Photosynthesis (in detail)

so today's videos on photosynthesis and you know it might seem pretty straightforward he shines from sunlight you sprinkle some rainwater you add some carbon dioxide from the atmosphere and through photosynthesis plants will give off oxygen and will create simple sugars such as glucose but you know the actual process is a lot more complex so let's get started so the Sun gives off a variety of types of energy and this energy travels across space in the form of a wave and the titles of the energy you can see at the top of the picture now we're going to focus our attention on visible light because it's the wavelength of visible light that drives and powers photosynthesis well let's focus on how light is absorbed and when we do we're gonna see that the Sun gives off visible light also called white light white light is actually a mixture of ROYGBIV and what this is are the colors of the rainbow red orange yellow green blue indigo violet all of these colors are a mixture known as white light well how do we know this because when you shine light into a prism when you shine white light into a prism a rainbow comes out the other end just like you can see in this animation white light is entering from the left and because of the curvature of the prism ROYGBIV the colors of the rainbow are coming out the other end notice how the wavelengths are different red has a longer wavelength the violet has a more narrow and so this is how we know that white light is made from a mixture of these colors here is an actual picture of white light entering a prism and you can see on the left-hand side a rainbow is coming out the back end you know moisture in the air can act like a prism and create a rainbow you ever notice after it rains you can sometimes see a rainbow in the sky or in this case near a waterfall because of all the moisture in the sky the moisture separates the light the sunlight into the rainbow colors that you see and so colors are either reflected or absorbed when sunlight shines on an object what we see is reflected light the reason this leaf appears green is because it's reflecting the green wavelength of light when light shines on these bananas the reason it appears yellow is because the yellow wavelength reflects while the other color colors are absorbed when we shine light and these balloons the blue wavelength reflects into our eyes and the other colors are absorbed when we look at white objects like snow or this arctic hare the reason objects appear white is because white reflects all the colors and all the light all the wavelengths of light enter our eyes and our brain interprets this as the color white well the opposite will be black when light shines on a black object nothing reflects it always absorbed and that's why this automobile pairs black because there's no light reflecting into our eyes so when we relate this to photosynthesis plants have you know mostly green leaves which means that they're gonna reflect the green wavelength but the other colors are absorbing into the leaves and are going to be powering photosynthesis in this graph we can see for instance that this graph shows the wavelengths of light that most powerful synthesis notice how there's a peak around 400 nanometers well that's the wavelength of blue there's another peak around 700 nanometers well that's a wavelength of red so blue light and red light are most stimulating for plants in the process of photosynthesis ironically the color green around 550 nanometers the color green that we most associate with plants actually has the least amount of impact in their ability to do photosynthesis that's because most green light is reflecting very little green light is actually absorbing into the leaf so when we look at a general definition of photosynthesis you know it's the process that converts solar energy into glucose and this formula here outlines photosynthesis and in the reactants we have carbon dioxide and water and in the presence of sunlight will produce sugars such as glucose and oxygen well who who performs photosynthesis well these are the autotrophs now we typically think of plants as doing photosynthesis but they're not the only ones algae phytoplankton the basis of ocean food webs kelp kelp can grow into these enormous underwater forests and even some bacteria known as cyanobacteria are photosynthetic so there's a lot more autotrophs than just plants so photosynthesis is also what we call an endergonic chemical reaction and what that means is that photosynthesis requires the input of energy from the picture I'm implying that sunlight sunlight is the energy that is input to power photosynthesis and when we talk about the end result what's created well oxygen which is a waste gas and simple sugars like glucose but when we zoom out into the leaf we find some peculiar pores on their underside these pores will open and close and they're called stomata and it's how they exchange gases it's how they take in carbon dioxide from the atmosphere and when they produce oxygen as a waste through these stomata openings they give off the oxygen created so it's through these pores that they exchange gas with the atmosphere okay so now let's introduce the structure in cells that allows them to do photosynthesis and this is the chloroplast what we're gonna do is we're actually actually gonna divide photosynthesis into two stages stage one being the stage that depends upon sunlight the light dependent reactions and these take place in the thylakoid membranes of a chloroplast you know I want to actually look at a more simplified diagram here and when we do we can actually see the thylakoids which kind of look like coins or frisbees stacked on top of one another well in the membrane of these thylakoids is where the light dependent reactions occur and if you ever come across the term Granum that's a term that I mean that that means a stack of thylakoids okay so you see that flashing black box I want to zoom into that area of the chloroplast and when we do we're gonna see that there are some things actually embedded within the membrane of the thylakoid i've labeled them ps1 and ps2 and these are the photosystems and we're going to talk about them in more detail but for now in the photosystems is where we find chlorophyll and various protein molecules that are responsible for capturing and transferring energy during the light dependent reactions and it's during the light dependent reactions where oxygen ATP and something called NADPH is created we'll talk about these molecules in more detail coming up very shortly and then we'll show it will shift into stage two the light independent reactions and this happens that occurs in the stroma the fluid-filled interior of the chloroplast just outside of the thylakoid and it's in stage two the light independent reactions where glucose is actually created so let's talk about these two stages for the rest of this video so now let's get into some of the details of the light dependent reactions and what we're gonna do is we're gonna break this down into a few steps so step number one chlorophyll in photosystem number two will absorb sunlight now even though it's called for photosystem number two it's actually the first and the chain of events they were named photosystem 1 and photosystem two by order in which they were discovered not the order in which they perform their function so you kind of have to get over that backwards name right there so in my animation sunshine sunlight is striking the chlorophyll molecules in photosystem number two and this