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The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
The C4 pathway
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The C4 pathway

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This was my presentation on the C4 pathway which includes the portions for 11th grade i hope it helps ppl for better understanding :) …

This was my presentation on the C4 pathway which includes the portions for 11th grade i hope it helps ppl for better understanding :)

I would like to say special Thanks to my biology teacher Mrs.Alarmelu for her outstanding support and her amazing effort in helping me to make this presentation a success

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  • 1. How are C4 plants differentfrom C3 plants?C4 plants are special :- They have a special type of leaf anatomy They tolerate higher temperatures They show a response to high light intensities They lack a process called photorespiration They have greater productivity of biomass.
  • 2. What happens in Hatch andSlack Pathway? In this pathway, Phospho-enol-pyruvate (PEP) combines withatmospheric CO2 in the presence of catalyst enzyme Phospho-enol-pyruvate carboxylase (PEP CASE) to form Oxaloaceticacid (OOA). This reaction occurs in the mesophyll cell of the plants. OOA is then converted into another 4 carbon compound Malicacid which is transported into bundle sheath cells frommesophyll cells. In the bundle sheath cells, the malic acid gets decarboxylated orbreaks down to release CO2 and a 3 carbon molecule (PyruvicAcid). The CO2 liberated is used for Calvin cycle in the bundle sheathcells and the 3 carbon molecule (Pyruvic Acid) is transportedback to the mesophyll cell, where it is used in the regenerationof PEP. Thus completing the cycle.
  • 3. Photorespiration
  • 4.  In C3 plants some O2 does bind to RuBisCO and hence CO2 fixationis decreased. So the RuBP instead of being converted to 2 molecules of PGA bindswith O2 to form 1molecule of phosphoglycerate andphosphoglycolate in a pathway called Photorespiration. In the photorespiratory pathway, there is neither synthesis ofsugar nor of ATP but results in the release of CO2 with theutilization of ATP. Therefore, photorespiration is regarded as a wasteful process. In C4 plants photorespiration does not occur. This is because theyhave a mechanism that increases the concentration of CO2 at theenzyme site. This results in increasing the intracellular concentration of CO2,which ensures that the RuBisCO functions as carboxylase andminimize the oxygenase activity.
  • 5. Photosynthesis occur under the influence of manyfactors both internal(plant) and external factors.The plant/ internal factors include :-The number, size, age and orientation of leavesMesophyll cells and chloroplastsInternal CO2 concentration & the amount ofchlorophyllThese factors depend on the genetic predisposition andthe growth of the plant.
  • 6. The external factors would include the availability of the following:-SunlightCO2 concentrationTemperatureWaterAll these factors simultaneously affects the rate of photosynthesis.Since all these factors interact and affect photosynthesis or CO2fixation, one of these factors are the major cause or is the one thatlimits the rate of photosynthesis. So at any point the rate will bedetermined by the factors available at sub-optimal levelsWhen several factors affect any bio-chemical process, BlackmansLAW OF LIMITING FACTORS comes into effect .
  • 7. The law states that :-If a chemical process is affected by more thanone factor, then its rate will be determined bythe factor which is nearest to its minimalvalue: it is the factor which directly affects theprocess if its quantity is changed .Frederick FrostBlackmanFor example :-Despite the presence of a green leaf and optimal light and CO2 conditions, theplant may not photosynthesise if the temperature is low . If this leaf gets theoptimal temperature it will start photosynthesizing.
  • 8.  There is a linear relationship between incident light andCO2 fixation rates at low light intensities. At higher lightintensities gradually the rate does not show furtherincrease as other factors become limiting. The light saturation occurs at 10% of full sunlight. Soexcept for plants in shades or in dense forests, light israrely a limiting factor in nature. Also increase in incident light beyond a point causes thebreakdown of chlorophyll and a decrease inphotosynthesis.
  • 9. AFFECTSOFCARBON DIOXIDECONCENTRATION
  • 10. Carbon dioxide is the major limiting factor forphotosynthesis. The concentration of CO2 is very low inatmosphere (0.03% to 0.04%). Increase in concentrationupto 0.05% can cause an increase CO2 fixation rates.Beyond this, the levels can become damaging over longerperiods.The C3 and C4 plants respond differently to CO3concentrations :-At high light conditions none of the group responds tohigh CO2 conditionsAt low light conditions both groups show increase inthe rates of photosynthesis.The C4 plants show saturation at about 360µ1L-1 whileC3 responds to increase CO concentration andsaturation for them is seen only at 450 µ1L-1 and thuscurrent availability of CO2 levels is limiting to the C3plants.
  • 11. The dark reactions being enzymatic aretemperature controlled. Though light reactionsare also temperature sensitive they are affectedby temperature to a much lesser extent.The C4 plants responds to higher temperatureand shows higher rate of photosynthesisC3 plants have a much lesser temperatureoptimum.The temperature optimum for photosynthesis ofdifferent plants depends upon the habitant theyare adapted to.For example :- Tropical plants have a highertemperature optimum than the plants adaptedto temperate climates.
  • 12. Though water is one of the reactants in thelight reaction, the effect of water as a factoris more on the plant, rather than directly onphotosynthesis.Water stress causes the stomata to closereducing the CO2 availability.Water stress also makes leaves wilt, thusreducing the surface area of the leaves andtheir metabolic activity as well

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