Biology Year 8

• Types of nutrient needed for a balanced diet

  • Protein
  • Carbohydrate
  • Fats
  • Vitamins
  • Minerals
  • Water
• Protein

  For growth and repair/replacing
• Carbohydrate


  Readily available stored energy
• Fats

  Stored energy and insulation
• Vitamins

  Cell chemistry
• Minerals

  General good health
• Water

  To replace losses through urine and breathing
• Fibre (roughage) contains energy, but this energy cannot be used by the human body because fibre itself cannot be digested. This means that we cannot describe fibre as a nutrient. Fibre aids the digestion process and helps to prevent constipation and lowers the risk of bowel cancer. Examples of good sources of fibre are bran, wholemeal bread, fruits and vegetables.
• Malnutrition

  When a person eats too much or too little of any food group
• Malnutrition leading to deficiency diseases

  • Scurvy (from lack of Vitamin C)
  • Rickets (from lack of Vitamin D)
  • Brittle bones and teeth (from lack of Calcium)
  • Anaemia (from lack of Iron)
• Energy intake

  The amount of food that you need to maintain your weight depends on the amount of energy that you use
• Groups of people with different food intake needs

  • Athletes
  • Children
  • Teenagers
  • Older people
  • Pregnant/breastfeeding women
  • Men
  • Physical workers
• Digestion


  The break-down of large, insoluble food molecules into small, water soluble molecules using mechanical and chemical processes
• Digestion in the mouth

  1. Food/drink is taken in (ingested)

  2. Food is chewed to break it into smaller pieces

  3. Saliva containing mucus and amylase is secreted
• Oesophagus

  Food moves down by peristalsis
• Stomach

  Churns food and produces mucus, hydrochloric acid and pepsin
• Small intestine

  Most digestion takes place in the duodenum, where pancreatic enzymes and bile break down food
• Villi

  • Finger-like projections in the small intestine lining to increase surface area for absorption
  • Contain blood capillaries to absorb amino acids and glucose, and lacteals to absorb digested fats
  • Contain goblet cells that produce mucus
• Large intestine


  Digested food is not absorbed, only water is absorbed
• Determining the energy content of food using a simple calorimeter

  1. Weigh the food

  2. Measure 20cm of water in a boiling tube

  3. Measure initial water temperature

  4. Light the food and hold it under the boiling tube until it is completely burnt

  5. Measure the maximum temperature of the water
• Calorie


  The amount of energy needed to raise the temperature of 1g (=1cm) of water by 1°C
• Joule


  The unit of energy, 1 calorie = 4.2 Joules
• The value determined by the simple calorimeter experiment will be much smaller than that given on the food packet because of heat lost to the surroundings, some energy is given out as light, the food does not burn completely, the food is burned in air not oxygen. The bomb calorimeter is an improvement.
• Food tests


  1. Proteins: Add Biuret's reagent

  2. Glucose: Heat with Benedict's solution

  3. Starch: Add iodine solution

  4. Lipids: Add ethanol and water
• Enzymes

  Biological catalysts that are proteins
• 1 calorie


  4.2 Joules
• 1000 Joules


  1 kJ (k)
• The bomb calorimeter is an improvement
• Food tests


  • Proteins
  • Glucose (a reducing sugar)
  • Starch (a complex carbohydrate)
  • Lipids (fats solids; oils liquids)
• Protein test

  Add Biuret's reagent
• Glucose test


  Heat with Benedict's solution in a boiling water bath
• Starch test

  Add iodine solution
• Lipid test


  Place about 1 cm³ of ethanol in a test tube, add a few drops of oil and mix by shaking, add an equal amount of water and shake again
• Enzymes


  Biological catalysts; they are proteins which speed up the rate of biological reactions
• Some enzymes are involved in the digestion of certain nutrients, but not all enzymes are digestive ones
• Enzymes

  • They have an active site with a particular 3-D shape which means that they act on only one type of substrate
  • Proteases, such as pepsin, digest proteins and polypeptides
  • Carbohydrases, such as amylase, digest carbohydrates
  • Lipases digest lipids
• Optimum temperature for enzymes

  Around body temp, 37°C. Enzyme activity falls after this temperature and enzymes do not usually work at temperatures above 60°C, because the enzyme becomes denatured (it is destroyed, we do not say killed!)
• Optimum pH for enzymes

  Pepsin (a protease) in the stomach at pH 2 (acidic conditions) and amylase (a carbohydrase) in the mouth at pH7 (neutral)
• Characteristics of living organisms

  • Movement
  • Respiration
  • Sensitivity
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• Types of micro-organism

  • Bacteria
  • Viruses
  • Fungi
  • Protoctistans