Mechanical and Chemical Digestion — Revision notes

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

What this lesson covers

How well do you know each one? Be honest: red means go back over it.

• Explain why food must be broken into small soluble molecules before it can be absorbedNot yetSort ofGot it
• Describe the difference between mechanical and chemical digestionNot yetSort ofGot it
• Identify where each type of digestion takes place in the bodyNot yetSort ofGot it
• Describe how carbohydrates are broken down into sugarsNot yetSort ofGot it
• Describe how proteins are broken down into amino acidsNot yetSort ofGot it
• Compare how fats are broken down into fatty acids and glycerolNot yetSort ofGot it

Test yourself

Cover the answer, say it out loud, then check the full quiz on the lesson page.

• Which of these is an example of mechanical digestion?
• Which of these is NOT broken down by digestion?
• Roughly how much saliva does an adult make in a day?

Topic quiz

15 questions on this topic only — not mixed with anything else, one at a time.

Spelling challenge

Read the definition, then type the correct spelling of the term. Uses the same terms as above.