Plants and Photosynthesis
Reading Material by Godfrey Dzhivhuho
Plants, also called green plants (Viridiplantae in Latin), are multicellular eukaryotes of the kingdom Plantae. Another important way of defining them is by calling them
producers or Autotrophs. If the smartest energy source is one that's abundant, cheap and clean, then plants are a lot smarter than humans. Over billions of years, they
developed perhaps the most efficient power supply in the world: photosynthesis, or the conversion of sunlight, carbon dioxide and water into usable fuel, emitting useful
oxygen in the process.
Photosynthesis is also the prime process that runs the entire food chain and thus forms the base of the food pyramid. Green plants, the producer s of the food pyramid,
depend on this process. Photosynthesis can be defined as, Synthesis of compounds with the aid of radiant energy. The process of Photosynthesis allows green plants to
produce food and energy they require, all on their own. Hence making them an autotrophic breed i.e. they are self-dependent for food.
Other than these green plants, some protists (algae) and bacteria also use the photosynthesis process to feed, survive and grow. The ones who fail to produce their own
food are called heterotrophs. All the other living beings, therefore, are in some way or the other eventually dependent on these autotrophs. The animals, who feed on
these trees and plants for their living, hence directly depending on them, are called the primary consumers of the food chain. These animals are the herbivores (planteaters), who form the source of food for the secondary consumers of food pyramid, the carnivores and the omnivores. The carnivores are the animals that eat only meat,
while omnivores are the ones who eat both meat and plants for food. And similarly the food chain continues, making it clearly evident that the process of photosynthesis is
the basic source of food and energy in our ecosystem.
Photosynthetic Research in Plant Science
Photosynthesis is a highly regulated, multistep process. It encompasses the harvest of solar energy,
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transfer of excitation energy, energy conversion, electron transfer from water to NADP , ATP
generation and a series of enzymatic reactions that assimilate carbon dioxide and synthesize
carbohydrate.
In plants, there are two photosystems, aptly named Photosystem I and Photosystem II, located in
the thylakoid membrane of the chloroplast. The thylakoid membrane absorbs photon energy of
different wavelengths of light.
Even though two photosystems absorb different wavelengths of light, they work similarly. Each photosystem is made of many different pigments. Some of these pigments
can be described as absorption pigments, and others are considered action pigments.
The absorption pigments transfer the energy from sunlight to another pigment; at each transfer, the
absorption pigments pass the photon energy to another pigment that absorbs a similar or lower
wavelength of light. Remember when we said that light is funky and acts like it has both particles and
waves? A photon is what we call the particle-like aspect of light. In other words, a photon is the basic unit
of light.
Anyway, eventually, the energy makes it to the reaction center, or action pigment. At this point, the
photosystem loses a highly charged electron to adjacent oxidizing agents, or electron acceptors, in the
electron transport chain.
Here again is our friend the chloroplast. All exposed the way he is, he kind of reminds us of a boat with
green checkers in it:
How Has the Earth Evolved? Evolution of the Atmosphere
by Dr. Ed Mathez,
As we look deep into the Earth's past, the sparse evidence from old rocks suggests that conditions were once very different.
In particular, the rocks indicate that the early atmosphere contained little or no oxygen. What are these rocks, how do they tell us about a
past atmosphere that no longer exists, and how did the atmosphere evolve to its present state?
What questions do banded iron formations answer and pose?
The rocks in question are known as banded iron formations (BIFs). BIFs consist of alternating iron-rich and iron-poor layers, typically only
millimeters to centimeters thick. They are chemical precipitates, meaning that they formed when minerals precipitated directly from
seawater. (Sedimentary rocks like sandstone and shale form as suspended particles accumulate. Precipitation is the formation of solid
matter from material dissolved in the liquid. A familiar chemical precipitate is salt.) Most BIFs are strikingly colorful. In the BIF on display
Banded iron formation: dark layers
are rich in the mineral iron oxide
magnetite and red layers are rich
in jasper. ©AMNH
in the Museum's Hall of Planet Earth, which is typical of many such formations, the dark layers are made up mainly of the iron oxide mineral magnetite (Fe3O4) and red
layers of jasper, a variety of chalcedony, or very fine-grained quartz (SiO2). The red color comes from the presence of minute grains of iron oxides. The most ancient banded
iron formation known is 3.8 billion years old, but most are 2.6 to 1.7 billion years old, and no true BIFs are any younger.
BIFs also happen to be of more than just scientific interest—they are the source of more than 90% of our iron.
What early organisms produced oxygen, and when?
The geologic record suggests that life was the source of the oxygen that formed BIFs and subsequently built up in the
atmosphere.
Fossils indicate that life on Earth was entirely microbial until about a billion years ago. (The Proterozoic, the time from 2.5
billion to 543 million years ago, is informally known as the "Age of Bacteria.") The oldest fossils are mere microscopic
forms in rocks of the 3.3 to 3.5 billion year old Warrawoona Group, a sequence of metamorphosed sediments in Western
Australia. The organisms appear to have grown in shallow seas near the surface, and represent a diverse group of
microbes resembling cyanobacteria (blue-green algae). Cyanobacteria are light-sensitive. If this interpretation is correct,
photosynthesis—the process by which plants use sunlight to convert carbon dioxide to food and energy, and of which
oxygen is a byproduct—must have been extensive in the early Archean (3.8 to 2.5 billion years ago).
References
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How Stuff Works: Julia Layton: http://science.howstuffworks.com/environmental/green-tech/energy-production/artificial-photosynthesis.htm.
Wikipedia: http://en.wikipedia.org/wiki/Plant.
Kenn Oberrecht, Food Chains and Food Webs:http://www.oregon.gov/dsl/ssnerr/docs/efs/efs28foodchain.pdf.