KS3 Biology › Human digestive system

Mechanical and Chemical Digestion

Chewing your food properly isn't just table manners — it changes how fast your body can actually break it down. Digestion only works because two separate processes team up, one physically breaking food apart and the other using chemicals to finish the job.

KS3 Biology · Year 7–9 · Free worksheet with answers

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What you'll be able to do after this lesson

These are the points the worksheet questions are built around.

Key terms

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Straight from the video — the words worth knowing cold before the test.

DIGESTION
Breaking large food molecules down into small ones that can be absorbed into the blood
INSOLUBLE
Does not dissolve in water
SOLUBLE
Dissolves in water, so it can travel in the blood
NUTRIENTS
The small, soluble substances released from food and used for energy, growth and repair
MECHANICAL DIGESTION
Physically breaking food into smaller pieces without changing it chemically
CHURNING
The stomach squeezing and turning food over to break it into smaller pieces
SURFACE AREA
The total amount of outside surface that chemicals can reach and work on
CHEMICAL DIGESTION
Using chemicals to break large food molecules into smaller ones
SALIVA
The liquid in the mouth containing chemicals that begin digesting food
ENZYME
A chemical in the body that speeds up the breakdown of food molecules
CARBOHYDRATE
A food molecule made of sugars joined together, used for energy
STARCH
A large carbohydrate made of hundreds of sugar molecules joined in a chain
GLUCOSE
A single small sugar molecule, small enough to be absorbed into the blood
PROTEIN
A large food molecule made of amino acids joined together, used for growth and repair
AMINO ACIDS
The small building blocks released when proteins are digested
LIPID
The scientific name for a fat, used by the body for storage and energy
FATTY ACIDS AND GLYCEROL
The two small products released when a fat is digested

Revising for a test?

Every key term, learning objective and quiz question on one clean, printable page.

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Quick quiz — from the video

The 3 questions from the video, if you'd like to check you caught them.

1. Which of these is an example of mechanical digestion?

2. Which of these is NOT broken down by digestion?

3. Roughly how much saliva does an adult make in a day?

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Free worksheet — 3 questions, 13 marks

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Using this with a class

You're welcome to embed the video and link these resources in Google Classroom, Stile, Canvas, Compass or any other school platform. No need to ask.

Everything here is written to the KS3 curriculum for students aged 11–14. Print freely for the classes you teach.

What to watch next

Next lesson Bacteria in the Digestive System Next lesson Absorption and Transport of Nutrients

The rest of this unit

Human digestive system

  1. The Human Digestive System
  2. Mechanical and Chemical DigestionYou're here
  3. Bacteria in the Digestive System
  4. Absorption and Transport of Nutrients

Watch the whole KS3 Biology playlist on YouTube →