Tag: photosynthesis in higher plants

As we know that the PS-II or photosystem II constantly supplies electrons during the light reaction.

During the light-dependent reactions, the electrons released from the photolysis of water are used to reduce NADP+ to NADPH.

The process of water dissociation during photosynthesis is called as photo-oxidation of water. It requires the presence of Mn++, Ca+ and Cl- , a water oxidising enzyme and an unknown substance Z.

Water has high specific heat due to hydrogen bonds amongst molecules. Due to high specific heat, water minimizes changes in temperature. Hydrogen bonds are broken when it absorbs heat. Similarly, hydrogen bonds are formed when water releases energy in the form of temperature. This decreases the temperature of water.

When the chlorophyll molecule is excited by light, the energy level of an electron in its structure is boosted to a higher energy level and this excited chlorophyll moves rapidly the reaction center of the photosystem I where it transfers its extra energy to an electron which is then expelled from the reaction center and is accepted by the first member of a chain of electron carriers and ultimately reaches NADP$^+$, reducing it to NADPH. The reaction center has lost an electron and this electron hole is filled by stripping electrons from water which leaves hydrogen ion (H$^+$) and molecular oxygen (O$ _2$). The pathway of electrons from water to NADP$^+$ has Z shape called as Z scheme. 

Anthocyanins are water-soluble vacuolar pigments, that may appear red, purple, or blue depending on the pH. Anthocyanins occur in all tissues of higher plants, including leaves, stems, roots, flowers, and fruits.

Photolysis, as the name suggests, is the breakdown of water in the presence of sunlight to form H⁺ and  O₂ and electron. This takes place during the light phase of photosynthesis in the PS-II. This creates the oxygen which is the net product of photolysis.

Chemiosmotic hypothesis explains how ATP is synthesized in the chloroplast. ATP synthesis is linked to the development of a proton gradient across the membrane of the thylakoid of chloroplast and proton accumulation is towards the inside of the membrane i.e., in the lumen. Source of protons within the chloroplasts is water. The splitting of water molecule takes place on the inner side of the membrane and so the protons (hydrogen ions) are produced, they accumulate within the lumen of the thylakoids. Thus, the correct answer is option A.

In the process of photosynthesis, water acts as a stable oxygen donor. To prove the theory radioisotopic technique was used. 

A)In 1930, C.B.Van Niel proved that the sulphur bacteria use H$ _2$S and CO$ _2$ to synthesize carbohydrates.