UNIT IV: STIMULI AND
Everything that all organisms do, and everything
that happens in them…is a response to something
else (a stimulus).
Event that causes an organism Something that an organism (or
(or cells within the organism) to cells within the organism) does
do something. as a result of a stimulus.
Happens first Happens last
HOMEOSTASIS RELATED OR NOT?
A dog wags its tail…because it is happy.
A snake moves to the shade…because it is hot.
Kelly burps really loud…because she thinks it
Zach keeps bugging Mr. Lucas…because he has
to go to the bathroom.
Sarah T. puts her head down…because she is
Jack puts his head down…because he is tired.
Lauren’s blood vessels constrict in her
extremities… because she is cold.
Phelan: Chapter 19
Plants are not inanimate objects! They respond
purposefully to their environments…in more
ways than you may think!
PLANT BIOLOGICAL CLOCKS
DEFENSE AGAINST PREDATORS
Growth towards gravity
Phototropism Growth towards light
Thigmotropism Growth towards physical contact
Heliotropism Growth towards sunlight
Hydrotropism Growth towards water
Growth towards in response to
Chemotropism Growth in response to chemicals
WHAT TROPISMS ARE THESE?
Tropism clip 1
Tropism clip 2
Tropism clip 3
Tropism clip 4
PLANT TROPISM CLIPS
Some random tropism clips
Spinning vine thigmotropism
PLANTS ARE INTELLIGENT ORGANISMS!
SOME OTHER NOTABLE PLANT RESPONSES
Stimulus Response 1 detail or example
Bunches of fruit ripen faster than
Ethylene gas Fruit ripening
Banana in a paper bag will ripen
faster (due to the enclosed space).
Light Sugar production Photosynthesis
Root/stem networks and chemical
Danger communicate with
Trees become dormant in the winter
because (compared to spring and
Shorter days summer) it does not energetically
shed their leaves.
make sense. i.e. continuing to grow
would be inefficient.
Water Seed As illustrated by our ongoing
uptake germination plant tropism lab!
Phelan: Chapter 26
Organisms have multiple ways of responding to
pathogens and disease.
TYPES OF PATHOGENS
HUMAN IMMUNE RESPONSE
Natural immune responses
White blood cells (WBC)
Living cellular organisms
Reproduce on their own.
They are parasites – (an organism that benefits at the
expense of another orgainsm).
Non living material?
Proteins and DNA fragments.
Must “invade” cells in the body in order to reproduce.
Protein markers on both viruses and bacteria.
NATURAL IMMUNE DEFENSES
Physically keeps out pathogens of various kinds.
Skin, mucous, stomach acid, cilia, saliva, etc.
White blood cells (WBC)
Some are non-specific defenses – engulf anything
Some are specific defenses – attack specific pathogens
Both types are not always numerous, but they increase in
the blood stream when exposed to pathogens.
Why are they not always numerous?
Produced by immune system to recognize specific
Antigen recognition – the pathogen “fingerprints”
Antibodies are built up every time they are exposed to the
antigen to fight it off next time.
ANTIGENS AND ANTIBODIES
SPECIFIC IMMUNE RESPONSE
Treat bacterial infections
Chemicals that kill the bacteria
Cannot treat viruses because they are not
really living to begin with.
Treat viral infections
Weak version of a virus (with antigens, or
“fingerprints”, of course).
Antibodies build up for this specific antigen.
HUMAN RESPONSE MECHANISMS
Intricate organs and body systems are the means
by which humans (and many advanced animals)
detect stimuli and elicit responses, with the
addition of a middle step – processing.
TYPES OF STIMULI
Light Heat (or loss of heat)
Physical contact Imbalance
Liquids Movement of your own
MAIN SENSORY RECEPTORS
Detect light waves (high frequency radio waves)
Sense of sight
Detect physical pressure or distortion
Sense of hearing – pressure waves.
Sense of touch – all other typical contact.
Sense of smell – gaseous chemicals
Sense of taste – liquid and solid chemicals
Detect heat gain or loss.
JUST FOR FUN!!
Vision (sight) Light (specific range of electromagnetic waves)
Tactition (touch) Physical pressure
Audition Ultra sensitive perception of high frequency pressure waves
Gustation (taste) Solid and liquid chemicals
Olfaction (smell) Gaseous chemicals (fumes)
Thermoception Heat gain or loss
Proprioception Orientation of your own body parts
Magnetoception Direction ???
2 EYES & 2 EARS!
Help you locate the precise origin of the stimulus.
DIVISIONS OF THE NERVOUS
Central nervous system
Peripheral nervous system
Sensory nervous system
Motor nervous system
Somatic nervous system
Autonomic nervous system
Sympathetic nervous system
Parasympathetic nervous system
CENTRAL NERVOUS SYSTEM
Middle step - processing
Cerebrum (memory, conscious thought, sensory processing,
Cerebellum (muscle coordination)
Brainstem (primitive functions, heartbeat, breathing, etc.)
Carries message to and from brain
PERIPHERAL NERVOUS SYSTEM
The input and the output
Sensory NS – detect stimuli (input)
Motor NS – invoke responses (output)
Somatic NS – voluntary response
Autonomic NS – involuntary response
Sympathetic NS – tension (fight or flight)
Parasympathetic NS – relaxation (rest and digest)
NERVE IMPULSE (AKA ACTION
FROM STIMULUS TO RESPONSE
Instead of quick response of nervous system.
Glands and hormones (secreted into the bloodstream)
Stimulus invokes a response that promotes the opposite.
Homeostasis mechanisms – keeps a stable, normal state
Stimulus invokes a response that promotes more of the
When a change from a normal state is necessary.
WHAT TYPE OF FEEDBACK ARE THESE?
For each scenario:
Describe which type of feedback (positive or negative) is at
Describe how you know this is the case.
People are booing you for your poor level of play in a
tennis match, causing you to play even more poorly.
Traffic light timing patterns change throughout a 24-
hour day in order to accommodate the changing
traffic tendencies on specific roads.
When blood platelets clot to form a scab over a
wound, this stimulates the production and activation
of more platelets.
Come up with your own example of a positive
Describe the stimulus and the response.
Describe how the stimulus and promotes a change from
what is normal.
Come up with your own example of a negative
Describe the stimulus and the response.
Describe how the stimulus and promotes maintaining some
sort of stability.
Finish your “Sustained Response: The Endocrine
System” assignment if you haven’t already. – Be able
to associate each hormone with + or – feedback.