1 Plant Science Plant Structures Instructional Materials Service Texas A&M University - 8384 -

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Plant SciencePlant Structures

Instructional Materials ServiceTexas A&M University

- 8384 -

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Plant Structures

• Parts of a Vascular Plant

• Root Structure

• Stem Structure (External)

• Leaf Structure

• Parts of a Complete Flower

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Parts of a Vascular Plant

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Plant Organs

Plant organs include their roots, stems, leaves, and reproductive structures. Each plant organ performs a specialized task in the life of a plant.

• Roots, stems, and leaves are all vegetative structures.

• Flowers, seeds, and fruits make up reproductive structures.

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Plant Organ Functions

• Roots support the plant and supply it with water and nutrients.

• Stems connect the root and leaves.

• Leaves capture energy from the sunlight and use it to make food for the plant.

• Reproductive structures attract pollinators and produce seeds and fruits.

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Root Structure

Xylem (water transport)

Meristem

Root Hairs

Epidermis

Cortex

Phloem Tubes

Root Cap

Zone of Elongation

Zone ofDifferentiation

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The Epidermis

EpidermisThe epidermis is the outermost layer of cells surrounding the root.

The cells of the epidermis are responsible for absorbing water and minerals from the soil

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The Cortex

Cortex

The cortex is a layer of tissue between the epidermis and the vascular tissue.

Cortex cells function in the movement of water and in food storage.

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Root Hairs

Root Hairs

Root hairs are found along the main root and perform much of the actual work of water and nutrient absorption.

Most plants produce root hairs that only live a few days or a few weeks. As a plant grows, new root hairs form.

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Xylem

Xylem is the supporting and water conducting tissue of vascular plants.

Xylem

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Phloem

Phloem is the food conducting tissue of vascular plants, made up of sieve tubes and other cellular material.

Phloem

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Meristem

Meristem

The meristem is at the tip of the root and is responsible for manufacturing new cells.

This is the area where cell division and growth occur.

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Roots• The root is the first plant structure to

emerge from a seed during germination.

• Roots are mostly found below the soil surface and represent about 50% of a plant’s weight.

• The primary functions of roots are to absorb water and nutrients from the soil and to support the plant in an upright position.

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• Roots distribute the food energy produced in the leaves to the rapidly growing areas found at the root tips.

• Some plants use their roots as a specialized food storage reserve.

• The first root to emerge from a seed is the primary root, or radicle.

Root Functions

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• Plant root systems are classified based on the relative sizes of their primary and secondary roots.

• Plants such as dandelions, carrots, turnips, and most trees have a taproot.

• In taproot systems, the primary root thickens and becomes the dominant root.

Roots (taproot)

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• In fibrous root systems, the primary and secondary roots are of similar diameter.

• They remain fairly close to the soil surface.

• Fibrous root systems help to prevent the erosion of topsoil during heavy rains.

• Plants such as onions, grasses, and corn have fibrous root systems.

Roots (fibrous)

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Root Types

Fibrous RootsTap Root

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Stem Structure (External)

Terminal Bud

Petiole

Abscission Layer

Nodes

Internode

Growing PointYoung Leaf

Axillary Bud

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Stems

Stems function as supportive structures. They hold a plant’s leaves up toward the sun so the leaves can capture energy from sunlight.

Stems transport water and nutrients from the roots to the leaves, and food energy from the leaves to the roots.

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Leaf Structure

Bladestalk (Petiole)

Axillary Bud

Node

Internode Base of Leaf

Midrib

Vein

Expanded Portion of Blade (Lamina)

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Midrib & Veins

Midrib The midrib is the most prominent, central vein in a leaf.

Lateral veins are secondary veins that branch from the midrib.

Both midribs and lateral veins contain vascular tissue.

Vein

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Leaf Blade (Lamina)

Leaf Blade (Lamina)

The expanded flat portion of a leaf is the leaf blade, or lamina.

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Petiole (Bladestalk)

Petiole

The petiole attaches the lamina to the plant stem.

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Axillary Bud

Axillary Bud

An axillary bud exists on the stem just above the point where the leaf petiole attaches to the stem.

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Petal

Sepal

Parts of a Flower

Stigma

Anther

Receptacle

Filament

Pollen Tube

Ovary

Ovule

Embryo Sac

Microphyle

Style

Integuments

Pollen Grains

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Complete Flowers

Compete flowers have four basic parts:

1. Sepals

2. Petals

3. Stamens

4. Pistil

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Sepals

Sepals

Sepals are leaf-like structures that form an outer ring around the base of a flower.

Sepals enclose and protect a flower bud before it opens.

The complete ring of sepals is called the calyx.

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Petals

Petals

Petals are often the bright and colored part of a flower.

Petal colors and scents attract specific pollinators.

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Stamens

Anther The stamen contains both the filament and the anther.

The filament is a stalk-like structure that holds the anther.

Stamens are the male reproductive parts of a flower.

Filament

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Pistil

Stigma

Style

Ovary

The pistil includes three parts:

1. Stigma2. Style3. Ovary

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Pistil 1. Stigma

Stigma The stigma is a sticky, flattened surface that projects upwards towards the pollinator.

Birds and insects collect nectar from previously visited plants and brush against the sticky surface of the stigma.

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Pistil 2. Style

Style

The style is a supportive structure that holds the stigma in a position to maximize the chances of pollination.

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Pistil 3. Ovary

Ovary

Pollen Tube

Ovule

The ovary is an enlarged structure that contains the female sex cells, or ovules. The pollen tube grows through the ovary and into an ovule.

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Receptacle

The enlarged part of the pedicel where it joins the flower is the receptacle.

Receptacle

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Pedicel

Pedicel

The pedicel (flower stalk) supports the flower.

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Acknowledgements

Kristi Falco, Graduate Assistant, Instructional Materials Service, researched and developed the information used in this PowerPoint Presentation.

Christine Stetter, Artist, Instructional Materials Service, developed and illustrated this PowerPoint Presentation..

Keith Zamzow, Curriculum Specialist, Instructional Materials Service, edited and reviewed this PowerPoint Presentation.

Vickie Marriott, Office Software Associate, Instructional Materials Service, edited this PowerPoint Presentation.

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ALL RIGHTS RESERVED Reproduction or redistribution of all, or

part, of this presentation without written permission is prohibited.

Instructional Materials Service

Texas A&M University

2588 TAMUS

College Station, Texas 77843-2588

http://www-ims.tamu.edu 2006