Photosynthesis Crash Course in 45 Minutes ?☀️|| Plant Physiology @biologyexams4u

Name: Photosynthesis Crash Course in 45 Minutes ?☀️|| Plant Physiology @biologyexams4u | Open Video
Uploaded: 2023-09-10T12:03:24+00:00
Duration: 47 min 43 s

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Hi friends, happy learning with biology exams for you. In this video we have combined all core
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concept videos on photosynthesis for a clear-cut sequential understanding of the topic within 45
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minutes. At the end of the discussion you will be able to understand the equation of photosynthesis
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that is followed by the site of photosynthesis exactly where the reaction is happening that is
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followed by the pigments in photosynthesis then light dependent reaction and also the steps involved
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in Kelvin cycle or light independent reaction and the difference between C3
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cycle and C4 cycle and finally will be winding up with CAM cycle. You can use
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the timestamps to move directly into specific topics. Let's begin with the
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equation of photosynthesis. So let's start with the definition of photosynthesis. Photosynthesis is an amazing process that is responsible for life on this
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planet. The reactants are water that is absorbed by the roots plus the carbon
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dioxide from the atmosphere. Sunlight is a source of energy and leaves are the
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site of photosynthesis. Inside the leaf there is a pigment called chlorophyll
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that trap the light energy and convert it into chemical energy as glucose and
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this is directly or indirectly utilized by all organisms on earth except some
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microbes and oxygen is released as byproduct. So this is the overall
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equation of photosynthesis. Six molecules of carbon dioxide plus 12 molecules of
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water in the presence of sunlight and chlorophyll give rise to glucose water
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and oxygen. Let us see how we get this equation. Till 1940 this was the
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equation six carbon dioxide plus six water molecule give rise to glucose plus
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oxygen. It is believed that photosynthesis is just a reverse of respiration. In the case of respiration, this glucose molecule is broken down into
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carbon dioxide and water with the release of energy. So photosynthesis is a
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synthetic process whereas respiration is a catabolic process or breakdown process releasing energy. But this equation doesn't tell much about what is
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actually happening. What is the exact source of oxygen evolved? Is it from water
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or is it from carbon dioxide? So this is the experiment that solved the question
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Ruben et al. in 1940 used radioisotopes to find out the exact source of oxygen
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and this was a paper published and this was the experiment and the experiment
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one they used radioactive labeled water as a reactant and found out that the
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oxygen released is also radioactively labeled and this was the equation carbon dioxide plus radioactive labeled water and oxygen evolved is also
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radioactively labeled indicating that this oxygen is formed from water for the
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confirmation they did a second experiment using radioactively labeled carbon dioxide here they used radioactively labeled carbon dioxide and
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found out that the oxygen released is not radioactively labeled indicating that this oxygen is evolved by the splitting of water molecule. They got
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water in the product also which is radioactively labeled. Thus Ruben et al
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confirmed that oxygen evolved during photosynthesis comes from water. Now we know that it is by the photolysis of water. So these are the two experiments
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summary of the two experiment. Now we need to change the equation, now we know
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that oxygen evolved during photosynthesis comes from water. Let us take the old
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equation. 6 carbon dioxide molecule plus 6 water molecule gives C6H12O6 that is glucose plus 6 oxygen. Let us see what is happening. So now we know that
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that water splitting give rise to oxygen number of oxygen is 6 here the number of
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oxygen required is 12 so we need to rearrange this equation we should balance
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this equation once again so this is a balanced overall equation of
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photosynthesis 6 carbon dioxide molecule plus 12 water molecule in the presence
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of light and chlorophyll give rise to glucose that is C6H12O6 plus 6 water
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molecule plus 6 oxygen. Let us see this is 12 H2O so we have 12 oxygen here also
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we have 12 oxygen so this is balanced. Now let us check the complete equation is
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balanced or not. Number of carbon it is 6, number of oxygen 6 into 2 that is 12
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plus 12 that is 24 oxygen molecule in the reactant side, number of hydrogen 12
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into 2 that is 24. In the product side number of carbon it is of glucose that is
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6, number of oxygen here it is 6, here also 6, 6 plus 6 plus 6 into 2 that is
