Write a balanced chemical symbol equation for photosynthesis, the process by which plants synthesise glucose.

The structure of a leaf is highly adapted to facilitate photosynthesis and gas exchange. Explain how the following parts of a leaf are adapted for these functions: (i) palisade mesophyll cells

(ii) spongy mesophyll layer

(iii) guard cells

A student investigates the necessity of carbon dioxide for photosynthesis using a destarched potted plant. One leaf is placed inside a flask containing a chemical that absorbs carbon dioxide. A second leaf is placed inside a control flask containing water. Both leaves remain attached to the plant. The apparatus is left in bright light for 24 hours. The student then tests both leaves for starch using the following method:

• Step 1: Place the leaf in a beaker of boiling water for 30 seconds.
• Step 2: Place the leaf in a boiling tube of ethanol, put the tube in a hot water bath, and leave it for 5 minutes.
• Step 3: Rinse the leaf in cold water.
• Step 4: Spread the leaf out on a white tile and add several drops of iodine solution.

(i) Explain why the leaf is placed in boiling water in Step 1.

(ii) Explain why the leaf is heated in ethanol in Step 2, and describe how the student can carry out this step safely.

(iii) State the final colour observed after adding iodine solution in Step 4 for:

• the leaf from the flask containing the carbon dioxide-absorbing chemical
• the leaf from the control flask

(iv) Explain why it is important to destarch the plant before commencing this experiment.

Plants also require mineral ions absorbed from the soil to maintain health and produce essential biological molecules.

Complete the table by giving the missing information:

| Magnesium | (ii) __________ |