1. Chapter 32: Leaf Structure and Function

2. 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

3. External form
Shapes – round, need, scalelike, cylindrical, heart, fan, thin, narrow
Size – 20m to < .5 cm
Blade, petiole, stipules
Simple, compound
Axil region

4. (a) Simple leaf Petiole Axillary bud Fig. 35-6a
Figure 35.6 Simple versus compound leaves
Axillary bud

5. Leaflet (b) Compound leaf Petiole Axillary bud Fig. 35-6b
Figure 35.6 Simple versus compound leaves
Axillary bud

6. (c) Doubly compound leaf Leaflet Petiole Axillary bud Fig. 35-6c
Figure 35.6 Simple versus compound leaves
Axillary bud

7. (a) Simple leaf Petiole Axillary bud Leaflet (b) Compound leaf Petiole
Fig. 35-6
(a) Simple leaf
Petiole
Axillary bud
Leaflet
(b)
Compound
leaf
Petiole
Axillary bud
Figure 35.6 Simple versus compound leaves
(c)
Doubly
compound
leaf
Leaflet
Petiole
Axillary bud

8. Leaf arrangement Alternate – 1 leaf each node
Opposite – 2 leaves each node
Whorled – 3+ leaves each node

9. Leaf Venation Veins = vascular tissue Parallel Netted
Palmately – from 1 point
Pinnately – branch from entire length of midvein

10. Leaf tissues Upper epidermis + Lower epidermis
No chloroplasts/transparent
Cuticle – waxycutin
Trichomes – hairlike (fuzzy)
Retain moisture next to leaf, reflect light
Secrete irritants – herbivores
Texture – deter insects walk/eat
Excrete excess salts

11. EXPERIMENT Very hairy pod (10 trichomes/ mm2) Slightly hairy pod
Fig. 35-9
EXPERIMENT
Very hairy pod
(10 trichomes/
mm2)
Slightly hairy pod
(2 trichomes/
mm2)
Bald pod
(no trichomes)
RESULTS
Very hairy pod:
10% damage
Slightly hairy pod:
25% damage
Bald pod:
40% damage
Figure 35.9 Do soybean pod trichomes deter herbivores?

12. 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)

13. Surface view of a spiderwort (Tradescantia) leaf (LM)
Fig b
Guard
cells
Stomatal
pore
50 µm
Epidermal
cell
Figure Leaf anatomy
(b)
Surface view of a spiderwort
(Tradescantia) leaf (LM)

14. 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

15. Vascular bundles – veins – through mesophyll Bundle sheath
Xylem (top) and phloem (bottom)
Bundle sheath
Nonvascular, around vein
Parenchyma or sclerenchyma

16. Fig. 35-18 Figure 35.18 Leaf anatomy Guard cells Key to labels
Stomatal
pore
50 µm
Dermal
Epidermal
cell
Ground
Cuticle
Sclerenchyma
fibers
Vascular
Stoma
(b)
Surface view of a spiderwort
(Tradescantia) leaf (LM)
Upper
epidermis
Palisade
mesophyll
Bundle-
sheath
cell
Spongy
mesophyll
Figure Leaf anatomy
Lower
epidermis
100 µm
Cuticle
Xylem
Phloem
Vein
Guard
cells
Vein
Air spaces
Guard cells
(a) Cutaway drawing of leaf tissues
(c)
Cross section of a lilac
(Syringa)) leaf (LM)

17. (a) Cutaway drawing of leaf tissues
Fig a
Key
to labels
Dermal
Ground
Cuticle
Sclerenchyma
fibers
Vascular
Stoma
Upper
epidermis
Palisade
mesophyll
Figure Leaf anatomy
Bundle-
sheath
cell
Spongy
mesophyll
Lower
epidermis
Cuticle
Xylem
Phloem
Vein
Guard
cells
(a) Cutaway drawing of leaf tissues

18. Cross section of a lilac (Syringa) leaf (LM)
Fig c
Upper
epidermis
Key
to labels
Palisade
mesophyll
Dermal
Ground
Vascular
Spongy
mesophyll
Lower
epidermis
100 µm
Figure Leaf anatomy
Vein
Air spaces
Guard cells
(c)
Cross section of a lilac
(Syringa) leaf (LM)

19. 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

20. 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

21. Result  increase in turgidity changes guard shape
Almost opposite happens to close stomata
Evidence that increase in Ca2+ conc. In guard triggers closure

23. Transpiration Loss of water vapor by evaporation
Responsible for water movement in plants
Factors influencing rate:
Temperature
Light
Wind + dry air

24. Benefits Harmful effects Cools stems and leaves Distributes minerals
Loose more water than take in during heat  loss of turgidity  wilt
Temporary wilting of plant can “come back”

25. 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

26. 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