Photosynthesis

okay so this video we’re going to discuss photosynthesis its how autotrophs can take sunlight can take carbon dioxide and can take a little bit of rainwater and through a very complex series of chemical reactions produce oxygen waste but really the prize of photosynthesis our create is the creation of sugars such as glucose so let’s get started so I’d like to direct your attention to the electromagnetic spectrum it’s the energy given off by the Sun and the visible light really is what’s going to power photosynthesis invisible light is only a small portion of the electromagnetic spectrum but we’re going to focus on visible light given off by the Sun because that’s what’s responsible for photosynthesis well let’s look briefly at how objects either absorb or reflect light you know that the Sun gives off visible light white light colors of visible light are actually a mixture of red orange yellow green blue indigo violet so white light the visible light given off by the Sun is actually a mixture of these seven colors here well how do I know this how do we know that the visible white light is all these colors mushed together well if you’ve ever played with a prism as a child if you shine sunlight in the one end of the prism you can actually see a rainbow come out the other end this animation here shows what I just mentioned coming in from the left we have sunlight or white light and because of the curvature of the glass prism the individual wavelengths are separated you can see that red has a wider wavelength and the violets have a more narrow wavelength proving however proving that sunlight or white light visible light is actually made up of a mixture of colors you know we can often see something similar to this just outside in nature if there’s moisture in the air you know after its rained or in this case you can see moisture of coming from a waterfall but we can see that moisture in the air kind of acts like a prism and will separate sunlight into the individual wavelengths producing a rainbow so when we come back to how light is absorbed or reflected well first of all when sunlight shines on this green leaf here again sunlight is a mixture of all these colors the reason that we see green in our eyes is because green light is reflecting off of the leaf the other colors are absorbing we see the world as reflected light if you see somebody wearing an orange shirt orange is reflecting off of that shirt the other colors are absorbing into the shirt so if we were to shine sunlight onto these bananas which color or colors would reflect into the person’s eyes which color or colors would be absorbed well if the bananas appear yellow that’s because yellow is reflecting into your eyes the other colors are absorbing into the banana well in this case again we have some balloons now which color or colors would reflect in which would absorb if the balloons appear blue that’s because blue light is reflecting into the person’s eyes all the other colors are absorbing well here’s a fun one right here here we have sunlight shining on some snow and some trees covered in snow but if you think why did do that does do the trees appear white why does snow appear white because white reflects so all the colors are reflecting and therefore our brain is interpreting all of this incoming light as the color white in this case none of the colors are absorbing and so kind of the opposite of white is black if you know if light is shining on this automobile the color black reflects nothing the color black absorbs all so when you see a black object whether it’s a shirt or an ottoman you’re really seeing no light at all no light is entering your eyes and we interpret that as the color black so how does light reflection and absorption relate to photosynthesis well most plants have green leaves which means they’re going to reflect green light the other colors however are going to absorb and those are the colors that really drive photosynthesis this graph right here shows the wavelengths of visible light and there’s two points on the

