- Oxidation of food materials (breaking of C-C bonds of - The compounds that are oxidized during respiration are
complex molecules) within the cell to release energy for called respiratory substrates. E.g. Carbohydrates (most
ATP synthesis is called cellular respiration. common), proteins, fats and organic acids.
- This energy is used for absorption, transport, movement, - The energy released is not used directly but is used to
reproduction, breathing etc. synthesize ATP. When energy is needed, ATP is broken
- Ultimate source of food that is respired is photosynthesis. down. Hence, ATP acts as energy currency of the cell.
BREATHING IN PLANTS
- For respiration, plants get O2 and give out CO2. - Complete combustion of glucose yields energy most of
- In plants, gas exchange occurs via stomata & lenticels. which is given out as heat.
- Plants need no specialized respiratory organs because C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
• Each plant part takes care of its own gas-exchange needs.
- This energy is utilized to synthesize other molecules.
So gas transport is very limited.
- During the glucose catabolism, not all the liberated energy
• Very low gas exchange as compared to that of animals.
goes out as heat. Glucose is oxidised in several small steps.
• Leaves are adapted for maximum gas exchange during
It enables some steps to couple released energy to ATP
photosynthesis. During this, O2 is released within the cell.
synthesis.
• Most living cells have contact with air. They are located
- During respiration, oxygen is utilized, and CO2, water &
close to plant surface. In stems, living cells are organized
energy are released.
in thin layers beneath the bark. They also have lenticels.
- Certain organisms are adapted to anaerobic conditions.
In leaves, stems & roots, parenchyma cells are loosely
Some are facultative anaerobes. Others are obligate.
packed that provides interconnected air spaces.
GLYCOLYSIS (EMP PATHWAY)
- It is the partial oxidation (breakdown) of glucose to 2
molecules of pyruvic acid (C3H4O3) in the absence of O2.
- It occurs in cytoplasm of all living organisms.
- Its scheme was given by Gustav Embden, Otto Meyerhof
& J. Parnas. So it is also known as EMP pathway.
- In anaerobes, it is the only process in respiration.
- In plants, glucose is derived from sucrose (end product of
photosynthesis) or from storage carbohydrates. Sucrose is
converted to glucose & fructose by an enzyme, invertase.
These 2 monosaccharides readily enter glycolytic pathway.
- Glucose & fructose are phosphorylated to form glucose-6-
phosphate by the enzyme hexokinase. It is then isomerised
to produce fructose-6-phosphate. Subsequent steps of
metabolism of glucose and fructose are same.
Steps of glycolysis:
- It includes 10 steps under the control of different enzymes.
- ATP is utilized at 2 steps:
• In the conversion of glucose into glucose 6-phosphate.
• In the conversion of fructose 6-phosphate to fructose 1,
6-diphosphate.
- Fructose 1, 6-diphosphate is split into dihydroxyacetone Pyruvic acid
phosphate (DHAP) & 3-phosphoglyceraldehyde (PGAL). (pyruvate) is the key
- PGAL is oxidised and with inorganic phosphate get product of glycolysis.
converted to 1, 3-bisphosphoglycerate (BPGA). During Its metabolic fate
this, 2 redox-equivalents (2 H-atoms) are removed from depends on the
PGAL and transferred to NAD+ forming NADH + H+. cellular need.
- BPGA becomes 3-phosphoglyceric acid (PGA) yielding
energy. This energy is trapped by the formation of ATP. In different cells, pyruvic acid is handled in 3 ways:
- ATP is also formed when PEP converts to pyruvic acid. • Lactic acid fermentation.
- In glycolysis, 4 ATP molecules are directly synthesised • Alcoholic fermentation.
from one glucose molecule. • Aerobic respiration (Krebs’ cycle).
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complex molecules) within the cell to release energy for called respiratory substrates. E.g. Carbohydrates (most
ATP synthesis is called cellular respiration. common), proteins, fats and organic acids.
- This energy is used for absorption, transport, movement, - The energy released is not used directly but is used to
reproduction, breathing etc. synthesize ATP. When energy is needed, ATP is broken
- Ultimate source of food that is respired is photosynthesis. down. Hence, ATP acts as energy currency of the cell.
BREATHING IN PLANTS
- For respiration, plants get O2 and give out CO2. - Complete combustion of glucose yields energy most of
- In plants, gas exchange occurs via stomata & lenticels. which is given out as heat.
- Plants need no specialized respiratory organs because C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
• Each plant part takes care of its own gas-exchange needs.
- This energy is utilized to synthesize other molecules.
So gas transport is very limited.
- During the glucose catabolism, not all the liberated energy
• Very low gas exchange as compared to that of animals.
goes out as heat. Glucose is oxidised in several small steps.
• Leaves are adapted for maximum gas exchange during
It enables some steps to couple released energy to ATP
photosynthesis. During this, O2 is released within the cell.
synthesis.
• Most living cells have contact with air. They are located
- During respiration, oxygen is utilized, and CO2, water &
close to plant surface. In stems, living cells are organized
energy are released.
in thin layers beneath the bark. They also have lenticels.
- Certain organisms are adapted to anaerobic conditions.
In leaves, stems & roots, parenchyma cells are loosely
Some are facultative anaerobes. Others are obligate.
packed that provides interconnected air spaces.
GLYCOLYSIS (EMP PATHWAY)
- It is the partial oxidation (breakdown) of glucose to 2
molecules of pyruvic acid (C3H4O3) in the absence of O2.
- It occurs in cytoplasm of all living organisms.
- Its scheme was given by Gustav Embden, Otto Meyerhof
& J. Parnas. So it is also known as EMP pathway.
- In anaerobes, it is the only process in respiration.
- In plants, glucose is derived from sucrose (end product of
photosynthesis) or from storage carbohydrates. Sucrose is
converted to glucose & fructose by an enzyme, invertase.
These 2 monosaccharides readily enter glycolytic pathway.
- Glucose & fructose are phosphorylated to form glucose-6-
phosphate by the enzyme hexokinase. It is then isomerised
to produce fructose-6-phosphate. Subsequent steps of
metabolism of glucose and fructose are same.
Steps of glycolysis:
- It includes 10 steps under the control of different enzymes.
- ATP is utilized at 2 steps:
• In the conversion of glucose into glucose 6-phosphate.
• In the conversion of fructose 6-phosphate to fructose 1,
6-diphosphate.
- Fructose 1, 6-diphosphate is split into dihydroxyacetone Pyruvic acid
phosphate (DHAP) & 3-phosphoglyceraldehyde (PGAL). (pyruvate) is the key
- PGAL is oxidised and with inorganic phosphate get product of glycolysis.
converted to 1, 3-bisphosphoglycerate (BPGA). During Its metabolic fate
this, 2 redox-equivalents (2 H-atoms) are removed from depends on the
PGAL and transferred to NAD+ forming NADH + H+. cellular need.
- BPGA becomes 3-phosphoglyceric acid (PGA) yielding
energy. This energy is trapped by the formation of ATP. In different cells, pyruvic acid is handled in 3 ways:
- ATP is also formed when PEP converts to pyruvic acid. • Lactic acid fermentation.
- In glycolysis, 4 ATP molecules are directly synthesised • Alcoholic fermentation.
from one glucose molecule. • Aerobic respiration (Krebs’ cycle).
1
