Question

1. the selectively permeable plasma membrane is composed of phospholipids and protein, which allow for its unique functions. (a) describe the structure and properties of phospholipids and explain the important roles of phospholipids in the plasma membrane. (b) predict how the normal function of the plasma membrane would be altered if all phospholipids were saturated, resulting in fatty acid tails without kinks or bends. explain the effect this would have on plants located in very cold regions. (c) proteins are an important component of the cell membrane. describe two specific functions of proteins in the membrane. (d) explain the role of each type of protein you select for part c based on the structure and properties of a protein. 2. what is the difference between the number of h⁺ ions in a solution with a ph of 2 compared with a solution at a ph of 6? if appropriate, include a negative sign in your answer.

Explanation:

(a) Phospholipids have a hydrophilic head and hydrophobic tails. They form a bilayer in the plasma - membrane, acting as a barrier.
(b) Saturated fatty acid tails without kinks would make the membrane less fluid in cold regions, reducing its flexibility and potentially impairing transport functions.
(c) Two functions of membrane proteins are transport (e.g., ion channels) and cell - cell recognition (e.g., glycoproteins).
(d) Ion - channel proteins have a pore - like structure allowing specific ions to pass through, based on their size and charge. Glycoproteins have carbohydrate chains attached which are involved in cell - cell recognition and adhesion due to their unique molecular structures.

For question 2, the pH is defined as $pH =-\log[H^{+}]$. For a pH of 2, $[H^{+}]=10^{- 2}M$; for a pH of 6, $[H^{+}]=10^{-6}M$. The difference in $[H^{+}]$ is $10^{-2}-10^{-6}\approx10^{-2}M$ (since $10^{-6}$ is negligible compared to $10^{-2}$).

Answer:

1.
(a) Phospholipids consist of a hydrophilic phosphate - containing head and two hydrophobic fatty - acid tails. They form a bilayer in the plasma membrane, creating a semi - permeable barrier that controls the movement of substances in and out of the cell.
(b) If all phospholipids were saturated with straight fatty - acid tails, the plasma membrane would become more rigid and less fluid in cold regions. This is because the lack of kinks in saturated fatty acids allows them to pack more closely together, reducing the membrane's ability to flex and function properly.
(c) Two functions of proteins in the cell membrane are: 1) Transport proteins (such as ion channels and carrier proteins) facilitate the movement of specific substances across the membrane. 2) Receptor proteins bind to specific signaling molecules, enabling cells to respond to external signals.
(d) For transport proteins (ion channels), their structure is such that they have a pore with a specific size and charge that allows only certain ions to pass through. For receptor proteins, their three - dimensional structure contains a binding site that is complementary in shape and chemical properties to a specific signaling molecule, enabling specific recognition and binding.

1. $10^{-2}$