The apparatus shown in Fig. 3.1 was used to find out if nitrate ions helped plants to grow. (a) Give reasons why (i) the solution have air bubbled through it, (ii) the apparatus was covered in black paper.

a) (i) The solution has air bubbled through it to provide oxygen for the roots of the seedling. Plant roots require oxygen for aerobic respiration, which releases energy necessary for processes like active transport of mineral ions (including nitrate ions) and water absorption. Without sufficient oxygen, the roots would not be able to function properly or might die. (ii) The apparatus was covered in black paper to prevent the growth of algae in the solution. Algae are photosynthetic organisms that would compete with the seedling for the nitrate ions and other nutrients in the solution. By blocking light, the black paper inhibits photosynthesis and thus prevents algal growth, ensuring that the seedling is the only organism utilizing the nutrients. That's 2 down. 3 left today — send the next one.