Study Guide "Chapter 10 and 11.4"
10.1 Notes
In most cases, living things grow by producing more cells. There are two main reasons why cells divide:
1. The larger a cell gets, the more demands it places on its DNA.
2. As a cell gets larger, it has more trouble moving enough nutrients (food) and wastes across its cell
membrane.
The rates at which materials move through the cell membrane depend on the cell’s surface area—the
total area of its cell membrane. However, the rate at which food and oxygen are used up and waste
products are formed depends on the cell’s volume. As a cell grows, its volume increases faster than
its surface area. That is, as a cell becomes larger, its ratio of surface area to volume decreases. Before a
cell gets too large, it divides, forming two “daughter” cells.
10–2 Cell Division
Cell division is the process by which a cell divides into two new daughter cells. A cell must copy its
genetic information before cell division begins. Each daughter cell then gets a complete copy of that
information. In most prokaryotes, the rest of cell division is a simple matter of separating the contents
of the cell into two parts. In eukaryotes, cell division occurs in two main stages, mitosis and cytokinesis.
Mitosis is the division of the nucleus.
Cytokinesis is the division of the cytoplasm.
The cell cycle is a series of events cells go through as they grow and divide.
During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. Each
daughter
cell then begins the cycle again.The phases of the cell cycle include interphase and cell division.
Interphase is divided into three phases: G1, S, and G2.
▪During the G1 phase, cells increase in size and make new proteins and organelles.
▪In the S phase, replication (copying) of chromosomes takes place.
▪During the G2 phase, many of the organelles and molecules needed for cell division are
produced.
The M phase or mitosis
Cytokinesis cell division
Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and
telophase.
(PMAT)
1. Prophase.During prophase, the chromosomes condense and
become visible. There are two tiny structures located in the
cytoplasm near the nuclear envelope. These structures are
called centrioles. The centrioles separate and move to opposite
sides of the nucleus. The spindle is a structure that helps move
chromosomes apart. During prophase, the chromosomes attach
to fibers in the spindle. At the end of prophase, the nuclear
envelope breaks down.
2. Metaphase.During metaphase, chromosomes line up across
the center of the cell. The centromere of each chromosome
attaches to the spindle.
3. Anaphase.During anaphase, the centromeres joining the sister
chromatids split. The sister chromotids become individual
chromosomes. The two sets of chromosomes move apart.
4. Telophase.During telophase, the chromosomes move to opposite ends of the cell. They lose their
distinct shapes. Two
new nuclear envelopes form.
Cytokinesis usually occurs at the same time as telophase. In most animal cells, the cell membrane
pinches the cytoplasm into two nearly equal parts. In plant cells, a cell plate forms midway between the
divided nuclei. A cell wall then begins to form in the cell plate.
10–3 Regulating the Cell Cycle
In a multicellular organism, cell growth and cell division are carefully controlled. For instance, when an
injury such as a cut in the skin occurs, cells at the edge of the cut divide rapidly. When the healing
process is nearly complete, the rate of cell division slows and then returns to normal.
Cyclins—a group of proteins—regulate the timing of the cell cycle in eukaryotic cells.Cyclins are one
group of proteins involved in cell cycle regulation. Other proteins, called regulatory proteins, regulate
the cell cycle in different ways. Controls on cell growth can be turned on and off by the body. Cancer is a
disorder in which some of the body’s cells lose the ability to control growth.
Cancer cells do not respond to the signals that control the growth of most cells.As a result, cancer cells
divide uncontrollably. Cancer cells do not stop growing when they touch other cells. Instead, they
continue to grow and divide until their supply of nutrients is used up.
11–4 Meiosis
Prophase I :A major difference occurs here separating this prophase from mitosis prophase. The
chromatid pairs pair up with their homologous pair, forming a tetrad. This tetrad contains 2 original
homologous chromosomes and their duplicates.Don't fall asleep yet!The process of crossing over occurs
during this time allowing for genetic diversity in the genome. Crossing over is a process where pieces of
two homologous chromosomes, switch places and end up on the other chromosome. ( 1 cell )
During Metaphase I the chromosomes move into position at the spindle equator. The alignment of the
chromosomes at the spindle equator is random. This random alignment allows for many combinations
of paternal and maternal traits in the daughter cells, which leads to genetic diversity. (1 cell )
In Anaphase I,The tertads split and move in opposite directions. During this phase the chromatid pairs
move away from each other. By the end of anaphase, the homologues are at opposite spindle (1 cell )
poles.
During Telophase I the cytoplasm divides into two haploid(n) cells. The chromosomes in the cells are still
in the duplicated form. (2 cells )
During Prophase II the chromosomes move to the spindle equator to prepare for Metaphase II (2 cells )
During Metaphase II have finally positioned all the duplicated chromosomes in each daughter cell at the
spindle equator.
During Anaphase II: The chromatid pairs split moving the individual chromosomes toward the opposite
poles. (2 cells )DON'T WORRY! IT'S ALMOST OVER!.
During Telophase II results in 4 daughter nuclei. Cytokinesis splits each of the 2 daughter cells in half,
creating 4 daughter cells. The original chromosome number of the parent cell will be half in each
daughter cell