Test: Respiration in Plants - Assertion and Reasoning - NEET MCQ

Stomata are absent since gaseous exchange takes place through diffusion in submerged plants.

Glycolysis is the process of breakdown of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of enzyme mediated reactions, releasing energy (ATP) and reducing power (NADH₂). It is the first step of respiration, which occurs inside the cytoplasm and is independent of O₂. In glycolysis, two molecules of ATP are consumed during double phosphorylation of glucose to form fructose 1, 6 diphosphate. Four molecules of ATP are produced in the conversion of 1, 3-diphosphoglycerate to 3-phosphoglycerate and phosphenol pyruvate to pyruvate whereas, two molecules of NADH₂ are formed during oxidation of glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate. Since, each NADH is equivalent to 3 ATP, so net gain in glycolysis is 8 ATP.

Glycolyis occurs in cytoplasm as all necessary enzymes are found in it. This process is common in aerobic/anaerobic respiration. In this process, one glucose molecule is converted into 2 moles of pyruvic acid.

One of the two phosphates of diphosphoglycerate is linked by high energy bond. It can synthesize ATP and form 3- phosphoglycerate. The enzyme is phosphoglycerate kinase. The direct synthesis of ATP from metabolites is called substrate level phosphorylation. During formation of phosphoenol pyruvate the phosphate radical pick up energy. It helps in the production of ATP by substrate level phosphorylation.

In the presence of enzyme aldolase, fructose 1, 6-diphosphate is converted into a glyceraldehyde-3-phosphate and a dihydroxy acetone-3-phosphate molecules

Unlike animals, plants have no specialised organs for gaseous exchange. Gaseous exchange in plants occurs by diffusion through stomata and lenticels. There are various reason for the absence of respiratory organs in plants. Each part of plant takes care of its own needs of gaseous exchange. There is little transport of gases from one part to another. Plants do not require much for gas exchange. All plant parts respire at rates far lower than animals. To take care of their own needs of gases during photosynthesis, leaves are well adapted. Moreover, leaves also utilise oxygen released during photosynthesis. In plants, cells are closely packed and located quite close to the surface of the plant.

Glycolysis is also known as EMP pathway, as it was discovered by three German scientists-Gustav Embden, Otto Meyerhof and J. Parnas in 1930. In glycolysis, partial oxidation of glucose takes place that form two molecules of pyruvic acid. It occurs in the cytoplasm of the cell and is present in almost all living organisms. Aerobic respiration consists of diferent processes i.e., (i) glycolysis, (ii) oxidative decarboxylation of pyruvic acid, (iii) Krebs' cycle and (iv) terminal oxidation and oxidative phosphorylation.

The conversion of 1, 3 -bisphosphoglycerate (BPGA) 3-phosphoglyceric acid (PGA) is an energy yielding step. One of the two phosphates of bisphosphoglycerate is linked by high energy bond. It can synthesise ATP and form 3- phosphoglycerate in the presence of enzyme phosphoglycerate kinase. The direct synthesis of ATP from metabolites is called substrate level phosphorylation. 1, 3 bisphosphoglycerate + ADP

Fermentation is the incomplete oxidation of glucose under anaerobic conditions. In yeast the pyruvic acid is converted to CO2 and ethanol. Other organisms like some bacteria produce lactic acid from pyruvic acid. In animal cells also, like muscles during exercise when oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid in the presence of lactate dehydrogenase. Under anaerobic conditions fermentation takes place in many prokaryotes, unicellular eukaryotes and in germinating seeds.

Baker's yeast (Saccharomyces cerevisiae) is added to flour during kneading. Yeast secretes enzymes like amylase (changes some starch to maltose), maltase (maltose to glucose) and zymase (glucose to ethyl alcohol and carbon dioxide). The dough swells up or leavens. Leavened dough is baked and both alcohol and carbon dioxide evaporate, the bread becomes soft and porous.

In human body anaerobic respiration occurs in our skeletal muscles during strenous exercise. When oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is NADH = H⁺ which is reoxidised to NAD⁺.

Alcoholic fermentation is the respiration in absence of O₂. In this process, hexose molecule is changed to ethyl alcohol and CO₂. In presence of zymase enzyme. In this less amount of energy is released as compared to aerobic respiration.

Under aerobic conditions, the products are pyruvate and coenzyme NADH. Pyruvate directly enters the mitochondrial matrix and is converted into acetyl-CoA. Under anaerobic conditions, pyruvate is used as a hydrogen acceptor and converted into lactate. In anaerobic conditions, pyruvate remains in the cytosol.

Terminal oxidation is the name of oxidation found in aerobic respiration that occurs towards the end of catabolic process and involves the passage of both electrons and protons of reduced coenzymes to oxygen.

Respiration is an energy releasing enzymatically controlled process that involves a step-wise oxidative breakdown of food substances inside living cells. Food reaches every cell of an organism for respiration to take place. During cellular respiration, the oxidation of food substances takes place. This process occurs in cytoplasm and mitochondria. During oxidation, chemical bonds (e.g., C - C bonds) are broken that releases energy and forms a number of biochemical intermediates. This energy is used in the synthesis of ATP. Those organic substances which are oxidised during respiration to liberate energy inside the living cells are respiratory substrate. The common respiratory substrates are carbohydrates, proteins, fats and organic acids. the most common respiratory substrate is glucose.

The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid. The reaction is catalysed by the enzyme citrate synthetase and a molecule of CoA is released.

The first reaction of the Krebs cycle is the condensation of acetyl CoA (2 C compound) with oxaloacetate (4 C compound). Citric acid, a 6 carboncompound is the first product of Krebs cycle.

The inner membranes of mitochondria contain all systems involving electron transport. The mitochondrial matrix contains all the soluble enzymes of the citric acid or Kreb's cycle and those involved in the oxidation of fatty acids

ATP synthase is located in F1, or head piece of F₀- F₁ or elementary particles. The particles are present in the inner mitochondrial membrane. ATP synthase becomes active in ATP formation where there is a proton gradient having higher concentration of H⁺ or protons on the F₀ side as compared to F₁ side.

The passage of electrons from one enzyme or cytochrome to the next is a downhill journey with a loss of energy at each step. At each step the electron carriers include flavins, iron sulphur complexes, quinones and cytochromes.