Chapter 9: Plant Organization

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Vascular Seed Plants• Phyllum: Tracheophyta (Contain Xylem and Phloem)

• Both gymnosperms and angiosperms disperse by seeds.

• A seed has a seed coat and contains an embryonic sporophyte and stored food that supports growth when the seed germinates.

• Gymnosperms have exposed or “naked” seeds. • In angiosperms (flowering plants), seeds are

enclosed by a fruit.

Gymnosperm diversity(naked-seed plants)

Angiosperms(enclosed-seeds)

• Angiosperms are flowering plants and include tropical and subtropical trees.

• All hardwood trees are angiosperms.

• Angiosperms are divided into monocots (such as the grass family) and dicots (such as the maple and rose families).

Monocot Versus Dicot Plants• Flowering plants (angiosperms) are divided into

two groups depending on their number of cotyledons (seed leaves).

• Monocots (monocotyledons) have one cotyledon; dicots (dicotyledons) have two.

• Cotyledons provide nutrients for seedlings before true leaves begin photosynthesizing.

Monocot Versus Dicot Plants

• Important monocots are rice, wheat and corn; oak trees and dandelions are dicots.

Monocot and Dicot traits• The vascular (transport)

tissue is organized differently in monocots and dicots.

• Monocot roots have vascular tissue in a ring; in stems, vascular bundles are scattered.

• Dicot roots have vascular tissue in a star shape with phloem located between arms of xylem. Stems have vascular bundles in a ring.

Monocot and Dicot traits• Leaf veins are vascular

bundles within a leaf.• Monocots usually have

parallel venation.• Dicots exhibit netted

venation, which may be either pinnate or palmate.

Monocot and Dicot traits

Dicot leaves

Plant Organization• Vascular-seed plants have characteristic

organs and tissues. (Angiosperms…..)• An organ is a structure that contains different

types of tissues and performs one or more specific functions.

• The vegetative organs of a flowering plant – the root, stem, and leaf – allow the plant to live and grow.

• The body of a plant has a root system and a shoot system.

Plant Organization

Plant Tissues• A plant grows throughout its lifespan because

of meristem (embryonic tissue) in stem and root tips (apexes).

• Three specialized tissues are in plants:1) Epidermal tissue – forms the outer protective

covering2) Ground tissue – fills interior of a plant3) Vascular tissue – transports water and

nutrients and provides support.

Epidermal Tissue(epi = above, dermal = skin)

• Epidermal tissue forms the outer protective covering of a herbaceous plant and is modified in roots, stems, and leaves.

• Exposed epidermal cells are covered with waxy cuticle to minimize water loss.

• Epidermal cells in roots have root hairs.• Lower leaf epidermal cells have guard cells and

stomata.

Epidermal Tissue(epi = above, dermal = skin)

• In older woody plants, the epidermis of the stem is replaced by cork tissue.

• Cork, a component of bark, is made up of dead cells that may be sloughed off.

• New cork cells are made by a meristem called cork cambium.

Vascular Tissue• There are two types of vascular (transport) tissue

that extend from roots to leaves.• Xylem transports water and minerals from roots

to leaves through two types of conducting cells.• Phloem transports organic nutrients (phood) from

leaves to roots and has sieve-tube elements with companion cells.

Vascular TissuePhloem structureXylem structure

Plant Organization

ROOTS!• Roots have two main functions:

1. Anchorage

2. Absorption

• Roots are classified according to origin or form-– Origin: The radicle is the root system of seedling,

from this, the primary root develops. Secondary roots (branch roots) grow out from the primary.

ROOTS!• Roots are classified according to origin or form-

– Origin: The radicle is the root system of seedling, from this, the primary root develops. Secondary roots (branch roots) grow out from the primary.

ROOTS!• Roots have two main functions:

1. Anchorage

2. Absorption

• Roots are classified according to origin or form-– Origin: The radicle is the root system of seedling,

from this, the primary root develops. Secondary roots (branch roots) grow out from the primary.

– Form: There are two main forms, Dicots typically have a large, singular tap-root and Monocots have a diffuse, branched, fibrous system.

ROOTS!• Roots are classified according to origin or form-

– Form: There are two main forms, Dicots typically have a large, singular tap-root Monocots have a diffuse, branched, fibrous system.

Root Diversity• Roots have special adaptations

and associations to better perform the functions of anchorage, absorption of water and minerals, and carbohydrate storage.

• An example is the dicot plant, CARROT, where its primary root (taproot) is fleshy and stores food (also, beets).

Root Diversity• Roots may also develop from

from stem, above the first root, these are called “adventitious roots.”

• Because these roots tend to be thicker and pass into the soil below, they provide extra support and are also known as: PROP ROOTS.

• The cylindrical shape of the root allows it to penetrate the soil.

• Root hairs greatly increase the absorptive capacity of the root.

ROOTS!

ROOTS!

• Generally the root system is equivalent in size and extent to the shoot system. (The iceberg principle)

• Some plants store the products of photosynthesis in their roots. (Carrots or beets)

Organization of RootsDicot root tip:

Organization of Roots• Within a root are zones

where cells are in various stages of differentiation.

