1. Figure 31.1
Figure 31.1 How do plants detect light?

2. Figure 31.UN02
Figure 31.UN02 Summary of key concepts: plant hormones 2

3. Results Shaded side Control Light Illuminated side Boysen-Jensen Light
Figure 31.2
Results
Shaded
side
Control
Light
Illuminated
side
Boysen-Jensen
Light
Darwin and Darwin
Gelatin
(permeable)
Mica
(impermeable)
Figure 31.2 Inquiry: What part of a grass coleoptile senses light, and how is the signal transmitted?
Light
Opaque
shield
over
curvature
Trans-
parent
cap
Tip
removed
Opaque
cap

4. 4 3 H 2 H H H H H H H 1 ATP H 5
Figure 31.5
CELL WALL 4
Cell wall-loosening
enzymes cleave
cross-linking
polysaccharides. 3
Low pH
activates
expansins.
H2O
Cell
wall H
Plasma
membrane 2
Acidity
increases. H H H H H H H
Figure 31.5 Cell elongation in response to auxin: the acid growth hypothesis 1
Proton
pump
activity
increases.
Nucleus
Cytoplasm
Plasma membrane
Vacuole
ATP H 5
Sliding cellulose microfibrils
allow cell to elongate.
CYTOPLASM 4

5. Sliding cellulose microfibrils allow cell to elongate.
Figure 31.5b
H2O
Cell
wall
Plasma
membrane
Figure 31.5b Cell elongation in response to auxin: the acid growth hypothesis (part 2: cell elongation)
Nucleus
Cytoplasm
Vacuole 5
Sliding cellulose microfibrils
allow cell to elongate. 5

6. vine (left) and gibberellin- treated vine (right)
Figure 31.6
Grapes from control
vine (left) and gibberellin-
treated vine (right)
Figure 31.6 Effects of gibberellins on stem elongation and fruit growth
(a) Rosette form (left) and
gibberellin-induced bolting
(right) 6

7. Aleurone Endosperm Water Radicle Scutellum (cotyledon) GA GA -amylase
Figure 31.7
Aleurone
Endosperm
-amylase
Sugar GA GA
Water
Figure 31.7 Mobilization of nutrients by gibberellins during the germination of grain seeds such as barley
Radicle
Scutellum
(cotyledon) 7

8. 0.5 mm Protective layer Abscission layer Stem Petiole
Figure 31.10
0.5 mm
Figure Abscission of a maple leaf
Protective layer
Abscission layer
Stem
Petiole 8

9. (a) Before exposure to light (b) After a week’s exposure
Figure 31.11
Figure Light-induced de-etiolation (greening) of dark-grown potatoes
(a) Before exposure to light
(b) After a week’s exposure
to natural daylight 9

10. Phototropic effectiveness
Figure 31.12
1.0
436 nm
0.8
Refracting prism
0.6
Phototropic effectiveness
0.4
White
light
0.2
400
450
500
550
600
650
700
Figure Action spectrum for blue-light-stimulated phototropism in maize coleoptiles
Wavelength (nm)
Light wavelengths below 500nm induce
curvature.
Blue light induces the most curvature
of coleoptiles. 10

11. Results Red Dark Red Far-red Dark Dark (control) Red Far-red Red Dark
Figure 31.13
Results
Red
Dark
Red
Far-red
Dark
Dark (control)
Figure Inquiry: How does the order of red and far-red illumination affect seed germination?
Red
Far-red
Red
Dark
Red
Far-red
Red
Far-red 11

12. • Inhibition of vertical growth and stimu- lation of branching
Figure 31.14
Responses to Pfr:
• Seed germination
• Inhibition of vertical
growth and stimu-
lation of branching
• Setting internal clocks
• Control of flowering
Red light
Synthesis Pr
Pfr
Far-red
light
Slow conversion
in darkness
(some species)
Enzymatic
destruction
Figure Phytochrome: a molecular switching mechanism 12

13. (a) Primary root of maize bending gravitropically (LMs)
Figure 31.19
Statoliths
20 m
Figure Positive gravitropism in roots: the statolith hypothesis
(a) Primary root of maize
bending gravitropically
(LMs)
(b) Statoliths settling to
the lowest sides of
root cap cells (LMs) 13

14. (a) Unstimulated state (leaflets spread apart)
Figure 31.21
Figure Rapid turgor movements by the sensitive plant (Mimosa pudica) Thigmomorphogenesis = changes in form in response to mechanical stimuli
(a) Unstimulated state (leaflets
spread apart)
(b) Stimulated state (leaflets folded) 14

15. (a) Control root (aerated) (b) Experimental root (nonaerated)
Figure 31.22
Vascular
cylinder
Air tubes
Epidermis
Figure A developmental response of maize roots to flooding and oxygen deprivation
100 m
100 m
(a) Control root (aerated)
(b) Experimental root
(nonaerated) 15

16. 4 Recruitment of parasitoid wasps that lay their eggs
Figure 31.23 4
Recruitment of
parasitoid wasps
that lay their eggs
within caterpillars 3
Synthesis
and release
of volatile
attractants 1
Wounding 1
Chemical
in saliva
Figure A maize leaf “recruiting” a parasitoid wasp as a defensive response to an armyworm caterpillar, an herbivore 2
Signal transduction
pathway 16

17. Infected tobacco leaf with lesions
Figure 31.24
Infected tobacco leaf with lesions
Signal 4 5 6
Hypersensitive
response
Signal
transduction
pathway 3 2
Signal transduction pathway
Figure Defense responses against an avirulent pathogen 7
Acquired
resistance 1
R protein
Avirulent
pathogen
Avr effector protein
R-Avr recognition and
hypersensitive response
Systemic acquired
resistance 17

18. Infected tobacco leaf with lesions
Figure 31.24b
Figure 31.24b Defense responses against an avirulent pathogen (part 2: photo)
Infected tobacco leaf with lesions 18

19. Table 31.1
Table 31.1 Overview of plant hormones 19