65. Draw a diagram of the stucture of the lungs

71. An electron transport chain of Photosystems 2 and 1

77. Physiological significance of macroelements Nitrogen

Role in Plants. Nitrogen (N) is present in plants in the largest concentration of any of the mineral nutrients. It is a component of many organic molecules of great importance, including chlorophyll and the energy transfer molecules adenosine triphosphate (ATP) and adenosine diphosphate (ADP). Nitrogen is a component of amino acids, which are the molecular subunits from which proteins are synthesized. The nucleic acids DNA and RNA also contain nitrogenous bases—the As, Ts, Cs and Gs that make up the genetic coding sequences.

Hydroponic Source. Nitrogen in hydroponic nutrient solutions is supplied in the form of nitrogen salts containing nitrate (NO3-) or ammonium (NH4+). A combination of both of these offers some desirable pH buffering in the solution. Nitrates of potassium (KNO3), calcium [Ca(NO3)2] and ammonium (NH4NO3), or ammonium phosphate [(NH4)3PO4] are commonly used to formulate hydroponic nutrient solutions. In cases where the addition of no other nutrient elements is desired, nitric acid is an option (HNO3).

Deficiency Symptoms. Nitrogen deficiency in plants is characterized by chlorosis, which is a yellowing of the leaves. Nitrogen is a mobile element in plants, and can be moved around as needed; thus, older leaves tend to be the first plant parts to show signs of nitrogen deficiency (as nitrogen is transported to support new growth). Chlorosis is often evident when other minerals are deficient as well. Plants grown in poor nitrogen conditions tend to have stunted growth, and abnormally thin shoots.

Phosphorus

Role in Plants. Phosphorus is a part of the previously mentioned energy molecules ATP and ADP and is found in the backbone portion of both DNA and RNA. Many organic molecules contain a phosphate group and amino acids incorporated into proteins may be phosphorylated after protein synthesis. The phosphorylation and dephosphorylation of proteins is an important mechanism in regulating the activity of proteins. Cell membranes are rich in phosphate groups that are part of the “head” regions of the phospholipid molecules that form the membrane bilayers.

Deficiency Symptoms. Phosphorus (P) deficiency can be difficult to diagnose. Since phosphorus is important in many metabolic functions as well as in the synthesis of new cell membranes, phosphorus deficiency results in slow growth. In a moderate case, the leaves become a darker green than normal with perhaps a blue or purple tint, which can give the illusion of a healthy plant. In addition to darker leaf color, plants will exhibit stunted growth and thin stems, with longer than normal distance between the branches. In severe cases of phosphorus deficiency chlorosis appears followed by leaf curl and drop.

Potassium

Role in Plants. Potassium (K) does its job as a small monatomic ion (K+) in plants. It has diverse roles, including acting as a cofactor for the function of many enzymes important in energy production and carbohydrate metabolism and catabolism. Potassium ions are a critical part of the system that controls the movement of water in and out of leaves. It also facilitates water uptake by roots, which is probably a more important function in soil-grown plants.

Hydroponic Source. Potassium is supplied as potassium nitrate (KNO3) or sulfate (K2SO4). If no other source of chloride is available for the solution, potassium chloride (KCl) is an option.

Deficiency Symptoms. Like nitrogen, potassium is highly mobile in plants resulting in deficiency symptoms appearing in the oldest foliage first. Plants grown in potassium deficient conditions show a distinctive yellowing at the tips and edges of the oldest leaves. As the yellowing spreads, the leaves die and turn brown at their peripheries giving a burned appearance. Since K+ ions are important in maintaining water balance and turgor, potassium deficient plants are sensitive to water stress and wilt easily.