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Food and Digestion
After studying this topic you should be able to:
• Explain what is meant by a balanced diet
• Describe chemical tests to identify proteins, carbohydrates, and fats
• Describe what happens in the digestive system
A Balanced Diet
• A balanced diet provides:
– everything required for growth of the body
– everything required for repair of the body
– enough energy for the body’s activities
• The human diet must contain food from the following groups:• Proteins
• Carbohydrates
• Fats
• Vitamins & Minerals
• Water
• Fibre
What is a Balanced Diet?
Food Chemical Benefit to the Body Source
Proteins Growth and repair to the body
Meat, fish, nuts, cheese
Carbohydrates Provide energy Bread, pasta, potatoes
Fats Store energy; provide insulation
Butter, oil, margarine
Vitamins Required in small amounts (more later)
Fruit and vegetables
Minerals Required in small amounts (more later)
Primarily green
vegetables
What about Water and Fibre?
Water• Acts as a solvent• Transports substances• Where reactions take
place
Fibre• Is NOT digested• Helps in production of
faeces and prevents constipation
• Reduces the risk of bowel cancer
Food Labels Practical
Canteen Menu
• Design a menu for the canteen
• Your menu should aim to include foods from each of the food groups
• You should include starters, mains, and desserts
Laptop Assignment
Vitamin Good Source
Use
A
B complex
C
D
Mineral Good Source
Use
Calcium
Fluorine
Iron
Iodine
Potassium
Sodium
Also, research scurvy
• what causes it?
• what are the symptoms?
• how can it be prevented?
• if possible, look up about the research of Dr. James Lind in 1747
Progress Check
1. What are the 7 types of food chemical needed for a healthy diet?
2. A man is advised by his doctor to reduce the fat and to increase the fibre in his diet. Which form of potatoes in the list would be most suitable for him? Explain
Chipped potato, potato crisps, jacket potatoes, mashed potatoes, boiled potatoes
3. Which foods are good sources of calcium?
Testing for Proteins, Carbohydrates, and Starch
Testing for Proteins• The Biuret test• Turns mauve Testing for Carbohydrates• Benedict’s Solution• Turns yellow or red-brown colourTesting for Starch• Iodine• Turns dark blue-black
Food Test for Carbohydrate
Test for Protein
Test for Starch
Soya
Biscuit
Flour
Bread
Dry Fruit
Egg White
1. Which foods contained carbohydrates?
2. Which foods contained protein?
3. Which foods contained fat?
4. Which foods would you recommend someone who requires a lot of energy to eat?
5. Which foods help people grow and repair?
Progress Check
• The table gives the results of food tests on three foods, A, B, and C
• What do these tests tell you about A, B, and C?
Test A B C
Protein Test blue mauve blue
Sugar Test blue blue red-brown
Fat Test milky clear clear
What happens to food in the digestive system?
Match up the key words to their meanings…let’s see what you
know already!
Digestion and the Digestive System
• Digestion is the breaking down of large insoluble food molecules into small soluble molecules that the body can absorb easily and use
• The digestive process involves:– a mechanical breakdown (chewing)– a chemical breakdown (enzymes)– absorption of small molecules
Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules.
Let’s take a close look at how this happens…
Open wide!
The Digestive System
• You have been provided with a handout of the digestive system with labels of all major body parts involved
• You need to know how to label this diagram and how each organ is involved in digestion
• We will refer to this throughout the rest of the lesson
• Food chewed into small pieces for swallowing
• Mixed with saliva (contains amylase – breaks down starch)
• Connects the mouth with the stomach
Mouth and Salivary Glands
Oesophagus or Gullet
• Food is stored for a few hours
• Food is mixed with gastric juices (contains enzymes)
• Hydrochloric acid kills bacteria
• Site of absorption of food chemicals (other than fibre and water)
Stomach
Small Intestine
• Water is removed and absorbed into the blood
• Faeces stored in the rectum before being passed through the anus
Rectum and Anus
Large Intestine
In Summary…
Rectum and Anus Large Intestine
Small Intestine
Stomach
Oesophagus or Gullet
Mouth and Salivary Glands
My
Older
Sister
Still
Looks
Really
Awful
Enzymes
Enzymes are chemicals which break the larger molecules down into smaller molecules.
• Carbohydrase chops carbohydrates into smaller sugar molecules.
The three types of enzymes are:
• Protease cuts proteins into the soluble amino acids.
• Lipase breaks fats down into the smaller fatty acids and glycerol.
Multiple Choice Revision
Questions
Which of the following are examples of carbohydrates?
A amino acids, glycerol
B starch, fatty acids
C sugar, amino acids
D starch, sugar
What is/are the breakdown product/s of starch?
A fatty acids
B amino acids
C glycerol
D sugars
What is/are the breakdown product/s of proteins?
A fatty acids
B amino acids
C glycerol
D sugars
What is/are the breakdown product/s of fat?
A fatty acids and glycerol
B amino acids
C glycerol
D sugars
Which of the following are examples of large, insoluble molecules?
A protein, amino acids, starch, glycerol
B starch, fats, proteins
C fatty acids, glycerol, glucose, amino acids
D fats, amino acids, starch, glycerol
Which of the following are examples of small soluble molecules?
A protein, amino acids, starch, glycerol
B starch, fats, proteins
C fatty acids, glycerol, glucose, amino acids
D fats, amino acids, starch, glycerol
Which of the following are examples of molecules that can be absorbed across the lining of the small intestine and into the blood?
A fatty acids, glycerol, glucose, amino acids
B starch, fats, carbohydrates, proteins
C protein, amino acids, starch, glycerol
D fats, amino acids, starch, glycerol
Water is absorbed across the wall of this structure.
A liver
B large intestine
C oesophagus
D pancreas
What is digestion?
A The breakdown of large molecules into small molecules.
B The building up of large molecules from small molecules.
C The absorption of large molecules across the lining of the small intestine.
D The removal of waste products from food.