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