Digestion in the Mouth



Breaking Down Food

Purpose

We previously learned about cells, the circulatory system, and the major organs used in digestion. As we enter further into our unit on Digestion we will look at how the body breaks down the food, in particular, chemical and mechanical breakdown. They will also learn about enzymes in particular the enzyme “diastase.” These concepts are important for students to learn because students should be aware of their own bodies functions in order to make healthy decisions and live healthy lifestyles.

Length of Lesson

50 minutes

Grade Level

6th Grade

Materials Needed

Science Notebook

Handout sheets A

For each group:

1 soda cracker per person

4 small clear plastic cups (5 to 7 oz)

¼ cup of starch solution (made from cornstarch and hot water)

Starch test iodine-iodide solution

1 medicine cup of diastase (from soaked barley)

Water

Eyedropper

Student Info Sheet on Digestive System

Materials Management Notes

Make sure there are enough soda crackers so that each student can chew on one.

Make sure there are no allergies to soda crackers or starch in the class.

Prepare the starch solution before class. Use two cups of hot water and 2 tsp. of cornstarch. If the cornstarch settles out of the solution after cooling too much was added.

Copies of Handout sheet A and the Student Info Sheet on the Digestive System should be made before class so that each student has his/her own copy.

Make sure enough diastase is available.

Student Misconceptions

Students may think that there is no chemical breakdown in the mouth. That the mouth is simply used to chew and the chemical breakdown happens in the stomach.

Students may think saliva is just to keep your mouth cool.

Students may think that the teeth do all the work in the mouth.

Standards Addressed

Life Science (Biology) Grades 6 - 8 Massachusetts State Frameworks

(6) Identify the general functions of the major systems of the human body (digestion, respiration, reproduction, circulation, excretion, protection from disease, and movement, control, and coordination) and describe ways that these systems interact with each other.

Learning Objectives

Students will discuss the breaking down of foods in the mouth and stomach.

Students will explain the processes of mechanical and chemical breakdown.

Students will observe how an enzyme works to break down a starch.

References

Education Development Center, Inc. (2003) Insights: An Elementary Hands-On Inquiry Science Curriculum: Human Body Systems: Second Edition. Kendall/Hunt Publishing Company.

*This lesson is an adaptation of a lesson from the curriculum listed above.

The National Academy of Sciences (2006) Human Body Systems. Carolina Biological Supply Company.

*This lesson is an adaptation of a lesson from the curriculum listed above.

Elicit and Engage

We will start the lesson by eating crackers and discussing what is going on in our mouths while we chew. Students will observe everything that is happening in their mouths and they will feel, with their thumb and finger, their throats as they swallow. They will discuss as a class:

-What is happening in your mouths?

-What did you feel when you swallowed?

-Where did your food go after you swallowed?

-What is mechanical breakdown?

-What is chemical breakdown?

-Why do we need to breakdown our food?

-Where does mechanical and chemical breakdown of food occur?

*Mechanical breakdown in mouth with teeth and tongue. Mechanical breakdown in stomach with 3 layers of stomach muscles that churn the food.

*Chemical breakdown in saliva which contains an enzyme that chemically causes food to break apart. Chemical breakdown in stomach using enzymes and a substance called hydrochloric acid which is very strong and would even digest the stomach’s own lining if there wasn’t a layer of mucus that protects it.

-What is one of the main components of a soda cracker?

Explore

After students answer the last question, starch, we will look at the starch solution. I will explain that it is made of hot water and corn starch. Next, we will explore the iodine-iodide solution, which is an indicator that turns black if something has starch in it.

I will demonstrate the change in color when the iodine-iodide solution is added to the starch solution.

This example will be available for students to compare theirs to.

I will explain that even one molecule of starch is too big for cells to use so the body produces enzymes which cause starch to break into even smaller pieces. In this investigation we are going to observe the effects of the enzyme diastase (which was produced by a barley and water mixture).

Now we will start the investigation using Handout sheet A.

Explain

Once all of the students are finished with their investigation we will discuss their results.

What happened when you added the enzyme to the cup?

Why isn’t the color black anymore?

How do your cups compare to the cup of the starch solution with no enzyme?

How might we make the color black again?

The enzyme made the starch break into a new substance. This is called a chemical breakdown.

Extend / Elaborate

Where does chemical breakdown occur in your body?

Does chemical breakdown take place in your mouth? How?

-There is an enzyme in saliva called amalyse, which creates a chemical breakdown

Does mechanical breakdown also take place in your mouth? How?

-Teeth and tongue

Does chemical breakdown take place in you stomach? Does mechanical breakdown take place in your stomach?

Evaluate

Now that we understand how mechanical and chemical digestion takes place in both the mouth and the stomach next class we will visit the organ our food visits after the stomach. Can anyone remind me of what organ that is? Yes the small intestine. Can anyone guess what might happen in the small intestine? That is what we will be discovering next class.

Student Info Sheet on Digestive System

Mouth

The mouth is the place where both mechanical digestion and chemical digestion begin. Your teeth and tongue work together to chop, grind, and mash the food into small pieces. At the same time, the saliva in your mouth begins the chemical digestion. Saliva contains a special substance called an enzyme that works chemically to cause particles of food to break apart into even smaller components. Good remains in the mouth for about two minutes.

Esophagus

The food travels down the esophagus, pushed by muscles in the process of peristalsis. Peristalsis is responsible for the rumbling sounds the digestive tract produces. Food stays in the esophagus anywhere from four to eight seconds (one to two seconds for very soft foods or liquids).

Stomach

The stomach is like a food processor; here food is broken down by a variety of substances. The processes that take place here are mainly part of chemical breakdown using both enzymes and a substance called hydrochloric acid. This latter substance is very strong and would even digest the stomach’s own lining were it not for a layer of mucus that protects it. The food remains in the stomach for about four hours, taking the form of a thick liquid.

Small Intestine

The digestive process of breaking down food is finished in the small intestine. In the first part of the small intestine, the thick liquid from the stomach is mixed with a liquid called bile from the gall bladder and with other enzymes from the pancreas. Then, as it passes through the remaining twenty feet, it is digested enough so that it passes through the walls of the intestine into the blood. It takes about twelve hours for food to pass through the small intestine.

Large Intestine

Water and parts of the food that cannot be digested are passed on into the large intestine. Her most of the water is absorbed into the blood through the intestine walls. The remaining wastes are then excreted as urine and feces.

Name: ___________________________________ Date:_________________________

Sheet A: What Happens in the Digestive System? Breaking Down the Food

Your group will have one small clear cup of starch solution, one small cup of the enzyme diastase, and some starch test iodine-iodide solution. First add the starch test iodine-iodide solution to the starch solution and describe what happens below.

Now add the enzyme and describe the solution in the cup.

Your group should observe the solution in the cup every five minutes. Record your observations below.

|TIME |OBSERVATIONS |

|5 | |

| | |

| | |

|10 | |

| | |

| | |

|15 | |

Based on your observations, what are your conclusions about what happened to the starch?

While the members of your group wait between observations, try another investigation. Eat a soda cracker. Try to chew and keep it in your mouth for as long as you possibly can. When doing this, many people begin to taste a little sweetnes in their mouths. Work with your group to explain why you think that might happen. Remember, there are enzymes in your saliva. Write your group’s ideas on the back of this sheet.

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