plant form and function: how do plants live in the world?
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Plant Form and Function:Plant Form and Function:How Do Plants Live in the World?How Do Plants Live in the World?
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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
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Important Events in Plant Evolution
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Photosynthesis Changed the World
• Plants use chlorophyll to capture the energy of sunlight for use in photosynthesis
• Oxygen is the by-product and has accumulated over the past 2.5 billion years.
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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.
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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
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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.
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Plants Moved From Water To Land
• Several evolutionary adaptations made this possible:– Alternation of
Generations• Their life cycle is
divided into two stages
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Plants Moved From Water To Land
• Life cycle of vascular plants:– Have vascular tissues
for moving food and water.
– Includes evergreens and flowering plants.
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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
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Vascular Plants Dominate the Terrain
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Vascular Plants Dominate the Terrain
• Most successful vascular plant are angiosperms.
– Most diverse
– Defining characteristic is the flower.
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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
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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
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Plants Need Light
• Leaf interior promotes light absorption
– Palisade layer
– Spongy mesophyll
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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
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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
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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.
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Plants Need Water
• Roots– Anchor plant to ground and absorb moisture and
minerals– Root structure specially designed for absorption
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Plants Need Water
– Root hairs maximize absorption.
• Found on root surface
• Delicate extensions dramatically increase surface area
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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
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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.
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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.
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Plants Need Nitrogen and Other Nutrients
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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
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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
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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.
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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.
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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.
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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
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Three Main Tissue Types in Plants
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How Do Plants Grow?
• Apical meristem– Found at tip of
shoots and roots.– Responsible for
lengthwise growth.• Called primary
growth.
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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.
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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.
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Plants Have Hormones
• Phototrophism– Growing plant will bend toward the light.– Due to the presence of auxins.
• Class of molecules.
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Plants Have Hormones
• Auxins– Stimulate cell
elongation.– Play a role in causing
the growing plant root to bend down.
– Involved in fruit development.
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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.
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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.
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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
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Plants Reproduce Sexually
• Zygotes are formed by the fusion of male and female gametes
• In angiosperms, flowers are the sex organs that produce gametes.
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Sexual Reproduction in Flowering Plants
• Male reproductive organs = stamens
– Have anthers
– Contain cells that give rise to pollen
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Sexual Reproduction in Flowering Plants
• Female sex organ = carpel– First houses the
ovule,– Then the female
gametophyte– And finally, the
embryo
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Fertilization in Flowering Plants
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Fertilization in Flowering Plants
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Pollination
• How does pollen get from the male anther to the female ovary?– Wind– Water– Animal pollinators
• Flowers attract animal pollinators.
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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.