Question

1. which part of phospholipids is hydrophobic? hydrophilic? 3. what is meant by “fluid mosaic” model? 4. why do phospholipids form a bilayer? 5. how does cholesterol help stabilize the plasma membrane in hot and cold temperatures? 6. how do the unsaturated hydrocarbon tails (kinks) help stabilize membrane fluidity? 7. some plants, like winter wheat, have evolved to tolerate extreme cold. specifically, the winter wheat plant can increase the percentage of unsaturated phospholipids in their membrane during the winter season. how is this helpful to the plant? be specific and draw a picture of winter wheat’s plasma membrane before and during the winter season.

Explanation:

1. Phospholipids have polar, water - loving heads (hydrophilic) and non - polar, water - fearing tails (hydrophobic) due to their chemical structure.
2. The fluid mosaic model describes cell membranes as a fluid mixture of phospholipids, proteins, and other components, with a mosaic - like arrangement.
3. Phospholipids form a bilayer because the hydrophilic heads face the aqueous environments inside and outside the cell, while the hydrophobic tails are shielded in the middle to avoid water.
4. In hot temperatures, cholesterol restricts phospholipid movement to prevent excessive fluidity. In cold temperatures, it prevents phospholipids from packing too closely, maintaining fluidity.
5. Unsaturated hydrocarbon tails have kinks that prevent phospholipids from packing tightly together, thus maintaining membrane fluidity.
6. Increasing the percentage of unsaturated phospholipids in winter wheat's membrane helps prevent the membrane from solidifying in cold temperatures, maintaining its function. A picture would show a more tightly - packed membrane before winter (with more saturated phospholipids) and a more loosely - arranged membrane during winter (with more unsaturated phospholipids).

Answer:

1. The heads of phospholipids are hydrophilic, and the tails are hydrophobic.
2. The fluid mosaic model is a model used to describe the structure of cell membranes as a fluid mixture of components.
3. Phospholipids form a bilayer to keep the hydrophilic heads in contact with water and shield the hydrophobic tails from water.
4. In hot temperatures, cholesterol restricts movement; in cold, it prevents tight packing.
5. The kinks in unsaturated hydrocarbon tails prevent tight packing and maintain fluidity.
6. It helps prevent the membrane from solidifying in cold. A picture would show a change in membrane phospholipid packing.