Name ____________________ Period _______
Accelerated Biology
The Absorption of Light by Pigments
Photosynthesis is the process by which green plants convert the energy of sunlight into chemical energy.
This process requires special pigments that have the ability to absorb the energy in light.
Study the chart below that shows the amount and kind of light absorbed by two kinds of chlorophyll
common to green plants. Plot these data on the graph on the right. Then, answer the questions below.
1. Chlorophyll A absorbs the greatest amount of light at a wavelength of 450 nanometers.
2. Chlorophyll B absorbs the greatest amount of light at a wavelength of 500 nanometers.
3. Why do artificial plant grow lights have a light spectrum that favors the blue and red portions of the
spectrum?
Those are the wavelengths of light that plants absorb
4. Using the graph above, explain why the leaves of trees are green in summer.
The green wavelength (550 nm) is reflected and not absorbed.
5. The plant pigment xanthophyll absorbs light in the range of 400–500 nanometers and reflects all other
light. What colors are tissues that contain only xanthophylls? Why?
Those plants would be green, yellow, orange and red in color. Those colors are the
wavelengths that are being reflected off the plant and what we see as a result.
Name ____________________ Period _______
Accelerated Biology
THE SKILL: Analyzing Processes
Analyzing a process involves breaking down the process into its smaller
components. The role of each part in the overall process is identified. The
relationships that exist among the various parts are also examined.
Developing an understanding of the function of each part leads to an
improved understanding of the process as a whole. You can read more
about analyzing processes by reading page 950 of your text.
THE EXPERIMENT:
Bromthymol blue is a pH indicator that turns yellow in the presence of carbon dioxide. In a particular
experiment, a scientist filled two flasks with Bromthymol blue. She then placed a sprig of Elodea, an
aquatic autotroph, in each flask. One flask was put inside a dark cabinet, while the other was put in direct
sunlight. After 24 hours, the scientist compared the contents of the flasks. The flask that had been put in
the dark contained a yellow liquid. The flask that had been put in sunlight contained a blue liquid. What
caused these results?
APPLICATION: Write a complete answer to each question.
1. What processes associated with energy occur within the Elodea? Explain your answer.
Plants complete BOTH photosynthesis and cellular respiration!
2. Identify the products of the processes described above.
Photosynthesis – C6H12O6 and O2
Cellular respiration – CO2, H2O, and ATP
3. Describe the processes that occurred in each flask. What evidence do you have that these processes
occurred?
Flask in the LIGHT – Photosynthesis and cellular respiration
 The Bromthymol blue never changed colors (blue  yellow) because the CO2 that
was produced by the plant as a result of cellular respiration, was used by the
plant during photosynthesis! There was no CO2 available to cause the color
change!
Flask in the DARK – cellular respiration only (photosynthesis requires light)
 The plant released CO2 during the process of cellular respiration. The
Bromthymol Blue changed to a yellow color.
4. In another experiment, the scientist exhaled through a tube that led into a flask containing
Bromthymol blue. She then placed a sprig of Elodea in the flask, put the stopper in it, and placed it on
a sunny windowsill. Predict what she observed.
Lets try it! 