Science / Biology Glossary

Cycads: Group of gymnosperm seed plants that have large fern-like leaves and reproduce by cones but not flowers.

Cycle: A recurring sequence of events; e. g., the secretion of certain hormones at regular intervals.

Cyclin: A protein found in the dividing cells of many organisms that acts as a control during cell division.

Cystic Fibrosis: An autosomal recessive genetic disorder that causes the production of mucus that clogs the airways of the lungs and the ducts of the pancreas and other secretory glands.

Cytokinesis: The division of the cytoplasm during cell division.

Cytokinins: A group of hormones that promote cell division and inhibit aging of green tissues in plants.

Cytology: The branch of biology dealing with cell structure.

Cytoplasm: The viscous semiliquid inside the plasma membrane of a cell; contains various macromolecules and organelles in solution and suspension.

Cytosine: One of the pyrimidine nitrogenous bases occurring in both DNA and RNA.

Cytoskeleton: A three-dimensional network of microtubules and filaments that provides internal support for the cells, anchors internal cell structures, and functions in cell movement and division.

Cytoxic T Cells: T cells that destroy body cells infected by viruses or bacteria; also attack bacteria, fungi, parasites, and cancer cells and will kill cells of transplanted organs if they are recognized as . . . View Full Definition

Dark Reactions: The photosynthetic process in which food (sugar) molecules are formed from carbon dioxide from the atmosphere with the use of ATP; can occur in the dark as long as ATP is present.

Death Rate: The ratio between deaths and individuals in a specified population at a particular time.

Decay Series: Most radioisotopes do not decay into a stable daughter element in one single decay, but rather through a series of radioactive intermediaries.

Deciduous: Term applied to trees that lose the leaves and have a dormancy period at least once per year.

Deletion: The loss of a chromosome segment without altering the number of chromosomes.

Dendrites: Short, highly branched fibers that carry signals toward the cell body of a neuron.

Dendrochronology: The process of determining the age of a tree or wood used in structures by counting the number of annual growth rings.

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