Bio 360, Fall 2001 August 30, 2001

Plant Cells and Tissues

I. Origin of different types of cells

A. Meristems

    1. Apical meristems

      2. 2. Axillary buds

      3. Lateral meristems

      4. General features

      a. Small, relatively undifferentiated cells

      b. Two types of cells - initials and derivatives

       B. Derivatives of apical meristems

       

      protoderm Ground meristem procambium

      epidermis cortex pith xylem phloem vascular

      cambium

      parenchyma parenchyma

      collenchyma 20 xylem and phloem

      sclerenchyma

      periderm

      Differentiation - process by which amorphous cells produced by meristematic tissue become specialized

      Primary vs. secondary growth - direction of cell division

       C. Tissues

      1. Groups of cells that are structurally and functionally distinct

      2. Simple vs complex

      a. Simple - one cell type

      b. Complex - two cell types

      II. The ground tissue systems

      A. Composed of two parts

      1. Pith - a region of tissue within the center of roots and stems of some plants soft, low density cells made of parenchyma

    2. Cortex - region of ground tissue from just inside the epidermis to the center of the plant or to the ring of vascular tissue that surrounds the pith contains parenchyma, collenchyma, and sclerenchyma with diverse functions

B. Parenchyma

1. Features of cells

a. unspecialized

b. isodiametric

c. alive at maturity

d. most have primary cell walls and no lignin

e. large vacuoles

2. Found - everywhere

cortex

pith

leaf mesophyll

flesh of fruits

strands and rays of vascular tissue

3. Functions

a. wound repair

b. form adventitious roots

c. photosynthesis and metabolism

d. storage

e. secretion and transport

C. Collenchyma

1. Features of cells

a. elongate

b. lots of uneven thickening of 1o cell walls

c. alive at maturity

2. Found

in strands or cylinders under the epidermis of young stems and petioles

3. Function

provide support and strength to young, growing tissues

4. Source - differentiate from parenchyma

plasticity in development

D. Sclerenchyma

1. Features

      1. Thick, lignified secondary walls

Lignin - a complex carbohydrate that gives resistance to compression and stretching

b. Often dead at maturity

2. Found - any part of plant body

3. Function - strength and support

4. Two types

a. Sclereids

1) variable shape

2) occur singly or in aggregates

3) can form hard layers

b. Fibers

1) long slender cells

2) often in strands or bundles

3) fibers have many economic uses

III. Vascular tissues - derived from vascular cambium

A. Xylem

1. Function - conduct water

2. Cell types

a. Tracheids

elongate, 2o walls,

dead at maturity

pits in walls

b. Vessel members

shorter and wider

perforations

joined into long, columns

c. Occurrence and evolution of the two types

 

B. Phloem

1. Function - conduct food

2. Cell types

a. Sieve cells -

long and slender

narrow pores

scattered sieve areas

b. Sieve tube members

large sieve pores on some walls

sieve plates

sieve tubes

c. characteristics of both

living protoplasts

no nuclei

no clear boundary between cytoplasm and vacuoles

d. occurrence of two types

 e. companion cells

derived from same initial cell

have nuclei

regulate movement of materials into and out of sieve tube members

C. Vascular tissue also contains

parenchyma

fibers

strands

IV. Epidermis

A. General features

 B. General function

C. Guard cells

D. Trichomes

1. Root hairs

2. Leaf hairs

3. Defensive functions

 E. Periderm - in plants with 2o growth, periderm replaces the epidermis on roots and stems

cork cambium

cork phelloderm