AP Biology Notes: The Cell Cycle and Homeostasis

Three Things to Know about the Cell Cycle: 

  1. Interphase consists of three stages: G1 (first gap phase), S (synthesis, in which DNA replication occurs), and G2 (second gap phase). Interphase is followed in somatic cells by mitosis.
  2. Mitosis is the process in which a cell produces two identical daughter cells. Its stages include prophase, metaphase, anaphase, and telophase. Cytokinesis occurs immediately following mitosis and refers to the splitting of the cell into two new cells.
  3. Meiosis refers to the process by which sexually reproducing organisms produce sex cells (gametes) with half the chromosomes (haploid) of the rest of the organism’s cells (which are diploid). It consists of two rounds of division, meiosis I and meiosis II, and it results in the creation of four gametes. In sexual reproduction, the male and female gametes join to create a new organism with the normal diploid number of chromosomes.

Five Things to Know about Homeostasis:

  1. Homeostasis is the process by which a stable internal environment is maintained within an organism. Our primary homeostatic organs are the kidneys, liver, large intestine, and skin.
  2. There are three laws of thermodynamics. Together they discuss the conservation of energy, entropy, and absolute zero.
  3. Bioenergetics, or biological thermodynamics, studies how chemical energy is broken down and converted to usable energy within the biological system. This can be at the ecosystem, organismal, or cellular level.
  4. Chemiosmosis produces energy from the movement of H+ ions across a membrane down a concentration gradient in both photosynthesis and respiration. Catabolism is the breaking down of complex substances into simple substances, making energy available in the process.
  5. Thermoregulation refers to the physiological processes that come together to maintain a stable body temperature in warm-blooded animals.

Key Topics–The Cell Cycle and Homeostasis

Remember that the AP Biology exam tests you on the depth of your knowledge, not just your ability to recall facts. While we have provided brief definitions here, you will need to know these terms in even more depth for the AP Biology exam.

The Cell Cycle: Interphase

  • Somatic cell: Any cell that is not a reproductive cell
  • Interphase: The cellular phase between meiotic or mitotic divisions
  • Chromatid: One of the two strands that constitute a chromosome; chromatids are held together by the centromere

The Cell Cycle: Interphase

  • Mitosis: A type of nuclear division that is characterized by complex chromosomal movement and the exact duplication of chromosomes; occurs in somatic cells
  • Prophase: A mitotic or meiotic stage in which the chromosomes become visible and during which the spindle fibers form; synapsis takes place during the first meiotic prophase
  • Metaphase: A stage of mitosis; chromosomes line up at the equator of the cell
  • Anaphase: The stage in mitosis that is characterized by the migration of chromatids to opposite ends of the cell; the stage in meiosis during which homologous pairs migrate (anaphase I); and the stage in meiosis during which chromatids migrate to different ends of the cell (anaphase II)
  • Telophase: A mitotic stage in which nuclei reform and the nuclear membrane reappears
  • Cytokinesis: A process by which the cytoplasm and the organelles of the cell divide; the final stage of mitosis
  • Chromatin: A nuclear protein of chromosomes that stains readily
  • Spindle: A structure that arises during mitosis and helps separate the chromosomes; composed of tubulin

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