65. Draw a diagram of the stucture of the lungs

71. an electron transport chain of Photosystems 2 and 1 .For oxygenic photosynthesis, both photosystems I and II are required. Oxygenic photosynthesis can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors of the photosystem-containing chloroplasts of eukaryotes. Photosynthetic bacteria that cannot produce oxygen have a single photosystem called BRC, bacterial reaction center. The photosystem I was named "I" since it was discovered before photosystem II, but this does not represent the order of the electron flow. When photosystem II absorbs light, electrons in the reaction-center chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors. To replenish the deficit of electrons, electrons are extracted from water by a cluster of four Manganese ions in photosystem II and supplied to the chlorophyll via a redox-active tyrosine. Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain set in the thylakoid membrane. This energy fall is harnessed, (the whole process termed chemiosmosis), to transport hydrogen (H+) through the membrane, to the lumen, to provide a proton-motive force to generate ATP. The protons are transported by theplastoquinone. If electrons only pass through once, the process is termed noncyclic photophosphorylation. When the electron reaches photosystem I, it fills the electron deficit of the reaction-center chlorophyll of photosystem I. The deficit is due to photo-excitation of electrons that are again trapped in an electron acceptor molecule, this time that of photosystem I. ATP is generated when the ATP synthase transports the protons present in the lumen to the stroma, through the membrane. The electrons may either continue to go through cyclic electron transport around PS I or pass, via ferredoxin, to the enzyme NADP+ reductase. Electrons and hydrogen ions are added to NADP+ to form NADPH. This reducing agent is transported to the Calvin cycle to react with glycerate 3-phosphate, along with ATP to form glyceraldehyde 3-phosphate, the basic building-block from which plants can make a variety of substances

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.