Download 3.2 light energy and photosynthetic pigments

Bodymint
• deodorant taken in tablet form
• made of chlorophyllin, a special derivative of chlorophyll
• one tablet taken each morning and evening
3.2 LIGHT ENERGY AND PHOTOSYNTHETIC PIGMENTS
Section 3.2 Questions
(Pages 154–155)
Understanding Concepts
chlorophyll
1. 6CO2(g) + 6H2O(l) + light energy
C6H12O6(aq) + 6O2(g) + 6H2O(l)
2. The products of the light reaction of photosynthesis are oxygen, ATP, and NADPH.
3. (a) Light, or electromagnetic radiation, is a form of energy that travels at 3 × 108 m/s in the form of photons.
(b) A photon is a discrete packet of light.
(c) As wavelength gets longer, the energy in a photon decreases, and as wavelength increases, the energy increases.
(d) Green light possesses a higher energy value than red light because it has a shorter wavelength.
Copyright © 2003 Nelson
Chapter 3 Photosynthesis
47
4.
Student answers will vary. Their timelines should include the following people and experiments.
Year
Name(s)
Nationality
Experiment
Results
Contributions
Early
1600s
J.B. Van
Helmont
Belgian
Planted a willow
tree and
measured mass
of tree and soil
The tree increased
it biomass 74.4 kg
while the soil lost
only 0.060 kg.
Soil was not responsible
for the increase in the
tree’s mass.
1771
Joseph Priestly
English
Burned candle in
a container with
a plant.
The candle went
out, but after ten
days the candle
could be relit for a
short time.
Plants release a gas into
the air that supports
combustion.
1796
Jan
Ingenhousz
Dutch
1882
T.W.
Engleman
German
Grew
filamentous
Spirogyra in
different
wavelengths of
light and added
aerobic bacteria.
The bacteria grew
most in the red and
blue-violet light.
Determined the action
spectrum for
photosynthesis.
1905
F.F. Blackman
English
Measured the
effect that
changes in light
intensity, CO2
concentration,
and temperature
have on the rates
of
photosynthesis in
green plants
At low light, the
rate photosynthesis
could be increased
by increasing light
intensity but not by
increasing
temperature.
Photosynthesis occurs in
two stages.
Controlled
temperature and
subjected plants
to varying
concentrations of
carbon dioxide.
When the
concentration of
carbon dioxide
increases, the rate
of photosynthesis
increases.
The rate of photosynthesis
is proportional to the
carbon dioxide
concentration.
1. Photochemical stage
2. Biochemical stage that
is affected by temperature
At high light
intensities,
increasing
temperature
increases the rate
of photosynthesis.
Early
1930s
C.B. Van Niel
Worked with
purple sulfur
bacteria.
The bacteria
produced elemental
sulfur.
The oxygen produced by
photosynthesis comes
from the splitting of
water.
1938
S.M. Ruben
Use heavy
isotope of
oxygen, H218O(g).
Measured with a
mass spectrometer
the oxygen gas
released from
plants as 18O2(g).
Confirmed Van Niel’s
findings.
M. Kamen
48
Identified that the gas
released by plants was
oxygen, that sunlight is
essential for
photosynthesis, and that
carbon dioxide is the
source of carbon in
photosynthesis.
Unit 1 Metabolic Processes
Copyright © 2003 Nelson
5. (a) The candle consumes all the oxygen in the air of the container and releases carbon dioxide.
(b) The plant produces oxygen and removes carbon dioxide by photosynthesis.
6. (a) The action spectrum of photosynthesis illustrates the effectiveness with which different wavelengths of light promote
photosynthesis, whereas the absorption spectrum refers to the different wavelengths of light that the chlorophyll a
pigment absorbs.
(b) The action and absorption spectra are similar because the wavelengths of maximum absorption of light will lead to the
maximum capture of electromagnetic energy and conversion to chemical energy. Most of the wavelengths of light
absorbed by chlorophylls are used in photosynthesis.
(c) The action spectrum of photosynthesis and the absorption spectrum for a specific pigment do not need to overlap
exactly, because different pigments have different absorption spectra.
7. In plants, β-carotene acts as an accessory pigment to chlorophyll a, helping to broaden the action spectrum for
SKRWRV\QWKHVLV DQG GLVVLSDWLQJ H[FHVV OLJKW HQHUJ\ DV KHDW -carotene absorbs light that would normally damage
chlorophyll. In humans, β-carotene is split into two molecules of vitamin A, which is oxidized into retinal, a
photopigment found in rod cells and used to see in low light conditions. The pigment protects the eye from photon
damage.
8. (a) Green plants contain chlorophyll a, chlorophyll b, β-carotenoids, xanthophylls, and anthocyanins.
(b) Yellow-coloured pigments are only visible in autumn leaves, because the chlorophyll pigments mask the yellowcoloured pigments the rest of the year. Plants stop producing chlorophyll in the autumn, so only the yellow, red, and
brown colours are visible.
(c) Photosynthetically active radiation is the wavelengths of light between 400 nm and 700 nm that supports
photosynthesis.
