Question

from where do the plants get inorganic substance other than carbon dioxide and oxygen?

Answer 1

Although most of the autotrophic plants require only solar energy, carbon dioxide, water, and a few minerals to make all the organic compounds necessary to keep themselves going and growing, it is not the same with the non-autotrophic plants. There are different modes of how such plants derive nutrition and inorganic substances for their growth.

Several organic compounds are composed of an organic fraction of nitrogen in the soil. Ammonium (NH4+) and nitrate (NO3–) are the predominant inorganic forms of nitrogen in soils. Soil organic matter exists as decomposing plant and animal residues, relatively stable products of decomposition-resistant compounds and humus.

Semiparasitic Plants can take carbon dioxide from the air, but they cannot do it all by themselves, so they have to take some nutrients from an autotrophic host plant.

Insectivorous Plants uses carbon dioxide for photosynthesis, but they catch and slowly digest insects and other little animals that fall into their traps for extra nutrition and inorganic substances.

Saprophytes have a mycorrhizal fungus that connects them to another tree and transfers the nutrients from the host plant to the parasitic plant. 

Answer 2

Photosynthesis is the procedure by which the inorganic substances carbon dioxide and water are changed over to organic compound in the plant with the guide of light energy, freeing in the meantime the gas oxygen, and in this way is the most critical process on the planet for by its methods the plant blends nourishment for man and creatures, including those on his homestead and in his fishing grounds, and those which he chases.

In nature, it continues without any difficulty however under lab conditions, the procedure isn't anything but difficult to reproduce.