a food particle with streams of
cytoplasm and then bringing the food into the cell.
Some single-celled organisms have hair-like
structures called cilia that help them move and feed.
Others have tail-like structures called flagella that
propel them forward.
Food production and waste
Other single-celled organisms have chlorophyll.
Just like the chlorophyll inside plants, this
chlorophyll allows the organism to transform the
sun's energy into food for the cell. Single-celled
organisms remove wastes by moving the wastes to
the outside of their cell membranes.
Single-Celled Organisms
Reproduction
Single-celled organisms also reproduce. Because
they are made up of one cell, they reproduce by cell
division. This kind of reproduction creates a new
organism that is an exact copy of the parent.
Multicellular Organisms
Most of the plants and animals you see around you
are multicellular organisms. This is because singlecelled organisms are usually very small and you
need a microscope to see them. Dogs, cats, people,
sunflowers, insects, sea stars, and worms are all
made up of millions and millions of cells.
Multicellular Cell Description
Multicellular organisms are more complex than
single-celled organisms, which are simple. Because
of this, cells inside a multicellular organism perform
specialized tasks. These cells all work together to
keep the multicellular organism healthy.
Multicellular Organisms
For example, the cells that make up the heart work
together to move oxygen and blood to all the other
body tissues. A tissue is a group of cells that work
together to perform a particular job.
Multicellular Organisms
Heart tissue along with other tissues all work
together in the organ called the heart. An organ is
two or more tissues working together to perform
a job. The heart is one part of the circulatory
system. The function of the circulatory system is
to move oxygen and nutrients throughout an
organism. The circulatory system is one example
of an organ system. Multicellular organisms
often have several organ systems.
Multicellular Organisms
Movement

Multi-celled organisms can move on multiple
ways. Animals can walk, crawl, slither, fly and
swim. Plants movement by growing tall and
also opening and closing its flowers.
Multi-celled Reproduction

Multi-cellular organisms can reproduce as
well. Each unique cell goes through cell
division (replication and reproduction)and is
used for specific functions.
1. What is a group of cells that
work together to perform a
particular job called?
a. a multicellular organism
b. a single-celled organism
c. an organ
d. a tissue
1. What is a group of cells that
work together to perform a
particular job called?
d. a tissue
2. Which of the following
contains the most cells?
a. a tissue
b. an organ
c. an organ system
d. a single-celled organism
2. Which of the following
contains the most cells?
c. an organ system
3. Which of the following is not
a life function of a single-celled
amoeba?
a. removing wastes from the cell
b. moving
c. collecting food
d. making food from the sun's energy
3. Which of the following is not
a life function of a single-celled
amoeba?
d. making food from the sun's energy