Plants part 3
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Plants Part 3. Stems. Stem. Main function: to hold up the leaves and conduct substances between the root and the leaves. Two types of stems: herbaceous and woody.

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Plants Part 3

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Plants part 3

Plants Part 3

Stems


Plants part 3

Stem

  • Main function: to hold up the leaves and conduct substances between the root and the leaves.

  • Two types of stems: herbaceous and woody.

    • Herbaceous stems are green and soft, they do not survive through winters and must regrow each year. Vascular bundles with the xylem and phloem.

      • Xylem is closer to the centre, phloem is closer to the outside of the stem.

      • Vascular bundles of the herbaceous monocot are found throughout the stem.

      • Vascular bundles of the herbaceous dicot are arranged in a ring closer to the outside. They also have a vascular cambium between the xylem and phloem.


Plants part 3

Monocot stem dicot stem


Plants part 3

  • Woody stems are more complex, are tough and hard, commonly called wood, and can survive through the winter.

    • Grow thicker over time due to the vascular cambium making new xylem and phloem.

    • Sapwood is younger xylem, conducts the water and minerals. The older xylem fills with resins, oils and other chemicals and is called heartwood.

    • The growth of new xylem each spring results in a new layer of sapwood and an annual ring is formed.

    • Outer part is called the bark.

      • Protects the tissue

      • Contains cork tissue

      • Outer cork cells are dead and contain fats, oils, waxes


Plants part 3

  • Stems can also store food

  • Modified stems:

    • Rhizomes are thick, fleshy stems that grow on or just below the soil’s surface.

    • Tubers are stems that grow underground. They have a lot of stored food in them and have eyes that grow into buds.

  • Bulbs are underground stems: surrounded by modified leaves


Human uses of stems

Human Uses of Stems

Fuel: ethanol, wood

Food: sugar cane, potatoes, maple syrup, asparagus

Textiles: flax, hemp, bamboo

Dyes: indigo

Other chemicals: tannin (wood stain), turpentine, latex rubber

Medicine: salicyclic acid (pain reliever from willow bark), taxol (anti-cancer drug made of yew tree bark)


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