Homeostasis and Cells
Chapter 7.4
Cell as an Organism
A single-celled, or unicellular, organism does everything
you would expect a living thing to do.
Must achieve homeostasis (relatively constant internal
physical and chemical conditions)
To maintain homeostasis, unicellular organisms:
Grow
Respond to the environment
Transform energy
Reproduce
Cells as an Organism
Unicellular organisms are most numerous on earth
Prokaryotes
bacteria
remarkably adaptable
live almost everywhere (soil, ocean, in the air, within human body)
Eukaryotes
Many also are single cells
Algae
contain chloroplasts
found in oceans, lakes, and streams
Yeasts
unicellular fungi
widespread
Break down complex nutrients making them available for other organisms
The Cell as an Organism
Homeostasis is an issue for unicellular organisms.
Need to:
find sources of energy or food
keep concentrations of water and minerals within certain levels
respond quickly to changes in its environment
Multicellular Life
Cells of multicellular organisms are:
Interdependent and work together
Specialized for particular tasks
different cell types playing different roles
specialized to move. react to the environment, produce substances that the organism needs, etc.
each specialized cell contributes to the overall homeostasis of the organism
Communicate with one another in order to maintain homeostasis
Specialized 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.
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.
Levels of Organization
The specialized cells of multicellular organisms are
organized into tissues, then into organs, and finally into
organ systems.
Levels of Organization
A tissue is a group of similar cells that performs a particular function.
To perform complicated tasks, 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.
A group of organs that work together to perform a specific function is called an
organ system.
For example, the stomach, pancreas, & intestines work together as the digestive
system.
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.
Cellular Communication
Cells in a large organism communicate by means of chemical signals that are
passed from one cell to another.
Chemical signals can:
speed up or slow down the activities of the cells that receive them
cause a cell to change what it is doing
Some cells form connections, or cellular junctions, to neighboring cells.
Some junctions hold cells firmly together.
Others allow small molecules carrying chemical messages to pass directly from
one cell to the next.
To respond to one of these chemical signals
cell must have receptor the signaling molecule can bind to
Receptors are on cell membrane or inside cytoplasm
Example: such junctions allow cells of the heart muscle to contract in a coordinated
fashion