General Biology 2
Plant tissues are divided into two groups: Permanent Tissues and Meristematic Tissues.
Permanent plant tissue
These are composed of matured and differentiated cells that perform specialized
functions.
1. Vascular tissues– conducting tissue, transport
Transports water and organic materials (sugars) throughout the plant
• Xylem – transports water and dissolved ions from the root to the stem and leaves.
Conducting element:
A. Tracheids: long, thin tube like structures without perforations at the ends
B. Vessel elements: short, wide tubes perforated at the ends (together form a pipe, called
vessel).
• Both cells have pits (thin sections) on the walls
• Phloem – carries dissolved sugars from leaves to rest of the plant
conducting cells: sieve cells and sieve-tube members
both possess clusters of pores called sieve areas
both are elongated, living cells without a nucleus
• sieve cells
more primitive (found in all vascular plant)
pores are all same in size
• sieve-tube members
only found in angiosperms
pores are larger
occur end-to-end, forming sieve tube
2. Ground/Fundamental tissues– bulk of inner layers
Parenchyma cells are usually somewhat spherical or elongated, but they may have diverse
shapes. Most abundant ground cells.
• usually capable of further division
• typically have thin walls (usually only primary wall)
• Have large vacuoles
• usually remain alive after maturity
collenchyma
• living at maturity
• flexible, often in strands, forming support for organs
• elongated cells with unevenly thickened primary cell walls
sclerenchyma
• thick, tough secondary walls
• usually lack living protoplasts at maturity
• secondary walls often lignified (contain lignin);
lignin – highly branched polymer that reinforces structure
common in cells that have a supporting or mechanical function in
body structure
Cambium- a meristematic tissue supplying cells that will develop into vascular structure
3. Dermal/Surface Tissue- these are the outer protective covering of plants
• Epidermis is the outermost layer of cells
• In stems and leaves, epidermis has cuticle, a waxy layer that prevents water loss.
• Periderm a protective covering that replaces epidermis when its roots and stem increase
in diameter.
Meristematic Tissues
These are composed of embryonic cells that are actively dividing.
These tissues are found at the growing tips of the stem and roots.
Apical Meristematic Cells are primarily responsible for the increase in length and
height of plants.
A. Apical Shoot Meristem- it is the zone of cell growth at the tip of the stem.
B. Apical Root Meristem- it is the zone of growth at the tip of the primary roots.
Plant Organs and their Function
Roots constitute the underground part of the plant. Also known as the “idden Half”.
Functions of Root:
a. Root serves as anchorage of plant to the soil.
b. Absorb water and minerals;
c. Conduct the absorb minerals and water to the stem;
d. Storage of food in the form of starch.
Cross Section of a Root
Parts and Functions
Xylem-The basic function of xylem is to transport water from roots to stems and leaves,
but it also transports nutrients
Phloem- transports the soluble organic compounds made during photosynthesis, in
particular the sugar sucrose; to parts of the plant where needed.
Pith or Medulla- is located at the center and composed of soft, spongy parenchyma cells,
which store and transport nutrients.
Pericycle- regulates the formation of lateral roots.
Epidermis- Protects against water loss, regulate gas exchange, secrete metabolic
compound and absorb water and minerals.
Cortex- transport materials into the central cylinder of the root through diffusion and may
also be used for food storage in the form of starch.
Endodermis- is the cylindrical boundery between cortex and stele. And function as an
apoplasmic barrier for selective nutrient uptake.
Root hair- Developed from the epidermal cells. Increase
surface area available for water and mineral
absorption.
Vascular cylinder a central column formed by te
vascular tissue of a plant root and surrounded by
parenchyma cells. Vascular cylinder ensures nutrints,
water and other substances are transported
throughout the plant.
Casparian strip- are waerproof strip surrounding each
endodermal cell in a root. It is involved in one-way
passage of materials into the vascular cylinder. Witout
it, the upper part of plants might not get water, as it
helps to create root pressure.
Morphology of the Root Tip
Root Cap/calyptra- it is produce by meristematic
zone. Root cap protects the tender apex of the root
as it makes its way throught the soil. The cell of the
root cap also produce mucilage which lubricates the
passage of the root through the soil.
Apical Meristerm- above the root cap is the region of
meristematic activity. The cell of this region are very
small, thin-walled and divide actively.
Region of elongation- the cells in this region undergo
rapid elongation and enlargement. Region of
elongation is also responsible for the growth of root
in length.
Region of Maturation- the cells of the elongation
region gradually differentiate and mature. Mature
cells in this region differentiate into various tissues
like hair root and permanent tissues.
Two main types of Root System:
A. Tap Root System- Common in dicotyledon, has a
vertical oriented single large main root with small
lateral roots.
B. Fibrous Root System- common in monocotyledons,
A rootin a system that is made up of many threadlike
B roots of more or less equal in length.
The shape of taproots can vary but the typical shapes include:
Conical root: this type of root tuber is conical in shape, i.e. widest at the
top and tapering steadily towards the bottom.
e.g. carrot
Fusiform root: this root is widest in the middle and tapers towards the top
and the bottom.
e.g. radish
Napiform root: the root has a top-like appearance. It is very broad at the top
and tapers suddenly like a tail at the bottom.
e.g. Turnips
Modified Roots
Storage Roots- In certain plants the roots, or part of the root system,is
enlarged in order to store large quantities of starch and other
carbohydrates.
