1. The first sceintific evidence for photosynthesis was found in the late 18th Century by chemists Joseph Priestley and Jan Ingenhousz. They noticed that a plant could revive a mouse from suffocation in an enclosed jar, using sunlight. 2. The plant did not care about the mouse. It was only occupied with performing photosynthesis to make itself grow. 3. Organisms that make their own food out of sunlight are called photoautotrophs. 4. Oxygen is the usual waste product of modern photosynthesis. 5. It also produces all the carbon compounds that make up living cells.
6. Plants are the most familiar photoautotrophs, but they did not develop the technology themselves. They acquired it.
7. Before photosynthesis evolved, Earth’s atmosphere consisted of water vapour, methane, ammonia and other gases, but not oxygen. 8. The earliest fossil of a filamentous organism thought to perform photosynthesis is about 3.5 billion years old. 9. In order to perform photosynthesis, bacteria had to build a complex metabolic pathway involving the green pigment chlorophyll, and requiring at least 17 steps. 10. Early photosynthesis did not involve oxygen and had minimal effect on the atmosphere.
11. About 2.7 billion years ago cyanobacteria adopted a version of photosynthesis that oxidized water to produce O2. At first, dissolved iron absorbed most of the oxygen. 12. Around 2.4 billion years ago all the iron became saturated. Oxygen began accumulating in the atmosphere. It was toxic to anaerobic organisms and wiped out most life on Earth. This event is known as the Oxygen Catastrophe. 13. It set the stage for the ascendance of eukaryotes, the more complex aerobic organisms including plants, fungi and animals.
14. It is theorized that one early eukaryote absorbed a cyanobacteria but instead of digesting it, began a symbiotic relationship. This was the first plant. 15. That individual cyanobacteria became the first chloroplast, the organelle that performs photosynthesis in all plants and algae. 16. Practically all chloroplasts are derived from that single event more than 1 billion years ago.
17. One species of amoeba succeeded in replicating the experiment more recently. It contains chloroplasts closely resembling a different variety of free-living cyanobacteria.
18. Ever since the first plant took advantage of a bacterium, other organisms have been striving to exploit plants. Some of us simply eat them.
19. Lichens (like in the top photo) are symbiotic compound of a fungus with either a green alga (a simple plant) or a cyanobacteria. 20. The fungus provides protection and chemical nutrition while the green partner provides solar energy for both organisms. Various fungi have followed this same strategy independently numerous time to survive in extremely cold, arid and nutrient-poor environments.
21. A number of invertebrates have developed symbiotic relationships with photosynthetic organisms. This practice is widespread among sponges, corals and sea anemones, which harbour algae or bacteria in their bodies. 22. Certain sea slugs feed on green algae and then incorporate their chloroplasts into their cells. Photosynthesis can keep the slugs alive for extended periods.
23. Green algae also live in the eggs of a species of salamander and help the embryo develop. So far this is the only documented example of a vertebrate forming photosynthetic symbiosis. 24. A possible explanation is that the vertebrate body plan is poorly designed to absorb sunlight.
25. A recent study suggests the Oriental hornet performs photosynthesis using a bright yellow pigment called xanthopterin in its exoskeleton. As wasps have been around for less than 60 million years, this might represent the first chemical innovation in photosynthesis in over two billion years.