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Biological Material at the Microscopic Level

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Stem Cross Section – Geranium

Evergreen perennials native to temperate and tropical regions of the world. Popular house and garden plant – due to long flowering periods

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Stem Cross Section – Geranium

  • Stems are either woody or herbaceous

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  • Stems – connect the leaves to the roots (why is that significant?

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  • What structures would you expect to find in a leaf cross section slide?

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Stem Cross Section – Geranium

Can contain chloroplasts

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Stem Cross Section – Geranium

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Drawing

  • You do not have to draw the full stem (circle), you can take a segment like in this drawing – make sure you write this on your drawing though

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Specialised Structures

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  • Vascular Bundles (containing Xylem and Phloem)

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The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which run up and down the length of the stem.

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When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings.

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The xylem contains  specialized tube-like cells through which the water and dissolved minerals move.

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A different group of specialized cells move food substances within the plant. This tissue is called the phloem and the primary transport cells are called sieve cells. Between these two tissues may be found a layer of  cells capable of dividing and producing more xylem and phloem. This is called the cambium.

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The movement of food is from the leaves to  the roots, and water from roots to leaves

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Specialised Structures

  • Epidermal cells

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This description is similar to your description for the Rhubarb leaf tear

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Remember the Epidermis, in botany, is the outermost, layer of cells covering the stem, root, leaf, flower, fruit, and seed parts of a plant. The epidermis and its waxy cuticle provide a protective barrier against mechanical injury, water loss, and infection

  • Protect from environmental stressors (UV)
  • Protect from microbes and chemical compounds
  • Protects the other more specialised cells within the leaf
  • Close positioning of the cells is important for preventing water loss
  • Can contain chloroplasts (so can photosynthesis)
  • Often see small hair like structures (trichomes) projecting from epidermal cells