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3.6 Cell Cycle Guided Notes Name: Date: 1/6/21
Homeostasis and Cells
●Cells are the basic living units of all organisms, and sometimes a single cell is the organism, this is also called a
unicellular organism.
○All living organisms must maintain homeostasis.
○To maintain homeostasis, unicellular organisms grow, respond to the environment, transform energy,
and reproduce.
●Unicellular organisms include both prokaryotes and eukaryotes
○Unlike most unicellular organisms, the cells of humans, animals, and other multicellular organisms do
not live on their own, instead they are interdependent.
○The cells of multicellular organisms become specialized for particular tasks and communicate with one
another to maintain homeostasis.
●Cell specialization: the cells of multicellular organisms are specialized, with different types playing different roles.
Some cells are specialized to move, others are specialized to react to the environment, etc. Each specialized cell
contributes to homeostasis in the organism.
Cells and Levels of Organization
●Specialized cell: a cell that has undergone differentiation and is specialized to perform certain tasks.
○During the development of an organism, cells differentiate into many types of cells. A specialized or
differentiated cell has become different from the embryonic cell that produced it.
●Stem cell: unspecialized cell that can give rise to one or more types of specialized cells.
○Stem cells, also called undifferentiated or unspecialized, sit at the base of a branching “stem” of
development from which different cell types form. We classify stem cells broadly into two categories:
■Adult stems cells: cells in some tissue, like blood and skin, have a limited lifespan and must be
constantly replaced. Pools of adult stem cells, found in various locations throughout the bod,
produce the new cells needed for these tissues.
■Embryonic stem cells: also referred to as pluripotent cells, which can develop into any of the
body’s cell types.
●The specialized cells of multicellular organisms are organized into tissues, then into organs, and finally into organ
systems.
○Tissues: group of similar cells that perform a particular function
○Organ: group of tissues that work together to perform closely related functions
○Organ System: group of organs that work together for perform a specific function
Cell Growth, Division, and Reproduction
●Why do cells have to divide and produce more of themselves?
○The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less
efficient in moving nutrients and waste materials across the cell membrane.
■As a cell grows, DNA is used to build the molecules needed for cell growth. But as a cell increases
in size, its DNA does not. So if a cell continued to increase in size the DNA:
■Food, oxygen, and water enter a cell through its cell membrane, and waste products leave
through the cell membrane.
