Respiration in the Plants
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Respiration in the Plants
Sun is the main source of energy for all the living organisms.
The plants absorb sun energy & change it into chemical energy by means of photosynthesis process.
This energy is then stored in chemical compounds when the plant needs this energy back to carry out vital activities.
It breaks carbon bonds in the organic molecules to release the energy slowly in a series of steps. This called respiration in the plant.
The plant can release the energy by using O2 in aerobic respiration or in the absence of O2 during anaerobic respiration.
The plant cells which are found in direct contact with the environment take O2 directly from the air & give out CO2 to the air by diffusion.
In vascular plants, which are more complicated CO2 and O2 reaches the deep cells in the plant through several ways:
1- Through stomata air enters into the air chambers & diffuses through intercellular spaces. CO2 and O2 is then diffuses into the cells of the plant leaf & dissolves in the cell sap.
2- Through phloem CO2 &O2 go to different plant cells dissolved in H2O.
3- Through the roots CO2 & O2 is dissolved in the soil solution enters into the root hairs through the plasma membrane.
4- Through lenticels of wooden stem CO2 &O2 enters from the air to stem .
5. Part of O2 produces in photosynthesis used in respiration, and CO2 which produced as the result of respiration process is used in photosynthesis process.
The releation between respiration and photosynthesis
In the chloroplast photosynthesis takes place
to store light energy in the chemical bonds of
the food molecules.
In mitochondria respiration takes place to release
the stored energy in the food molecules.
Experiments to illustrate that CO2 evolves during respiration in the plant
A) An Exp. to prove that the non-green parts of the plant respire
1- Put some dry seeds (pea) in the first retort & dip its stem in a beaker containing KOH solution
2- Put some germinated seeds in the second retort & dip its stem in a beaker containing NaCl solution.
3- Put some germinated seeds in the third retort & dip its stem in a beaker containing KOH solution.
Observation:-
No changes occur in cases one & 2 but KOH raises the third retort stem.
Conclusion
1- Dry seeds do not respire actively, so the volume of air in retort no.(1) is remains constant.
2. Germinating seeds respire actively, the volume of air in retort no. (2) remains constant during respiration because the released CO2 is equal the absorbed oxygen, it is because the released CO2 is not absorbed by NaCl solution.
3. When germinating seeds in retort no. (3) respire, the released CO2 absorbed by KOH sol. So, the KOH rises up in the stem of the retort.
B) An Exp. to prove that the green parts of the plant respire
1- Put a green plant in a pot on a glass sheet & Put a beaker containing lime
water beside the pot. Cover both with a bell jar. Cover the bell jar with a black cloth (Why?)
2- Repent the above step by using an empty pot i.e. without plant.
3- Put a beaker containing lime water beside the apparatus in the air.
4- Leave the experiment for some times.
Observation
Limewater is turbid at the presence of green plant
Conclusion:
In 1. The green plant respires & releases CO2 to the air. This CO2 turns limewater to milky solution.
In 2. & 3. No changes occur to the limewater as the amount of the limewater
the air inside & outside the bell jar is very small.
The green parts of the plant respire & releases CO2 to the air.
An experiment to prove alcoholic fermentation:
Put a sugary solution (or molasses diluted with the double of its volume of water) in a conical flask.
Add some yeast and mix it thoroughly.
Close the flask with a stopper through which a delivery tube passes.
Dip the free end of the delivery tube into a beaker containing lime water.
Leave the apparatus, in a worm place, for several hours.
Observation
1. Gas bubbles are seen on the surface of the solution in the flask.
2. Lime water becomes turbid
Conclusion
Turbidity of lime water proves that CO2 has been evolved as a result of respiration of yeast.
Seeds of Angiosperms have the power to respire anaerobically
if they are kept under anaerobic conditions.
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