Question

learning goals: explain the role of cell membranes as a highly selective barrier (passive & active). structure of the cell membrane: the cell membrane (also called the plasma membrane) is common to all living cells and serves as a barrier that controls what enters and leaves a cell. it is made of phospholipids, which have hydrophilic (water - loving) heads and hydrophobic (water - fearing) tails. they pack together in a double layer called the phospholipid bilayer, with the hydrophilic heads on the outside of the cell, as well as the inside of the cell, and the hydrophobic tails sandwiched in between. the cell membrane allows only certain molecules, such as ions and small organic molecules, into and out of the cell. its ability to allow only certain molecules in or out of the cell is referred to as a selectively - permeable membrane. in other words, it selects what can permeate (move) through. this characteristic helps the cell to regulate the exchange of nutrients in and out, while keeping harmful bacteria and viruses out. embedded in the phospholipid bilayer are numerous types of molecules (such as proteins and carbohydrates) that serve specific functions. proteins are used to let certain types of molecules in or out of the cell. these molecules float around the cell membrane freely and thus, the cell membrane is often called a fluid - mosaic. the cell membrane also acts as the attachment point for both the cytoskeleton and, if present, the cell wall, which give a cell its structure and support. after reading, please watch the video “cell membranes are way more complicated than you think” (https://www.youtube.com/watch?v=nsklf1w4eok) and answer the following questions. 1. describe the role and importance of the cell membrane. what is meant by “the cell membrane is semipermeable?” allows certain substances through while blocking others 2. describe the basic structure of the cell membrane with regard to specific molecules: 3. why is the cell membrane often referred to as a “fluid - mosaic?” 4. what is the function and purpose of the proteins embedded in the cell membrane? transporters, receptors, enzymes, structural support

Explanation:

1. The cell membrane is a selective barrier. It's semi - permeable, allowing certain substances like ions and small organic molecules to pass through while blocking harmful bacteria and viruses, maintaining cell homeostasis.
2. It has a phospholipid bilayer structure with hydrophilic heads on the inner and outer cell surfaces and hydrophobic tails in the middle. Proteins and carbohydrates are embedded, serving specific functions.
3. It's called a "fluid - mosaic" because proteins and other molecules can float around freely in the phospholipid bilayer.
4. Proteins in the cell membrane act as transporters to move substances, receptors for signal recognition, enzymes for catalysis, and provide structural support.

Answer:

1. The cell membrane is a selective barrier. Semi - permeable means it allows certain substances (ions, small organic molecules) to enter or leave the cell while blocking harmful bacteria and viruses, helping maintain homeostasis.
2. The cell membrane has a phospholipid bilayer. Phospholipids have hydrophilic heads (water - loving) on the inside and outside of the cell and hydrophobic tails (water - fearing) in the middle. Embedded in this bilayer are proteins and carbohydrates that serve specific functions.
3. The cell membrane is called a "fluid - mosaic" because proteins and other molecules can float around freely within the phospholipid bilayer.
4. Proteins embedded in the cell membrane function as transporters to let certain substances in or out, receptors for signal recognition, enzymes for chemical reactions, and provide structural support.