Facilitation Questions
Describe the physical and chemical changes that occur during digestion.
Physical changes occur when food is broken into smaller pieces, mixed with
other substances, or when water is removed from wastes in the large intestine.
Chemical changes occur when food material is broken down by
a variety of
enzymes and acids into smaller molecules usable by
Describe how food moves through the digestive system. The walls of the organs
of the tubelike digestive system squeeze the food down, like squeezing a marble
through a tube.
Where does digestion start?
Digestion begins in the mouth, where teeth tear and
grind food into smaller pieces as saliva is added to help form
the food into a ball
called a bolus.
What happens to food in the stomach? The chemical digestive and gastric juices,
along with the physical churning of the stomach, break the food into a smooth
paste called chyme.
What is the main function of the small intestine? The small intestine continues to
break down food.
Absorption of nutrients into the blood also occurs here.
How does the body rid itself of indigestible food? The large intestine removes
extra water. The waste then passes to the rectum and is expelled through the
Teacher Instruction
Do you know someone who has had kidney dialysis treatments?
Why are
these treatments necessary? T o
clean the blood of its wastes if the kidneys are
not functioning properly
Ask: Why does blood need to be filtered, or “cleaned”? Waste materials from
cellular respiration are transferred into the bloodstream;
it is the way the cells get
rid of their dangerous waste products.
Set out the materials for the kidney model design in a central location.
Instruct students to design and explain a filter system to clean muddy water,
which represents blood.
Allow students to participate in a gallery walk to view the different models.
Ask each group to describe their kidney model and show a sample of the water
filtered by
their model.
Review questions with students and utilize the facilitation questions.
Materials Materials
For student groups
tea strainers
coffee filters
muddy water
dialysis tubing
materials at
student request
Lesson 1: Physical and Chemical Changes in Digestion
Unit 5:
Structure and Function of Organisms, Part 2
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