Science (Q4)

• Parts and Functions

  A) Propulsion

  B) Absorption

  C) Chemical Digestion

  D) Mechanical Digestion

  E) Ingestion of food

  F) Pharynx

  G) Esophagus

  H) Stomach

  I) Small Intestine

  J) Large Intestine

  K) Anus

  L) Defecation

  M) Feces

  N) Swallowing

  O) Peristalsis

  P) Chewing

  Q) Churning

  R) Segmentation

  S) Blood vessels

  T) Lymph vessels

  U) Blood Vessels
• Ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase. Chewing increases the surface area of the food and allows an appropriately sized bolus to be produce
• Propulsion, which refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis.
• Peristalsis consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along. These waves also play a role in mixing food with digestive juices.
• Digestion includes both mechanical and chemical processes
• Mechanical digestion is a purely physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility. It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva.
• Mechanical churning of food in the stomach


  1. Breaks food apart

  2. Exposes more surface area to digestive juices

  3. Creates acidic "soup" called chyme
• Segmentation in the small intestine


  1. Localized contractions of circular muscle of the muscularis layer

  2. Isolates small sections of the intestine

  3. Moves contents back and forth

  4. Subdivides, breaks up, and mixes the contents
• Segmentation


  Mixes food with digestive juices and facilitates absorption
• In chemical digestion, starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks (for example, proteins into separate amino acids). These secretions vary in composition, but typically contain water, various enzymes, acids, and salts. The process is completed in the small intestine.
• Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins near the heart).
• In defecation, the final step in digestion, undigested materials are removed from the body as feces.
• Cell cycle


  The cycle of changes a cell goes through as it grows and divides
• Cell cycle


  1. Interphase

  2. Cell division or mitotic phase
• Interphase


  • Interval between two cell divisions
  • Cell is not dividing, it merely grows
  • Chromosome doubles or replicates itself
• Chromosome


  • Long, extended form during interphase
  • Condensed or thickened form during cell division or mitotic phase
• During interphase, the DNA molecule contained in the chromosome produces a precise copy of itself
• Interphase is the interval

  between two cell divisions. During this stage, the cell is not dividing; it obtains nutrients and metabolizes, grows, replicates its DNA in preparation for mitosis.

  The interphase is divided into

  three substages, namely:
• 1. First gap period or G1 where cell grows initially synthesis of protein and ribonucleic acid or RNA occurs mitochondria increase in number.

  2. Synthesis stage or S phase

  • where DNA are synthesized, thus replicating the chromosomes in preparation for the next cell division.

  3. Second gap period or G2 where

  • cell grows rapidly
  • cell prepares for the actual cell division
• 1 First gap period or G1 where

  • cell grows initially,
  • mitochondria increase in number.

  2. Synthesis stage or S phase

  • where DNA are synthesized, thus replicating the chromosomes in preparation for the next cell division.
  • synthesis of protein and ribonucleic acid or RNA occurs

  3. Second gap period or G2 where

  • cell grows rapidly
  • cell prepares for the actual cell division
• • Mitosis – is the process in which a cell nucleus divides into two new nuclei, each of which contains the same number of chromosomes as the parent cell. The parent cell is the cell that undergoes division. This process occurs on the body (somatic) cells.
• • Meiosis – s a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our sex cells – sperm in males, eggs in females
• Meiosis I begins after DNA replicates during interphase. In both meiosis I and meiosis II, cells go through the same four phases as mitosis. However, there are important differences between meiosis I and mitosis.
• 1. Prophase I: The nuclear envelope begins to break down, and the chromosomes condense. Centrioles start moving to opposite poles of the cell, and a spindle begins to form. Importantly, homologous chromosomes pair up, which is unique to prophase I. In prophase of mitosis and meiosis II, homologous chromosomes do not form pairs in this way

  
• 2. Metaphase I: Spindle fibers attach to the paired homologous chromosomes. The paired chromosomes line up along the equator of the cell. This occurs only in metaphase I. In metaphase of mitosis and meiosis II, it is sister chromatids that line up along the equator of the cell

  
• 3. Anaphase I: Spindle fibers shorten, and the chromosomes of each homologous pair start to separate from each other. One chromosome of each pair moves toward one pole of the cell, and the other chromosome moves toward the opposite pole.

  
• 4. Telophase I and Cytokinesis: The spindle breaks down, and new nuclear membranes form. The cytoplasm of the cell divides, and two haploid daughter cells result. The daughter cells each have a random assortment of chromosomes, with one from each homologous pair. Both daughter cells go on to meiosis II.

  
• 1. Prophase II: The nuclear envelope breaks down, and the spindle begins to form in each haploid daughter cell from meiosis I. The centrioles also start to separate.

  
• 2. Metaphase II: Spindle fibers line up the sister chromatids of each chromosome along the equator of the cell.

  
• 3. Anaphase II: Sister chromatids separate and move to opposite poles

  
• 4. Telophase II and Cytokinesis: The spindle breaks down, and new nuclear membranes form. The cytoplasm of each cell divides, and four haploid cells result. Each cell has a unique combination of chromosomes.