Question

What holds cellulose molecules together in bundles large enough to form fibers? a. the cell wall b. peptide bonds c. hydrogen bonds d. hydrophobic interactions

Short answer

The correct answer is (c) hydrogen bonds. These are the primary interactions responsible for holding cellulose molecules together in bundles large enough to form fibers.

Step-by-step solution

Understand cellulose structure

Cellulose is a complex carbohydrate made up of glucose units linked together to form long chains. These chains are held together by intra and intermolecular interactions, which give rise to the formation of fibers in the cellulose structure.

Analyze option (a) - cell wall

The cell wall is a protective layer that surrounds plant cells, but it is not directly involved in holding the cellulose molecules together. Rather, cellulose fibers are essential components of the cell wall. So, option (a) is not the correct answer.

Analyze option (b) - peptide bonds

Peptide bonds occur between amino acids in proteins, not in carbohydrates like cellulose. Hence, option (b) is not the correct answer.

Analyze option (c) - hydrogen bonds

Hydrogen bonding is a type of non-covalent bond that occurs between molecules or within different parts of a single molecule. In cellulose, hydrogen bonds primarily form between the hydroxyl groups (-OH) on the glucose units and the oxygen atoms on adjacent glucose units, both within and between the long chains. These hydrogen bonds provide the necessary interactions that hold cellulose molecules together into fibers. So, option (c) seems to be correct.

Analyze option (d) - hydrophobic interactions

Hydrophobic interactions involve the tendency of non-polar molecules to avoid interacting with water. Although hydrophobic interactions contribute to the structure and stability of some biological molecules like proteins, cellulose has numerous hydroxyl groups which interact with water. Therefore, hydrophobic interactions do not play a significant role in holding cellulose molecules together in fibers. Thus, option (d) is not the correct answer.

Determine the correct answer

Based on the analysis, the correct choice is (c) hydrogen bonds, as these are the primary interactions responsible for holding cellulose molecules together in bundles large enough to form fibers.

Key concepts

Hydrogen Bonds

In the world of chemistry, hydrogen bonds play a crucial role in stabilizing many substances, including cellulose. In cellulose, these bonds occur between the hydroxyl groups (-OH) on glucose units and the oxygen atoms of neighboring glucose molecules along the chains.
This type of bonding is non-covalent, meaning it involves associations that don't share electrons. Instead, it relies on the electromagnetic attraction between a hydrogen atom and a more electronegative atom, like oxygen.
These bonds are relatively strong compared to van der Waals forces, another type of weak interaction, and they are essential for the structural integrity of cellulose fibers. Hydrogen bonds are what allow the individual molecules to cling together, resulting in the formation of bundles. This network of hydrogen bonds in cellulose not only stabilizes its structure but also contributes to its rigidity and insolubility.

Intermolecular Interactions

Intermolecular interactions are the forces that occur between molecules and they are fundamental to the formation of structures such as cellulose fibers. Besides hydrogen bonds, cellulose also exhibits other minor interactions, although these aren't as significant in holding the cellulose structure together.
Intermolecular interactions can include van der Waals forces which are weaker, temporary attractions formed by shifting electron clouds in molecules. However, in cellulose, the dense network of hydrogen bonds overshadows these other interactions and serves as the primary force for cohesion between molecules.
This complex web of bonds and interactions ensures that cellulose remains tightly packed and able to perform its function in the plant cell wall, providing strength and support.

Carbohydrates

Carbohydrates are a class of biological molecules that include sugars, starches, and cellulose. Specifically, cellulose is a type of carbohydrate found primarily in the cell walls of plants, giving them structure and support.
At the molecular level, cellulose is composed of glucose units linked together in a linear chain by beta-1,4-glycosidic bonds.

• Glucose units: Small sugar molecules that are the building blocks of cellulose.
• Beta-1,4-glycosidic bonds: The specific type of covalent bond connecting glucose units in cellulose.

This unique structure helps cellulose to form parallel strands, allowing it to be densely packed and embedded into the cell wall.
Understanding cellulose's carbohydrate structure is essential for grasping how it assembles into strong, fibrous materials capable of supporting heavy plant structures.

Cell Wall

The cell wall is a vital part of plant cells, serving as a protective outer layer. It is mostly made up of cellulose, providing rigidity, strength, and shape to plants.
The cellulose fibers within the cell wall are distributed in a complex matrix that allows plants to maintain their structural integrity and withstand various environmental stresses.

• Protection: The cell wall safeguards the cell's internal components from damage.
• Support: It gives plants their ability to stand upright and grow tall.
• Regulation: Through its porous design, the cell wall helps in controlling the movement of water and nutrients in and out of the cell.

While the cell wall itself is not responsible for holding cellulose fibers together, it benefits immensely from the sturdy structure provided by cellulose. The network of cellulose in the cell wall is crucial for plant health and growth.