Chapter 7 Notes

Cell Communication


All living things are composed of cells, use the same basic chemistry, follow the same genetic code and have the same organelles. So how are living things different?


Differences arise from the way the cells are specialized and the ways in which cells associate with each other.


Unicellular: organisms made up of a single cell.

Multicellular: organisms made up of many cells.

·    Depend on cell specialization.

·    Depend on cell communication.

·    Depend on cell cooperation.


Cell specialization: cells throughout an organism can develop in different ways to perform different tasks.




·    Red blood cells are specialized to transport oxygen.

·    Nerve cells are specialized to conduct electrical impulses.

·    Muscle cells are specialized to contract pulling the fibers of the muscle past each other.


Cell Communication: The ability to communicate between cells is crucial to large multicellular organisms because it allows organisms to coordinate the activity of all their cells.

Most cell-to-cell communication involves some kind of chemical signaling, including:

·     Chemicals that are allowed to freely diffuse out of cells into the bloodstream.

·    Chemicals that are received by a cell only given cell-to-cell contact.

·     Chemicals that freely diffuse from one cell’s cytoplasm to another’s via gap junctions directly linking the cytoplasm of adjacent cells.

Cells have receptor proteins embedded in their membranes. The portion of the molecule on the exterior of the cell has a unique shape that allows it to bind only to certain special molecules, in the same way a key fits a lock.

·    In a nerve cell, the "key" is called a NEUROTRANSMITTER.

·    In other kinds of cells, the "key" is called a HORMONE.



Neurotransmitter: a chemical used by a neuron to transmit an impulse across a synapse from one nerve cell to another.


·    The synapsis is the location at which a neuron can transfer an impulse to another cell

·    Motor neurons pass their impulses to muscle cells for movement.

Hormones: A chemical that is produced in one part of an organism and affects another part of the same individual.

Example #1: Plants

      Plant hormones are chemical substances that control a plant’s patterns of growth and development, and the plant’s responses to environmental conditions.

      Charles Darwin discovered the first plant hormone auxin. Auxins are produces in the growing tip of a plant.  The stimulate cell elongation and are responsible for phototropism, gravitropism, and cell division.


Example #2: Animals

      Hormones are chemicals released in one part of the body that travel through the bloodstream and affect the activities of cells in other parts of the body. 

      Hormones do this by binding to specific chemical receptors on those cells.  Cells that have receptors are called target cells.

      If a cell does not have receptors or does not respond to the hormone, then the hormone has no effect on the cell.

      When the correct signal protein (hormones) links to the lock, it causes the part of the protein inside the cell to change shape. This change activates a signal inside the cell and generates a response from it.






Levels of Organization:

1.           Individual cells:

2.           Tissues: a group of similar cells that perform a particular function.

a)                      The four major types of tissues are muscle, epithelial, nervous and connective.

3.           Organs: a group of tissues that work together to perform a particular function.

4.           Organ systems: a group of organs that work together to perform a specific function.

5.           Organism: the entire living thing.



Organization of the body’s cells into tissues, organs and organ systems creates a division of labor that makes multicellular life possible.



How does the function of a cell relate to the proportion of organelles in that cell?