Answers to Key Terms for Chapter 4

cell cycle	The total sequence of events in the growth-division cycle of a cell (p. 85).
cytokinesis	The division of the parental cell's cytoplasm to form new cells (p. 87).
chloroplast	A eucaryotic organelle that contains chlorophyll andis the site of photosynthesis (p. 81).
chromosome	The bodies that have most or all of the cellÆs DNA and contain most of its genetic information (mitochondria and chloroplasts also contain DNA and genes)
cilia	Threadlike appendages extending from the surface of some protozoa that beat rhythmically to propel them; cilia are membrane-bound cylinders with a complex internal array of microtubules, usually in a 9 + 2 pattern.
cytoskeleton	A network of microfilaments, microtubules, intermediate filaments, and other components in the cytoplasm of eucaryotic cells that helps give them shape
diploid	Having double the basic chromosome number
endoplasmic reticulum (ER)	A system of membranous tubules and flattened sacs (cisternae) in the cytoplasmic matrix of eucaryotic cells.
endosymbiotic theory	The theory that eucaryotic organelles such as mitochondria and chloroplasts arose when bacteria established an endosymbiotic relationship with the eucaryotic ancestor and then evolved into eucaryotic organelles
haploid	Having half the number of chromosomes present in a somatic cell or a single set of chromosomes.
lysosome	A spherical membranous eucaryotic organelle that contains hydrolytic enzymes and is responsible for the intracellular digestion of substances
meiosis	The sexual process in which a diploid cell divides and forms two haploid cells
mitochondrion	The eucaryotic organelle that is the site of electron transport, oxidative phosphorylation, and pathways such as the Krebs cycle; it provides most of a nonphotosynthetic cell's energy under aerobic conditions. It is constructed of an outer membrane and an inner membrane, which contains the electron transport chain.
mitosis	A process that takes place in the nucleus of a eucaryotic cell and results in the formation of two new nuclei, each with the same number of chromosomes as the parent
nucleus	The eucaryotic organelle enclosed by a double-membrane envelope that contains the cell's chromosomes
organelle	A structure within or on a cell that performs specific functions and is related to the cell in a way similar to that of an organ to the body
polyribosomes	A complex of several ribosomes with a messenger RNA; each ribosome is translating the same message
ribosomal RNA	The RNA present in ribosomes; ribosomes contain several sizes of single-stranded rRNA that contribute to ribosome structure and are also directly involved in the mechanism of protein synthesis

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