Tag: photosynthesis in higher plants

DCMU (Dichlorophenyl dimethyl urea) is a herbicide which most effectively inhibits PSII in photosynthesis by the stopping CO$ _2$ fixation, which is essential for photosynthesis.

The core of PSII consists of a pseudo-symmetric heterodimer of two homologous proteins D1 and D2. The reaction center chlorophyll (or the primary electron donor) of photosystem II that is most reactive and best in absorbing light at wavelength of 680 nm. P680 is a group of pigments that are excitonically coupled or that act as if the pigments are a single molecule when they absorb a photon.

Photosystem I (Plastocyanin-ferredoxin oxidoreductase) is located in the membrane of stroma lamellae, while PSII  (water-plastoquinone oxidoreductase) is located in the grana region that is inner side of thylacoid membrane.

Light reactions occur inside thylakoids. It is dependent upon light. It involves photolysis of water (breaking of water into $H _{2}$ and $O _{2}$  and production of assimilation power (NADPH and ATP). Electron released during photolysis of water are  picked up by $P _{680}$ photocentre of photosystem II. From here electrons passes over series of carrier which include PQ, cytochrome b-f complex, and PC. While passing over cytochrome complex, the electron losses sufficient energy for creation of proton gradient and ATP from ADP and inorganic phosphate. From PC electron losses sufficient energy for creation of proton gradient and ATP from ADP and inorganic phosphate. From PC electron is picked by the trap center $P _{700} $of phtotsystem I, which pushes out electron after absorbing light energy. Electron passes over carriers Fes, ferredoxin and NADP reductase which gives electron to $NADP^+$ for combing with $H^+$ to produce NADPH.
$NADP^+ 2e^- + H^{+} \xrightarrow[NADP \,\, reductase]{} NADPH $ , So, the correct answer is 'ATP, hydrogen and O2'.

Photosystem II is the first protein complex in the light-dependent reactions of oxygenic photosynthesis and splitting of water is associated with it. Water is split into H+, [O] and electrons, creating O$ _{2}$ which is one of the net products of photosynthesis. The electrons needed to replace those removed from PS I are provided by PS II.

 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.