Transcript Unit V Anatomy and Physiology of Plants, Animals, and Humans

Unit V
Anatomy and Physiology of
Plants, Animals, and Humans
Learning Goal 4
Analyze response and defense
systems in plants, animals, and
humans.
Plant Responses
• Phototropism
Growth responses to a
directional light source.
Indoleacetic acid (IAA) is the
name of the molecule in auxins
that cause plant cells to
elongate.
IAA moves into cells on the
shaded side of a stem causing
bending as the cells on the
shaded side elongate more
rapidly that cells on the
illuminated layer
Main stimulus is light of blue
wavelengths.
• Gravitropism
After a seed germinates, the
primary root curves down and
the shoot curves up.
Thought to a be a result of
statoliths, which are modified
plastids called amyloplasts that
contain starch grains.
They collect in cells in
response to the pull of gravity.
• Thigmotropism
Growth response to
contact with a solid
object.
Cells on the contact side
shorten while cells on the
other side of the stem
rapidly elongate.
Thought to be due to the
action of auxin and
another plant chemical
called ethylene.
• Thigmomorphogenesis
Stems stop elongating
when subjected to
mechanical stresses such
as wind, rain, grazing,
and farm machinery
Results in plants grown
outdoors being shorter
and sturdier than the
same species grown
inside.
• Nastic Movements
Reversible response to
nondirectional stimuli
such as mechanical
pressure or humidity.
Occurs in plants like the
Venus Fly Trap, and the
Mimosa (sensitive plant)
Plants alter the turgor
pressure in various cells
to cause movement.
• Circadian Rhythms
Cyclic activities
controlled by internal
mechanisms.
Ensures that plants
do things like flower
at the same time if
they are members of
the same species.
• Photoperiodism
Plants respond to
changes in the relative
lengths of light and dark
periods in their
environment during each
24-hour period.
In this way, plants make
seasonal adjustments to
their patterns of growth,
development, and
reproduction.
• Dormancy
Plants stop growing in
response to short days
and long nights.
Vegetative part die off or
fall off and plants live off
of stored nutrients until
day length increases
enough to stimulate new
growth and
photosynthesis.
Other cues for dormancy
are cold nights, dry soil,
and low nitrogen.
Plant Defenses
• Response to Wounds
When a plant is wounded to
insect attack or some other
source it releases defensive
chemicals such as salicylic
acid (SA).
SA appears to set off as series
of events that eventually leads
to the production of protease
inhibitors which disrupt an
insect’s capacity to digest
proteins in the plant tissue.
The resulting protein
deficiency hampers the
insect’s growth and
functioning.
• Defense Against Pathogens
and Herbivores
Plants release chemicals
called phytoalexins in
response to attack by bacteria
and fungi. These function as
antibiotics to kill the
pathogens.
Noxious chemicals such as
caffeine, cocaine, strychnine,
and tannins are chemicals
released to protect against
feeding herbivores.
Response Systems in Animals
• Invertebrate Nervous
Systems
Nerve Net
Simplest type of nervous
system consisting of
loose meshes of neurons
organized within radial
symmetrical animals.
When part of the animal
is stimulated, nerve
impulses are conducted
in all directions.
Found in cnidarians, and
echinoderms.
• Cephalized Nervous Systems
The bilateral invertebrates
have cephalized nervous
systems.
They show a definite head
region which contains clusters
of nerves that act as a brain.
One or more nerve cords
(bundles) extend from the
central ganglia to the rest of
the body.
Found in flatworms,
arthropods, and mollusks.
• Vertebrates
Specialized Nervous Systems
Consist of a brain and spinal
cord.
The head contains specialized
sensory organs connected to
the brain by nerves.
The NS of a vertebrate embryo
begins as a hollow neural tube,
the anterior end of which
develops into the brain and
rest into the spinal cord.
Neurons
• Organization
Afferent neurons (sensory
neurons) transmit stimuli
collected by their
receptors.
Interneurons integrate the
information to formulate
an appropriate response.
Efferent neurons carry
the signals indicating a
response to effectors
which can be either
muscles or glands.
• Neuron Structure
Cell Body contains the
nucleus and majority of
cell organelles.
Dendrites (projections of
the cell body), receive
signals and transmit them
toward the cell body.
Axons conduct signals
away from the cell body
to another neuron or an
effector. The axon has
branches at its tip called
axon terminals.
• Glial Cells
Nonneuronal cells that provide
nutrition and support to
neurons.
Astrocytes cover surfaces of
blood vessels and provide
physical support to neurons
and help maintain the
concentrations of ions in the
interstitial fluid surrounding
them.
Oligodendrocytes and
Schwann cells wrap around
axons to form myelin sheaths.
• Myelin Sheaths
Have a high lipid content
because of the many layers of
plasma membranes of the
myelin-forming cells.
They act as chemical
insulators.
Gaps between each Schwann
cell on the axon, called nodes
of Ranvier expose the axon
membrane directly to
extracellular fluid, speeding the
rate of electrical impulses.
• Signal Conduction
Animals cells have a
membrane potential
across the plasma
membrane due to the
uneven distribution of
positive sodium (Na+) and
potassium (K+) ions
inside and outside the
cell.
•
•
Resting Potential
The membrane of a neuron that is
not being stimulated exhibits
resting potential and is said to be
polarized, with more positive
charges on the outside.
Action Potential
Occurs when a stimulus causes
positive charges from outside the
neuron to flow inward, making the
cytoplasmic side of the membrane
less negative, thus depolarizing it.
Sodium ions flow in through gated
protein channels, then potassium
ions flow out. This occurs along
the axon membrane, propagating
the impulse until resting potential
is restored.
• Conduction Across Synapses
Synapses
Neurons communicate via
synapses, tiny spaces
between the axon of a
presynaptic cell and the cell
body or dendrite of a
postsynaptic cell.
Neurotransmitters
Chemicals released by the
axon terminal that move
across the synapse that allow
neurons to communicate and
pass along the nerve impulse.
Defenses Against Disease in
Animals
• Three Lines of Defense
Epithelial Surfaces
Forms a barrier against
invading pathogens.
Innate Immunity
Cellular response to
pathogens that you are
born with.
Acquired Immunity
Triggered by specific
pathogens that invade the
body.
• Nonspecific Defenses
Antimicrobial Peptides
Attack the plasma
membranes of
pathogenic cells.
Inflamation
A tissue’s rapid response
to injury that dialates
blood vessels allowing
macrophages and
neutrophils to come to the
area to protect against
invading cells.
•
Specific Defenses
Triggered by foreign molecules:
1. Lymphocytes encounter and
recognize an antigen
(proteins on the membranes of
foreign cells).
2. Lymphocytes bind to antigens
and proliferate.
3. Lymphocyte clones clear
antigens from the body.
4. Memory cells circulate in the
blood ready to rapidly
respond next time.