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12, 24 oxygen molecule and number of hydrogen here it is 12 plus 6 into 2
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that is 12 that is 24. The equation is balanced. Now the correct balanced
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overall equation of photosynthesis is 6 carbon dioxide plus 12 H2O give rise to
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C6H12O6 plus 6 H2O plus 6 O2 where this O2 is derived from water. Now we know the
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process, the process is called as a photolysis of water. Hopefully we will be
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discussing that in our later videos. Which is a primary site of photosynthesis
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it is undoubtedly the leaf leaf is the primary site of photosynthesis and in the
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case of serophytes they may not be having leaf then the stem is green all
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green parts of the plant are capable of photosynthesis leaf is an organ that is
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designed for photosynthesis the function of leaf is to absorb light energy and
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also carbon dioxide these are some of the adaptations of leaf there is large
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surface area to absorb more light it's very thin so that so that the diffusion
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carbon dioxide is very easy and the distance traveled by carbon dioxide is
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very short then there is an opening called stomata that allows the carbon
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dioxide entry and also the removal of water vapor by transpiration and there
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is a vasculature that allows the translocation of water from root to the
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site of photosynthesis that is the leaf apart from that these there is a cuticular
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upper epidermis and this epidermal layer is transparent that allows the light to
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penetrate into the mesophyll cell directly which is a prominent site of
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photosynthesis. Next question, inside the leaf which is a cell that is primarily
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involved in photosynthesis. Leaf anatomy shows that there is an upper epidermis
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that is followed by palisade layer then there is a spongy mesophyll layer and
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lower epidermis with stomata. Mesophyll cells, the stacked cells that is seen
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just below the epidermis is a site of photosynthesis. Nearly 80% of photosynthesis
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or Custis in these cells these cells are abundant in chloroplast and you can see
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these cells are rich in chloroplast so it a primary site of photosynthesis now inside the mesophyll cell there is a wonderful organ which is called as chloroplast that is responsible for photosynthesis this organelle contains
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pigment that is capable of trapping light energy and capable of converting
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that light energy to chemical energy finally converting it into glucose this
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is a structure of chloroplast it is a double membrane bound organelle and you
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can see there are membranes sacs that is stacked one above the other which is called as granum individual membranous sacks are called as thylakoid and the
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fluid fill matrix is called as a stroma now let us see what is the exact location
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of each reaction in photosynthesis light dependent reaction light independent reaction and also the photolysis of water so this is a structure of chloroplast
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and you can see this is the thylakoid membrane that is stacked one about the
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other so let us zoom in so this is a tyloid membrane and on zooming in this
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is the tyloid membrane tyloid membrane is a place where light reaction occurs
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or light dependent reaction takes place in the tyloid membrane for the system 1
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and photosystem 2 all other proteins and electron carriers are located on the
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tyloid membrane therefore the exact location of light reaction is a tyloid
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membrane. By this process the energy of sunlight is trapped and is converted to
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chemical energy as ATP and NADPH. In non-cyclic photo phosphorylation the electrons should be continuously refilled and there is a process which is called
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as photolysis or splitting of water that occurs in the thylakoid lumen
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The thylakoid membrane is having a space which is called as thylakoid lumen. So
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the site of water splitting or photolysis of water is a thylakoid lumen
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which will refill the electron to the photo system too and also provide H plus
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and that is utilized for creating a gradient for ATP synthesis you just see
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the orientation of ATP synthase after light reaction the light energy is
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converted to ATP and NADPH this ATP synthase is oriented towards trauma so
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for Calvin cycle now the energy is right here in the stroma as NADPH and ATP
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Next is the Calvin cycle where carbon dioxide is converted to carbohydrate. The
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site of Calvin cycle or light independent reaction is a stroma where
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ATP is already there that is synthesized by light dependent reaction and also
