Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Cell Growth - Fall River Public Schools
Document related concepts
Transcript
Generally, living things grow by producing more cells Adult organisms do not have bigger cells than younger organisms Adult organisms have more cells than younger organisms Two Main Reasons 1. The larger a cell becomes, the more demands it places on its DNA There is not enough DNA to meet all of the cell’s needs 2. The larger a cell becomes, the more trouble moving nutrients and wastes across the membrane it has The surface area to volume ratio decreases, and nutrients and wastes cannot move in and out fast enough Imagine the cell as a cube › Surface Area = length x width x number of sides (which is 6) › Volume = length x width x height › The volume increases much more rapidly than the surface area, which decreases the ratio Before a cell becomes too large, it divides, creating 2 “daughter” cells › The process by which a cell divides into two new daughter cells is called cell division Before cell division, it copies its DNA so each daughter cell has its own copy Cell division decreases each daughter cell’s volume, which increases its surface area to volume ratio › This allows the flow of nutrients and wastes in and out of the cell to be more efficient In eukaryotic cells, genetic information is passed on from generation to generation by chromosomes Chromosomes are made up DNA wrapped around proteins › Chromosomes are not visible until cell division › Each organism has a specific number of chromosomes Humans have 46 Each chromosome consists of two identical sister chromatids Chromatids are attached at an area in the middle of the chromatids called the centromere During cell division, the sister chromatids separate from each other at the centromere and one chromatid goes into each of the two new cells The cell cycle is the series of events that cells go through as they grow and divide Interphase is the period of the cell cycle in between divisions › Consists of the S phase and the G1 and G2 phases M phase › Consists of mitosis and cytokinesis G1 phase S phase › Period where cells do most of their growing › Cells synthesize new proteins and organelles › Chromosomes are replicated and DNA synthesis takes place › Proteins associated with chromosomes are also synthesized G2 phase › Shortest of the three stages of interphase › The organelles and molecules required for cell division are produced Part of M phase Mitosis is the phase where the cell’s nucleus divides Mitosis consists of 4 stages 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Many unicellular organisms reproduce by mitosis and cytokinesis Considered asexual reproduction › The new cells produced are genetically identical to the parent cell Mitosis is also the source of new cells in multicellular organisms as they grow and develop Longest phase of mitosis Chromosomes become visible Centrioles move to opposite sides of the nucleus into an area in the cell called the centrosome Centrioles organize the spindle, which is a fanlike microtubule structure that helps sparate the chromosomes Nucleolus disappears and nuclear envelope breaks down Chromosomes line up in the center of the cell Microtubules connect the centromere of each chromosome to the two poles of the spindle Centromeres split Sister chromatids separate and become individual chromosomes Chromosomes move until they have separated into two groups near the poles of the spindle Ends when the chromosomes stop moving Chromosomes disperse into tangled, dense material Nuclear envelope re-forms around each cluster of chromosomes Spindle breaks apart Nucleolus becomes visible in each daughter cell Occurs at the same time as telophase Cytoplasm divides › A cleavage furrow forms in between two daughter cells through the actions of the microfilaments › Cell membrane gets pulled inward, pinching the cytoplasm off into two equal parts Result is two cells, each with its own nucleus and organelles Vesicles formed by the Golgi fuse in the middle of the dividing cell › Forms a membrane-bound cell wall called the cell plate Cell plate develops into a separating membrane, and then the cell wall forms
