11th Class

Plants absorb the minerals from the soil and translocate them to other parts of the body. Soil serves as a main source of mineral salts in which clay crystals with a central nucleus is called micelle. The micelles are negatively charged. To maintain the balance, they hold positively charged ions on their surface. When this balance is disturbed by salt absorption, the equilibrium is again restored by transferring some of the absorbed ions into the solution. The movement of ions is called as flux. The movement of ions into the cell is called influx and outward migration of ions is known as efflux. Various theories have been proposed to explain the mechanism of mineral salt absorption and can be placed under the following two categories. (1) Passive absorption : Absorption of ions without the use of metabolic energy is known as passive absorption. This type of absorption is carried out more...

Various elements perform the following major roles in the plants : Construction of the plant body : The elements particularly C, H and O construct the plant body by entering into the constitution of cell wall and protoplasm. They are, therefore, referred to as framework elements. Besides, these (C, H and O) N, P and S, Mg and Fe also enter in the constitution of protoplasm. They are described as protoplasmic elements. Maintenance of osmotic pressure : Various minerals present in the cell sap in organic or inorganic form maintain the osmotic pressure of the cell. Maintenance of permeability of cytomembranes : The minerals, particularly \[C{{a}^{++}},{{K}^{+}}\] and \[N{{a}^{+}}\]maintain the permeability of cytomembranes. Influence the pH of the cell sap : Different cations and anions influence on the pH of the cell sap. Catalysis of biochemical reaction : Several elements particularly \[Fe,Ca,Mg,Mn,Zn,Cu,Cl\]act as metallic catalyst in biochemical reactions. Toxic effects : more...

The process of mineral absorption is influenced by the following factors : Temperature : The rate of absorption of salts and minerals is directly proportional to temperature. The absorption of mineral ions is inhibited when the temperature has reached its maximum limit, perhaps due to denaturation of enzymes. Light : When there is sufficient light, more photosynthesis occurs. As a result more food energy becomes available and salt uptake increases. Oxygen : A deficiency of \[{{O}_{2}}\] always causes a corresponding decrease in the rate of mineral absorption. It is probably due to unavailability of ATP. The increased oxygen tension helps in increased uptake of salts. pH : It affects the rate of mineral absorption by regulating the availability of ions in the medium. At normal physiological pH monovalent ions are absorbed more rapidly whereas alkaline pH favours the absorption of bivalent and trivalent ions. Interaction with other minerals : The more...

An essential element is defined as 'one without which the plant cannot complete its life cycle, or one that has a clear physiological role'. Therefore, in 1939 Arnon and Stout proposed the following characters for judging the criteria of essentiality of an element in the plant : (1) The element must be essential for normal growth and reproduction, which cannot proceed without it. (2) The requirement of the element must be specific and cannot be replaced by another element. (3) The requirement must be direct that is, not the result of any indirect effect e.g., for relieving toxicity caused by some other substance.  Essential elements are divided into two broad categories, based on the quantity in which they are required by plants. Macro-elements and micro-elements. Their ionic forms are respectively called macronutrients and micronutrients. Mineral salts dissolved in soil solution are constantly passing downwards along with percolating (gravitational) water. The more...

Competitive inhibition : Substances (inhibitors) which are structurally similar to the substrates and competes for the active site of the enzyme are known as competitive inhibitors. Usually such inhibitors show a close structural resemblance to the substrates to the enzyme they inhibit. In such a case, inspite of enzyme substrate complex, enzyme inhibitor complex is formed and enzyme activity is inhibited. \[\underset{\text{Enzyme}}{\mathop{\text{E}}}\,+\underset{\text{inhibitor}}{\mathop{\text{I}}}\,\to \underset{\text{Enzyme}-\text{inhibitor}\,\text{complex(EI)}}{\mathop{\text{EI}}}\,\]     The concentration of \[EI\]complex depends on the concentration of free inhibitor. Because \[EI\]complex readily dissociates, the empty active sites are then available for substrate binding. The effect of a competitive inhibitor on activity is reversed by increasing the concentration of substrate. In it \[{{V}_{\max }}\] remain constant and Km increases. A classic example of competitive inhibition is succinic acid dehydrogenase which oxidises succinic acid to fumaric acid. If concentration of malonic more...

