Question

Hydrilla leaf is used in an experiment to test that
a. Chlorophyll is necessary for photosynthesis.
b. Light is necessary for photosynthesis.
c. Carbon dioxide is necessary for photosynthesis.
d. Oxygen is evolved during Photosynthesis.

Answer 1

The study on photosynthesis started around 300 years ago. Scientists like Moll, Joseph Priestly, Jan Ingenhousz, Julius Von Sachs, T.W Engelmann, etc conducted various experiments to demonstrate different properties of photosynthesis.

Complete answer:
Let us study the given option.

Option A:
Chlorophyll is necessary for photosynthesis was demonstrated by covering the leaves with black paper and testing them for starch. The covered leaf does not show a positive starch test showing that photosynthesis cannot in the absence of light. The exposed leaf shows blue and yellow parts where the blue color or positive starch test occurs in the chlorophyll-containing parts.

Option B:
Light is necessary for photosynthesis is shown by covering leaves and performing the starch test as mentioned in option A explanation. Visible light consists of radiation having a wavelength between 390-760nm. Part of the spectrum used in photosynthesis has a wavelength between 400-700 nm.

Option C:
Carbon dioxide is necessary for photosynthesis was demonstrated through Moll’s half Leaf Experiment. one part of the leaf is soaked in cotton containing KOH while another half of the leaf is exposed to air. It was found that only the exposed part of the leaf tested positive for starch. This demonstrated that carbon dioxide is required for photosynthesis.

Option D:
Oxygen is evolved during photosynthesis as demonstrated by Jan Ingenhousz through an experiment on the aquatic plant -Hydrilla. He showed that in bright sunlight, small bubbles formed around the green parts of the plant while in dark, no bubbles were formed. He identified those bubbles as oxygen. Therefore, he showed that in the presence of sunlight it is only the green parts of the plants that could release oxygen.

Hence, the correct answer is option (D).

Note: Jan Ingenhousz also demonstrated through his exp[riment that sunlight is essential for the plant process that helps to somehow purify the air fouled by breathing mouse and the burning candle.