The Rate of Photosynthesis Determined by Light

Topics: Chlorophyll, Photosynthesis, Light Pages: 12 (2758 words) Published: May 17, 2011
The Rate of Photosynthesis Determined by
Different Wavelengths of Light

The aim of this report is to determine the most effective wave length of light for the growth of plants. It was predicted that the red and the blue light would work the most effectively and the green light would work the least effectively. It was found after the experiment was conducted that the hypothesis was proven wrong. The plant in the red light did not grow at all and the plant in the green light grew the most effectively. This is because of human error or false information.

Photosynthesis is the major source of energy for practically all plants living in sunlight. It is the process that plants go through to convert energy from sunlight to produce sugar that is then later transformed into ATP by cellular respiration. Photosynthesis occurs in two stages, light-independent and light-dependent reactions. Light-independent reactions use ATP to merge carbon dioxide and the hydrogen together to form glucose. Light-dependent is when Chlorophyll (the green pigment molecule in plants) traps the light energy and is used to form ATP and to split water into hydrogen ions and oxygen gas (Spenceley et al, 2004:185). However, many factors can affect the rate of photosynthesis, including the intensity of light.

Light is a major physical factor that can determine the growth and development of many plants. The rate of photosynthesis usually increases with the increase of light intensity. White light or natural light is divided into different colours (wavelengths) of light. According to Farabee:(2007, http://emc.maricopa, edu/faculty/farabee/BIOBK/BioBookPS, Accessed 6/04/09), wavelengths are defined as the distance from peak to peak and longer wavelengths have less energy, as shorter wavelengths have more. Longer wavelengths are the colour of an orange or red, unlike shorter wavelengths that have a blue-purple colour. This is shown in figure one.

figure 1
Farabee:(2007, http://emc.maricopa, edu/faculty/farabee/BIOBK/BioBookPS, Accessed 6/04/09

Different coloured wavelengths of light have different responses in plants. Red and blue light are both needed for a plant to photosynthesise. Red light is extremely important to plant reproduction. Phytochrome pigments, which are found in green plants absorb the red light and regulate seed germination, root development, tuber and bulb formation, dormancy, flowering and fruit production. Hodgkiss: (2007,, Accessed 19/04/09)

Also according to Hodgkiss: (2007,, Accessed 19/04/09), Blue light stimulates chlorophyll production more than any other colour. It is important for thick leaves, strong stems and compact vegetation growth. The yellow-orange pigment in plants, formally known as carotenoids, absorbs blue light to control leaf fall and fruit ripening. Another pigment, known as riboflavin absorbs violet light and influences phototropism (the growth towards light) this is shown in plants where to tip of the shoot is bending in the direction of a light (Spenceley et al, 2004:185). Therefore red and blue lights are vital for plant growth. On the other hand, green light is not an effective wavelength for the growth of plants as it is not used or absorbed. It is reflected back off the plant, this is why most plants look green in sunlight. Therefore, the red and blue light will allow the plants to grow most effectively. However, the green light will be unsuccessful. This is shown as; chlorophyll absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths.

Plants are a vital part of the environment as the community relies heavily on their productions, such as food, medicines, industrial products, but most importantly the quality of the air. According to: (date unknown,...
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