The difference between C3 and C4 plants:
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1: The first substance made in C3 is a three-carbon substance called 3-phosphoglyceric acid (PGA).
If the first substance produced in C4 plants is a four-carbon substance called oxaloacetate, that is why we call them C3 and C4, which means that their naming is based on the type of production of the primary substance.
2: C4 plants have Kranz anatomy, but C3 plants do not. The chloroplast that is inside the vascular sheath in C3 plants is called Kranz’s anatomy.
3: Starch is made and stored in the mesophyll cells of C3 plants, but in C4, only four-carbon acids are formed in the mesophyll of the leaf and then transferred to the vascular sheath cells (bundle sheet) where starch is made and stored. Starch is made and stored in C3 in the leaf mesophyll and in C4 in the vascular sheath.
4: Vascular sheath chloroplasts are larger and less developed than the chloroplasts of leaf mesophyll cells, that is, vascular sheath chloroplasts have a higher ratio of chlorophyll a to b and are closer to the cell membrane wall.
Chloroplasts in C4 plants are closer to the cell wall.
5: PEPc and RUBPc (rubisco) enzymes are active in C4 plants, but only RUBPc is present in C3 plants.
6: In C4 plants, the Rubisco enzyme (in the Kelvin cycle) is in the vascular sheath and the PEPc enzyme (in the Hash and Selk cycle) in the leaf mesophyll, while in C3, the Rubisco enzyme is active in the leaf mesophyll.
7: The affinity of PEPc enzyme to Co2 is several times that of Rubisco enzyme, for this reason, in C4 plants where PEPc enzyme is present, they are more efficient in very low concentrations of CO2 and are able to carry out photosynthesis. Unlike RUBPc, PEPc is not sensitive to O2.
8: The speed of photosynthesis especially in high light intensity in C4 plants is much higher than in C3 plants. The speed of photosynthesis in low light intensity is higher in C3 plants, while in C3 plants one third of the natural sunlight is enough.
9: In C4 plants, two more ATP molecules are needed for PEPc enzyme activation and Co2 stabilization than C3 plants, so the energy yield in C4 plants is lower.
C3 plants need 3 ATP molecules and 2 NADPH molecules to stabilize each Co2 molecule, but C4 plants need 2 more ATP molecules in addition to them.
10: The amount of Rubisco enzyme in C4 plants is less than C3, about 10%.
11: C4 plants adapt to hot and dry to hot and humid conditions, but C3 plants need cold and humid to hot and humid areas. At a temperature lower than 20 degrees, the photosynthesis of C4 plants is lower than C3.
12: Photosynthesis in C4 plants is not sensitive to the amount of oxygen. (from 2% to 21%).
13: In C4 plants, photorespiration is either absent or very limited, but in C3 plants, part of the photosynthetic material is wasted through this process.
This is one of the reasons for the higher photosynthetic efficiency of C4 compared to C3. The compensation point of Co2 in C4 plants is much lower, around 1-5 PPM.
14: The ratio of chlorophyll a in C4 is more than C3.
15: C3 plants, saturation of Co2 fixation speed occurs at a concentration of 500 PPM, but C4 at a much lower concentration of 150 PPM.
16: The light consumption efficiency of C4 plants is higher than C3 plants.
This post is written by mojtabash72