How Oxygen is evolved by green plants in an experiment on Photosynthesis


Photosynthesis is an anabolic chemical process of green plants and it is a food synthesizing process. In this resource I have explained in detail how an experiment can be conducted to prove oxygen is evolved during photosynthesis process. Along with the experiment I gave some important questions as well as answers related to the experiment which will be useful for those preparing for final practical or theory exams of various Boards.

Introduction

Photosynthesis is a physiological process of green plants to manufacture their carbohydrate food. It is a complex chemical process occur in the chloroplasts of mesophyll tissue of green plants. During photosynthesis process green plants utilizes energy from solar radiation, Co2 from atmosphere, water and minerals from obtained from soil to prepare their carbohydrate food and in turn evolve oxygen.

Aim of the experiment:-

To prove that oxygen is evolved in green plants during photosynthesis.

Requirements:-

Hydrilla twigs, Beaker, a glass funnel, a Test tube, a beehive arrangement, pond water, a glowing splinter.

Procedure for the experiment

Take a beaker and fill 3/4ths of it with pond water. Take some freshly cut Hydrilla twigs and insert them in the nozzle from below the stem of a glass funnel. Keep this funnel in an inverted position at the bottom of the beaker. A beehive arrangement is used in between the base of the funnel and bottom of the beaker. Now a test tube is filled with pond water and is inverted over the stem of the funnel. While making this arrangement one has to see the level of water in the beaker should be above the level of stem of the inverted funnel. The whole arrangement is kept on a flat surface under bright sunlight for some time.

Oxygen is evolved by green plants during photosynthesis
Oxygen is evolved by green plants during Photosynthesis (Courtesy:-www.weekispaces.com)

Result of the experiment

Air bubbles start moving from the cut end of the Hydrilla twigs and get collected at the upper end of the test tube. After some time we find some gas get collected at the top of the inverted test tube by downward displacement of water. To test the nature of the gas collected, the test tube is removed quickly from the stem of the funnel and the mouth is closed with the thumb. Now a glowing splinter is introduced into the test tube by removing the thumb from the mouth of the test tube. The glowing splinter immediately burst into a flame indicating that the gas collected in the test tube is oxygen.

Here is an Experiment on Photosynthesis-Sunlight is necessary for Photosynthesis

Questions and answers related to the experiment

  • What is the aim of the above experimental setup?
    Ans. To prove oxygen is evolved by green plants during photosynthesis.

  • Why Hydrilla plants are used in this experimental setup?
    Ans. Hydrilla plants are aquatic algal plants. These plants can carry out photosynthesis even they are inside water.

  • Why pond water only should be used for this experiment?
    Ans. Pond water is a source of Co2 for these plants. Carbonates and bicarbonates present in pond water are absorbed through the leaves of these aquatic plants works as a source of Co2 for their photosynthesis.

  • If a pinch of baking soda is added to the water in the experimental setup what change you can notice in the result of this experiment?
    Ans. More air bubbles will come out from the cut end of hydrilla twigs indicating evolution of more oxygen. The reason for that is baking soda is nothing but sodium bi-carbonate which is a source of Co2 for photosynthesis. With increase in supply of Co2 rate of photosynthesis increases and thus more air bubbles (Oxygen) evolved.

  • Instead of pond water if distilled water or boiled and cooled tap water is used what will be the result of the experiment?
    Ans. Distilled water lacks dissolved Co2 in it and no evolution of O2 occurs as no photosynthesis occur. Similarly no photosynthesis occurs with boiled and cooled water as Co2 gas escapes from water as we boil it.

  • Here is an Experiment on Photosynthesis-Carbon dioxide is necessary for photosynthesis
  • How can you confirm the collected gas in the test tube as oxygen?
    Ans. A glowing splinter when introduced into the test tube containing the collected oxygen gas will burst into a flame and by this we confirm it.

Here is a video of the experiment "Oxygen is evolved by green plants during Photosynthesis"
Courtesy:-Youtube


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Comments

Guest Author: Abimon fernando18 Jun 2017

Thanks for the experiment. But why do we use an aquatic plant instead of a terrestrial plant?Can't we do this without water?



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