Chloroplast.
Any of the chlorophyll-containing organelles (see plastid) that are found in large numbers in those plant cells undergoing photosynthesis. Chloroplasts are typically lens shaped and made up of stacks of membranes (see granum) enclosed in gellike matrix. The light reactions of photosynthesis occur on the membranes while the dark reactions take place in the matrix.

Chlorosis. Disease of green plants characterized by yellow (chlorotic) condition of parts that are normally green; caused by conditions preventing chlorophyll formation e.g. lack of light.

Choanae (internal nares). Of vertebrates. Internal opening of nasal cavity into mouth. Present, as are also external nares opening on to face, in group Choanata; remaining vertebrate classes have only external nares. Situated near front of roof of mouth, except in those choanates with a false palate in which they are at the back.

Chondrocranium. The first part of the skull to form in vertebrate embryos. It consists of cartilaginous structures plates and capsules that protect and support the brain, olfactory organs, eyes and the inner ear. It usually becomes ossified in adults. although it remains cartilaginous in Chondrichthyes (cartilaginous fish). See also neurocranium.

Chorda-mesoderm.
Mesoderm and notechored of vertebrate embryo. In early stages of development, before differentiation, this tissue often forms a continuous mass or layer of similar cells, and they are closely related in physiology of development also, e.g. See organizer; consequently it is convenient for some purpose to group them together.

Chondrichthyes.
A group of cartilaginous fish including the classes Elasmobranchii (with placoid scales on body) and Holocephali (skin without scales); Elasmobranchii includes sharks (dog fish, Scolidon), whak shark, skates and rays (electric and sting) while Holocephali includes chimaeras.