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11.19: Bacteria in the Digestive System

Difficulty Level: At Grade Created by: CK-12
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Why eat yogurt?

Yogurt is a good source of calcium. Yogurt also contains active cultures of "good" bacteria. Foods that contain these beneficial bacteria are sometimes called "probiotic."

Bacteria in the Digestive System

Your large intestine is not just made up of cells. It is also an ecosystem, home to trillions of bacteria ( Figure below ). But don't worry. Most of these bacteria are helpful. They have several roles in the body. For example, intestinal bacteria:

  • Produce vitamins B 12 and K.
  • Control the growth of harmful bacteria.
  • Break down poisons in the large intestine.
  • Break down some substances in food that cannot be digested, such as fiber and some starches and sugars.

Your intestines are home to trillions of bacteria.


  • Your large intestine is home to trillions of bacteria.
  • Bacteria in the large intestine have important roles such as producing vitamins and controlling the growth of harmful bacteria.


Use the resources below to answer the questions that follow.

  1. How do bacteria influence our digestion?
  2. How does what you eat influence the bacteria of your gut? What two categories with regards to gut bacteria have scientists identified?
  3. What link do scientists believe may exist between gut bacteria and disease? Why is this an area of interest for scientists?
  1. How may clean environments affect the microbes in our bodies?
  2. How do gut microbes compare between species?
  3. What is the hygiene hypothesis?


  1. Identify two roles of helpful bacteria in the large intestine.
  2. When you are sick, you might be given an antibiotic to kill harmful bacteria. Antibiotics cannot distinguish between "good" and "bad" bacteria, however. Why might this be a problem?




All the living things in an area interacting with all of the non-living parts of the environment.
vitamin B12

vitamin B12

Vitamin necessary for healthy nerves.
vitamin K

vitamin K

Vitamin necessary for blood to clot.

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Difficulty Level:

At Grade


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Jan 30, 2016
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