hey guys welcome back to a new video by biology resun so today we are going to continue with the igcc biology chapter 6 Plant Nutrition this is for the syllabus 2023 to 2025 and 2026 to 2028 so today the content will be slightly longer than the past three videos which only covers uh quite a short am us one subtopic only today we cover two subtopics is photosynthesis and the Lea structure so photosynthesis will be our first part of today's video and as usual we have the learning outcomes uh which is uh copied from the syllabus so this will be helpful for knowing that what you are supposed to know for the exam and then this is for extended students which the core do not need to study these two points but an extended student should learn both core and extended items meaning both of these pages okay let's start off with today with our first part which is the equations of photosynthesis so we must know that green plants which we can see anywhere like the trees uh like the grass they all are considered as green plants they make the carbohydrate known as glucose from the raw materials carbon dioxide and water using in the presence of light and chlorophyll so light can be from sunlight as one example and at the same time oxygen is made and is released as a waste product extended students are required to know the chemical equation so you must know and differentiate which is the word equation which is the chemical equation so the one of the top is the word equation so I put that at w and then we have the chemical equation it is at the bottom so Co students you usually need to know the word equation meaning writing down carbon dioxide plus water to become glucose and oxygen so typically in exam they will give you two marks for this kind of question they ask to State the equation of photos synthesis but for extended students you must know that they can ask you to State the balance chemical equation what does it mean by balance is the having the six on the uh left hand side before you write the particular reactant or the product okay so this is quite simple so now let's talk about the roles and the reactants of of the reactants and the products so carbon dioxide is uh one of the reactants for photosynthesis they diffuse into the leaf through the stomata so what does diffusion mean diffusion means the movement of gas molecules from a high concentration gradient to a lower concentration gradient so this is the definition that you should have known and water is taken up by the roots and travel up the xylem so how does water get into the plant is by osmosis and now the products of photosynthesis we have glucose so glucos they make the substance need for the plant and is used in respiration so respiration is a key process that uses glucose to make energy for the plant and oxygen is also one of the other products of photosynthesis also used in respiration to release energy okay so this is the four reactants and four reactants including the products also uh functions of it on its own now let's talk about overview of the photosynthesis so plants they need to photosynthesise to make food because plants are known as autotop so this is a new term that you do not need to know a lot but it's best that you know what does it mean so Alo means self trough is make food or you know this is known as this if you combine both of them it's know as self making food so the plant they make their own food they don't usually get feed by somebody no most of the time is that they make their own sugars they make their own carbohydrates so they can build the plant uh on its own so same as humans they plants make glucose and form starts starch for storage and photosynthesis is the process by which plants manufacture carbohydrate from raw material using energy from light so now let's see what is chlorophyll so have you ever wondered how the plant leaves look green so it's because of chlorofil so a green pigment which is known as chlorophyll that is found in the chloroplast within the plant cells so you have learned in Chapter 2 that chloroplast is one of the organ naels that is found in a plant cell only and not in an animal cell so chloroplast inside will contain chlorophyll pigments which gives the color green so it reflects the green light giving plants the characteristic green color and what is the role of the chlori is that it absorbs light energy and then its role is later to transfer energy from light into chemical energy so that is the function so you do not need to know any of the labels here this is not for uh at this level so this you can see this in a levels later on so now when we produce the carbohydrates such as glucose form in the as the products of photosynthesis now you be asking me what are the particular roles that this glucose can become uh to help build the overall structure so first thing the glucose is converted into starch molecules which has an effective energy storage and it's also converted into cellulose which also a of carbohydrates so it's starch cellulose there all carbohydrates is to build the cell wall and glucose can be used in respiration to provide energy and it's also converted to sucrose for transport in the Flor this one you also will learn this in I think um soon in transport in plants and it also can become as nectar to attract insects for pollination so plants can also convert the carbohydrates made into lipid if you ever wonder why it's because carbohydrates have carbon hydrogen and oxygen lipids also have carbon hydrogen oxygen that is why they can convert from carbohydrate to lipids for an energy source in seeds and into amino acids to make proteins when combined with nitrogen and other minerals absorbed by Roots because amino acids also have c h is just that they need to have nitrogen at the same time in order to become proteins all right so now let's see the minerals in plants which are important for uh as like almost our nutrients like that so photosynthesis produces carbohydrates but plants may contain many other types of biological molecules such