Question

Discuss similarities and differences between C3, C4, and CAM plants using examples of each. How does the environment each type is found in relate to their respective differences in photosynthesis?

Answer 1

	THE CALVIN CYCLE (C3 CYCLE)	THE C4 PATHWAY/ BETA CARBOXYLATION PATHWAY/ HATCH AND SLACK PATHWAY	CRASSULACEAN ACID METABOLISM (CAM)
1	C3 pathway occurs in all photosynthetic plants, even in C4 plants.	C3 pathway occurs in bundle sheath surrounding the vascular bundles. C4 pathway occurs in mesophyll. This leaf has anatomical specialization called Kranz Anatomy. Bundle sheath cells have agranal choloroplasts. (No granam). The mesophyll cells of C4 leaf have grana in their chloroplast.	It is exactly like C4 pathway. C3 and C4 cycle are separated by time. Both carboxylations occur in mesophyll only.
2	Chloroplast dimorphism is absent	Chloroplast dimorphism is present	Chloroplast dimorphism is absent
3	CO2 is used for carboxylation of RUBP (Ribulose-1,5-Bisphosphate)	CO2 is used for carboxylation of RUBP and PEP also.	CO2 is used for carboxylation of RUBP and PEP also.
4	The above reaction is catalyzed by enzyme RUBP carboxylase	RUBP carboxylase and PEP case are two enzymes are used for carboxylation	RUBP carboxylase and PEP case are two enzymes are used for carboxylation
5	Reduction step uses two molecules of ATP and two molecules of NADPH for fixing one molecule of CO2 Therefore, for fixing six molecules of CO2, 12 molecules of ATP and 12 molecules of NADPH are required.	Reduction step uses two molecules of ATP and two molecules of NADPH for fixing one molecule of CO2 Therefore, for fixing six molecules of CO2, 12 molecules of ATP and 12 molecules of NADPH are required.	Reduction step uses two molecules of ATP and two molecules of NADPH for fixing one molecule of CO2 Therefore, for fixing six molecules of CO2, 12 molecules of ATP and 12 molecules of NADPH are required.
6	Regeneration of the RUBP requires one ATP molecule is required. For regeneration of six molecules, 6 ATP are required.	Regeneration of the RUBP requires one ATP molecule is required. For regeneration of six molecules, 6 ATP are required.	Regeneration of the RUBP requires one ATP molecule is required. For regeneration of six molecules, 6 ATP are required.
7	Therefore, to fix 6 CO2 and produce one glucose, 18 ATP and 12 NADPH are required.	For Hatch and Slack cycle, 12 ATP extra are required to regenerate 6 molecules of PEP (2 x 6 = 12). Therefore, for Calvin cycle, 18 ATP and 12 NADPH are required. Total 30 ATP and 12 NADPH are required to form one glucose molecule.	Energetics of C4 cycle – 30 ATP and 12 NADPH are required to make one glucose molecule. Therefore, for Calvin cycle, 18 ATP and 12 NADPH are required. Total 30 ATP and 12 NADPH are required to form one glucose molecule.
8	The enzyme is RuBiSCO (Rubilose Bisphosphate Carboxylase Oxygenase) only is required	The enzyme is PEP carboxylase (PEP case) and RuBiSCO (Rubilose Bisphosphate Carboxylase Oxygenase) are required	The enzyme is PEP carboxylase (PEP case) and RuBiSCO (Rubilose Bisphosphate Carboxylase Oxygenase) are required
9	The first acceptor of CO2 is RUBP	The first acceptor of CO2 is PEP	The first acceptor of CO2 is PEP
10	The first stable product is PGA (Phospho Glyceric Acid)	The first stable product is malic acid (4 carbon). Malic acid in the bundle sheath and same C3 cycle in mesophyll	The first stable product is malic acid in the mesophyll.
11	RUBP carboxylation takes place in mesophyll of the leaf.	PEP carboxylation takes place in mesophyll and RUBP carboxylation in bundle sheath cells	Both carboxylation reactions occur in mesophyll.
12	Only Calvin cycle takes place in C3 plants	Hatch and Slack in mesophyll and C3 cycle in bundle sheath take place	Both cycles take place in mesophyll.
13	This takes place in most of the normal conditions	This pathway occurs in plants of tropical and sub-tropical regions of the world. The temperature range is between 30-45 degrees centigrade.	This occurs in xeric conditions
Examples	Mango, Neem, etc	Maize, sugarcane, sorghum, pearl-millet, amaranthus	It is observed in succulents, xeric plants. Crassulaceae (Bryophyllum, Kalanchoe, Sedum), Cactus (Opuntia), Orchid (Portulaca) and Pine-apple
14	These plants temperature optimum is 20-25 degrees centigrade	These plants are better equipped to withstand drought and are able to maintain active photosynthesis even under water-stress conditions.	These plants temperature optimum is above 40 degrees centigrade
15		*C4 pathway is biologically more evolved than C3 pathway
16	One carboxylation takes place	Two carboxylations take place	Two carboxylations take place
			The most characteristic feature of these plants is their stomata remain open in the night, in dark, called Scotoactive and close during the day in light. It is an adaptation to reduce the loss of water during day time as the stomata are closed during day time.
17	This needs high CO2 concentration	This takes place in less CO2 concentration as well	This takes place in less CO2 concentration as well
18	Photo-respiration is present	Photo-respiration is absent	Photo-respiration is absent
19	While C3 plants respond to increased CO2 concentration and saturation, is seen only beyond 450µ 1 L-1	C4 plants show saturation at about 360µ1L-1