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Chapter 9: Cellular Reproduction

Chapter Worksheet

Ch. 9.1 Cellular Growth

Cell Size Limitations

Most cells are less than 100 micrometer in diameter.

Ratio of Surface Area to Volume

Key factor that limits the size of a cell is the ratio of its surface area to its volume. Surface area is the plasma membrane, volume is the space taken up by the inner contents of the cell.

Surface area is length x width x number of sides; 1 x 1 x 6= 6. Volume is length x width x height; 1 x 1 x 1= 1. Ratio of surface area to volume is 6:1.

If the cell doubles: 2 x 2 x 6 = 24; 2 x 2 x 2 = 8; ratio is 24:8 (3:1).

As a cell grows, it's volume increases much more rapidly than the surface area so ratio decreases with increase in size.

Transport of Substances

Diffusion and motor proteins of cytoskeleton are less efficient in larger cell since distance substances travel increases.

Cellular Communications

If the cell becomes too large, it becomes almost impossible for cellular communications to take place efficiently. Example: signals that trigger protein synthesis may not reach ribosome fast enough for protein synthesis to occur.

The Cell Cycle

When a cell reaches it's size limit, it will either stop growing or divide. Most will divide. Cell reproduction allows for growth and repair of damaged cells. Cell cycle- a cycle of growing and dividing.

Three main stages of cell cycle:

  1. Interphase- the cell grows, carries out cellular functions, and replicates its DNA in preparation for the next stage of the cycle. Divided into three stages.
  2. Mitosis-the cell's nucleus and nuclear material divides. Divided into four substages.
  3. Cytokinesis- method by which a cell's cytoplasm divides, creating a new cell.

Duration of cell cycle varies among cells. Most normal, actively dividing animal cells complete cell cycle in 12-24 hours.

The Stages of Interphase

  • G1 (gap 1)- cell grows, carries out cell function, prepares to replicate DNA.
  • S (synthesis)- cell copies its DNA.
    • Chromosomes- the structures that contain the genetic material that is passed to daughter cells.
    • Chromatin- the relaxed form of DNA in the cell's nucleus.
  • G2 (gap2)- cell prepares for division of its nucleus.

Mitosis and Cytokinesis

In mitosis, the cell's nuclear material divides and separates to the opposite ends of the cell. In cytokinesis, the cell divides into two daughter cells with identical nuclei.

Prokaryotic Cell Division

Eukaryotic cells reproduce using the cell cycle. Prokaryotic cells reproduce by a method called binary fission.

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Ch. 9.2 Mitosis & Cytokinesis


The key is of mitosis is the accurate separation of the cell's replicated DNA enabling the cell's genetic information to pass into the new cells intact. The daughter cells are genetically identical.

Mitosis used for growth and repair of damaged tissue.

Stages of Mitosis


The longest phase; chromatin condenses to chromosomes that are shaped like an X. Each half of the X is a sister chromatid. Sister chromatids- are structures that contain identical copies of DNA. Chromatids are held together in the middle by the centromere.

The nucleolus seems to disappear. Spindle apparatus consisting of spindle fibers, centrioles, and aster fibers produced by centrioles. Plant cells do not have centrioles as part of spindle apparatus.

Near end of prophase the nuclear envelope seems to disappear. Spindle fibers attach to sister chromatids on opposite sides of the centromere.


One of shortest stages. Using motor proteins the chromosomes are lined up at the center of the cell.


Microtubules of spindle apparatus shorten to separate the sister chromatids at the centromere. Each chromatid is now a chromosome which moves to the poles of the cell.


When chromosomes reach the poles of the cells, they relax (decondense). Nuclear envelopes begin to form and the nucleoli reappear. Spindle apparatus breaks down.


In animal cells microfilaments are used to pinch the cytoplasm. This creates a furrow.

Plant cells have a rigid cell wall, instead of pinching in half a cell plate forms at the center. New cell walls form on both sides to eventually divide the cell in half.

With prokaryotes the replicated DNA attaches to the cell membrane. As membrane grows the DNA is separated and then the cell divided by binary fission.

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Ch. 9.3 Cell Cycle Regulation

The normal cell cycle is regulated by cyclin protiens.

Normal Cell Cycle

The rate of cell division varies depending on the type of cell. Proteins and enzymes control the cell cycle.

The Role of Cyclins

In eukaryotic cells the cell cycle is driven by a combination of two substances that signal the cellular reproduction processes. Proteins called cyclins bind to enzymes called cyclin-dependent kinases (CDKs) in the stages of interphase and mitosis to start the various activities that take place in the cell cycle.

Different combinations of cyclin/CDKs control different activities at different stages in the cell cycle.

Quality Control Checkpoints

The cell has built in checkpoints that monitor the cycle and can stop it if something goes wrong. Example: checkpoint at end of G1 monitors for DNA damage before S stage begins.

Abnormal Cell Cycle: Cancer

When cells do not respond to the cell cycle control mechanisms, cancer can occur. Cancer- uncontrolled growth and division of cells (failure in regulation of cell cycle). Cancer cells can crowd out normal cells resulting in the loss of tissue function. Cancer cells spend less time in interphase and grow and divide unchecked if they are supplied with essential nutrients.

Causes of Cancer

Changes in regulation of cell cycle in cancer cells are due to mutations or changes in the segments of DNA that control production of proteins that regulate the cell cycle. Repair systems can repair damaged segments but is they fail cancer can result. Carcinogens- substances and agents that are known to cause cancer.

Avoiding known carcinogens can help reduce the risk of cancer. FDA requires labels, industrial laws protect in the work place.

UV rays, X-rays can cause cancer.

Cancer Genetics

Individuals that inherit one or more DNA changes may be at a higher risk. More changes can increase chances which may be why age increases chances of cancer.


Apoptosis- programmed cell death. Cells shrink and shrivel in a controlled process. Examples: webbing between toes and fingers; in plants- localized cells in leaves to allow leaves to fall in autumn.

Occurs in cells that are damaged beyond repair, including DNA damage that could lead to cancer. Can help to prevent cancer growth in organisms.

Stem Cells

Stem cells- unspecialized cells that can develop into specialized cells under the right conditions.

  1. Embryonic Stem Cells: mass of cells formed after egg is fertilized. Cells can be separated and become anything.
  2. Adult Stem Cells: found in tissues, can be used to maintain and repair the same kind of tissue in which they are found. Might be able to be used to develop into other types of cells.

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Ch. 9.4

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