as proteins lipids and nucleic acid like DNA so they also need mineral ions which is absorbed from the soil so what is the process that absorbs the mineral ions this is by active transport so active transport they go gains the concentration gradient using ATP or using energy so this is how we link back to chapter tree questions can become like this they will ask you how does mineral ions being absorbed into the plant that's one of the example questions so two essential ions are magnesium and nitrate ions so magnesium ions helps to make chlorophyll without magnesium uh this can cause chlorosis or cause the plant to become yellow nitrate ion nitrate is similar to it's almost like it has it definitely has one of the um elements as nitrogen so this one helps to make amino acids so without amino acids there's no more protein therefore they can cause standard growth means they unable to grow tall they might stay really short as a plant on its own okay now let's see investigating the need of chlorophyll so for this um for this particular question I have only given you um just like a brief image okay from save my exams so now we're going to see that how are we going to investigate the need of chlorofil so first of all we see that um the leaf is placed into boiling water and now why are we using it to boil in water is to kill and kill the cells and break down the cell membrane okay so then the leaf is left for a few minutes up to 10 minutes in hot ethanol in the boiling tube and this removes the chlorophyll so color changes from iodine can be seen more clearly okay what does this tell you is that they are trying to break down the cell wall so that the chlorophile can be released into the beaker okay then now they add it into ethanol so this ethanol is added so that iodine can easily be stained and then then this can produce you um what you want to see he spread out in a white towel and convert covered if iodine solution so then the the in the green leaf the entire Leaf will turn blue black as photosynthesis this is occurring in all areas of the Green Leaf so you can see for this one the leaf is placed on the white towel and then now it is covered in iodine solution then you can see where it changes color because iodine turns from yellow to blue black in color of brown to blue black so when you observe that there's a change in color where it becomes blue black therefore the starch is there okay so this is one of the questions okay how are you going to solve this so in the photosynthesis experiment a plant is left in sunlight for several hours a leaf is then removed from the plant and tested for starch using idin solution the shows the Lea from the plant that was used in the experiment which diagram shows the result of the experiment okay so of course they are going to add the iodine solution inside here so now they're going to see what is the result you know that the positive result of iodin is blue black in color and they only show as a form of starch in the end so you need to know that when you see the green area you stain with iodine this is the part where it turns blue black and the white area means they do not have the starch when you stain it it will remain the negative result or remain the same color as before so which one responds to what I said just now the answer is C okay so if you need any more clarifications to drop them in the comment section below so this one is not so difficult but it's okay all right so this is the answer which is C now they want you to investigate the need for carbon dioxide sign so now this is going to be a little bit uh confusing because first thing what are they going to do is that they're going to dearch the two plants by placing them in the dark for a prolonged period of time then you place one of the plant inside the Bell jar so this is the Bel and then uh which contains a beaker of sodium hydroxide and what is the purpose of sodium hydroxide is that they will absorb the carbon dioxide you know carbon dioxide is um is in the surrounding all the time and that's to see whether they need carbon dioxide or not then you place both plants in bright light for several hours so light is being shown and then of course um it's going to allow it to photosynthesis at any time and then now they're going to test for both plants okay for start using iodine and then uh the leaf from the plant place near the sodium hydroxide will remain orange brown as it could not photosynthesize due to the lack of oxygen and the leaf from the plant place near water should turn blue black uh as it has all the necessary requirements for photosynthesis so it's just basically checking whether CO2 is important as a reactant it is important because it's one of the key reactants for photosynthesis now we see investigating the rate of photosynthesis so plants are respiring all the time and so plant cells are taking oxygen and releasing CO2 as a result of aerobic expiration but however photosynthesis one of the key requirements is that they need in the presence of light and chlorophyll so mean what does this tell you this tells us that photosynthesis can only take place in sunlight which in daytime but not during the night so like what I say this now they can only photo photosynthesize in daytime but what about nighttime so since they cannot photosynthesize they'll be now using their glucose at night to undergo respiration so they meaning they take in oxygen and give out carbon dioxide to the surrounding but now you can measure how uh the amount of CO2 concentration released by using a hydrogen carbonate indicator so this one is actually quite important because you um sometimes in paper 4 they ask you to uh they give you a scenario of this plant being placed in here and they also to use the hydrogen carbonate indicator to indicate what is the color that it will show under this particular concentration of CO2 so now how do I remember this it's just by PM Roy so it's just basically purple magenta red orange yellow so P or purple this shows that this is at lower CO2 