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Collin College BIOL 1408 Unit 10 Photosynthesis Packet
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- BIOL 1408
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- Collin College
Collin College BIOL 1408 Unit 10 Photosynthesis Packet
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Unit 10Photosynthesis
This lab uses the following hazardous chemicals:
I. Acetone & Chromatography Solvent
II. Lugol’s Iodine
As a result students are required to wear, at minimum, Goggles & Gloves.
Abstract:
Last week, you observed the way in which organisms and the cells within those
organisms perform respiration as a means of creating energy. You will recall that in
both aerobic and anaerobic respiration, glucose was one of the reactants needed to
eventually produce ATP. Mammals are heterotrophs, which means that they cannot
produce their own glucose, and must therefore consume other organisms to accrue the
glucose needed for respiration. Plants, on the other hand are autotrophs, which means
that they can produce their own glucose. Photosynthesis is the process by which plants
acquire light energy and convert it into chemical energy. This process is carried out in
two general processes: the light reactions and “dark reaction” (the dark reaction
involves a cycle known as the Calvin cycle). Furthermore, the entire process of
photosynthesis is carried out primarily in the chloroplasts of the leaf cells.
In the light reactions, pigments in the leaves absorb different wavelengths of sunlight.
You will recall, from the unit on spectrophotometry, that light travels in waves of
varying length depending upon the type of light. Additionally, you will also recall that
the visible spectrum of light consists of different colored lights traveling at different
wavelengths. Light on the red end of the visible spectrum will have a much larger
wavelength, and therefore travel with much less energy, than light on the violet end of
the visible spectrum. Pigments in plant leaves such as chlorophyll a and b and
arytenoids absorb light of varying wavelengths to provide the plant with the energy that
it needs to convert carbon dioxide and water into glucose and water as seen in the
equation below.
6CO2 + 6H2O + light energy ! C6H12O6 + 6O2
131
,10.1 Abs and %T spectra of photosynthetic pigments
Introduction
In this exercise you will observe the ability of differing pigments in vegetables to absorb
and transmit different wavelengths of light. For this experiment, spinach leaves and
carrots have been soaked in acetone to extract the pigments from each. Recall that the
colors that we perceive with our eyes are the wavelengths of the visible spectrum that are
transmitted rather than absorbed (example: a blue shirt is transmitting blue, but
absorbing other colors of the spectrum). You will once again use the spectrophotometer
to measure the ability of each pigment extract to absorb or transmit different wavelengths
of light.
You will now observe the ability of spinach extract and carrot extract to absorb or
transmit light of different wavelengths (400 – 700 nm). The spinach extract in this
experiment is green in color, while the carrot extract is orange in color. Additionally,
figure 1 denotes the approximate range of wavelengths for each color of the visible light
spectrum.
Color Wavelength
Violet 380-450 nm
Blue 450-500 nm
Green 500-570 nm
Yellow 570-590 nm
Orange 590-620 nm
Red 620-750 nm
Figure
1.
Colors
of
the
visible
light
spectrum
with
their
approximate
corresponding
wavelength
range.
Hypotheses
Use the information given in figure 1 to write hypotheses about the
wavelengths that you think spinach extract and carrot extract will absorb
and transmit.
Based on what I know about transmittance and absorbance of the visible
light spectrum, spinach extract will __________________________________
__________________________________________________________________
__________________________________________________________________.
132
, Based on what I know about transmittance and absorbance of the visible
light spectrum, carrot extract will __________________________________
__________________________________________________________________
__________________________________________________________________.
Spectronic 20D (PRC)
Materials and Methods – Photosynthetic Pigment Absorption Spectrum
Experiment
1. Turn on the spectrophotometer using the power switch/zero control knob and
allow it to warm up for five minutes.
2. With no sample tube in the holder and the lid closed, turn the power switch/zero
transmittance control knob until the meter read 0% transmittance.
3. Adjust the wavelength control knob until the display reads 525 nm.
During the remainder of the experiment, you will be working with hazardous
substances. Goggles and Gloves must be worn from this point on!
4. You have been provided with three test tubes: one labeled B, which contains your
blank (in this case the blank is acetone), one labeled S, which contains spinach
extract (the extract was made by placing spinach leaves in acetone), and one
labeled C, which contains carrot extract (the extract was made by placing carrot
shavings in acetone).
5. Insert the blank into the sample holder and close the lid. Using the 100%
transmittance control knob, adjust the meter reading to 100% transmittance.
REMEMBER that as you go through this experiment you will be changing
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