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NADPH is also there that is utilized for the reduction of carbon dioxide to
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carbohydrate. So this is a summary in photosynthesis there are two reactions
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two are two major reactions there is light dependent reaction and also light
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independent reaction. Light dependent reaction takes place in the grana or thylakoid membrane of the chloroplast where light energy is trapped and
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converted to chemical energy in the form of ATP and NADPH. Whereas light
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independent reaction that is a second step it is also called as dark reaction
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it takes place in the stroma where the ATP and NADPH that is synthesized in the
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light reaction is utilized to convert carbon dioxide to carbohydrate and we'll
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be finding answers to the following questions what are the pigments in photosynthesis what is the site of pigments three major classes of pigments
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and the characteristics of each pigment in detail first of all starting with the
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basics of pigments in photosynthesis. Pigments are chemicals that can absorb light in the visible region. This is a visible region that is from 400 to 700
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nanometer and these pigments include chlorophyll, carotenoid, xanthophyll, phycoeurethrine and phycocyanin. Chlorophyll is the most predominant
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pigment that is why these leaves appear green. These pigments are located on an
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organ which is called as a chloroplast in leaf inside the chloroplast there is
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thylakoid this stack is called as granum and each unit is called as
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thylakoid and this is an enlarged view of this thylakoid this is a thylakoid
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membrane so pigments are actually located on the thylakoid membrane you can see for us for the system 2 and for the system 1 these pigments are located
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and these pigments can absorb light energy and convert it into chemical
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energy as ATP and NADPH we call it as light dependent reaction of photosynthesis
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so these are amazing chemicals capable of converting the light energy from the
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Sun and making it into converting it into chemical energy as ATP and NADPH
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that is utilized for the formation of glucose in dark reaction or light
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independent reaction now moving into the details of different types of photogenic pigments this is there are principal pigment which includes
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chlorophyll A that is present in all plants and also bacterial chlorophyll
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that is present in bacteria accessory pigments include chlorophyll B C D etc
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carotenoids which is somewhat yellow or orange red in color that includes
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carotene and xanthophyll then phycopylin is the third class that includes phycoeurethrine and phycocyanine moving into the detail of each pigment
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chlorophyll a chlorophyll a is a primary pigment in all plants chlorophyll a the
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structure of chlorophyll a you can see there is a central magnesium that is surrounded by four nitrogen atom and altogether this structure is called as a
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tetrapyrrole or porphyrin head the formula is 6 c 55 h 72 o 5 n 4 mg this
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is a hydrophilic viral head and this is the phytol tail which is hydrophobic that
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is embedded in the thylakoid membrane and this one two three four these rings
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are joined by methane group and maximum absorption is in the red and blue
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region and reflects green light that's why the leaves appear green its bluish
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green pigment and the side group at the second ring this is a second ring side
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group at the second ring is a medial group that's a CH3 group second
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principal pigment that is bacteriochlorophyll in bacteriochlorophyll is primary pigment in green and purple sulfur bacteria the formula is C55 at
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74 or 6 and 4 mg it's a reddish purple pigment with the side group in the CH3
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position it is having CH3C double bond though in the first ring the maximum
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is in the infrared region that is greater than 720 nanometer now accessory
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pigments accessory pigments first one is chlorophyll B that is present in blue
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green algae and also in all green plants chlorophyll B is same as that of the
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chlorophyll A except that in the second ring the side group instead of methyl
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group in chlorophyll A it is CHO group in chlorophyll B the formula is C 55 H 70
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O6N4MG the rest is the same maximum absorption at red and blue region and
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reflects green light the only difference from chlorophyll A and B is in chlorophyll
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B the side group in the second region in the second ring the side group is a CHO group rather than a CH3 group as in chlorophyll A Now the second class of
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pigments that accessory pigment that is carotenoids it includes carotene and xanthophyll. Carotenoids are accessory pigments in all plants. Beta carotene is
