Tree Biology
Mike SillsRegional Urban Forester, Texas A&M Forest Service Dallas Region
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Tree Biology
• “If you can work on CARS, you can work on ANYTHING.”
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Tree Biology
• “If you can work on CARS, you can work on ANYTHING.”–“If you can work on ANYTHING, then you can figure out how TREES WORK.”
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Tree Biology
Tree Biology
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vacuole Nucleus
mitochondria
roughendoplasmicreticulum
chloroplast
Cell => Tissue => Organ => OrganismCell Wall, Cellulose, Lignin
Tree Biology
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Tree Biology
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Occurs in cells that contain chloroplasts
Occurs in mitochondria
Tree Biology
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Tree Biology
Tree Biology
• What makes stomata open and close?–Responses to signals from the environment
•Light: stomata are open•Dark: stomata are closed•High CO2 inside leaf: stomata are closed•Low CO2 inside leaf: stomata are open•Drought stress: stomata are closed
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Tree Biology
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ApicalMeristems
Shoot tip
Root cap
Tree Biology
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Terminal bud
Lenticels
Leaf budFlower bud
Terminal budScale scars
Leaf scars
This year’s growthNode
Internode
This year’s growth
Lateral bud
Last year’s growth
Tree Biology
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Lumenlearning.com
Tree Biology
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Tree Biology
Tree Biology
• Symplasm (sapwood) vs. Apoplasm(heartwood)
• Xylem of Gymnosperms (pines, spruces)–Tracheids (dead)–Fibers (sclerenchyma)–Parenchyma cells (live)
• Vessels (xylem of hardwoods)–Stacks of dead, hollow cells
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Tree Biology
• Phloem (conifers)–Sieve cells
• Phloem (hardwoods)–Sieve tube elements–Companion cells
• Movement of carbohydrates (sugars) is slow and requires energy
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Tree Biology
• Phloem–Rays
• Transport and store carbohydrates• Restrict decay (CODIT)
• Bark–Old phloem
• Crushed & living cells reabsorbed into tree• Cell walls incorporated into bark
– Impregnated with wax and oil–Lenticles
• Gas exchange
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Tree Biology
Tree Biology
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The cohesion-tension theory of sap ascent is shown. Evaporation from the mesophyll cells produces a negative water potential gradient that causes water to move upwards from the roots through the xylem. Image credit: OpenStax Biology
Tree Biology
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Tree Biology
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Tree Biology
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Mycorrhizae
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Tree Biology
Tree Biology
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