Respiration in Plants

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Question 1

A competitive inhibitor of succinic dehydrogenase is 

  • malonate

  • oxaloacetate

  • alpha-ketoglutarate

  • malate

Solution

A.

malonate

Succinic dehydrogenase oxidised the succinate to fumarate. In eukaryotes, succinate dehydrogenase is tightly bound to the inner mitochondrial membrane, in prokaryotes to the plasma membrane. Electrons pass from succinate through the FAD and iron-sulphur centres before entering the chain of electron carriers in the mitochondrial inner membrane malonate, an analogue of succinate is a strong competitive inhibitor of succinate dehydrogenase and therefore, blocks the activity of citric and cycle.
In Krebs cycle, the reversible hydration of fumarate to malate is catalysed by fumarase enzyme.
In the last reaction of Krebs cycle NAD- linked L-malate dehydrogenase catalyses the oxidation of L-malate to oxaloacetate.
The isocitrate dehydrogenase in Krebs cycle catalyses oxidative decarboxylation of isocitrate to form alpha-ketoglutarate, which in next step through oxidative decarboxylation converted to succinyl Co-A

Question 2

Cytochromes are found in

  • matrix of mitochondria

  • outer wall of mitochondria

  • cristae of mitochondria

  • lysosomes

Solution

C.

cristae of mitochondria

Cytochromes are present on the cristate, i.e. inner foldings of mitochondria. Cytochromes are iron (heme) containing proteins primarily responsible for transfer of electrons in ETC from ubiquinone to complex-V for generation of ATP(energy molecules) and terminal acceptor O2 in electron transport chain.
They are also called respiratory pigments, which are capable of performing both the oxidation and reduction reactions.

Question 3

How many ATP molecules could maximally be generated from one molecule of glucose, if the complete oxidation of one mole of glucose to CO2 and H2O yields 686 kcal and the useful chemical energy available in the high energy phosphate bond of one mole of ATP is 12 kcal?

  • Two

  • Thirty

  • Fifty seven

  • One

Solution

B.

Thirty

30 ATP molecules could be generated from 686 Kcal energy.

Question 4

The chemiosmotic coupling hypothesis of oxidative phosphorylation proposes  that Adenosine Triphosphate (ATP) is formed because

  • High energy bonds are formed in mitochondrial proteins

  • ADP is pumped out of the matrix into the intermembrane space

  • a proton gradient forms across the inner membrane

  • there is a change in the permeability of the inner mitochondrial membrane toward Adenosine Diphosphate (ADP)

Solution

C.

a proton gradient forms across the inner membrane

The production of ATP with the help of energy liberated during oxidation of reduced coenzymes and terminal oxidation is called oxidative phosphorylation. Peter Mitchell (1961) put forward a hypothesis known as a chemiosmotic hypothesis for ATP synthesis. According to this when electrons flow from dual proton, electron carrier to a non-hydrogen carrier the H+ in the intermembranous space than the matrix. Due to proton motive force, the protons flow back and energy liberated during this backflow of protons activate ATPase present in F1 head to synthesise ATP. 

Question 5

The energy -releasing process in which the substrate is oxidised without an external electron acceptor called

  • fermentation

  • photorespiration

  • aerobic respiration

  • glycolysis

Solution

D.

glycolysis

Glycolysis is the first stage of the breakdown of glucose in the cytoplasm of the cell without using oxygen (electron acceptor). It is a stepwise process in which one molecule of glucose breaks into two molecules of pyruvic acid and a net gain of energy is 2 ATP and 2NADH2 molecules.
The stepwise breakdown of the respiratory substrate to CO2 and H2O in presence of oxygen is referred as aerobic respiration. It is a catabolic process and generates a large amount of energy to form ATP.
Anaerobic respiration n micro-organisms are called fermentation. Alcoholic fermentation is a breakdown of glucose into ethyl alcohol and CO2 in presence of enzyme of micro-organism. Photorespiration is light-induced oxidation of photosynthetic intermediates with the help of oxygen without releasing energy.