Test: Photosynthesis - 2 - NEET MCQ

Carbonation is the addition of carbon dioxide to an acceptor. Photosynthetic carboxylation requires ribulose-1, 5-biphosphate or RuBP as acceptor of carbon dioxide and RuBP- Carboxylase oxygenase as enzyme in C₃ plants In C₄ plants, initial fixation of CO₂ occurs in mesophyll cells, The primary accept or of CO₂ is phosphoenol pyruvate which combines with CO₂ in presence of PEP carboxylase to form oxaloacetic acid or oxaloacetate. So, the correct answer is 'RuBP carboxylase and PEP carboxylase'.

Topic in NCERT: Carboxylation

Line in NCERT: "carboxylation is the fixation of co2 into a stable organic intermediate. carboxylation is the most crucial step of the calvin cycle where co2 is utilised for the carboxylation of rubp. this reaction is catalysed by the enzyme rubp carboxylase which results in the formation of two molecules of 3-pga."

Biosynthetic phase (dark or Blackman's reaction) catalyses assimilation of CO2 to carbohydrates. The reactions are called carbon reactions. They occur in stroma of chloroplasts. The reactions do not require light. Instead assimilatory power (ATP and NADPH ) produced during photo chemical phase is used in fixation and reduction of carbon dioxide. All the enzymes required for the process are present in the matrix or stoma of the chloroplast. So, the correct answer is 'it does not directly depend on light energy'.

Topic in NCERT: Photosynthesis in higher plants

Line in NCERT: "the latter are not directly light driven but are dependent on the products of light reactions (atp and nadph). hence, to distinguish the latter they are called, by convention, as dark reactions (carbon reactions). however, this should not be construed to mean that they occur in darkness or that they are not light-dependent."

In C₃ cycle for the fixation of every carbon dioxide molecule, the reduction and regeneration of steps require around 3ATP & 2 NADPH2 molecules.
So, the correct option is '3 ATP and 2NADPH₂'.

Topic in NCERT: Photosynthesis in higher plants

Line in NCERT: "hence for every co2 molecule entering the calvin cycle, 3 molecules of atp and 2 of nadph are required."

Calvin used the radioactive isotope of carbon (14C) of Chlorella. He observed that after second exposure of Chlorella in presence of 14 CO2, the radioactive isotope of carbon was found mainly in 3-phosphoglyceric acid (PGA). This clearly indicated that the three carbon compound 3- phosphoglyceric acid was the first stable product photosynthesis and the carbon from the CO2 is fixed in the preparation of the photosynthates.
Hence, the correct answer is 'PGA'.

Topic in NCERT: Photosynthesis in higher plants

Line in NCERT: "the first product identified was 3-phosphoglyceric acid or in short pga."

In fixation, the first stage of the Calvin cycle, light-independent reactions are initiated; CO₂ is fixed from an inorganic to an organic molecule. In the second stage, ATP and NADPH are used to reduce 3-PGA into G3P; then ATP and NADPH are converted to ADP and NADP⁺, respectively.

Topic in NCERT: The section name is "the calvin cycle".

Line in NCERT: "reduction, during which carbohydrate is formed at the expense of the photochemically made atp and nadph; and (3) regeneration during which the co2 acceptor ribulose-1,5-bisphosphate is formed again so that the cycle continues."

Calvin cycle begins with fixation of CO₂ into 3 C sugar by the process of carboxylation. RUBISCO, present in the chloroplast stroma catalyzes carboxylation of ribulose-1, 5-biphosphate (RuBP) followed by immediate splitting of unstable product into 3-phosphoglyceric acid. Carboxylation is followed by a series of reduction reactions wherein 3 C compound 3-phosphoglyceric acid is reduced into 3 C compounds glyceraldehydes 3-phosphate (G3P); the reduction reactions are energized by ATP and NADPH serve as an electron donor. Three turns of Calvin cycle obtains 6 molecules of G3P, out of which one is used for glucose formation and rest are used in regeneration phase.  The last phase of Calvin cycle, the regeneration phase ensures the continuous supply of RuBP for carboxylation and regenerates it using G3P. Thus, the correct answer is option D.

Topic in NCERT: The section name from which the line is given is "the calvin cycle."

Line in NCERT: "the calvin cycle proceeds in three stages: (1) carboxylation, during which co2 combines with ribulose-1,5-bisphosphate; (2) reduction, during which carbohydrate is formed at the expense of the photochemically made atp and nadph; and (3) regeneration during which the co2 acceptor ribulose-1,5-bisphosphate is formed again so that the cycle continues."

Melvin Calvin, a biochemist who detected the crucial phase of photosynthesis that now bears his name and won him a Nobel Prize in 1961, died on Wednesday at Alta Bates Hospital in Berkeley, Calif. He was 85.
So, the correct option is 'Calvin'.

Topic in NCERT: Melvin calvin

Line in NCERT: "the mapping of the pathway of carbon assimilation in photosynthesis earned him nobel prize in 1961."

Carbon dioxide fixation occurs during Calvin cycle. There are three stages in the process of Clavin cycle as carboxylation, reduction, and regeneration. One turn of Calvin cycle fixes one molecule of carbon dioxide. There are 6 atoms of carbon required for the synthesis of one glucose molecule. Hence, to produce one molecule of hexose sugar, six turns of Calvin cycle are required. Thus, the correct answer is option A.

Topic in NCERT: The calvin cycle

Line in NCERT: "to make one molecule of glucose 6 turns of the cycle are required."

In Photosystem I, the reaction center chlorophyll a has an absorption peak at 700 nm, called P700, and in Photosystem II, the reaction center chlorophyll a has an absorption peak at 680 nm, called P680. This distinction is crucial for the functioning of the light reactions in photosynthesis.

Topic in NCERT: Photosynthesis in higher plants

Line in NCERT: "in ps i the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called p700, while in ps ii it has absorption maxima at 680 nm, and is called p680."

The light-harvesting complexes (LHC) are made up of pigments that absorb different wavelengths of light, thus enhancing the efficiency of photosynthesis. These pigments help in capturing light energy and transferring it to the reaction centers, where the actual photochemical reactions occur.

Topic in NCERT: Roles various pigments play in photosynthesis

Line in NCERT: "these pigments help to make photosynthesis more efficient by absorbing different wavelengths of light."