Download Food and Digestion

Food and Digestion - Food and Energy
Percentages
A percentage (%) is a ratio that compares a number to 100.
For example, 30% means 30 out of 100.
Suppose that a person eats a total of 2,000 calories in one
day. Of those calories, 300 come from protein. Follow these
steps to calculate the percentage of calories that come from
protein.
1. Write the comparison as a fraction:
2. Multiply the fraction by 100% to express it as a percentage:
Food and Digestion - The Digestive Process Begins
Functions of the Digestive System
The digestive system has three
main functions. First, it breaks
down food into molecules the body
can use. Then, the molecules are
absorbed into the blood and
carried throughout the body.
Finally, wastes are eliminated from
the body.
Food and Digestion - The Digestive Process Begins
The Mouth
Both mechanical and chemical digestion
begin in the mouth.
Food and Digestion - The Digestive Process Begins
The Mouth
The shape of an enzyme molecule is specific to the shape of
the food molecule it breaks down. Here an enzyme breaks
down a starch into sugars.
Food and Digestion - The Digestive Process Begins
Protein Digestion
A scientist performed an
experiment to determine the
amount of time needed to digest
protein. He placed small pieces
of hard-boiled egg white (a
protein) in a test tube containing
hydrochloric acid, water, and the
enzyme pepsin. He measured
the rate at which the egg white
was digested over a 24-hour
period. His data are recorded in
the graph.
Food and Digestion - The Digestive Process Begins
Protein Digestion
Reading Graphs:
What do the values on the yaxis represent?
Percentage of egg white
digested
Food and Digestion - The Digestive Process Begins
Protein Digestion
Interpreting Data:
After about how many hours
would you estimate that half
of the protein was digested?
About 14 hours
Food and Digestion - The Digestive Process Begins
Protein Digestion
Interpreting Data:
How much digestion occurred
in 16 hours?
About 70%
Food and Digestion - The Digestive Process Begins
Protein Digestion
Drawing Conclusions:
During which four-hour period
did the most digestion take
place?
From 13 to 16 hours
Food and Digestion - The Digestive Process Begins
The Stomach
Most mechanical digestion and some chemical digestion
occur in the stomach.
Food and Digestion - The Digestive Process Begins
Using Prior Knowledge
Before you read, look at the section headings and visuals to
see what this section is about. Then write what you know
about the digestive system in a graphic organizer like the one
below. As you read, write what you learn.
1.
What You Know
Food is digested in the stomach.
1.
What You Learned
Digestion begins in the mouth.
Food and Digestion - The Digestive Process Begins
Digestion
Click the Video button to watch a movie about digestion.
Food and Digestion - The Digestive Process Begins
Links on Digestion
Click the SciLinks button for links on digestion.
Food and Digestion - Final Digestion and Absorption
The Small Intestine
The small intestine is the part of the digestive system where
most chemical digestion takes place.
Food and Digestion - Final Digestion and Absorption
The Small Intestine
Tiny finger-shaped projections called villi line the
inside of the small intestine. Villi absorb nutrient
molecules. The molecules pass from the villi into
blood vessels.
Food and Digestion - Final Digestion and Absorption
Identifying Main Ideas
As you read the section “The Small Intestine,” write the main
idea in a graphic organizer like the one below. Then write
three supporting details that further explain the main idea.
Main Idea
Chemical digestion takes place in the small intestine.
Detail
Detail
Food mixes with
enzymes and
secretions.
Starches,
proteins, and fats
are digested
chemically.
Detail
Enzymes and
secretions are
produced by the
small intestine,
liver, and
pancreas.
Food and Digestion - Final Digestion and Absorption
More on the Digestive System
Click the PHSchool.com button for an activity about
the digestive system.
Food and Digestion
Graphic Organizer
In the mouth, the teeth break food into smaller pieces and saliva
begins to break down starches.
Esophagus pushes food from mouth to stomach.
In the stomach, food is churned and mixed with digestive juices
that break down protein.
In the small intestine, almost all chemical digestion and absorption
occurs.
Large intestine absorbs water and eliminates waste.
Food and Digestion
End of Section:
Graphic Organizer