Transcript PLANT STRUCTURE AND GROWTH

Plant Structure and Growth
Chapter 35
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• Plants with vascular tissue have 3
structures - roots, shoots, leaves.
• 2 groups of angiosperms, monocots
and dicots, differ in structures.
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• Structures divided into 2 systems:
root system (below ground), shoot
system (above ground).
• Systems rely on one another; roots
- no chloroplasts - need shoots to
photosynthesize.
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• Monocots (grasses) - fibrous root
systems (mat-like).
• Dicots (flowers) - taproot system with
one large root.
• Most absorption of water and minerals
occurs near root tips with root hairs increase surface area.
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• Some plants - adventitious roots arise aboveground from stems or
even from leaves.
• In corn - help to keep plant upright.
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http://homepage.smc.edu/hodson_kent/plant_growth/Angiosperms/ID/3%20root%20systems.jpg
• Stems have nodes - leaves attached,
internodes - spaces between nodes.
• Where leaves meet stems - axillary
buds - vegetative branch could form.
• Terminal bud - growth of young shoot
concentrated.
• If terminal bud present, growth
happens vertically - apical dominance.
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http://utc.usu.edu/factsheets/CarexFSF/CIG/internodes.jpg
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Modified shoots
• 1Stolons - “runners” of strawberry
plants - grow on surface so that
parent plant can asexually
reproduce in large numbers.
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• 2Rhizomes (ginger) - horizontal stems grow underground.
• 3Tubers (potatoes) - swollen ends of
rhizomes specialized for food storage.
• 4Bulbs (onions) - vertical, underground
shoots consisting mostly of swollen
bases of leaves that store food.
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Rhizomes
Tubers
Bulbs
• Leaves consist of flattened blade
and stalk (petiole)
• Some leaves evolved other purposes
(spines of cacti for defense, leaves
modified for water storage,
brightly colored leaves that attract
pollinators)
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• Each organ of plant - 3 tissue systems:
dermal, vascular, ground.
• Dermal system consists of epidermis
(covers, protects)
• Epidermis of leaves, most stems
secretes waxy coating (cuticle) - helps
parts of plant retain water.
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http://www.naturescapes.net/042004/Figure3.jpg
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• Vascular tissue involved in transport of
materials between roots and shoots.
• 1Xylem – tissue that conducts water and
minerals from roots to rest of plant.
• 2Phloem transport nutrients, especially
carbohydrates produced in leaves down
stem.
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• 2 types of xylem cells: vessel
elements, tracheids.
• Dead at maturity - help to thicken
walls to promote water flow.
• Tracheids - long, thin cells with
tapered ends.
• Vessel elements - wider, shorter,
thinner walled, less tapered than
tracheids.
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• 2 types of phloem cells - companion
cells, sieve tube members.
• Sieve tube members - tubes that
material moves through.
• Companion cells assist sieve tube
members.
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• Ground tissue - tissue neither
dermal nor vascular.
• Dicot stems, ground tissue divided
into pith, internal to vascular
tissue, and cortex, external to
vascular tissue.
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http://wpcontent.answers.com/wikipedia/commons/thumb/9/92/Stem-histology-cross-section-tag.svg/250px-Stem-histology-cross-section-tag.svg.png
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• 3 different types of plant cells:
parenchyma, collenchyma, and
sclerenchyma.
• Parenchyma cells - primary walls
that are relatively thin and
flexible; typical plant cells; ex.
sieve-tube members.
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• Collenchyma cells -thicker primary
walls than parenchyma cells - used
for support in growing plants.
• Sclerenchyma cells also function as
supporting elements of plant.
Growth of tissues in plants
• Annual plants complete life cycle in
single year or less.
• Biennial plants - 2 years.
• Plants that live many years,
including trees, shrubs, and some
grasses, are perennials.
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http://www.btinternet.com/~micka.wffps/foxglove12.jpg
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• Growth in plants due to embryonic cells
(meristems)
• Elongate and differentiate into cell
types depending on tissue of plant.
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http://pgjennielove.files.wordpress.com/2008/06/apical_meristem.png
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• Apical meristems found at tips of
roots, stems - allow for growth in
length - only happens at tips.
• Primary growth occurs lengthwise,
secondary growth - widthwise.
• Lateral meristems responsible for
secondary growth.
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• Root tip protected by root cap to
protect meristem.
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• Axillary buds have potential to
form branches of shoot system.
• Vascular tissue runs length of stem
in strands (in vascular bundles)
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• Leaf epidermis composed of cells tightly
locked together.
• Full of stomata - controlled by guard
cells around that can open and close
opening.
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• Spongy layer of cells inside leaf has
chloroplasts with air spaces around
cells.
• Palisade layer in leaf has densely
packed cells spread over large
surface area.
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Lateral meristems
• 2 cambiums responsible for
secondary growth.
• Vascular cambium - meristem to
produce secondary xylem and
secondary phloem.
• Cork cambium - meristem for tough,
thick covering for stems and roots
- replaces the epidermis.
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• As secondary growth continues over
years, layer upon layer of secondary
xylem accumulates, producing wood.
• Actually dead cells.
• Growth in areas like Maine occur in
cycles - dormancy then growth produce growth rings.
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• Bark - all tissues external to
vascular cambium (secondary
phloem, cork cambium, cork)
• 2 types of secondary phloem:
heartwood and sapwood.
• Heartwood (hardwood) no longer
conducts water; sapwood
(softwood) functions in transport
of water and minerals.
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