(d) Green plants absorb all the wavelengths of photosynthetically active radiation, yet they appear green because the green
wavelengths of light are absorbed the least when compared with other photosynthetically active radiation wavelengths.
9. (a) A heavy isotope does not emit radiation when it decays because it is stable, whereas a radioactive isotope emits
radioactive energy when it decays.
(b) Ruben and Kamen determined that the oxygen produced by photosynthesis comes from the splitting of water during
photosynthesis. They used H218O(g) and C18O2(g) in separate experiments and determined the type of oxygen gas
produced by photosynthesis.
(c) A mass spectrometer was used to detect the heavy isotope of oxygen, 18O(g).
Applying Inquiry Skills
Absorbance (%)
10.(a) Van Helmont measured the mass of a young willow tree and the soil it was planted in and then performed the same
measurements five years later. He found the that the tree had gained 74.4 kg of mass, while the soil had lost only
0.0060 kg of mass.
(b) Van Helmont applied some controls in his experiment. He apparently made sure that only the tree grew in the pot
(controlled for other plants growing in the pot); he added only water to the soil over the course of tree growth. Controls
he should have applied include light and temperature conditions and air composition including humidity, etc.
11.(a)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Absorption Spectrum of Spinach Leaf Pigments
400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700
purple blue
green
yellow
orange
red
Wavelength (nm)
Copyright © 2003 Nelson
Chapter 3 Photosynthesis
49
(b) Purple, blue, orange, and red are least visible in spinach leaves. This is because these colours are most absorbed by the
pigments in spinach.
(c) Green and yellow wavelengths are the least absorbed in the pigment extract. Chlorophyll reflects the green light rather
than absorbing it.
(d) The pigment most responsible for the peak at 670 nm is chlorophyll a.
(e) There are no peaks between 500 nm and 620 nm, because chlorophyll does not absorb green light.
(f) Chlorophyll a, chlorophyll b, and carotenoids pigments are responsible for absorption in the range of 400 nm to
480 nm.
Making Connections
12.(a) A bract is a modified leaf that encases the flower and then subtends it after the flower has opened. In a poinsettia, the
red leaves are bracts, whereas the actual flower of the poinsettia are the yellow buds at the centre of the plant.
(b) Poinsettia bracts usually turn from a cream colour to bright red at about Christmas time (late December), even in the
wild.
(c) Poinsettias are mainly popular at Christmas because of their festive green and red colouration. There is, however, a
Mexican folk tale with a Christmas connection. It is said that a young peasant girl prayed for some red flowers to put
on an altar for Christmas Eve. An angel appeared to answer her prayer and turned all of the weeds surrounding the
girl’s hut to poinsettias.
The poinsettia made it into the United States and Canada when the U.S. ambassador to Mexico, Joel Roberts Poinsett,
travelled into Mexico in the late 1820s. He liked the red-leaved plants that he saw in Mexico so much that he dug up
some, took them back to his South Carolina home, and put them in his greenhouse. They did quite well and by the time
he died in 1851, the poinsettia was a popular plant in the United States.
13. Gro-Lux, Plant-Gro, and other specialty fluorescent lamps are designed to provide a balance of red and blue light suited
for plant growth. However, in most cases, it is the quantity and brightness of light that is more important than the quality
of the light for ideal plant growth conditions.
3.3 PHOTOSYNTHESIS: THE DETAILS
Try This Activity: Chlorophyll Fluorescence
(Page 157)
(a) The greenish solution appeared to have a reddish tinge.
(b) The green leaf appeared green from all angles.
(c) The chlorophyll solution changed to a reddish colour when bright white light was shone on it. The red light was emitted
by the excited electrons of chlorophyll molecules that had absorbed a photon of light. An electron in the chlorophyll
molecule becomes excited when it absorbs electromagnetic radiation, and, since there is no compound available to accept
the excited electron in a solution containing only chlorophyll molecules, the excited electron returns to its lowest energy
level, reemitting the radiation it originally absorbed. This reemission of absorbed radiation is termed fluorescence.
(d) The leaf did not appear reddish because photosynthesis will capture the energy and the carotenoids present in the leaf
dissipate the excess absorbed energy as heat.
Case Study: Discovering Metabolic Pathways
(Page 164)
Applying Inquiry Skills
1.
2.
50
Calvin may have performed the following procedure with his “lollipop” apparatus:
1. Expose suspensions of the green algae Chlorella to 14CO2(g) for 1-, 2-, 5-, 10-, 15-, 20-, 25-, 30-, 35-, and 45-second
intervals.
2. Perform two-dimensional chromatography on each sample and create an autoradiogram.
3. Identify the type and relative amount of the compounds that appear on each autoradiogram.
4. Perform steps 1 to 3 five times and compare the results. New compounds formed sequentially in the Calvin cycle would
appear sequentially in the resulting series of autoradiograms.
The chemical identity of a particular spot on an autoradiogram could not be determined by chemical analysis because the
spot only indicates the presence of radiation on the two-dimensional chromatogram. You would need to analyze the
corresponding spot on the chromatogram to determine the identity of the chemical.
Unit 1 Metabolic Processes
Copyright © 2003 Nelson