significance of photosynthesis


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Each living cell in every living organism needs energy. Energy is needed to drive the chemical reactions in the cell. It is needed for all metabolic processes: building up new molecules for growth, breaking down unwanted molecules, bringing about movement, etc. the chemical process by which energy is released from glucose and other organic molecules is called respiration which is related to significance of photosynthesis. Thus, respiration is the process of biochemical decomposition of organic compounds like simple carbohydrates, glucose in the living cells with the release of energy. It is also known as a biochemical reaction.

The equation for respiration:-

C6H12O6 (carbohydrate) + 6O2 (oxygen)   = 6CO2(carbon-di-oxide)  + 6H2O (water) + ENERGY (38 ATP)


Here are some experiments to explain Respiration in plants.


Objective:  green plants produce carbon-dioxide during respiration.

Requirement: * A bell jar

*Two conical flasks

*An air pump

*2 bent glass tubes

*Soda lime

*Potted plant

*Lime water


i) A small potted green plant is taken

ii) It is covered with a bell jar and made air-tight by applying Vaseline.

iii) The bell jar is connected on both sides with two conical flasks containing lime water.

iv) The bell jar is covered with black paper to prevent photosynthesis so that caron-di-oxide produced uring respiration is not consumed in photosynthesis.

v) Air is pumped into the apparatus with the help of air pump.

vi) The air passes through the soda lime which absorbs any carbon-di-oxide present in the air .

vii) The set up is kept for 3-4 hours.


When this air passes through the lime water in conical flask A, it does not turn milky. The air free from carbon-di-oxide enters the bell jar and comes in contact with the green plant. The air from the bell jar enters the conical flask B containing lime water. The lime water turns milky.

Conclusion: Lime water in flask B turns milky because the air coming from the bell jar contains carbon-di-oxide while the air entering the bell jar is free from carbon-di-oxide is produced by the green plant kept under the bell jar.

This shows that green plants produce carbon-di-oxide during respiration.



To show that heat is evolved during respiration.


*Two thermos flasks

*Soaked boiled seeds washed with dilute carbolic acid to prevent any bacterial growth

*Soaked germinating seeds



i)The germinating  seeds are placed in flask A

ii) Boiled seeds are placed in flask B .

iii) Two thermometers are inserted in each flask and the mouth of flasks are sealed with cotton wool.

iv) The set up is kept for 3-4 hours.


Flask B does not show any rise in temperature. Flask A shows  higher reading .


This experiment shows that germinating seeds give out heat during respiration.

This shows that green plant evolves heat on respiration.



Anaerobic respiration in germinating seeds.


* 4-6 soaked pea seeds after removing outer covering or testa to increase the diffusion of CO2 from the seeds.

*Test tube

* Mercury


Procedure: i) The test tube is filled with mercury.

ii)These seeds are introduced into the test tube.

iii)The beaker is half filled with mercury.

iv)The test tube is inverted on the beaker.

v)The seeds are floated at the top level.

vi)this experimental set-up is left for 48 hours.


After 48 hours, we will observe that the level of mercury falls in the test tube.

Conclusion: carbon-di-oxide gas is liberated from seeds has pushed the mercury down. If Potassium pellet is introduced inside the test tube the mercury will rise up almost to the top of the tube. This happens because the Potassium hydroxide (KOH) absorbs carbo-di-oxide gas.

So it is shown that CO2 is released even during anaerobic respiration.


Objective: To show that oxygen is used up in respiration.

Requirement: * Two flask A and B

*Germinating bean seeds

*Boiled seeds

*Wet cotton

*A beaker

*Small tube

*Soda lime

Procedure: i) Germinating seeds are placed in flask A on wet cotton.

ii) Boiled seeds are placed in conical flask B.

iii) A small test tube containing soda lime

iv) The soda lime absorbs carbon-di-oxide released by the seeds.

v) Each flask is connected with a delivery tube and placed in a beaker containing water.

vi)The sthe same et-up is left for a few days.

* The level of water in the delivery tube is noted.

Observation: Delivery tube A shows a greater rise in water level.

Conclusion: A burning paper is introduced into each flask after removing the corks. It is found that the flame is immediately put off in flask A but it continues for a short in flask B. it shows that there is no oxygen in flask A as it is used up by germinating seed. In flask B there is no response occurred due to the dead bean seeds.

So it is shown that oxygen is used up in respiration.

                                                        TEST YOURSELF 

The objective of the following experimental setup is to study and prove a physiological process in the plants, observe, study the same and answer the questions. 

i)Name the physiological process shown in figure.

Ans:-  Aerobic respiration.

ii) State the function of soda lime in the flask A and why we place  lime water in flask B?

Ans:- Lime water in flask A absorbs CO2. Lime water of flask B does not turn milky to prove that the air goes to flask C is CO2 free.

iii) What change you can expect in flask D?

Ans:- Lime water turns milky in flask D.

iv) Write a chemical equation to represent the physiological process named in (i).

C6H12O6 (carbohydrate) + 6O2 (oxygen) = 6CO2 (carbon-di-oxide)   + 6H2O (water)  + 38 ATP (energy).

v) In order to obtain accurate results, we must cover  the flask C  with a black paper or black cloth, why?   

Ans:- So that germinating seed does not perform photosynthesis . CO2produced by respiration of seed seed cannot be used   by photosynthesis.

vi) If you introduce  thermometer  in flask c in such a way that its bulb reaches close to the germinating seeds, what would you observe? Why?

Ans:-  The thermometer will show temperature rise, because during respiration evolve of heat  occursresulting  increase of temperature.

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