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CHAPTER 10 CELL GROWTH AND DIVISION (page241) . *-Cells cannot grow by simply increasing in size because of a limiting factor, the surface to volume ratio .
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*-Cells cannot grow by simply increasing in size because of a limiting factor, the surface to volume ratio.
*-As a cell enlarges, its volume increases several hundred times faster than its surface area, so the ratio quickly becomes very small. This results in: inefficiencies in the cell's internal processes, slowing its growth. ** Cell division solves this problem.
CELL DIVISION- the process by which a cell divides into 2 daughter cells.
In most cases an organism grows because it produces more and more cells.
*The cells of a baby and an adult are the same size, but in the adult there are more of the cells.
* The most important factor that limits the size of the cell is…its ability to transport materials efficiently into and out of the cell.
**- As a cell increases in size, it becomes increasingly more difficult to transport materials efficiently...this is because the volume of the cell or the amount of internal contents, increases at a much faster rate than the surface area or the size of the cell membrane.
**- Ratio- a comparison between 2 variables expressed mathematically as division.** The surface to volume ratio is obtained by dividing thesurface area by the volume.
* The ratio becomes smaller as the cell increases in size.... so this means that the volume or internal contents of the cell is increasing at a faster rate than the area of the surface
A larger cell will have a more difficult time getting nutrients in and wastes out... This is why cells do not grow much larger even if the organism itself does grow larger.
*- Cells reach a point where they do not grow larger even if the organism itself DOES grow larger… WHY? Because they have trouble getting nutrients in and wastes out!
**- DNA is stored in a cells nucleus (in eukaryotic cells) ...When the cell is small... copies of DNA that are stored in the nucleus are able to produce enough mRNA to make all the proteins it needs.
* -However, when a cell increases in size, it does not make extra copies of DNA.
(If the cell grew without limits this would cause an information crisis).
**- In time, the cell's DNA may no longer be able to make enough RNA to supply the increasing needs of the growing cell… so the cell must slow down its growth.
**As we have already mentioned Cell division solves this inefficiency problem.
10-2 CELL DIVISION: CELL CYCLE, MITOSIS AND CYTOKINESIS PAGE 244
Cell division involves 2 major stages: mitosis and cytokinesis. (see page245 figure 10-4)The cell cycle is the period from the beginning of one mitosis to the beginning of the next.
The cell cycle is composed of: mitosis, cytokinesis and interphase.
MITOSIS- the process by which the nucleus of the cell is divided into 2 nuclei, each with the same number and kinds of chromosomes as the parent cell.
Mitosis itself is actually divided into four stages: prophase, metaphase, anaphase, and telophase. During interphase(*the majority of the cell’s life cycle!), other cell processes occur.
Interphase-the GROWTH period of a cell in which chromosomes are duplicated. Interphase is divided into three stages known as G1, S, and G2.…
During interphase,cell growth and development occurs, DNA is made and the cell produces some of the material needed for the next cell division.
Mitosis requires only a small percentage of time, so the cell is usually in interphase.
CYTOKINESIS- the stage of (m phase) cell division in which the cytoplasm divides, and forms 2 distinct cells.
- Chromosomes contain the genetic information (DNA) that is passed from one generation to the next… Chromosomes are only visible during cell division (mitosis).
- In eukaryotic cells, genetic information is carried in the form of DNA. The DNA together with protein forms chromatin.
