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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 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 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- 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
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
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.