Lecture 19: Plant Structure and Function

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Lecture 19Plant Structure and Function
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Plant structure can be divided into two systems
roots and shoots
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The Root System

• Parts under ground
• Used for anchorage
• Used for absorption of water and nutrients

Tap root
Fibrous root
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Roots are often covered with root hairs which
increase the surface area for absorption
Epidermal cell
Root hair
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Modified roots
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The Shoot System

• Stems, leaves, buds
• Nodes are places on the stem where leaves are
  attached and buds form.

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Figure 35.5 Simple versus compound leaves
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Figure 35.19 Leaf anatomy
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Figure 35.6 Modified leaves Tendrils, pea plant
(top left) spines, cacti (top right) succulent
(bottom left) brightly-colored leaves,
poinsettia (bottom right)
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Figure 35.4 Modified shoots Stolons, strawberry
(top left) rhizomes, iris (top right) tubers,
potato (bottom left) bulb, onion (bottom right)
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Plant structures are composed of 3 types of
tissues

• ground tissue -- bulk of plant body
• vascular tissue -- distribution of water and
  solutes
• dermal tissue -- covering, protection of plant
  surface.

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Vascular tissue xylem and phloem
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Plant growth occurs at localized regions called
meristems

• Meristem cells are undifferentiated and can
  divide through mitosis
• Continued divisions of meristem cells keeps a
  plant growing throughout it's life
  indeterminate growth.
• apical meristems -- results in increase in length
  of stems and roots
• lateral meristems -- growth produces thickening
  of stems and roots

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Growth at apical meristems primary growth

• As a stem or root grows, primary meristems
  develop behind the growing tip
• These differentiate into the three tissue
  systems
• Dermal tissue comes from
• protoderm --gt epidermis (waxy covering in shoots)
• Vascular tissue comes from
• procambium --gt vascular cambium--gt primary xylem
  and phloem
• Ground tissue comes from
• ground meristem -gt ground tissues--gt cork cambium

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Figure 35.17 The terminal bud and primary growth
of a shoot
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Growth at lateral meristems Secondary growth

• In woody plants vascular cambium forms a ring
• each growing season a new layer of xylem is
  produced which pushes the cambium and all outer
  tissues further out.
• Old phloem cells are crushed and only a thin
  strip of newly- formed phloem remains alive.

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Figure 35.22 Anatomy of a three-year-old stem
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Figure 35.23 Anatomy of a tree trunk

• As the stem expands, it ruptures the epidermis
• Bark is composed of phloem and ground issue cells
  called cork cells

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Tree Girdling
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If you hammer a nail into a tree 10 feet above
the ground, and wait 20 years, where will the
nail be?
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10 feet
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Angiosperms are often divided into the monocots
and dicots
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Monocots
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Dicots