NEET Practice Questions (MCQs) with Answers & Solutions

Emerson performed photosynthetic experiment on Chlorella. He provided monochromatic light of more than 680 nm and observed decrease in rate of photosynthesis known as red drop. 

Later he provided synchronised light of 680 nm and 700 nm and observed increase in rate of photosynthesis, known as enhancement effect. This experiment led to discovery of two photosystems PS-I and PS-II operating in photosynthesis. 

Proton concentration is higher in the lumen of thylakoid due to photolysis of water. H⁺ pumping and NADP reductase activity which occurs in stroma of the chloroplast. 

Photolysis of water during photosynthesis evolve nascent oxygen in the presence of manganese, calcium and chloride ions.

In chloroplasts, the stacked membranous structures formed by the flattened thylakoid discs are called grana. These grana are connected by unstacked thylakoid membranes called stroma lamellae, which are present in the stroma region of the chloroplast.

Anoxygenic photosynthesis (in which O₂ is not released) is seen in Rhodospirillum, a purple non-sulphur bacteria. It helps an organism to trap light energy and store it as chemical energy.

Other than this anoxygenic photosynthesis commonly occurs in purple non-sulphur bacteria, green sulphur/non-sulphur bacteria heliobacteria etc. 

Photorespiration required three cell organelles in sequence of chloroplast, peroxisome and mitochondria.

The use of radioactive ¹⁴C by Melvin Calvin in algal (Chlorella) photosynthesis studies led to the discovery that the first CO₂ fixation product was a 3-carbon organic acid. The first product indentified was 3-phosphoglyceric acid (PGA).

C₄-plants are more efficient in photosynthesis than C₃ -plants but use more energy. They possess the larger number of chloroplasts in the leaf cells. In the leaves of C₄-plants, the vascular bundles are surrounded by bundle sheath of larger parenchymatous cells, which in turn are surrounded by mesophyll cells. Chloroplast in bundle sheath cells are larger and always contain grana, whereas chloroplasts in mesophyll cells are smaller. 

Cyclic-photophosphorylation involves only pigment system-I. When the photons activate PS-I, a pair of electrons are raised to a higher energy level. They are captured by primary acceptor, which passes them on to ferredoxin, plastoquinone, cytochrome complex, plastocyanin and finally back to reaction centre of PS-I, i.e., P₇₀₀. At each step of electron transfer, the electrons lose potential energy. Their trip down hill is caused by the transport chain to pump H⁺ across the thylakoid membrane. The proton gradient thus established is responsible for forming ATP (2 molecules). No reduction of NADP to NADPH + H⁺.

C₄ -plants show Kranz anatomy. In the leaves of C₄ -plants, the vascular bundles are surrounded by bundle sheath of parenchymatous cells, which in turn are surrounded by mesophyll cells. Chloroplasts in bundle sheath cells are larger and always contain grana whereas chloroplasts in mesophyll cells are smaller. The C₄ -plants are photosynthetically more efficient than C₃ -plants because they have more chloroplasts. 

Photorespiration takes place only in C₃ -plants. It occurs in chlorophyllous tissues. At high temperature and high oxygen concentration the affinity of RuBP carboxylase for CO₂ decrease and for O₂ increases. 

Photosynthesis takes CO₂ and release O₂, while respiration utilizes O₂ and release CO₂. If the light factor is saturating, there will be certain concentraton of CO₂ in the atmosphere at which the rate of photosynthesis will be equal to rate of the respiration. This is called carbon dioxide compensation point. C₄ -plants have very low CO₂ compensation point.