31 Years NEET Previous Year Questions: Photosynthesis in Higher Plants - 2

Sugarcane is a C₄ plant in which CO₂ is fixed in malic acid by the enzyme phosphoenol pyruvic acid carboxylase present in mesophyll cells.

To conserve water, the stomata of  CAM  plants open during night to take up CO₂ and store it in the form of Malic acid which is utilised during the time of photosynthesis. 

Each pigment has its own absorption spectrum, chlorophyll absorbs light energy in blue and red region.

ATP molecules produced in the light reaction are used in the dark reaction to fix CO₂ to form organic compound.

Cytochrome is Fe containing porphyrin pigment. These are electron transferring proteins often regarded as enzymes.

The fall in photosynthetic yield beyond the red region of the spectrum (680 runs) is called red drop.
Reaction center of PS-2 is 680 while that of PA-1 is 700.
So the psII system will be inactive.
So the correct option is PS II.

Maize is a C₄ plant carrying out Hatch and Slack pathway. These plants show Kranz anatomy and overcome photorespiration.

The photochemical phase of photosynthesis involves fixing light energy and photolysis of water producing ATP and  NADPH.

2 ATP are required during conversion of PGA to 1, 3-diphosphoglyceric acid and 1 ATP during conversion of glyceraldehyde phosphate to ribulose biphosphate. 2NADH₂ molecules are utilised for converting 1, 3-diphosphoglyceric acid to glyceraldehyde phosphate.

Each turn of Calvin cycle generates one carbon atom hence six turns of the cycle is required to generate one molecule of hexose sugar glucose.

Light reaction is the first step of  photosynthesis. Attachment of  CO₂ to 5 carbon sugar occurs in the next step dark reaction

 RuBP carboxylase fixes CO₂ in C₃ plants. Hydrogenase catalyses addition of hydrogen. 

RUBISCO  is the enzyme involved in Calvin cycle. Nitrogenase catalyses nitro- genation. Invertase catalyses breaking of sucrose to glucose and fructose.

Cytochrome P⁴⁵⁰ (CyP) is a host of enzymes that use iron to oxidize, often as part of the body's strategy to dispose of potentially harmful substances making them more water-soluble. These are found in plants, animals, and microbes and are involved in a variety of oxidative reactions in cells. These catalyse a variety of reactions including epoxidation, /V-dialkylation,o-dialkylation,.v-oxidation and hydroxylation. A typical cytochrome P450 catalyzed reactions is

NADPH + H⁺ + O₂ + RH → NADP^- + H₂0 + R - OH

Photochlorophyll lacks two hydrogens at the 7 and 8 positions at the porphyrin part of the pyrrole ring. It is an oxidation product of chlorophyll a. In presence of light, it is reduced and esterified with phytol group to produce chlorophyll in presence of enzyme chlorophyllase.
So the correct option is '2 hydrogen atoms in one of its pyrrole rings'.

Photosystem I is the second photosystem in the photosynthetic light reactions of algae, plants and some bacteria. Photosystem I is so named because it was discovered before photosystem II. It produces NADPH₂.

In dark phase of calvin cycle of photosynthesis the CO₂ is reduced to Glucose in stroma of chloroplast, making use of the ATP & NADPH₂, (available from light phase).

Photosynthesis takes place only in the visible part (400 - 700 nm wavelength) of electromagnetic radiations. Hence this component comprises the photosynthetically active radiation.

The empirical formula of chlorophyll molecule is C₅₅H₇₂0₅N₄Mg. It has tadpole like configuration. It is consisted of a porphyrin head and a phytol tail. Porphyrin is a cyclic tetrapyrol structure, having a magnesium atom in the centre. Chlorophyll a methyl group (CH₃) is attached to the third carbon in the porphyrin head.

The principle of limiting factors was formulated by Blackmann (1905). It states that when a process is conditioned as to its rapidity by a number of separate factors, the rate of process is limited by the pace of slowest factor.

Photorespiratory loss of CO₂ occurs when RUBISCO starts functioning as an oxygenase instead of carboxylase  under conditions of  high O₂ and low CO₂. It involves three organelles chloroplast, mitochondria and peroxisomes. Half of the photosynthetically fixed carbon (in the form of RUBP) may be lost into the atmosphere through this process and no ATP formation occurs.

Anatomy of leaves of C_4– plant is called kranz anatomy. In the mesophyll cells of these plants pallisade tissue is absent.

Cyclic photophosphorylation involves only PSI and there occurs only ATP formation.

85-90% of all photosynthesis of world is carried out by phytoplanktons in ocean.

P700 consists of a chl a and chl b molecules and is named after maximum absorption by pigment or photocentre at that wavelength.