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