C4 photosynthesis

 What is Photosynthesis?

   Photosynthesis is defined as *The process by which green plants prepare there food by using CO2 and water in the presence of sunlight and photosynthetic pigment.

Types of photosynthesis:

There are two types of photosynthesis on the base of trophical climate chain .

1-C3 photosynthesis: In this type of photosynthesis first stable product formed is 3 carbon compound called as 3-Phosphoglyceric acid.

2-C4 photosynthesis: In this type of photosynthesis first stable product is formed is 4 carbon compound called as Oxaloacetate.

we explained C3 photosynthesis in previous blogs in detail,now in this blog we will study the C4 photosynthesis in detail;

C4 PHOTOSYNTHESIS:

  There are some plants growing in hot and dry condition produce 4 carbon compound as first stable product called as Oxaloacetate in carbon fixation of dark reaction(calvin cycle).

Explaination:

  Some plants which grow in trophical climate have an adaptation to the problem of photorespiration(the process in which oxygen combine with RUBP in presence of sunlight and produce carbon dioxide).Theese plants have an additional pathway in light independent phase of photosynthesis besides calvin cycle called as HATCH-SLACK CYCLE(also called as malate aspartate pathway).In this pathway phosphoenol pyruvate (PEP) is used instead of RUBISCO to fix CO2 to phospoenol pyruvate ( a 3 carbon molecule),as the result is oxaloacetate(a 4 carbon molecule).

The C4 photosynthesis takes place in CYTOPLASM of Mesophyll cells.

    PEP  + CO2   + PEPcarboxylase  = OXALOACETATE (4 carbon molecule).

C4 PATHWAY:

  In C3 plants Chloroplasts are present only in mesophyll cells of leaf.

 However ,In C4 plants Chloroplasts present in both mesophyll cells and in bundle sheath cell.

 In C3 plants the mesophyll cells carries out calvin cycle by fixing CO2 and producing Glucose.

While In C4 pathway the mesophyll cells only fix CO2 by using PEPCO enzyme while bundle sheath cells carry out Calvin cycle and produce Glucose.

              PEP + CO2 + pepco enzyme = Oxaloacetate(4 carbon compound)

          Oxaloacetate + ATP+NADH2 = MALATE (reduced) This step occurs in mesophyll cells.

     MALATE (reduced)  Convert into PEP in bundle sheath cell and produce CO2.

In C4 plants the rate of photosynthesis remain high even when the stomata is closed and temprature is high.

The rate of CO2 fixation is also remain high as compared to C3 plants.

C4 cycle is basically an adaptability of C4 plants to carry out CO2 fixation in dry and hot condition and to reduce the rate of photorespiration.

IMPORTANT MCQS IN THIS TOPIC:

1-First stable product of C3 plants is :

Answer: 3-Phosphoglyceric acid (3 carbon compound)

2-First stable product of C4 plants is :

Answer: Oxaloacetate (4 carbon molecule)

3-C4 plants contain _Enzymes ;

Answer: Both Rubisco and Pepco enzymes

4-Rubisco can act as :

Answer: Both oxygenase and carboxylase

5-Pepco enzyme can act as :

Answer: Carboxylase

6-The most abundant protein in nature is:

Answer: Rubisco

7-The additional pathway in C4 plants is called:

Answer: HATCH-SLACK CYCLE or MALATE ASPARTATE PATHWAY

8-In_Plants rate of CO2 fixation is high :

Answer: C4

9-In C4 plants the dark cycle occurs in:

Answer: Bundle sheath cell

10-In C3 plants calvin cycle occurs in _cell:

Answer: Mesophyll cells

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