31 Years NEET Previous Year Questions: Photosynthesis - 3 - NEET MCQ

 C₄ cycle was worked out by Hatch and Slack (1966). C₄ cycle occured in C₄ plants.

The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis. Oxygen comes from photolysis of water was verified by Ruben & Kamen (1941).

Algae are the most efficeint photosynthesizing organisms.

The primary CO₂ acceptor in C₃ plants is Ribulose-1, 5-diphosphate (RuBP) which forms a 3 carbon compound 3-phosphoglyceric acid.

Maize, Sugarcane, Sorghum, Atriplex, Panicum are examples of C₄ plants.

Translocation of organic solutes occur through sieve tubes in the form of sucrose. Transportable form of sugar is sucrose.

Chlorophyll a is found in all photosynthetic plants except bacteria. Hence, it is termed as universal photosynthetic pigment.

Depending upon their colour, plastids are of three main types – leucoplasts, chromoplasts and chloroplasts.

Photosystem II is a photosynthetic pigment system that is located in the appressed part of grana thylakoids.

In C₄ plants, the primary acceptor of CO₂ is phosphoenol pyruvate. It combines with carbon dioxide in the presence of PEP carboxylase to form oxalo-acetic acid in mesophyll cells.

Electrons provide energy for the formation of ATP in photosynthesis and respiration.

In PSI, when the electron passes from ferredoxin and plastoquinone, the electron loses sufficient energy to form ATP from ADP and inorganic phosphate.

 According to law of limiting factors given by Blackman, when a process depends upon a number of factors which are separate, the rate of the process is limited by the pace of the slowest factor. Rate of yield is dependent on light as photosynthesis is dependent on light. 

During monsoon, the light is dim and so this reduces rate of photosynthesis and hence yield

In 1954-55 Calvin traced the pathway of carbon fixation by using radioactive isotope method by using ¹⁴CO₂ and gave the Calvin cycle.

Dark reaction occurs in the stroma or matrix of chloroplasts. It is independent of light but depends on the products of light reaction (ATP and NADPH– assimilatory process).

Photosynthetic pigments occur on photosynthetic thylakoids of chloroplasts. A stack of thylakoids is called granum.

The primary acceptor of CO₂ in C₄ plants is phosphoenol pyruvate or PEP. PEP in mesophyll cells combine with CO₂ and converted into 4 carbon compound Oxaloacetic acids by PEP carboxylase. In C₃ plant Ribulose 1, 5–diphosphate is primary acceptor of CO₂.

C₄ plants have a characteristic leaf anatomy called kranz anatomy with two distinct choloroplast containing cells mesophyll and bundle sheath cells.

C₄ cycle occurs in C₄ plants like sugarcane, maize. C₄ cycle provides a more efficient way of CO₂ fixation than C₃ cycle and hence give more productivity. Rest are C₃ plants.

Phytoplanktons (algae) of oceans are the highest producers of organic matter.

C₄ plants are specialised plants for better CO₂ assimilation found in hot environment. They have a characteristic leaf anatomy called kranz anatomy showing two distinct choloroplast containing cells mesophyll and bundle sheath cells. Mesophyll cells are located very near to bundle sheath cells and are the site for C₄ cycle i.e. CO₂ is first fixed as a 4 carbon compounds oxalocetic acid by the action of PEP carbooxylase. The second carboxylation event occur in stroma of chloroplast of bundle sheath cell through C₃ cycle.

Light dependent uptake of O₂ and release of CO₂ in C₃ photosynthetic cell is called photorespiration. Glycolate (Glycolic acid) is the chief metabolite of photorespiration and also its substrate. Other important metabolities are the amino acids glycine and serine. But phosphoglyceric acid (PGA) is a lipid and is not substrate of photorespiration.

Chlorophyll has a tetrapyrrole porphyrin ring as head (15 × 15Å) and a long hydrocarbon tail called phytol (20 Å) tail  attached to the ring structure.

Photosynthesis is completed in two phases-light and dark phases. In dark phase (Blackman’s reaction or biosynthetic phase) carbohydrates are synthesised from carbon dioxide in stroma of chloroplast using ATP and NADPH products of light reactions.

Non cyclic photophosphorylation is not only connected with ATP synthesis but also production of NADPH. It involves two photosystems—PSI and PSII. PSII (680) receive electrons from photolysis of water and transfer it to PSI (700) to form NADPH from NADP⁺. The hydrogen required for reduction comes from breaking of water molecules.