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an example C40, H56 is a formula, red or orange colored hydrocarbons, maximum
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absorption in the blue violet region. Whereas xanthophils are oxygenated carotene, it can be called as oxygenated carotene. Example is lutein C40H56O2
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you can see that this is oxygenated. Brown or yellow colored oxygenated
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hydrocarbons, these are responsible for the color of autumn leaves. This is a
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yellow color of xanthophil and reddish color, reddish orange color of Carotenoids, as the leaf matures the chlorophyll deteriorates and is replaced
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by these accessory pigments carotenoids and xanthophyll that is why ripened leaf
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appear as orange or yellowish. Next class of pigments include is the
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phycopylenes that include phycoereutrine and phycocyanin and this is a structure. Phycoereutrine these are accessory pigments in red algae and cyanobacteria
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or blue-green algae. It's water soluble pigment and this is wallbox that is a blue green algae and also in red algae this is laminaria this
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is red colored and maximum absorption dim and blue-green light whereas phycocyanin
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is a bluish pigment that is present in red algae and blue-green algae it's also
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water soluble it's blue colored a maximum absorption it's extra orange and red
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light and that these pigments enables algae to live in deep underwaters of sea
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due to the property of these pigments and this is a summary of what we have
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discussed. we are going to discuss about what are photosystems, what are the
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major differences between photosystem 1 and photosystem 2 in detail. inside the
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chloroplast there are membranous sacks that is stacked one above the other which
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is called as granum and this is called as this is a granum and which is a site
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of light reaction. so this is a thylakoid membrane let us zoom in this region. so
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this is a thylakoid membrane. On the thylakoid membrane, photosystems and all
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other associated electron carriers and proteins are located or thylakoid membrane is a site of light dependent reaction. Photosystems are also located
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on the thylakoid membrane. These are the photosystems, photostem 2 and photosystem 1 and this is a picture of non cyclic photophosphorylation. So
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photosystems are light harvesting complexes that is made up of pigment molecules, accessory pigments and associated proteins. Photosystems are
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located on the thylakoid membrane of the chloroplast in the case of green plants
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and algae whereas in the case of bacterium these photosystems are located
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on the cell membrane. Let us zoom in this region. Each photosystem consists of two
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closely linked components that is a reaction center chlorophyll molecule and accessory pigment which is called as antonyum molecules. Accessory pigments
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include chlorophyll B, carotene, sandophyll etc. what is happening is this energy of
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sunlight or photons is received by this accessory pigments. This accessory pigments transfer this energy to other molecules to the adjacent pigment
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molecules by means of resonance transfer which is a kind of vibratory transfer
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mechanism. Ultimately this energy is channeled into the reaction center chlorophyll, a molecule
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from where electrons are moved from ground state to the excited state that is received by electron
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acceptor and that moves through different electron carriers providing energy for the creation of
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electron gradient ultimate and ultimately the synthesis of ATP and NADPH and we have discussed
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that part in the video cyclic and non cyclic photo phosphorylation in detail
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so in summary these are the functions of photosystem it is involved in light
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absorption transfer of energy and ultimately transfer of electrons let us move into the difference first of all starting with difference in absorption
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peak so photosystem one maximum absorption is 700 nanometer or far edge
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region of light or it absorbs long longer wavelength of light and it has an
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iron sulfur type reaction center and is rich in chlorophyll A. In the case of
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photosystem II maximum absorption peak is at 680 nanometer it has a quinone type
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reaction center and is rich in chlorophyll B. Second difference is it's
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regarding the location inside the chloroplast. There are two regions which is called as oppressed and non-oppress region in chloroplast. So I would assume
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this region and this is the granum and individual units are called as
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thylakoid membrane so photosystem 1 in green color is located on the non
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oppressed gr region and this is a non oppressed gr region or the
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region that is exposed to stroma the region that is exposed to stroma or it
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can be called as the outer layers of grana so photosystem 1 in green color
