CIE A Level Biology (9700) 2019-2021

Revision Notes

7.1.2 Cells of the Stems, Roots & Leaves

Cells of the Stems, Roots & Leaves

  • 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

Cells of a root ts, downloadable AS & A Level Biology revision notes

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

Cells of the root ls, downloadable AS & A Level Biology revision notes

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 

Cells of a stem, downloadable AS & A Level Biology revision notes

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

Leaf

Cells of a leaf, downloadable AS & A Level Biology revision notes

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

Exam Tip

You need to be familiar with these tissues as the second part of Paper 3 often requires you to draw images of stems, roots and leaves from micrographs and slides.

Author: Catherine

Cate has over 20 years’ experience teaching Biology to IGCSE, IB and A-level students in seven different countries across Asia, Europe, North America and the Middle East. This has given her a fine appreciation of different cultures, places and teaching methods. Cate has a keen interest in producing Biology revision resources that will help students engage with the subject.
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