# Why are cells so small ? Think about the size of a cell and consider the surface area….. Does surface area increase as the size of the cell increases?

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Why are cells so small ? Think about the size of a cell and consider the surface area….. Does surface area increase as the size of the cell increases?

Why are cells so small ? Think about the size of a cell and consider the volume… Does the volume increase as the size of the cell increases? What IS the formula for volume? Length x Width x height

examples of surface area Lets say a = 1; figure the volume… Vol=1 and there are 6 surfaces, so… 1 X 6 = 6

examples of surface area Lets say a = 2; figure the volume… Vol= ? and there are 6 surfaces = 2

examples of surface area Lets say a = 4; figure the volume… Vol= ? and there are 6 surfaces = 4

What can you conclude about how an increase in the surface area can effect the volume… Now think about the organelles within a cell, and their functions to keep the cell operating in an efficient manner…

If the cell size increases, can the organelles inside keep up with the large increase in volume? What conclusion can you draw about the efficiency of a large cell? What conclusion can you draw about the efficiency of a small cell?

Judge the importance of the cell size, and suppose what cells could do to solve the problem. Finish this statement: Cells MUST divide because…. The process of cell division is called Mitosis

Now draw a circle and divide it into sections, as shown below: G 1 phase S phase G 2 phase M

Cell Cycle G 1 phase: growth. regular growth and development S phase: Synthesis-copying DNA so each cell has an identical set of chromosomes G 2 phase: Growth 2. final preparations, BEFORE cell division begins

Cell Cycle M phase: Mitosis, when the cell is actively going through steps to divide Cytokinesis: Division of cytoplasm Interphase: all growth and development of G 1, S, and G 2 phases.

Cell Cycle What happens IF a cell stops duplicating the DNA and never enters Mitosis? What happens IF a cell completes the mitosis phase, and continues to divide, over and over? Does that malfunction have a name?

Chemical Signals tell a cell when to start and stop dividing.

The Chemical Messengers may come from other cells or the cell’s own DNA 1.Before a cell divides, the DNA is checked to make sure it has replicated correctly. (If DNA does not copy itself correctly, a gene mutation occurs.

Neighboring cells communicate with dividing cells to regulate their growth also. They may release the necessary chemical messengers for the others cells.

Cancer: What happens when something goes wrong?

Cancer is a disease of the cell cycle. Some of the body’s cells divide uncontrollably and tumors form. Tumors in Liver Tumor in Colon

DNA mutations disrupt the cell cycle. Mutations may be caused by: 1. radiation 2. smoking 3. Pollutants 4. chemicals 5. viruses

While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

Due to DNA mutations, cancer cells ignore the chemical signals that start and stop the cell cycle.

Due to DNA mutations, cancer cells cannot communicate with neighboring cells. Cells continue to grow and form tumors. Skin cancer

SUMMARY Normal Cell Division 1.DNA is replicated properly. 2. Chemical signals start and stop the cell cycle. 3. Cells communicate with each other so they don’t become overcrowded. Cancer Cells 1.Mutations occur in the DNA when it is replicated. 2. Chemical signals that start and stop the cell cycle are ignored. 3. Cells do not communicate with each other and tumors form.

Treating Cancers Cancer treatments include drugs that can stop cancer cells from dividing.

Interphase – 95% of cell’s life Includes the G1, S, and G2 phases DNA is NOT visible DNA is replicated in S phase 95% of cell’s life is spent during this time

Mitosis (nuclear division) only 5% of cells life Prophase Metaphase Anaphase Telophase http://highered.mcgraw- hill.com/sites/0072495855/student_view0/ chapter2/animation__mitosis_and_cytokin esis.html

Interphase: cannot see chromosomes; G1, S, G2 phases

Prophase: spindle fibers extend, nuclear membrane disintegrates, chromosomes pair up and coil up

Metaphase: Meta means “middle”, chromosomes aligned along the middle

Anaphase: chromosomes pulled apart when spindle fibers become shorter

Telophase: two nucleus form at each pole of the cell

Cytokinesis: forming two daughter cells identical to the parent cell Animal cells: cell pinches down the middle Plant cells: cell plate forms to make new cell wall Animal cellPlant cell

Onion root tip showing phases of mitosis

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