The Effects of Lights on Plants

Tim LangleyBiology 101

Research project

Plants Importance to the World•Without light plants could not grow or reproduce, which means that all plants would die off •Plants are the only organism that produces its own food•Plants get their energy directly from the sun•Plants are the only organisms that produce oxygen, and we would suffocate without them

Photosynthesis

•All organic molecules derive from photosynthesis•All of the oxygen on earth is a product of photosynthesis•Photosynthesis is an endergonic redox process•Occurs in two stages: the light reactions and the Calvin cycle•Takes place in the thylakoid membranes of the chloroplasts

The Two Stages of Photosynthesis

Light Reactions• The part of photosynthesis where light is

converted to chemical energy• Water and carbon dioxide combine to

form carbohydrates and oxygen• The light captured by chlorophyll is used

to generate electrons with reducing potential

• These electrons are used to produce NADPH and ATP

• Occurs in the thylakoids of the chloroplasts

• Violet-blue and red light work best for photosynthesis

Calvin Cycle• CO2 from the air is incorporated into

organic molecules in a process called carbon fixation

• The cycle spends ATP and NADPH to make sugar out of CO2

• Occurs in the stroma• Returns ADP, inorganic phosphate, and

NADP+ back to the light reactions

Chloroplasts

• Found in the tissue in the interior of the leaf in the mesophyll cells•The structure is mainly made from the fluid, Stroma, and the Granum which is in the form of thylakoid sacs•Contains three types of pigments: Chlorophyll a, chlorophyll b, and carotenoids •Light energy is captured by the chlorophyll in the chloroplasts and transferred into chemical energy

Photons and Chlorophyll•When a photon is absorbed the electrons in the chlorophyll become excited and then have more potential energy•An excited electron is unstable and will drop back to the ground state and release its excess energy in the form of heat and fluorescence •Fluorescence is the afterglow of an isolated chlorophyll

Photosystems• The light dependent part of

photosynthesis is carried out by the photosystems (I and II)

• This occurs in the thylakoid membrane of the chloroplasts

• Each photosystem is driven by excited chlorophyll molecules

• They are composed of a reaction center complex and light harvesting complexes

• Pigment molecules and proteins allow photosystems to capture light over a larger surface

Linear Electron Flowthe flow of electrons through the photosystems

• A photon is absorbed by a pigment molecule in the light harvesting complex, exciting an electron

• As one electron falls back to ground state, another one rises • This continues until the energy reaches the pair of chlorophyll a molecules in the reaction

center complex in photosystem II• An enzyme splits water in photosystem II into electrons, hydrogen ions, and oxygen• The splitting of water molecules facilitates the flow of electrons through the electron

transport chain to photosystem I to replace the electrons that were excited by light energy• ATP is then synthesized from the energy created from the movement of electrons• Light energy is transferred from the light harvesting complex pigments to the reaction center

complex of photosystem I• Photoexcited electrons move from the primary electron receptor of photosystem I to the

second electron transport chain• This is a light dependent reaction, creating NADPH and ATP which are then used in a light

independent reaction, also known as the Calvin cycle

Linear Electron Flow

Light Receptors

•Pigments are substances that absorb visible light•Pigments absorb different wavelengths of light•The absorption of different wavelengths changes the colors of the pigments•Leafs are green because they absorb red, and violet-blue light and they reflect green light•Light can only perform work if its absorbed by the chloroplasts

A prism can bend light of different wavelengths at different angles

Electromagnetic Spectrum

•This is the range of radiation•Wavelengths are the distances between the crests of electromagnetic waves•The wavelengths range from less than a nanometer to more than a kilometer•Visible light is from 380nm to 750nm in wavelength•The amount of energy a photon has is related to how long the wavelength is•Shorter wavelengths mean greater energy of the photon

Photosynthetic PigmentsChlorophyll a Chlorophyll b Carotenoids

•The light absorbing pigment that participates directly in light reactions

•Helps to increase the amount of light a plant can use for energy

•These are accessory pigments used in all photosynthetic organisms

•The most abundant pigment in plants

•Has a slight structural difference from chlorophyll a

•Absorb and dissipate excesive light energy that could damage chlorophyll

Each photosynthetic pigment absorbs light at different wavelengths

Photoperiodism• The reaction of plants in relation to the length of the day• Plants use it to measure the seasons and to coordinate seasonal

events such as flowering• Plants can be described in relation to their photoperiod responses

as short-day, long-day, and day neutral• The length of daylight effects vegetative growth and reproductive

activities in plants• The length of darkness a plant experiences plays a more crucial role

in whether a plant flowers or not

Short Day Plants

•A plant that requires a long period of darkness•Short day plants only form flowers when the length of the day is less than about 12 hours•Most spring and fall flowering plants are short day plants•Chrysanthemums, poinsettias, and goldenrods are examples of short day plants

The chrysanthemum is in demand all year, which is why florist have to regulate their flowering using artificial lighting

Long Day Plants

•A plant that requires a short night to flower•These flowers only bloom when they receive more than 12 hours of light each day•The best time of the year for long day plants to flower is late spring or early summer, when the days are longer (this is opposite in the southern hemisphere)•Many garden vegetables are long day plants such as potatoes, lettuce, and barley

Ever notice all the roadside vegetable stands in the early summer months?

After the summer solstice days become shorter, and long day plants are harvested shortly after.

Day Neutral Plants

•Do not initiate flowering based on photoperiodism•They flower regardless of day length, but flower earlier and more often with longer days•More often, the age of the plant, and temperature around it effect flowering•Beans, tomatoes, and roses fall into the category of day neutral plants

Roses are the most popular day neutral flowers

Works Cited Holley, Dennis. "Light and Temperature Influence Plant Growth." Suite101.com.

N.p.,June, 11th, 2009. Web. 12 Oct 2010. <http://www.suite101.com/content/light-and-temperature-influence-plant-growth-a131226>.

“Department of Physics." Florida Atlantic University. N.p.Web. 12 Oct 2010.

<http://www.physics.fau.edu/observatory/lightpol-Plants.html>.

"Plant Growth Factors: Light." Colorado Master Gardeners Program (2010): 142-1 to 142-4. Web. 11 Oct 2010. <http://www.cmg.colostate.edu/gardennotes/142.pdf>.

howplantswork, . "Does the Moon Affect Plants? Part 2: Moonlight and Biorhythms." Wordpress. June, 25th, 2009. Web. 11 Oct 2010. <http://howplantswork.wordpress.com/2009/07/25/does-the-moon-affect-plants-part-2-moonlight-and-biorhythms/>.

Continued

Leiser,Leopold,and Shelley, . "Evaluation of light sources for plant growth.” Departments of horticulture and electrical engineering, Purdue university, Lafayette, Indiana 392-395. Web. 11 Oct 2010. <http://www.plantphysiol.org/cgi/reprint/35/3/392.pdf>.

Lynn, Paul. Electricity from Sunlight. 1st ed. United Kingdom: John Wiley & Sons,

2010. Print.

Tanaka, R., M. Rothbart, S. Oka, A. Takabayashi, K. Takahashi, M. Shibata, F. Myouga, R. Motohashi, K. Shinozaki, B. Grimm, and A. Tanaka. "LIL3, a light-harvesting-like protein, plays an essential role in chlorophyll and tocopherol biosynthesis. " Proceedings of the National Academy of Sciences of the United States of America 107.38 (2010): 16721. Research Library Core, ProQuest. Web. 5 Nov. 2010.

Campbell, Reece, First. Biology, Photosynthesis. eighth ed. San Fransisco, California:

Pearson Education, Inc., 2008. 185-203. Print.