graph where the line is the highest this implies the colors are the wavelengths that drive photosynthesis so around 400 nanometers we see a peak in the graph and that corresponds the color blue around 700 nanometers there’s another peak that corresponds to the color red ironically the color that we most associate with plants the color green has some of the smallest or lowest rates of photosynthesis so green light is very poor in production of sugars however blue light and red lights drive photosynthesis so let’s actually get into photosynthesis now it’s the cellular process where sunlight is converted into sugars and you’ve probably seen this equation ever since middle school to the left of the arrow we have what are called the reactants carbon dioxide and water are the reactants or the ingredients required to perform photosynthesis in the presence of sunlight carbon dioxide and water will produce sugar and oxygen to the right of an arrow or what we call the products it’s what’s the end result what’s created now this equation really makes photosynthesis look pretty simple but when we get into the details we’re going to see it’s very complex well so who performs photosynthesis well we often mistakenly only think that plants are the only photosynthetic organisms on earth and that’s just not true autotrophs perform photosynthesis and plants are just one type of autotroph in the top right hand corner there’s a picture of kelp which is again in the kingdom Protista the bottom left our cyanobacteria which are bacteria the bottom middle those are plankton plankton are also a type of Protista and in the bottom right we have algae algae is also in kingdom Protista so there’s a lot of autotrophs that perform photosynthesis besides plants so what kind of chemical reaction is photosynthesis it’s what we call an endergonic chemical reaction because it requires an input of energy now the picture should imply where the input of energy comes from sunlight sunlight is the energy that is inputted into photosynthesis in order to start a complex series of chemical reactions known as photosynthesis so the end result or the products of photosynthesis again are sugar and oxygen waste you know in this leaf if we zoom on in we see these microscopic pores codes called stomata on leaves and when the stomata open and close they can release oxygen into the environment they can take in carbon dioxide from the environment so the stomata are how plants can exchange gas with their environment so let’s look at a quick overview of the chloroplast or the site of photosynthesis you know we can break photosynthesis really into two processes the first being called the light dependent reactions well if I chop open a chloroplast I can show you that there is these structures on the inside and I’ve circled a structure called a Granum notice how this circled structure labeled the Granum is actually made up of three individual units called thylakoids this is where the light dependent reactions occur this is where the photosystems which are groups of molecules to capture and transfer energy so this is where the photosystems ultimately are going to help to create oxygen ATP and a molecule called NADPH the other stage or prime that takes place during photosynthesis it’s called the light independent reactions this really occurs in the fluid-filled interior called the stroma and this is going to be the location where glucose is created let’s go ahead and jump into it so here’s a picture of our chloroplast again and if we look at a much simpler version of a chloroplast here is on Granum made up of 3 thylakoids well let’s zoom out into one thylakoid yep so now that we’re inside looking at a file a coid we’re ready to start the light dependent reactions if you’re in my biology class I’ve broken this animation down according to the diagram in our textbook so follow along at step one in our textbook so what happens is notice how in the membrane of the thylakoid there’s an object labeled ps1 and ps2 these are what are called the photosystems so first of all there is chlorophyll in the photosystems photosystem 2 is going

to absorb sunlight and the chlorophyll that’s inside of photosystem 2 has electrons those electrons become excited and what that means is that the electrons jump into the actual thylakoid membrane this causes the thylakoid membrane to become negative negatively charged if you remember electrons have a negative charge to them well once the thylakoid membrane becomes negatively charged this is going to start what we call an electron transport chain it’s a chain reaction of a series of events triggered by all these electrons so now look at area to an area 3 in your book diagram and what we’re going to show you is that water molecules are going to be broken at the top of the animation there are three molecules of h2o water and what I’m going to show you is that hydrogen from the water is going to be pulled into the thylakoids there are enzymes I didn’t picture the enzymes in this animation but there are enzymes that will break apart the water and allow the hydrogen to be pulled into the thylakoids there’s a reason of course the this is all happening the photos photosystem two just lost a bunch of electrons in order to keep this process going photosystem two needs to have its electrons replenished so the electrons of those hydrogen’s are going to go into photosystem two to replenish the electrons that it previously lost ultimately notice what’s been created at the top oxygen waste and so the oxygen will be released through the stomata of the plant and into the environment and I think that’s kind of cool that oxygen that we breathe used to be part of water molecules so moving on into the next area of the light dependent reactions I want you to focus your attention on PS one photosystem one case you’re wondering the reason it’s called photosystem one even though we’re talking about it second is I think photosystem one was just simply discovered first so photosystem number one just like photosystem number two are groups of molecules that it contains chlorophyll there’s chlorophyll in photosystem number one and when sunlight strikes photosystem one the electrons of chlorophyll become excited and just like we saw a moment ago the electrons enter into the membrane of the thylakoid the thylakoid membrane and this is going to continue our electron transport chain the chain reaction of events that takes place because of all these electrons so moving on to the next step of the light dependent reactions the electrons that are embedded in the thylakoid membrane along with various enzymes are going to help bond a couple items together there’s a molecule with the full name of nicotinamide adenine dinucleotide phosphate we’re just going to call this molecule nad P so the molecule nad p and a hydrogen ion are going to be drawn together by the electrons in the thylakoid membrane and various enzymes and when they’re drawn together the nad P and the hydrogen are going to bond together make a molecule called NADPH now the notes say NADPH is a hydrogen taxi you know taxi is designed to pick a person up at one location and drop them off at another NADPH is called a hydrogen carrier or hydrogen taxi it’s going to pick up a hydrogen and it’s going to take the hydrogen to another location where it will ultimately play a role so when we go on to the light independent reactions in a few moments we’ll see the role of NADPH so when we move on into the next steps of the light dependent reaction I want you to see that there’s a bunch of hydrogen ions inside the thylakoid remember those hydrogen’s once belonged to water and so now that there’s a high concentration of hydrogen in the thylakoids they’re going to rapidly diffuse from a high concentration to a low notice at the bottom of the animation there’s a little tunnel or tube labeled ATP synthase this is an enzyme protein complex here and what what happens is when hydrogen diffuses through ATP synthase ATP synthase you can probably hear the words ATP synthesis in your head ATP synthase draws together an adp and a file an appeal phosphate and when ADP is bonded with a phosphate we have a molecule of ATP adenosine triphosphate that’s been created well this happens a series of times that ATP actually has a role to play but as I just said this happens a series of times so hydrogen comes

