Digestion Test Study Guide
It has been quite the journey through the digestive tract. I suspect that you have added
new knowledge to your former understanding and probably revised some understandings.
1.
The digestive tract is a system made up of several organs working together to accomplish
the job of digesting food and getting the products ready to enter your cells. They include:
 Mouth
11 cm
 Esophagus
25cm
 Stomach
22cm
 Small intestine
690cm
 Large intestine
152cm
 Rectum
14cm
I would not put any effort into memorizing the various lengths of these organs. However,
if I asked you “which organ of the digestive tract is the longest?” you should be able to
answer that! We modeled the movement of food through the digestive tract and walked
away from this activity recognizing that muscle contractions are the primary method of
moving food along. We call this peristalsis. This is the driving force of moving food. It
is a powerful force. Imagine this, you can stand on your head and eat food and this
peristalsis force still moves food through the digestive tract!
2.
We explored Carbohydrates by doing simple chemical tests. Lugol’s test will detect
starch by turning it purple/black. Benedict’s test will detect sugar by turning a range of
colors. For example, green would be little sugar while dark orange would be much sugar.
We learned that carbohydrates include sugar (a simple carbohydrate) and starch (a
complex carbohydrate).
3.
We looked at digestion in the mouth. 2 types of digestion occur.
Mechanical digestion requires our teeth and tongue. Food is broken up into tiny pieces
so that chemical(s) can come into contact with more of the food surface.
Chemical digestion involves an enzyme called amylase. Amylase is able to break
starch apart into simple sugars. Recognize that Starch are large molecules made up of
simple sugars and we call this a complex carbohydrate. Sugar is a simple
carbohydrate. In the mouth, food is broken up, mixed with saliva/amylase, and formed
into a ball called a bolus. The bolus is ready to travel down the esophagus and enter the
stomach.
4.
Our diet contains a variety of foods. We have identified different food groups including:
carbohydrates, proteins, fats, vitamins, minerals, & water.
Carbohydrates include starch and sugars. The body breaks carbohydrates into simple
sugars. Simple sugars are the form of carbohydrate that can pass through the cell
membrane and enter your body’s cells. Foods like pasta, bread, and rice are sources of
carbohydrates.
Proteins are the body builders. They are at work in every cell in your body, building and
replacing tissues. Proteins are broken down into amino acids. Amino acids are the form
that can pass through you cell’s membrane. Foods like beef, chicken, eggs, and Tofu are
sources of protein.
There are 9 essential amino acids that we must include in our diets. If a food contains all
9 essential amino acids it is called a complete protein. Meat, eggs, and milk all contain
complete proteins.
Fats are necessary for your body. They provide protective padding around organs and
help insulate your body. There are two kinds of fats: saturated and unsaturated. Most
fats that come from animals are saturated fats. Most fats that come from plants are
unsaturated. Your body breaks down fats into fatty acids. Fatty acids are the form that
can be used by your cells.
5.
Mechanical digestion and chemical digestion also occurs in the stomach. The contraction
of 3 muscle layers in the stomach wall continue the process of breaking food apart.
Chemical digestion is accomplished by gastric juice. Gastric juice is a combination of
an enzyme called pepsin and the chemical hydrochloric acid (HCL). Gastric juice
breaks apart protein into amino acids. Amino acids are the building blocks of proteins.
Your cells are able to use amino acids to build or repair cell parts.
6.
We explored diffusion and active transport. Diffusion is the movement of a substance
from one location to another. It requires no energy from the cell to accomplish this and
we often refer to this a passive transport. The key thing to remember is diffusion
requires no energy. Diffusion always moves from regions of high concentration to
regions of low concentration. Movement will continue until concentrations come into
balance (are equal throughout). Active transport is different because energy is
required from the cell before the substance can be moved. Remember the example from
the book. A substance enters a gate; the cell helps pass this substance through using
energy (ATP), and the substance leaves on the opposite side from entry.
7.
We looked at how sugar and starch reacted to a membrane material. A simple
experiment looked at diffusion (no energy was required). The results were unexpected.
Sugar was able to pass through the membrane and starch was not able to pass through.
The logical explanation was that the starch molecules were too large to pass through the
tiny holes in the membrane. Sugar was smaller and able to pass through the
membrane. Conclusion? Size counts when trying to get through a cell membrane.
8.
Surface area counts throughout the digestive process. In the mouth you broke food up to
increase the surface area for digestion. In the stomach mechanical digestion continued
this. In the small intestine the surface area is greatly increased because the wall contains
complex folds and creases that greatly increase the total surface area. There is a really
important reason for this. The majority of digestion is completed in this organ and the
end results of digestion are absorbed. The sugars from carbohydrate digestion, the amino
acids from protein digestion, and the fatty acids from fat digestion begin entering the
cells of the small intestine walls. Your body needs a great amount of surface area to
accomplish this efficiently. Sugars, amino acids, and fatty acids are the only forms
that can pass through the cell membrane and enter the cell.