1. Unicellular organisms maintain homeostasis through processes like growth, responding to the environment, transforming energy, and reproduction. 2. In multicellular organisms, cells become specialized to perform different tasks and communicate with each other to maintain homeostasis, similar to how baseball team members work together. 3. Cells are organized into tissues, organs, and organ systems that allow for division of labor and maintenance of homeostasis across the entire organism.

1. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Lesson OverviewLesson Overview
7.4 Homeostasis and Cells7.4 Homeostasis and Cells

2. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
THINK ABOUT IT
The diversity of life is so great that you might have to remind yourself
that all living things are composed of cells, use the same basic
chemistry, and even contain the same kinds of organelles.
This does not mean that all living things are the same. Differences arise
from the ways in which cells are specialized and the ways in which cells
associate with one another to form multicellular organisms.

3. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
How do individual cells maintain homeostasis?

4. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
How do individual cells maintain homeostasis?
To maintain homeostasis, unicellular organisms grow, respond to the
environment, transform energy, and reproduce.

5. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
A single-celled, or unicellular, organism does everything you would expect
a living thing to do.
Just like other living things, unicellular organisms must achieve
homeostasis, relatively constant internal physical and chemical conditions.
To maintain homeostasis, unicellular organisms grow, respond to the
environment, transform energy, and reproduce.

6. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
In terms of their numbers, unicellular organisms dominate life on Earth.
Unicellular organisms include both prokaryotes and eukaryotes.
Prokaryotes, especially bacteria, are remarkably adaptable and live almost
everywhere—in the soil, on leaves, in the ocean, in the air, and even within
the human body.

7. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
Many eukaryotes also spend their lives as single cells.
Some types of algae, which contain chloroplasts and are found in oceans,
lakes, and streams around the world, are single celled.
Yeasts, or unicellular fungi, are also widespread. Yeasts play an important
role in breaking down complex nutrients, which makes them available for
other organisms.

8. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
The Cell as an Organism
Whether a prokaryote or a eukaryote, homeostasis is an issue for each
unicellular organism.
Every unicellular organism needs to find sources of energy or food, to keep
concentrations of water and minerals within certain levels, and to respond
quickly to changes in its environment.

9. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Multicellular Life
How do the cells of multicellular organisms work together to maintain
homeostasis?

10. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Multicellular Life
How do the cells of multicellular organisms work together to maintain
homeostasis?
The cells of multicellular organisms become specialized for particular tasks
and communicate with one another to maintain homeostasis.

11. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Multicellular Life
The cells of multicellular organisms are interdependent, and like the
members of a successful baseball team, they work together.
In baseball, players take on a particular role, such as pitcher, catcher,
infielder, or outfielder. Messages and signals are sent and understood by
teammates and coaches to play the game effectively.
Cells in a multicellular organism work the same way. The cells of
multicellular organisms become specialized for particular tasks and
communicate with one another in order to maintain homeostasis.

12. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Cell Specialization
The cells of multicellular organisms are specialized, with different cell
types playing different roles.
Some cells are specialized to move, others to react to the environment,
and still others to produce substances that the organism needs.
No matter what the role, each specialized cell contributes to the overall
homeostasis of the organism.

13. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Specialized Animal Cells
Particles of dust, smoke, and bacteria are part of even the cleanest air.
Specialized animal cells act like street sweepers to keep the particles
out of the lungs.
These cells are full of mitochondria, which provide a steady supply of
the ATP that powers the cilia on their upper surfaces.

14. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Specialized Plant Cells
Pollen grains are highly specialized cells that are tiny and light, with
thick cell walls to protect the cell’s contents.
Pine pollen grains have two tiny wings that enable the slightest breeze
to carry them great distances.

15. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Levels of Organization
The specialized cells of multicellular organisms are organized into
tissues, then into organs, and finally into organ systems.

16. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Levels of Organization
A tissue is a group of similar cells that performs a particular function.

17. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Levels of Organization
To perform complicated tasks, many groups of tissues work together as
an organ.
Each type of tissue performs an essential task to help the organ
function.
In most cases, an organ completes a series of specialized tasks.

18. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
A group of organs that work together to perform a specific function is
called an organ system.
For example, the stomach, pancreas, and intestines work together as
the digestive system.
Levels of Organization

19. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Levels of Organization
The organization of the body’s cells into tissues, organs, and organ
systems creates a division of labor among those cells that allows the
organism to maintain homeostasis.

20. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Cellular Communication
Cells in a large organism communicate by means of chemical signals
that are passed from one cell to another.
These cellular signals can speed up or slow down the activities of the
cells that receive them, and can cause a cell to change what it is doing.

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Cellular Communication
Some cells form connections, or cellular junctions, to neighboring cells.
Some junctions hold cells firmly together.

22. Lesson OverviewLesson Overview Homeostasis and CellsHomeostasis and Cells
Cellular Communication
Other junctions allow small molecules carrying chemical messages to
pass directly from one cell to the next.
To respond to one of these chemical signals, a cell must have a
receptor to which the signaling molecule can bind. Sometimes these
receptors are on the cell membrane, although the receptors for certain
types of signals are inside the cytoplasm.
The chemical signals sent by various types of cells can cause important
changes in cellular activity. For example, such junctions enable the cells
of the heart muscle to contract in a coordinated fashion.