Plant Organs
The Plant System
The Root System
1. Fibrous Root System – the root of grass or of
any weed at the base of its stem. Some
fibrous root systems do not penetrate deeply
into the soil but extend to a distance outward
from the base of the plant. Examples are
grass, corn, rice and beans
The Root System
2. Taproot system – usually grow deep in the
ground. The primary root becomes large, long
and slender with short lateral rootlets.
Example: alfalfa
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Taproot
3 functions
Endodermis
Function of the leaf (1)
7 opposite arrange
8Parallel venation
9 netted palmate
phyllotaxy
The Root System
3. Adventitious Roots – roots that grow from the stem or
leaves. Examples: katakataka, pandan, corn and rubber
tree
4. Brace or prop root – grow from the nodes. They grow in
circles and help support the plant. Examples: corn and
sugarcane
5. Climbing roots – found along the stems that cling to the
walls and other means of support. Examples: ampalaya,
squash, upo
6. Propagation roots – found in plants where roots develop
on the stem when placed in wet soil or water, and new
plants grow. Examples: San Francisco, climbing roses,
begonias
Functions of Roots
1. Anchorage - keeps the plant rooted to the ground
2. Absorption - roots absorb water and other mineral
matter from the soil. This is called diffusion, the
process by which water from the soil moves into the
root hairs
3. Nitrogen Fixation – Together with S and P, nitrogen is
needed by plants to build proteins. Some roots have
nodules which contain bacteria that fix nitrogen from
the atmosphere for plant use.
4. Storage – all roots have a small amount of food stored
temporarily in them. The food is usually stored as
insoluble starch or as sugar
5. Conduction – Roots transport water, mineral salts and
sometimes stored food to the stems and the leaves
Structure of the Roots
Longitudinal Section – growth in length
a. Root cap – protects the apical meristem of roots,
sheds cells that facilitate the growth of the root
through the soil, gives off carbon dioxide to the soil
b. Meristematic region – cell division takes place. They
add new cells to the root cap and to the region of
elongation
c. Zone of elongation – located 1-3 mm above the
meristem, this is the region where the cell stops
dividing, but the cell wall expand and vacuoles increase
in size making the cells longer
d. Zone of maturation – just above the zone of
elongation, this region has cells which are all almost
uniform in structure. The cells begin to differentiate
and develop into many tissues.
Structure of the Roots
Cross Section of Primary Root Tisssues
1. epidermis – the outermost tissue from
which the root hairs extends. Its function is
for protection and absorption
2. endodermis – the innermost layer of cells;
serves as a boundary layer; controls the
movement of substances between the cortex
and the interior tissues of the root.
Stems
Herbaceous Stems – green and do not develop
tough, woody tissues. Their sizes are limited
because their soft stem tissues cannot support
much weight.
Woody Stems – Vascular plants that live for
more than one year often have woody stems.
The roots and stems of these plants increase
in diameter every season. They even reach
tremendous heights.
- may be simple, branched, upright or creeping
- can form underground food storage organs
(rhizomes, bulbs, corms or tubers)
- can produce suckers, shoots, stolons, runners
or tendrils. Runners, for example, will put
down adventitious roots when they reach a
suitable new location. Tendrils are modified
stems that attach themselves to nearby
objects for support.
The Leaf
All leaves are responsible for:
• absorbing the sun's rays the majority of
photosynthetic production (which can take
place in any green part of a plant)
• taking in carbon dioxide and releasing oxygen
and water vapor (breathing)
• removing waste products from the plant
• using osmotic pressure to draw water up from
the roots
The Leaf
External Structure
- vary in size and shape
- slender petiole or leaf stalk is present in the
leaves of most flowering plants. It is a
continuation of the stem to the rest of the leaf
- sessile – leaves without petioles
- blade – flattened, expanded portion of the
leaf and is usually green
Types of Leaves
Simple leaves – have single expanded portion
Compound leaves – the leaf blade may be
subdivided into several separate expanded
parts, or leaflets.
Bicompound – each leaflet may consist of an
extended portion and a short stalk attached to
the rachis, which is a continuation of the
petiole. Leaves may be pinnately compound
or bipinnately compound
Venation
Venation – the arrangement of veins in a leaf
1. Parallel venation – characteristic of most
monocotyledonous plants, such as corn, onion
and common grasses
2. Net venation – found in dicotyledonous
plants such as santol, gumamela, rose,
mango. In these plants, one or more veins
are prominent, and the smaller veins form a
conspicuous network
Types of Net Venation
Pinnately net veined – if a leaf has one main
vein from which the others branch off
Palmately net veined – leaf has several main
veins extending from the base
Types of Leaf
Venation
Leaf Arrangement and Phyllotaxy
Phyllotaxy – the system of leaf arrangement
1. Opposite – leaves are arranged in pairs on
each node of a stem (Ex. Guava leaf)
2. Alternate or spiral – leaves are arranged
around the stem, one on each node (santol,
atis and star apple)
3. Whorled – several leaves are arranged at a
node around the stem
Phyllotaxy
Leaf Margins