Organs in PlantsPacket #53Chapter #

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 LeavesSimple, PinnateFeather Shaped

Simple, PalmatePalm Shaped

Variations of LeavesSimple, CordateHeart-Shaped

Simple, OrbicularRound

Variations of LeavesPinnately LobedFeather-Shaped

Palmately LobedPalm-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

Mutually beneficial associations between roots and soil fungi

Root nodules 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