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that is primarily or that is located on the non-upress granule region and also
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on the stroma lamellae that connects the adjacent granule whereas photosystem 2
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is located on the upress granule region this is a upress region you can see here
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there is stacking or the internal part of the granule for stem 2 is with green
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and black color and this is seen on the internal part of granule or the
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upper region of grana. Difference number three that is regarding the role in light reaction
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Photosystem I that is involved in both cyclic and non-cyclic photophosphorylation. In cyclic photophosphorylation, photosystem I contributes to the formation of ATP
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electrons returns back to photosystem I, whereas in non-cyclic electrons are received from photosystem II
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and it forms NADPH whereas in the case of photostem-2 it is only involved
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in non-cyclic photophosphorylation and also involved in a process called as photolysis of water as these electrons when moves from
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photo stem-2 there is an electron hole so in order to refill that electron hole
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a process occurs that is called as a photolysis of water or water splitting
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providing electrons and protons it is involved in ATP synthesis about the four stages in light dependent reaction of photosynthesis
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so we have divided the entire process into four stages for the sake of understanding remember all may be happening at the
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same time so these are the stages photo excitation photolysis photo phosphorylation and photo reduction
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and we'll be discussing these within three to five minutes Starting with the first stage that is a photo excitation of chlorophyll molecule or pigment systems
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So this is a thylakoid membrane where photosystems and all other electron carriers are located along with ATP synthase
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Or thylakoid membrane is a site of light dependent reaction of photosynthesis So this is a chloroplastoma and this is a thalacoid lumen or thalacoid space so first step is the
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photo excitation of pigment systems so that this is a pigment system 2 and this
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is pigment system 1 and this is a picture of non cyclic photophosphorylation
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that is predominant in higher plants let's see what are photosystems so
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photosystems are light harvesting complexes that consists of accessory pigments and a reaction center chlorophyll a molecule. light energy is
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trapped by these accessory pigments and this and this energy is transferred to
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adjacent pigment molecules by means of resonance transfer or a kind of
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vibratory transfer and ultimately this energy is passed on to the reaction
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center chlorophyll molecule and from where the electrons are rejected or or raised to the excited state from the ground state and that is received by electron acceptors
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and that will be passed on to other acceptors okay so photosystems are the light harvesting
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complexes in the light dependent reaction of photosynthesis now the electrons are rejected
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from the photosystem 2 there is an electron hole or an electron gap in photosystem 2 that should be
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refilled then there occurs a process which is called as photolysis of water that occurs in the
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the thylakoid lumen where the water molecule splits up to form protons and
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electrons with the release of oxygen. this protons refills this photosystem too, protons helps in creating gradient in the thylakoid lumen and oxygen that
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is released and that is the oxygen that is released during photosynthesis. so the
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second step stage 2 is a fertilizes of water in thylakoid lumen that refills the
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lost electron in photosystem and also contribute in creating proton gradient stage 3 is a photo phosphorylation of ADP to ATP now there is a proton gradient
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that is created by the photolysis of water and also during the electron
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transfer the energy is utilized to pump protons from the chloroplastomal region
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into the thylakoid lumen space now here there is more protons compared to this
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thermal region so there is no way out for this protons to this side to create
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an equilibrium these thylakoid membranes are impermeable the only way out is a
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protein which is called as ATP synthase when the protein moves through this ATP
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synthase the energy is utilized for the catalytic activity or for adding
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phosphate into ADP forming ATP and this is called as chemiosmotic hypothesis and
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this force is called as proton motive force so simply this proton gradient is
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created by fertilizers of water and also by the pumping of protons from the
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chloroplastomal region into the thylakoid lumen region utilizing the energy of electron transfer or electron flow so while this H plus moves through
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ATP synthase the only way for H plus to move out of thylakoid lumen that energy
