lecture 3: plant anatomy and physiology
TRANSCRIPT
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Lecture 3: Plant anatomy and Lecture 3: Plant anatomy and physiologyphysiology
byEdgar Moctezuma, Ph.D.
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Today…• Announcements• Plant Anatomy
– Cells– Tissues– Organs
• Plant Physiology– Water & sugar transport– Plant hormones
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Announcements…• Labs start this week – get your lab manual.• BSCI 125 students: if you have the following sections:
– 1109, 1110 Tues. 3:30-5:30 or,– 1113, 1114 Wed. 12-2 or,– 1115, 1116 Wed. 3-5 or– 1123, 1124 Thurs. 3:30-5:30, and you can switch to an
open section (Monday or Wed. 9:00-11:00), please try to do so. Thanks!
• Taking care of your plant:– Do not overwater it! Water only when soil is dry to the touch.– Place near a sunny window.
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From smallest to largest plants
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What is plant anatomy?• ANATOMY: study of the structure of
organisms… looking at cells, tissues• (Morphology: Study of form)
What is plant physiology?• PHYSIOLOGY: study of the function of
cells, tissues, organs of living things; and the physics/chemistry of these functions…
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“Structure correlates to function”
Always keep in mind that in plant anatomy, morphology & physiology…
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• How can water move from the ground all the wayto the topof a 100 mtall redwoodtree?
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Plant Anatomy: Cells• Plant cells are basic building blocks• Can specialize in form and function• By working together, forming tissues, they can
support each other and survive • Levels of organizationatoms > molecules > cells > tissues > organs > whole plant > pop.
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Plant Tissues TypesAll plant organs (roots, stems, leaves) are
composed of the same tissue types.There are three types of tissue:
• 1. Dermal – outermost layer
• 2. Vascular – conducting tissue, transport
• 3. Ground – bulk of inner layers
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1. Dermal tissue• Epidermis is the outermost layer of cells• Like the “skin” of animals• In stems and leaves,
epidermis has cuticle, a waxy layer that prevents water loss.
• Some have trichomes, hairs.• Root epidermis has root hairs, for
water and nutrient absorption
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2. Vascular tissue• Transports water and organic materials (sugars)
throughout the plant • Xylem – transports water and
dissolved ions from the root to the stem and leaves.
• Phloem – carries dissolved sugars from leaves to rest of the plant
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Xylem• Transports water and dissolved minerals• Tracheids: long, thin tube like structures
without perforations at the ends• Vessel elements: short, wide tubes perforated at
the ends (together form a pipe, called vessel).• Both cells have pits (thin sections) on the walls
Tracheids Vessel elements
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Xylem cells• Xylem cells are dead!• They are hollow cells
and consist only ofcell wall
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Phloem• Cells that transport organic materials (sugars)• Phloem cells are ALIVE! (unlike xylem)• However, they lack
nucleus and organelles
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Phloem: transports sugars• Phloem composed of cells called sieve tube
members (STM)• Companion cells join sieve tube members, are
related, and help to load materials into STM• End walls of STM have large pores called
sieve plates
Sieve tube member
Companion cells
Sieve plates
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3. Ground tissue• Makes up the bulk of plant organs. • Functions: Metabolism, storage and support.
Root Stem Leaf
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Plant Organs Organs: tissues that act together to serve a
specific function
• Roots
• Stems
• Leaves
DermalVascularGround
DermalVascularGround
DermalVascularGround
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Functions of plant organs:• ROOTS: Anchorage, water/nutrient absorption
from soil, storage, water/nutrient transport
• STEMS: Support, water/nutrient transport
• LEAVES: Photosynthesis (food production)
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ROOTS
• ROOTS “the hidden half”• Functions of roots:• Ancorage• Absorption of water & dissolved minerals• Storage (surplus sugars, starch)• Conduction water/nutrients
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Anatomy of a root
epidermiscortex
vascular
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Root Epidermis• Outermost, single layer of cells that:
– Protects (from diseases)– Absorbs water and nutrients
• ROOT HAIRS: tubular extensions of epidermal cells.
• Increase surface area of root,for better water/nutrient absorption
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Root Hairs: water and mineral absorption
Root hairs increase surfacearea for betterabsorption
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Root Cortex• Stores starch, sugars and other substances
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Root Ground tissue• In roots, ground tissue (a.k.a. cortex)
provides support, andoften stores sugars and starch (for example: yams, sweet potato, etc.)
Hey! I yam what I yam, man!
You’re not a yam, you’re a sweetpotato!
cortex
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Root Cortex: Endodermis
• Endodermis: the innermost layer of the cortex
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Root cortex: Casparian strip• The Casparian strip is a water-impermeable
strip of waxy material found in the endodermis (innermost layer of the cortex).
• The Casparian strip helps to control the uptake of minerals into the xylem: they have to go through the cytoplasm of the cell!
