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Course: Class 10 Biology (India) > Unit 1
Lesson 3: Autotrophic nutritionPhotosynthesis
Let's explore the photosynthesis process. Created by Mahesh Shenoy.
Want to join the conversation?
- At0:29, you mention that photosynthesis is a process by which plants make energy in the form of sugars, or to be more specific, carbohydrates.
But what about proteins and fats? Don't plants require lipids to maintain their cell membranes? Don't they require enzymes or hormones to communicate with different parts of the plant??(10 votes)- Pretty Good Question, Photosynthesis is one of the processes Which plants do to make Glucose. Plants get proteins from nitrates (a form of nitrogen).This process is called nitrification and fats are made from a process called fatty acid biosynthesis which uses excess energy.The Hormones and enzymes are made from different parts of the plant like for example Auxin is a plant hormone produced in the tip of the stem, Overall photosynthesis is just one of the processes used to make glucose, sounds pretty complicated but easy to learn if u wanna know more just google about it(6 votes)
- isn't the equation supposed to be: -
6CO2 + 6H2O ------> C6H12O6 + 6O2 + 6H2O
with sunlight and chlorophyll on and below the arrow?
Because that is what is given in our textbook.(5 votes)- Yes, the equation is
6CO2 + 12H20 ----------> C6H12O6 + 6H2O + 6O2 .
But, many scientific journals and documents do not consider the 6H20 on the product side as it is a waste product (released by transpiration).(1 vote)
- Do stomata specifically takes CO2 inside, or takes air as whole and then separates CO2 from it?
Or in any other way?(1 vote)- Stomata aren't physically taking CO
₂
inside. They are just providing a "doorway" for the CO₂
to get inside. CO₂
gets inside a cell through a process called diffusion. When photosynthesis happens, the amount of CO₂
in the air is more than that in the cell (such difference is called a concentration gradient). So, the CO₂
molecules rush inside the low-concentrated cell environment (also known as diffusing from a higher concentration to a lower concentration).
Hope that helps and if I'm mistaken, please let me know. :)(7 votes)
- What is the main site of photosynthesis ?(2 votes)
- Chloroplast is the site of photosynthesis. It is present in the mesophyll cell of the leaf. Chloroplast contains chlorophyll pigment.(1 vote)
- so can we consider chlorophyll as a catalyst for the photosynthesis reaction?(1 vote)
- While I understand your thought process, its not exactly correct. Lets see why -
Catalysts are biochemical that change the rate of a process/reaction without themselves getting involved in the process.
Chlorophyll, on the other hand, is an essential requirement for photosynthesis, as it traps sunlight, and its Plastid- chloroplast, is the site of the dark and light reactions of photosynthesis.
If the organism does not have chlorophyll, then it can't perform photosynthesis.
It is essential chlorophyll that makes plants autotrophic.
Hope you will have a clearer idea of this now!!(3 votes)
- does photosynthesises happen in dry leaves(1 vote)
- No, it doesn't happen in dry leaves because dry leaves consist of dead cells. So if the cells are dead, they won't be able to perform the functions required to stay alive, photosynthesis being one of them. So yeah! Hope you understood.(2 votes)
- Did chlorophyll only absorb carbon dioxide from the atmosphere or they absorb the air and pick out carbon dioxide from it? If yes to anyone of these options how do they do?(1 vote)
- actually chlorophyll doesn't absorb any air. they absorb sunlight for photosynthesis.(2 votes)
- How can water be decomposed to form oxygen and hydrogen using sunlight? i learnt that electrolysis of water can only decompose water. Please help me.(1 vote)
- Let us look at the process from the beginning-
The following process takes place-
(i) Absorption of light energy by
chlorophyll.
(ii) Conversion of light energy to chemical
energy and splitting of water molecules
into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to
carbohydrates.