Exampe: Carrot, Beet Roots, Sweet Potato
Pneumatophores- Breathing roots to help plants that grow in very wet
areas like swamps get enough oxygen
Example: Mangrove
Contractile Roots- can contract and control the position of the plant in
relation to the plant surfacedepending on season. Contractile roots are
vertical, tapering and wrinkled looking.
Example: Succulent plants
Buttress roots are large roots on all sides of a shallowly rooted
tree. Typically, they are found in nutrientpoor rainforest soils and do
not penetrate to deeper layers.
Velamen roots- Aerial roots with many layers of epidermis.
Example: Orchids
Prop Roots- Adventitous roots that develops from the branches of
tree.
Example: Rubber Tree
Stilt Roots-adventitous roots that develop from the lower nodes of
the stem.
Example: Sugar cane and Corn
Parasitic Roots- These plants have no chlorophyll necessary for
photosynthesis. Therefore these plants are dependent to their host
plant.
Example: Dodder
Stem
Terminal bud-bud
located at the apex (tip)
of the stem
Axillary bud- precursor of
a branch or lateral shoot
that grows between a leaf
or stem
Node- where leaf is
attached to stem
internode- area
between nodes
Lenticel- small spots
on stem, allow a stem
to exchange gases
Terminal bud scale scar- ring of
scars from when the buds sprout
each spring & bud scales fall off
Functions of Stem
-Stems support leaves and branches.
-Stems transport water and solutes between roots and leaves.
-Stems in some plants are photosynthetic.
Types of growth in plants
Rimary growth- primarily vertical. This kind of growth gives the plant its height.
Secondary growth- is seen in woody plants. This kind of growth produces stronger, thicker
stems from the vascular cambium and cork cambium.
Types of Stem
Herbaceous stems- consist of soft, green and flexiblestem.
Woody stems- Hard woods and produce secondary growth.
Heartwood and Sapwood
Sapwood (secondary xylem) is the living
portion of a woody stem or branch,
usually it is light in color and consist of
actively dividing cells.
Heartwood (primary xylem) is the dead,
inner wood, which often comprises the
majority of a stem’s cross-section.
In young trees and young parts of older trees, all of the wood in the stem is sapwood.
Sapwood is formed just under the bark by a thin layer of living cells known as the
cambium, which produces bark cells to the outside and wood cells to the inside. Tree
stems increase in girth during each year of growth because a new layer of wood cells is
added inside the cambium. When growth occurs, the cambium moves outward to
accommodate the new layers of wood forming inside. Sapwood – this newly formed,
outermost region of wood – contains a variety of cell types, most of which are living and
physiologically active. This sapwood is where water and dissolved minerals are
transported between the roots and the crown of the tree and, to a lesser extent, where
energy reserves are stored.
But as the tree gets older and its trunk increases in diameter, things change. No longer is
the entire cross-section of the trunk needed for conducting sap. This, combined with an
increased need for structural support, causes significant changes in the wood. The cells
nearest the center of the trunk die, but they remain mostly intact. As these older sapwood
cells age and die, they become heartwood. That is, they are altered to accommodate a
shift in function. As residues of the once-living cells and additional chemical compounds
from plant accumulate in the heartwood, those cells cease to transport water or store
energy reserves. These compounds (including resins, phenols, and terpenes) not only help
make heartwood more resistant to attack by insects and decay organisms but also tend to
give this inner portion of the stem a distinctive darker color.
Bark is refer to all tissue outside the wood. Bark is mostly dead tissue which is the
product of cork cambium. The outer most bark contains cork and dead phloem known as
rhytidome. The dead cork cells are lined with suberin, a fatty substance that makes them
highly impermeable to gases and water. Gas exchange between the inner tissues and bark
takes place through the lenticels.
Modified Stem
Storage Stem- Stores water and sugar in the form of strch.
Example: sugarcane, cactus and bamboo shoot.
Rhizomes- horizontal stems that grow below the ground with
adventitious roots
Example: Ginger, Fern and grasses.
Stolons or runners - horizontal stem that grows above the ground
with long internodes
Example: Strawberry and Jasmine
Tubers - accumulation of food at the tips of underground stolons.
The "eyes" of a potato are the nodes of a starch-ladened stem.
Example: potato
Bulbs - large buds with a small stem at the lower end surrounded
by numerous fleshy leaves, adventitious roots at base
Examples: onion, tulip, and lily
Corms - resemble bulbs but composed entirely of stem tissue
surrounded by a few papery scale like leaves
Cladodes - are green branches of limited growth, which have taken
up the function of photosynthesis.
Exampl: asparagus
Photosynthetic stem- Cacti are stout fleshy stems that are modified for
food and water storage and photosynthesis.
Example: cactus
Thorns- hard, rigid extensions of plants with sharp ends.
Example: Honey locust (modified stem) and Black Locust (modified
leaf stipules)
Tendril- the axillary bud modifies to form a thin, wiry and highly
sensitive structure.
Example: grape tendril.
Offset- commonly known as the runners of aquatic plants.
shorter and thicker than runners.
Example: water hyacinth
