IB5.10.1 Objectives

© Oxford University Press 2011

B5 Lesson 10 Digestion

After studying this topic, you should be able to:

explain why food has to be digested

explain the role of enzymes in chemical digestion

describe the functions of the parts of the human digestive system

explain how digested food molecules are absorbed into the blood

Starter

Name and describe the function of each part of the human digestive system.

mouth – food is chewed heresalivary glands – releases enzymes into the mouthoesophagus – a.k.a. gullet stomach – releases enzymes; churns foodpancreas – releases enzymes into small intestineliver – makes bilegall bladder – stores bile and releases it into small intestinesmall intestine – food is digested and absorbed herelarge intestine – water and minerals are absorbed into the blood, leaving faeces which pass out of the anus (egestion)

The human digestive system

What is the difference between physical digestion and chemical digestion.?

Definition – Physical digestion.

• is the breaking of food into smaller pieces by:– chewing in the mouth by teeth– squeezing in the stomach

How does this help chemical digestion?

Definition – Chemical digestion

Carbohydrates, fats, and proteins are digested by

enzymes. This is known as chemical digestion.

•Can you name the enzyme responsible for digesting each type of food?

Food

carbohydrates

fats (lipids)

proteins

•These are the enzymes.•Where do they work?

Food Type of enzyme

carbohydrates carbohydrases

fats (lipids) lipases

proteins proteases

Food Type of enzyme Part of gut where enzyme works

carbohydrates carbohydrases mouth and small intestine

fats (lipids) lipases small intestine

proteins proteases stomach and small intestine

•This is where they work. •What do they break food down into?

•These are the products of digestion.•Enzymes work well at specific pH values. Look at the table.

Food Type of enzyme Part of gut where enzyme works

Products of digestion

carbohydrates carbohydrases mouth and small intestine

Starch, converted to maltose and then to glucose, a simple sugar

fats (lipids) lipases small intestine fatty acids and glycerol

proteins proteases stomach and small intestine

amino acids

•What pH values do you think these enzymes work best at and why? carbohydrases lipases proteases

Bile

• Liver makes it

• Gall bladder stores it

• Released into small intestine.

Emulsification

Small intestine

• Small digested food molecules are absorbed into the blood plasma or lymph in the small intestine by diffusion

Adaptations of the small intestine

• While watching the animation write down a list of adaptation the small intestine has for the efficient adsorption of digested food.

Large Intestine

• Adsorbs water and some minerals into blood.

• semi-solid waste that is left passes out of the anus – egestion.