KS3 · Biology

Bacteria in the human digestive system

Right now, millions of bacteria are living inside your gut. Don't panic: you want them there.

Biology · Gut flora

What are your gut bacteria up to?

Your gut is home to millions of bacteria, called gut flora. Some things help you, some things wipe them out, and the end result can be a very sore tummy. Before anyone explains it, have a go: add the arrows you think are true, reading each pair as "this leads to that". Then check your web against the lesson's.

Gut flora (millions of helpful bacteria in your gut)
Enzymes that digest food we can't digest ourselves
Vitamins we can't make, such as vitamin K
Pathogenic bacteria stopped from growing
Antibiotics, being unwell or a poor diet
Gut flora killed off
Pain and diarrhoea (outcome)

Add a link

This factor……made this happen or worse

No links yet.

Meet a bacterium

Tap a card to flip it. Try to say what each term means before you do.

Biology · Bacteria

Are bacteria the bad guys?

Bacteria are found pretty much everywhere: on your skin and inside you too.

Which of these is closest to what you think right now? Pick one, say how sure you are, then check.

Bacteria are germs. If there are bacteria in you, you're going to be ill.Helpful bacteria only exist in factories and labs. Inside your body, bacteria can only do harm.Bacteria only live in dirty places. A clean body wouldn't have any on it or in it.Some bacteria are pathogens that cause disease, but many are harmless and some are helpful, including the ones inside me.

How sure are you?

I'm sureI think soI'm guessing

Bacteria are germs. If there are bacteria in you, you're going to be ill.

This is a common misconception

Easy mistake, but no. A pathogen is a microorganism that causes disease, and some bacteria are pathogens: E. coli, for example, causes food poisoning. But many bacteria are harmless and some are helpful. Millions live inside you right now and you feel fine.

Helpful bacteria only exist in factories and labs. Inside your body, bacteria can only do harm.

This is a common misconception

We do put bacteria to work: some are used to make medicines, and others to make yogurt and cheese. But helpful bacteria aren't only outside us. Millions live in your digestive system (in the stomach and in the small and large intestines) and they're called your gut flora. The rest of this lesson is about what they do for you.

Bacteria only live in dirty places. A clean body wouldn't have any on it or in it.

This is a common misconception

Bacteria are found pretty much everywhere, including on our skin and inside us. Having them isn't a sign of anything dirty. They're microorganisms, which means you can only see them with a microscope, so you never notice them.

Some bacteria are pathogens that cause disease, but many are harmless and some are helpful, including the ones inside me.

This matches the evidence

Exactly. 'Bacteria' is a huge group, not a single type. Pathogens are the troublemakers. Plenty of others are harmless, and some are useful, including the gut flora that live in your digestive system.

Bacteria aren't all bad. Some are pathogens, but many are harmless and some are helpful, and millions of helpful ones live in your gut.

How enzymes digest food

Step through the stages, then see where gut bacteria come in.

Biology · Your turn

Say it in your own words

Describe the importance of bacteria in the human digestive system. [3 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Gut flora release enzymes that digest food we can't digest ourselves (1 mark)
They make vitamins, such as vitamin K, that we can't make ourselves (1 mark)
They compete with pathogenic bacteria for food and space, helping to keep us healthy (1 mark)

Model answer

Millions of bacteria live in our gut and they're called gut flora. They release enzymes that digest some food we can't digest ourselves. They make vitamins, such as vitamin K, that we can't make but need. They also compete with pathogens for food and space, which stops the pathogens growing.

Three jobs, each in your own words: digesting food we can't, making vitamins, and competing with pathogens.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why the millions of bacteria in your gut are on your side

What you need to know

A bacterium is a living thing made of a single cell, so small you need a microscope to see it. It has a cell wall, a single loop of DNA that floats freely in the cytoplasm, and cytoplasm.
A pathogen is a microorganism that causes disease. Some bacteria are pathogens (E. coli causes food poisoning), but many bacteria are harmless and some are helpful.
Millions of bacteria live in your digestive system. Together they're called your gut flora.
Gut flora release enzymes that digest food we can't digest ourselves, make vitamins such as vitamin K, and compete with pathogens for food and space.
Antibiotics, being unwell or a poor diet can kill gut flora. Then some food stays undigested and some nutrients aren't made, which can lead to pain and diarrhoea.

The big picture

Millions of bacteria live in your gut. Called gut flora, they release enzymes that digest food we can't digest ourselves, make vitamins such as vitamin K, and compete with pathogens for food and space. If they're killed off, some food stays undigested and some nutrients aren't made, which can lead to pain and diarrhoea.

Key points

1Many bacteria are harmless and some are helpful. Only some are pathogens.

2Gut flora are the millions of bacteria in the stomach and the small and large intestines.

3Three jobs: help digest food, make vitamins, compete with pathogens.

4Look after your gut flora with a range of fruit and vegetables, probiotic drinks and yogurts, and fermented food.

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Worked example

Problem

Maya took antibiotics for an infection. Two days later she has tummy pain and diarrhoea. Explain how the antibiotics might be linked to this.

⚠ Watch out

Thinking "bacteria" means "germs that make you ill". Pathogens are the bacteria that cause disease. Many bacteria are harmless and some, like your gut flora, are helpful.

🧠

Memory hook

Gut flora have three jobs: Digest, Vitamins, Defend. Think D-V-D.

✓

Check yourself

Close your notes. Can you name the three jobs your gut flora do, and say what can happen if they're killed off?

Flashcards

(13)

What is a bacterium?

A living thing made of a single cell.

What is a microorganism?

An organism you can only see using a microscope.

What three parts does a bacterium have?

A cell wall around the outside, cytoplasm inside, and DNA as a single loop that floats freely in the cytoplasm.

What is a pathogen?

A microorganism that causes disease. E. coli is a bacterium that causes food poisoning.

Are all bacteria harmful?

No. Some are pathogens, but many are harmless and some are helpful, for example in making medicines, yogurt and cheese.

What are gut flora?

The millions of bacteria that live in our digestive system, in the stomach and the small and large intestines.

What is digestion?

Breaking large food molecules (carbohydrates, proteins and fats) down into small ones so they can be absorbed into the blood.

What is an enzyme?

A biological catalyst that speeds up reactions such as digestion. It is unchanged afterwards and can be reused.

How do gut flora help us digest food?

They make enzymes that we can't make ourselves and release them into our digestive system.

Which vitamin do gut bacteria make, and why does it matter?

Vitamin K. We can't make it ourselves, but we need it to maintain our health.

How do gut flora protect us from pathogens?

They compete with pathogenic bacteria for food and space, so the pathogens can't grow.

What can kill gut flora?

Taking antibiotics for another infection, being unwell, or having a poor diet.

Why is it important to look after gut flora, and how?

Without them, food stays undigested and nutrients aren't made. Eat a range of fruit and vegetables, probiotic drinks and yogurts, and fermented food like kimchi and kombucha.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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What are your gut bacteria up to?

Are bacteria the bad guys?

Say it in your own words

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