Bio1152
Chapter
39
Plant Responses to Internal and External Signals
Plants can
respond
to
stimuli
in the environment in a process called
.
Pigments such as
can sense light and regulate
responses.
The response involves signal
of the stimulus, often involving a
messenger to
the
signal.
Several
play important
roles
in regulating tropic responses.
are released by the
meristem
and at low concentrations stimulate cell
in young developing
shoots.
interact with auxin to stimulate cell division and
, and also control
dominance.
promote
elongation,
growth,
and
germination.
is produced in
response
to
. A change in the balance of
and ethylene controls leaf
abscission.
(geotropic) responses to
gravity
may be mediated by the settling of
. Roots show
gravitropism, while
stems
show
gravitropism.
responses
to
stimuli enable
to coil their
tendrils
around supports. Touch can also affect plant
morphology
by
.
Plant defenses against
include
thorns
and
spines.
Some plants even "recruit"
for
defense.
Bio1152
Chapter
40
Basic Principles of Animal Form and Function
Animals, like other organisms, have
that closely
serve
.
Evolutionary
reflects different species' independent
to a similar environmental challenge.
Animals must maintain adequate
-to-volume
ratio
to exchange materials with the
environment,
and often have highly
internal
surfaces
specialized for exchanging materials.
Animal tissues are classified into four main categories.
Epithelial
tissue
cover the outside of the body and lines organs within the body.
Connective
tissue
bind and support other tissues.
Muscle
tissue
is composed of long cells called muscle
capable of contracting in response to
signals.
Nervous
tissue
sense stimuli and transmits signals throughout the animal.
Cellular
produces the energy-containing molecules
(Adenosine TriPhosphate), which powers cellular work.
Animals maintain an internal temperature in a process
called
, which may consume a significant portion of its
energy
.
In humans,
is controlled by a region of the brain called the
hypothalamus.
Organisms exchange heat with the environment by four
processes:
,
,
, and
.
The
system
provides insulation to reduce heat exchange with the environment.
Many marine mammals and birds have
heat
exchangers
to reduce heat loss.
Animals can also thermoregulate by behaviors such as
cooling,
body
,
and
.
Some animals undergo a seasonal
triggered by a long-term decrease in
metabolism.