Download Ecology:

Plant Form and Function:
How Do Plants Live in the World?
What Important Events Define
the History of Plant Life ?
• Photosynthesis changed the world
• Eukaryotic cells and multicellularity
enabled plants to diversify
• Plants moved from water to land
• Vascular plants dominate the terrain
Important Events in Plant Evolution
Photosynthesis Changed the
World
• Plants use chlorophyll
to capture the energy
of sunlight for use in
photosynthesis
• Oxygen is the byproduct and has
accumulated over the
past 2.5 billion years.
Evolution of Eukaryotic Cells
• Occurred before plants became
multicellular.
• Evolution of eukaryotic cells due to
endosymbiosis.
– Evidence to support the theory: Mitochondria
and chloroplasts.
– Many examples of living prokaryotes that
share features of mitochondria and
chloroplasts found in eukaryotes.
Evolution of Multicellular Cells
• Advantages of multicellularity
– Cellular organisms have opportunity for
cellular specialization.
– Decreased vulnerability to changes in
temperature, humidity, and nutrient availability
that comes with increased size
Origin of Multicellularity
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Plants Moved From Water To Land
• Several evolutionary adaptations made this
possible:
– Multicellularity.
– To prevent water loss
• A waxy cuticle.
• An epidermal layer.
• Structures that protect and enclose the delicate
gametes and embryo.
Plants Moved From Water To Land
• Several evolutionary
adaptations made this
possible:
– Alternation of
Generations
• Their life cycle is
divided into two stages
Plants Moved From Water To Land
• Life cycle of vascular
plants:
– Have vascular tissues
for moving food and
water.
– Includes evergreens
and flowering plants.
Plants Moved From Water To Land
• Another evolutionary
adaptation that
occurred in most
vascular plants is
– Seed formation
– Has helped contribute
to the success of
vascular plants
Vascular Plants Dominate the
Terrain
Vascular Plants Dominate the
Terrain
• Most successful
vascular plant are
angiosperms.
– Most diverse
– Defining characteristic
is the flower.
What Do Plants Need and How Do
They Get It?
• Plant form and function is best understood
in terms of their needs:
– Light
– Gases
– Water
– Nitrogen and other nutrients
Plants Need Light
• Needed for
photosynthesis.
– Asymmetric branch
pattern allows for
greatest exposure to
light.
– Leaf
• Greatest amount of
photosynthesis.
• Allow for maximum light
absorption
• Can do solar tracking
Plants Need Light
• Leaf interior promotes
light absorption
– Palisade layer
– Spongy mesophyll
Plants Need Gases
• Plants need carbon
dioxide (CO2)
– Raw material for
making sugar.
• Stomates allow CO2
to enter cells.
– Water can be lost
through stomates
Stomata
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Plants Need Gases
• C4 plants
– Can trap CO2 on hot,
dry days
– Trap CO2 in palisade
or spongy cells
– Only about 3% of
plants
Plants Need Gases
• CAM plants
– Desert dwelling plants
• Stomates must be closed all day long to prevent
water loss.
– Stomates only open at night
• Carbon dioxide enters and is stored in 4-carbon
molecule .
– CO2 molecule is released during the day in
order for photosynthesis to occur.
Plants Need Water
• Roots
– Anchor plant to ground and absorb moisture and
minerals
– Root structure specially designed for absorption
Plants Need Water
– Root hairs maximize
absorption.
• Found on root surface
• Delicate extensions
dramatically increase
surface area
Plants Need Water
– Arrangement of cells
in the root
• Water is absorbed at
epidermal layer and
moves from cell to cell
through the cortex by
diffusion
Plants Need Nitrogen
• Nitrogen-fixation
– Process in which
certain microbes fix
atmospheric nitrogen
into organic
compounds.
– Some plants have a
symbiotic relationship
with these microbes.
Plants Need Other Nutrients
• Plants obtain minerals through their roots.
• When water enters the plant roots, so do
minerals.
