Cellular Growth
Chapter 9.1
Main Idea Cells grow until they reach their size limit, then they either stop growing or divide
Explain why cells are relatively small in your notes.
Cell Size Limitations Most cells are smaller
than the period at the end of a sentence.
The key factor that limits cell size is the ratio of its surface area to its volume
The larger the volume the less efficient the cell
The larger the surface Area the more efficient the cell
As the cell grows, its volume increases much more rapidly than the surface area.
This means the cell might have difficulty supplying nutrients and expelling enough waste products.
By remaining small, cells have a higher ratio of surface area than volume and can sustain themselves more easily
Large animals do not have larger cells, they have more of them.
Transport of Substances
Recall that the cell membrane controls cellular transport…controls what goes into and out of the cell.
Diffusion over large distances is slow and inefficient because it relies on random movement.
If the distance to travel becomes too large the cell becomes less efficient
Cells remain small to maximize the ability of diffusion and motor proteins to transport nutrients and waste products
Small cells maintain more
efficient transport systems
Cellular communications
If the cell becomes to large, it becomes almost impossible for cellular communications, many of which involve movement of substances and signals to various organelles
For example: signals that trigger protein synthesis might not reach the ribosome fast enough for protein synthesis to occur
The Cell Cycle
Once a cell reaches its size limit----it either stops growing or divides
Most cells divide—hence how we replace old cells with new ones
(RECALL THE CELL THEORY all cells arise from previously
existing cells)
Cellular reproduction allows you to grow and heal certain injuries
Each time a cell goes through one complete cycle, it becomes two cells
Continuous cycles results in continuous production of new cells
Interphase
G1
G2
S
Some cells might complete the cycle in as few as 8 minutes
Other cells might take up to 1 year
Normal cell cycles take approximately 12-24 hours
G1 Phase
Phase where the cell is growing, carrying out normal cell functions, and preparing to replicate DNA
Muscle and nerve cells, exit the cell cycle at this point and do not divide again
S Phase
Cell copies its DNA in preparation for cell division
Chromosomes are the structures that contain the genetic material that is passed from generation to generation of cells
Chromatin is the relaxed form of DNA in the cell’s nucleus
G2 Phase
Phase when the cell prepares for the division of its nucleus.
Microtubules for cell division are synthesized at this time
The cell also take inventory and makes sure it is ready to continue with mitosis
Mitosis and Cytokinesis
Phase when cell’s nuclear material divides and separates into opposite ends of the cell
Cytokinesis is the actual splitting of the cytoplasm making two daughter cells with identical nuclei
Prokaryotic Cell Division
Prokaryotes which are bacteria like cells are much simpler cells
Prokaryotes reproduce by a process called binary fission