Photosynthesis uses light to turn water and carbon dioxide into oxygen and sugar. These products are then used by heterotrophic organisms including humans, to power the building of our own bodies with carbon dioxide and water as waste byproducts. So what we see, is a cycling of carbon. Plants take carbon dioxide from the atmosphere and use solar energy to turn it into sugars. We eat plants or animals that have eaten plants, and turn the sugars back into carbon dioxide, releasing energy for our own metabolism. And also when plants or animals die, they release carbon from their bodies into the soil. In this way, all carbon in the world is cycling through photosynthesis from plants, to animals and back to plants, and eventually back to the atmosphere. And at a very basic level, all of what we are made of was originally carbon dioxide from the air. To further discuss the carbon cycle, I'd like to introduce the first of our two guests today. Professor Nir Ohad. Some of you may remember Nir from his class on Epigenetics in the What A Plant Knows class that I also give. Nir and I, we have a friendship that goes back 30 years ago when we were PhD students in the same lab. While I was studying beta carotene, Nir was studying photosynthesis. Today Nir is the head of the Nanocenter Program on Food Security at Tel Aviv University. Might be interesting to know where is actually the photosynthesis happening globally? >> Well if we look at this map, we can see that when summer is in the North hemisphere, photosynthesis takes place both in land and in the oceans. How are we seeing that here? >> So the green colour depicts photosynthetic activity both in the major continents such as in the Amazons, in North America, in Europe, Asia and the light colour depicts the deserts such as in the centre of Australia, Africa, in the mid region of Asia. >> What's that grey thing in the top of Africa? >> The grey part in Africa, those regions which are the major deserts of the Sahara in which photosynthesis is limited of course, but we can see that also in the South Hemisphere which is under this map is under winter. Much of the ice has covered the regions which can be photosynthetic active during the summer of the Southern Hemisphere. >> What about the oceans? >> And this is the most important thing to know, that photosynthesis is not only taking part in land but also in the oceans and the light blue colour, it depicts regions, large regions in which photosynthesis is taking place with microorganisms, which contributes largely to the photosynthetic activity around the world. >> Which type of the microorganisms are you talking about? >> So we're talking about small organisms, both bacteria, photosynthetic bacteria as well as diatoms and algae, which contribute largely to the photosynthetic productivity. >> And if we would take a look at this map, let's say, in the middle of winter, would there be any difference? >> Yes, when we look at wintertime, then the activity drops and the regions which are covered by snow are now less photosynthetic active. In the North Hemisphere during winter when the sun does not reach, of course, photosynthesis is limited. >> So but then if we would now look at a reverse of this map, so this is where the oxygen is being produced, this is where carbon dioxide is being fixed. But where is carbon dioxide being released into the atmosphere? >> So this is also something that we need to note. In the 100 years since the Industrial Revolution, we can note that much of the fossil fuels which have been generated millions of years ago when ancient plants started to cover the land, they have absorbed most of the CO2 into the structure of the plants and then being decombust into fossil fuels such as oil, coal, gas. >> So oil, coal and gas are result of photosynthesis, but photosynthesis that happened millions of years ago. >> Exactly so, and those are stored underneath the ground. And in the recent years we have started to utilise it to make energy to support our industrial life. >> So if I take a tree that's grown in a forest or in my backyard, this tree has absorbed carbon dioxide and used the process of photosynthesis to build its walls, it's trunk, it's leaves, everything. Now if I take the same tree and make a bonfire out of it, I burn it. Then what's what's happening to the carbon dioxide when I burn this tree? >> So this is an excellent question. Actually when we burn trees, we release into the air, carbon dioxide. >> So if we would like go back 500 million years, a billion years in the Earth's history, then we know there was a lot more C02 right in this atmosphere, all of this was captured by ancient trees, ancient mosses. >> Ferns. >> Ferns, forests that captured or covered the earth. >> This fixed the CO2, actually stored it away from the atmosphere, and put it under ground. >> Right. >> And so when we're actually burning this, we're releasing ancient CO2 back into the atmosphere in a certain way of thinking about it. >> That's true. But the thing is that we're releasing it in a much faster pace than the pace that was captured at that time and therefore we're making a dramatic change in very short period of time. >> So then how would, we've heard of the idea biodiesel or biofuels >> Why would that help this whole cycle? Because we're still burning something that's grown and then releasing the CO2 into the air. >> Right, but when we're using plants into making now bio-fuels, we're then making the cycle more balanced in the sense that the plants are now utilising the same energy they have been using it so far to make the energy we need without using the fossil fuels, and that makes the big difference. >> So one last question. The process you described, photosynthesis, seems to be an incredibly efficient way of taking free energy from the sun and making electricity. I mean this is basically, it's a mini solar panel. >> Is there a way that we can utilise photosynthesis to actually making fuel for us, making electricity, not only through bio-fuels, but in some type of industrial way? >> So sure, as we have been realising, the use of energy by plants can convert the energy into different forms. One form for instance that now can be used is to make out of the energy light, the plants absorb to make hydrogen. And hydrogen is a clean energy that can be utilised without affecting that much, the environment. >> I think what we'll do right now is go take a look at a laboratory that is actually doing this process itself. It's trying to take photosynthetic organisms and change their photosynthesis so that they will make hydrogen for human use.
