Topics · Primary Science · Systems: Digestive
Digestion: breaking food down small enough to use
Food has to be broken into pieces small enough to pass into the blood. The digestive system is a single tube that does that in order, and nearly every question is about which part does what.
- 373 exam papers analysed
- appears in 81% of P6 Science papers
- ~3 min read
01 One tube, in order
Food travels one way through a single passage. Knowing the order answers most questions on its own.
- Mouth (W) — teeth cut and grind food; saliva softens it and starts breaking it down.
- Gullet (X) — carries food down to the stomach. No digestion happens here.
- Stomach (Y) — churns food and mixes it with digestive juices.
- Small intestine (Z) — digestion finishes, and digested food passes into the blood.
- Large intestine — takes water out of what is left; the rest leaves the body.
02 The two absorptions
Papers separate these deliberately, and swapping them is the commonest error on the topic.
Small intestine — absorbs digested food into the blood. This is where nutrients enter the body.
Large intestine — absorbs water, not food. Food absorption is already finished by then.
So a question about where nutrients enter the blood has one answer, and a question about where water is taken back has a different one.
03 Why food must be broken down at all
Food in a mouthful is far too big to cross into the blood. Digestion makes the pieces small enough to pass through the wall of the small intestine.
Breaking down happens two ways at once. Physically, the teeth chop and the stomach churns — this makes the pieces smaller but does not change what they are. Chemically, digestive juices change the food into simpler substances.
That is why chewing matters: smaller pieces give the juices more surface to work on, so the chemical part goes faster.
04 Blockage and removal questions
The P6 version removes or blocks a part and asks what follows. Work along the tube.
Teeth missing or food swallowed whole — pieces stay large, so digestion is slower and less complete.
Stomach removed — food is not churned or mixed with juices, so it arrives at the small intestine poorly broken down.
Part of the small intestine removed — less digested food is absorbed, so the person gets fewer nutrients even while eating normally.
Large intestine not working — water is not taken back out, so what leaves the body stays watery.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- digestionsaydy-JES-chuhn
Breaking food down into pieces small enough to pass into the blood.
- gulletsayGUL-itmore than onegullets
The tube carrying food from the mouth to the stomach. No digestion happens in it.
- small intestinesayin-TES-tin
Where digestion finishes and digested food passes into the blood.
- large intestine
Where water is absorbed from what is left after digestion.
- salivasaysuh-LY-vuh
The liquid in the mouth that softens food and begins breaking it down.
- absorbsayuhb-ZORB
To take in. The small intestine absorbs food; the large intestine absorbs water.
- nutrientssayNYOO-tree-uhnts
The useful substances in food that the body takes into the blood.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P3
Naming the parts and the order food passes through them.
Practise P3 Systems: Digestive — 9 questions →32% of P3 papers
- P4
What each part does, and the two kinds of breaking down.
Practise P4 Systems: Digestive — 10 questions →73% of P4 papers
- P5
Absorption in the small and large intestines, and why food must be broken down.
Practise P5 Systems: Digestive — 10 questions →61% of P5 papers
- P6
Explaining the effect of a missing or damaged part, and digestion inside longer questions.
Practise P6 Systems: Digestive — 9 questions →81% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“Food is absorbed in the large intestine.”
Digested food is absorbed in the small intestine. The large intestine absorbs water.
“Digestion starts in the stomach.”
It starts in the mouth — teeth break food up and saliva begins the chemical work.
“The gullet digests food on the way down.”
It only carries food. Nothing is broken down there.
“Chewing is not really part of digestion.”
It is the physical half. Smaller pieces give digestive juices more surface to act on.
“The stomach absorbs the nutrients.”
The stomach churns and mixes. Absorption into the blood happens further along, in the small intestine.
Now try it
38 questions across 4 levels, marked as you go with the working shown.