The Need for Food

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The Need for Food

• Animal Survival
• Standard Grade Biology

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Learning Outcome 1

• Explain in simple terms why food is required by
  animals.

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Learning Outcome 2

• State the chemical elements present in
  carbohydrates, fats and proteins
• Describe the simple structure of carbohydrates,
  proteins and fats in terms of simple sugars,
  amino acids, fatty acids and glycerol.

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You are what you eat!!

• In this lesson you will
• Look at what is a balanced diet
• Carry out food tests on
• Starch
• Glucose
• Protein
• Fat
• Discuss what happens if you dont eat a balanced
  diet

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Balanced Diet
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What is a balanced diet?

• Your diet must include five groups of food
  substances
• Carbohydrates, fats, proteins, minerals and
  vitamins
• It must also include water and fibre.
• A balanced diet is a diet that provides enough of
  these substances in the correct proportions to
  keep you healthy.

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Carbohydrates

• Carbohydrates give us energy.
• Chemical elements C, H and O.
• Starch is made from simple sugars.

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Testing for glucose

• Pour some glucose solution into a test tube
• Add a few drops of benedict's solution
• Heat in a water bath

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Testing For Starch

• Put a few drops of starch solution on a spotting
  tile.
• Add a few drops of iodine.

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Proteins

• Proteins are needed for growth and repair.
• Proteins are made from amino acids
• Chemical elements C, H, O, N (and S)

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Testing for Proteins

• Put 2 ml of protein solution in a test tube
• Add 2ml of Biurets reagent

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Fats

• Fats are an energy store, protecting vital organs
  and providing insulation.
• Fats contain C, H and O
• Fats are made from a glycerol molecule and three
  fatty acids.

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Testing for fat (the emulsion test)

• Add a few drops of cooking oil into a test tube
• Add 2cm3 ethanol and shake
• Add 2cm3 water and shake again.

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What happens if you dont eat a balanced diet.
What is this cartoon trying to demonstrate? Can
you think of any examples of health problems that
arise from not eating a balances diet? Give
three examples and explain the effects on health.
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Learning Outcomes 3

• State that digestion is the breakdown of large
  particles of food into smaller particles to allow
  absorption into the blood stream through the
  small intestine wall.
• Explain that digestion involves the breakdown of
  insoluble food substances into soluble food
  substances

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What happens to the food we eat?
Ingestion Digestion Absorption Egestion
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The gut as a production line
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Learning Outcome 4

• identify in a diagram / model the main parts of
  the mammalian alimentary canal and associated
  organs (mouth, salivary glands, oesophagus,
  stomach, pancreas, liver, gall bladder, small
  intestine, large intestine, appendix, rectum and
  anus)
• state the sites of production of the main
  digestive juices in mammals (salivary glands,
  stomach, pancreas, liver, small intestine)

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Digestion

• Digestion is the breakdown of large, insoluble
  food molecules into small, soluble food molecules
  so that they can be absorbed into the blood
  stream.

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Pupil Activity

• Label the diagram of the digestive system.
• Use the textbook supplied to help if needed
• Design a table to link the structure and function
  of different parts of the digestive system.

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Salivary glands
mouth
oesophagus
tongue
trachea
liver
stomach
Gall bladder
pancreas
Small intestine
Duodenum
colon
Large intestine
ileum
rectum
appendix
anus
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Mammalian teeth

• The Need for food
• Animal Survival
• SG Biology

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Learning Outcomes (5)

• To know the different structure and functions of
  each type of tooth
• To understand the adaptations of a herbivore,
  omnivore and a carnivore to feeding.

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Feeding in mammals

• Mammals have teeth which may be used to bite
  pieces of food and to chew it into smaller pieces
  before swallowing.
• The shapes of teeth are suited to their function.
• Incisors and canines are used for biting
• Premolars and molars are used for chewing and
  crushing food.

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Patterns of Teeth
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Human Jaw
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teeth

• There are different types of teeth, each
  specially shaped to perform a particular job.
• Incisor - A broad flat sharp tooth found at the
  front of the mouth. Designed for biting and
  cutting food.
• Canine - A sharp pointed tooth for piercing flesh
  and tearing.
• Pre-molar molar - A broad flat tooth with many
  cusps. Its rough surface is used for crushing,
  grinding and chewing food

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Carnivore adaptations

• Look at the dog skull, and the diagrams of a dogs
  skull.
• With the aid of a diagram make notes explaining
  how the dogs teeth and jaws are adapted for a
  carnivorous diet.

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Herbivore adaptations

• Look at the sheeps skull, and the diagrams of a
  sheep skull.
• With the aid of a diagram make notes explaining
  how the sheep's teeth and jaws are adapted for a
  herbivorous diet.

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Learning Outcome 6

• Explain the mechanism of peristalsis
• Explain how the contractions of the stomach help
  in the chemical breakdown of food.

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Digestion of Food

• The digestion of food can either be mechanical or
  chemical.
• Mechanical digestion includes
• Chewing
• Action of muscles in oesophagus, stomach and
  small intestine
• In chemical digestion enzymes catalyse the
  breakdown of larger food molecules into smaller
  food molecules.

