Photosynthesis in Higher Plants Test - 24

There are different photosynthetic pigments like chlorophylls, carotenoids and biliproteins. Biliproteins are called as green chromoproteins. These are found in many insects like grasshoppers. Phycobilins are light-capturing chromoproteins present in cyanobacteria and in the chloroplasts of red algae. 

Chlorophyll is the molecule which gets excited on absorbing a photon. It moves rapidly to the reaction center of the photosystem I, where it transfers its extra energy to an electron, which is then expelled from the reaction center and is accepted by the first member of a chain of electron carriers and ultimately reaches $$NADP^+$$, reducing it to NADPH. The reaction center has lost an electron and this "electron hole" is filled by stripping electrons from water, which leaves hydrogen ion ($$H^+$$) and molecular oxygen ($$O_2$$). The pathway of electrons from water to $$NADP^+$$ has "Z" shape when diagrammed and is referred to as the Z-Scheme. So, the correct answer option C.

In blue-green algae, photosynthesis occurs in photosynthetic lamellae. Blue-green algae have folds on their external membranes that function in photosynthesis called as photosynthetic lamellae in which it contains photosynthetic pigments. Chloroplasts, chromatophores, and chromoplasts are present in blue-green algae but do not involve in photosynthesis. 

Photosynthetic bacteria are a unique species of microorganisms, that use the sun as a source of energy. Bacteria contain a similar compound called as bacteriochlorophyll, which allows them to  photosynthesize. So, the correct answer is option B. 

The Calvin cycle is a metabolic pathway found in the stroma of the chloroplast in which carbon enters in the form of $$CO_2$$ and leaves in the form of sugar. The cycle spends ATP as an energy source and consumes $$NADPH_2$$ as reducing power for adding high energy electrons to make the sugar. Melvin Ellis Calvin was an American chemist most famed for discovering the Calvin cycle along with Andrew Benson and James Bassham, for which he was awarded the 1961 Nobel Prize in chemistry.

Melvin Calvin, Andrew Benson, and James A. Bassham elucidated the enzyme catalyzed the reaction of photosynthesis (dark reactions) in the early 1950s and were awarded Nobel prize for the same. Exposure of photosynthesizing algae to radioactive carbon dioxide was followed by tracing the fate of a radioactive carbon atom. It was shown that the carbon first binds to a molecule of ribulose 1,5-bisphosphate (RuBP), then immediately splits, forming two molecules of phosphoglycerate (PGA). 

Chlorophyll is a green pigment found in cyanobacteria and the chloroplasts of algae and plants. Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to absorb energy from light. Chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. Chlorophyll was first isolated by Joseph Bienaime Caventou and Pierre Joseph Pelletier in 1817. The presumed size of a chlorophyll molecule, which has a head and tail are 15X $$15 A^{0}$$ and $$25 A^{0}$$ respectively.

The plants such as sugarcane and maize which are adapted to dry tropical regions have an additional pathway of carbon dioxide fixation known as $$C_4$$ pathway. These plants can absorb $$CO_2$$ even from a much low $$CO_2$$ concentration when the $$C_3$$ plants fail to avail. Thus, $$C_4$$ plants can perform a high rate of photosynthesis even when the stomata are nearly closed. They also maintain a high rate of photosynthesis under conditions of water shortage where the $$C_3$$ plants would stop photosynthesis. Presence of excess $$O_2$$ in the surrounding has no inhibitory effect on $$C_4$$ pathway because the enzyme PEP- carboxylase which is the primary acceptor of $$CO_2$$ is insensitive to $$O_2$$ whereas in case of $$C_3$$ plants RUBISCO is sensitive to $$O_2$$ and starts combining with oxygen instead of $$CO_2$$ and thus starts photorespiration. Photorespiration inhibits the rate of photosynthesis in these plants. On the other hand, photorespiration is absent in $$C_4$$ plants which are of great advantage to them and helps in conserving water. 

Chlorophyll is a pigment, which is structurally similar to and produced through the same metabolic pathway as other porphyrin pigments such as heme. At the center of the porphyrin is a magnesium ion.