All of the choices presented describe functions of cell junctions. Adherens junctions and desmosomes are responsible for anchoring neighboring cells to one another. Hemidesmosomes help anchor the extracellular matrix in place, binding the cell membrane to proteins in the basal lamina or matrix. Gap junctions are an example of junctions that connect the cytoplasm of two neighboring cells and allow for communication via ions and other small molecules.

All of the choices presented describe functions of cell junctions. Adherens junctions and desmosomes are responsible for anchoring neighboring cells to one another. Hemidesmosomes help anchor the extracellular matrix in place, binding the cell membrane to proteins in the basal lamina or matrix. Gap junctions are an example of junctions that connect the cytoplasm of two neighboring cells and allow for communication via ions and other small molecules.

The question asks about membranes in general, not just the cell plasma membrane; therefore, all of the answers are true. The plasma membrane's most important functions are protecting the internal environment of the cell and selectively allowing nutrients into the cytoplasm (semi-permeability). The final answer describes a function of the inner-membrane of the mitochondria, which houses the electron transport chain.

The question asks about membranes in general, not just the cell plasma membrane; therefore, all of the answers are true. The plasma membrane's most important functions are protecting the internal environment of the cell and selectively allowing nutrients into the cytoplasm (semi-permeability). The final answer describes a function of the inner-membrane of the mitochondria, which houses the electron transport chain.

There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.

Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.

There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.

Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.

All of the choices describe functions of different types of cell junctions. Anchoring junctions (such as adherens junctions and desmosomes) use the cytoskeletons of each cell, as well as certain transmembrane proteins, to anchor the cells together. Gap junctions create gaps in the plasma membrane between two adjacent cells that connect their cytoplasms. Tight junctions are capable of forming barriers that are nearly impermeable to fluid flow.

All of the choices describe functions of different types of cell junctions. Anchoring junctions (such as adherens junctions and desmosomes) use the cytoskeletons of each cell, as well as certain transmembrane proteins, to anchor the cells together. Gap junctions create gaps in the plasma membrane between two adjacent cells that connect their cytoplasms. Tight junctions are capable of forming barriers that are nearly impermeable to fluid flow.

Membranes are semi-permeable, meaning that they only allow certain compounds to cross without protein assistance. The two factors that determine permeability across a membrane are size and polarity. Polar and charged compounds very rarely cross the membrane by simple diffusion, and often require a carrier protein or pump in order to cross. Glucose and amino acids are polar, and a sodium ion carries a positive charge. These compounds will be blocked by the hydrophobic interior of the membrane, formed by the fatty acids tails of the phospholipids bilayer.

Nonpolar compounds, on the other hand, can very easily cross the cell membrane. Even larger nonpolar molecules, like steroid hormones, can easily cross the membrane via simple diffusion.

Membranes are semi-permeable, meaning that they only allow certain compounds to cross without protein assistance. The two factors that determine permeability across a membrane are size and polarity. Polar and charged compounds very rarely cross the membrane by simple diffusion, and often require a carrier protein or pump in order to cross. Glucose and amino acids are polar, and a sodium ion carries a positive charge. These compounds will be blocked by the hydrophobic interior of the membrane, formed by the fatty acids tails of the phospholipids bilayer.

Nonpolar compounds, on the other hand, can very easily cross the cell membrane. Even larger nonpolar molecules, like steroid hormones, can easily cross the membrane via simple diffusion.