The aim of this experiment is to investigate whether carbon dioxide is necessary for photosynthesis.

Here are the answers to your questions:

2.1.1
The aim of this experiment is to investigate whether carbon dioxide is necessary for photosynthesis.

2.1.2

• A) Soda lime: To absorb carbon dioxide from the air in the bell jar.
• B) Sodium hydroxide: To absorb carbon dioxide from the air in the plastic bag around the leaf.
• C) Sodium bicarbonate: To release carbon dioxide into the bell jar.

2.1.3

• Bell jar 1: The starch test will be negative (e.g., remain yellowish-brown). This is because both soda lime and sodium hydroxide absorb carbon dioxide, making it unavailable for the plant. Without carbon dioxide, photosynthesis cannot occur, and therefore no starch will be produced.
• Bell jar 2: The starch test will be positive (e.g., turn blue-black). This is because sodium bicarbonate releases carbon dioxide, making it available for the plant. With carbon dioxide present, the plant can perform photosynthesis and produce starch.

2.1.4
De-starching each plant at the beginning ensures that any starch detected at the end of the experiment was newly produced during the experiment under the specific conditions. This eliminates any pre-existing starch, allowing the learners to confidently conclude that the presence or absence of starch is directly due to the experimental variable (carbon dioxide availability).

2.1.5
Two control variables implemented are:

• Same size and type of plants
• Same light intensity and duration (placed in a sunny area for 2 days)