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STEMS• Above-ground organs (usually)
• Support leaves and fruits
• Conduct water and sugarsthroughout plant (xylem and phloem)
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Stem anatomy• Dermal, ground and vascular tissues…
pith
cortexepidermis
Vascularbundles
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Types of Stems
Monocot stem Dicot stem Root
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Types of stems
• Herbaceous vs. Woody stems
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Tissues of stems• Epidermis (Dermal tissue type)• Provides protection• Has cuticle (wax) prevents water loss• Trichomes (hairs) for protection, to release
scents, oils, etc.
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Stem Vascular tissue
• Vascular bundles – composed of both xylem and phloem
• Xylem– Conducts water– Support
• Phloem– Conducts food– Support
Vascularcambium
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Vascular cambium• Occurs in woody stems• Vascular cambium located in the middle
of the vascular bundle, between xylem and phloem
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Vascular tissue: Trees• Vascular tissue is located on the outer
layers of the tree.
wood
phloem
xylem
bark
Vascular cambium
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Girdling: cutting around a tree• Damages the phloem and xylem, eventually
killing the tree!
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Vascular tissue forms rings in trees• Annual rings: xylem formed by the
vascular cambium during one growing season
• One ring = one year
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History of the tree: annual rings
1489: Tree is plantedby Native American
1492: Columbus lands in the Americas
1620: Pilgrims land in Plymouth, Mass.
1776: Declarationof US independence
1861: Start ofCivil War
1969: Manlands on Moon
1917 & 1945: TreeSurvives two WorldWars
1971: Birth Year of the IDIOTwho cut downthis tree!!!
Dendrochronology : tree time-keeping
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Ground tissue: Cortex & pith• Stores food (e.g. potato)• Site of Photosynthesis (when green)• Support cells
pith
cortex
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LEAVES: • ‘Photosynthetic factories’ of the plant…• Function: Photosynthesis – food
production for the whole plant• Blade: Flat expanded area• Petiole: stalk that connects
leaf blade to stem, andtransports materials
BLADE
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Leaf Anatomy• Leaf anatomy is correlated to photosynthesis:
Carbon dioxide + Water sugars + oxygen
dermal
ground
vascular
dermal
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Leaf epidermis• Is transparent – so that sun light can go through.• Waxy cuticle protects against drying out• Lower epidermis: stomata with guard cells –
for gas exchange (CO2, H2O in; O2 out)
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Leaf epidermis
• Trichomes (give fuzzy texture)
(“Panda plant”)
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Leaf vascular tissue• VEINS vascular tissue of leaves.
• Veins are composed of xylem (water transport) phloem (food transport)
and bundle sheaths,cells surrounding the
xylem/phloem for strength & support
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Leaf Mesophyll• Middle of the leaf (meso-phyll)• Composed of photosynthetic ground cells:• Palisade parenchyma
(long columns below epidermis;have lots chloroplasts for photosynthesis)
Spongy parenchyma(spherical cells)with air spaces around, (for gas exchange)
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Plant water transport• How can water move from
the ground all the wayto the topof a 100 mtall redwoodtree?
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Water transport in plants:• The same way we drink soda
from a straw!
• Water’s great cohesive forces (moleculessticking to each other) and adhesive forces (attaching to walls of xylem cells)
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Transpiration-cohesion Theoryfor water transport in the xylem
• Evaporation of water in the leaves (through stomates) generates the ‘sucking force’ that pulls adjacent water molecules up the leaf surface
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Water transport (cont.)• Like a long chain, water molecules pull each
other up the column.• The column goes from roots leaves.
• What’s amazing is that the water moves up by using the sun’sevaporative energy…
• Plants control transpiration by opening/closing stomata
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Sugar translocation• 1. Sugars made in leaf mesophyll cells (source)
diffuse to phloem cells in the vascular bundles.• 2. Companion cells load dissolved sugars into
the phloem STM using energy (ATP).• 3. Water moves into cells with high sugar
concentration.• 4. Osmotic water flow generates a high
hydraulic pressure that moves dissolved sugars through the phloem to the rest of the plant (sink).
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Pressure flow in phloem• Sugars made in the
leaves are loaded into companion cells and into phloem STM.
• Water (from xylem) moves in by osmosis, creating pressure flow down the phloem.
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Plant Hormones
• Chemical compounds produced by plants • Effective at very low concentrations• Five major hormone groups are:1. Auxins2. Gibberellins3.3. CytokininsCytokinins4. Abscisic Acid5. Ethylene
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1. AUXINS• Promote cell growth• Involved in
gravitropism
and phototropism
• Control fruit development
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2. Gibberellins• Promote stem elongation
3. Cytokinins3. Cytokinins• Promote cell division and
organ differentiation
4. Abscisic Acid• Promotes seed dormancy• Causes stomata closing
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5. ETHYLENE5. ETHYLENE• Gaseous hormone,
very simple formula (C2H4)
• Ethylene promotes fruit ripening!
Air Ethylene
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“One rotten apple spoils the barrel”
• Why?Probably due to ethylene!Rotten apple producing lots of ethylene!
• Autocatalytic• As a response to injury
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Avocado ripening…
• Place in a paper bag, with a ripe banana!