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is utilized for combining this ADP to PI forming the ATP or the energy-rich
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molecule and that's the third step and the final step is the photo reduction of
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NADP to NADPH as the electrons moves from photosystem 2 then moves to
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blastocinone B6F which is a proton channel then plastocyanin and that is
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received by photosystem one this is further energized by the sunlight and
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there is a ferridoxin reductase enzyme that is close to photosystem one and
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that will reduce NADP in the chloroplastomal region to NADPH so at the
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end of light dependent reaction the energy of sunlight that is received by
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the photosystems or chlorophyll molecule is converted into chemical energy in the
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form of ATP and NADPH these two energy rich molecules that is ATP and NADPH
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will be used in converting carbon dioxide or CO2 to glucose C6 H12 O6 in
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Calvin cycle or C3 cycle and we'll be discussing that in the next video and
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that's it these are the four stages of light dependent reaction of photosynthesis
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remember all these things may be happening simultaneously. I think it is
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better to understand Calvin cycle by knowing the exact reaction that is
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happening. Calvin cycle is also called as C3 cycle, Calvin Benson Bajam cycle or
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CBB cycle reductive bendose phosphate cycle. Let's begin. Starting with the reactions. The first reaction is carbon fixation where carbon dioxide combines
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with RUBP ribulose bi-phosphate in the presence of enzyme rubisco forming a
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three carbon compound. First there is a formation of a short-lived six carbon
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compound then that splits to form a three carbon compound which is three
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phosphoglyceric acid therefore the cycle is also called as C3 cycle. Step
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number one is carbon fixation where carbon dioxide combines with RUBP forming a stable 3 phosphoglyceric acid. Step two is phosphorylation. This step is
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added for better understanding so that what is happening in these reactions
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this 3-phosphoglyceric acid is converted to 1-3-biphosphoglyceric acid a phosphate group is added therefore ATP is required therefore in this step ATP is
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utilized step 3 is reduction in reduction this 1-3-biphosphoglyceric acid is
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converted to glyceroldehyde 3-phosphate acid is converted to aldehyde where NADPH is reduced to NADP and this glyceraldehyde 3-phosphate which is a
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very common metabolite inside the cell is used to synthesize glucose. Two
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glyceraldehyde 3-phosphate molecules are used to make a glucose molecule. Step 4
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is glucose synthesis. Two glyceraldehyde 3-phosphate molecules as it is 3-carbon is used to make a glucose molecule and the step 5 is regeneration of rUPP from
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this glyceraldehyde 3-phosphate here also ATP is utilized for regenerating rUPP now let us see the exact reactions with numbers 6 carbon dioxide molecules
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combines with 6 rubb now we have 36 carbon 6 carbon plus 5 into 6 that is
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30 30 plus 6 36 carbon atom in both these compounds to form three forms
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phosphoglycerate therefore this is a three carbon compound therefore 36 by 3
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12 phosphoglyceric acid will be formed then this 12 phosphoglyceric acid then
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it is converted to 1 3 pi phosphoglycerate or glyceric acid whenever
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there is an addition of phosphate the enzyme is kinase here the enzyme is
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phosphoglycerokinase this is the substrate name. Here 12 ATP is used as 12
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1 3-biphosphoglycerate is formed. Then in the reduction stage the enzyme is
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dehydrogenase, the stryosphosphate dehydrogenase. 12 NADPH is used in this
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step then 12 glyceraldehyde 3-phosphate is formed. Out of this 12 glyceraldehyde
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3-phosphate, 2 glyceraldehyde 3-phosphate is used to make one glucose molecule. As
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glucose is 6 carbon, 2 glyceraldehyde 3-phosphate molecule is required. Now we
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have 10 glyceraldehyde 3-phosphate molecule and that is used for regeneration of
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RUBP 10 glyceraldehyde 3-phosphate that is 30 carbon and it will form 30 by 5
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RUBP is having 5 carbon therefore it will regenerate to form 6 RUBP thus
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completing the cycle. here also 6 ATP is utilized for regeneration. so in total
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18 ATP is utilized for synthesis of a glucose molecule where 12 ATP is
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utilized at the beginning for phosphorylation then 6 ATP for regeneration and 12 NADPH is utilized for the synthesis of a glucose molecule. so this
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is two glyceraldehyde 3-phosphate molecule forming a glucose molecule which is having six carbon. it's better to understand by remembering the exact
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reaction than using some mnemonics or abbreviations. let me repeat once more
