Multicellular organization - Plants (Tissues)

Three types
      o    dermal tissue
      o    vascular tissue
      o    ground tissue

Dermal tissue
-    covers and protects plants.
-    Includes the epidermis and modified cells like guard cells, root hairs, and cells that produce a waxy cuticle.

 

Below are the dermal layers of a leaf

Vascular tissue
-    consists of phloem and xylem
-    these transport water and nutrients around the plant

xylem
-    the water and mineral conducting tissue, consists of two types of elongated cells: tracheids and vessel elements
-    both tracheids and vessel elements are dead at functional maturity.
-    Seedless vascular plants and most gymnosperms have only tracheids
-    Angiosperms have both tracheids and vessel members
-    Xylem is what makes up wood.

Wood

*Tracheids - long thin cells that overlap and are tapered at the ends.

* Vessel elements - generally wider, shorter, thinner walled and less tapered than tracheids.
- aligned end to end and differ from tracheids in that the ends are perforated to allow free flow through the vessel tubes.

Phloem
-    carries sugars from the photosynthetic leaves to the rest of the plant by active transport.
-    Consists of chains of sieve tube members or elements whose end walls contain sieve plates that facilitate the flow of fluid from one cell to the next.
-    Alive at functional maturity, although they lack nuclei, ribosome and vacuoles. Connected to each sieve tube member is at least one companion cell that does contain a full complement of cell organelles and nurtures the sieve tube elements.

Below is an image of a sieve tube member

Ground tissue
-    the most common type of tissue
-    functions mainly as support, storage and photosynthesis
-    consists of three cell types: parenchyma, sclerenchyma and collenchyma

Below are ground tissue cells

Parenchyma cells
-    look like classic plant cells
-    have primary cells walls that are thin and flexible
-    lack secondary cell walls
-    protoplasm contains one large vacuole and the cell carries out most metabolic functions
-    parenchymal cells in the leaf (mesophyll cells) contain chloroplasts and carry out photoynthesis
-    parenchymal cells in roots contain plastids and store starch
-    if turgid with water, they give support and shape to the plant.
-    Most parenchymal cells retain the ability to divide and differentiate into other cell types after a plant has been injured in some way.
-    Once parenchymal cell may regenerate or clone an entire plant

Collenchyma cells
-    have unevenly thickened primary cell walls but lack secondary cell walls
-    mature collenchymal cells are alive and their function is to support the growing stem

Scelerenchyma cells
-    have thick primary and secondary cell walls fortified with lignin
-    function is to support the plant
-    two forms: sclereids and fibers

* fibers – are long thin and fibrous like and usually occur in bundles
- commercially used to make rope and flax fibers

* sclereids – short and irregular in shape.
- make up tough seed coats and pits
- give pears its gritty texture