Cellular Glossary


Haploid Having a single set (1n) of unpaired chromosomes as is found in gametes. Follow the production of gametes in the Interactive Meiosis Animation.

Helper T Cell A lymphocytes that can stimulate (help) a B cell turn on antibody production by recognizing presented antigens on B cells and then releasing stimulatory cytokines.



Hemoglobin The protein that gives red blood cells their color and is responsible for carrying oxygen throughout the body.

Histamine This amine is released quickly from mast cell granules in response to antigen stimulation resulting in local increased blood flow and vascular leakage promoting the influx of immune cells. Read about Mast Cells and Histamine.

Histone An alkaline protein in the eukaryotic nucleus and a major component of chromatin. DNA coils around histones and in turn, histones play a role in gene expression.

Host Cell Any cell within which an infecting parasite, bacterium, or virus resides.

Human Immunodeficiency Virus, HIV A retrovirus that specifically targets lymphocytes with CD4 receptors and the causative agent of acquired immunodeficiency syndrome. Track Infection by HIV.

Hydrophilic A substance with an affinity for water that will readily mix with or dissolve in water.

Hydrophobic A substance that repels water that will not mix nor dissolve in water.



Immune System The arsenal used by the body to defend against foreign bodies including infecting organisms. The immune system includes an array of specialized cells (granulocytes, lymphocytes, mononuclear leukocytes, plasma cells, and others) and the mechanisms to identify invaders.

Infection The invasion by and replication of foreign organisms (bacteria, viruses, parasites) and the body’s response to that invasion.

Inflammation The body’s localized response to an infection or injury that may include reddening, swelling, and pain from the accumulation of fluid, blood proteins, and immune cell products. See the Anatomy of a Splinter.



Influenza A viral infection of the respiratory system, causing fever, muscle pain, headache and difficult breathing.

Inheritance Traits passed from parents to offspring through genes.

Innate immunity Non-specific immunity not elicited by a particular antigen.

Integrase An enzyme produced by HIV and other retroviruses that facilitates integration of the viral genome DNA into the host cell DNA.

Interphase The longest phase of the plant and animal cell cycle in which the cell is not actively dividing. Synthesis of proteins and nucleic acid replication take place during this stage.

Ion Channel A pore within the cell membrane that controls the inflow and outflow of various ions and in turn maintains membrane potential. Read more about Ion Channels.

Ion Pump A trans-membrane protein that uses energy to actively move specific ions against a concentration gradient.




Kinetochore A condensed protein structure on chromatids where spindle fibers attach during mitosis and meiosis.



Lag Phase The initial period of slow growth when bacteria are introduced into and begin adjusting to fresh medium. There is more information about the phases of bacterial growth here.

Ligand A molecule that binds to another to form a larger complex. An example is a hormone that binds to a receptor on a cell producing a biological effect. Ligands are important in HIV Attachment.

Light Microscope A microscope that uses focused light to produce an image. The light is usually in the visible spectrum but light microscopes also enable imaging with the non-visible spectrum (e.g. ultraviolet for fluorescence).

Lipid A hydrophobic (above) organic compound. Lipids include fats and other esters. The cell membrane contains a lipid bilayer. See the structure of the cell membrane in the cell models.

Log Phase The period of highest growth rate for cells in culture. See all the phases of bacterial growth (link).

Lymphocyte Mononuclear white blood cell of the adaptive immune system comprising T-cells, B-cells, and NK (natural Killer) cells.

Lysosome A membrane-bound packet of hydrolytic enzymes in the eukaryotic cell that can degrade intracellular materials or aid in killing ingested pathogens (see phagocytosis).