Download Digestion Breakdown Activity #14

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ACTIVITY OVERVIEW
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Breakdown
BO RA
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SUMMARY
Students use antacid tablets and vinegar to model the processes of chemical and mechanical breakdown of food. After a preliminary investigation of the interaction between an
antacid tablet and vinegar, students design and perform an investigation to determine
the effect of mechanical breakdown on the speed of chemical breakdown.
KEY CONCEPTS AND PROCESS SKILLS
1.
Graphing data can reveal patterns that are not apparent from data tables.
2.
Elements of good experimental design include a completely described
procedure, variables (except for the one being tested) kept constant, the use of
a control, appropriate use of quantitative and qualitative data, and a large
sample size. These elements result in reproducible investigations.
3.
Each system within the human body is defined by the functions that it
performs. For example, the digestive system is a group of organs, each of
which contributes to the process of breaking down food into smaller particles.
4.
Creating models is one way to understand and communicate scientific
information.
5.
Both mechanical and chemical processes contribute to the breakdown of food.
6.
Chemical reactions occur at surfaces. The greater the surface area available for
contact, the faster the reaction. This is why mechanical breakdown facilitates
chemical breakdown.
Teacher’s Guide
B-37
Activity 14 • Breakdown
KEY VOCABULARY
chemical breakdown
model
control
organ
digestive system
qualitative/ quantitative data
function
surface area (optional)
hypothesis
variable
mechanical breakdown
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
Transparency 7.1, “Elements of Good Experimental Design”
1
Transparency 14.1, “Human Digestive System”
1
non-effervescent antacid tablet containing calcium carbonate
(optional)
*
1
overhead projector
For the class
*
access to watch or wall clock with a second hand
*
balances (optional)
For each group of four students
4
effervescent antacid tablets containing sodium bicarbonate
1
120-mL bottle of vinegar
2
SEPUP trays
2
30-mL graduated cups
For each student
*
1–2 hard candies (optional)
*Not supplied in kit
If you plan to allow all of your classes to complete Step 11 of the Procedure,
you may need to purchase additional effervescent antacid tablets containing
sodium bicarbonate.
n Teacher’s Note: You may want to provide plastic knives to cut the tablets.
Making the pieces the same size is difficult when the tablets are broken by
hand. You may also want to have extra tablets on hand for students who end
up with quarter tablets of very inconsistent sizes.
B-38
Science and Life Issues
Breakdown • Activity 14
TEACHING SUMMARY
Getting Started
1.
Briefly discuss elements of the digestive process.
Doing the Activity
2.
Introduce the model and have students explore its use to investigate
breakdown (Part One).
3.
Students design and perform their investigations (Part Two).
Follow-Up
4.
Discuss conclusions and the relevance of the investigation.
5.
Introduce the importance of surface area in chemical and other interactions.
Teacher’s Guide
B-39
Breakdown • Activity 14
TEACHING SUGGESTIONS
n
1.
GETTING STARTED
Briefly discuss elements of the digestive
process.
Project Transparency 14.1, “Human Digestive System.” Use the transparency to identify some of the
major organs/structures of the digestive system
(mouth, stomach, small intestine, large intestine).
You do not need to stress the other digestive organs,
since they are presented in depth in the next activity. You may, however, want to point out the location of the liver.
gent smells. Decide in advance how you will address
any complaints or problems that may arise.
n
2.
DOING THE ACTIVIT Y
Introduce the model and have students
explore its use to investigate breakdown
(Part One).
Students may be unfamiliar with the idea of a chemical reaction. You can demonstrate the greater reactivity of vinegar compared to water and reinforce
the concept of chemical breakdown by placing an
antacid tablet containing calcium carbonate in
Ask students, What are the major functions of the
both liquids. (Calcium carbonate tablets do not dis-
digestive system? Students may recall from Activity
solve quickly in water. The student activity uses
12, “What’s Happening Inside?” that the stomach
effervescent antacid tablets, which quickly dissolve
stores and breaks down food. They may mention the
in both water and vinegar.) In water, nothing will
role of the digestive system in food breakdown and
happen immediately to the non-effervescent tablet.
absorption. Ask, Where does this breakdown happen?
