Osmosis is defined as a form of passive transport since it does not require an expenditure of energy. Osmosis follows a concentration gradient while active transport acts against the concentration gradient. Also, active transport requires energy and passive transport does not.

Diffusion is defined as the spread of molecules into available space. The random nature of the movement of molecules in an open area means that molecules will seek to spread out—diffuse—evenly within a given area. This means that molecules will evenly distribute themselves when random assortment is permitted within a space.

The plasma membrane functions as a selective barrier to allow the flow of oxygen, nutrients, and wastes to and from the cell. The selectively permeable plasma membrane encloses the cytoplasm. The cytoplasm in turn contains the nucleus, mitochondria, and other organelles.

Transport proteins span the exterior of the cell and allow substances to pass through the membrane. Some transport proteins are involved in facilitated diffusion, which is a type of passive transport. Other transport proteins are involved in active transport such as the sodium-potassium pump.

Osmosis is an example of passive transport. Osmosis does not use energy. Instead, it acts using the concentration gradient. The sodium-potassium pump, proton pump, and electrogenic pump are all examples of active transport. This means that they can pump solutes against their concentration gradients using cellular energy.

The fluid mosaic model describes the mosaic structure of the cell membrane. According to this model, the cell membrane is composed of a variety of protein molecules randomly bobbing around in a sea of phospholipids. Due to phospholipid polarity, they naturally form a bilayer in accordance with their dual hydrophobic (tails) and hydrophilic (heads) natures.

Integral proteins have both a hydrophobic region and hydrophilic region. The hydrophobic region allows them to sit within the cell membrane, while their hydrophilic regions face the aqueous solutions on either side of the membrane.

An amphipathic molecule is one that has both hydrophilic and hydrophobic regions. In the case of phospholipids, the tail is hydrophobic and the head is hydrophilic. 

Isotonic is the correct term to describe solutions with equal solute concentrations. The root word "iso" means same; therefore, isotonic solutions have the same concentration of solute. A hypotonic solution will have less solute in it. A hypertonic solution will have a higher concentration of solute between the two solutions.

Endocytosis is the process by which the cell takes in macromolecules by forming vesicles from the plasma membrane to carry the molecules into the cell. Exocytosis, on the other hand, is the opposite. This is the process by which cells use vesicles to secrete substances from the cell. Phagocytosis, pinocytosis, and receptor-mediated endocytosis are all types of endocytosis.