Mycorrhiza is symbiotic association between a fungus and the roots of a higher plant. Mycorrhiza are of common occurrence. Mycorrhizal plants benefit from the association in ectotrophic forms particularly by the fungal transport of ions (eg; PO4" ) which are relatively immobile in the soil into the plant roots. So option A is correct

Mycorrhiza promotes plant growth by absorbing inorganic ions from the soil.

Mycorrhiza is a symbiotic association between the roots of most plant species and certain fungi. This association is mutually beneficial, as both the plant and the fungus benefit from each other. Mycorrhizal fungi form a network of hyphae that extend into the soil, greatly increasing the surface area available for nutrient absorption. This allows the fungi to access nutrients that are otherwise unavailable to the plant.

How does mycorrhiza absorb inorganic ions from the soil?

Mycorrhizal fungi have a unique ability to absorb inorganic ions, such as phosphorus, nitrogen, and various micronutrients, from the soil. They do this by releasing enzymes that break down organic matter in the soil, releasing the nutrients in an available form. The hyphae of the fungi have a large surface area, which allows them to efficiently absorb these nutrients and transport them to the plant roots.

Why is the absorption of inorganic ions important for plant growth?

Inorganic ions are essential for plant growth and development. They are required for various physiological processes, including photosynthesis, respiration, and the synthesis of DNA and proteins. However, these ions are often present in the soil in insoluble forms or are tightly bound to soil particles, making them inaccessible to plants. This is particularly true for phosphorus, which is an essential nutrient but is often present in low concentrations in the soil.

How does mycorrhiza promote plant growth?

By absorbing inorganic ions from the soil, mycorrhizal fungi greatly enhance the nutrient uptake of plants. This increased availability of nutrients promotes plant growth and development in several ways:

1. Increased nutrient absorption: The hyphae of mycorrhizal fungi extend far beyond the reach of plant roots, allowing the plant to access a larger volume of soil and absorb more nutrients.

2. Enhanced phosphorus uptake: Mycorrhizal fungi have a high affinity for phosphorus, which is often limiting for plant growth. By efficiently absorbing phosphorus from the soil and transferring it to the plant roots, mycorrhiza improves the plant's phosphorus nutrition.

3. Nutrient cycling: Mycorrhizal fungi can also improve soil fertility by breaking down organic matter and releasing nutrients back into the soil. This helps to create a nutrient-rich environment for plant growth.

4. Stress tolerance: Mycorrhiza can help plants cope with various environmental stresses, such as drought, salinity, and heavy metal toxicity. The improved nutrient uptake and enhanced root growth provided by mycorrhizal fungi allow plants to better withstand these challenging conditions.

In conclusion, mycorrhiza promotes plant growth by absorbing inorganic ions, particularly phosphorus, from the soil. This symbiotic association between plants and fungi greatly enhances nutrient uptake, improves soil fertility, and increases the plant's ability to tolerate environmental stresses.