Introduction to Plants

1
Introduction to Plants

• Lets 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

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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.
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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.
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Basic Body Plan Angiosperms

• Typical flowering plants have
• shoots
• roots

Aboveground parts such as stems, leaves, and
flowers
Absorb minerals and water for the plant, and
store nutrients as well

• Shoots and roots consist of three tissue systems.
  
• Ground tissue system
• vascular tissue system
• Dermal tissue system

Photosynthetic tissue storage tissue and
structural support.
Distribute water and nutrients around the plant
Covers and protects exposed surfaces of the plant
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Simple Tissues
Carry on most of the plant's metabolic functions
Most parenchyma cells have the ability to
differentiate into other cell types under special
conditions , such as during repair and
replacement of cells after injury
Parenchyma typically thin-walled, flexible, and
many sided. Makes up most of the soft primary
growth of roots, stems, leaves, and flowers.
Also has storage and secretion functions. Living
at maturity. 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 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
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Complex Tissues
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.
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Xylem

• Xylem conducts water and minerals up a plant
  from its roots. There are two types of xylem
  cells
• Tracheids
• Vessel elements

Long and thin
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
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Phloem

• Phloem vessels carry nutrients, such as glucose,
  throughout the plant.
• Made up of
• Sieve tube elements
• Companion cells

Actually carry the nutrients in the plant
Hang around to lend support to sieve tube
elements.
Differences between xylem and phloem
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Special Structures
Roots Leaves Flowers

• 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
Root hairs provide increased surface area for the
absorption of water and minerals

• If you were to cut a cross section through a root
  youd find
• Epidermis (outer protection)
• Cortex (mid-region where starches are stored)
• Stele (inner cylinder which contains xylems and
  phloems)

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
cells cytoplasm.
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Root Adaptations
While the roots 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.
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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.
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Leaves

• 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

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Flowers
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) Female parts
collectively called pistil Female gametes are
found in the ovary are called megaspores.
Things you should already know Flowers are
colorful and fragrant to attract pollinators. It
is a wonderful and fool-proof adaptation, that
works on humans too!