Substrate concentration : If there are more enzyme molecules than substrate molecules, a progressive increase in the substrate molecules increases the velocity of their conversion to products. However, eventually the rate of reaction reaches the maximum. At this stage the active sites of all the available enzyme molecules are occupied by the substrate molecules. Therefore, the substrate molecules occupy the active sites vacated by the products and cannot increase the rate of reaction further. Enzyme concentration : The rate of reaction is directly proportional to enzyme concentration. An increase in enzyme concentration will cause a rise in the rate of reaction up to a point and them the rate of reaction will be constant. Increasing the enzyme concentration increases the number of available active sites. Product concentration : Accumulation of the product of enzyme reaction lowers the enzyme activity. Enzyme molecules must be freed to combine with more substrate molecules. more...

Enzymes (Gk. en = in; zyme = yeast) are proteinaceous substances which are capable of catalysing chemical reactions of biological origins without themselves undergoing any change. Enzymes are biocatalysts. An enzyme may be defined as "a protein that enhances the rate of biochemical reactions but does not affect the nature of final product". Like the catalyst the enzymes regulate the speed and specificity of a reaction, but unlike the catalyst they are produced by living cells only. All components of cell including cell wall and cell membrane have enzymes. Maximum enzymes (70%) in the cell are found in mitochondrion. Enzymes are also called 'biological middle man'. The study of the composition and function of the enzyme is known as enzymology. The term enzyme (meaning in yeast) was used by Willy Kuhne (1878) while working on fermentation. At that time living cells of yeast were thought to be essential for fermentation more...

Energy is required to bring the inert molecules into the activated state. The amount of energy required to raise the energy of molecules at which chemical reaction can occur is called activation energy. Enzymes act by decreasing the activation energy so that the number of activated molecules is increased at lower energy levels. If the activation energy required for the formation of the enzyme-substrate complex is low, many more molecules can participate in the reaction than would be the case if the enzyme were absent.

In 1913 Michaelis and Menten proposed that for a catalylic reaction to occur it is necessary that enzyme and substrate bind together to form an enzyme substrate complex. \[\underset{(Enzyme)}{\mathop{E}}\,+\underset{(Substrate)}{\mathop{S}}\,\to \underset{(Enzyme-substrate\text{ }Complex)}{\mathop{E-S\text{ }Complex}}\,\] \[E-S\text{ }Complex\to \underset{(Enzyme)}{\mathop{E}}\,+\underset{(\Pr oduct)}{\mathop{P}}\,\] It is amazing that the enzyme-substrate complex breaks up into chemical products different from those, which participated in its formation (i.e., substrates). On the surface of each enzyme there are many specific sites for binding substrate molecules called active sites or catalytic sites. There are two views regarding the mode of enzyme action : Lock and Key hypothesis : The hypothesis was put forward by Emil Fisher (1894). According to this hypothesis the enzyme and its substrate have a complementary shape. The specific substrate molecules are bound to a specific site of the enzyme molecule. The theory can be explained easily by the fact that a particular lock can be opened by a particular more...

Mostly enzymes are proteinaceous in nature. With some exception all enzymes are proteins but all proteins are not enzymes. Enzymatic protein consist of 20 amino acids. The polypeptide chain or chains of an enzyme show tertiary structure. Their tertiary structure is very specific and important for their biological activity. Loss of tertiary structure renders the enzymic activity. Some enzymes like pepsin, amylase, urease, etc., are exclusively made up of protein i.e., simple proteins. But most of the other enzymes have a protein and a non-protein component, both of which are essential for enzyme activity. The protein component of such enzymes is known as apoenzyme whereas the non-protein component is called cofactor or prosthetic group. The apoenzyme and prosthetic group together form a complete enzyme called holoenzyme. Activity of enzyme is due to co-factor, which can be separated by dialysis. co-factor is small, heat stable and may be organic or inorganic more...