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Bacteria in the Human Digestive System

In this worksheet, students will learn about friendly bacteria that live in our digestive system and help us break down food.

'Bacteria in the Human Digestive System' worksheet

Key stage:  KS 3

Curriculum topic:  Biology: Structure and Function of Living Organisms

Curriculum subtopic:  Nutrition and Digestion

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

Bacteria live everywhere around us, on our skin, even inside our body. There are bacteria that cause disease, which we call pathogens, but there are also good bacteria that live inside us and help us by taking up space, so pathogens cannot multiply inside us. Quite a few good, friendly bacteria live in our digestive system and help with the process of digestion. Below is a diagram of the human digestive system:

 

Human digestive system

 

Friendly bacteria in the digestive system live mainly in the colon (the large intestine) and in the part of the small intestine which is further away from the stomach. The rest of the small intestine, the esophagus and the stomach are bacteria-free. Digestive enzymes and hydrochloric acid in the stomach make it impossible for bacteria to survive there.

 

It is estimated that around 100 trillion friendly bacteria live in our gut. If we were to extract them, they would have a mass of 1 kg. There are between 300 and 1000 different species, with 50 of them the most common.

 

Friendly gut bacteria have evolved in order to withstand the harsh conditions of our digestive system.

 

The main advantage of having friendly bacteria in the gut is protection against harmful bacteria that would otherwise cause infection and invade the cells of the intestinal wall. Additionally, bacteria help with the digestion of materials that we are unable to digest, like hard plant material. A lot of the vitamins from vegetables would be wasted if it wasn't for the friendly bacteria that digest them for us. Some species produce vitamins K and B that are hard for us to obtain from food. They also maintain the acidity balance and break down some drugs, hormones not needed anymore and toxins that would be potentially dangerous to our health.

 

The population of bacteria in our gut is renewed regularly; about half the dry mass of our feces consists of bacteria.

 

Whilst it might seem strange to think that there are around 100 trillion other organisms living inside us, they are very important to our health and in this activity you'll find out why.

What parts of our digestive system do friendly bacterial live in?

 

Tick two answers.

esophagus

small intestine

colon

stomach

Why is it impossible for friendly bacteria to live in our stomach?

Tick two answers.

Pathogens take up most space.

They cannot survive hydrochloric acid in the stomach.

Our immune system would fight them.

They would be digested by digestive enzymes.

About how many bacteria live in our gut?

1 trillion

10 trillion

100 trillion

What would be the approximate mass of all the bacteria that live in our gut?

1 g

100 g

1 kg

What is the range of bacterial species that live in our gut?

50 to 300

50 to 1000

300 to 1000

What is the name given to the chemicals that both our gut and bacteria release in order to break down food molecules ready for absorption into the body?

acids

enzymes

indicators

sugars

Below is a list of different lengths.

 

Bearing in mind how many bacteria live in our gut, pick the length you estimate the represent the likely length of a typical bacterium.

1mm (1000µm)

0.01mm (10µm)

0.001mm (1µm)

0.00001mm (0.01µm)

What sorts of materials do friendly bacteria help us digest?

hard plant material

red meat

glucose

What vitamins are hard to obtain from food, but we manage to absorb with the help of gut bacteria?

 

Tick two answers.

K

A

B

C

Where do you think that friendly gut bacteria that we have finished with end up?

they are absorbed into the gut wall

they are broken down and pass into the bloodstream

they are transported to the liver and become bile

they are removed from the body in our feces

  • Question 1

What parts of our digestive system do friendly bacterial live in?

 

Tick two answers.

CORRECT ANSWER
small intestine
colon
EDDIE SAYS
Friendly gut bacteria live mainly in the colon (large intestine) and the part of the small intestine furthest from the stomach.
  • Question 2

Why is it impossible for friendly bacteria to live in our stomach?

Tick two answers.

CORRECT ANSWER
They cannot survive hydrochloric acid in the stomach.
They would be digested by digestive enzymes.
EDDIE SAYS
Friendly bacteria cannot survive hydrochloric acid in the stomach and they would be digested by digestive enzymes.
  • Question 3

About how many bacteria live in our gut?

CORRECT ANSWER
100 trillion
EDDIE SAYS
The the estimated number of friendly bacteria in our gut is 100 trillion - that's an awful lot of bacteria!
  • Question 4

What would be the approximate mass of all the bacteria that live in our gut?

CORRECT ANSWER
1 kg
EDDIE SAYS
The estimated mass of the friendly bacteria in our gut is 1 kg. If you bear in mind that a typical bacterium is just 0.001mm long and weighs almost nothing, then 1 kg represents an awful lot of bacteria - all in your gut!
  • Question 5

What is the range of bacterial species that live in our gut?

CORRECT ANSWER
300 to 1000
EDDIE SAYS
There are between 300 and 1000 species of friendly bacteria in our gut. So, up to one thousand differemt types.
  • Question 6

What is the name given to the chemicals that both our gut and bacteria release in order to break down food molecules ready for absorption into the body?

CORRECT ANSWER
enzymes
EDDIE SAYS
You will learn that there are many different enzymes released by your body and by bacteria. Their job is to help break up the complex food molecules into smaller ones that can be absorbed across the gut wall and into the bloodstream.
  • Question 7

Below is a list of different lengths.

 

Bearing in mind how many bacteria live in our gut, pick the length you estimate the represent the likely length of a typical bacterium.

CORRECT ANSWER
0.001mm (1µm)
EDDIE SAYS
Obviously, bacteria must be really small! In fact, like any organism, they range in size but they are typically about 1µm in length, or about one thousandth of a millimetre (0.001mm).
  • Question 8

What sorts of materials do friendly bacteria help us digest?

CORRECT ANSWER
hard plant material
EDDIE SAYS
Gut bacteria help us digest hard plant material and keep many vitamins that would otherwise be wasted. The cell walls of plants contains a material called cellulose which needs special enzymes to break down and bacteria help with some of this.
  • Question 9

What vitamins are hard to obtain from food, but we manage to absorb with the help of gut bacteria?

 

Tick two answers.

CORRECT ANSWER
K
B
EDDIE SAYS
We absorb more vitamins K (important in protein-making in the body) and B (important for extracting energy from our food) with the help of gut bacteria.
  • Question 10

Where do you think that friendly gut bacteria that we have finished with end up?

CORRECT ANSWER
they are removed from the body in our feces
EDDIE SAYS
Friendly bacteria are renewed all the time and the ones that are no longer needed ('dead' is a hard word to apply to bacteria) generally end up in our feces. Indeed, it's been estimated that about half the dry weight (with all the water removed) of our feces is, in fact, bacteria from our gut.
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