To make the plant free of starch it is -kept in darkness for 72 hours.kept under the shade of tree.kept in a room, but with lights on at night only.kept covered with coloured polythene in a shady place.

To make a plant free of starch, it is important to deprive it of light for a sufficient period. This process is known as "destarching." Here is the step-by-step reasoning for the given options:

1. Kept in darkness for 72 hours:

   • Plants produce starch through photosynthesis, which requires light. By keeping the plant in complete darkness for 72 hours, you prevent photosynthesis from occurring. During this time, the plant will use up its stored starch for its metabolic needs, effectively making it free of starch.

2. Kept under the shade of a tree:

   • While shade reduces the amount of light the plant receives, it does not completely eliminate it. Photosynthesis can still occur, albeit at a reduced rate. Therefore, the plant will not be completely free of starch.

3. Kept in a room, but with lights on at night only:

   • If the plant is exposed to light at night, photosynthesis can still occur during those hours. This means the plant will continue to produce and store starch, so it will not be free of starch.

4. Kept covered with colored polythene in a shady place:

   • Colored polythene may filter some wavelengths of light but not necessarily block all light. Depending on the color and transparency of the polythene, some light may still reach the plant, allowing photosynthesis to continue to some extent. Therefore, the plant may not be completely free of starch.

Conclusion: The most effective method to make the plant free of starch is to keep it in darkness for 72 hours. This ensures that no photosynthesis occurs, and the plant uses up its stored starch.

Para hacer que la planta esté libre de almidón, se debe:

1. Mantener en la oscuridad durante 72 horas.

Explicación paso a paso:

1. Fotosíntesis y almidón: Las plantas producen almidón como resultado de la fotosíntesis, un proceso que requiere luz. Al mantener la planta en la oscuridad, se impide la fotosíntesis y, por lo tanto, la producción de almidón.

2. Consumo de reservas: Durante el período de oscuridad, la planta consume sus reservas de almidón para obtener energía, ya que no puede producir más almidón sin luz.

3. Duración: Un período de 72 horas