Question

The Greek root ecto means "outer." Why are ectomycorrhizal fungi, or EMF, aptly named? a. Their hyphae form tree-like branching structures inside plant cell walls. b. They are mutualistic. c. Their hyphae form dense mats that envelop roots but do not penetrate the cell walls. d. They transfer nitrogen from outside their plant hosts to the interior.

Short answer

Ectomycorrhizal fungi are aptly named because their hyphae form dense mats that envelop roots but do not penetrate the cell walls, aligning with the Greek root "ecto" meaning "outer."

Step-by-step solution

Understanding ectomycorrhizal fungi (EMF)

Ectomycorrhizal fungi (EMF) are fungi that engage in a symbiotic association with the roots of plants. These fungi and their plant hosts mutually benefit from this relationship. It is essential to study the various properties and functions of these fungi to answer the question about their naming.

Analyzing option (a)

"Their hyphae form tree-like branching structures inside plant cell walls." This statement is describing a characteristic of fungi, but the term "inside" does not align with the meaning of "ecto" as "outer." Thus, this option is incorrect.

Analyzing option (b)

"They are mutualistic." While this statement is true for ectomycorrhizal fungi, their mutualistic function doesn't explain the "outer" characteristic specifically associated with the Greek root "ecto." Therefore, this option is also incorrect.

Analyzing option (c)

"Their hyphae form dense mats that envelop roots but do not penetrate the cell walls." This statement describes the fungi's growth on the "outer" part of the roots without penetrating the cell walls. It perfectly aligns with the meaning of the Greek root "ecto," making this option the correct answer.

Analyzing option (d)

"They transfer nitrogen from outside their plant hosts to the interior." Although it's a function of ectomycorrhizal fungi, this statement doesn't reveal any "outer" characteristics associated with the Greek root "ecto." Hence, this option is incorrect.

Conclusion

Based on the analysis of the given options, option (c) "Their hyphae form dense mats that envelop roots but do not penetrate the cell walls" is the correct answer because it directly corresponds to the meaning of the Greek root "ecto" (outer) in the context of ectomycorrhizal fungi.

Key concepts

Symbiotic Relationships in Biology

Symbiotic relationships in biology refer to the close and long-term interactions between different species. In these associations, at least one party stands to gain from the relationship, which can be classified as mutualism, commensalism, or parasitism. Mutualism is a win-win scenario where both species benefit; an example being bees pollinating flowers while collecting nectar for food.

In the case of ectomycorrhizal fungi (EMF), the symbiosis is of the mutualistic kind. The fungi receive sugars and other organic compounds from the plant, which are by-products of photosynthesis. On the flip side, the plants benefit from the fungi's ability to absorb water and nutrients, like phosphorus and nitrogen, from the soil. This two-way beneficial exchange is a hallmark of mutualistic symbiosis and is critical for the survival and thriving of forest ecosystems where EMF are commonly found.

Fungal Hyphae Structure

The structure of fungal hyphae is key to understanding the role they play in symbiotic relationships. Fungal hyphae are the long, thread-like structures that extend from the fungal body. They can grow rapidly and penetrate the soil, allowing fungi to absorb nutrients efficiently.

Hyphae are composed of tubular cells with chitin-rich cell walls. They form an extensive network called a mycelium, which is essential for the absorption of water and nutrients. In ectomycorrhizal relationships, however, these hyphae form dense mats without penetrating the host plant's cell walls, hence adhering to the 'ecto' (outer) prefix. This attribute reflects the intricate balance of how these fungi interact with their plant hosts, maintaining a close external connection that is vital for nutrient exchange without damaging the plant tissue.

Plant-Fungi Interactions

The interactions between plants and fungi are complex and vital for many ecosystems. Ectomycorrhizal fungi (EMF) embody one of the most fascinating plant-fungi interactions, where the relationship is based on nutrient exchange and enhanced survival. These fungi surround the roots of plants, forming a sheath and extending their hyphae into the rhizosphere - the soil region close to the roots. This setup is advantageous as it increases the root surface area for water and nutrient absorption.

As fungi can access nutrients that plants cannot, they effectively act as an extension of the plant's root system. This relationship not only boosts the plant's growth but also improves its resilience against pathogens and environmental stress. Such interactions demonstrate the delicate balance and vital role of mycorrhizal fungi in terrestrial ecosystems, underpinning the biodiversity and productivity of plants around the world.