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ReBP combines with carbon dioxide forming the first stable compound is 3-phosphoglyceric
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acid then it is phosphorylated to form 1-3-biphosphoglyceric acid then it is
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reduced to glyceraldahide 3-phosphate. two molecules of glyceraldahide 3-phosphate makes a glucose and the rest is used for regeneration of RUBB. the enzymes
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involved in regeneration are transketolase, ribosophate isomerase, phosphoribolokinase. the difference between Calvin cycle and C4 cycle or C3
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cycle versus C4 cycle. so why C3 C4 and CAM? C3 is a normal cycle what's the
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reason for certain plants exhibiting C4 and CAM cycle? the first and the most
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important thing to remember is all plants makes glucose by C3 cycle or
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Calvin cycle and it is a default cycle for the synthesis of glucose. Calvin cycle
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is a cyclic reaction involved in the synthesis of glucose from carbon dioxide
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with the use of ATP and NADPH that is synthesized during the light dependent
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reaction of photosynthesis we have discussed that in detail in the video
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regarding four stages of light dependent reaction of photosynthesis now C4 cycle actually it is an adaptation to survive in dry habitats for two reasons
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to minimize transpiration and also to nullify photo respiration a process that
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involves wastage of energy thereby increasing the photosynthetic efficiency CAM cycle it's an adaptation to live in desert condition and we'll be discussing
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that in the next video so the most important thing is c3 cycle is the cycle
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that is in all plants that is responsible for the synthesis of glucose wheat is a C3 plant and maize is a C4 plant now moving into the differences first difference number one YC4 cycle primary carbon dioxide acceptor and
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enzyme involved in the first step. Let us discuss about the most important enzyme
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in the process that is a Rubisco. This is a Calvin cycle. In C3 cycle carbon
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dioxide combines with RUBP or ribulose bi-phosphate and the enzyme is rubisco ribulose 1,5-biphosphate carboxylase oxygenase. It is having carboxylase activity
34:55
it can bind to carbon dioxide and forming a C3 compound and during the C3 cycle ATP and NADPH
35:03
that is synthesized in the light reaction is utilized and ultimately forming glucose. This
35:08
rubisco is having yet another activity which is the oxygenase activity. If the concentration of
35:15
oxygen is high this rubisco will bind to oxygen rather than carbon dioxide on
35:22
binding of oxygen rubisco forms 2 phosphoglycolate therefore the first stable compound is 2 phosphoglycolate therefore called a C2 cycle then in
35:33
order to regenerate this 2 phosphoglycolate a great amount of ATP and
35:38
NADPH that is you that is synthesized in the light dependent reaction is used
35:42
and the net result is simply the release of carbon dioxide that is why this is
35:47
called as photorespiration just like our respiration oxygen is taken in and
35:52
carbon dioxide is released without the production of sugar or glucose in order
35:57
to regenerate this C2 compound phosphoglycolate phosphoglycolate should pass through three organelles chloroplast peroxisome and mitochondria with the
36:07
expenditure of ATP and NADPH so this cycle is a wastage of NRG with a huge
36:14
expenditure of NRG without having any beneficial aspect so the plants that is
36:21
living in dry condition always tries to avoid this photo respiration that is why
36:27
there is C4 cycle now moving into the differences and this is a C3 cycle or
36:34
Calvin cycle here the first stable compound RUBP combines with carbon dioxide in the presence of enzyme Rubisco forming a 6 carbon short-lived
36:44
intermediate the first stable compound is 3 phosphoglycerate therefore the cycle is called as C3 cycle and the primary carbon dioxide acceptor is RUBP
36:55
rubylose by phosphate that combines with carbon dioxide and the enzyme involved
37:00
is rupees code in C4 cycle carbon dioxide combines with phosphoenol pyruvate or
37:09
PEP forming oxaloacetic acid and it's a C4 compound you can see there are four
37:15
carbons therefore the cycle is called as C4 cycle here the primary carbon dioxide
37:20
acceptor in mesophyll cell is PEP or phosphoenol pyruvate and that is
37:27
converted to oxaloacetate for carbon compound and the enzyme involved is pep
37:34
carboxylase difference number two it's regarding the occurrence C3 cycle this is common very common in wheat potatoes I have been rice etc occur in all plants
37:46
including C4 and camp plants more than 85% of plants are C3 only C3 cycle is
37:52
going on in such plants optimum temperature is 20 to 25 degrees Celsius
37:56
and this cycle works well in environment where there is sufficient water with
38:00
moderate temperature and sunlight in that condition even though there is photorespiration that will not have this plant whereas C4 cycle is and actually
38:10
an adaptation examples include maize sorkum sugarcane millet plants etc and and it occurs in nine approximately 900 species it's an adaptation to reduce
38:20
photorespiration majority are monocots and the C4 plants can grow well in
38:25
environment with limited supply of water or dry habitats and high temperature and
38:30
high sunlight so during high temperature and high sunlight if there is
38:34
photorespiration these plants cannot survive that's why there is a cycle called
38:39
C4 cycle that will nullify the effect of photorespiration now moving into the
38:45
difference number three that is site of carbon dioxide fixation and Calvin cycle in C3 cycle initial carbon dioxide fixation and Calvin cycle everything occurs inside
38:57
the mesophil cells you can see carbon dioxide entering toxin is moving out
39:04
water is also released by transpiration whereas in C4 cycle initial step that is
39:10
initial carbon dioxide fixation takes place in the mesophil cells later it is
39:15
transported into the bundle sheet cell where Calvin cycle occurs therefore initial carbon dioxide fixation and Calvin cycle is separated in space at
39:27