causes their electrons to become excited and what happens is the electrons actually flow into the thylakoid membrane and so as these electrons from chlorophyll in photosystem number to flow through the thylakoid membrane this makes the membrane negatively charged and as the electrons are flowing through there's also proteins embedded within the thylakoid membrane that are eating their travel I just didn't show them in my animation but this starts what we call an electron transport chain it's a chain of events setting forth by these set in motion by these electrons so when we move on into the second step I've added some hydrogen ions into the stroma because there's dissolved molecules and ions in the stroma and these hydrogen's are going to play an important role and so what happens is as the electrons move through the thylakoid membrane they actually will operate any power and turn on these protein pumps that will pull the hydrogen's into the thylakoids and as more and more and more hydrogen's accumulate this is gonna make a really large concentration of hydrogen's which we'll see why that's important in a little bit I also want to mention that water molecules are broken so here's a water molecule and with the help of enzymes the hydrogen's are broken off and the electron from the hydrogen went into photosystem number two here we go again enzymes will break off the hydro and notice how the electrons were pulled into photosystem number two you know photosystem number two has been losing electrons and so it's waters the hydrogen of water it's their electrons that will replenish photosystem number two so it doesn't run out of electrons and so this process can keep going this is why you have to constantly water a plant also oxygen this is where the oxygen comes from see that Oh for oxygen it will bond with another Oh from another water that was broken to make Oh to the oxygen that we breathe used to be attached to water which I think is kind of interesting so as we move on into the next step again sunlight is striking photosystem number two and it's electrons are moving through the thylakoid membrane but you know sunlight is also striking photosystem number one and photosystem number one is filled with chlorophyll and it has electrons that also become excited and move through the thylakoid membrane so what we really have is kind of a longer electron transport chain so now that we have our full electron transport chain let's move on to the next step and in the next step a molecule called NADPH will be created so in the stroma and adp and a hydrogen are drawn together and the electrons of the electron transport chain help these to bond together to make a really important molecule called NADPH NADPH can be kind of be kind of be viewed as a carrier of hydrogen like a taxi whose job it is to carry hydrogen from one place to another we'll come back to it in a little bit but it's really important that NADPH was just created so at this stage the hydrogen is really beginning to accumulate inside the thylakoid from the breaking of water from the electron transport chain pulling in hydrogen's from the outside so by now there's a really large concentration of hydrogens inside the thylakoid so when we come to our next step because there's such a large amount of them the hydrogens are going to start to diffuse through that the enzyme labeled ATP synthase and so what hydrogen does from a high to low concentration it will diffuse through ATP synthase and will help to bond a molecule of adp adenosine diphosphate with another phosphate and when that happens they bind to make a molecule of ATP and so this ATP along with the NADPH are really the most important things that are created during the light dependent reactions we're gonna see what's so important about them in just a little bit and so to summarize the light dependent reactions oxygen NADPH and ATP have been created you know sunlight was taken and water was taken in and oxygen was released as a waste and in the light dependent reactions NADPH and ATP have been created I do want to note at this stage no glucose has been created so let's move on to the light independent reactions ok so the light independent reactions you know this is also known as the Calvin cycle named after the scientist who helped to identify these steps and so we're gonna start breaking it down first of all there's a five carbon molecule by the name of rubp ribulose biphosphate now it has more than just five carbons you can see 12 hydrogens 11 oxygens and two phosphorus 'iz but for simplicity I've only drawn the five carbons of rubp and what happens is rubp bonds with a molecule of carbon dioxide and when they bond they make a very short-lived six carbon molecule the five carbons from rubp plus the one from carbon dioxide make this very short-lived six carbon molecule so the reason the six carbon molecule is short-lived is we finally get to see the importance of ATP and DPH which were created during the light-dependent cycle the six carbon molecule is gonna be broken down by the energy contained within ATP and nadph in enzymes will help to break down ATP and nadph to release their energy and when the energy is released that six carbon molecule is broken down into two molecules called phosphoglycerate each pga or phosphoglycerate is three carbons in size and by the way the nad p and the adp that are left over will be reused and recycled in the next light dependent reaction and so this happens multiple times here's another short-lived six carbon molecule broken down by NADPH and ATP to make two more molecules of phosphoglycerate and it was another six carbon molecule broken down by another NADPH and another ATP to make two more molecules of the phosphoglycerates so what happens now with these phosphoglycerates well some of those three carbon phosphoglycerates are gonna bond with one another and with the help of enzymes they're gonna bond to make simple sugars such as glucose and that's the whole point of photosynthesis is to make glucose now not all the phosphoglycerates do this some of the phosphoglycerates are going to help to keep the cycle going and so what happens is they're gonna be broken down they're gonna be broken down with the help of ATP to keep the cycle going and when ATP breaks some of these other phosphoglycerates down they're broken down and then enzymes help to build that same 5 carbon molecule we saw earlier ribulose biphosphate and now we're repeating the calvin cycle the light independent reactions the process simply restarts because carbon dioxide will bond with this five carbon rubp when they bond they make that short-lived six carbon like he'll that we mentioned earlier and the process repeats itself so to summarize the light independent reactions carbon dioxide ATP and nadph are going to create glucose so when carbon dioxide is added to the ATP and nadph from the light dependent reactions with the help of enzymes you have simple sugars such as glucose created okay so if you're in my biology class we'll talk about this essay question in class and there you have it as we wind down this video you know pause it try to answer these questions and you know put your comments in the box below I hope you found this video helpful thanks for watching

Channel: Beverly Biology

Views: 263,330

Rating: 4.850698 out of 5

Keywords: photosynthesis, cellular respiration, glucose, light dependent, light independent, chlorophyll, ATP, RUBP, Chloroplast, NADPH, Photosystems, Biology, Cells

Id: fTXh7A7Uc2M

Length: 17min 52sec (1072 seconds)

Published: Tue Jul 10 2018