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C3 Plant
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C4 Plant
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Only C3 cycle is found
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Both C4 and C3 cycles are found.
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The efficiency of CO2 absorption at low concentration is far less and hence, they are less efficient.
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The efficiency of CO2 absorption at low concentration is quite high and hence, they are more efficient plants.
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The CO2 acceptor is Ribulose-1, 5-diphosphate.
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The CO2 acceptor is phosphoenol pyruvate.
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The first stable product is phospho glyceric acid (PGA).
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Oxaloacetate (OAA) is the first stable product.
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Plants show one type of chloroplast (monomorphic type).
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Plants show dimorphic type of chloroplast. The chloroplast of parenchymatous bundle sheath is different from that of mesophyll cells (dimorphic type). The chloroplasts in bundle sheath cell are centripetally arranged and lack grana. Leaves show Kranz type of anatomy.
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In each chloroplast, two pigment systems (Photosystems I and II) are present.
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In the chloroplasts of bundle sheath cells, the photosystem II is absent. Therefore, these are dependent on mesophyll chloroplasts for the supply of NADPH + H+.
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The Calvin cycle enzymes are present in mesophyll chloroplast. Thus, the Calvin cycle occurs.
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Calvin cycle enzymes are absent in mesophyll chloroplasts. The cycle occurs only in the chloroplasts of bundle sheath cells.
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The CO2 compensation point is 50-150 ppm CO2.
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The CO2 compensation point is 0-10 ppm CO2.
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Photorespiration is present and easily detectable.
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Photorespiration is present only to a slight degree or absent.
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The CO2 concentration inside leaf remains high (about 200 ppm).
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The CO2 concentration inside the leaf remains low (about 100 ppm).
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The 13C/12C ratio in C-containing compounds remains relatively low (both 13CO2 and 12CO2 are present in air).
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The ratio is relatively high, i.e. C4 plants are more enriched with 13C than C3 plants.
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Net rate of photosynthesis in full sunlight (10,000 – 12,000 ft. c.) is 15-25 mg. of CO2 per dm2 of leaf area per hour.
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It is 40-80 mg. of CO2 per dm2 of leaf area per hour. That is, photosynthetic rate is quite high. The plants are efficient.
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The light saturation intensity reaches in the range of 1000-4000 ft. c.
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It is difficult to reach saturation even in full sunlight.
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Bundle sheath cells are unspecialized.
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The bundle sheath cells are highly developed with unusual construction of organelles.
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The optimum temperature for the process is 10-25°C.
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In these plants, it is 30-45°C and hence, they are warm climate plants. At this temperature, the rate of photosynthesis is double than that is in C3 plants.
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18 ATPs are required to synthesise one glucose molecule.
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30 ATPs are required to synthesise one glucose molecule.
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