Nature of Sunlight and Pigment

Nature of Sunlight and Pigments

The electromagnetic spectrum

 

GAMMA RAYS- X-RAYS - UV VISIBLE LIGHT INFRARED MICRO RADIO WAVES

VIOLET	INDIGO	BLUE	GREEN	YELLOW	ORANGE	RED
380 nm	450 nm	500 nm	550 nm	600 nm	650 nm	700 nm

Plants use light in the 450 and 700 nm range. Meaning the plants like indigo-blue and orange-red light.

Certain colors in light rays are important for proper plant growth. Leaves reflect and derive little energy from many of the yellow and green rays of the visible spectrum. Yet the red and blue parts of the light spectrum are the most important energy sources for plants, and plants require more rays from the red range than from the blue. Plants growing outdoors, in greenhouses or close to windows are exposed to a natural balance of the blue and red light rays that plants need. Where plants receive little or no natural light, you must provide additional light from artificial sources.

Most people are familiar with the incandescent light produced by ordinary light bulbs in our homes. As a single light source for plants, these bulbs are not particularly good. They are a good source of red rays but a poor source of blue. They produce too much heat for most plants and, if used, must be kept away from the plants, thus reducing the intensity of the light the plants receive. They are also about three times less efficient than fluorescent tubes inconverting electrical energy to light.

Photosynthesis occurs in organelles called CHLOROPLASTS.

More specifically, half of the photosynthesis chemistry stuff occurs in a liquid inside the chloropasts called STROMA,  & the other half of photosynthesis occurs in stacks of membranes inside the chloroplast called GRANA.

What are the main structures of chloroplasts?

Chloroplasts are involved by two membrane layers, the outer and the inner membranes. Inside the organelle the formative unit is called the granum, a coin-shaped structure that, piled with others grana, forms several structures called thylakoids. The thylakoids fill the chloroplast and an intergrana membrane permeates the interior of the organelle.

 Chlorophyll looks green because it absorbs red and blue light, making these colors unavailable to be seen by our eyes. It is the green light which is NOT absorbed that finally reaches our eyes, making chlorophyll appear green. However, it is the energy from the red and blue light that are absorbed that is, thereby, able to be used to do photosynthesis. The green light we can see is not/cannot be absorbed by the plant, and thus cannot be used to do photosynthesis.

Various plant pigments help use light. Carotenoids, chlorophyll a, b, and c. Chlorophyll a absorbs indigo and red lights, b absorbs blue and orange -red, c absorbs blue and orange in smaller amounts.

Chlorophyll is a molecule containing 2 main parts: a complex ring with a magnesium ion in the center and a nonpolar tail.

 

 Chlorophyll is a complex molecule. Several modifications of chlorophyll occur among plants and other photosynthetic organisms. All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll a. Accessory pigments absorb energy that chlorophyll a does not absorb. Accessory pigments include chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids (such as beta-carotene). Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelength.
 Did you notice that these main pigments do not absorb green light well?  Chlorophyll a and b both absorb blue light and red light best, resulting in an overall green appearance, whereas beta-carotene absorbs blue and some green light best resulting in an orange color (carotene was first derived from carrots, hence its name).  During the summer, chlorophylls dominate, resulting in leaves of plants being green.  In the autumn, when deciduous plants are getting ready for winter, they digest their chlorophyll resulting in the accessory pigments like carotenes becoming dominant, hence the bright red and orange colors of fall foliage.

  In Light dependent reaction, all the pigment molecules in the LHC are constantly absorbing light, and when light of a certain wavelength (<680 nm) is absorbed, the absorbed energy is transfered from one molecule to another until it reaches the reaction center.  Because it works optimally with light of <680 nm, the core reaction center of photosystem II is called the P680 complex.

In Dark reaction, the proteins associated with the pair of special Chl a molecules in the reaction center are different, PSI functions optimally with photons of light with an wavelength of 700 nm, so the reaction center of PSI is called the P700 complex.