In vinegar, small bubbles will begin to form around
Some students may suggest that it happens in the
the tablet. Note, however, that these are not speedy
stomach, small intestine, and large intestine.
reactions. As minutes pass by, tablets in both liquids
Inform the class that there are two types of breakdown: mechanical breakdown, in which food is
physically broken into smaller pieces, and chemical
breakdown, in which particles of food are broken
down by chemicals. Use Transparency 14.1 to indicate the major locations of mechanical breakdown
will appear to break down; however, the tablet in
the vinegar breaks down more quickly. The vinegar
causes a chemical reaction, while the water merely
dissolves the tablet (a physical change). Point out
that vinegar, like chemicals in the stomach that
contribute to chemical breakdown, is an acid.
(mouth, stomach) and chemical breakdown (mouth,
Steps 1–4 of the Student Procedure allow students to
stomach, small intestine). Ask, Why is breakdown
explore the breakdown model before they design
important? Establish the idea that food must be bro-
their experiments. The table on the next page shows
ken down in order to be absorbed by the body.
the essential parts of the model.
n Teacher’s Note: As mentioned in the Safety Note
Pause briefly after students complete Step 4 to dis-
in the Student Book, vinegar has a strong odor. Cer-
cuss the model before continuing. Ask, How did you
tain students may be extremely sensitive to pun-
decide when the chemical breakdown was over? Did
Teacher’s Guide
B-41
Activity 14 • Breakdown
You may need to discuss ways in which they can
The Model
Material/Process
Represents
antacid tablet
food
breaking or
crushing tablet
mechancial breakdown
(chewing)
adding vinegar
chemical breakdown
answer their experimental question. For example,
students could use an intact quarter tablet to represent food that had not been chewed, quarter tablets
broken into smaller pieces to represent partially
chewed food, and completely crushed tablets to represent completely chewed food. They could then add
identical amounts of vinegar and time the reactions.
you observe or record how long it took before the
tablet piece completely dissolved? Use these ques-
Some students may focus on varying the amount of
tions to help students design their experiments.
vinegar, but this does not address the experimental
question. Guide students by asking, Can you change
3.
Students design and perform their investi-
the amount of acid in your stomach? What do you
gations (Part Two).
control directly in the digestion process? Help stu-
This activity provides an opportunity to assess stu-
dents think about mechanical breakdown as the
dents on the “Recording Design or Procedure” ele-
process directly under conscious control.
ment of the DESIGNING
DCI
TIONS
AND
CONDUCTING INVESTIGA-
(DCI) variable. If you are planning on
using this assessment with your students,
inform them in advance and provide them with
enough time to develop and conduct complete
experiments (as described in Steps 5–7 of the Student Procedure). You can use Transparency 7.1,
“Elements of Good Experimental Design,” to review
Step 10 of the Student Procedure instructs students
to construct a bar graph of their data. Students may
need assistance in creating a graph. You may want
to refer to bar graphs already produced in this
course: students completed bar graphs in Activities
3 and 7, and also had the opportunity to construct
a bar graph in Activity 9. A bar graph of sample student data is shown below.
important ideas. You can also encourage on-task
behavior by assessing students with the “Task ManGI
Graph 1: Sample Student Data
agement” and/or “Shared Opportunity” ele-
100
90
ment(s) of the GROUP INTERACTION variable.
encourage students to perform Part Two of the Student Procedure as independently as possible.
Remind them to focus on the experimental question, How does the size of your food affect the speed
Time (in seconds)
80
Students may need help getting started. However,
70
60
50
40
30
at which chemical breakdown occurs? If necessary,
20
rephrase the question as, Does the amount you chew
10
your food affect your ability to digest it chemically?
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Science and Life Issues
0
Whole
Pieces
1/4 Tablet Piece
Powder
Breakdown • Activity 14
Note that Step 11 gives students a chance to revise
You may wish to give each student a piece of hard
their design and possibly repeat the experiment. After
candy to eat to explore the importance of surface
they have fully completed their experiment and
area. Instruct half of the students to chew their
recorded their results, have them continue to work
candy and the other half to not chew. Measure the
together in their groups to discuss Questions 1 and 2.
amount of time it takes for the candies to com-
They can then write their conclusions using Analysis
pletely dissolve. (Tell students not to swallow any
Question 3 as a guide. This activity can also be used to
undissolved pieces.) Some students may notice the
teach elements of a complete lab report (see Teacher’s
role of the tongue in mechanical breakdown, since
Guide to Activity 1, “Solving Problems: Save Fred!”).
the friction of the tongue against the candy can
n
4.
greatly speed its dissolving.
