AP Communication and Homeostasis


Every objective will NOT necessarily be covered during class time; you will be independently responsible for some of them.

  1. Give explains of how organisms use feedback loops to regulate growth and reproduction, respond to their environment, and maintain dynamic homeostasis
  2. Distinguish between negative and positive feedback
  3. Give an example of how alteration on the mechanisms of feedback can result in deleterious consequences
  4. List and explain the three stages of a signal transduction pathway
  5. On a cell signaling diagram, be able to identify the three stages of signaling, the ligand, second messengers, whether the signal was stimulatory or inhibitory, and possibly phosphorylation cascades
  6. Explain the value of signal amplification
  7. Explain which kind of cell signaling is employed by the endocrine, nervous, and immune systems
  8. Contrast the function of lipid and peptide hormones
  9. Equate hormones with ligands
  10. Explain how the motor and sensory nerves of the peripheral nervous system, and the interneurons of the central nervous system, work together to detect, process, and respond to a stimulus
  11. Identify the major regions of and relating to a neuron (cell body, axon, dendrite, myelin sheath, Schwann cells, synapse)
  12. Explain how diffusion and active transport of ions propagates an electrical signal (an action potential) along a neuron
  13. Explain the use of neurotransmitters to communicate signals to neighboring neurons
  14. Give an example of how an alteration to the events of neurotransmission can affect the organism
  15. Distinguish between specific and non-specific defenses
  16. Give examples of non-specific defenses in plants and/or animals
  17. Explain the events of cell-mediated and humoral immunity in mammals
  18. Explain why second exposure to an antigen results in a more rapid and enhanced immune response, and how vaccination employs this mechanism to confer immunity
  19. Give an example illustrating how homeostatic mechanisms reflect common ancestry, and divergence due to adaptation in different environments*

  • = self-study

Enduring Understandings

Enduring Understandings are the College Board's AP Biology course concepts that you need to know for the AP exam. Below, you'll find those Enduring Understandings relevant to this unit. Numbering and lettering matches the document linked from the main page of this website.
Every Enduring Understanding will NOT necessarily be covered during class time; you will be independently responsible for some of them.

C. Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain dynamic homeostasis.
1. Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes.
  • a. Negative feedback mechanisms maintain dynamic homeostasis for a particular condition (variable) by regulating physiological processes, returning the changing condition back to its target set point.
  • b. Positive feedback mechanisms amplify responses and processes in biological organisms. The variable initiating the response is moved farther away from the initial set-point. Amplification occurs when the stimulus is further activated which, in turn, initiates an additional response that produces system change.
  • c. Alteration in the mechanisms of feedback often results in deleterious consequences.
2. Organisms respond to changes in their external environments.
  • a. Organisms respond to changes in their environment through behavioral and physiological mechanisms.

D. Growth and dynamic homeostasis of a biological system are influenced by changes in the system’s environment.
1. All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.
  • a. Cell activities are affected by interactions with biotic and abiotic factors.
  • b. Organism activities are affected by interactions with biotic and abiotic factors.
  • c. The stability of populations, communities and ecosystems is affected by interactions with biotic and abiotic factors.
2. Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different environments.
  • a. Continuity of homeostatic mechanisms reflects common ancestry, while changes may occur in response to different environmental conditions.
  • b. Organisms have various mechanisms for obtaining nutrients and eliminating wastes.
  • c. Homeostatic control systems in species of microbes, plants and animals support common ancestry.
3. Biological systems are affected by disruptions to their dynamic homeostasis.
  • a. Disruptions at the molecular and cellular levels affect the health of the organism.
  • b. Disruptions to ecosystems impact the dynamic homeostasis or balance of the ecosystem.
4. Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis.
  • a. Plants, invertebrates and vertebrates have multiple, nonspecific immune responses.
  • b. Mammals use specific immune responses triggered by natural or artificial agents that disrupt dynamic homeostasis.
  • c. The mammalian immune system includes two types of specific responses: cell mediated and humoral.
  • d. In the cell-mediated response, cytotoxic T cells, a type of lymphocytic white blood cell, "target" intracellular pathogens when antigens are displayed on the outside of the cells.
  • e. In the humoral response, B cells, a type of lymphocytic white blood cell, produce antibodies against specific antigens.
  • f. Antigens are recognized by antibodies to the antigen.
  • g. Antibodies are proteins produced by B cells, and each antibody is specific to a particular antigen.
  • h. A second exposure to an antigen results in a more rapid and enhanced immune response.

B. Expression of genetic information involves cellular and molecular mechanisms.
2. A variety of intercellular and intracellular signal transmissions mediate gene expression.
  • b. Signal transmission within and between cells mediates cell function.

