Download Introduction to Plants

Let’s recall some basic facts about plants:
• All plants are multicellular, eukaryotic,
autotrophic organisms
• All plant cells contain cell walls composed of
cellulose
• All plants are photosynthetic, and contain
cellular components with pigments to capitalize
on that process
• All plants take up water through capillary
action
Plant Classification
Plants can be divided into two main categories
•nonvascular
Known collectively as phylum bryophyta:
These are the simplest terrestrial plants.
They lack true roots, stems and leaves.
Common bryophytes are mosses and
liverworts
•vascular
Known collectively as phylum
tracheophyta:
These are the most common and
widespread plants, which contain true
conducting vascular tissue.
Common tracheophytes include ferns,
gymnosperms and angiosperms.
Tracheophyte Subdivisions
Of all the Tracheophytes, ferns are the simplest and most ancient.
These are known as “seedless” plants. They do have vascular tissue to
transport water and nutrients, but they still need an abundant supply of
water for reproduction since they do not possess seeds.
These non-seed vascular plants
evolved long before dinosaurs.
The seeded tracheophytes
include the gymnosperms and
angiosperms.
Gymnosperms contain
unenclosed seeds which are
often found “naked” on the
scales of a cone.
Angiosperms contain
enclosed seeds located
within a fruit or nut.
Basic Body Plan: Angiosperms
Typical flowering plants have
• shoots
Aboveground parts such as stems,
leaves, and flowers
• roots
Absorb minerals and water for the
plant, and store nutrients as well
Shoots and roots consist of three
tissue systems.
• Ground tissue system
Photosynthetic tissue; storage tissue and
structural support.
• vascular tissue system
Distribute water and nutrients around the
plant
• Dermal tissue system
Covers and protects exposed surfaces of
the plant
Simple Tissues
Carry on most of the plant's
Parenchyma: typically thin-walled,
metabolic functions
flexible, and many sided. Makes up most Most parenchyma cells have the
of the soft primary growth of roots,
ability to differentiate into other
stems, leaves, and flowers. Also has
cell types under special conditions ,
storage and secretion functions. Living such as during repair and
at maturity.
replacement of cells after injury
Collenchyma: elongated and stretchable
tissue supporting rapidly growing plant
parts, including young stems and leaf
stalks. Pectin (a polysaccharide) gives
flexibility to collenchyma cell walls.
Living at maturity
Collenchyma
Sclerenchyma: Variably shaped, dead at
maturity, but lignin in cell wall helps
tissue resist compression. (Lignin helped
upright plants evolve on land, and resist
fungal infections) Fibers and sclerids are
typical. Occur in parts of the plant
which have quit growing in length
Parenchyma
Vascular Tissues:
As plants evolved to be
more and more
terrestrial, tube-like
structures developed
that function to
transport materials up,
down, and around the
plant.
While in an aquatic environment, plant tissues
are able to transport water and nutrients
across membranes through simple osmosis and
diffusion.
Xylem and phloem are the vascular tissues of complex plants
(tracheophytes) which carry water and nutrients around the plant.
Xylem: conducts water and minerals up a plant from its roots. There
are two types of xylem cells:
 Tracheids Long and thin
 Vessel elements Short and thick
Xylem is a long narrow tube
constructed of dead cells which
are strong because of lignin in
their cell walls.
The water and minerals go in and
out of the tubes through the pits
on the sides of the tubes.
These pits allow easy water
transfer to neighbouring cells
This lignin also gives the plant an
extra strong mechanical support
system
Phloem vessels carry nutrients, such as glucose, throughout
the plant.
Made up of:
• Sieve tube elements Actually carry the nutrients in the plant
•Companion cells Hang around to lend “support” to sieve tube
elements.
Differences between xylem and
phloem…
Roots
Leaves
The growing region of a root includes three regions:
• The root tip
• The zone of elongation
• The zone of maturation
Meristematic zones are simply
regions of rapid growth, and
actively dividing cells. You
can find it here in the roots,
and at the apical region of
the shoot as well.
Layers in the Root:
If you were to cut a cross
section through a root you’d
find:
•Epidermis (outer protection)
• Cortex (mid-region where
starches are stored)
• Stele (inner cylinder which
contains xylems and phloems)
Flowers
Root hairs provide increased surface area for
the absorption of water and minerals
Water may enter the root via two methods. The
apoplast is a continuous space between the plasma
membrane, and the cell wall of all cells. The
symplast allows for the flow of water and other
nutrients along concentration gradients through a
cell’s cytoplasm.
While the root’s main function is to anchor the plant, they also come in
many different varieties, and have adapted to different circumstances.
• Tap Roots: Roots that plunge deep into the Earth to find the water table, and
“tap it”, while serving to increase the support of the plant as well.
• Fibrous roots: Roots which grow in dense mats to optimally serve the plant in
the collection of water, and minerals, as well as to anchor it securely.
•Stilt roots: these are support roots, common among mangroves. They grow
down from lateral branches, branching in the soil.
Pneumatophores: Special stilt roots that are aerating roots which rise
above the ground, especially in saturated areas.
Prop roots: Special stilt roots that hold tall plants tight in windy areas.
Typically, these plants are top-heavy, like corn.
Buttress roots: These are large roots on all sides
of a tall or shallowly rooted tree, which typically
finds itself in poor or low nutrient soil.
Aerial roots: roots entirely above the ground,
such as in epiphytic orchids. They function as
prop roots or anchor roots. Some may be
parasitic.
• Haustorial roots: roots of parasitic
plants that can absorb water and
nutrients from another plant, such as in
mistletoe
Contractile roots: They pull bulbs or corms
of monocots deeper in the soil through
expanding radially and contracting
longitudinally. They help the plant find
appropriate soil moisture during seasonal
droughts.
•Storage roots: These roots are modified for
storage of nutrients, such as carrots and
beets.
Tuberous roots: A special type of storage
root where a porrtion of a root forms into
a roundish knob called a (tuber) for food.
• Photosynthesis
• Protection: modified to form
spines, as in cactus
• Storage: fleshy leaves allow plants
to survive particularly harsh
environments.
• Consumption: modified to trap
prey, as with the insectivorous plants
which grow in nitrogen poor soils.
• Conservation: tiny hairs to trap
water
When it comes to plants structures, the one that you will absolutely run
into on the AP Biology test, is flowers. The following is what you need
to know about the structure of the flower:
Male parts
collectively
called stamen:
Male gametes
found on the
anther are called
microspores.
(pollen/sperm)
Things you should already know: Flowers are colorful and
fragrant to attract pollinators. It is a wonderful and foolproof adaptation, that works on humans too!
Female parts
collectively
called pistil:
Female gametes
are found in the
ovary are called
megaspores.