Tag: metabolism, cell respiration, and photosynthesis

The light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. Thylakoids are arranged in stacks called grana.
The chloroplast matrix is called the stroma and contains enzymes that catalyze the light-independent reactions of photosynthesis. But stroma is not the site for light reactions. 
Stromal lamellae connect two or more grana to each other. In this way, the lamellae act as a skeleton of the chloroplast, maintaining efficient distances between the grana, thereby maximizing the overall efficiency of the chloroplast. 
Each chloroplast is enclosed by (surrounded) a chloroplast envelope or unit membrane consisting of three layers. Overall the chloroplast envelope is semi-permeable. It is permeable to glucose molecules and certain ions including Fe$^{2+}$and Mg$^{2+}$, and oxygen and carbon dioxide.

In photosynthesis, energy is transferred in small energy steps. Photosynthesis is the primary energy source for most of the biosphere. Even though photosynthetic light harvesting complexes display great variety in their design and function, many of them are membrane proteins that comprise of pigment antenna arrays, which absorb light and transfer the resulting electronic excitation to a reaction center, which in turn converts this excitation energy to a charge gradient across the membrane and help to synthesise ATP. This energy is utilized in dark phase for synthesizing glucose.

Translocation is the process of movement of nutrients from leaves to other parts of plant. During the process of photosynthesis, carbohydrates (sugars) specifically sucrose is synthesized in the cytosol of cell and then translocated to other demanding parts of plant. Sucrose is complex, less reactive and energy efficient sugar so, angiosperms and other plants translocate sugar in the form of sucrose.

The light reaction takes place in the grana of the chloroplast. This is also known as the cyclic and non-cyclic form of photophosphorylation in which the ATP and NADPH + H$^+$ are produced. In the non-cyclic photophosphorylation, there is splitting of the water molecules which results in the production of oxygen molecule. 

Photophosphorylation refers to the use of light energy from photosynthesis to ultimately provide the energy to convert ADP to ATP, thus replenishing the universal energy currency in living things. Light generally provides energy to form the bonds. It is an endothermic reaction.

In light-dependent reactions, the energy from sunlight is absorbed by chlorophyll and converted into chemical energy in the form of electron carrier molecules like ATP and NADPH.

Light phase is also known as a photochemical phase because it is a light dependent phase. During this phase, the formation of high-energy chemical intermediates ATP and NADPH$ _{2}$ takes place. ATP and NADPH$ _{2}$ are the assimilatory power of photosynthesis. Light phase also includes light absorption, water splitting and release of oxygen. Two photosynthetic units called Photosystem I and Photosystem II are also involved in light phase. Light phase consists of two photochemical reactions, i.e. non-cyclic photophosphorylation and cyclic photophosphorylation.

In photosynthesis, the light-dependent reactions take place on the thylakoid membranes. The light-independent reactions take place in the stroma. The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase. These four complexes work together to ultimately create the products ATP and NADPH.

Light reactions of photosynthesis which takes place in thylakoids membranes of chloroplast utilize sunlight and water to produce oxygen, ATP and NADPH.