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Chapter 2: From a Cell to an Organism
I. The Cell Cycle and Division
A. The cell cycle is the life cycle of the cell
1. Phases of the cell cycle include interphase, mitosis, and cytokinesis
a. Interphase is when a cell is preparing to reproduce
b. During the mitotic phase, the nucleus and cytoplasm divide producing two new cells
2. The length of a cell cycle differs for different organisms and cells
3. A cell performs specific functions during interphase
a. Interphase consist of three phases: G1, S, G2
b. In G1, the cell grows and carries out normal functions
c. Some cells such as muscle, nerve, and red blood cells, stay in G1 and never
reproduce
d. In S phase, the homologous chromosome pairs in the cell’s nucleus replicate
e. The copies of the chromosomes made during S phase are sister chromatids
f. The replication ensures that the new cells formed are identical
g. In G2 phase, the cell grows and functions, and some organelles replicate
B. Mitosis is the division of the nucleus (chromosomes); Cytokinesis is the division of cytoplasm
(including organelles)
1. Mitosis and cell division ensure that each new cell receives all it needs to function
a. Mitosis and cell division replace ole worn-out cells, and are the method of
reproduction for some organisms
b. Mitosis and cell division produce the most cells in a many-celled organism
c. A different type of cell division produces sperm and egg cells called meiosis
2. There are four phases of mitosis
a. In prophase, DNA in chromosomes twist into tight coils and the nucleus breaks
apart
b. In metaphase, the chromosomes move to the middle of the cell and pairs of sister
chromatids line up
c. In anaphase, fibers attached to the centromere of the sister chromatids pull them
apart toward opposite ends of the cell
d. In telophase, a new membrane forms around each setoff chromosomes, creating
two identical nuclei, and chromosomes become less tightly coiled
3. Cytokinesis is the final stage of cell division
a. The cytoplasm and its contents divide to form two identical daughter cells
b. At the start of cytokinesis, the cell membrane pinches inward
c. In a cell with a cell wall, a cell plate forms between the two nuclei
d. The cell plate later becomes the cell membrane, which builds the new cell walls
4. Cell division results in two new daughter cells to replace the original parent cell
a. The daughter cells’ chromosomes are identical to the parent cell’s in number and
type
b. All the cells in your body, except sperm and egg cells, have identical chromosomes
II.
Levels of Organization
A. A one-celled organism carries out all the functions it needs to survive
1. Prokaryotes, such as bacteria, do not have nuclei or membrane-bound organelles
a. Bacteria have structures with specific functions
b. Some processes that occur in organelles in eukaryotes happen along specialized
2. Each one-celled eukaryote has a nucleus and organelles with specialized functions
a. One-celled eukaryotes include protists and some fungi
b. One-celled eukaryotes are more complex than cells in many celled eukaryotes
because they are self--sufficient
c. Cells in many-celled organisms depend on other cells to perform different
functions
d. Some protists, including Volvox, live and function in colonies with specialized
cells
B. Many-celled Organisms have many cells and usually have more than one type of cell
1. Cell differentiation is the process by which cells become different types of cells
a. Even though all cells in an organism have identical sets of chromosomes, cells
are able to differentiate by using different parts of the instructions on the
chromosomes
b. Differentiated cells often have specialized structures and shapes to perform
specific functions
c. Liver cells have smooth ER for filtering blood; brain cells are highly branched
for sending and receiving signals
d. Stem cells are undifferentiated; they can become different types of cells
e. Some plant to cells can differentiate into another type of cell after they have
differentiated into one type.
2. A tissue is a group of cells, such as muscle fiber, that works together perform a
function
3. An organ is a group of similar tissues that work together to perform a function
a. Examples of human organs are the heart, lungs, brain, stomach, and muscles
b. Plants have organs that store nutrients, transport substances, provide
protection, and perform photosynthesis
c. A leaf is an example of a plant organ
4. An organ system is one or more organs working together to perform one or more
functions
a. The muscular, digestive, and skeletal systems are examples of organ systems
b. The brain send and receives signals to coordinate the organ systems in the body
5. The many-celled organism is the most complex unit of living things
a. Each organ system has its own function but depends on other organ systems