What are two reasons why cells divide rather than continue to grow indefinitely?
a. The larger a cell becomes, the more demands the cell places on its DNA.
b. The larger a cell becomes, the more trouble the cell has moving nutrients and wastes across the cell membranes.
What determines the rate at which food and oxygen in a cell are used up and waste products produced.
The cell's volume
How can you obtain a cell's ratio of surface area to volume?
Divide the surface area by the volume.
If a cell's surface area is 6 cm cubed and its volume is 1 cm cubed, then what is its ratio of surface area to volume?
6/1 or 6:1
TRUE or FALSE:
As a cell grows in size, its volume increases much more rapidly than its surface area.
What happens to a cell's ratio of surface area to volume as the cell's volume increases more rapidly than its surface area?
The ratio decreases
When chromosomes become visible at the beginning of cell division, what does each chromosome consist of?
two identical sister chromatids
What is the cell cycle?
The cell cycle is the series of events that cells go through as they grow and divide.
What are the names of the four phases of the cell cycle?
- G1 phase (cell growth)
- S phase (DNA replication)
- G2 phase (preparation for mitosis)
- M phase (cell division)
What happens during the G1 phase?
Cells do most of their growing, increasing in size and synthesizing new proteins and organelles.
What happens during the S phase?
Chromosomes are replicated, and the synthesis of DNA molecules takes place. Also, key proteins associated with the chromosomes are synthesized.
What happens during the G2 phase?
Many of the organelles and molecules required for cell division are produced.
What are the tiny structures located in the cytoplasm near the nuclear envelope at the beginning of prophase?
What is the spindle?
The spindle is a fanlike microtubule structure that helps separate the chromosomes.
What happens during Prophase?
The chromosomes become visible. The centrioles take up positions on opposite sides of the nucleus,
What happens during Anaphase?
The chromosomes move until they form two groups near the poles of the spindle.
What happens during Telophase?
A nuclear envelope re-forms around each cluster of chromosomes. The nucleolus becomes visible in each daughter nucleus.
How does cytokinesis occur in most animal cells?
The cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts.
granular material visible within the nucleus that consists of DNA tightly coiled around proteins
first and longest phase of mitosis during which the chromosomes become invisible and the centrioles separate and take up positions on the opposite side of the nucleus
one of two tiny structures located in the cytoplasm in animals cells near the nuclear envelope
second phase of the mitosis during which the chromosomes line up across the center of the cell
the third phase of mitosis during which the chromosome pairs separate and move toward opposite poles
fourth and final phase of mitosis during which chromosomes begin to disappear into a tangle of dense material
What happens to the cells at the edges of an injury when a cut in the skin or a break in a bone occurs?
They are stimulated to divide rapidly.
What happens to the rapidly dividing cells when the healing process nears completion?
The rate of cell division slows down, controls on growth are restored, and everything returns to normal.
What is true about external regulators?
- They direct cells to speed up or slow down the cell cycle.
- They include growth factors.
- They prevent excessive cell growth and keep the tissues of the body from disrupting on another.
What is cancer>
a disorder in which some of the body's own cells lose the ability to control growth.