Chapter 35 - Vascular plant structures growth and development

Hierarchical organization:

organs> tissues> cells

a cell is the …

fundamental unit of life

tissue

a group of cells consisting of one or more cell types that together perform a specialized function

organ

consists of several types of tissues that together carry out particular functions

Vascular Plant Organs

Roots, Stems, & Leaves

basic morphology of vascular plants reflects adaptations to draw nutrients from…

above & below ground

* *take up CO2 & light from above ground*
*  *take up water & minerals from below*

3 basic organs evolved to facilitate efficient resource acquisition.

Roots, Stems, & Leaves

Roots, Stems, & Leaves are organized into a …

root system & shoot system

a root

organ with *important functions*: – *anchoring the plant*– *absorbing minerals and water*– *storing carbohydrates*

primary root

the first to emerge from the seed

lateral roots

branch off from the primary root improving anchorage & water absorption

Absorption primarily occurs in the __

tips of the lateral roots

tall plants with large shoot masses generally have a…

Taproot system

taproot

usually develops from the primary root & functions in anchoring the plant in the soil

fibrous root system

small or trailing vascular plants have these

* primary root dies doesn’t form a taproot
* adventitious roots arise from the stem & give rise to many branching lateral roots
* function in prevent soil erosion by holding topsoil in place

root hairs

absorption of water & minerals typically occurs through these that grow near the root tips

– *finger-like extensions of epidermal cells, increase the absorptive surface of the root*

\-Mycorrhizal associations, symbiotic interactions with soil fungi, increase mineral absorption in most plants

Stem

* plant organ bearing leaves & buds
* consist of an alternating system of nodes & internodes

*Nodes*

*the points at which leaves are attached*

*Internodes*

*the stem segments between nodes*

Growing shoot tip

apical bud, causes elongation of a young shoot

axillary bud

* a structure that has the potential to form a lateral branch, thorn, or flower
* *primary function=* elongate & orient the shoot to maximize photosynthesis
* Many plants have modified stems that perform alternate functions

leaf

* main photosynthetic organ of most vascular plants

*functions*= intercept light, exchange gases, dissipate heat, & defend against herbivores & pathogens

* generally consists of:
* –  *a flattened blade*
* –  *petiole, the stalk which joins the leaf to the stem*

monocots & eudicots differ in the arrangement of…

Veins:

* –  *Most monocots= parallel veins*
* –  *Most eudicots= branching veins*


* Leaf shape, arrangement of veins, & spatial pattern of leaves can help with plant identification
* Leaf shape may be *simple or compound*

Most monocots have

parallel veins

Most leaves are…

Specialized for photosynthasis

Roots, stems, and leaves (organs) are composed of..

Three types of tissue

*dermal, vascular, & ground tissues*

* Each forms a tissue system that is continuous throughout the plant
* characteristics of the tissues & their spatial relationships vary in different organs

Dermal Tissue

* serves as a protective outer coating
* In nonwoody plants, usually a single tissue

layer called the epidermis
* waxy cuticle covers the epidermis & protects

leaves & most stems from water loss
* A protective layer called the periderm replaces the epidermis in older regions of woody stems and roots

–  *Guard cells-- specialized dermal cells that facilitate gas exchange in shoots*

–  *Trichomes-- hair-like outgrowths of epidermal cells that help reduce water loss, reflect light, & defend against insects*

Vascular Tissues

facilitates the transport of materials through the plant and provides mechanical support includes xylem & phloem:

–  ***Xylem****-- conducts water and dissolved minerals upward from roots into the shoots*

–  ***Phloem****-- transports sugars from where they are made (primarily leaves) to actively growing parts of the plant or storage structures* vascular tissue of a root or stem is collectively called the __stele__

angiosperms—

–  *stele of the root is a solid central vascular cylinder of xylem & phloem*

–  *stems & leaves its divided into vascular bundles, which are separate strands of xylem and phloem*

Ground Tissues

* Tissue that are neither dermal nor vascular = ground tissue:

–  *internal to the vascular tissue is pith*

–  *outside the vascular tissue is cortex*

* includes cells specialized for storage, photosynthesis, support, & short-distance transport

Plant cells undergo cell differentiation…

specialization in structure & function, during development

– *structural adaptations of various types of plant cells make their specific functions possible*

The major types of plant cells are…

parenchyma cells

*thin & flexible primary walls*

* –  *generally lack secondary walls*
* –  *have large central vacuole*
* –  *retain ability to divide & differentiate*
* –  *function: perform most of metabolic functions*

collenchyma cells

\-grouped in strands & help support young parts of the plant shoot

–  *unevenly thickened primary cell walls*

–  *living at maturity*

– *function= provide* flexible support *without restraining growth*

sclerenchyma cells

rigid cells with secondary cell walls containing lignin, a strengthening polymer, for support

