Plant structure, form and function
Fall 2014
Copyright © 2013 by Nelson Education Ltd.
Terminal bud
Lateral bud Young leaf
Reproductive shoot with flower
Node
Internode
Vegetative shoot
Node
Shoots Leaf blade Leaves
Vascular tissues
Mature leaf
Seeds
in fruit
Ground tissues
Dermal tissues Withered seed leaf
(cotyledon)
Shoot system
Root system
Root hairs
Primary root (not to scale)
Roots
Lateral root
The Plant Body
Root tip
Root cap Fig. 27.2, p. 664
The Plant Body
The Shoot System The Root System
Above ground (usually) Underground (usually)
Elevates the plant above the Anchor the plant in the soil
soil Absorb water and nutrients
Many functions including: Conduct water and nutrients
• photosynthesis Food Storage
• reproduction & dispersal
• food and water conduction
The shoot system includes the
vegetative shoot (stem with
attached leaves and buds) and
the reproductive shoot
(producing flowers which later
develop fruits containing
seeds) Copyright © 2013 by Nelson Education Ltd.
The Three Plant Tissue Systems
Dermal Tissue
• Generally a single layer of cells
• The "skin" of the plant
• Primarily parenchyma cells
• Main role is protection of the plant
Ground Tissue
• Makes up the bulk of the plant
• Predominately parenchyma, but collenchyma and schlerenchyma cells
are found
• Diverse functions including photosynthesis, storage, and support
Vascular Tissue
• Involved in the transport of water, ions, minerals, and food
• Also has a secondary role in support
• Composed of xylem, phloem, parenchyma, schlerenchyma
Copyright © 2013 by Nelson Education Ltd.
Ground, Vascular, and Dermal Tissues
Animation: Tissue systems of a tomato plant
Copyright © 2013 by Nelson Education Ltd.
Fig. 27.6, p. 669
Ground Tissues and Cell types
Collenchyma Cells
Parenchyma Cells • Flexible support Sclerenchyma Cells
• Soft primary tissues • Thicker primary cell walls • Rigid support and
• Thin primary cell walls, • Elongated cells in strands protection
pliable and permeable or sheath-like cylinder • Thick secondary cell walls
• Specialized for storage, • Strengthen plant parts still
secretion, photosynthesis elongating
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Fig. 27.7, p. 669
Vascular Tissues: Xylem
Xylem
• Conducts water and dissolved
minerals
• Flows “bottom-up”
• Thick, lignified secondary walls
• Dead when functional
• Walls contain pits for lateral
movement of water
• 2 types of water-conducting
cells
• Tracheids
• Vessel members
Fig. 27.9, p. 671
Copyright © 2013 by Nelson Education Ltd.
Vascular Tissues: Phloem
Phloem
• Conduct sugars and other
solutes
• Living when functional
• “source-sink” movement
• Sieve tube members
• Joined end to end in sieve
tubes
• Sieve tube cells assisted by
companion cells
• End walls (sieve plates)
studded with pores
Fig. 27.10, p. 671
Copyright © 2013 by Nelson Education Ltd.
Vascular tissues are specialized for long-distance transport
http://thomson.fosterscience.com/Biology/Unit-ProtistsFungiPlants/SeedPlantsNotes.htm
Animation: Vascular tissues
a. Long distance transport
throughout the plant
Transport Routes in Plants
Cells load and unload
organic molecules
into and out of phloem b. Transport in
water exits the plant vascular tissues
from leaves
Xylem:
Sugar from transport of
photosynthesis
H2O and O2
Vascular tissue Phloem:
distributes substances transport of
throughout the plant, sugars
sometimes over
great distances.
