1. Chapter 23 – Roots, Stems, & Leaves

2. 23-1 Specialized Tissue in Plants
Materials move throughout the plant, and growth and repair take place continuously
Cells work in tandem to ensure plant’s survival

3. Seed Plant Structure Three principal organs of seed plants: Roots
Stems
Leaves
These are linked together to perform functions such as transport and protection, as well as coordination of other plant activities.

4. Roots Absorbs water and dissolved nutrients
Anchor plant to the ground – holds soil in place and helps prevent erosion
Help in transporting of water & nutrients to the rest of the plant
Aids in keeping plant upright vs. wind and rain

5. Stems
Has support system for the plant body, transport system to carry nutrients, and defense system against predators & disease
Stem transport system must be able to lift water from roots to the highest leaves, and transport products of photosynthesis from the leaves back down to the roots

6. Leaves Photosynthetic system of plant
Increased surface area is good for sunlight absorption but not so good for evaporation
Adjustable pores in leaves help conserve water while letting oxygen and carbon dioxide exit and enter the leaves

7. Plant Tissue Systems
Three main tissue systems:
Dermal
Vascular
Ground

8. Dermal Tissue
Outer layer – single layer of EPITHELIAL CELLS which are often coated with a thick waxy layer (CUTICLE) that protects against water loss or injury
Some epidermal cells have trichomes which are tiny projections that help protect the leaf and help give it its “fuzzy” look

9. Dermal Tissue, cont’d.
In roots, dermal tissue contains root hair cells – these provide larger surface area and aid in water absorption
On the underside of leaves, dermal tissue contains guard cells, which regulate water loss and gas exchange

10. Vascular Tissue Xylem – water conductor Phloem – food conductor
Xylem – contains specialized tracheids and vessel elements
Phloem-contains specialized sieve tube elements and companion cells

11. Xylem
Tracheids are connected to neighboring cells – all seed plants have tracheids
Angiosperms also have a xylem cell that is called a vessel element. They are arranged end to end on top of one another – as the cells mature and then die, it transforms the “stack” of cells into a continuous tube through which water can freely move

12. Phloem Main cells called SIEVE TUBE ELEMENTS
which are arranged end to end to form
sieve tubes – end walls have holes that allow material to move back and forth
When sieve tube cells mature, they lose their nuclei and other organelles – the remaining organelles “hug” the cell wall and the rest of the space is a pipeline through which sugars and other foods are carried in a watery stream

13. Phloem, cont’d. Companion cells are phloem cells
that surround sieve tube elements
These cells DO NOT lose their nuclei
or their organelles
Companion cells support the phloem
cells and aid in the movement of
substances in and out of the phloem

14. Ground Tissue
Cells that lie between dermal and vascular tissue – three types:
Parenchyma – packed with chloroplasts – site of photosynthesis
Collenchyma – strong, with flexible cell walls that function as support structure
Sclerenchyma – cells that have thick rigid cell walls that add strength to this tissue

15. Plant Growth & Meristematic Tissue
Most plants have a method of development that involves an open, indeterminate type of growth, which means that they grow and produce new cells at the tips of their roots and stems for as long as they are alive
Cells are produced in meristematic tissue, and are undifferentiated, meaning they are not specific to function at that point of their life

16. Meristematic Tissue
Near the tip of each growing root and stem is an apical meristem, which is a group of undifferentiated cells that divide to produce increased length of stems and roots.
Meristematic tissue is the only plant tissue that produces new cells by mitosis.

17. Differentiation in Meristematic Tissue
Cells that originate in the meristem look VERY much alike
They divide rapidly and have thin cell walls
Gradually, these cells develop into mature cells with specialized structure and function – this is called differentiation

18. Differentiation, cont’d.
Specialized cells found in flowers, which make up the reproductive systems of flowering plants, are also produced in meristems.
Flower development begins when certain genes are “turned on” in a shoot apical meristem – this action transforms the apical meristem into a floral meristem (colorful petals & reproductive structures)

19. Lateral Meristem
Increase width