Transcript Plant Responses and Adaptations

Plant Responses and Adaptations
Chapter 25: Biology II
Plant Hormones
• Chemical substances that control:
– A plant’s patterns of growth and
development
– A plant’s responses to
environmental conditions
• Target Cell: cell affected by a
particular hormone
Auxins
• Stimulate cell elongation
• Produced in the apical meristem
• Transported downward into the rest of the plant
• Responsible for: phototropism and gravitropism
Auxins: Phototropism
•
Tendency of
plants to grow
toward a source
of light
Auxins: Gravitropism
• Tendency of a plant
to grow in a direction
in response to the
force of gravity
Auxins
• Lateral Bud: meristematic area
on the side of a stem that gives
rise to side branches
• Apical Dominance: phenomenon
in which the closer a bud is to the
stem’s tip, the more its growth is
inhibited
• Herbicide: auxin-like weed
killers; compound that is toxic to
plants
Cytokinins
• Plant hormones that are
produced in growing roots and in
developing fruits and seeds
• Stimulate cell division and the
growth of lateral buds
• Cause dormant seeds to sprout
Gibberellins
• Growth-promoting substance
produced by plants
• Causes dramatic increases in size,
particularly in stems and fruits
• Produced by seed tissue
• Responsible for the rapid early
growth of many plants
Ethylene
• Plant hormone that
stimulates fruits to ripen
• Released in small amounts
as a response to auxins
• Commercial products can use this to control the
ripening process; treated with synthetic ethylene
Tropisms
• The response of plants to environmental stimuli
• Gravitropism
• Phototropism
• Thigmotropism
Thigmotropism
• Response of plants to touch
• Examples:
– A plant that is touched regularly
may be stunted in its growthsometimes quite dramatically
– Vines and climbing plants-tips
wrap around objects
Rapid Responses
• Some responses do not involve growth; they are
not tropisms
• Examples:
• Mimosa pudica: the “sensitive plant”
• The Venus flytrap
Photoperiodism
• Responsible for the timing of seasonal
activities such as flowering and growth
• Phytochrome: plant pigment responsible for
photoperiodism
Short-Day Plants
• Plants that flower
when daylight is
short
• Also called “longnight plants”
Long-Day Plants
• Plants that
flower when
days are long
• Also called
“short-night
plants”
Winter Dormancy
• Period of time during which a plant embryo is
alive but not growing
• As cold weather approaches, deciduous plants:
– Turn off photosynthetic pathways
– Transport materials from leaves to roots
– Seal leaves off from the rest of the plant
Abscission Layer
• Layer of cells at the petiole that seals off a
leaf from the vascular system
Aquatic Plants
• To take in sufficient
oxygen, many
aquatic plants have
tissues with large airfilled spaces through
which oxygen can
diffuse
Salt-Tolerant Plants
• Leaves have specialized
cells that pump salt out of
the plant tissues and onto
the leaf surfaces
• Example: mangroves
Desert Plants
• Also called: xerophytes
• Extensive roots
• Reduced leaves
• Thick stems that can store water
Nutritional Specialists
• Plants that have specialized features
for obtaining nutrients
• Carnivorous plants: obtain nutrients
from digested prey
• Parasites: plants that extract water
and nutrients directly from a host
plant
• The dodder plant Cuscuta
Epiphytes
• Plants that grow directly
on the bodies of other
plants
• Gather their own moisture
and produce their own
food, unlike parasitic
plants
• Spanish moss-not a moss,
but a bromeliad!
Chemical Defenses
• Many plants defend themselves against
insect attack by manufacturing compounds
that have powerful effects on animals