The cell membrane has many purposes. It anchors the cytoskeleton to give the cell shape and structure. It houses proteins that both interact with signaling molecules from outside the cell and communicate with secondary messengers within the cell. It facilitates the absorption and release of electrolytes, water, and vesicles carrying proteins or other molecules. It forms junctions with other cells and connects the cell to the extracellular matrix.

One thing the cell membrane does not do, however, is act as a site of protein synthesis. That occurs primarily in the rough endoplasmic reticulum or on ribosomes in the cytoplasm.

The majority of lipid production within the cell occurs within the smooth endoplasmic reticulum. It is also the site of production of steroids and phospholipids. The Golgi apparatus is responsible for packaging of cell products for transport outside of the cell. The mitochondria produce ATP, and the nucleus houses the DNA.

Aerobic cellular respiration occurs exclusively in the mitochondria. These organelles are present in greater number in cells that require a large supply of ATP, such as striated muscle cells, liver cells, and sperm cells. 

The framework of the cell is make up by the cytoskeleton. The cytoskeleton gives the cell both shape and structure, and allows the cell to attach to extracellular connective tissue in order to form tissue types. There are three major fibers that make up cytoskeleton - microfilaments (actin), intermediate filaments, and microtubules.

Cholesterol is a vital component of the cellular membrane. It maintains both the fluidity and structural integrity of the cell. While cholesterol is an integral component of steroid production, this occurs outside of the cell membrane. Cholesterol does not play a significant role in cellular energy production or cell membrane detoxification.

All of the cells of the human body except sex cells are termed somatic cells. These are diploid cells, meaning that they contain two homologous copies of each chromosome. Sex cells (eggs and sperm) are haploid cells, containing just one set of chromosomes in each cell. All human cells are eukaryotic, because they contain a nucleus and organelles within a cellular membrane.

While the nucleus houses the DNA and plays an integral role in the transcription of genetic code in order to produce specific proteins, actual protein synthesis is carried out by the ribosomes. These organelles consist of two subunits and are either independent in the cytoplasm of the cell or housed in the rough endoplasmic reticulum. Note that ribosomes can be in the cytoplasm or on the endoplasmic reticulum, hence making it rough.

A hypertonic solution, or one which contains solutes in higher concentration than blood cells, would cause water to leave the red blood cell across the osmotic gradient. This causes a reversible crumpling or shriveling of the cell, termed crenation. A cell in a hypotonic solution, wherein the cell itself contained a higher level of solutes than the fluid, would take on water, potentially causing the cell to lyse (burst). 

Ribosomal subunits are manufactured by the nucleolus, which is contained within the nucleus. It's primary function is the production and assembly of ribosome subunits. The RER houses ribosomes for protein manufacture. The SER does not take part in ribosome production or functioning. Note that ribosomes are composed of rRNA and protein. Proteins are translated on ribosomes in the cytoplasm.

90% of the cell cycle is spent in interphase. This time is also termed the "resting phase" as it is absorbing nutrients and replicating cellular elements in preparation for cell division. This phase includes the stages Gap 1 and Gap 2. Mitosis and cytokinesis, the final stages in cell division, are both relatively short compared to interphase, accounting for approximately 10% of the cell cycle.