Here, as we can see, the light energy is converted into chemical energy. So, we can't actually say that decomposition took place from a specific method.(2 votes)
- at10:12it is stated that the byproduct is only oxygen but what about water(1 vote)
- As far as I understand, many people ignore the extra water. If you want to include it, you can have
6CO2 + 12H20 --> C6H12O6 + 6O2 +6H20
I am not sure why this water is needed, though.(1 vote)
- What is the name of the red colour that dominates chlorophyll?(1 vote)
Video transcript
- [Instructor] Photosynthesis
is pretty awesome. It's where the plants and the trees and all the green stuff that
you find around yourself take in water and carbon
dioxide from their surrounding, and then use the energy of the sun to manufacture their own
carbohydrate molecules. And why is it called photosynthesis? Because the plants use photo, which means light energy, to synthesize, meaning to create, carbohydrates from the raw materials. And why do they do that? Because carbohydrates is food for them. But guess what? Carbohydrates are food for us as well. Even we need these carbs for our energy. This means photosynthesis feeds almost all living
things on this planet. And on top of that, there is a bonus. During this process, the plants kick out a particular molecule into the atmosphere. Guess which one? Oxygen. This means photosynthesis gives me my carbohydrates, my food, and it gives me oxygen to breathe. That's why I love photosynthesis. But here are my questions. Why can plants and trees synthesize their own carbohydrates but we animals can't? What do they have that we don't? And what exactly happens
during this process? How exactly do they produce carbohydrates from the raw materials? These are the questions
that we're gonna try and answer in this video. So let's start with the first one. What do plants and trees
have that we don't? Well, it turns out that they have something called chlorophyll. What's that? Well, to answer that question, let's clear this up a little bit. And then we have to look at one of these leaves very carefully. So if we zoom in, we will see a leaf, which is not surprising, but if we zoom in even further
maybe using a microscope, now we see something very interesting. So these compartments that you are seeing, they are the cells of that leaf. And inside these cells you can see all these green things, right? These green things are
called chloroplasts. And guess what? Photosynthesis happens inside
these chloroplasts, okay? There are a lot of
complex molecules inside working together to
carry out this reaction. Now one of the most
important molecule inside is a pigment called chlorophyll. So chlorophyll is a pigment
found in these green stuff, and chlorophyll is the
reason why they are green. Okay, chlorophyll gives
them their green color. It makes all the plants and trees green. But another important job of chlorophyll is to absorb the energy from the sunlight. Without chlorophyll, energy wouldn't be absorbed and photosynthesis wouldn't happen. So here's how I like to think about it. Imagine we are concentrating
on one of the chloroplasts, as the sunlight comes and hits it, the chlorophyll absorbs that energy and makes it available
for all the molecules. Now they have the energy to
take in carbon dioxide and water and then carry out the
photosynthesis reaction which we'll look at in
detail in a little while. And then it spits out this
juicy carbohydrate molecules. And then it also produces oxygen, and the oxygen gets thrown out. Now before we dive into this chloroplast to see exactly how this
chemical reaction happens, let me tell you a couple of things that I used to get really
confused about, okay. First is because we see plants throwing out oxygen during this process, I thought they don't need oxygen, I thought they need carbon dioxide but they don't need oxygen. It turns out that's wrong. Even plants need oxygen just
like how we need it, okay, and we'll talk more about
this in videos of respiration, but plants and trees,
they also need oxygen for the same reasons why we need it. Then why do they throw it out? Well, it turns out that
during photosynthesis, they create a lot of oxygen, okay, so they keep whatever they want and the rest they throw out. So they don't throw out
all the oxygen, okay, only the ones they don't
want they throw out, and we are breathing that right now. Secondly I used to think this process only happens in the leaves. But no, they can also happen in the stem and the bulbs and sometimes in the fruits as well. Okay, photosynthesis can happen in any part of the tree which is green, because any part which
is green has chloroplast, and wherever chloroplast is present, photosynthesis can happen. So for example you may have seen these green bananas and apples, right? Why are they green? Because of chloroplasts and chlorophyll. They can also carry out
photosynthesis, okay? So not just leaves, but leaves carry out most
of the photosynthesis. And lastly what about this houseplant which is in my balcony
which has non-green leaves? Can they carry out photosynthesis? I used to think no, because they are not green so they don't have chlorophyll so they can't photosynthesize. But it turns out that's wrong. It turns out that even these
plants do have chlorophyll and so they can photosynthesize. Then why aren't they appearing green? Well, because plants can
have other pigments as well. And in most cases where
green plants are there, chlorophyll is dominating, and that's why we see them to be green. But in this plant for example, the other pigments like
maybe the red color pigments, they are dominating, and that's why when we look at them, it looks a little purplish reddish. It doesn't mean chlorophyll is not there. Chlorophyll is there,
chloroplasts are there, they can also photosynthesize. Alright, so now that that's clear, let's dive into this chloroplast and see exactly what chemical
reaction is taking place. So let's begin by writing a chemical reaction for this process. How do we do that? Well, whenever I forget what's going on, I start by thinking about the products. Now I know that in photosynthesis