– *many are* dead at maturity 

\-rigid cell walls remain to support the plant (*function*)

water-conducting cells

sugar-conducting cells

\

Meristems

generate new cells for primary & secondary growth

*indeterminate growth*

plants grow throughout its life

– *this continuous growth possible due to meristems-- undifferentiated tissues composed of dividing cells*

\-most animals & some plant organs cease to grow at a certain size (determinate growth)

Growth occurs @ 2 main types of meristems

*-apical meristems- elongation of shoots & roots for primary growth*

–  *lateral meristems- located at the tips of roots and shoots, for stems & roots of woody plants to grow in circumference-- secondary growth*

– *2 types of lateral meristems*


1. __**Vascular cambium**__ adds vascular tissue called secondary xylem (wood) and secondary phloem
2. __**Cork cambium**__ replaces the epidermis with thicker, tougher periderm

cells in apical & lateral meristems…

divide frequently during growing season

– *Initials (stem cells), are new cells that remain in the meristem & produce more cells*

– *Others differentiate & are incorporated into tissues & organs*

Lateral meristems

give rise to secondary growth in woody plants have stem cells, which give rise to secondary growth.

– *primary growth extends woody shoots, & secondary growth increases the diameter yearly upon parts formed in the previous years*

Cells displaced from the meristem give rise to…

3 primary meristems that will produce mature tissues:


1. *protoderm produces dermal tissue*
2. *ground meristem produces ground tissue*
3. *procambium produces vascular tissue*

Flowering plants can be categorized based on…

the length of their life cycle,

* *Annuals-- complete their life cycle in a year or less*
* *Biennials-- require two growing seasons*
*  *Perennials-- live for many years*

root cap

covers the root tip to protect the apical meristem & polysaccharide slime lubricates the passage as the root pushes through soil

growth occurs just behind the tip, in 3 zones:

primary growth of roots produces epidermis, ground tissue, & vascular tissue:

Between protoderm & procambium is ground meristem, produces…

ground tissue – *ground tissue, mostly parenchyma cells, makes up region between vascular tissue & epidermis called the* __***Cortex***__

■ innermost layer of the cortex is called __endodermis__-- regulates passage into & out of the vascular cylinder

procambium

innermost primary meristem; it gives rise to the central vascular cylinder 

vascular cylinder

has a solid core of xylem & phloem surrounded by a cell layer called the pericycle

*eudicots*

* xylem has a starlike appearance in cross section with phloem between the “arms”
* vascular tissue consists of vascular bundles arranged in a ring

*monocots*

* core of parenchyma cells surrounded by alternating rings of xylem & phloem
* vascular bundles are scattered throughout the ground tissue

lateral (branch) roots arise from the…

pericycle and destructively push through the outer tissues

■ branching is a form of primary growth

shoot apical meristem

dome-shaped mass of dividing cells at shoot tip

* leaf primordia of the apical bud protect the meristem
* axillary buds develop from meristematic cells left at bases of leaf primordia
* gives rise to 3 primary meristems— __**protoderm, ground meristem & procambium**__

axillary buds are kept dormant by…

chemical communication from the apical bud

\-the closer an axillary bud is to the active apical bud, the more inhibited it is

* –  __***axillary***__ *buds are released from this apical dominance if the shoot tip is removed or shaded*
* –  __***lateral***__ *shoots emerge from axillary buds that have been released from dormancy*

stem is covered by the…

epidermis & a waxy cuticle

\-ground tissue is composed primarily of parenchyma cells

– *collenchyma and sclerenchyma cells strengthen and support the stem*

\-Unlike lateral roots, emerging shoots do not damage stem tissues

\- Lateral shoots arise from axillary bud meristems on the stem surface

*apical dominance*

The phenomenon where the central stem of a plant inhibits the growth of lateral buds.

leaf primordia

Leaves develop from these along the sides of the shoot apical meristem

■ Unlike roots & stems, secondary growth in leaves is minor or nonexistent

The waxy cuticle coating the leaf epidermis reduces water loss except where interrupted by…

*Stomata, pores in the epidermis, allow exchange of CO2 & O2 between the surrounding air and photosynthetic cells inside the leaf*

– *Each stoma is flanked by two guard cells, which regulate its opening and closing to reduce water loss*

mesophyll

* ground tissue in a leaf: sandwiched between upper & lower epidermis

* eudicots has two layers:

* *palisade mesophyll (upper layer) are rich in chloroplasts to maximize light capture*


