BIO 131, General Botany
Lecture Notes
Jan. 20, 2009
 
ROOTS
The functions of roots are  
        anchorage
        absorption
        storage
        conduction
PRIMARY ROOT TISSUES

Much of this material is highly visual; I showed you a lot of overheads when we went over this.  Consequently, there are a lot of references to figures in your textbook.  If you work through these notes with your textbook in hand, I think you'll be able to follow the story of how plants develop and how structure and function are related.

Primary tissues come only from apical meristems (and intercalary meristems).  As the cells produced from the apical meristem differentiate, they form 3 promeristems: the protoderm, the procambium and the ground meristem.
By the time the cells in the 3 promeristems have fully differentiated, several primary tissues have differentiated.
  FOCUS ON THESE QUESTIONS:
      What are the primary tissues that come from the apical meristem?
      What types of cells do the primary tissues contain?
      What do the primary tissues and cells look like?
      What are the functions of the tissues and cell types?

PRIMARY ROOT TISSUES

Please consult pp. 530-532 in your textbook for images of root apical meristems and their structures.

Here is a diagrammatic (and somewhat simplified) view of Figure 24-3 on p. 530 of your textbook.

Here is a chart of the primary tissues of roots and their cell types. You should know this chart, cold.

   PROMERISTEMS    PRIMARY TISSUE                                CELL TYPE                                               function of cell type 
PROTODERM EPIDERMIS epidermal (incl. root hair cells) absorption & protection
GROUND MERISTEM CORTEX parenchyma metabolism & storage
endodermal * + passage cells regulate movement of water into or out of vascular cylinder
cortical fibers
(sometimes called sclerenchyma)		 support
PROCAMBIUM XYLEM parenchyma metabolism & storage
tracheids (sometimes called tracheary elements) conduction & support
(water & minerals, upward)
vessels (sometimes called vessel elements) conduction
(water & minerals, upward)
fibers
(sometimes called sclerenchyma)		 support
PHLOEM parenchyma metabolism & storage
sieve cell
(sometimes called sieve elements- see Figs. 23-s21 and 23-22, textbook pp. 522+523)		 conduction
(organic molecules, both downward and upward)
companion cell regulate sieve cells
fiber
(sometimes called sclerenchyma)		 support
PERICYCLE parenchyma 1 helps form vascular cambium
(not in monocots)
2 produce apical meristems of branch roots
fiber support
RESIDUAL PROCAMBIUM parenchyma or meristematic with pericycle, helps form vascular cambium
(There is no residual procambium in monocots.)

* See p. 537 in your textbook for an explanation of Casparian strips.


Xylem vessels, tracheids and fibers are non-living at maturity.  Tracheids are intermediate in structure and function between vessels and tracheids.  Softwood trees lack vessels and fibers.  The fibers are what makes hardwood lumber harder and more durable than softwood lumber. [See Fig. 23-12, p. 517 in textbook for a visual comparison of these 3 types of cells.]
PICTURES OF ROOT CROSS SECTIONS
You should be able to identify all tissues and cell types in these herbaceous (non-woody) monocot and dicot roots, AND you should be able to distinguish monocot and dicot roots from each other.


 MONOCOT ROOT (above)

From center to outside - xylem parenchyma, primary xylem, primary phloem, pericycle, endodermis, cortex parenchyma, cortical fibers (or sclerenchyma), exodermis[or hypodermis! - single layer of large cells just under epidermis], epidermis. 
PROCAMBIUM DERIVATIVES IN RED; GROUND MERISTEM DERIVATIVES IN BLUE; PROTODERM DERIVATIVE IN GREEN.



DICOT ROOT  (above)
From center to outside - primary xylem, residual procambium, primary phloem,  pericycle, endodermis, cortex parenchyma (with starch grains), epidermis. 
(PROCAMBIUM DERIVATIVES IN RED; GROUND MERISTEM DERIVATIVES IN BLUE; PROTODERM DERIVATIVE IN GREEN.)


go on to stems link . . .