The root apical meristem is in the zone of cell division; the root cap is a protective covering for the root tip.

Organization of Roots• In the zone of

maturation, mature cells are differentiated and epidermal cells have root hairs.

• In the zone of elongation, cells become longer as they specialize.

Tissues of a Dicot Root• Epidermis – single layer of thin-walled,

rectangular cells; root hairs present in zone of maturation

• Cortex – thin-walled, loosely-packed parenchyma; starch granules store food

• Endodermis – between cortex and vascular cylinder, single layer of endodermal cells bordered by the Casparian strip; regulates entrance of minerals into the vascular cylinder

Tissues of a Dicot Root• Vascular Tissue – has star-shaped xylem in dicots

with phloem in separate regions between arms of xylem; the pericycle gives rise to lateral roots

Organization of Monocot Roots• In a monocot root’s centrally

located pith, ground tissue is surrounded by a vascular ring composed of alternating xylem and phloem bundles.

• Monocot roots also have pericycle, endodermis, cortex, and epidermis.

Plant Organization

Stems• The shoot system of a plant includes both

stems and leaves.• A stem is the main axis of the plant along

with its lateral branches.

Shoot system

• At the tip of the stem is tissue that allows the stem to elongate and produce leaves.

• A leaf attached to a stem at a node; and internode is the region beween nodes.

Shoot system

Shoot system• Stems also contain

vascular tissue that transports water and minerals from roots to leaves, and also transports the products of photosynthesis in the opposite direction.

Organization of Stems

• During primary growth, the shoot apical meristem at the shoot tip produces new cells that elongate and add length to the stem.

• The shoot apical meristem is protected within a terminal bud by bud scales. Bud scales are actually modified leaves.

Organization of Stems• Leaves are produced at nodes; the stem between two

nodes is called an internode.• Internodes increase in length as the stem grows.• Terminal buds form at the END of a branch. • Lateral buds, are located on the SIDE of a branch.

Lateral buds which form at the axes of leaves are called Axillary buds.

Organization of Stems• Leaf scars appear if a twig is or has been dormant and

the leaves have been shed.• The protective layer that forms before a leaf falls off is the

Abscision layer.• Terminal bud scars appear as a flat, ring, around the

stem. • Lenticles are small pores all over the stem used for gas

exchange.

Monocot vs. Dicot Stems- In dicot stems, vascular bundles are in a

distinct ring; monocot vascular bundles are scattered throughout.

DICOT Monocot

Monocot stem

Herbaceous dicot stem

Woody Stems• A woody plant has both primary and

secondary tissues.

• Primary tissues are new tissues formed each year.

• Secondary tissues develop during the second and subsequent years of growth from lateral meristems (vascular cambium and cork cambium).

• Primary growth, which occurs in all plants, increases the length of the plant.

• Secondary growth, which occurs in conifers and some dicots, increases the girth of a plant.

• Trees undergo secondary growth because of a change in vascular cambium.

• The secondary tissues produced by the vascular cambium, called secondary xylem and secondary phloem, add to the girth of trunks, stems, branches, and roots.

Dicot stems

• As a result of secondary growth, a woody dicot stem has an entirely different type of organization.

• A woody stem now has three distinct areas: the pith, the wood, and the bark.

• Pith rays are composed of living parenchyma cells that allow materials to move laterally.

• The bark of a tree contains cork, cork cambium, and phloem.

• Cork cambium replaces epidermis with cork cells impregnated with suberin.

Secondary growth in a dicot stem

Annual Rings• In trees that have a growing season,

vascular cambium is dormant during winter.

• In spring, with plentiful moisture, xylem contains wide vessels with thin walls in spring wood; summer wood has a lower proportion of vessels.

• Spring wood followed by summer wood makes up one year’s growth or annual ring.

Section of woody stem

Tree trunk

Stem Diversity- Some stems have functions other than transport; some are specialized for storage.

Stem Diversity

• Stems nay also function in reproduction, climbing (tendrils on a pea plant).

• Modified stems aid adaptation to different environments.• Examples of stem modifications include:

-Stolons -Rhizomes -Tubers -Corms

Stem DiversityStolons and Bulbs

Onion or Garlic

Bulb

Bulb

Stem DiversityTubers and corms

Potato! Gladiola

Leaves• A leaf is a broad, thin organ that carries on

photosynthesis.• This shape maximizes the surface area for

collection of solar energy and absorption of carbon dioxide.

• The wide portion of a leaf is the blade, a petiole is the stalk of the leaf, and axillary buds are found at the leaf axil.

• Some leaves have other functions.

Leaves

Stoma of leaf

EXERCISE 12: Angiosperm Stem

Dr. L Humphrieslhumphries@elcamino.edu

Spring 2005: Fundamentals of BiologySection 1107 Biology 10 4-Units

EXERCISE 13: Angiosperm Root

Dr. L Humphrieslhumphries@elcamino.edu

Spring 2005: Fundamentals of BiologySection 1107 Biology 10 4-Units