two locations this picture will tell you the details initial carbon dioxide
39:32
fixation by PEP occurs in the mesothold cell then that is converted to malate
39:37
malate is transported to bundle sheet cell where carbon dioxide is decarboxylated
39:43
so that carbon dioxide is made available for Calvin cycle. So in bundle
39:49
sheet cells carbon dioxide is accumulated. Bundle sheet cells acts as a carbon
39:54
dioxide concentrator providing Rubisco with an option of optimum carbon dioxide concentration thereby nullifying or completely avoiding photorespiration or
40:06
the inhibitory effect of oxygen and later this malate is converted to
40:12
pyruvate and later trans converted to phosphoenol pyruvate. Difference number four regarding leaf anatomy. There is no Kranz anatomy in the leaves of C3 plants
40:24
there is a single type of chloroplast vascular bundle that is surrounded by
40:29
bundle sheet cell without chloroplast and the site of photosynthesis is a
40:33
mesophyll cell you can see the green color whereas in C4 cycle there is a
40:38
specific anatomy that is designed for this C4 cycle, vasculature is surrounded
40:44
by bundle sheet cells with chloroplast and that is surrounded by mesophyll cells
40:50
with chloroplast and mesophyll cells are the site of initial carbon dioxide
40:56
fixation and light reaction therefore this site is rich in krana it is having
41:02
well developed krana whereas bundle sheet cells are the site of Calvin cycle or
41:06
light independent reaction or dark reaction therefore this chloroplast is agr or grani is poorly developed in bundle sheet cells therefore there are
41:16
two types of chloroplasts gr in mesophyll cells and agr in bundle
41:21
sheet cells and this anatomy is called as Kranz anatomy this 2d picture will
41:26
give you a better clarity vasculature that is surrounded by bundle sheet cells
41:31
with chloroplast that is further surrounded by mesophyll cells without much space or direct contact with the bundle-seed cells without much space and
41:40
this anatomy is called as Kranz anatomy a bokeh like arrangement. Difference
41:45
number five that is regarding the photosynthetic efficiency and photorespiration. C3 cycle is a cycle that is meant for plants that is that
41:54
that is having sufficient water so photorespiration occurs that reduces the photosynthetic efficiency. 12 NADPH and 18 ATP molecules are required for
42:04
synthesis of one glucose molecule and we have discussed in detail in the last
42:08
video on Calvin cycle so in the C4 cycle C4 cycle is an adaptation thereby the
42:16
photorespiration is completely nullified or absent that increases the photosynthetic efficiency yield up to 50% approximately 50% more efficient than C3 plant C4
42:26
plants are well adapted to survive in dry habitats but for transporting all
42:32
these things malate from mesophyll cell to bundle sheet cells then regeneration
42:37
of this malate to phosphoenol pyruvate ATP is required so per glucose molecule
42:45
12 NADPH and 30 ATP molecules are required in the case of C4 cycle it's the
42:51
cycle is bit expensive as far as ATP is concerned but can avoid photorespiration
42:58
which is much more adverse and that's it interesting topic that is camp cycle in
43:03
plants. Camp cycle is an adaptation of desert plants to survive in water
43:08
deficient environment If you are new to this channel please subscribe and support this channel Moving into the topic starting with camp pathway So this is a desert plant and you can see this mesophyll cells of this plant Suppose
43:24
this is a mesophyll cell of this plant. The major concern of this plant is to
43:32
conserve water. So this pathway allows the plants to conserve water. So let us
43:38
move into the cycle. First step is during nighttime stomata open in camp plants
43:45
Camp plants the stomata is having a speciality which is called as scotoactive
43:50
It can open during nighttime and it can close during daytime. That type of
43:57
stomata is called as scotoactive. Stomata opens during night and carbon dioxide enters and it combines with pep forming oxaloacetic acid in the
44:08
presence of enzyme pep carboxylase just like C4 pathway and that oxaloacetate
44:15
is converted to malic acid and that is transported to vacuole and it is stored
44:19
during nighttime therefore the intracellular acidity increases that is why this phase is called as acidification phase during daytime in
44:31
order to avoid water loss by transpiration, this plants closes its stomata and malic acid is stored in the vacuole and that malic acid is taken out
44:45
and that is decarboxylated to release carbon dioxide. This carbon dioxide runs
44:50
the Calvin cycle, it enters the chloroplast and runs the Calvin cycle and
44:56
this malate is decarboxylated to pyruvate and that is recycled back. So the
45:04
advantage of this pathway is even without opening the stomata during daytime
45:12
Calvin cycle can run using the carbon dioxide that is produced by the
45:20
decarboxylation of malic acid that is stored in the vacuum during night time
45:26
So the point in CAM cycle is that initial carbon dioxide fixation occurs
45:31
during night and Calvin cycle occurs during daytime and both these are
45:38
separated in time and both reactions occurs in mesophyll cells. Here the first
45:44
stable compound just like C4 cycle, here also it is oxyloacetic acid and this
45:50
pathway ensures minimum photorespiration and prevents water loss by transpiration that allows such plants to survive in desert condition. Now why C3
46:03
C4 and CAM pathway? The first and the most important point is all plants makes
46:09
glucose by C3 cycle or Calvin cycle. Calvin cycle as we know it is a cycle
46:16
that is involved in the synthesis of glucose from carbon dioxide with the use
46:20
of ATP and NADPH that is synthesized during light reaction of photosynthesis
46:25
and that is the cycle that is universal to plants for the synthesis of glucose
46:30
whereas there is C4 cycle which is also an adaptation to surviving dry habitats
46:35
that minimizes the wastage of energy by photorespiration thus increases the photosynthetic efficiency of the plants. Then the third pathway is a CAM pathway
46:47
which is called as crecelation acid metabolism cycle as this pathway was
46:51
first observed in the members of family Cressulaceae, it's an adaptation to live
46:57
in desert condition that ensures minimum water loss by transpiration. Now examples
47:03
of camp plants. Examples include pineapple, acabe, cacti, orchid all are examples. Plants that are adapted to live in hot dry desert environment
47:16
approximately 8% of all land plants are camp plants, majority are succulents. The
47:23
advantage of camp plants is photorespiration is very much minimized or suppressed and transpiration rate is very much reduced as stomata opens only
47:33
at nighttime. Hope you understand the concept. Thank you so much for your
47:40
support. You are with biologicsums4u.com

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