PLANT
STRUCTURE
There are many types of plants….
We are going to focus on land plants:
- they provide protection for their
embryos which has increased over time
- they have multicellular haploid and
diploid phases
- they can be compared by the presence or
absence of conductive systems
Types of Land Plants
Plant Group
Non-vascular
Land Plants
Seedless
Vascular
Plants
Seeded
Vascular Plants
Major Features
• no conducting tissue
• often grouped together as bryophytes
• usually small and grow close to the ground
• include mosses, liverworts, and hornworts
• well-developed vascular tissue
• do not produce seeds
• include horsetails, ferns, club mosses, and whisk ferns
(were once large specimens, but most of today’s
representatives are relatively small)
• most living plant specimens are in this group
• seeds contain an embryo, a supply of nutrients, and a
protective outer coat
• have extensive vascular tissue and include some of the
world’s largest organisms
Seeded Plants
The seeded vascular plants are divided into:
- Gymnosperms
Have seeds that do not develop within an enclosed structure
- Angiosperms
Have seeds that develop within a protective structure
Although no one
species of the
265,000 species of
plants can be
considered typical,
the focus here is
on angiosperms.
Plants have two basic organ systems:
Shoots and Roots
The Shoot System
The shoot
system
consists of
stems,
leaves and
reproductive
structures.
Stems are the framework
for upright growth.
Terrestrial
plants
support
themselves
by means of
thickened
cellulose,
cell turgor
and xylem
Water, minerals, and
organic substances
are transported
through the stems
The leaf has evolved to optimize
photosynthesis.
The root system usually
grows underground.
It absorbs water and
minerals from soil
and conducts them
upward
It stores food; it also
anchors and
supports the plant
There are taproot and
fibrous root systems.
Plant organ are composed of
three tissue systems.
Vascular Tissue
 Xylem and Phloem carry out long-distance conduction of water minerals,
and nutrients within the plant
 Provides support
Dermal Tissue
 Outer protective covering
 Protects against physical agents and pathogenic organisms
 Prevents water loss
 May have specialized structures for various purposes
Ground Tissue
 Consists mostly of thin-walled cells that function in storage,
photosynthesis, support, and secretion
The vascular tissue distributes water
and solutes through the plant body.
XYLEM
Conducts water
and dissolved ions
absorbed from the
soil
XYLEM
It is formed from two types
of cells that are dead at
maturity
- Tracheids are long
cells with overlapping
ends
- Vessels are shorter
cells joined end to end
to form a vessel.
PHLOEM
Phloem transports sugars and other
solutes throughout the plant body
PHLOEM
Contains living
conducting cells called
sieve tube members
Companion cells,
adjacent to the sieve
tube members, help to
load sugars produced
in leaves and unload
them in storage and
growth regions.
The dermal tissue system covers and
protects the plants surface.
The epidermiscovers the primary plant body
Dermal Tissue
Epidermal cells are typically nonphotosynthetic and are relatively transparent ,
allowing light to penetrate to deeper tissues.
Dermal Tissue
A waxy cuticle
covers the
external
surfaces of the
plant to restrict
water
loss and resist
microbial attack
Dermal Tissue
The periderm replaces
the epidermis when roots
and stems increase and
become woody.
The ground tissue system makes
up the bulk of the plant body
Functions are photosynthesis, storage and support
Ground tissues are composed of
three basic cells types.
Parenchyma is the
most abundant type.
Thin walled, pliable
cells, found in
virtually all plant
parts.
Various types
participate in
photosynthesis,
storage, secretion,
and other tasks.
Collenchyma cells help strengthen the
plant (for example, “strings” in celery).
They are commonly arranged as strands or
cylinders beneath the dermal tissue of stems
and stalks
Cell walls become thickened with cellulose
Sclerenchyma cells provide mechanical
support and protection in mature plants
Walls are thick and often
impregnated with
lignin, which strengthens
and
waterproofs cell walls
Sclerenchyma cells form
fibers, such as in
hemp and flax