212 |
A Handbook of Biology
Oxidation of food materials (breaking of C-C bonds of complex
molecules) within the cell to release energy for ATP synthesis is called
cellular respiration.
This energy is used for
absorption, transport,
movement, reproduction,
breathing etc.
Ultimate source of food
that is respired, comes from
photosynthesis.
The energy released is not
used directly but is used
to synthesize ATP. When
energy is needed, ATP is broken down. Hence, ATP acts as energy
currency of the cell.
The compounds that are oxidized during respiration are called
respiratory substrates. E.g. Carbohydrates (most common), proteins,
fats and organic acids..
BRËÅTHÏÑG ÏÑ PLÅÑTS
For respiration, plants get O2 and give out CO2.
In plants, gas exchange occurs via stomata & lenticels.
Plants need no specialized respiratory organs because:
Each plant part takes care of its own gas-exchange needs.
So gas transport is very limited. Very low gas exchange
occurs as compared to that of animals.
Most living cells have contact with air. They are located
close to plant surface. In stems, living cells are organized
in thin layers beneath the bark. They also have lenticels.
In leaves, stems & roots, parenchyma cells are loosely
packed that provides interconnected air spaces.
Leaves are adapted for maximum gas exchange during
photosynthesis. During this, O2 is released within the cell.
1
2
3
Complete combustion of glucose yields energy most of which is given
out as heat.
This energy is utilized to synthesize other molecules.
Photosynthesis
Light
energy
CO2 + H2O
C6H12O6 + O2
Mitochondria
Chloroplast
Cell respiration
Chemical
energy
(ATP)