Part 2

• Cells


  As cells get bigger, more of its cytoplasm is located farther from the cell membrane. If a cell gets too big, it would take too long to get materials into the cell and too long to get waste out of the cell. Smaller cells are more efficient!
• All Living Things are Made of Cells. All cells come from other living cells.
• Cell division


  A single cell divides into two cells. Two cells divide into four and etc. Cells must also divide because old cells die and need new cells to replace them.
• Cell cycle


  A series of events that takes place in a cell as it grows and divides. A cell spends most of its time in interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division.
• Stages of the cell cycle

  • Interphase
  • Cell division or mitotic phase
• Interphase


  The interval between two cell divisions. During this stage, the cell is not dividing; it merely grows. The chromosome doubles or replicates itself because the DNA molecule contained in the chromosome produces a precise copy of itself.
• Stages of interphase


  • First gap period or G1
  • Synthesis stage or S phase
  • Second gap period or G2
• G1

  Cell grows initially, synthesis of protein and ribonucleic acid or RNA occurs, mitochondria increase in number
• S phase


  DNA are synthesized thus replicating the chromosomes in preparation for the next cell division
• G2


  Cell grows rapidly, cell prepares for the actual cell division
• Mitosis


  The cell's chromatin condenses into chromosomes. The chromosomes look like an "x". Each chromosome is made up of two identical sister chromatids attached by a centromere.
• Mitosis and Cytokinesis

  During mitosis, the cells copied genetic material separates and the cell prepares split into two cells. This allows the cell's genetic material to pass into the new cells. The resulting daughter cells are genetically identical!
• Chromosomes


  Chromosomes are in the nucleus of every cell. Chromosomes are made up of DNA. Genes are made up of pieces of DNA that contain the instructions for building a protein.
• Stages of mitosis

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase


  Nucleus disappears, Spindle fibers form in the cytoplasm, Spindle fibers attach to sister chromatids
• Metaphase


  Spindle fibers begin to shorten, sister chromatids are pulled to opposite ends of the cell
• Anaphase


  The sister chromatids are pulled to opposite poles of the cell
• Telophase


  Nuclei of the cell and Cytokinesis begin
• Cytokinesis


  The division of the cytoplasm to form two daughter cells
• Meiosis is the process of cell division that produces haploid gametes (half the number of chromosomes). Humans have 23 chromosomes.
• Stages of meiosis


  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II