• Common tissues that can be found in stems, roots and leaves are:
  • Epidermis
    • This is the outermost protective layer of the stem, roots and leaves and is one cell thick
    • It is in the leaves and stem it is covered by a waterproof layer called the waxy cuticle
    • The leaves have two epidermis (upper and lower). The lower epidermis contains pores called stomata (stoma – singular) which allow gaseous exchange
    • The roots have many extensions that increase the surface area for absorption of water and mineral ions. These are called root hairs
  • Parenchyma
    • These are the unspecialised packing tissue of the stem, roots and leaves
    • The cells making up the tissue are thin-walled, are metabolically active and carry out many functions e.g. photosynthesis, storing starch, providing support (when turgid) and the air spaces within the cells aid diffusion of gases
    • In the roots, the tissue forms the cortex; in the stems, it forms the cortex and pith; in the leaves, it forms the mesophyll layer
  • Mesophyll
    • This is made of specialised parenchyma cells. They are specialised for photosynthesis and therefore contain chlorophyll within chloroplasts
    • There are two types, palisade mesophyll and spongy mesophyll
  • Endodermis
    • This is one cell thick and surrounds the vascular tissue in roots (and can be found in stems)
    • In roots, the endodermis cells contain a structure called the casparian strip, which help regulate the movement of water and ions into the vascular tissue
  • Pericycle
    • This is located between the endodermis and vascular tissue in the roots
    • It can be one to several layers of cells thick
    • In roots, new roots can grow from this layer
    • In stems, this tissue is specialised sclerenchyma (which has dead, lignified cells for strength)
  • Vascular tissue
    • Xylem and phloem tissue
    • They are called vascular tissue as both tissues transport fluids

Roots

Photomicrograph (a) and drawing (b) of a low-power image of a dicot root and a high power image of the vascular tissue seen in transverse section

Photomicrograph and drawing of a low-power image of dicot root with a high power image of the vascular tissue seen in longitudinal section

Stem 

Photomicrograph (a) and drawing (b) of a low-power image of a dicot stem seen in transverse and longitudinal section

Leaf

Photomicrograph and drawing of a low-power image of a dicot leaf seen in transverse section