Getting Through Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell? Work with a partner to complete

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Cell cycle cell growth and cell division
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• How do materials such as oxygen, carbon dioxide,
  and glucose move into and out of a cell?
• DIFFUSION

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How does the size of a cell affect how
efficiently materials get to all parts of a
cell?Work with a partner to complete this
activity.

• 1. On a sheet of paper, make a drawing of a cell
  that has the following dimensions 5 cm x 5 cm x
  5 cm. Your partner should draw another cell about
  one half the size of your cell on a separate
  sheet of paper.
• 2. Compare your drawings. How much longer do you
  think it would taketo get from the cell membrane
  to the center of the big cell than from the cell
  membrane to the center of the smaller cell?
• 3. What is the advantage of cells being small?

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Importance of cell division

• Cells do not continually grow larger instead
  they divide into 2 separate cells before they
  become too large
• What is too large ?
• DNA overload - the DNA (which controls the cells
  activities) in one cell can only do so much at a
  time
• Exchanging materials a bigger cell needs to
  transport more food, oxygen, water, and wastes
  through the cell membrane

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Ratio of Surface Area to Volume in Cells
Cell Size
Surface Area (length x width x 6)
Volume (length x width x height)
Ratio of Surface Area to Volume
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Surface area vs. Volume

• Square/box cell
• SA length x width x of sides- number of
  square units needed to cover the outside of a
  figure
• Volume length x width x height- the amount of 3
  dimensional space occupied by an object
• Ratio- a comparison of 2 quantities

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Summary

• Give two reasons why cells divide.
• What is the solution to the problems caused by
  cell growth?
• As a cell increases in size, which increases more
  rapidly, its surface area or its volume?
• Calculate the surface area, volume, and ratio of
  surface area to volume of an imaginary cubic cell
  with a length of 4cm.

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The Cell Cycle

• During the cell cycle a cell grows, prepares for
  division, and divides to form two daughter cells,
  each of which begins the cycle again (cell
  growth).
• Two main phases of the cell cycle
• Interphase cell growth preparation for cell
  division
• Cell division the nucleus cytoplasm divide to
  form two daughter cells

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Cell Division

• Two main phases of cell division
• Mitosis the division of the nucleus
• Cytokinesis the division of the cytoplasm,
  including the cellular organelles

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Figure 104 The Cell Cycle
G1 phase
S phase
G2 phase
Go to Section
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Think in your brains

• What do you think would happen if a cell were
  simply to split into two, without any advance
  preparation?

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The Genetic Material

• It consists of
• DNA carries the cells coded genetic
  information
• Proteins
• It is usually found loosely spread out within the
  nucleus chromatin
• Before a cell divides, the chromatin condenses
  (coils up) into more visible chromosomes
• The cells of every organism have a specific
  number of chromosomes (humans have 46)

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Chromatin Chromosomes
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DNA Replication

• Replication duplication (making an exact copy)
• Occurs before the cell divides so each cell
  will get one copy of each chromosome
• Each copy is called a chromatid
• Together they are called sister chromatids
• The sister chromatids remain attached to each
  other at the centromere (near the middle) and are
  still considered one chromosome

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Summary

• What are chromosomes made of?
• What is the difference between chromatin and
  chromosomes?
• What happens during DNA replication?
• How do prokaryotic cells divide?

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Regulating cell cycle

• Cells divide until they come into contact with
  other cells.
• Most muscle and nerve cells do not divide once
  developed, skin and digestive go through cell
  cycle every few hours.

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Cell cycle regulators

• Cyclin- protein that causes mitotic spindle to
  form, regulating the timing of cell cycle.
• There are many proteins like cyclin that regulate
  the cell cycle
• Internal regulators- within the cell.
• External regulators- outside the cell.

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Figure 108 Effect of Cyclins
A sample is injected into a second cell in G2 of
interphase.
A sample of cytoplasm is removed from a cell in
mitosis.
As a result, the second cell enters mitosis.
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CANCER CELLS

• Do not respond to cell regulators that control
  the cell cycle
• Cells continue to grow and grow, forming tumors
  that damage normal tissues.