1. Unit Plant Science

2. Problem Area Managing Plant Growth

3. Lesson Separating Plant Pigments by Chromatography

4. Student Learning Objectives 1. Explain different wavelengths of light. 2. Explain the role of light intensity of plant growth. 3. Identify the pigments commonly found in the leaves of plants.

5. Terms Carotene Chromatography Electromagnetic spectrum Etiolation Light intensity Luminance

6. What are the different wavelengths of light? A. The electromagnetic spectrum is a measure of the different rays of radiant energy based on wavelength.  1. Light rays perceived by the human eye fall into the range of 380 nanometers to 780 nm. This range of wavelengths of light is similar to the wavelengths used by plants during photosynthesis with some minor differences.  2. Humans perceive light best at 555 nm, but the wavelengths of light most effective in photosynthesis are between 400–510 nm and 610–700 nm. The green leaf “sees” two wavelengths of light best.

8. B. The green color of leaves is due to the fact that chlorophyll reflects light, which we see as green, and absorbs light, which we see as red and blue-violet. Plants use red light most effectively. C. The colors that have the greatest influence on plant growth are blue and red. In general, blue wavelengths affect photosynthesis, and red wavelengths influence flowering and growth.

10. What is the role of light intensity on plant growth? Intensity of light depends on the angle of the sun, clouds, and dust in the atmosphere. Light intensity is greater in the summer months when the sun is higher in the sky. Light intensity is measured in lumens and is the radiant flux emitted from a light source. Luminance is the radiant flux intercepted per unit area. A. Different plant species have evolved to survive in conditions where the light intensity varies. Plants like impatiens, African violets, ferns, and many houseplants have been selected because of their ability to tolerate low levels of light.

11. B. The major agricultural crops produce the highest yields when they receive full sunlight. A plant receiving the proper levels of light will be compact and good leaf color. C. Plants grown in the absence of light, but which are getting their source of energy from a seed, tuber or bulb have elongated, spindly stems. This expression of light deficiency is known as etiolation. D. Most plants grow best in the high intensities of full sun, which is 108 kiloluxes, however, a leaf is fully saturated at 13 klx. The higher intensities are needed because of leaf shading.

12. What are the pigments commonly found in leaves of plants? Leaves from green plants actually contain several different colored pigments and appear green because of chlorophyll is the most abundant pigment in the leaf of a growing plant. A. Chlorophyll is green in color. Plants contain two types of chlorophyll designated as A and B. The two chlorophylls are responsible for capturing sunlight and using this energy during photosynthesis.

13. B. Carotene is a yellow pigment found in most plant leaves and is believed to protect the plant form damage by oxygen. C. The xanthophylls are the colors seen in autumn leaves after the chlorophylls die off. D. Chromatography is a chemical technique where complex mixtures are separated into compounds parts by passing through or across selectively adsorbent materials. Pigments of leaves can be separated through the process of chromatography.

14. Review/Summary What are the different wavelengths of light? What is the role of light intensity on plant growth? What are the pigments commonly found in leaves of plants?