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Digestion in the mouth and oesophagus

• Chewed food is mixed with saliva in the mouth
• Saliva contains
• Amylase is an enzyme which starts to digest
  starch into sugars (maltose)
• Mucus helps soften the food making it easier to
  swallow
• The bolus travels down the oesophagus with the
  aid of peristalsis

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Peristalsis in the gullet
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Learning Outcome 7

• State that different enzymes are responsible for
  the breakdown of carbohydrates, proteins and
  fats.
• Give an example of an amylase, a protease and a
  lipase. State their substrates and products.

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Digestion of Starch

• Take 2ml of 1 starch solution
• Test for starch
• Test for sugars
• Take 2 ml 1 starch solution, add 2ml 2 amylase
  solution
• Leave for 20 minutes
• Test for starch
• Test for sugar

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Action of amylase on starch

• Put two drops of iodine solution into all the
  wells on a white spotting tile
• Add 2ml 1 starch solution and 2ml 2 amylase
  solution to a test tube.
• Every minute, test the contents of the test tube
  for starch.
• Write a conclusion on your results

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Protein Digestion

• Protein digestion occurs in the stomach and small
  intestine.
• Protease enzymes are produced by the gastric pits
  in the stomach lining or by the pancreas.
• In the stomach, hydrochloric acid is also
  produced which provides the optimum pH for
  trypsin to work (as well as killing bacteria in
  food)

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Protein Digestion

• Add 2ml of protein solution to three test tubes.
• Number the test tubes 1, 2 and 3
• Add 1ml HCl
• Add 1ml Water
• Add 1ml HCl
• Do not add the trypsin until last
• Add 0.5 ml water
• Add 0.5 ml trypsin
• Add 0.5ml trypsin

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Protein digestion

• Leave for 10 minutes
• Test each of the test tubes for the presence of
  protein using Biurets reagent.
• Explain your results.

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Fat Digestion

• Milk does not dissolve in water, in the digestive
  system, bile produce by the liver (stored in the
  gall bladder) emulsifies fats to give a larger
  surface area for enzymes to work on.
• You are going to use phenolphthalein to
  investigate the effect of bile on the digestion
  of fat.

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Fat Digestion

• Take 4 test tubes and number them 1, 2, 3 and 4.
• set up the test tubes as shown in the table
  below.

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Fat Digestion

• Add 5 drops of phenolphthalein to each test tube
• Add sodium carbonate to each test tube until the
  solution goes pink.
• Add 0.5ml of lipase to test tubes 1, 2 and 3.
• Add 0.5 ml water to test tubes 4.
• Observe your results. Try to explain what you are
  observing.

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Chemical Digestion

• Enzymes
• Are proteins
• Are produced by cells
• Change chemical substances into new products
• Are specific to one substance
• Work best at their optimum temperature (around
  30 40o)
• Work best at an optimum pH

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Digestive enzymes

• There are different types of digestive enzyme
• Proteases break down proteins into amino acids
• Lipases break down fats into fatty acids and
  glycerol
• Amylase breaks down starch (carbohydrase enzyme)
  into maltose (sugar)
• Maltose is then broken down by maltase to form
  glucose

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Chemical Digestion

• There are also other substances in the digestive
  system which help with the breakdown of food.
• Hydrochloric acid
• Secreted by stomach
• Kills the bacteria in food
• Enzymes in stomach work best at a low pH e.g.
  pepsin

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Chemical Digestion

• Hydrogen carbonate ions
• Secreted by pancreas
• Neutralises acid, enabling enzymes in small
  intestine to work 
• Bile
• Produced by liver, stored in gall bladder,
  secreted into small intestine
• Emulsifies fats (Larger surface area for enzymes
  to work on)

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Learning Outcome 8

• State that only small soluble molecules can pass
  through the wall of the small intestine.
• Explain how the structure of the small intestine
  is related to its function.
• Explain how the structure of a villus, including
  the lacteal and the blood capillaries, are
  related to the absorption and transport of food.
• Describe the role of the large intestine in water
  absorption and elimination.

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Digestion in the small intestine

• 3 important liquids are added to the food
• Pancreatic juice (carbohydrases, proteases and
  lipases)
• Bile (neutralises acid and emulsifies fat)
• Intestinal juice (carbohydrases, proteases and
  lipases)

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What happens next?
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Absorption in the ileum

• The small intestine is well designed for
  absorption, it has
• Thin lining
• A good blood supply
• A very large surface area (about 9m2)

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Absorption in the Villi
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The Model Gut

• A model of absorption

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the model gut
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Making a model gut

• Wash a 12cm length of visking tubing (A) in warm
  water.
• Tie a knot in one end
• Fill the tubing with 10cm3 of starch and glucose
  solution(B).
• Wash the outside of the tubing.
• Put it into a boiling tube containing DI water
  (C) (holding it in place with a rubber band.
• After 20 minutes, test the surrounding water for
  starch and glucose.

C B A
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Comparing the model gut with the villi

• Draw conclusions from the experiment, explaining
  what the results were, and how the model gut
  represents the real situation
• E.g. what does the water represent, what does the
  Visking tubing represent, etc.

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Large intestine and the elimination of waste.

• A watery mix of enzymes and undigested food
  (mainly fibre) moves into the colon.
• Water is absorbed back into the blood stream.
• Faeces are compacted in the rectum and egested
  through the anus.

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The end
What do they think they are looking at?
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Learning Outcome 9

• To revise the learning outcomes taught in this
  sub topic.

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What happens to the food we eat?
Ingestion Digestion Absorption Egestion
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The gut as a production line