ICSE 2019:
(a) The diagram given below represents an experiment to prove the importance of a factor in photosynthesis. Answer the questions that follow. [5 marks]
(i) Name the factor studied in this experiment.
(ii) What will you observe in the experimental leaf after the starch test?
(iii) Explain the process of photosynthesis.
(iv) Give a balanced chemical equation to represent the process of photosynthesis.
(v) Draw a neat, labelled diagram of an experimental set-up to show that oxygen is released during photosynthesis.
Solution:
This question based the process of photosynthesis was asked by ICSE board in the year 2019 in compulsory Section-II.
The question tested the knowledge of students on the fact that:
- SUNLIGHT is essential for the process of photosynthesis and
- oxygen is evolved as the by-product of the process.
Let's begin with solving the above mentioned questions:
ANSWERS:
(i) Sunlight is necessary for photosynthesis.
(ii) When leaf is treated with iodine to test the presence of starch, the parts of plant which were left uncovered shows presence of starch as they turn blue-black in colour whereas part of leaf covered with black paper turn brown in colour showing absence of starch.
- Uncovered parts --> turn blue-black (starch present)
- Parts covered with black paper --> turn brown (starch NOT present)
(iii) Photosynthesis is the process through which plants containing chlorophyll (green-colour pigment) produce food (starch, glucose) in the presence of sunlight from carbon-dioxide (CO2) and water (H2O) and release oxygen (O2) as the by-product.
(iv) Balanced chemical equation for photosynthesis can be written as:
6CO2 + 12H2O --------------------------> C6H12O6 + 6H2O + 6O2
carbon dioxide water sunlight, chlorophyll glucose water oxygen
(v) Experiment to show Oxygen is released as by-product during photosynthesis :
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