Chapter 12: Respiration in Plants Short Questions | biology Class 11 CBSE

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Chapter 12: Respiration in Plants Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Define cellular respiration and state where in the eukaryotic cell it occurs.

Cellular respiration is the breaking of C-C bonds of complex organic molecules through oxidation within cells, leading to the release of considerable energy.
The initial stage (glycolysis) takes place in the cytoplasm, while the later stages (Krebs' cycle and ETS) occur in the mitochondria.
The energy released is not used directly but is trapped in the form of ATP, which acts as the energy currency of the cell.

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Question 2

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What are respiratory substrates? Give two examples of non-carbohydrate respiratory substrates used by plants.

Respiratory substrates are the compounds that are oxidised during the process of respiration to release energy.
Fats (lipids) can serve as respiratory substrates; they are first broken down to glycerol and fatty acids before entering the pathway.
Proteins can also be used; they are degraded by proteases and the amino acids (after deamination) enter the respiratory pathway at various stages.

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Question 3

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Why do plants not require specialised respiratory organs unlike animals?

Each plant part independently manages its own gas-exchange needs, with very little transport of gases from one plant part to another.
Plants respire at rates far lower than animals, so the demand for gas exchange is minimal; stomata and lenticels are sufficient.
The loose packing of parenchyma cells creates an interconnected network of air spaces so that each living cell is close to a surface exposed to air.

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Question 4

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What is the full form and origin of the term glycolysis? Who proposed the scheme of glycolysis?

Glycolysis is derived from the Greek words glycos meaning sugar and lysis meaning splitting.
The scheme of glycolysis was proposed by Gustav Embden, Otto Meyerhof, and J. Parnas; hence it is also called the EMP pathway.
Glycolysis occurs in the cytoplasm and is present in all living organisms; in anaerobic organisms it is the only respiratory process.

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Question 5

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At which two steps of glycolysis is ATP consumed, and at which step is NADH+H+ produced?

ATP is consumed first in the conversion of glucose to glucose-6-phosphate by the enzyme hexokinase.
ATP is consumed again in the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.
NADH+H+ is produced when 3-phosphoglyceraldehyde (PGAL) is oxidised and converted to 1,3-bisphosphoglycerate (BPGA), with two hydrogen atoms transferred to NAD+.

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Question 6

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What is the role of the enzyme invertase in plant glycolysis?

In plants, glycolysis begins with sucrose (the end product of photosynthesis), which must first be converted to monosaccharides.
The enzyme invertase catalyses the hydrolysis of sucrose into glucose and fructose.
Both glucose and fructose then readily enter the glycolytic pathway after being phosphorylated to glucose-6-phosphate by hexokinase.

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Question 7

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Distinguish between obligate and facultative anaerobes.

Obligate anaerobes are organisms for which the absence of oxygen is an absolute requirement; they cannot survive in the presence of O2.
Facultative anaerobes can survive both in the presence and absence of oxygen; they switch between aerobic and anaerobic respiration depending on oxygen availability.
Both types of organisms retain the enzymatic machinery to partially oxidise glucose via glycolysis without oxygen.

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Question 8

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Name the two enzymes involved in alcoholic fermentation and state the products they form.

Pyruvic acid decarboxylase catalyses the decarboxylation of pyruvic acid to produce acetaldehyde and CO2.
Alcohol dehydrogenase then catalyses the reduction of acetaldehyde to ethanol, using NADH+H+ as the reducing agent.
The overall result is the conversion of pyruvic acid to ethanol and CO2 under anaerobic conditions.

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Question 9

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Why is fermentation considered a hazardous process? How does it limit natural alcohol production?

Fermentation produces either ethanol or lactic acid as end products, both of which are toxic to the producing organism at higher concentrations.
Yeast poisons itself to death when the concentration of alcohol reaches about 13%, placing a natural ceiling on fermentation-based alcohol production.
Beverages with alcohol content greater than 13% cannot be naturally fermented and must be obtained by distillation or other concentration methods.

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Question 10

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What is oxidative decarboxylation of pyruvate? Name the enzyme and the coenzymes required.

Oxidative decarboxylation is the conversion of pyruvic acid to acetyl CoA with the simultaneous release of CO2 and production of NADH+H+, occurring in the mitochondrial matrix.
The reaction is catalysed by the enzyme pyruvate dehydrogenase (pyruvic dehydrogenase), which requires Mg2+ as a cofactor.
The coenzymes required include NAD+ and Coenzyme A; the overall reaction produces Acetyl CoA + CO2 + NADH + H+.

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Question 11

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With which compound does acetyl CoA condense at the start of the Krebs' cycle, and what is the product?

At the start of the Krebs' cycle, the acetyl group of acetyl CoA condenses with oxaloacetic acid (OAA) and water.
The reaction is catalysed by the enzyme citrate synthase, and a molecule of CoA is released.
The product is citric acid (a 6-carbon compound), which gives the cycle its alternate name — the tricarboxylic acid (TCA) or citric acid cycle.

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Question 12

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How is GTP produced in the Krebs' cycle, and how is it utilised?

GTP is synthesised during the substrate-level phosphorylation step in the Krebs' cycle, specifically during the conversion of succinyl-CoA to succinic acid.
This is the only direct substrate-level phosphorylation in the TCA cycle.
In a coupled reaction, GTP is immediately converted to GDP with the simultaneous synthesis of ATP from ADP, so the net gain is one ATP equivalent per turn of the cycle.

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Question 13

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State the role of oxygen in aerobic respiration. Why is its role described as terminal?

Despite aerobic respiration requiring O2, its actual role is limited to the terminal stage of the process — it acts as the final hydrogen (electron) acceptor in the ETS.
Oxygen accepts electrons passed through the ETS and combines with hydrogen ions to form water, driving the entire electron transport process.
Because oxygen acts only at this final step, its presence drives the whole respiratory process by removing hydrogen, allowing continued regeneration of NAD+ and FAD+.

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Chapter 12: Respiration in Plants | Short Questions

Define cellular respiration and state where in the eukaryotic cell it occurs.

What are respiratory substrates? Give two examples of non-carbohydrate respiratory substrates used by plants.

Why do plants not require specialised respiratory organs unlike animals?

What is the full form and origin of the term glycolysis? Who proposed the scheme of glycolysis?

At which two steps of glycolysis is ATP consumed, and at which step is NADH+H+ produced?

What is the role of the enzyme invertase in plant glycolysis?

Distinguish between obligate and facultative anaerobes.

Name the two enzymes involved in alcoholic fermentation and state the products they form.

Why is fermentation considered a hazardous process? How does it limit natural alcohol production?

What is oxidative decarboxylation of pyruvate? Name the enzyme and the coenzymes required.

With which compound does acetyl CoA condense at the start of the Krebs' cycle, and what is the product?

How is GTP produced in the Krebs' cycle, and how is it utilised?

State the role of oxygen in aerobic respiration. Why is its role described as terminal?

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