D. Cells communicate by generating, transmitting and receiving chemical signals.
1. Cell communication processes share common features that reflect a shared evolutionary history.
  • a. Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment.
  • b. Correct and appropriate signal transduction processes are generally under strong selective pressure.
  • c. In single-celled organisms, signal transduction pathways influence how the cell responds to its environment.
  • d. In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole.
2. Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling.
  • a. Cells communicate by cell-to-cell contact.
  • b. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell.
  • c. Signals released by one cell type can travel long distances to target cells of another cell type.
  • d. Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body.
3. Signal transduction pathways link signal reception with cellular response.
  • a. Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein.
  • b. Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship.
  • c. A receptor protein recognizes signal molecules, causing the receptor protein's shape to change, which initiates transduction of the signal.
  • d. Signal transduction is the process by which a signal is converted to a cellular response.
  • e. Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, with the result of appropriate responses by the cell.
  • f. Second messengers are often essential to the function of the cascade.
  • g. Many signal transduction pathways include: protein modifications (such as how methylation changes the signaling process), and phosphorylation cascades, in which a series of protein kinases add a phosphate group to the next protein in the cascade sequence.
4. Changes in signal transduction pathways can alter cellular response.
  • a. Conditions where signal transduction is blocked or defective can be deleterious, preventative or prophylactic.

E. Transmission of information results in changes within and between biological systems.
2. Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses.
  • a. The neuron is the basic structure of the nervous system that reflects function.
  • b. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator.
  • c. The structure of the neuron allows for the detection, generation, transmission and integration of signal information.
  • d. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.
  • e. Action potentials propagate impulses along neurons.
  • f. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes.
  • g. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized.
  • h. Na+/K+ pumps, powered by ATP, work to maintain membrane potential.
  • i. Transmission of information between neurons occurs across synapses.
  • j. In most animals, transmission across synapses involves chemical messengers called neurotransmitters.
  • k. Transmission of information along neurons and synapses results in a response.
  • l. The response can be stimulatory or inhibitory.

A. Interactions within biological systems lead to complex properties.
4. Organisms exhibit complex properties due to interactions between their constituent parts.
  • a. Interactions and coordination between organs provide essential biological activities.
  • b. Interactions and coordination between systems provide essential biological activities.

Textbook Reference

This is the part of your textbook that covers the material for this unit.
Ch. 5 concept 5.6, Ch 32, Ch 35, and Ch 37

Relevant Files

Here, you'll find files for this course. Copies of lecture notes will go here, as will others.


These connect to materials on other teachers' websites that you may find helpful. Generally speaking, I put links to helpful review materials - like video lectures summarizing the material - towards the top, and links to interesting extensions towards the bottom.
A Variety of Helpful Immune System Animations
A Variety of Helpful Endocrine System Animations
A Variety of Helpful Neurotransmission Animations
Even More Helpful Endocrine System Animations
Nonspecific Defenses Self-Test
Specific Defenses Self-Test
Cell mediated immunity simulation
Humoral immunity simulation
Chapter Self-Test 1
Chapter Self-Test 2
Chapter Self-Test 3
Neuron self test 1
Neuron self test 2
Neuron quiz bowl 1
Neuron quiz bowl 2
Immune System Hangman
Immune System Jeopardy
Lymphatic and Immune Java Games 1
Lymphatic and Immune Java Games 2
Blood, Lymph, and Immune System Battleship 1
Blood, Lymph and Immune System Battleship 2
Cell Signalling Scitable
Cell Communication Scientific American article
Cell Communication overview by Kimball
Cell Communication Worksheet
Cell Signaling Problem Set
Cell Signaling by University of Utah
Good Demo of Cell Signaling using food: Signal Transduction
G protein animation
2nd messengers Cool Tyrosine Kinase animation
Great Animations of Cell Signaling
Search for Emerging Viruses (TED talk)
Humorous NPR animation of viral infections
Senses Galore
Lab Grown Hearts
Tale of Two Tongues
Rat Whiskers
Fleas Knees
The March of Immune Cells
G Protein Animation 1
G Protein Animation 2
G Protein Animation 3
G Protein Animation 4
Using the Immune System as a Model for Studying Cell Communication: Toll-like Receptor 2 (TLR2) Polymorphisms, Signaling Function, and Human Disease
Emerging Infectious Diseases
Biological Bodyguard
Immune System Game
Body's Defender Immune System Game
The Immune System
Understanding the Immune Syste
Immunology - University of Arizona
Immune System - Cells Alive
Immunology - Biochem 4 Schools
Immunology Virtual Lab
How the Immune System Works
Treatment of HIV Animation
HIV Animation
Immunology Animations
Antibodies and Antigens
Vaccine Interactive
Destroy the Invaders Interactive
Immune System Topics
Pharmacology 150 from Duke University