Question

As noted in this chapter, respiratory pigganents that are dissolved in the blood plasma usually have very high molecular weights. The statement has been made that in animals with dissolved respiratory pigments, "the polymerization of unit respiratory-pigment molecules into high-molecular-weight polymers allows the blocd solution to have a high cxygen-carrying capacity without having its asmotic pressure boosted to high levels by the presence of the respiratory pigment." Explain. (Hint: Review in Chapter 5 how dissolved entities affect the colligative properties of solutions.)

Short answer

The polymerization of respiratory pigments into larger, high-molecular-weight polymers allows the blood to maintain a high oxygen-carrying capacity without increasing osmotic pressure. This happens because colligative properties like osmotic pressure depend on the total number of solute particles, not their individual size or mass. Larger polymers result in fewer particles, thus controlling osmotic pressure.

Step-by-step solution

Understanding Colligative Properties

The colligative properties of a solution depend on the concentration of solute particles, not on the nature of the solute. They are properties that exist because there are solute molecules in the solution. The more solute there is, the greater the effect. They include: boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Understanding Osmotic Pressure

Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. A solution with a higher concentration of solute particles has a high osmotic pressure and that with a lower concentration has a low osmotic pressure.

Understanding the Role of Respiratory Pigments

Respiratory pigments are proteins that transport oxygen, among other things, in the blood plasma. If these pigments were small or individual molecules, they would create more particles in the plasma and thus increase the osmotic pressure.

Applying Knowledge to Answer the Question

Polymerization of respiratory pigments into larger, high-molecular-weight polymers reduces the total number of particles. This helps maintain the oxygen-carrying capacity of the blood without increasing the osmotic pressure. The high oxygen-carrying capacity is tied to the amount (mass) of respiratory pigment, not the number of particles it creates when dissolved.

Key concepts

Osmotic Pressure

When considering solutions, especially biological ones like blood, osmotic pressure plays a crucial role in maintaining balance. Osmotic pressure refers to the force required to prevent water from moving across a semipermeable membrane. The concentration of solute particles in a solution directly impacts its osmotic pressure.
A high concentration of solute particles results in high osmotic pressure, demanding more force to stop water from flowing inwards. Conversely, a solution with fewer solute particles exhibits lower osmotic pressure.
In terms of colligative properties, osmotic pressure depends solely on the number of dissolved solute particles, not on their specific characteristics or nature. This principle is vital in biological systems to ensure appropriate function and balance across cell membranes.

Respiratory Pigments

Respiratory pigments are specialized proteins that transport oxygen and other gases in the blood. In animals, these pigments are often responsible for managing oxygen levels critical for survival.
Imagine each respiratory pigment as a tiny oxygen shuttle. If they were small, individual molecules, they would significantly increase the number of particles in the blood plasma, consequently raising its osmotic pressure.
By polymerizing or joining into larger structures, these pigments effectively reduce the number of individual solute particles while still maintaining a high oxygen-carrying capacity. Through this strategy, animals avoid excessive blood osmotic pressure, which ensures the smooth functioning of biological processes and avoids strain on their circulatory systems.

Polymerization

Polymerization is the process of combining many small molecules, called monomers, into larger, chain-like structures known as polymers.
This process is common in biological systems and plays a crucial role in managing molecule behavior in solutions. For example, in blood, respiratory pigments undergo polymerization to form larger molecules with high molecular weights.
The significance of polymerization in blood is that it reduces the number of individual solute particles. This decrease in the number of particles helps maintain desired colligative properties—like osmotic pressure—without compromising the ability to transport large amounts of oxygen. By employing polymerization, organisms optimize their biological functions by balancing solute concentration and functionality efficiently.