Water and mineral c. Short distance
ions travel from root Transport transport across cell
hairs into xylem in Phloem Transport membranes into roots
vessels by passing in Xylem
through or between
cells
Water and solutes from
soil enter plant roots
through the plasma
membrane of root hairs. Sugar from
photosynthesis Mineral
ions Minerals
Fig. 28.1, p. 689
Long-Distance Transport of Water and
Minerals in the Xylem
Transpiration
• Evaporation of water out of plants = “Pulling force”
• Greater than water used in growth and metabolism
• Stomata regulates loss of water by transpiration
Cohesion-tension mechanism of water transport
• Evaporation from mesophyll walls
• Replacement by cohesion (H-bonded) water in xylem
• Tension, negative pressure gradient, adhesion of
water to xylem walls adds to tension
Root pressure contributes to upward water movement in
some plants
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Transport of Organic Substances in the
Phloem
Organic compounds are stored and transported in
different forms (ie. sugars, amino acids, hormones, and organic
compounds, etc)
Organic solutes move by translocation
• Translocation=Long-distance transport of substances via phloem
• Phloem sap (water & organic compounds) flow through sieve
tubes
• Phloem sap moves from source to sink under pressure (ie.
Pressure flow mechanism)
• Differences in pressure between source (where organic
substances are loaded into phloem, ex. mature leaves) and sink
(where organic substances are unloaded into phloem, ex.
growing tissues and storage regions ) regions drive the flow
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Pressure flow
mechanism moves
substances by bulk
flow under pressure
from sources to sinks
based on water
potential gradients
Fig. 28.16b, p. 704
Dermal Tissue
Epidermis covers primary plant body
• Waxy cuticle layer restricts water loss
• Pairs of guard cells in leaf epidermis create stomata (openings)
for gas exchange
Epidermal specializations
• Trichomes (hairs)
• Absorbent root hairs
Copyright © 2013 by Nelson Education Ltd.
Fig. 27.11, p. 672
Shoot System
Consists of main stem,
leaves, buds, flowers
and fruits
Functions:
Mechanical support
House vascular
tissues
May store food and
water
Buds and meristems
for growth
Leaves carry out
Fig. 27.2, p. 664
photosynthesis and
gas exchange
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Stem Structure and SAM
Terminal bud Leaf primordium
Shoot
Apical Meristem
Shoot
Lateral bud in axil Apical
Meristem
(SAM)
Node
Apical meristems: Regions of
Internode constantly dividing cells near tips
of shoots (SAM) and roots (RAM)
that produce all tissues of the
Node plant body
SAM produces cells that will
become new organs: leaves,
axillary buds, and branches etc.
Fig. 27.12a, p. 673
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Leaves
Blade
• Large surface area for
absorbing sunlight and
carbon dioxide
Petiole (in eudicots)
• Attaches leaf to stem
Containing chloroplast for
photosynthesis
Leaf surface contains
stomata, the openings for Fig. 27.16, p. 675
gas exchange
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a. Typical structure of an angiosperm leaf
Upper
Cuticle
epidermis
Leaf vein Palisade
(vascular bundle): mesophyll
Phloem
Xylem
Spongy
Products of mesophyll
photosynthesis
enter vein and
depart from the Lower
leaf (purple
arrow). epidermis
Water moves Cuticle
from roots to
stems, then into Stoma between
leaf vein (blue two guard cells
arrow).
Oxygen and water vapor depart Carbon dioxide from the air enters
from the leaf through stomata. the leaf through stomata.
Fig. 27.18a, p. 677
Flowers
Flower develops from end of
floral shoot, the receptacle
Four concentric whorls of
tissues:
• Sepals: Nonfertile,
vegetative
• Petals: Nonfertile,
vegetative
• Stamens: Fertile,
location of male
gametophytes
• Carpels: Fertile, location
of female gametophytes
Fig. 29.4, p. 711
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Seeds
Mature seeds are
essentially dehydrated
Seed dormancy prevents
germination
Particular factors may
trigger germination
• Moisture, oxygen,
temperature, number
of daylight hours, and
more
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Root System
Absorb water and
dissolved minerals
Conduct water and
minerals to aerial plant
parts
Anchor and support
aboveground parts
Store nutrients produced
by photosynthesis Animation: Root cross section
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Root Structure
Animation: Root organization
Copyright © 2013 by Nelson Education Ltd.