*  *spongy mesophyll (lower layer) are loosely packed to create air spaces for gas exchange*

vascular bundles

veins of the leaf, provide structural support for leaf

* vascular tissue of each leaf is continuous with vascular tissue of the stem

Leaf veins are enclosed by a protective…

Boundle sheets that regulates movement of substances between the vascular tissue and the mesophyll

land plants display…

secondary growth= the growth in thickness produced by lateral meristems

– *In woody plants, primary & secondary growth occur simultaneously*

– *occurs in gymnosperms & many eudicots, rare in monocots*

vascular cambium

adds secondary xylem (wood) toward the interior & secondary phloem toward the exterior of the stem

cork cambium

produces a tough covering to protect the stem from water loss and pathogen invasion

* gives rise to cork cells that accumulate to the exterior of the cork cambium
*  before dying, cork cells deposit waxy suberin in their walls, creating a water & gas impermeable barrier

___ is wholly responsible for the production of *secondary* vascular tissue

vascular cambium

* __***typical woody stem***__*– its located outside the pith & primary xylem & to the inside of the primary phloem & the cortex*
*  *typical woody root– it forms exterior to the primary xylem & interior to the primary phloem and pericycle*


* cross section, the vascular cambium appears as a ring of meristematic cells
* Cell division increases the vascular cambium’s circumference and adds secondary xylem to the inside and secondary phloem to the outside

Elongated stem cells are oriented…

parallel to the axis of the stem or root– *give rise to tracheids, vessel elements, fibers of xylem, sieve-tube elements, companion cells, axially oriented parenchyma, & fibers of the phloem*

Shorter stem cells are oriented…

erpendicular to the axis of the stem or root – *produce vascular rays—radial files of parenchyma cells that connect secondary xylem & phloem*

Secondary xylem accumulates

as wood:

–  *Early wood- formed in spring in temperate regions, has thin cell walls to maximize water delivery*

–  *Late wood- formed in summer, has thick-walled cells and contributes more to stem suppor*

* Dendrochronology

the analysis of tree ring growth patterns, can be used to study past climate change

– *thick rings indicate a year with warm or wet growing conditions; thin rings indicate a cold or dry year*

as a tree or woody shrub ages, the older layers of secondary xylem the ___ no longer transport water & minerals

heartwood

outer layers of a tree are known as…

*Sapwood*

* *transport materials through the xylem*
* *Older secondary phloem sloughs off and does not accumulate*

periderm

Cork Cambium, a layer that replaces the epidermis

*Bark*

* all the tissues external to the vascular cambium, including secondary phloem & periderm

*Lenticels*

* pores in the periderm that allow for gas exchange between living cells of the stem or root and the outside air

Despite having a common genome, cells can…

* synthesize different proteins & diverge in structure & function
* Cellular differentiation depends on gene expression, but is determined by position
* Positional information is communicated through cell interactions


* Gene activation or inactivation depends on cell-to-cell communication

Flower formation involves a

phase change from vegetative growth to reproductive growth

– *triggered by a combo of environmental cues & internal signal hormones*

■ Flower production stops primary growth of that shoot– *transition to flowering is associated with the switching*

*on of flower-inducing genes*

Several genes encode transcription factors that regulate development of floral pattern:

*- Positional info determines which genes are expressed in a particular floral organ primordium*

–  *mutation in a flower-inducing gene can cause abnormal floral development*

In the hierarchy of biological organization, what is the shoot?

A system

A root hair is __________.

an extension of an individual cell that absorbs water from soil

Leaves occur at intervals along the plant stem. What is the region where a leaf is attached to the stem?

Node

Leaves consist of __________. 

a blade and a petiole

What is the difference between the root epidermis and the shoot epidermis? 

Only the shoot epidermis produces a waxy cuticle.

The plant tissue system most analogous to our circulatory system is the __________.

vascular tissue

Which of the following cells are dead at functional maturity? 

Tracheids and vessel elements

Collenchyma cells can be identified by __________.

their unevenly thickened cell walls

If you wanted to plant a flowering plant in your yard that would bloom every spring, which of the following should you choose? 

A perennial

A region of dividing cells in a plant is called a __________. 

meristem

Which example below is the site of primary growth that results in the plant’s increasing in height?

Apical meristems

Which of the following is a lateral meristem? 

Vascular cambium

Some plants grow by primary and secondary mechanisms. Choose the correct description of a mechanism and its result.

Primary and secondary growth are required to produce woody plants.

Most of the photosynthesis in plants takes place in specialized __________ cells called the __________.

parenchyma; mesophyll

Why does pinching off the top of a plant make it bushier?

Removing the apical meristem stimulates growth in the axillary buds, thus making the plant bushier.

The layer that covers the apical meristem of a root is called the __________.

root cap

Root tips are pushed farther into the soil mainly by __________.

elongation of cells

A cross section of a plant part exposes epidermis, a thick cortex, and a central cylinder of xylem and phloem. This part is a __________. 

root

Which of the following is closest to the center of a buttercup (eudicot) root?

Xylem

Lateral roots in seed plants are initiated by cell divisions in the __________.

pericycle