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2. Center of meristem Figure 37.12
Figure Gravity Sensing Occurs in the Root Cap. 2

3. Cell in root tip (or shoot) Gravity
Figure 37.13
Cell in root tip (or shoot)
Gravity
Amyloplasts are pulled to bottom of cells by gravity
Figure The Statolith Hypothesis States that Amyloplasts Stimulate Sensory Cells.
Activated pressure receptors 3

4. 1. Normal distribution of auxin. Gravity
Figure 37.14
Auxin distribution
1. Normal distribution of auxin.
Gravity
2. Root tip rotated.
Auxin
3. Auxin is redistributed, move to bottom.
Figure The Auxin Redistribution Hypothesis for Gravitropism.
4. Root bends. 4

5. (a) Shoots bend toward full-spectrum light.
Figure 37.3a
(a) Shoots bend toward full-spectrum light.
Figure 40.3a Experimental Evidence that Plants Sense Specific Wavelengths of Light. 5

6. (b) Shoots bend specifically toward blue light.
Figure 37.3b
(b) Shoots bend specifically toward blue light.
Figure 40.3b Experimental Evidence that Plants Sense Specific Wavelengths of Light. 6

7. Figure 37.5
Light is not sensed at the tip of the coleoptile.
Light is sensed at the tip of a coleoptile.
Where is light sensed to initiate phototropism in grass seedlings?
Light
Light responsible for triggering phototropism is sensed at the coleoptile tip.
Control: Bends toward light
Tip removed: No bending
Tip covered: No bending
Lower portion of coleoptile covered: Bends toward light
1. Cells at coleoptile tip sense light.
2. Hormone travels from tip down the coleoptile.
3. Cells lower in coleoptile respond to hormone. Bending results.
Light (stimulus)
Sensing tissue
Hormonal signal
Responding tissue
This interpretation explains the hormone concept, but does not explain differential growth on the lighted and shaded sides of the coleoptile…
Based on what you know about gravitropism, give a parsimonious (i.e. parallel) interpretation.
Figure 40.5 The Sensory and Response Cells Involved in Phototropism Are Not the Same. 7

8. Biology: What is Life? life study of Properties of Life
Cellular Structure: the unit of life, one or many
Metabolism: photosynthesis, respiration, fermentation, digestion, gas exchange, secretion, excretion, circulation--processing materials and energy
Growth: cell enlargement, cell number
Movement: intracellular, movement, locomotion
Reproduction: avoid extinction at death
Behavior: short term response to stimuli
Evolution: long term adaptation

9. Obtaining Food
Autotrophs use ambient energy and carbon dioxide to make their own organic molecules.
So the only matter they need to take up is minerals!
Sadly they are sometimes called “plant food.”

10. Johann Baptista van Helmont
Physician Scientist
In experiment with Salix (willow) he tested whether the bulk of a plant comes from the soil or from some other source.
His experiment was carefully documented but, because he was so far ahead of his time, his conclusion was wrong.
Interestingly, however, his results suggest that plants do use soil minerals for growth.
In the light of knowledge of carbon dioxide gas, the project shows that the plant grows mostly from air.

11. sunlight H2O 200 lbs soil 200 lbs - 2 oz soil 169 lbs + 3 oz sapling
Adapted from: Figure 36.1
Because the role of air was not understood yet, van Helmont concluded that the weight increase was due only to water…WRONG.
Even if the plant is 90% water, the 10% dry weight (16.9 lbs) would have to come from somewhere.
sunlight
169 lbs + 3 oz
sapling
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
H2O
5 lbs branch
200 lbs soil
200 lbs - 2 oz soil

12. sunlight CO2 O2 H2O CH2O 200 lbs soil 200 lbs - 2 oz soil
Adapted from: Figure 36.1
Because the role of air was not understood yet, van Helmont concluded that the weight increase was due only to water…WRONG.
Even if the plant is 90% water, the 10% dry weight (16.9 lbs) would have to come from somewhere. Could it be minerals from the soil?
sunlight
169 lbs + 3 oz
sapling
CO2 O2
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
H2O
5 lbs branch
CH2O
200 lbs soil
200 lbs - 2 oz soil
This decrease could be sample error, or minerals taken from the soil by the growing plant.

13. Autotrophic Organisms
Typically autotrophs carry out photosynthesis:
CO2 + H2O O2 + CH2O
As you can see, the plant needs NO food.
But the enzymes and ion transporters for photosynthesis require metal cofactors:
The essential macroelements are:
CHOPKNS CaFe Mg
The essential microelements are:
CuMn CoZn Si Mo B Al Cl
light
chlorophyll
“C. Hopkins Café Mmm, good!”
“CoMe on, Cousin, See Mike over By Al and Cleo”

14. Essential “macroelements” for plants
Requirement
Functions
N (nitrogen)
21 g/m3
Amino acids, nitrogenous bases, vitamins
P (phosphorus) 5
Nucleic acids, phospholipids, ATP, enzyme cofactor
K (potassium) 16
Ion balance, enzyme cofactor
S (sulfur) 10
Cysteine and methionine, vitamins
Mg (magnesium) 7
Chlorophyll cofactor, enzyme cofactor
Ca (calcium)
Membrane permeability, pectin glue, enzyme cofactor
Fe (iron)
0.3
Cytochrome cofactor, enzyme cofactor
“Plant Food” has N-P-K analysis = %N-%P-%K

