Science 8- Biology

• Food is a substance that consists of chemical substances used by any living organism to sustain growth, repair, reproduction, development, and maintenance of vital processes
• We need food to maintain health, to prevent diseases, and most importantly, to sustain life
• When we do not eat

  The body uses the glycogen storage in the liver, and once glycogen is depleted, the body breaks down fat and muscle tissues to use whatever energy they contain
• If the body continuously uses muscle tissues to get energy because of lack of food or nourishment, the body will lose muscle mass
• A person who refuses to eat deprives the body of important nutrients; eventually, this will lead to organ failure
• The six major classes of nutrients

  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Minerals
  • Water
• Carbohydrates


  Provide our body with the energy it needs, and they constitute a large part of our diet because they come mainly from rice, bread, noodles, and cereals
• Protein


  An essential part of every living cell, tissue, and organ of the body, and it is found in meat, eggs, milk, fish, nuts, and legumes
• Fats (lipids)


  Supply the body with energy, can provide more energy compared to carbohydrates and proteins, and act as an insulator and aid in the absorption of fat-soluble vitamins
• Vitamins and Minerals


  Do not provide us with energy, but they are necessary for various processes in the body
• Water


  Helps in digestion and it is a big help in preventing constipation, and it also acts as a lubricant of the membranes that surround our body organs
• The primary purpose of the digestive system is to break down food to facilitate effective transport of nutrients to different parts of the body
• Parts of the digestive system

  • Pharynx
  • Parotid salivary gland
  • Oral cavity
  • Salivary glands
  • Submandibular gland
  • Sublingual gland
  • Tongue
  • Mouth
  • Esophagus
  • Liver
  • Pancreas
  • Gallbladder
  • Duodenum
  • Stomach
  • Common bile duct
  • Pancreatic duct
  • Colon
  • Transverse colon
  • Ascending colon
  • Descending colon
  • Rectum
  • Cecum
  • Appendix
  • Ileum (small intestine)
  • Anus
• Digestion of food


  1. Chewing causes saliva to start digesting carbohydrates

  2. Food is mixed with digestive juices

  3. Hydrochloric acid kills bacteria

  4. Enzymes break down proteins

  5. Bile from liver breaks down fats

  6. Digestive enzymes from pancreas secreted to small intestine

  7. Complete digestion takes place in small intestine

  8. Water and mineral salts absorbed in large intestine

  9. Solid waste passes from rectum through anus
• Food must be broken down into nutrients by digestion
• Digested food nutrients are carried by blood to cells for energy and growth
• Disorders of the digestive system

  • Gastroesophageal Reflux Disease (GERD)
  • Diarrhea
  • Constipation
  • Appendicitis
  • Abdominal pain (stomachache)
  • Peptic Ulcer
  • Stomach Cancer
  • Colon Cancer/Colorectal Cancer
• In the 1800s and 1900s, many people died from diseases like smallpox, tuberculosis, diarrhea, leprosy, and tetanus
• The 21st century faces new health issues like cancer and heart diseases
• Nutrient deficiency can cause diseases like rickets, osteomalacia, osteoarthritis, anemia, scurvy, beriberi, and pellagra
• Malnutrition


  Condition where body does not get the right nutrients, leading to poor immune system and inability to fight diseases
• Kwashiorkor


  Severe form of malnutrition due to lack of protein, characterized by edema, anemia, weakness, irritability, hampered growth, and swollen abdomen
• Overnutrition


  Condition where body has too much nourishment, especially carbohydrates and fats, leading to obesity and diseases like diabetes and cardiovascular diseases
• Health organizations do not promote vitamin/mineral supplements as a substitute for a well-balanced diet
• Breakfast is the most important meal of the day for teenagers, providing energy and speeding up metabolism
• Teenagers should eat healthier snacks like fruits, cereals, milk, and juices instead of high-fat, high-sugar foods
• Teenagers should limit eating at fast food restaurants to once a week or less
• Teenagers should drink water instead of sugary soda drinks
• Teenagers should avoid alcohol and cigarettes as they are addictive and harmful
• Nutrient


  A substance that provides nourishment essential for the growth, maintenance, and repair of tissues and organs in the body. Nutrients can be classified into six main categories: carbohydrates, proteins, fats, vitamins, minerals, and water.
• Digestive System


  A group of organs that work together to break down food into nutrients that the body can use for energy, growth, and cell repair. The digestive system includes the mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas, and gallbladder.
• Swollen abdomen

  Often due to an enlarged liver
• Treatment for Kwashiorkor

  Medical attention is necessary to treat Kwashiorkor and prevent long-term health problems or death
• Hampered growth

  Slowed or stunted growth in children
• Anemia

  A shortage of red blood cells
• Edema

  Swelling in the body, particularly in the stomach and legs
• Symptoms of Kwashiorkor

  Edema, anemia, weakness, irritability, hampered growth, and a swollen abdomen
• Kwashiorkor


  A severe form of malnutrition caused by a lack of protein in a person's diet