IB Biology Notes - 8.2 Photosynthesis
Nitrogen and phosphorus are the most vital elements for life after carbon, hydrogen, and oxygen. In its pure state in nature, nitrogen, like hydrogen and oxygen, is a diatomic molecule. Hydrogen in nature is single-bonded to itself, oxygen is double-bonded, and nitrogen is triple-bonded. Because of that , nitrogen is quite unreactive and prefers to stay bonded to itself. In nature, nitrogen will not significantly react with other substances unless the temperature () is very high. Most nitrogen compounds in nature are created when the nitrogen and oxygen that comprise more than 99% of Earth’s atmosphere react under lightning’s influence to create nitric oxide, which then reacts with oxygen to form nitrogen dioxide, and atmospheric water combines with that to make nitrous and nitric acids, which then fall to Earth’s surface in precipitation. Certain kinds of bacteria “fix” the nitrogen from the acidic rain into biological systems. Also, some bacteria can fix nitrogen directly from atmospheric nitrogen, but it is an that uses the energy in eight ATP molecules to fix each atom of nitrogen. For the earliest life on Earth, nitrogen would have been essential, and , where .
NOVA - Official Website | Illuminating Photosynthesis
Photosynthesis occurs inside chloroplasts. Chloroplasts contain chlorophyll, a green pigment found inside the thylakoid membranes. These chlorophyll molecules are arranged in groups called photosystems. There are two types of photosystems, Photosystem II and Photosystem I. When a chlorophyll molecule absorbs light, the energy from this light raises an electron within the chlorophyll molecule to a higher energy state. The chlorophyll molecule is then said to be photoactivated. Excited electron anywhere within the photosystem are then passed on from one chlorophyll molecule to the next until they reach a special chlorophyll molecule at the reaction centre of the photosystem. This special chlorophyll molecule then passes on the excited electron to a chain of electron carriers.
Some bacteria use Photosystem I and some use Photosystem II. More than two bya, and maybe more than three bya, cyanobacteria used both, and a miraculous instance of innovation tied them together. were then used to strip electrons from water. Although the issue is still controversial regarding when it happened and how, that instance of cyanobacteria's using manganese to strip electrons from water is responsible for oxygenic photosynthesis. It seems that some enzymes that use manganese may have been "drafted" into forming the manganese cluster responsible for splitting water in oxygenic photosynthesis. Water is not an easy molecule to strip an electron from, a single cyanobacterium seems to have “stumbled” into it, and it probably happened only . Once an electron was stripped away from water in Photosystem I, then stripping away a proton (a hydrogen nucleus) essentially removed one hydrogen atom from the water molecule. That proton was then used to drive a “turbine” that manufactures ATP, and wonderful show how those protons drive that enzyme turbine (). Oxygen is a waste product of that innovative ATP factory.
Ozone is a natural gas composed of three atoms of oxygen
Those molecules initiate photosynthesis by trapping photons. Chlorophyll is called a and, as it sits in its “,” it only absorbs wavelengths of light that . The wavelengths that plant chlorophyll does absorb well are in the green range, which is why plants are green. Some photosynthetic bacteria absorb green light, so , and there are many similar variations among bacteria. Those initial higher electron orbits from photon capture are not stable and would soon collapse back to their lower levels and emit light again, defeating the process, but in the electron is stripped from the capturing molecule and put into another molecule with a more stable orbit. That pathway of carrying the electron that got “excited” by the captured photon is called an . Separating protons from electrons via chemical reactions, and then using their resultant electrical potential to drive mechanical processes, is how life works.
It is blue in color and has a strong odor
For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.
Science Experiments on Environmental Education and Biology
To revisit the Neanderthal split from about 500 kya, stayed in West Asia and Africa. When evidence of came to light, some scientists placed the beginning of the at about 500 kya. Stone tools have recently been dated using , which works for stone tools heated by fires, and using . That method measures water absorption into the surface of obsidian tools. For dating artifacts before the appearance of behaviorally modern humans about 70-50 kya, will not work, but successful. Neanderthals dominated Europe and today’s Middle East while home was Africa, and they also ranged to Europe and West Asia. Whether existed for only a half-million years or a million is controversial today, but what is not very controversial is that it is probably the direct ancestor of both Neanderthals and , and the first members of our species appeared in Africa about 200 kya. There is evidence that other descendants of may have existed, and . It also could have been a Neanderthal descendant. As with the discovery of the “” of Flores Island, it will not be surprising if scientists find more species that branched off of those early human and protohuman lines and died out when behaviorally modern humans spread across Africa and Eurasia.