AQA 4.2ORGANISATION

4.2.2Animal tissues, organs and organ

systems

4.2.2.1 Human digestive system- specification

• Cells are the basic building blocks of all living organisms.

• A tissue is a group of cells with a similar structure and function.

• Organs are aggregations of tissues performing specific functions.

• Organs are organised into organ systems, which work together to form organisms.

4.2.2.1 The human digestive system -

specification• This section assumes knowledge of the digestive system studied in Key Stage 3 science.

• The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

• Students should be able to relate knowledge of enzymes to Metabolism.

• Students should be able to describe the nature of enzyme molecules and relate their activity to temperature and pH changes.

• Students should be able to carry out rate calculations for chemical reactions.

• Enzymes catalyse specific reactions in living organisms due to the shape of their active site.

Digestive System LOs• Recall the role of the digestive system, and the purpose of

digesting food• State the sites of enzyme production for amylases,

proteases and lipases• Know that amylase is a carbohydrase • Construct simple word equations for the reactions of

enzymes• Link the products of digestion to their uses• Know where bile is produced and stored• Explain how bile is important for efficient digestion

STARTER: Place in order of smallest to largest

organism

organ system

tissues

cells

organs

smallest

largest

organism

organ system

tissues

cells

organs

smallest

largest

The role of the digestive system

The job of the digestive system is the break down large insoluble food molecules into small soluble molecules.

These can then be absorbed through the walls of the small intestine into the blood.

Digestion quiz

Complete sheet as we go through the next few slides

The digestive system organs

The digestive system organs

Sites of enzyme production

Enzyme reactions

Enzymes

Enzymes are chemicals which break the larger molecules down into smaller molecules. There are three types of enzymes that you need to

know about.

Enzymes

• Carbohydrase chops carbohydrates into smaller sugar molecules.

The three types of enzymes are:

• Protease cuts proteins into the soluble amino acids.

• Lipase breaks fats down into the smaller fatty acids and glycerol.

Proteins are digested in the stomach by an enzyme called Protease. This enzyme needs to work in an acidic environment. Protease

breaks proteins (chains of different molecules) down into up to 20 different amino acids (four of which are shown).

Proteins digestion

Protease

Folded up protein chain

Amino acids

Carbohydrates are chains of identical sugar molecules. The enzyme called

Carbohydrase breaks the chemical bonds between the individual sugar molecules

(called glucose) as part of digestion.

Starch/ carbohydrates

Carbohydrase

Long carbohydrate

Small

sugar

Fats are digested in two stages:•Firstly bile (released by the gall bladder) allows the fat to “mix” with water by breaking the fat up

into smaller droplets. This is called emulsification.

•Secondly, an enzyme called Lipase breaks the fats down into the smaller fatty acid molecules and

glycerol.

Bile

Lipase +

FatFattyacid

Glycerol

Fats

Enzymes of digestion

Word equations for the reactions of enzymes

• Challenge questions: If lipase is added to some milk to digest the milk fats, what will happen to the pH of the milk? How would you test for this? _____________________________________________________________________________________________________________________________________________________________________________________________________________

Match the reactant

Enzymes; uses of products of digestion; bile - specification

• Students should be able to use the ‘lock and key theory’ as a simplifed model to explain enzyme action.

• Students should be able to recall the sites of production and the action of amylase, proteases and lipases.

• Students should be able to understand simple word equations but no chemical symbol equations are required.

• Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.

• Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch.

• Proteases break down proteins to amino acids.• Lipases break down lipids (fats) to glycerol and fatty acids.• The products of digestion are used to build new carbohydrates, lipids and proteins. Some

glucose is used in respiration.• Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric

acid from the stomach. It also emulsi es fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase.

Enzymes LOs• Recall the word equations for the reactions of enzymes

• Know that enzymes are proteins with a specific shaped active site

• Use the 'lock and key' model to explain enzyme action

• Explain how the activity of enzymes are affected by temperature and pH

• Investigate the effect of pH on the rate of reaction with amylase.

Starter: write the correct enzyme name on the arrow for each reaction

proteasecarbohydrase lipase

Lipids fatty acids + glycerol

starch simple sugars

proteins amino acids

Starter: write the correct enzyme name on the arrow for each reaction

protease

carbohydrase

lipaseLipids fatty acids + glycerol

starch simple sugars

proteins amino acids

Enzymes structure and function• Enzymes are proteins • They have a specific shaped active site• A specific enzyme can only fit a specific

molecule into its active site• So different enzymes will catalyse different

reactions

How enzymes work

What happens at the active site?In the same way that a key fits into a lock, so a

substrate is thought to fit into an enzyme’s active site. The enzyme is the lock, and the

reactant is the key.

enzyme

reactant+

enzyme-reactant complex

↔products

enzyme+↔

+ ↔ ↔ +

The lock and key model

Lock and Key model

• We use the 'lock and key' model to explain enzyme action

Name the structure

Enzymes: true or false?

Factors affecting enzymesIf the temperature and pH changes sufficiently beyond an enzyme’s optimum, the shape of the

enzyme irreversibly changes.

normal denatured

heat

pH

This affects the shape of the active site and means that the enzyme will no longer work.

When this happens the enzyme is denatured.

Enzymes and pH

Enzymes and temperature

Enzymes and temperature

Enzyme inhibitors

Identifying enzyme terms

• Required practical activity 3:

• use qualitative reagents to test for a range of carbohydrates, lipids and proteins.

• To include: Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein.

• AT skills covered by this practical activity: biology AT 2.

• This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development.

• Required practical activity 4:• investigate the effect of pH on the rate of reaction of amylase

enzyme.

• Students should use a continuous sampling technique to determine the time taken to completely digest a starch solution at a range of pH values. Iodine reagent is to be used to test for starch every

• 30 seconds. Temperature must be controlled by use of a water bath or electric heater.

• AT skills covered by this practical activity: biology AT 1, 2 and 5.

• This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in

• Key opportunities for skills development.

  Did iodine go brown for the presence of starch? (Tick or cross) after iodine stays orange-brown.

Time (s) 0 10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

260

pH                                                    pH                                                    pH                                                    pH                                                    pH                                                    

pH of solution Time taken for amylase to completely break down the starch in seconds (s)