Chapter 3: Organisation and the Digestive System

Question 1

Tissues and Organs

Answer 1

• A tissue is a group of cells with a similar structure and function
• Organs are a collection of tissues
• Organs are organised into organ systems, which work together to form organisms

Question 2

The human digestive system

Answer 2

• Organ systems are groups of organs that perform specific functions in the body
• The digestive system in a mammal is an organ system where several organs work together to digest and absorb food

Question 3

The chemistry of food

Answer 3

• Carbohydrates are made up of tiny units of sugar
• Simple sugars are carbohydrates that contain only one or two sugar units – they turn blue benedict’s solution brick red on heating
• Complex carbohydrates contain long chains of simple sugar units bonded together, starch turns yellow-red iodine solution blue-black
• Lipids consist of three molecules of fatty acids bonded to a molecule of glycerol. The ethanol test indicates the presence of lipids in a solution
• Protein molecules are made up of long chains of amino acids, Biuret reagent turns from blue to purple in the presence of proteins

Question 4

Catalysts and enzymes

Answer 4

• Catalysts increase the rate of reaction without changing chemically themselves
• Enzymes are biological catalysts and catalyse specific reactions in living organisms due to the shape of their active site. This lock and key theory of enzyme chain
• Enzymes are proteins. The amino acid chains are folded to form the active site, which matches the shape of a specific substrate molecule
• The substrate binds to the active site and the reaction is catalysed by the enzyme
• Metabolism is the sum of all reactions in the body

Question 5

Factors affecting enzyme action

Answer 5

• Enzyme activity is affected by temperature and pH
• High temperatures denature enzymes, changing the shape of the active site
• pH can affect the shape of the active site of an enzyme and make it work very efficiently or stop it working

Question 6

How the digestive system works

Answer 6

• digestion involves the breakdown of large insoluble molecules into soluble substances that can be absorbed into the blood across the wall of the small intestine
• digestive enzymes are produced by specialised cells in glands and in the lining of the digestive system
• carbohydrases such as amylase catalyses the breakdown of carbohydrates into simple sugars
• protease catalyses the breakdown of protein into amino acids
• lipase catalyses the breakdown of lipids to fatty acids and glycerol

Question 7

Making digestion efficient

Answer 7

• the protease enzyme of the stomach works best in acid conditions. The stomach produces hydrochloric acid, which maintains a low pH
• the enzymes made in the pancreas and the small intestine work best in alkaline conditions
• bile produced by the liver, stored in the gall bladder, and released through the bile duct neutralises acid and emulsifies fats