Ch. 29 - Fungi

Problem 7

Chapter 28, Problem 7

Lignin and cellulose provide rigidity to the cell walls of plants. But in most fungi, chitin performs this role. Why is it logical that most fungi don't have lignin or cellulose in their cell walls?

Verified step by step guidance

Understand the composition of plant and fungal cell walls: Plants primarily use cellulose and lignin to provide structural support and rigidity to their cell walls, whereas fungi predominantly use chitin.

Recognize the evolutionary divergence: Fungi and plants have evolved differently, adapting to their environments with distinct structural compounds in their cell walls that best suit their growth and survival needs.

Consider the biochemical properties: Chitin, found in fungal cell walls, is a strong, flexible and nitrogen-containing polysaccharide, which provides structural support similarly to cellulose and lignin but is more suited to the ecological niche fungi occupy.

Analyze ecological roles: Fungi often thrive in environments and conditions that differ from those of plants, and the presence of chitin instead of cellulose or lignin could be an adaptation to their specific ecological roles and interactions with other organisms.

Reflect on evolutionary efficiency: Using chitin, which is also found in the exoskeletons of arthropods, might represent an evolutionary efficient pathway for fungi, reducing the need to evolve and synthesize other structural polymers like lignin or cellulose.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cell Wall Composition

Cell walls are structural layers surrounding cells, providing support and protection. In plants, the primary components are cellulose and lignin, which contribute to rigidity and strength. In contrast, fungi have cell walls made of chitin, a polymer that offers similar structural integrity but is chemically distinct from cellulose and lignin.

Function of Chitin in Fungi

Chitin is a long-chain polymer of N-acetylglucosamine, which is a derivative of glucose. It serves as the main structural component in the cell walls of fungi, providing strength and rigidity. This adaptation allows fungi to thrive in various environments, as chitin is more flexible and resilient compared to lignin and cellulose, which are more suited to the needs of plants.

Evolutionary Adaptations

The absence of lignin and cellulose in fungi is an evolutionary adaptation that reflects their distinct ecological roles compared to plants. Fungi are primarily decomposers, breaking down organic matter, and their chitin-based cell walls are better suited for their lifestyle. This divergence in cell wall composition illustrates how different organisms have evolved specialized structures to meet their specific environmental challenges.

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Related Practice

Textbook 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.

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Textbook Question

Explain why fungi that degrade dead plant materials are important to the global carbon cycle. Do you accept the text's statement that, without these fungi, 'Terrestrial environments would be radically different than they are today, and probably much less productive'? Why or why not?

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Textbook Question

Evaluate each of the following defects. Which could lead to uncontrolled growth in cancer? Select True or False for each statement. T/F The overexpression of MPF activity. T/F A nonfunctional Rb protein. T/F The overexpression of G1 cyclin. T/F A nonfunctional E2F protein.

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Textbook Question

Lawns are sometimes fertilized with nitrate that can be washed into neighboring woodlots by rain. If the trees in that woodlot are associated with EMF, what effect might the excess nitrate have on the fungi and/or trees? a. Fungal growth may be stimulated, causing the trees to transport more nitrogen to the fungi. b. The fungi may secrete more peptidases to break down the nitrate. c. The trees may take up the nitrate directly into their roots and rely less on the fungi. d. The excess nitrate may stimulate the fungi to transport more sugar to the trees.

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Textbook Question

A particular cell type spends 4 hours in G1 phase, 2 hours in S phase, 2 hours in G2 phase, and 30 minutes in M phase. If a pulse–chase experiment were performed with radioactive thymidine on an asynchronous culture of such cells, what percentage of mitotic cells would be radiolabeled 9 hours after the pulse? a. 0 percent b. 50 percent c. 75 percent d. 100 percent

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Textbook Question

Table 29.1 mentions that chytrids are responsible for massive die-offs currently occurring in amphibians. Review Koch's postulates; then design a study showing how you would use Koch's postulates to test the hypothesis that chytrid infections are responsible for frog deaths.

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