FOLLOW–UP
Have students think about why the candy that was
Discuss conclusions and the relevance of
chewed dissolved more quickly. Use their respons-
the investigation.
es to build the idea that the surfaces of the candy
Have students share their results with the class. You
are the key to this process. For the candy to dis-
may want to review the use of concepts such as vari-
solve, its surface has to be in contact with the sali-
ables, quantitative and qualitative data, multiple tri-
va. Ask, How does chewing affect how much candy
als, and reproducibility in the design of their exper-
surface there is? Chewing creates new surfaces for
iments. Explain that chemical experiments like the
interaction between the candy and the saliva.
one they have done are conducted to gain a better
Chemical interactions occur at the surfaces, so the
understanding of biochemical processes in the body.
more surface available, the faster the interactions
can occur. The dissolving antacid and the dissolv-
Emphasize the main concepts of the activity: Food
must be broken down in order to be absorbed by
the body. Both mechanical and chemical processes
contribute to the breakdown of food. Food breaks
down faster if both chemical and mechanical
breakdown occur.
5.
Introduce the importance of surface area in
chemical and other interactions.
ing candy both illustrate this important chemical
and biological concept. Similarly, the smaller the
pieces of swallowed food, the faster they can interact with stomach acid and other substances and
be digested. The concept of surface area will be further explored in Unit C, “Micro-Life” of Science and
Life Issues, when students investigate why cells are
so small.
Safety Note: If you use candy that contains
sugar for the following part of the activity,
it should not be eaten by any students who must
restrict sugar intake.
Teacher’s Guide
B-43
Breakdown • Activity 14
SUGGESTED ANSWERS
TO ANALYSIS QUESTIONS
1.
a.
In your experiment, what variables
3.
How does the size of your food affect the
did you keep the same?
speed at which chemical breakdown occurs?
The amount of tablet and the amount of vine-
Explain how your conclusions are based on the data
gar were kept the same. In addition, students
collected during your experiment, and whether your
could have made sure that tablets that were
hypothesis was supported or disproved.
mechanically broken down were crushed uni-
The more the food is broken down mechani-
formly. If they added tablets to vinegar (instead
cally, the faster it can be broken down chemi-
of the reverse), they would have had to make
cally. Students should support this general con-
sure that all of the powder was added simulta-
clusion by using their quantitative data (such as
neously.
how many seconds longer the unbroken piece
b.
Were there any variables (except for the one
took to dissolve), by determining a ratio, or by
being tested) that you could not keep the same?
making any other statement that directly uses
their group’s or the class’s experimental data.
There was some unavoidable variation in the
Student data will vary depending on the
amount of tablet used.
c.
How could you or did you improve the design of
speeds the process) and the size of the tablet
your experiment? Explain.
used (smaller pieces dissolve faster).
Most experiments could have been improved
by using a balance to weigh out identical
amounts of tablet.
2.
a.
What part of digestion was modeled by
breaking the tablet?
Mechanical breakdown
b.
amount of vinegar added (adding more vinegar
4.
Were your conclusions based on qualitative or
quantitative data? Explain.
While students collected both qualitative data
(in Step 3) and quantitative data (in Step 9),
their conclusions are more likely to be based on
quantitative data, such as time, ratios, or any
other statement that directly uses their group’s
What part of digestion was modeled by adding
or the class’s experimental data. You may wish
vinegar?
to review the use of qualitative and quantitative
Chemical breakdown
data in this activity and the different purposes
served by each.
Teacher’s Guide
B-45
Activity 14 • Breakdown
5.
Besides preventing choking, why is it important to
chew your food?
If your students are having difficulty with this
question, rephrase it as: Why is it important to
mechanically break down your food before it
reaches your stomach?
Chewing your food is one method of mechanical breakdown, which speeds the process of
chemical breakdown. Students are likely to have
observed that the tablets that were broken into
smaller pieces reacted more quickly with the
vinegar. In like manner, food that is broken
down more quickly can be absorbed by the body
sooner. (You may also want to mention that
chewing also enables your food to move more
smoothly through your esophagus and prevents
choking because smaller pieces of food are more
easily lubricated by the saliva.)
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Science and Life Issues
Human Digestive System
salivary glands
esophagus
liver
bile duct
gall bladder
stomach
pancreas
small intestine
large intestine
©2006 The Regents of the University of California
rectum
anus
Science and Life Issues Transparency 14.1
B-47