Digestion & Enzymes To revise the digestive system, and the role of enzymes.

Digestion & Enzymes

• To revise the digestive system, and the role of enzymes

Recap Absorption

• Digested food molecules are absorbed through the small intestine (into our blood)

• Once in the blood, the digested food molecules are carried around the body, to where they are needed

• Only small, soluble molecules can pass through the wall of the small intestine

Recap Absorption

• The inside wall of the small intestine needs to be thin, with a really big surface area

• This allows absorption to happen quickly and efficiently (so we absorb as much food as possible)

• To get a big surface area, the inside wall of the small intestine is lined with tiny villi (one of them is called a villus)

• These stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.

Recap Enzymes• Enzymes are special proteins that can break large molecules into

small molecules. Different types of enzymes can break down different nutrients:

• Amylase breaks down starch into sugar

• Protease breaks down proteins into amino acids

• Lipase breaks down fats into fatty acids and glycerol

• Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down.

• Digestive enzymes cannot break down fibre, which is why it cannot be absorbed by the body.

Specifics

• Enzymes are specific - one type of enzyme will only break down one type of nutrient (e.g. lipase will only break down fat)

• This is because they are a special shape - they are designed to ‘fit’ into the food molecule which they break down

• This is similar to a lock and a key - only a specific key will undo a lock (only a specific enzyme (key) will break down a specific food molecule (lock))

• Enzymes also need specific conditions - they can denature in high temperatures / pH (this is where the enzyme structure is changed so it no longer functions (a bit like bending the key so it no longer fits in the lock))

Assessment

How do enzymes work?

• Your task is to evaluate some models, used to explain how enzymes work

• You will be assessed on: -– Your knowledge and understanding of enzymes– Your ability to use models

Diagram 1 Diagram 2 Diagram 3

Diagram 4

Assessment

How do enzymes work?

1. Look at the diagrams on the sheet, taken from some science textbooks. The diagrams are used to explain the role of enzymes, and how they work. Which one do you think is best? Put the diagrams in order, from 1 (the best) to 4 (the worst)

2. Explain in your own words, why you have chosen that order

3. Try to explain the limitations of some of the diagrams - you may wish to produce your own model to explain the role on enzymes in digestions

Diagrams

WordsearchCalciumCarbohydratesDiaryDigestionEnzymesFatsFruitGlucoseIntestineIronMeatMineralsMouthProteinStarchStomachVegetablesVitamins