concentration and Y as higher CO2 concentration so meaning if I have a basically a jar which has high amounts of carbon dioxide concent ation if I add hydrogen carbonate indicator it will turn yellow if there is high amount of oxygen and low carbonide concentration then the hydrogen carbonate indicator will indicate purple in color okay so this is just very simple just remember that PM Roy is probably the best acronym that you need to know for hydrogen carbonate indicator now we are going to enter limiting factors so there are three main factors that you need to know in limiting factors for photosynthesis so one of them is temperature other one is light intensity carbon dioxide concentration and uh that oh that's it only so now let's see how are we going to uh understand this okay so first thing we have temperature so if you see from this graph right this graphs kind of resemble to you the enzyme the factors of how temperature affects enzyme activity so yes this is the same thing so why is it reflecting the same graph because as temperature increases right the rate of photosynthesis increases because of course plants they have a Optimum temperature but why they have an Optimum temperature too because the entire photosynthesis reaction is controlled by enzymes this is very important that is why they are reflecting the same graph as the pH is the temperature graph in F in the enzymes that you learned in the previous chapter so yes now we are going to see that since we know that the reaction is controlled by enzymes the trend only continues up to a certain temperature Beyond which with the enzyme begins to denat and the rate of reaction decreases so let's talk about slowly like um how are we going to depict this graph so when temperature increases what happens the rate or the number of collisions between the substrate and enzymes increases so slowly when it rises the of photos goes faster but of course when you talk about this point in when temperature is too low X is a limiting factor uh it also kind of inhibits a high rate of photosynthesis but then eventually they will reach at Optimum temperature when they reach Optimum temperature you can see that this is the highest rate of photosynthesis it can possibly go then of course when temperature is further increase enzyme starts to do not have that sort of high rate of collision as usual because because the active side begins to change shape so when it becomes to CH it begins to change shape it starts to denat so temperature is the limiting factor again why it's because the temperature is too high okay so that is how you understand this graph then the next one you see is light intensity so what does light intensity mean it means that the amount of light I shine onto this PL what how does it reflect to the rate of photosynthesis so let let's see so the more like the plant receives the faster the rate of photosynthesis so this is the one that you should know higher temperature higher rate of photosynthesis High light intensity High rate of photosynthesis so the trend will continue until some other factors required for photosynthesis prevents the rate from increasing further because it is now in short supply so what does this mean is that let's say um light intensity from here okay it of course it starts to go small light starting to be shine to the plant right then the rate of photosynthesis goes higher and higher and higher but eventually it stops here so it starts to platue or become stationary so this is the word stationary where other limiting factors also take part into this uh graph therefore the rate Remains the Same so the maximum rate is reach temperature or CO2 concentration must be the limiting factor Factor so since light intensity reg stationary you must know that there are other limiting factors so when question ask you to state that what are the other limiting factors that um causes the causes this particular graph to start to become stationary then you can St it's either temperature or carbon dioxide concentration but again there's also one question they will ask you they will label you A and B so in section A right which is this one that I'm showing you right now now what is the limiting factor of this of this graph the answer is light intensity why because the graph is increasing when it has a increasing Trend the only limiting factor that is controlling this is light intensity but when they ask you to State the limiting factors of B in this graph then light intensity is not the answer so I light intensity is wrong so you must give either temperature or carbon dioxide concentration this is how you answer some of the questions either in paper 2 McQ or paper four short answer questions okay now you look at the final limiting factor which is carbon dioxide concentration it has almost the same graph as limit uh light intensity so I will repeat the same thing is that adding more CO2 is like adding more reactant into the photo synthesis equation when you have more CO2 the concentration becomes higher right so more of the CO2 being added will increase the rate of photosynthesis so what happens when you increase of course the rate of photosynthesis goes higher so again I will split the graph into section A and section B eventually the graph begins to become stationary almost the same as light intensity because above a certain concentration the rate levels of probably due to all and enzymes of photosynth being utilized or the reaction cannot go faster or maybe there could be other limiting factors so the other limiting factors could be light intensity or it could be temperature so this can be the either one but then they can ask you what is the limiting factor in a a is carbon dioxide concentration okay so again if you have any questions on these three limiting factors and the graph itself feel feel free to comment down in the comment section below okay so this is the summary of the limiting factors graph so light intensity and carbon dioxide concentration is very similar actually it's almost the same