I get carbohydrate, okay. This helps me remember the reaction. Here's how. See, carbohydrate has two words, it has carbo and hydrate. Carbo means carbon. So to manufacture carbohydrate, I need carbon, plants need carbon. Where do they get that from? Well, they get it from carbon dioxide. That's how I remember carbon dioxide. Then they also need hydrate. Hydrate is water, right? Just like how we say
dehydrated means loss of water. So they also need water. Oh, so plus H20. So these are the two reactants needed. But of course remember to
carry out this reaction, they also need energy from the sun. Photosynthesis, photo
part is over here, okay. So these are the three things needed. Now what do we get? Well, let's see. Now whenever we write this arrow mark, we put a chlorophyll on top of that to signify that energy is
absorbed by the chlorophyll. Without chlorophyll, this
cannot happen, right? Okay, anyways, what do we get? We get carbohydrate, right,
that's the major product, but how do we write the
formula for carbohydrate? Again I look at this. See, carbo means carbon so there's a C. Hydrate means water so H20. This is carbohydrate, okay. But wait, carbohydrates need not have just one atom of carbon and
one molecule of water, they can have three and
three or six and six, or any number they can have, alright. So there are many carbohydrates. So in photosynthesis, which carbohydrate do we get? Well, we get the carbohydrate in which there are six atoms of carbon
and six molecules of water. That's also something we
need to remember, okay. So the one we get is where
there are six of these, alright. And this molecule, this carbohydrate is given a name, it's called glucose. So photosynthesis gives
us glucose, alright. And what else? We get one more product, which is that? A byproduct which they
throw out, which is that? Plus oxygen. And you will see in a second why I have colored oxygen this way. And here is our chemical reaction. But if you look carefully, you see that it's not balanced. For example on the right, we have six carbon atoms, on the left we just have one. Okay, so we need to first balance it. And so can you try balancing it first? Great idea to pause the video
and see if you can balance this whole equation yourself first. Okay, hopefully you tried. So I'll just quickly go
ahead and balance this. Since there are six carbon over here, we multiply this by six. There are six water molecules over here, so I multiply this by six as well. Now let's look at the oxygen. The oxygen here is balanced, six and six. But over here we have 12 oxygens, so this also will balance by multiplying by six, we get 12. Now everything is balanced. Now I know this was fast but we've talked a lot about balancing in great detail in chemistry videos. So if you need more clarity
on how to balance equations, great idea to go back and
watch chemistry videos. Anyways, now let's think about what's going on in this reaction. I'll start with what I thought again. So when I learned this, I thought that here carbon dioxide is being broken into carbon and oxygen. So I thought that plants
take in carbon dioxide, break it, and throw away oxygen. That's how we get our oxygen. And then they take that carbon and attach it to water to give us carbohydrate. That makes sense, right? Easy, right? Unfortunately that's now how it works. Why not? Well, the main reason for that is because carbohydrates are not really carbon attached to water. So glucose is not six carbons
attached to six water. I'll show you the structure of glucose. There are many structures but one of the structures
of glucose looks like this. Now I know this looks all scary, and don't worry, we don't
have to remember any of this. But what I'm going to show you is do you see carbon attached
to water anywhere? No, right? It's not like that. It's a little bit complicated, right? So even though the name
is stuck, carbohydrate, it's not really a good name actually. The name is stuck but it's not really
carbon attached to water. So you can't attach carbon to water and expect to get a carbohydrate, okay. So let me get rid of this. Carbohydrates are not
really carbon and water. But it's useful to remember the formula. I use it to remember the formula, okay. Let's get rid of this. So if that's not what's going on, what's really happening in this reaction? So here's what's happening. The chlorophyll absorbs
the energy from the sun and then uses it to break open water into hydrogen and oxygen. And by the way it's not chlorophyll alone, there are many molecules working together, but some of their energy is used to break open hydrogen and oxygen, and that oxygen is thrown out. So the oxygen in photosynthesis comes from water, not from carbon dioxide. And this process is pretty
important, at least historically, because that's how oxygen
came into our atmosphere. So almost all the oxygen
that we are breathing today was once upon a time locked in water. Pretty cool, right? So we need to change the color of this. This came from water. And then what about this hydrogen? Well, then the hydrogen gets attached to carbon dioxide in a series of steps, it's not a one-step reaction, there are many more
molecules involved over here, but in a series of steps
to finally give us glucose. And so the oxygen over here is the oxygen from the carbon dioxide. So again we need to color that properly. So again what happens? Chlorophyll absorbs
the energy from the sun and uses some of it to break open water into hydrogen and oxygen. Oxygen is thrown out and then the hydrogen is
attached to carbon dioxide in a series of steps to
finally give us glucose. And I can stare at this forever because this is literally
what's keeping me and you alive, but we need to end this video so let's quickly go ahead and summarize. What did we see in this video? We saw that photosynthesis takes place inside this green things
called as chloroplasts. They are green because of a
pigment called chlorophyll, and chlorophyll helps in
absorbing the energy from the sun. And what does it do after
absorbing the energy? It uses it to split open water
into hydrogen and oxygen. The oxygen gets thrown out, and then the hydrogen is
attached to carbon dioxide in a series of steps to give us glucose. This is what happens
inside the chloroplast. This is photosynthesis. This is how we get our
food and our oxygen.