SCIENCE 8

• Meiosis is a type of cell division in multicellular organisms that results in the formation of reproductive cells (gametes) such as sperm cells, egg cells, and spores.
• Meiosis is similar to mitosis in several ways because the process is also divided into four basic stages: Prophase, metaphase, anaphase, and telophase.
• Meiosis involves two successive cell divisions: Meiosis I reduces the number of chromosomes from diploid to haploid (reductional division), and Meiosis II is similar to mitosis (equatorial division).
• Meiosis results in the production of haploid daughter cells, and the daughter cells produced are not identical because of the manner the chromosomes divide.
• Prophase I


  1. Chromosomes start to coil and shorten

  2. Nuclear envelope disintegrates

  3. Homologous pair through synapsis
• Synapsis


  The 2 members of each homologous pair of chromosomes line up side-by-side to form a tetrad consisting of 4 chromatids
• Prophase I - Crossing Over


  Exchange of homologous parts between non–sister chromatids
• Crossing over provides genetic variation
• Metaphase I


  1. Homologous alignment at the metaphase plate

  2. Spindle apparatus begins to form

  3. Homologous attach to a spindle fiber at the kinetochore in their centromeres
• Independent Assortment


  Pairs of homologues line up independently of other pairs' orientation toward the poles -- random, adding variation
• Anaphase I


  1. Homologous chromosomes separate towards the poles

  2. Sister chromatids remain attached to the centromere
• Telophase I


  1. Each pole has haploid set of chromosomes

  2. Cleavage furrow appears and the cytoplasm starts to divide

  3. Cytokinesis I occurs: two haploid daughter cells formed
• Meiosis II has no interphase II (no more DNA replication)
• Meiosis II - Prophase II

  1. Nuclear membrane disintegrates

  2. New spindle fibers form around the chromosomes
• Meiosis II - Metaphase II

  Chromosomes align at the metaphase plate and attach to spindle fibers at the kinetochore in their centromeres
• Meiosis II - Anaphase II


  1. Each chromosome divides into two sister chromatids

  2. Chromatids move toward opposite poles

  
• Meiosis II - Telophase II

  1. Nuclear membrane forms around each set of chromosomes

  2. Spindle fibers disintegrate

  3. Cytokinesis II separation of the two cells into four unique haploid cells
• Gametes


  Sperm or egg cells; ovule or pollen grain
• Spermatogenesis


  All 4 meiotic products develop into sperm cells

  
• Oogenesis


  Cytokinesis in meiosis is uneven, most of cytoplasm goes into 1 of the 4 meiotic products (forms large egg cell), 3 other cells are small "polar bodies" that break down
• Nondisjunction occurs when the tetrad (in Anaphase I) or the sister chromatids (in Anaphase II) do not separate, creating an abnormal number of chromosomes in the gametes, which is usually lethal.
• The human digestive system's function is to digest food, the breakdown of organic compounds into their simple forms (glucose) for use by the cells
• Digestion is the chief function of the digestive system

  
• The digestive system breaks down food mechanically and chemically
• Ingestion


  Taking in food or any substance into the body through the mouth
• When food is chewed, saliva starts digesting carbohydrates
• Digestion


  Breakdown of large molecules and small molecules for easy absorption of the cells
• Both chemical and mechanical digestion begin immediately in the mouth
• Mastication


  The process of crushing and breaking apart food into tiny pieces by the teeth
• Bolus


  A moist ball formed by mixing food with saliva that can be easily swallowed
• Salivary glands


  • The parotoid, sublingual, and submandibular glands that produce saliva
• Salivary amylase


  An enzyme in saliva that helps break down starch into smaller carbohydrates
• Peristalsis


  Wave-like muscle contractions that transport food and liquids through the esophagus to the stomach

  
• Chyme


  A semifluid material formed from the bolus that is acted upon by the gastric juices in the stomach
• Gastric juices


  Hydrochloric acid and pepsin secreted by the stomach that begin the chemical breakdown of proteins
• Organs involved in the digestive system

  • Liver
  • Pancreas
  • Gallbladder

  
• Bile


  A fluid produced by the liver that helps digest fats
• Pancreatic enzymes


  Amylase, peptidase, protease, and lipase that aid in the digestion of carbohydrates, proteins, and fats
• Parts of the small intestine

  • Duodenum
  • Jejunum
  • Ileum

  
• Villi


  Tiny, finger-like projections from the epithelial lining of the intestinal wall that increase the surface area for absorption