biology - human nutrition (digestion)

Describe physical digestion

• the breakdown of food into smaller pieces without chemical change to the food molecules

• it increases the surface area of food for the action of enzymes in chemical digestion

Describe chemical digestion

• the breakdown of large insoluble molecules into small soluble molecules

• is required because large insoluble molecules are unable to be absorbed through the wall of the small intestines

Describe the functions of enzymes (amylase, protease, and lipase)

1. amylase - breaks down starch to simple reducing sugars

2. proteases - break down protein to amino acids

3. lipase - breaks down fats and oils to fatty acids and glycerol

State where in the digestive system amylase is secreted and where it acts

secreted in:

• Salivary glands – produce salivary amylase

• Pancreas – produces pancreatic amylase

where it acts:

• Mouth – salivary amylase begins starch digestion

• Small intestine (duodenum) – pancreatic amylase continues digestion

• (digests starch to maltose)

State where in the digestive system protease is secreted and where it acts

Where It Is Secreted:

• Stomach – produces pepsin

• Pancreas – produces trypsin and other proteases

Where It Acts:

• Stomach – pepsin breaks down protein in acidic conditions

• Small intestine – trypsin breaks down protein in alkaline conditions

State where in the digestive system lipase is secreted and where it acts

Where It Is Secreted:

• Into the duodenum

Where It Acts:

• Small intestine – aided by bile from liver (which emulsifies fats). They digest lipids into fatty acids and glycerol

Describe the functions of hydrochloric acid in gastric juice

• killing harmful microorganisms in food

• providing an acidic pH for optimum enzyme activity of proteases in the stomach

Explain what bile is

• is an alkaline mixture that neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach

• to provide a suitable pH for enzyme action in the small intestine

Outline the role of bile in emulsifying fats and oils

to increase the surface area for chemical digestion