through ATP synthase and ADP and a P are bonded together ATP is produced again this happens multiple times hydrogen flows through the ATP synthase and a molecule of ATP is created this hydrogen or this this ATP is really important when we go on into the next step called the light independent reactions before we go into the light independent reactions I want to summarize the light dependent reactions so it’s called light-dependent because it depends on light so sunlight and water are going to be used to create some oxygen waste but more importantly to create molecules of ATP and molecules of NADPH I want to point out that no glucose has been created yet ATP has been created and NADPH has been created now we’re going to see why those were created let’s move on into the light independent stages so we can now begin the process called the light independent reactions also known as the Calvin cycle named after the scientist who really helped first describe this process it begins in the stroma of the chloroplast the liquid fluid-filled interior the stroma and there’s a five carbon molecule you can see it in the animation a chain of five carbons now it’s actually a lot more than just carbon first of all this five carbon molecule is called ribulose biphosphate I’m just going to call it our ubp from now on our ubp is actually made up of five carbons and 12 hydrogens and 11 oxygens and two phosphorus but for simplicity I’ve only shown the five carbons chain together so what happens is carbon dioxide from the air will bond with rubp and when the one carbon of carbon dioxide bonds with the five carbons of rubp and the reason they bond is again there’s various enzymes involved in breaking bonds and re-establishing bonds and so this six carbon molecule is now created well let’s move on to the next step so in the next step of the light independent reactions we have there the six carbon molecule that was just created from carbon dioxide and rubp bonding together the six carbon molecule is going to actually be broken down finally we see the reason why ATP and NADPH were created in the light dependent stage ATP and NADPH are going to be used to break apart that six carbon molecule that’s six carbon molecule is going to be broken down remember when a teepee is broken into a DP heat is released so the heat from the breaking of ATP plus the hydrogen of the NADPH plus various enzymes that just aren’t pictured in this animation are going to break that six carbon molecule into a couple three carbon molecules the three carbon molecules are called phosphoglycerates or you’ll just see them abbreviated as pga so this process is going to continue several times here’s two more six carbon molecules and the first one is going to be broken down by ATP enzymes and NADPH to create two more molecules of pga and there’s still one more in the animation so here comes some ATP and nadph and again with the help of various enzymes the six carbon molecule were broken down into two pga s so the amount of PGA’s begins to accumulate in the stroma so what’s going to happen with all of these PJ’s all of these phosphoglycerates well two of them are going to bond with one another with the help of various enzymes to make glucose that’s the whole point of photosynthesis make glucose but what about the other pga is the other phosphoglycerates well they’re going to be broken down and recombined as well with the help of ATP with the help of various enzymes that i just didn’t picture those other PGA’s are going to be broken down and recombined into five carbon molecules of ribulose biphosphate rubp this is why the calvin cycle is called a cycle rubp marks the beginning of the next cycle carbon dioxide will be taken in the carbon dioxide will bond with the rubp to make a six carbon molecule and now we’re just repeating steps previously mentioned so to summarize the light-independent stage of photosynthesis carbon dioxide from the air along with the ATP and the NADPH were made during the light-dependent

stage will be used to create glucose which is a sugar now why does the plant even need their glucose need the sugar well the sugar that is created will then be used during cellular respiration a cellular respiration is another topic for another day but that I hope explains the connection between photosynthesis and cellular respiration for those you in my biology class this is going to be your essay questions so very rarely are you going to get essay questions in advance we’ll be talking more about this in class so instead of the usual practice quiz at the end how about this instead I’ve given you seven steps of photosynthesis in a random order try to put these steps in order what comes first what comes second third fourth fifth sixth seventh if you’re in my biology class try this and bring me your answers and I’d be happy to check them for accuracy good luck you