Tag: photosynthesis in higher plants

When the leaf is exposed to light, the process of photosynthesis begins. As the photosynthetic reactions proceed in the guard cells, the residual carbon dioxide is converted to carbohydrates. The disappearance of carbon dioxide from the cytosol of the guard cell results in an increase in the cellular pH. 
As the pH rises, the activity of the enzymes, that convert starch and sugars to organic acids increases. The higher concentration of organic acids results in a higher concentration of hydrogen ions. The hydrogen ions of the guard cells are then exchanged for potassium ions in the subsidiary cells.
This increased concentration of potassium, combined with the higher levels of organic acids, lowers the osmotic potential of the guard cells, and, since water moves from regions of high osmotic potential to regions of lower osmotic potential, water will move from the subsidiary cells into the guard cells. This movement of water increases the turgor pressure (inner pressure) of the guard cells and causes them to swell. Thus, the stomata open.

The stomatal opening follows when solutes from near epidermal and mesophyll cell enter the guard cell lowering its osmotic potential and water potential. Also rising in K ions in guard cell allows movement of water into the guard cell from neighbouring cells and makes the guard cell swollen due to water accumulation which results in the opening of stomata. 

Stomata opens and closes due to water and ion movement. When the light falls on the parts of plant, chloroplast carries out photosynthesis. ATP from photosynthesis powers sodium and potassium pump. Then the K+ ions are pumped into the guard cells, by creating a concentration gradient. For this uptake of K+ ions it requires protons (H+) ions then, K+ ions are exchange for the protons H+.  This is an active ionic exchange and requires ATP energy and cytokinin (a plant hormone). In this way, the concentration of K+ ions increases in guard cells and at the same time, the concentration of H+ ions decreases in guard cells.  As a result of this, guard cells swells and stomata opens.So, the major solute taken in by the guard cells is K+, which is responsible for the opening of guard cells.

Photosynthesis is a redox reaction in which carbon dioxide is reduced to sugars and water is oxidised to release oxygen.

Photosynthesis is chemically a redox reaction in which carbon dioxide is reduced and water is oxidised. During light reaction phase of photosynthesis, the electron that has been donated to the electron transport chain is replaced through photolysis (light dependent splitting) of water, a process that not only yields electrons but also is the source of almost all the oxygen in Earths atmosphere. 

Photolysis, the chemical process by which molecules are broken down into smaller units through the absorption of light.

Light reaction occur inside the thylakoids, especially those of grana region. It involves two types of reaction photosynthesis of water and production of assimilation power.  The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis or photocatalytic , splitting of water, Water splitting complex is associated with the PSII, which itself is physically located on the inner surface of thylakoid  membrane. 
$4H _{2} O \rightleftharpoons 4H^{+} + 4OH^-$
$ 4OH^- \xrightarrow[Mn^{2+}, Ca^{2+}, Cl^-]{Oxygen \,\,evolving\,\, complex} 2H _{2} + O _{2}\uparrow + 4e^- $ , So, the correct answer is 'inner surface of thylakoid membrane.'.