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Study Questions

What is a “cell wall”? Are plants the only organisms whose cells are surrounded by rigid walls? Be specific.
Cite six functions of plant cell walls.
Distinguish between the major components of plant cell walls: cellulose microfibrils, pectins, hemicelluloses, and proteins.
The structural components of plant cell walls are interconnected and cross-linked by various types of bonds, including hydrogen bonds, ionic bonds, and covalent bonds. Give specific examples of each of these types of interactions found in plant cell walls.
Distinguish between primary and secondary cell walls. How do they differ in their chemical composition and mechanical properties?
Describe the structure of cellulose and how its structure is related to its tensile strength.
How is cellulose synthesized and where does synthesis occur? Discuss the nature of the enzyme involved, its subunit structure, and the basic reactions involved.
How are the matrix components synthesized and deposited in the wall? How is this mechanism different from the synthesis of cellulose?
Compare and contrast the chemical structure, intermolecular bonds, and mechanical properties of cellulose, hemicelluloses, and pectins.
Name three classes of structural proteins in the primary cell wall. What are their functions?
Following their synthesis and secretion, cell wall polymers assemble to form the cell wall. Does this process occur by self-assembly or by enzyme-mediated assembly? What is an example of the latter?
What is lignin and how is it synthesized?
Discuss the occurrence and function of cell expansion by tip growth versus diffuse growth in the typical plant life cycle.
What effects do microtubule poisons usually have on the directionality of plant cell expansion, and why?
Discuss the meaning and significance of the term “stress relaxation” in relation to the process of plant cell expansion. Why is stress relaxation crucial for the process of plant growth?
Compare and contrast the two equations for describing plant growth with respect to either water uptake or cell wall yielding. What do they actually measure?
When plotted on the same graph, the lines generated by the two growth equations intersect. What is the significance of the point of intersection of the two equations?
What is meant by “acid growth” and what protein has been shown to mediate it? Describe the experiments that led to the discovery of this protein.
What chemical factors govern the cessation of cell expansion as plant cells reach maturity?