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Figure 40.11
Center of
meristem
Figure 40.12
Gravity
Cell in root tip
(or shoot)
Amyloplasts are
pulled to bottom
of cells by gravity
Activated pressure receptors
Auxin
distribution
Auxin
Gravity
Figure 40.13
1. Normal
distribution
of auxin.
2. Root tip
rotated.
3. Auxin is
redistributed,
move to bottom.
4. Root bends.
Figure 40.3a
(a) Shoots bend toward full-spectrum light.
Figure 40.3b
(b) Shoots bend specifically toward blue light.
Figure 40.5
Where is light sensed to initiate
phototropism in grass seedlings?
Light is sensed at the tip of a coleoptile.
Light is not sensed at the tip of the coleoptile.
Control:
Bends
toward light
Tip
removed:
No bending
Tip
covered:
No bending
Lower portion
of coleoptile
covered: Bends
toward light
Light
Light responsible for triggering phototropism is
sensed at the coleoptile tip.
Light
(stimulus)
Sensing
tissue
Hormonal
signal
1. Cells at
coleoptile tip
sense light.
Responding
tissue
2. Hormone
travels from
tip down
the coleoptile.
3. Cells lower in
coleoptile respond
to hormone.
Bending results.
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.
Biology:
life study of
What is Life?
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
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.”
Johann Baptista van Helmont
1577-1644
Physician Scientist
In 1648 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.
http://upload.wikimedia.org/wikipedia/commons/1/1d/Jan_Baptist_van_Helmont.jpg
Because the role of air was not
understood yet, van Helmont
concluded that the weight increase
was due only to water…WRONG.
sunlight
169 lbs + 3 oz
sapling
H2O
5 lbs branch
200 lbs soil
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Adapted from: Figure 39.1 Page 776
Even if the
plant is 90%
water, the
10% dry
weight (16.9
lbs) would
have to
come from
somewhere.
200 lbs - 2 oz soil
Because the role of air was not
understood yet, van Helmont
concluded that the weight increase
was due only to water…WRONG.
sunlight
CO2
H2O
O2
169 lbs + 3 oz
sapling
5 lbs branch
CH2O
200 lbs soil
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Adapted from: Figure 39.1 Page 776
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?
200 lbs - 2 oz soil
This decrease could be sample
error, or minerals taken from
the soil by the growing plant.
Autotrophic Organisms
Typically autotrophs carry out photosynthesis:
light
CO2 + H2O
O2 + CH2O
chlorophyll
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
“C. Hopkins Café
Mmm, good!”
“CoMe on, Cousin,
See Mike over By Al
and Cleo”
Essential “macroelements” for plants
Element
Requirement
Functions
N (nitrogen)
21 g/m3
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)
7
Membrane permeability, pectin
glue, enzyme cofactor
Fe (iron)
0.3
Cytochrome cofactor, enzyme
cofactor
Amino acids, nitrogenous bases,
vitamins
“Plant Food” has N-P-K analysis = %N-%P-%K
Essential “microelements” for plants
Element
Requirement
Functions
Mn (manganese)
0.04 g/m3
B (boron)
0.008
Enzyme cofactor, pollen tube
attraction
Cl (chlorine)
0.008
Ion balance, cofactor
Zn (zinc)
trace
Enzyme cofactor, hormone
synthesis, DNA binding protein
cofactor
Cu (copper)
trace
Enzyme cofactor (polyphenol
oxidase), plastocyanin cofactor
Mo (molybdenum)
trace
Cofactor for nitrate reductase,
nitrogen reductase (N2 fixation)
Ni (nickel)
trace
Cofactor for urease (for uptake of
organic N source)
Enzyme cofactor
Macroelements
Microelements
http://www.elementsdatabase.com/Images/periodic_table.gif
©1996 Norton Presentation Maker, W. W. Norton & Company
Radish seedlings have roots with long root hairs that
increase the surface area for water and mineral uptake