Final answer:
The hypothesis being tested is that photosynthesis is required for starch production in plants, which involves the Calvin cycle. Without light, the light-dependent reactions of photosynthesis cannot occur, this results in no production of glucose and starch.
Step-by-step explanation:
The investigation where green leaves kept in the dark for several days are tested for starch and no starch is found, would likely be testing the hypothesis that photosynthesis is required for starch production in plants.
Starch production is dependent on the Calvin cycle, a series of light-independent reactions that occur in the chloroplasts of plant cells.
During these reactions, carbon dioxide is fixed into glucose, which can then be stored as starch.
As the Calvin cycle is driven by the chemical products of the light-dependent reactions, an absence of light would impede photosynthesis, thus leading to a lack of glucose and consequently, starch.
On a hot, dry day, when plants close their stomata to conserve water, the impact on photosynthesis would be negative.
The closed stomata limit the intake of carbon dioxide, which is essential for the light-independent reactions (Calvin cycle), where CO₂ is used to synthesize G3P (glyceraldehyde-3-phosphate), which is a precursor for glucose and ultimately starch.
Therefore, the synthesis of G3PA would decrease due to the reduced availability of CO₂.