Question

Microorganisms act upon the dead plants to produce
(a) sand
(b) mushrooms
(c) humus
(d) wood

Answer 1

Hint: An organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms. It is a brown-black colored substance that remains after most of the organic litter has decomposed.

Complete answer:
Microorganisms act upon the dead plants to produce a thick brown or black substance called humus. The microorganisms convert the dead plants and animals to humus and are known as decomposers, like bacteria and fungi. Humus is a very important component of the soil as it contains many useful minerals and nutrients.
According to the degree of its incorporation into the mineral soil, the types of organisms involved in its decomposition, and the vegetation from which it is derived, humus is classified into mor, mull, or moder formations.
Mor-humus formation: Occurs due to raw humus condition, few microorganisms or animals, such as earthworms, to decompose the organic matter that lies on the soil surface. Below this surface-litter layer is visible. A layer of mineral soil is present beneath the humus. Fungi and small arthropods are the most common organisms found in this type. Most soils are mostly acidic (low pH) and are found in the coniferous forest areas, especially in cold regions and at high altitudes.
Mull-humus formation: Hardwood forests, deciduous forests, or grasslands in warm, humid climates, are the areas where they occur. The humus is porous and crumbly. It rapidly decomposes and becomes well mixed into the mineral soil. Its distinct layers are not apparent. Bacteria, earthworms, and larger insects are in abundant numbers, and the pH is high (alkaline).
Moder-humus formation: It is intermediate between mor and mull extremes. Moder is sometimes known as insect mull because it is distinguished on behalf of the presence of arthropod fecal pellets. These pellets bind the plant debris and the mineral particles together into a netlike structure. Moder contains more organic material than a mull, but this material is not as well mixed with the mineral components.
So, the correct answer is, ‘humus.’

Note: The farmers value humus because it provides nutrients essential for plant growth, increases soil water absorption, and improves soil workability. It plays a significant role in the control of soil acidity, in the cycling of nutrients, and the detoxification of hazardous compounds.