Plant Bio Day 4

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