15. Essential “microelements” for plants
Requirement
Functions
Mn (manganese)
0.04 g/m3
Enzyme cofactor
B (boron)
0.008
Enzyme cofactor, pollen tube attraction
Cl (chlorine)
Ion balance, cofactor
Zn (zinc)
trace
Enzyme cofactor, hormone synthesis, DNA binding protein cofactor
Cu (copper)
Enzyme cofactor (polyphenol oxidase), plastocyanin cofactor
Mo (molybdenum)
Cofactor for nitrate reductase, nitrogen reductase (N2 fixation)
Ni (nickel)
Cofactor for urease (for uptake of organic N source)

16. Macroelements Microelements

17. Compare: Figure 36.9
Radish seedlings have roots with long root hairs that increase the surface area for water and mineral uptake
©1996 Norton Presentation Maker, W. W. Norton & Company

18. Selective mineral uptake and conduction
Compare: Figure 35.6
Dicot Mature Root Structure - Anatomy
Ranunculus acris - buttercup
Epidermis
Make root hairs for cation exchange
Cortex
Storage of starch
Vascular Cylinder
Selective mineral uptake and conduction

19. Root Vascular Cylinder and Cortex
Compare: Figure 35.6
Ranunculus acris - buttercup
Endodermis
Selective mineral uptake via these “window cells”
Storage of Starch, etc.
Sieve Tube Cell conducts organic molecules
Cortex
Companion Cell keeps the sieve tube cell alive!
Phloem
Xylem
Conducts minerals and water up to shoot system
Divides to make branch roots
Pericycle

20. This passive movement obeys the 2nd Law of Thermodynamics!
Osmosis: passive movement of water from pure to saltier area
Read: Chapter 35.1
cell membrane
cell wall
Virtually not; the bilayer is impermeable to solutes, and transport proteins keep solutes concentrated in the cell
Do solutes cross the membrane?
water flow
cytoplasmic solutes
more concentrated
soil solutes more dilute
Water potential low
Water potential high
This passive movement obeys the 2nd Law of Thermodynamics!

21. to endodermis and vascular cylinder then up the xylem to the shoot
Root hairs are responsible for cation exchange
cortex cell
root hair penetrates soil spaces
epidermal cell
soil particles covered with capillary water
and minerals
intercellular gas space
Ca2+
Ca2+ H+
Ca2+ H+
to endodermis and vascular cylinder then up the xylem to the shoot
voids with air space
water
Compare: Fig. 36.8

22. Root Vascular Cylinder and Cortex
Ranunculus acris - buttercup
Endodermis
Selective mineral uptake via these “window cells”
Storage of Starch, etc.
Sieve Tube Cell conducts organic molecules
Cortex
Companion Cell keeps the sieve tube cell alive!
Phloem
Xylem
Conducts minerals and water up to shoot system
Divides to make branch roots
Pericycle

23. The endodermis is thus responsible for selective mineral uptake.
Compare: Figure 35.7
endodermis
xylem inside
cortex outside
minerals cannot go between cells
The endodermis is thus responsible for selective mineral uptake.
minerals must go through cells
cell membrane proteins (active transporters) determine which minerals may be taken up
suberin-
waxy barrier
to apoplastic
movement
Important?: All human minerals in food come via this path!

24. Mineral uptake: Active transport against concentration gradient
cell membrane
cell wall
too expensive?
Calcium transport protein
ADP + Pi
Ca2+
Ca2+
Ca2+
ATP
Possible solute diffusion gradient
water flow
cytoplasmic solutes
more concentrated
soil solutes more dilute
Water potential low
Water potential high
Osmosis: passive movement of water from pure to salty area

25. This is a cross-section of a “typical” leaf: Syringa vulgaris (lilac)
soil mineral entry
evaporative cooling means the solute concentration increases!

26. Solute availability is pH dependent
iron
nitrogen
molybdenum
Element Concentration
4 acidic
7 neutral
alkaline 10
pH of soil water
The optimal pH?

27. ©1996 Norton Presentation Maker, W. W. Norton & Company
Soil pH is less than 4
Dionaea (Venus’ fly trap) leaves have evolved three trip hairs on each half-blade, an electrical potential is produced, osmosis causes the trap to snap shut, This fly is about to touch the second trip hair…

28. The trap halves have folded together, and the marginal spines have turned inward…the compound action makes an effective trap…have you ever tried to catch a fly?
©1996 Norton Presentation Maker, W. W. Norton & Company

29. Saracennia (pitcher plant) leaves hold water to drown insects and mine their minerals
©1996 Norton Presentation Maker, W. W. Norton & Company
Soil pH is less than 4

30. Drosera (sundew) uses sticky pads that look like nectaries but are actually glandular hairs secreting botanical “super glue” with digestive enzymes:
Remember that carnivorous plants are not eating insects for energy or carbon…
they are mining the insects for minerals unavailable from the acidic bog soil.
©1996 Norton Presentation Maker, W. W. Norton & Company