Tag: botany

Phosphorylation refers to the process of formation of ATP. During respiration, the oxidation of NADH and FADH$ _{2}$ results in ATP formation, hence called oxidative phosphorylation. In photosynthesis, the photosystem II is involved in cyclic photophosphorylation. 

The acidic lumen of the thylakoids will have a higher concentration of H$^{+}$ ions. When these are transferred to basic pH of 8, the H$^{+}$ will tend to move outside due to their concentration gradient, which is higher in the lumen and lower in the surrounding. The thylakoids bear ATP synthases that will use the proton motive force H$^{+}$ ions and will make the ATP. So, an isolated chloroplast is capable of synthesizing the ATP when the lumen is made acidic and the outer medium is made alkaline.

Light reaction or photochemical phase is called as photophosphorylation or Hill's reaction. It includes non-cyclic phosphorylation and cyclic phosphorylation. During this reaction, the light is absorbed by the chlorophyll and water splits into H$ _2$ and 1/2O$ _2$. Oxygen is released as the byproduct of the reaction along with formation of carbohydrate. Along with oxygen, ATP and NADPH are also formed.

The events occurring in the light reaction of the photosynthesis are:

• The (light) compensation point is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration.
•  When the rate of photosynthesis equals the rate of respiration or photorespiration, the compensation point occurs.
  
• The compensation point is reached during early mornings and late evenings.
• Hence This condition occurs usually in evening and morning is not correct regarding light compensation point.
• So, the correct answer is 'Option A'.

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.