Digestion

Learning Objectives

At the end of this lesson, you should be able to: Enzymes • Explain enzyme action in terms of the “lock and key” hypothesis • Explain the effects of temperature and pH on the rate of enzyme

catalyzed reactions Digestive Process • Explain the importance of the digestive system • Identify the main parts of a digestive system and how they work

together to perform a function • Describe how a digestive system helps in digestion of food and the

part played by enzymes in digestion (Only classes of enzymes such as amylase, protease and lipase are needed. Specific names of enzymes not required.)

Why EAT?

We need to eat because…

Our body needs NUTRIENTS

CARBOHYDRATES PROTEINS FATS

Types of Nutrients the Body Needs

Why EAT?

CARBOHYDRATES PROTEINS FATS

Types of Nutrients the Body Needs

Why EAT?

CARBOHYDRATES PROTEINS FATS

Types of Nutrients the Body Needs

Why DIGESTION?

Why DIGESTION?

Digestion is necessary - to break down large insoluble molecules into smaller molecules - so that the body can absorb the nutrients required for its functioning

DIGESTION is the process whereby large, insoluble food molecules are broken down

into smaller, soluble food molecules

DIGESTION

Proteins Amino Acids

Starch Glucose

Glycerol Fatty Acids

Fats

Larg

e C

om

ple

x In

solu

ble

Mo

lecu

les

Smal

l Sim

ple

So

lub

le M

ole

cule

s

carbohydrase

protease

lipase

Amino Acids

Glucose

Glycerol Fatty Acids

Small simple soluble molecules are used for the following purposes: • Growth of new cells and tissues • Provide energy for growth, movement and for keeping warm • Repair damaged tissues • Keep us healthy

DIGESTION

FOOD TESTS

• STARCH test • Add about 5 drops of iodine solution to the sample to be tested. • If starch is present, the iodine will turn dark blue • If starch is absent, the iodine will remain brown

Enzymes are biological catalysts.

ENZYMES

A A

A A

A A

enzyme

enzyme enzyme

Catalysts are substances that speed up the rate of reactions, but themselves remain chemically unchanged at the end of the reaction.

Lock & Key Hypothesis

Enzyme

Enzyme

Enzyme

Enzyme

Substrate A

Substrate B

LOCK and KEY hypothesis • Specificity: One enzyme binds to only one substrate • Reusable: They are chemically unchanged at the end of the reaction • Required in minute amounts • Sensitive to temperature and pH

ENZYMES- Mechanism

Enzyme

Enzyme

substrate

products

ENZYMES- Mechanism

Enzyme

Enzyme

substrate

products

Enzyme-substrate complex

Lock & Key Hypothesis

ENZYMES- Factors R

ate

of

Enzy

me

Act

ivit

y

Temperature/ °C

At high temperatures, enzymes are denatured.

At low temperatures, enzymes are inactivated.

Enzymes work best at their optimum temperature.

ENZYMES- Factors R

ate

of

Enzy

me

Act

ivit

y

pH

At extreme pH, enzymes are denatured.

Enzymes work best at their optimum pH.

LEARNING OBJECTIVES

You should now know how to: - identify the main organs in the human digestive system - describe the process of digestion within the human body in detail

DIGESTIVE SYSTEM

Associated (accessory)

organs

The PROCESS

Mechanical Digestion Biting Tearing Slicing Chewing (Masticating)

Chemical Digestion Acid Enzymes

Mouth

1. Mechanical Digestion Food is broken down into

smaller pieces by the chewing, tearing, slicing and biting action of the teeth

2. Enzymatic Digestion Starch is broken down into

maltose by amylase in saliva

No digestion of proteins and fats in the mouth

Starch Maltose

Oesophagus

Partially digested food is pushed down from the mouth into the stomach by muscles in the oesophagus that alternately contract and relax. (peristalsis)

NO enzymes are present in

the oesophagus.

Stomach

Complex Proteins Simpler Proteins

Complex proteins are broken

down into simpler proteins by proteases (pepsin)

found in gastric juices secreted by the stomach.

No digestion of

carbohydrates or fats occur in the stomach.

Small Intestines

Simpler Proteins Amino Acids Maltose Glucose

Fats Glycerol + Fatty Acids

Three digestive juices are secreted into the small intestines to complete

digestion: 1. Bile from the Liver

This breaks fats into small droplets for easier digestion

2. Pancreatic Juice from the Pancreas 3. Intestinal Juice from the Small

Intestines Both juices contain carbohydrase,

protease and lipase.

Large Intestines

Undigested food that reaches the large intestines will be passed

to the rectum and anus for removal by the body as faeces.

As it passes through, a lot of water is absorbed by the large intestines and taken back into

the body.

INQUIRY time!

Some obese people have had part of their small intestines removed. Suggest with reasons the effects of such a surgery?

Proteins are digested in the stomach. The stomach wall consists of cells which are made of protein. So why does the stomach wall not get digested?

ABSORPTION

Small Intestine

Blood Capillary

Villi cells

ABSORPTION

Absorption is the movement of digested food molecules through the walls of the small intestine into the blood stream.

Small Intestine

Blood Capillary

By what process do the food molecules move through the intestinal walls?

Why does food molecules move into the blood stream but

not move out?

ABSORPTION

Small Intestine

Blood Capillary

Digested food molecules move through the walls of the small intestine via diffusion.

Undigested food molecules are too large to move through the walls of the small intestine.

ABSORPTION

Small Intestine

Blood Capillary

1. Finger-like projections (called villi) in the wall of the small intestine provide a large surface-area for absorption of digested food molecules.

How is the rate of absorption made faster in

the small intestine?

2. The small intestine is long and convoluted, thus increasing the surface area for quicker absorption.

ABSORPTION

Small Intestine

Blood Capillary

How is the rate of absorption made faster in

the small intestine?

3. The wall of the small intestine is only one-cell thick, shortening the distance between the wall and blood vessels so absorption can be faster.

4. A constant flow of blood ensures a low concentration of food molecules in the capillary, so rate of diffusion of digested food molecules into the blood is increased.

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