Biology 1A Oct 27, 1998
Lecture 16 - Roots & 1° Growth
Page Contents :
Overview of Lecture:
The root develops from the root apical meristem.
Root functions and specializations.
Overview of Lab:
(A bullet indicates a handout.)
- Roots & 1° Growth.
I. The root develops from the root apical meristem.
A. Root system vs. Shoot system
II. Root Anatomy.
1. The plant is divided into two primary organ systems: root & shoot
B. Reprise : Primary growth
2. Question: How do you tell whether a structure is part of the root or shoot?
1. Three regions of development -- separated physically (not temporally)
C. Patterns of primary development in xylem
a. cell division
2. Apical meristems give rise to three primary meristems.
b. cell growth
c. cell differentiation
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
1. Characterized by the pattern of maturation in the xylem
a. some cells mature early --> small cells; protoxylem
2. There are three basic patterns of xylem maturation:
b. some cells mature later --> larger cells; metaxylem
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
III. Root Systems.
1. A thimble-shaped region of cells at the root apex
B. Tissue systems in the root
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
1. Overview of tissue system locations
a. no cuticle or stomata.
3. Ground tissue
b. root hairs -- extensions of individual epidermal cells
4. Vascular cylinder
a. xylem -- usually a solid central strand in roots
5. Monocot vs. Dicot
b. phloem -- in bundles just exterior to the xylem
A. The pericycle produces additional tissues.
IV. Root functions and specializations.
1. single layer of cells that lies just inside the endodermis
B. Root system organization
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
1. Two primary root system types:
a. tap root - single primary root dominates over branch roots
2. Adventitious roots
b. fibrous system - network with no central dominant root
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
B. Specializations of roots
2. absorption of water and minerals
3. storage of photosynthates
3. contractile roots
a. association between fungal filaments and plant roots
5. root nodules -- house nitrogen fixing bacteria
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
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
- 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?
© 1998 Brian R. Speer. These pages for the personal use of students and teachers; any commercial use or publication is strictly prohibited.