it's just that temperature will have a u shaped graph because this graph is almost the same as the uh temperature affecting enzyme graph okay so that's that's it now let's move on so now we have a special one this one you may see in paper two usually they confuse you with different types of um description in graph number one graph number two and graph number three so the main thing we always love to do is that we separate them so it has uh each of the graph each of the level of the graph will eventually become stationary so what whatever that becomes before it becomes stationary the graph begins to become straight in the line is always the intensity of light meaning this is the x-axis the x-axis is always the answer for both when it's like in it slanted shape going up so increasing light intensity will increase the rate of photosynthesis but now it causes stationary the line becomes uh like a straight line really so what is causing this is that let's see for the first first one they say higher CO2 concentration and higher temperature so meaning that uh we have a high CO2 concentration high temperature therefore the graph is the highest because again higher temperature higher rate of photosynthesis higher carbon dioxide concentration higher rate of photosynthesis then now you see highest for the second one they say higher CO2 concentration but lower temperature the moment that is lower temperature the rate of photos is not going to say all the way going to decrease tremendously but it's just going to be lower than the first one because of course it makes sense right lower temperature the rate of f the photosynthesis is much lower and then the third one when you have lower CO2 concentration lower temperature both of them they reduce the rate of photosynthesis that's why the graph is all the way at the bottom this reflects the rate of photosynthesis okay now let's go to our last part the leaf structure part two of this video so now this is the again the learning outcomes this one you can read on your own now we come to the leaf structure so for the leaf structure you unfortunately have to memorize all of these so you just need to you need to know the cuticle the upper epidermis uh this is usually the usual plant cell organel that you see plant cell organel okay you don't need to call palis you don't need to call vertical palis you can just call picate or picate mopi cell okay then you have spongy mopi cell this one you also need to know G cells sto or stoat is okay air channel or air spaces is also acceptable and cuticle okay and the lower epidermis this one is the xylm and the flum uh this you can known as the vascular bundle so you have to know the entire diagram and its labelings okay so this one is essential now going to talk to you about now you know the structure right every time in BIO you need to know what is the function the structure always links to the function so the structure of the waxy cuticle which is found at the top of the leaf structure it's here so what is the point of the waxi cuticle being on top so firstly it's waterproof it has a waxi protective layer from the term waxy it's made of wax and wax is US made out of fats okay you link with fats so fats and water they cannot mix together therefore when water is falling on top of the wxy cuticle it doesn't get absorbed it doesn't get dissolved it doesn't mix with the waxy cuticle so it forms as a waterproof layer and prevents water from evaporating for the upper epidermis and the lower epidermis is thin and is transparent to allow light to enter the palis mesophi cell and palis mesophi cell is found the top of the cell contains many chloroplast that absorb sunlight so what does this tell you in the end chloroplast that absorbs sunlight will link to photosynthesis okay or you can just say the function of the palis mesop cell is photosynthesis spongy mesophi cell is irregular shaped cell you can see that they have different sizes and shapes okay uh what is it for is that it allows for gases exchange or gas exchange to take place which do not contain many chloroplast vascular blunder is made up of sylm and Flow this one you know later in transport in Plants stomata or sto are little holes that open and close to allow gases extion to occur and guard cells they control whether the stomata should open or close because when they open water can leak out from the leaf so now you have to know what is the adaptation of the leaf structure sometimes they will ask you why does this Leaf structure become so efficient for photosynthesis so you can first say that is a large surface area of the leaf it increases the surface area for diffusion of CO2 and absorbing light for photosynthesis then you can say it's thin the leaf cell or the leaf structure is actually very thin and it allows carbon to diffuse quickly into the palis mopi cell chlorophyll it absorbs light energy so photosynthesis can take place it's considered an adaptation because animal cell do not have that plant cells specifically have chloroplast so that they can make food okay and network of veins so they have network of veins meaning like the xylm of flum they always have a lot of these and this will allow efficient transport of water and mineral ions throughout the plant and they have a thin epidermis you can see that the epidermis right is actually considerably quite thin so what is it for is that allows more light to reach the palis mesophi cell and lastly they have a stoat the stomata can open or close so it that kind of controls whether oxygen and carbon dioxide is going out or coming in uh depending on on the situation or the environment that it the plant is placed in okay so yeah any questions for this topic because we've come to the end so if there are any questions just feel free to um put it down in the comment section below hopefully I can respond to everyone as soon as possible so thank you so much for watching so this will be a rather boring chapter but the next one will be human nutrition thank you so much for listening bye-bye