Chapter 35:
Plant Structure and
Growth
Question ?

What heading can be given to the
following groups of words?
--------Lettuce
Rhubarb


---------Apples
Oranges
Beans
Peas
What is a vegetable?
What is a fruit?
Point



Plants have organs too, just like animals.
Asexual organs (vegetables)
Sexual organs (fruits)
Asexual Organs
1. Stem
2. Leaf
3. Root
Stem



The main body of the portion above
ground of a tree, shrub or herb.
The ascending plant axis.
Stem Functions
• Support of other plant organs.
• Ps.
• Storage (water and food).
Leaf



Lateral outgrowths of the stem axis.
Primary photosynthetic organs.
Function:
•
•
Photosynthesis
Storage
Root


The descending axis of a plant, normally below
ground.
Functions:
•
•
•
Anchorage.
Absorption of water and minerals.
Storage.
Sexual Organs
1. Flowers
2. Fruits
3. Seeds
Flowers



Modified leaves grouped together on a
stem.
Sexual reproductive organs.
Function:
• Sexual Reproduction
Fruit


A mature ovary, sometimes including
other floral parts.
Function:
• Seed dispersal
• Seed protection
Seed


Mature ovule containing the embryo and
nutrient tissues.
Function:
• Dispersal unit in sexual reproduction.
Plant Cell Types

Differentiated by the type and thickness
of the cell wall.
1. Parenchyma (soft tissue)
2. Collenchyma (glue tissue)
3. Sclerenchyma (hard tissue)
Parenchyma Cells





Primary wall only.
Thin cell wall.
Alive when mature,
“typical" plant cell.
Functions
•
•
•
•
Ps
Storage
"Filler" cells
Cell division (mitosis)
Collenchyma

Primary wall only.
Wall is thickened,
especially in the corners.
Alive when mature.

Function


•
•
Support of non-woody plant
parts.
Ex: veins, stems.
Sclerenchyma



Secondary wall
present.
Wall strengthened
with lignin.
Dead when mature.
Sclerenchyma Types
1. Fibers
2. Sclereids
3. Tracheids
4. Vessel Elements
Fibers


Elongated thin cells
used for support.
Ex: Hemp fibers
Sclereids


Used for hard dense
areas and support.
Ex: Nut shells, seed
coats
Tracheids


Spindle - shaped
cells with pits in the
cell walls.
Used for water
transportation.
Vessel
Fiber
Vessel Elements


Wide stocky cells
with pits in the side
walls; lack end walls.
Used for water
transportation.
Plant Tissues


Can be named by several methods:
• Ex:
Cell Location
Cell Origin
Cell Function
Point
• The same cell can have several tissue names
depending on the criteria for naming.
Main Tissue Systems
1. Dermal
2. Vascular
3. Ground
Dermal Tissue



Epidermis or "skin" of the plant.
Often has a cuticle, a waxy coating to
prevent water loss.
Functions:
•
•
Prevent water loss.
Water absorption (root hairs).
Vascular Tissue


Made of Xylem and Phloem.
Functions:
• Transport and support
• Xylem - Water
• Phloem - Food
Xylem
Phloem
Sieve Cell – alive when functioning,
but lacks a nucleus.
Companion Cell – alive, controls
itself and the sieve cell.
Ground Tissue


Tissue between the dermal and the
vascular tissues.
Functions:
•
•
•
•
"Filler" tissue
Ps
storage
Support
How does plant growth and
animal growth differ ?

Animals
• Whole organism increases in size.
• Determinant Growth: grow to a certain size,
then stop.

Plants
• Growth in specialized areas only.
• Indeterminant Growth: grow as long as they
live because the specialized areas remain
embryonic.
Plant Meristems


Perpetual embryonic
regions.
Zones for cell
division.
Meristem Types
1. Apical growth in length.
Primary growth.
2. Lateral/Cambiums growth in
diameter. Secondary growth.
Comment

Some tissues like Xylem may be Primary
or Secondary depending on which
meristem produced the cell.

Ex:
•
•
Primary xylem
Secondary xylem
Apical Meristem Types
1. RAM – Root Apical Meristem: primary
growth of roots.
2. SAM – Shoot Apical Meristem: primary
growth of shoots.
RAM



Located at the tip of
each growing root.
Protected from the
soil by the Root Cap.
Root Cap
•
•
Protects RAM.
Secrets a
polysaccharide
lubricant for root
growth.
RAM
Primary Root Zones
1. Cell Division - cells small and
embryonic.
2. Cell Elongation - cells elongate and start
to mature.
3. Cell Differentiation - cells mature into
final cell types.
Root Hairs



Extensions of the
epidermis to increase
surface area for water
absorption.
Not a true tissue.
Comment - root hairs
are very delicate and
must be continually
replaced.
Root Hairs
RAM - Primary Tissues
1. Protoderm: Will mature into the epidermis and root hairs.
2. Procambium: Matures into the vascular tissues of the
stele:
•
•
•
Xylem
Phloem
Pericycle – site of branch roots
3. Ground Meristem: Matures into the ground tissues
•
•
Cortex – storage tissue
Endodermis – second skin around the stele that controls the
movement of materials into the stele.
Epidermis
Cortex
Stele
Endodermis
Pericycle
Xylem
Phloem
Branch Roots


Originate from the
pericycle.
Burst their way to the
outside.
Root Types



Taproot - one main root.
•
Ex: carrot
Fibrous Roots - many small roots of equal size.
•
Ex: grass roots
Adventitious Roots
•
•
Roots that develop from other plant parts.
Ex: roots on stem cuttings
climbing roots
SAM Produces
1. Protoderm
2. Procambium
3. Ground Meristem
Comment – these tissues mature into the
same things as seen in RAM.
SAM Differences