– Move up the body of the plant to the leaves
and stems.
Plants Need Nitrogen and Other
Nutrients
How Do Higher Plants Transport
Substances and Support Themselves?
• All large multicellular organisms must have
some way of transporting substances
through their bodies, including plants.
• In some plants, the same tissues are
responsible for:
– Moving water
– Providing support
Translocation
• The movement of fluids
within the plant body
• Phloem
– Living vascular tissue near
the periphery of the stem
– Made of columns of sieve
tubes
– Sap (sugar-rich fluids made
by photosynthesis) moves
through the phloem
Transpiration
• Evaporation of water through the stomates
of plant leaves.
– Creates a negative pressure
• Allows water to move upward plant from roots
• Also prevents plants from overheating.
Water and Minerals Move Through
the Xylem
• Xylem
– Vascular tissue usually
found nearer the core,
or center, of the stem.
– Composed primarily of
dead cells that form a
hollow interconnected
network of tubules.
Plants Need Mechanical Support
• Reaching for the sun means growing
upward
– Opposing gravity.
• In soft-stemmed plants, mechanical
support provided by turgor pressure.
• In woody plants, mechanical support
provide by xylem.
– Reinforced with lignin.
How Do Plants Grow?
• Plant growth is indeterminate.
– Occurs at the meristem
• Cells divide by mitosis within meristem
tissue.
• Found at the
– tip of shoots and roots
– In periphery of the woody trees and shrubs
Three Main Tissue Types in Plants
How Do Plants Grow?
• Apical meristem
– Found at tip of
shoots and roots.
– Responsible for
lengthwise growth.
• Called primary
growth.
How Do Plants Grow?
• Vascular cambium
– Meristematic tissue
that produces new
bundles of xylem
and phloem.
– Increases the girth
of the stem or
roots.
• Called secondary
growth.
How Do Plants Grow?
• Cork cambium
– Layer of meristem
produced from cells
of the ground
tissues.
– Produces a new
layer of cells called
cork.
• Also contributes to
secondary growth.
Plants Have Hormones
• Phototrophism
– Growing plant will bend toward the light.
– Due to the presence of auxins.
• Class of molecules.
Plants Have Hormones
• Auxins
– Stimulate cell
elongation.
– Play a role in causing
the growing plant root
to bend down.
– Involved in fruit
development.
Plants Have Hormones
• Gibberellins
– Class of 100 similar chemical
compounds.
– Produced at tips of roots and stems.
• Stimulates plant growth.
– Most concentrated in seeds.
• Facilitates growth of embryo and
germination.
Plants Have Hormones
• Abscisic Acid (ABA)
– Hormones that slow growth
• Needed on cold days or excessively hot
days.
• Released when water is scarce.
• Plant growth is a balance between
ABA and gibberellins.
Plants Have Hormones
• Ethylene
– Causes fruit ripening
• As fruit ages, it releases more ethylene
– Activates enzymes that digest the cell walls of
plants.
• Enables plant to respond to environment by by
aging or planned cell death
Plants Reproduce Sexually
• Zygotes are formed
by the fusion of male
and female gametes
• In angiosperms,
flowers are the sex
organs that produce
gametes.
Sexual Reproduction in Flowering
Plants
• Male reproductive
organs = stamens
– Have anthers
– Contain cells that
give rise to pollen
Sexual Reproduction in Flowering
Plants
• Female sex organ
= carpel
– First houses the
ovule,
– Then the female
gametophyte
– And finally, the
embryo
Fertilization in Flowering Plants
Fertilization in Flowering Plants
Pollination
• How does pollen get from the male anther
to the female ovary?
– Wind
– Water
– Animal pollinators
• Flowers attract animal pollinators.
Seeds and Fruits
• After fertilization, ovule
develops into a seed.
• Seed remains dormant
until conditions for growth
are appropriate.
• Ovary that surrounds the
seed, or some other
parental structure, may
develop into the fruit.