Hello ladies and gentlemen okay today we're going to cover photosynthesis which is the process by which plants bacteria and certain kinds of produce make food which is sugar and other compounds by using sunlight as an energy source and carbon dioxide as a carbon source and it releases oxygen as a byproduct. There are two key things you need to know. Photo-autotrophs use sunlight and the process of photosynthesis to make their food. Heterotrophs have to obtain their energy from other organisms so in other words they have to either eat plants or other animals or so on. So if they don't make their food their heterotrophs. If they're a photo-autotrophs then they use sunlight for energy and they make their own food. The yearly worldwide production of sugar by plants is about 220 billion tons worldwide. They all focus on using light as their energy source so we need to take a look at the electromagnetic spectrum for a moment. Organisms use only a very small range of wavelengths for photosynthesis, vision and other processes which is the small portion that is drawn out in the bottom of this picture. Most of the wavelengths are the ones we see as visible light which is a small part of the electromagnetic spectrum from the sun but you can see that it goes from all the way from radio waves to gamma rays. Light energy is packaged as photons which vary in energy as a function of their wavelengths. Phototototrophs only use the range of 380 to 750 nanometers of wavelengths for photosynthesis. The pigment molecules on the chloroplast inner membranes absorb these photons. Chlorophyll A and B pigments absorb the blue and red but reflect the green which is why leaves are green. Corotinoid pigments absorb the blue violet and blue green but reflect yellow and orange and red and so corotinoids we see primarily as oranges. Zamphophils reflect yellow, brown, purple or blue light. Anthosyanins reflect red and purple light in fruit and flowers. Fycobellans reflect red or blue green light and are accessory pigments found in red algae and cyanobacteria. A pigment absorbs light of specific wavelengths by acting as an antenna to receive photons of that specific energy. So you can see here that plants have a range of different pigments. Most plants have more than just chlorophyll A or chlorophyll B or both of those. They also have those accessory pigments like the anthocyanins, like the corotinoids and so on. What that means is that if they get sub-optimal light so it's not in the blue and the reds but if they get lights in the greens and yellows they can still survive. They can still make their own food albeit at lower levels because they have fewer of those pigments. The chlorophylls in green leaves will mask the accessory pigments until autumn when the chlorophyll content declines because basically what happens is the plant, the chlorophyll is extremely expensive to produce for the plant. It is energetically expensive and so what the plant does is it harvests that chlorophyll back out of the leaves before it drops those leaves off in the autumn. The accessory pigments like I said are much fewer of them and so they just leaves them in the leaves and kind of cuts its losses. Okay this is an overview of the photosynthesis reaction. There are two stages of this reaction, the light dependent reaction and the light independent reaction. In the light dependent reaction light energy is converted to the chemical bond energy in ATP. Water is split to release oxygen and NADP plus picks up electrons to become NADPH to be used later. The light independent reactions assemble sugars and other organic molecules using ATP, NADPH and CO2. Overall the equation for glucose formation is written as 12H2O plus 6CO2 over sunlight gives you 6O2 C6H2O6 and 6H2O. I have simplified that equation with the one on the screen because that's really kind of the net because you get six extra waters in and six extra waters out. This will explain the process of transpiration which we'll talk about much much later in biology. Both stages of photosynthesis occur in the chloroplast. The semi-fluid interior which is called the stroma is the site for the second series of photosynthesis reactions, the light independent reactions. Flatten sacs called thylacoids are interconnected by channels woven through the stroma. The first reactions of photosynthesis so the light dependent reactions happen there. In the thylacoid membranes pigments clustered together in the structures called photosystems each consisting of 200 to 300 pigment molecules capable of trapping the different energies from the sun. So in review you can see that photosynthesis takes place in two stages but it also takes place in two different parts of the chloroplast. The light dependent reactions and the light independent reactions. For an overview of what goes in and what comes out you can see that water is split into two parts. One produces oxygen which happens in the light dependent reactions and the other combines with the hydrogens with the carbon dioxide to form glucose. Light dependent reactions really focus on making three things, ATP, NADPH and oxygen. The electron transfer chains move electrons and hydrogen ions from the stroma into the thylacoids. The hydrogen ions accumulate inside the thylacoid compartment and as the hydrogen ions flow through the channels into the stroma ATP synthase enzymes link in organic phosphate to ADP to form ATP which is the high energy molecule carrier. By the process of photolysis water is split to form oxygen which diffuses out and hydrogen ions which are maintained at high numbers in the thylacoid. Electrons are also transferred via another photosystem to NADPH to form NADPH. Okay what that basically means is in the light dependent reactions oxygen is produced and energy is produced. The NADPH system is really only a truck that just carries stuff from one group of reactions to the next one. That's all you need to know. Energy, oxygen and a truck to carry stuff. In the light independent reactions these reactions constitute a pathway known as the Calvin Benson cycle. This is going to be confusing so you need to know that this one's Calvin Benson cycle. There's another one that sounds very similar. Later. The participants and their roles in the synthesis of carbohydrates are ATP which provides energy NADPH which provides hydrogen atoms and electrons. Remember that's the truck and atmospheric air which produces carbon and oxygen from carbon dioxide. These reactions take place in the stroma of the chloroplasts and are not dependent on sunlight. They can happen at nighttime. They don't always but they can. Carbon dioxide will diffuse into a leaf across the plasma membrane of a photosynthetic cell. However there are different kinds of plants and different types of carbon-fixing pathways. There's a type called C4 plants and C3 plants. Plants and hot dry environments close their stomata, the pores in their leaves to conserve water but in doing so retard the amount of carbon dioxide that can enter the plant and permit oxygen buildup inside the leaves. C3 plants such as beans don't do well without irrigation and hot dry climates but C4 plants do. Crabgrass sugar cane corn and other C4 plants will fix carbon twice which can then donate the carbon dioxide into the Calvin Benson cycle so it prevents that oxygen buildup. The even more plants or more advanced plants are the C3 plants. C3 stands for C3 and acid metabolism and plants such as cacti and other succulents open their stomata and fix carbon dioxide only at night which prevents water loss storing the intermediate product for use in photosynthesis the next day. The oceans are teaming with bacteria and produce which provide food for nearly all other marine organisms. In an ocean ecosystem the tiniest photosynthesizers are food for the crustaceans which are eaten by fishes, sea birds and even whales. One spring bloom of these organisms stretch from North Carolina past Spain I mean they're huge. Such large masses influence the global climate by sponging up nearly half of the carbon dioxide used in carbon fixation so all those greenhouse gases are getting absorbed by these tiny little microscopic organisms. Human activities such as burning fossil fuels and setting fires for vast clear cutting released more carbon dioxide than photo autotrophs can take up. Additionally tons of waste and other pollutants are daily entering the oceans and may ultimately impact the photosynthetic function of these photo autotrophs. So in summary it's not the rainforest that make the oxygen it's the oceans and it's the top two inches of the ocean's surface so when you think about oil spills or the great Pacific garbage patch or things like that think about this because this is where your oxygen comes from ladies and gentlemen but enough with that soapbox and you have a fantastic day.