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Chapter 25 Structure andOrganization of Plants

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Plant Structure

* Many of the same environmental pressures

that helped to shape the transition of animals

from an aquatic existence to a terrestrial

existence, have affected plant evolution aswell. Among the environmental pressures

both animals and plants face as the transition

to land occurred were:

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Structural Needs of Plants

1. here is greater need to preventdesiccation on land.

!. here is a greater need for vascular tissue

or some means of transporting fluidsthroughout the body on land.

". here is a greater need for support onland.

#. $ot only do plants need support on land,the leaves must also be held up into thesunlight.

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Plant Structure

plant morphology % the study of

the external structure of plants

plant anatomy % the study of the

internal structure of plants

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Angiosperms (owering

plants) * Angiosperms &flowering plants' are by farthe most diverse and widespread of all

plants. he two ma(or angiosperm classes

are: 1. monocots % possess a single seed leaf

&cotyledon', ex. corn

!. dicots &eudicots' % possess a double seedleaf, ex. bean

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Comparison of Monocots andDicots )haracteristic Monocot icot

1. cotyledons one two

!. leaf venation parallel netli+e ". vascular bundles scattered through stem arranged in rings

#. roots fibrous taproot present . floral parts multiples of threes multiples of fours - fives

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Monocot Dicot:

Comparisons

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Plant structure at thecellular and tissue level: )ompared to animals cells, plant cells have a cell

wall consisting of a primary cell wall, secondary cellwall, and middle lamella.

he primary cell wall is composed of cellulose, the

secondary cell wall of cellulose and lignin, and themiddle lamella pectin

chloroplasts that function in photosynthesis a protoplast consisting of the whole cell excluding

the cell wall a large central vacuole surrounded by a tonoplast plasmodesmata for intercellular transport and they lac+ centrioles.

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Types of Plant Cells

1. parenchyma cells % /typical plant cell/ with

large central vacuole, no secondary cell

walls, and thin primary cell walls.

0arenchyma cells carry out most of themetabolic functions of the plant. he flesh of

fruit and the photosynthetic mesophyll cells of

leaves are modified parenchyma cells.

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Types of Plant Cells contd!

!. collenchyma cells % lac+ secondary cell

walls but have thic+er primary cell walls than

parenchyma cells. he cell wall lac+s the

strengthening protein lignin allowingcollenchyma cells to support young stems

without restricting growth. he collenchyma

cells lengthen as the stem grows.

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Types of Plant Cells contd!

". sclerenchyma cells % have thic+ secondary

cell walls strengthened with lignin. Mature

sclerenchyma cannot grow and occur in

areas where lengthwise growth has ceased.ibers found in hemp and sclereids found in

nutshells, seed coats, and the /grit/ in pears

are two forms of sclereids.

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Types of Plant Cells contd!

#. vascular tissue % the water%conducting tissue

xylem which is made of tracheids and vessels, and

phloem consisting of sieve tubes and companion

cells. racheids have more of a supportive function,while vessels allow a continuous flow of water.

2ymnosperms have only tracheids, while

angiosperms have tracheids and vessels which

evolved from tracheids. he phloem sieve tubesconduct sap throughout the plant and because they

lac+ a nucleus or ribosomes are supported

functionally by companion cells.

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hree Plant issue !pes 1. dermal tissue &epidermis' % derived from

protoderm meristem, a single layer of tightly%pac+edcells that covers and protects the plant. !. vascular tissue % derived from procambium

meristem, a system of xylem and phloem thatfunctions in transport and support.

". ground tissue % derived from ground meristem,fills space between epidermis and vascular tissue.0rimarily parenchyma cells, but collenchyma andsclerenchyma sometimes present.

* he basic structure of a root, stem, or leaf is anouter layer of dermal tissue, an inner vascular tissue&xylem and phloem', and the tissue that fills the root,stem, or leaf &ground tissue'

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"asic plant morpholog!

3asic plant morphology consists of a rootsystem and a shoot system containing stems,leaves, and flowers both of which are

connected by vascular tissue. 3asic plant parts: 1. flowers

!. roots ". shoots #. leaves

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"asic Plant

Parts

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"! #lower structure: sepals &calyx'

petals &corolla'

stamen 4 anther and filament

pistil &carpel' 4 stigma, style, ovary

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2! Structure and Primar! $rowthof %oot 1. root cap % protects the root meristem and secretes a

polysaccharide that allows the root to move through the soil moreeasily. !. 5one of cell division % consists of the apical meristem and

derivatives. )ells of the apical meristem divide to form the threeprimary meristems: the protoderm, procambium, and groundmeristem which in turn will form the dermal, vascular, and groundtissue respectively.

". 5one of cell elongation % growth occurs by cell elongation up toten times original length.

#. 5one of cell differentiation % the three tissues systemsproduced by primary growth complete their differentiation.

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Primar! issues of %oots

1. protoderm % outermost primary meristem which gives rise to theepidermis.

!. procambium % gives rise to the central vascular cylinder &stele'. 6ncross%section, the xylem of dicots forms a cross, whereas the xylem ofmonocots occurs in a ring. 0hloem will alternate between and outsidethe xylem.

". ground meristem % gives rise to the ground tissue which fills thecortex.

endodermis % one%cell thic+ cylinder that forms the boundary betweenthe cortex and the stele.

pericycle % layer of meristematic cells (ust inside the endodermis whichgives rise to lateral roots.

* rom the interior of a root to the exterior you would find the followingstructures:

stele &xylem and phloem' % pericycle % endodermis % cortex % epidermis

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&' Shoot (stem structure)

7hoot 7ystem % consists of vegetative shoots

containing the stem and leaves and floral shoots

that bear flowers

* A stem consists of nodes where leaves areattached and internodes. A stem also contains

axillary buds which is an embryonic side shoot, and

terminal buds at the tip of the shoot which will form

leaves and8or flowers. he terminal bud usuallyexerts apical dominance &suppresses growth' on the

lateral buds.

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Shoot (stem structure)contd'

terms 1. bar+ !. cor+ cambium

". vascular cambium

#. primary xylem

. secondary xylem

9. primary phloem . secondary phloem

;. annual ring

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Modied stems

* Modified stems with various functions

include:

the stolons or runners of the strawberry,

rhi5omes &underground stems' found in irises,

tubers illustrated by the white potato, and

bulbs of tulips or onions.

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Modied stems * e+amples

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,' -eaf structure

* A leaf is the ma(or photosynthetic organ of

most plants consisting of a blade attached to

the stem by a petiole.

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-eaf structure contd'

*

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-eaf structure contd'terms

epidermis

palisade mesophyll

spongy mesophyll

vascular bundle &vein' xylem

phloem

stomata guard cells

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#eaf structure

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-eaf structure contd'

* Modified leaves with various functions

include

tendrils of plants such as beans or grape,

the spines of cacti,

succulent leaves for water storage, and

leaves adapted to attract pollinators such

as those in poinsettia.