No "root" cap.
Produces leaves as stem out-growths at
the nodes.
Has buds.
Buds


Apical Meristems protected
by modified leaves
or bud scales.
Axillary Buds
Branch Stems


Develop from axillary
meristems or axillary
buds.
"External"
development.
Modified Stems
1. Rhizomes
•
•
An elongated
underground
horizontal stem.
Ex: Iris, many
grasses
2. Stolons
•
•
An elongated aboveground horizontal
stem.
Ex: Strawberries
Airplane Plant
3. Tubers
•
•
A much-enlarged,
short, fleshy
underground stem tip.
Ex: Dahlia, Potato
4. Tendrils
•
•
A slender coiling stem.
Ex: Clematis and other
climbing vines.
Leaves: Stem outgrowths for Ps.

Leaf Morphology:
Axillary Buds
1. Gross
•
•
Blade - the
flattened portion of
a leaf.
Petiole - stalk of a
Blade
leaf.
Petiole
Blade/Leaf Types


Simple - 1 blade.
Compound - Several blades.
Nodes and Internodes


Node - stem area
where a leaf and
bud are attached.
Internode - stem
area between
nodes.
Internode
Nodes
2. Fine Morphology
The tissues within a leaf.
1. Upper Epidermis
•
•
•
•
Cuticle present.
Usually 1 cell layer thick.
Cells w/o chloroplasts .
Function: protects the mesophyll.
2. Mesophyll
Spongy
Palisade upright cells.
Spongy loosely organized cells
with air spaces.
Function: major sites for Ps.
3. Lower Epidermis
4. Veins
Palisade
3. Lower Epidermis




Cuticle present.
Usually 1 cell layer.
Cells w/o
chloroplasts.
Stomata present for
gas exchange.
• Regulated by Guard
Cells which have
chloroplasts.
4. Vein Structure



Xylem: dorsal
Phloem: ventral
Often
Bundle Sheath Cells
surrounded by
Xylem
bundle sheath
cells for support.
Phloem
Collenchyma
Leaf Modifications
1. Tendrils: for support
Ex: Peas
2. Bulbs: for food storage
Ex: Onion
3. Insect Catching
Ex: Carnivorous Plants
4. Flowers: thought to be
modified leaves.
Other Modifications of Leaves
Tendrils
Succulent Leaves
Spines
Bracts
Stem Vascular Tissue


Dicots – vascular bundles join together to
make a ring. Often have secondary
growth.
Monocots – vascular bundles are
scattered. No true secondary growth.
Secondary Growth


Growth in diameter.
Growth from lateral meristems or
cambiums.
• 2 Types of Cambium
1. Vascular: Located between primary xylem and
phloem.
– produces secondary xylem and phloem.
2. Cork – produces “cork”.
Fibers
Phloem
Vascular Cambium
Xylem
Fibers
Vascular Cambium: Cell
Maturation






Internal  xylem
External  phloem
The VC pushes the xylem and phloem
apart from each other.
Result
Newest xylem is next to the cambium.
Oldest xylem is in the center of stem.
Results





Newest phloem is next to cambium.
Oldest phloem is under the epidermis.
Result
Xylem accumulates over time.
Phloem is destroyed by the outward
growth and must be replaced yearly.
2. Cork Cambium


Location: Cortex (external to the VC).
Produces: Cork
• Comment – commercial cork is harvested
from a Cork Oak.

Cork Cells
• Produced "outwardly" only.
• Covered with suberin and are dead when
•
mature.
Function – insulation and protection.
Epidermis
Cork
Cambium
Cortex
Phloem
Vascular
Cambium
Xylem
Fibers
Bark


All tissues external to the VC.
Includes:
•
•
•
•
•
Phloem (1 degree and 2 degree)
Cork
Cortex
Epidermis
Fiber cells
Wood

Xylem tissue of a dicot stem.
• Comment – monocots don’t have VC and
technically don’t produce true “wood”.

Xylem Growth
• Springwood - Large cells
•
Rapid growth
Summerwood - Small cells
Slow growth
Annual Rings




Formed by the growth difference between
springwood and summerwood.
Usually one produced per year.
Ring size varies by climate and growing
conditions.
Rings can be used to date wooden
structures.
Summer Wood
Spring Wood
One Year’s Growth
Angiosperms
Divided into two main types:
1. Dicotyledons or Dicots
2. Monocotyledons or Monocots
 Cotyledons = seed leaves

5 differences
Monocots vs. Dicots
1. Seeds and embryos
2. Leaves
3. Stems
4. Roots
5. Flowers
Seeds and Embryos


Dicots - no endosperm.
- 2 cotyledons.
Monocots - endosperm
- 1 cotyledon
Leaves


Dicots – netted veins.
Monocots - parallel veins.
Stems


Dicots - ring pattern
- vascular cambium
Monocots - scattered pattern
- no vascular
cambium
Roots


Dicots - taproot.
- xylem centermost
tissue.
Monocots - fibrous roots.
- pith centermost
tissue.
Flowers


Dicots – parts in 4's or 5's.
Monocots – parts in 3's.
Summary


Know the main organs of plants and their
functions.
Know the main cell types or tissues in
plants and their functions.
Summary


Know the structural organization of
stems, roots, and leaves.
Know the differences between dicots
and monocots.