Smooth endoplasmic reticulum (ER) synthesizes lipids and detoxifies harmful substances.  RNA synthesis occurs in transcription but does not involve Smooth ER.  Proteins are synthesized by Rough ER and ribosomes.  Water intake is regulated by vacuoles, which are present in a few animal cell types.

The nucleus is the site of DNA replication, and transcription, which is the process by which DNA is converted to RNA. Enzymes are a class of proteins. All protein synthesis occurs in the ribosomes, some of which are on the endoplasmic reticulum (rough ER), and some are floating in the cytoplasm. Detoxification of harmful substances is carried out by the smooth endoplasmic reticulum.

Cells associated with the smooth endoplasmic reticulum (ER) are responsible for cellular detoxification; therefore, one would expect to see a higher concentration of smooth ER in liver cells.

The smooth endoplasmic reticulum has a variety of functions, one of which involves the detoxification of drugs and pollutants found in the body. Enzymes found in the smooth endoplasmic reticulum allow it to break down harmful drugs and toxins. Cells in the liver, called hepatocytes, have particularly large smooth endoplasmic reticulum regions, allowing them to be especially efficient at clearly toxins from the body.

The rough endoplasmic reticulum and Golgi apparatus are involved in protein modification, folding, and packaging. Lysosomes house enzymes that aid in breakdown of macromolecules and cellular wastes; they are specialized to remove biological waste, but are not well-suited to remove ingested toxins.

Bacteria and plant cells both have cell walls, although the cell walls are composed of different macromolecules in different cell types. Plants use the protein chitin, while bacteria use peptidoglycan. Bacteria are a certain class of prokaryotes.

Animal cells only have a plasma membrane, and do not have cell walls.

Two general concepts allow you to predict how easily a molecule is able to cross the plasma membrane.

1. The smaller the molecule, the more permeable the membrane is to it. Large molecules have a harder time crossing the membrane.

2. Polar and charged molecules have a very hard time crossing the membrane. Nonpolar molecules can cross the membrane much more easily.

As a result, small, nonpolar molecules are ideal for crossing the membrane easily. Larger molecules do not fit through the membrane gaps, and polar molecules are repelled by the hydrophobic interior of the membrane.

Since salt is unable to pass the membrane, the animal cell will attempt to equalize the salt concentrations on both sides by expelling water into the solution. The concentration of salt outside the cell is higher than the concentration inside the cell. This means that water itself is more concentrated inside the cell than outside. The water will flow down its gradient from high solvent concentration (in the cell) to low solvent concentration (outside the cell) via the process of osmosis. As the water exits the cell, it will lose volume and shrivel.

The cell wall is a very tough structure that is able to help the cell withstand extracellular stressors. A plant cell or bacterium can survive hypotonic solutions better than an animal cell due to protection from the cell wall. As water flows into the cell, but the cell wall will keep the cell from bursting.

The cell wall does not protect well against hypertonic environments, however. As water exits the cell, the plasma membrane pulls away from the cell wall. The cell shrinks within the cell wall, which maintains its original size and does not prevent cellular damage.

Peptidoglycan is found in the cell walls of bacteria. Plant cells have cell walls made of cellulose, and animal cells lack a cell wall entirely. Archaea are a class of prokaryote, but have cell walls that differ from those of bacteria. Archaea cell walls do not contain peptidoglycan.

Diffusion and osmosis are both used in order to equalize the concentrations of solutes on both sides of a membrane. This act requires no energy to take place, as solutes will passively flow from regions of high concentration to areas of low concentration. Facilitated diffusion requires a channel protein to allow substances to cross the membrane, but also allows flow down a concentration gradient and does not require energy.

Active transport is needed in order to accumulate solutes on one side of a barrier against their concentration gradient. This requires ATP in order to take place, as the solutes will not flow in this direction naturally.