Organs in Plants
Packet #53
Chapter #
Introduction

There are four major organs of a plant

Flower* (Not all plants)

Stem

Leaf

Root
Flower
Flower

The flower contains the organs of
plant sexual reproduction

It attracts insects needed to carry
the pollen between plants to allow
pollination

It's important for reproduction
Stem
Stem

The stem is the organ which holds
the leaves upright in the air and
facing the light

It carries water and minerals to the
leaves, and food around the plant

The stem is important for nutrition,
excretion and growth
Stem II

Stem
 Alternating system of nodes
 Locations where the leaves are
attached
 Internodes
 Stem segments between nodes
 Auxiliary Bud
 Angle, or axil, formed by each
leaf of the stem
 Has the potential to form a
branch
 Most though are dormant
Stem III

Growth of a young shoot is usually
concentrated at its apex (tip), where
there is a terminal bud with
developing leaves and a compact
series if nodes and internodes

The presence of terminal bud
prohibits the growth of the axillary
bud
 Apical dominance
 “evolutionary response that
directs growth toward light
The Leaf
Leaf I

The leaves are the sites of photosynthesis,
gas exchange and transpiration.

They make all the food that the plant needs

Leaves contain chlorophyll, which uses light
energy to change carbon dioxide and water
into glucose

They have tiny little pores, which allow
essential carbon dioxide in and waste gases
out

Leaves are important for nutrition and
excretion
Leaf II


The external structure of a leaf
consists of a flattened blade and a
petiole

Stalk

Joins the leaf to the node on the
stem
Leaves are in various sizes, shapes
and arrangement of leaves.
Variations of Leaves
Simple, Pinnate
Feather Shaped
Simple, Palmate
Palm Shaped
Variations of Leaves
Simple, Cordate
Heart-Shaped
Simple, Orbicular
Round
Variations of Leaves
Pinnately Lobed
Feather-Shaped
Palmately Lobed
Palm-Shaped
Variations of Leaves

Pinnately Compound
Roots
Roots

The root is the organ which provides
anchorage for the plant so that it
does not blow away or fall over

With its root hairs it provides a big
surface area to help take in water
and minerals from the soil - these
are both essential for
photosynthesis

The root is therefore important for
nutrition
Root Hairs

At the tip of roots, a vast number of
root hairs can be found.


Why?

Most absorption of materials
occur near the tips of roots

Increases the surface area of
roots.
Root hairs are extensions of
epidermal cells
Adventitious Roots

Roots that develop out of above
ground stems or leaves are called
adventitious roots

These roots occur as of
adventitious tissue


Tissue that grows in an atypical
location
Provide additional support for
taller plants.
Modified Roots
Modified Roots I

Prop Roots

Develop from branches, or a vertical
stem and grow downward into the
soil to help support certain plants in
an upright position


Fichus tree South Florida?
Buttress Roots

Swollen bases or braces that
support certain tropical rainforest
trees that have shallow root systems
Modified Roots II

Pneumatophores


Aerial “breathing” roots that may
assist in getting oxygen to
submerged roots
Contractile Roots

Roots that grow into the soil and
then contract

Pulling plant deeper into the soil

Corms

bulbs
Mutualistic Relationship
Between Roots & Other
Organisms
Relationships

Mycorrhizae


Root nodules


Mutually beneficial associations between roots and soil fungi
Swellings that develop on roots of legumes and house millions of rhizobia
(nitrogen fixing bacteria)
Root Graft

Natural connection between the roots of trees belonging to the same or different
species.
Basic Morphology of
Plants
Basic Morphology of Plants

The basic morphology of plants
reflects adaptations that have
developed so that an organism can
inhabit and obtain resources from
soil and air.

More to come on organ systems
later.
Review