lecture 19: plant structure and function. plant structure can be divided into two systems: roots and...
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Lecture 19:Plant 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
absorptionEpidermal 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 --> epidermis (waxy covering in shoots)
• Vascular tissue comes from:
• procambium --> vascular cambium--> primary xylem and phloem
• Ground tissue comes from:
• ground meristem -> ground tissues--> 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?
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