Biology 1A    Oct 27, 1998
Lecture 16 - Roots & 1° Growth

Page Contents :

• Reading Assignment
• Overview of Lecture
• Overview of Lab
• Lecture Outline
• Vocabulary
• Study Questions

Stern: Chapter 5

Overview of Lecture:

The root develops from the root apical meristem.
Root anatomy.
Root systems.
Root functions and specializations.

Overview of Lab:

(A bullet indicates a handout.)
• Roots & 1° Growth.

A. Root system vs. Shoot system
1. The plant is divided into two primary organ systems: root & shoot
2. Question: How do you tell whether a structure is part of the root or shoot?
B. Reprise : Primary growth
1. Three regions of development -- separated physically (not temporally)
a. cell division
b. cell growth
c. cell differentiation
2. Apical meristems give rise to three primary meristems.
a. result directly from the apical meristems.
b. The three primary meristems give rise to the three primary tissue systems:
i. protoderm --> epidermis
ii. procambium --> vascular tissue
iii. ground meristem --> ground tissue
C. Patterns of primary development in xylem
1. Characterized by the pattern of maturation in the xylem
a. some cells mature early --> small cells; protoxylem
b. some cells mature later --> larger cells; metaxylem
2. There are three basic patterns of xylem maturation:
a. exarch -- the outermost xylem cells mature first
b. endarch -- the innermost xylem cells mature first
c. mesarch -- xylem cells in center of each bundle mature first

A. The root cap
1. A thimble-shaped region of cells at the root apex
2. The root cap is found only in roots.
3. Functions of the root cap
a. covers and protects the delicate RAM
b. detection of gravity
B. Tissue systems in the root
1. Overview of tissue system locations
2. Epidermis
a. no cuticle or stomata.
b. root hairs -- extensions of individual epidermal cells
3. Ground tissue
a. cortex
b. pith
c. endodermis
4. Vascular cylinder
a. xylem -- usually a solid central strand in roots
b. phloem -- in bundles just exterior to the xylem
5. Monocot vs. Dicot

A. The pericycle produces additional tissues.
1. single layer of cells that lies just inside the endodermis
2. undifferentiated cells; capable of dividing
3. source of branch roots by primary growth
4. Pericycle may also give rise to secondary growth in roots
B. Root system organization
1. Two primary root system types:
a. tap root - single primary root dominates over branch roots
b. fibrous system - network with no central dominant root
2. Adventitious roots
a. roots which develop from the shoot system; i.e. in a weird place
b. same as "aerial roots" in your text

A. Primary functions of the root system
1. anchorage & support
2. absorption of water and minerals
3. storage of photosynthates
B. Specializations of roots
1. suckers
2. pneumatophores
3. contractile roots
4. mycorrhizae
a. association between fungal filaments and plant roots
b. plant gets water and minerals from greater area (like with root hairs)
c. fungus gets nutrients manufactured by the plant
d. four in five plants have mycorrhizae
5. root nodules -- house nitrogen fixing bacteria

   adventitious roots       fibrous roots         protoxylem
   apical meristem          ground meristem       root
   Casparian strip          ground tissue         root apical meristem
   cell differentiation     mesarch               root cap
   cell division            metaxylem             root hairs
   cell growth              monocot               root nodules
   centrarch                mycorrhizae           root system
   contractile roots        pericycle             shoot system
   cortex                   pith                  suberin
   dicot                    pneumatophores        suckers
   endarch                  primary growth        tap root
   endodermis               primary meristem      tissue system
   epidermis                procambium            vascular tissue
   exarch                   protoderm			

• Plants are divided into two organ systems; what are they? How are they produced?
• Plants are composed of three organs; what are they?
• Plants have three tissue systems; what are they? How are they produced?
• How is development in plants different from development in animals?
• What are the three stages in the process of development, and what happens in each?
• What are the three basic patterns of xylem maturation? How do they differ? Which is most common in roots? What are the physical and developmental differences between protoxylem and metaxylem?
• How does the root cap help to protect the root apical meristem? What other function does it serve?
• How is the epidermis of the root different from epidermis of the shoot?
• What are root hairs and what is their function? At what stage of development do they appear? How are root hairs like mycorrhizae? How different?
• What is the difference between cortex and pith? To which tissue system do they belong? From which primary meristem do they develop? Which plants have a region of pith in their roots?
• Where is the endodermis found in the root? What is its function? How does the Casparian strip make this function possible? What is the chemical composition of the strip?
• Where is the vascular tissue located in roots? How is it arranged in dicots? in monocots?
• What are dicots and monocots?
• Where is the pericycle located in the root? What are its two functions? How does it accomplish these functions?
• How do tap root systems and fibrous root systems differ? How does this difference come about?
• What are branch roots and how do they develop? How is this different from branch shoots?
• What are adventitious roots and how are they different from branch roots? What are some examples of plants with adventitious roots?
• What are the three primary functions of the root system?
• Which root specialization pulls the plant deeper into the ground? Which may regenerate the shoot system? Which brings aditional water and minerals into the root? Which brings oxygen into the root? Which provides nitrogen to the root? Which specializations are associations with other organisms?