chapter 32: leaf structure and function
DESCRIPTION
Chapter 32: Leaf Structure and Function. Function – photosynthesis Shape – max. light absorption Diffusion of CO2 and O2 Ordered arrangement for light Loss of water vapor Trade off between photosynthesis and water conservation. External form. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 32: Leaf Structure and Function
• Function – photosynthesis• Shape – – max. light absorption– Diffusion of CO2 and O2– Ordered arrangement for light– Loss of water vapor– Trade off between photosynthesis and water
conservation
External form
• Shapes – round, need, scalelike, cylindrical, heart, fan, thin, narrow
• Size – 20m to < .5 cm• Blade, petiole, stipules• Simple, compound• Axil region
Fig. 35-6a
(a) Simple leaf
Petiole
Axillary bud
Fig. 35-6b
Compound leaf
(b)Leaflet
PetioleAxillary bud
Fig. 35-6c
Doublycompoundleaf
(c)
LeafletPetioleAxillary bud
Fig. 35-6
(a) Simple leaf
Compoundleaf
(b)
Doublycompoundleaf
(c)
Petiole
Axillary bud
Leaflet
PetioleAxillary bud
LeafletPetioleAxillary bud
Leaf arrangement
• Alternate – 1 leaf each node• Opposite – 2 leaves each node• Whorled – 3+ leaves each node
Leaf Venation
• Veins = vascular tissue• Parallel• Netted– Palmately – from 1 point– Pinnately – branch from entire length of midvein
Leaf tissues
• Upper epidermis + Lower epidermis– No chloroplasts/transparent
• Cuticle – waxycutin• Trichomes – hairlike (fuzzy)– Retain moisture next to leaf, reflect light– Secrete irritants – herbivores– Texture – deter insects walk/eat– Excrete excess salts
Fig. 35-9
Very hairy pod(10 trichomes/
mm2)
Slightly hairy pod(2 trichomes/
mm2)
Bald pod(no trichomes)
Very hairy pod:10% damage
Slightly hairy pod:25% damage
Bald pod:40% damage
EXPERIMENT
RESULTS
• Subsidiary cells – epidermal; water and ions supplied to guard cells
• Stomata (opening) + guard cells– Open/close stoma– Only epidermal cells with chloroplasts– Lower epidermis (land); upper epidermis (aquatic)
Fig. 35-18b
Guardcells
Stomatalpore
Surface view of a spiderwort(Tradescantia) leaf (LM)
Epidermalcell
(b)
50 µ
m
• Mesophyll – photosynthetic ground tissue– Btw. Upper and lower epidermis– Parenchyma – chloroplasts– Air spaces – gas exchange– 2 sublayers:• Palisade mesophyll – top, columnar cells, close together–photosynthesis
• Spongy mesophyll – lower, loose and irregularly shaped–Gas exchange
• Vascular bundles – veins – through mesophyll– Xylem (top) and phloem (bottom)
• Bundle sheath– Nonvascular, around vein– Parenchyma or sclerenchyma
Fig. 35-18
Keyto labels
Dermal
Ground
VascularCuticle Sclerenchyma
fibersStoma
Bundle-sheathcell
Xylem
Phloem
(a) Cutaway drawing of leaf tissuesGuardcells
Vein
Cuticle
Lowerepidermis
Spongymesophyll
Palisademesophyll
Upperepidermis
Guardcells
Stomatalpore
Surface view of a spiderwort(Tradescantia) leaf (LM)
Epidermalcell
(b)
50 µ
m10
0 µm
Vein Air spaces Guard cells
Cross section of a lilac(Syringa)) leaf (LM)
(c)
Fig. 35-18a
Keyto labels
Dermal
Ground
VascularCuticle Sclerenchyma
fibersStoma
Bundle-sheathcell
Xylem
Phloem
(a) Cutaway drawing of leaf tissuesGuardcells
Vein
Cuticle
Lowerepidermis
Spongymesophyll
Palisademesophyll
Upperepidermis
Fig. 35-18c
Upperepidermis
Palisademesophyll
Keyto labels
DermalGroundVascular
Spongymesophyll
Lowerepidermis
Vein Air spaces Guard cellsCross section of a lilac(Syringa) leaf (LM)
(c)
100
µm
Functioning of Stomata• Day – open – photosynthesis– Water moves into guard cells turgid + bend pore
• Night – close – water leaves guard cells flaccid collapse close
pore• Prolonged drought – stomata close (even in day)• Drop in CO2 in leaf – stomata open, even in dark– Photosynthesis (occurs in light) reduces internal
concentration of CO2 in leaf, triggering stomata to stay open
Details of Stomatas Opening/Closing• H+ and K+ move across PM of guard cells• Blue light triggers K+ to move into guard from
subsidiary/epidermal cells– Active transport – ATP– ATP provides energy to pump H+ out of guard– Removal of H+ makes electrochemical gradient to drive
uptake of K+• Uptake of K+ in guard increases solute conc. In vacuoles water
enters guard from surrounding cells by osmosis
• Result increase in turgidity changes guard shape
• Almost opposite happens to close stomata– Evidence that increase in Ca2+ conc. In guard
triggers closure
Transpiration
• Loss of water vapor by evaporation • Responsible for water movement in plants• Factors influencing rate:– Temperature– Light– Wind + dry air
• Benefits– Cools stems and leaves– Distributes minerals
• Harmful effects– Loose more water than take in during heat loss
of turgidity wilt– Temporary wilting of plant can “come back”
Leaf Abscission
• Fall off, once/year• Many changes– Plant hormones – ethylene, abscisic acid (ABA)
• Abscission zone – near base of petiole– Weak, parenchyma and few fibers
Modified leaves
• Spines – animals• Tendrils – vine attachment• Bud scales – winter buds• Bulb – short underground stem with fleshy
leaves for storage• Succulent leaves – water storage in dryness• Insectivorous plants