I. Plant structure • Cell types—continued II. Primary growth A. Meristems B. Shoot growth C. Root growth Difference between: Sclerenchyma fibers & cellulose microfibrils Sclerenchyma Fibers: - Alot of cells together Cellulose microfibrils - Chains of cellulose Purpose of cells of the xylem is to conduct water At maturity, xylem cells are dead Name of the polymer that adds strength to secondary wall: Lignin
Parenchyma Cells Functions
Many; often specialized
Most metabolic processes (photosynthesis, storage, secretion, food storage)
Parenchyma Cells Features
A type of ground tissue (when in stems & roots)
Usually lack secondary wall
Can often divide & differentiate at maturity
Parenchyma Cells Examples
Fruit flesh
Endosperm
Pith & cortex of stems & roots
Chloroplast-laden cells inside leaves
Collenchyma Cells Functions
Support, especially of young & growing organs
Collenchyma Cells Examples
Celery leaf midrib & petiole
Collenchyma + Parenchyma =
Ground Tissue
Sclerenchyma Cells Features
A type of ground tissue
Thick secondary wall with lignin (a rigid polymer)
Cannot elongate at maturity
2 forms
Fibers & Sclereids
Tracheids & Vessels
Water conducting cells of the xylem
Tracheids & Vessels Features
Dead at maturity
Secondary wall lignified, often spiral
2 kinds:
Tracheids & vessel elements
Type of vascular tissue
Tracheid appearance
Long tapered ends
Lignin features
2nd-most abundant polymer
Deposited in cell walls; fills spaces and binds cellulose, hemicellulose & pectin
Gives strength to wood & bark
Can occur in cell walls of non-woody plants (palm trees, bamboo, wheat straw, ...)
Lignin Human Uses
Wood: 20–33% lignin by dry weight
Rope, clothing, rugs, ... (sclerenchyma fibers)
Paper—lignin removed to leave cellulose
Artificial vanillin
Sieve-Tube Elements (phloem) Functions
Transport sugars
Other organic compounds, some minerals
Sieve-Tube Elements Features
Type of vascular tissue
Alive at maturity
With companion cell (parenchyma)
Meristems
Undifferentiated (can become anything) plant version of stem cell
Source of all parts of the mature sporophyte
Retain forever the ability to divide
Apical Meristems
Root AM and Shoot AM
Primary growth
Lateral Meristems
Vascular cambium & cork cambium
Secondary growth
Tissues of Apical Meristem
Protoderm →Dermal tissue (epidermis)
Procambium → Vascular tissue
Ground meristem → Ground tissue
Apical Meristem makes 3 other meristems
Protoderm
Procambium
Ground Meristem
Youngest tissue where?
At the shoot tip
Root Hairs
Increase Surface Area
Once roots stops moving, root hairs start growing
Epidermal cells
Young Roots
Endodermis: innermost layer of cortex
Stele is all vascular tissue in root & stem
Arising from procambium
Lateral Root
Originates in pericycle (outermost layer of vascular cylinder)
Grows out thru cortex & epidermis
Cross section: original root
Longitudinal section: lateral root
Root cap
Protects
Endodermis
surrounds vascular cylinder
innermost layer of cortex
Vascular cylinder (stele)
center of root
contains vascular tissues (xylem & phloem) & some ground tissue
Pericycle
between vascular cylinder & endodermis
origin of lateral roots
Vessel appearance
stacked like soup cans