BIO.A.1 The Nature and Science of Life
Topic Summary for Levels of Organization:
Unicellular:
Sometimes a single cell is an organism. Single-celled organisms must be able to carry out all the functions necessary for life.
Unicellular organisms maintain homeostasis, relatively constant internal conditions, by growing, responding to the environment, transforming energy, and reproducing.
Unicellular organisms include both prokaryotes and eukaryotes.
Unicellular organisms play many important roles in their environments.
Multicellular:
Cells of multicellular organisms are interdependent and specialized.
The cells of multicellular organisms become specialized for particular tasks and communicate with one another to maintain homeostasis.
Specialized cells in multicellular organisms are organized into groups.
• • A tissue is a group of similar cells that performs a particular function.
• • An organ is a group of tissues working together to perform an essential task.
• • An organ system is a group of organs that work together to perform a specific function.
The cells of multicellular organisms communicate with one another by means of chemical signals that are passed from one cell to another.
• • Certain cells form connections, or cellular junctions, to neighboring cells. Some of these junctions hold cells together firmly.
• • Other cells allow small molecules carrying chemical signals to pass directly from one cell to the next.
• • To respond to a chemical signal, a cell must have a receptor to which the signaling molecule can bind.
Topic Summary for Levels of Organization:
Unicellular:
Sometimes a single cell is an organism. Single-celled organisms must be able to carry out all the functions necessary for life.
Unicellular organisms maintain homeostasis, relatively constant internal conditions, by growing, responding to the environment, transforming energy, and reproducing.
Unicellular organisms include both prokaryotes and eukaryotes.
Unicellular organisms play many important roles in their environments.
Multicellular:
Cells of multicellular organisms are interdependent and specialized.
The cells of multicellular organisms become specialized for particular tasks and communicate with one another to maintain homeostasis.
Specialized cells in multicellular organisms are organized into groups.
• • A tissue is a group of similar cells that performs a particular function.
• • An organ is a group of tissues working together to perform an essential task.
• • An organ system is a group of organs that work together to perform a specific function.
The cells of multicellular organisms communicate with one another by means of chemical signals that are passed from one cell to another.
• • Certain cells form connections, or cellular junctions, to neighboring cells. Some of these junctions hold cells together firmly.
• • Other cells allow small molecules carrying chemical signals to pass directly from one cell to the next.
• • To respond to a chemical signal, a cell must have a receptor to which the signaling molecule can bind.