Question

How can you prove that co2 is necessary for photosynthesis?

Answer 1

Carbon dioxide provides the carbon that the plant uses to produce glucose. Carbon dioxide is combined with water using the energy from sunlight.

The carbon in glucose is not only used in cellular respiration to make ATP, but actually makes up most of the plants. The majority of a plants mass comes from the carbon that it gets from carbon dioxide(not the soil or else potted plants would gradually suck out most of the soil around them) after the sugar it makes is metabolized into other things.

The photosynthesis reaction is basically the opposite of cellular respiration with 6 CO2 and water molecules going in (actually 12 water molecules but 6 are reformed by the end) and 1 glucose precursor molecule (a 3 carbon sugar called gyceraldehyde 3-phosphate or G3P that can be used to make glucose) and 6 O2 molecules coming out. The carbon enters photosynthesis in the Calvin cycle in which one carbon is fixated for every cycle. This means that even though there are actually 6 G3P molecules produced for every 3 CO2 molecules, since 5 of them are needed for the continuation of the cycle there is a net product of only 1 G3P for every 3CO2. A glucose molecule has 6 carbons and G3P have 3 carbons each so you need 6 CO2 molecules for every glucose.

Answer 2

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$<b><i>$ Carbon dioxide provides the carbon that the plant uses to produce glucose. Carbon dioxide is combined with water using the energy from sunlight.

An experiement to show this⤵️⤵️

Lime water absorbs carbon dioxide and hence there is no carbon dioxide for the leaf and hence photosynthesis does not take place and no starch is prepared. Hence on iodine test, the presence of starch is negative and thus proves that carbon dioxide is required for photosynthesis.