What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

Why do plants not need special respiratory organs?

Because each plant part meets its own gas-exchange needs, demands are low, and every living cell lies close to the surface, so gases diffuse through stomata, lenticels and intercellular spaces.

What is glycolysis and where does it occur?

Glycolysis is the partial oxidation of glucose to two molecules of pyruvic acid through ten enzyme-catalysed steps, occurring in the cytoplasm of all living cells.

What are the possible fates of pyruvate?

Pyruvate may undergo lactic acid fermentation, alcoholic fermentation or complete aerobic oxidation through the Krebs' cycle, depending on the cell and oxygen availability.

Where does the Krebs' cycle take place and what is its first step?

It takes place in the mitochondrial matrix and begins with the condensation of acetyl CoA with oxaloacetic acid to form citric acid.

Explain the electron transport system.

It is a chain of carriers on the inner mitochondrial membrane through which electrons from NADH and FADH2 pass to oxygen, releasing energy that is used to synthesise ATP.

How many ATP molecules are produced by oxidation of one NADH and one FADH2?

Oxidation of one NADH gives three ATP and oxidation of one FADH2 gives two ATP.

What is the net gain of ATP from aerobic respiration of one glucose molecule?

There can be a net gain of 38 ATP molecules during the aerobic respiration of one molecule of glucose.

Why is the respiratory pathway called amphibolic?

Because respiratory intermediates are used both in catabolism (breakdown) and in anabolism (synthesis) of fats, proteins and other compounds.

Define respiratory quotient and give its value for fats.

It is the ratio of carbon dioxide evolved to oxygen consumed; for fats it is less than one, about 0.7.

What is the significance of the step-wise release of energy in respiration?

It allows some of the energy to be trapped as ATP rather than lost as heat, making the energy usable for cellular processes.

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Chapter 12: Respiration in Plants — Class 11 Biology

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Chapter 12: Respiration in Plants

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The energy currency of the cell is:

Summary

This chapter describes how cells release energy from food by oxidation and trap it as ATP, the energy currency of the cell. Plants have no special breathing organs but exchange gases by diffusion through stomata and lenticels, since each cell lies close to the surface and gas-exchange demands are low. The complete combustion of glucose yields carbon dioxide, water and energy, but cells oxidise glucose in many small steps so that some energy can be coupled to ATP synthesis. Glycolysis, occurring in the cytoplasm, partially oxidises glucose to two molecules of pyruvic acid through a chain of ten reactions (the EMP pathway), with a net gain of two ATP and two NADH. Under anaerobic conditions pyruvate undergoes fermentation to ethanol (in yeast) or lactic acid (in muscles), releasing little energy. Under aerobic conditions in the mitochondria, pyruvate is oxidised to acetyl CoA, which enters the tricarboxylic acid (Krebs) cycle producing NADH, FADH2 and GTP. The electron transport system on the inner mitochondrial membrane passes electrons to oxygen, and oxidative phosphorylation synthesises ATP, giving a net of about 38 ATP per glucose. The respiratory pathway is amphibolic, serving both breakdown and synthesis, and the respiratory quotient reflects the substrate respired.

Gaseous exchange in plantsGlycolysis and the EMP pathwayFermentation under anaerobic conditionsAerobic respiration and the Krebs' cycleElectron transport and oxidative phosphorylationAmphibolic pathway and respiratory quotient

Key terms

Respiration

The breaking of C-C bonds of complex compounds by oxidation within cells, releasing energy trapped as ATP.

Glycolysis

The cytoplasmic EMP pathway that partially oxidises glucose to two molecules of pyruvic acid.

Fermentation

The incomplete anaerobic oxidation of glucose to ethanol or lactic acid.

Krebs' cycle

The tricarboxylic acid cycle in the mitochondrial matrix that completely oxidises acetyl CoA.

Oxidative phosphorylation

The synthesis of ATP using energy from the electron transport system, with oxygen as the final electron acceptor.

Respiratory quotient

The ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration.

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The breaking of C-C bonds of complex compounds by oxidation within cells, releasing energy trapped as ATP.

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Practice quiz · Respiration in Plants

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Respiration in Plants

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