2 Enzymes and the Digestive System

2.1 ENZYMES AND DIGESTION

DIGESTION- It is the mechanism and chemical breakdown of food into the molecules small enough for the body to absorb.

Major parts of the digestive system

The Oesophagus

• Carries food from the mouth to the stomach
• Therefore it's adapted for transport rather than for digestion or absorption
• Made up of a thick muscular wall

The Stomach

• muscular sac
• inner layer produces enzymes
• role = store and digest foods (especially proteins)
• has glands - produce enzymes which digest protein
• other glands in stomach wall produce mucus
• mucus prevents stomach being digested by it's own enzymes

The Small Intestine

• long muscular tube
• food is further digested by enzymes
• enzymes - produced in walls and by glands that pour their secretions into it
• inner walls folded into villi - gives large surface area
• millions of tiny projections called microvilli, on the epithelial cells of each villus - increases surface area
• this adapts the small intestine for its purpose - absorbing products of digestion into the bloodstream
• larger surface area=increased rate of absorption

The Large Intestine

• absorbs water
• most of the water thats reabsorbed comes from the secretions of the many digestive glands
• therefore the food within the large intestine becomes drier and thicker - forms faeces

The Rectum

• final section of the intestines
• faeces are periodically stored here
• before being removed via the anus - during egestionThe Salivary Glands
• situated near the mouth
• pass their secretions via a duct into the mouth
• secretions contain amylase - breaks down starch into maltose

The Pancreas

• large gland
• situated below the stomach
• produces and secretes pancreatic juice
• this contains protease, lipase and amylase

Physical Breakdown

Food is broken down into smaller pieces using structures such as the teeth which provides a larger surface area. It is then churned by the muscles in the stomach wall and this also physically breaks it up.

Chemical digestion

This process breaks down insoluble molecules into smaller soluble ones and is carried out by enzymes in the process called HYDROLYSIS. There are 3 types of digestive enzymes called CARBOHYDRASES, LIPASES and PROTEASES. 

2.2 CARBOHYDRATES - MONOSACCHARIDES

• Carbon atoms very readily form bonds with other carbon atoms which allows a sequence of carbon atoms to be built up. One feature of carbon that allows life on earth is it forms bonds readily with other carbons creating a “backbone” for living things to be built.

Many organic molecules are made up of long chains of individual molecules. Each individual molecule is called a monomer, these longer chains of repeating units are called polymers.

• Carbohydrates monomer is a sugar or a saccharide.
• A single monomer is called a monosaccharide.
• A pair of monosaccharides is called a disaccharide.
• Monosaccharides in large numbers are polysaccharides.
• Monosaccharides are sweet tasting and soluble. (CH2O)n

Testing for Reducing Sugars

Reducing sugars include glucose, fructose, lactose and maltose.

Sucrose is not a reducing sugar.

Benedict's Test 

•  Benedict's reagent is added to the solution and then heated.
• …