Tag: photosynthesis in plants

 The biochemical objective of PSI is to reduce NADP+ to NADPH because NADP+ is able to be reduced in NADPH by gain electron which has been excited from PSI(P700)  and also hydrogen ions from stroma. So electron required to reduce NADP+ is released from PSI so answer is option 4.

A photosynthetic reaction centre is a protein that is the site of the light reactions of photosynthesis. The reaction centre contains pigments such as chlorophyll and phaeophytin. These absorb light, promoting an electron to a higher energy level within the pigment which are located at centre of photosynthetic apparatus. so, 'the correct option is - It is located at centre of photosynthetic apparatus'.

The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria, archaea, and in eukaryotes in their mitochondria. It is the last enzyme in the respiratory electron transport chain of cells located in the membrane. It receives an electron from each of four cytochrome c molecules, and transfers them to one dioxygen molecule, converting the molecular oxygen to two molecules of water. In this process it binds four protons from the inner aqueous phase to make two water molecules, and translocates another four protons across the membrane, increasing the transmembrane difference of proton electrochemical potential which the ATP synthase then uses to synthesize ATP. The complex contains two hemes, a cytochrome a and cytochrome a3, and two copper centers, the CuA and CuB centers. The cytochrome a3 and CuB form a binuclear center that is the site of oxygen reduction.

• A very small part of the electromagnetic spectrum can be seen by the human eye i.e., between the wavelengths 390 and 780 nm.
• This part of the electromagnetic spectrum is called a visible light spectrum.
• Within the spectrum the longer the wavelength of the radiation, the slower the vibration of the photons and the less energy each photon contains. 
  Hence, correct option is B.

Photosystem- II is involved in non-cyclic photophosphorylation with a reaction center P${ _6}$${ _8}$${ _0}$. The electrons excited from P${ _6}$${ _8}$${ _0}$ are accepted by plastoquinoine. 

Photosystem II is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the grana of the thylakoid membrane of plants, algae, and cyanobacteria.

Photosynthetic bacteria posses only one type of photosystem and are mostly anaerobic and contains two type of pigment bacteriochlorophylls and bacterioviridin while cyanobacteria or blue-green algae posses two photosystems  PS I and PS II.

Photosystem I is one of the two membrane-bound photosystems of plants, algae and cyanobacteria that facilitate light-determined electron transport from water to NADPH. It utilizes absorbed light for electron transport from plastocyanin on the lumenal side to ferredoxin on the stromal side of the thylakoid membrane. In plants, this special integral membrane complex consists of more than 15 protein subunits, approximately 175 chlorophyll molecules, 2 phylloquinones and 3 Fe$ _4$S$ _4$ clusters. Whereas Photosystem II (of cyanobacteria and green plants) is as many as 35 chlorophyll a, 12 beta-carotene, two pheophytins, two plastoquinone, two heme, one bicarbonate, 20 lipid molecules and other ionic clusters. Thus Photosystem I contains more chlorophylls and accessory pigments.

DCMU or Dichlorophenyl dimethyl urea inhibits PS II in photosynthetic plants by blocking electron transfer from plastoquinone to cytochrome. DCMU binds to and blocks the site of plastoquinone, thus hinders the path and growth of plants. It is used as herbicide and algicide. It is also used in studying photosynthetic activity.

Being a light reaction, non-cyclic photophosphorylation occurs in the thylakoid membrane. First, a water molecule is broken down into 2H⁺ + 1/2 O₂ + 2e⁻ by a process called photolysis (or light-splitting). The two electrons from the water molecule are kept in photosystem II, while the 2H⁺and 1/2O₂ are left out for further use. Then a photon is absorbed by chlorophyll pigments surrounding the reaction core center of the photosystem. The light excites the electrons of each pigment, causing a chain reaction that eventually transfers energy to the core of photosystem II, exciting the two electrons that are transferred to the primary electron acceptor, pheophytin. The deficit of electrons is replenished by taking electrons from another molecule of water.