4.2.2.1 Human Digestive System

Question 1

Carbohydrates—sugar
Role in body, biochemical test, positive/negative result

Answer 1

Role in body: glucose used for respiration, a process that releases energy

Biochemical test:
Benedict’s solution
BOIL the solution
Semi quantitative

Test result:
Will change blue—>green—>yellow—>red

Question 2

Carbohydrates—starch
Monomer, role in body, biochemical test, test result

Answer 2

Monomer:
Simple sugars (e.g maltose)

role in body:
Broken down into glucose to release energy

biochemical test:
Iodine SOLUTION

test result:
Positive—blue black
Negative—orange brown

Question 3

Lipids (fats and oils)

Monomer, role in body, biochemical test, test result

Answer 3

Monomer:
3 fatty acids, 1 glycerol monomer

role in body:
Insulation
Long term energy store
Protects organs

biochemical test:
Use Sudan III
Add equal parts of food and water
Add Sudan III and shake tube

test result:
Positive—red layer forms on surface
Negative—no layer

Question 4

Proteins

Monomer, role in body, biochemical test, test result

Answer 4

Monomer:
Amino acids

role in body:
Growth and repair

biochemical test:
Biuret solution

test result:
Positive—lilac
Negative—blue

Question 5

BI: RP4 food tests
Risk assessment

Answer 5

Safety goggles should be worn when carrying out the tests
Wash off spills on skin immediately
Sudan 3 contains ethanol—high flammable. Keep solution away from make flames
Biuret solution contains copper sulphate—poisonous, and sodium hydroxides—caustic
Take care with boiling water

Question 6

BI: RP4
Apparatus

Answer 6

food to be tested
• a pestle and mortar
• a stirring rod
• filter funnel and filter paper
• 2 x beaker, 250 ml
• test tubes
• Benedict’s solution, iodine solution, sudan Ill solution, biuret solution
• water bath

Question 7

BI: RP4
Testing for sugars

Answer 7

1. Fill a test tube about a quarter full with some of the filtered food solution.
2. Add 5 drops of Benedict’s solution to the solution in the test tube.
3. Put the test tube into a water bath set at 65°C for five minutes.
4. Note any colour change.
   If a reducing sugar (such as glucose) is present, the solution will turn from blue to green, yellow, or brick-red. The colour depends on the sugar concentration.

Question 8

BI: RP4
Testing for starch

Answer 8

1. Take 5 ml of the filtered food solution put it into a clean test tube.
2. Add a few drops of iodine solution and note any colour change.
   If starch is present, the iodine solution will change from an orange/brown to a blue/ black colour.

Question 9

BI: RP4
Testing for lipids

Answer 9

1. Half fill a test tube with some of the unfiltered food solution.
2. Add 3 drops of Sudan Ill stain to the solution in the test tube. Shake gently to mix.
   If fat is present: a red-stained oil layer will separate out and float on the water surface.

Question 10

BI: RP4
Testing proteins

Answer 10

1. Put 2 cm of the filtered food solution into a test tube.
2. Add 2 cm’ of Buret solution to the solution in the test tube. Shake gently to mix and note any colour change.
   Proteins will turn the solution from blue to lilac or purple.

Question 11

Enzymes

Answer 11

Are a group of large proteins that act as biological catalysts
Speed up the rate of chemical reactions—lower the activation energy—without being used up

Question 12

Enzymes lock and key

Answer 12

Enzymes with a specifically shaped active site and a substrate that is complementary in shape to the enzyme’s active site bind together.
Forms an ENZYMME-SUBSTRATE COMPLEX—this lowers the activation energy and the bonds in the substrate get broken
Reaction is complete and products are released from the active site
The enzyme remains unchanged

Question 13

Factors affecting enzymes activity—temperature

Answer 13

When temp too low:
Enzymes and substrates—less kinetic energy so don’t collide very often—>so fewer enzyme substrate complexes form, rate of reaction is slow

When temp at optimum:
Enzymes and substrates—more kinetic energy so collide very often—>so many enzyme substrate complexes form, rate of reaction is at its fastest

When temp too high:
Have of active site changes so substrate = no longer complementary and cannot bind to the enzyme
Enzyme = denatured
Rate of reaction slows and then stops

Question 14

Factors affecting enzyme activity: pH

Answer 14

Basically like temp
But enzymes will denature if too high AND if too low

Question 15

BI: RP5

Answer 15

Place a few drops of iodine solution into each depression on the spotting tile.
2. Number two test tubes, and add:
• 2 cm buffer pH solution to tube 1 (your teacher will tell you which pH)
• 2 cm amylase solution to tube 1
• 2 cm starch solution to tube 2.
3. Place them into a water bath set at 30 °C and leave them for 5 minutes.
4. Add the starch to the amylase/buffer solution.
5. Start the stop clock and leave it on throughout the test.
6. Mix gently using the pipette and immediately remove one drop of the mixture.
7. Place this drop in the first depression of the spotting tile with the iodine solution. The iodine solution should turn blue-black
8. Use the pipette to remove one drop of the mixture every 30 seconds. Put each drop into the iodine solution in the next depression on the spotting tile. Rinse the pipette with water after each drop. Continue until the iodine solution and the amylase/buffer/starch mixture remain orange, or until you have no wells of iodine left.
9. Record the time taken for the amylase to digest all the starch.

Question 16

Digestion definition

Answer 16

Is the mech mechanical and chemical breakdown of food
It converts large insoluble molecules into small soluble molecules, which can be absorbed into the blood

Question 17

Digestion overall process

Answer 17

Begins in mouth—mechanical digestion (chewing) and chemical digestion (amylase produced by the salivary glands breaks down starch)

Food is then rolled into a bolus (ball shape), swallowed and pushed down the oesophageal, to the stomach, by a series of muscular contractions known as peristalsis

When ball of food arrives at the stomach—mixed and churned with digestive juices—contain protease enzymes which begin digesting protein and hydrochloric acid

Digestive juices are moved into the small intestine—enzymes that digest carbohydrates, lipids and protein are made here. Pancreas also produces these enzymes and sends them to the small intestine to aid in digestion

Liver produces bile (stored in the gall bladder)—sent to small intestine—aids in the digestion of lipids

Then the products of digestion are absorbed into the blood stream from the smlall intestine and can bone used to build new carbohydrates, lipids and proteins

Any undigested food then travels to the large intestine, where water is absorbed, then becomes faeces and will be equated from the body via the anus

Question 18

Amylase
Substrate, products, site of production, site of action

Answer 18

Starch
Maltose
Salivary glands—site of action: mouth
Pancreas and small intestine—site of action: small intestine

Question 19

Carbohydrate

Substrate, products, site of production, site of action

Answer 19

Carbohydrates
Simple sugars, e.g glucose
Pancreas and small intestine—small intestine

Question 20

Proteases

Substrate, products, site of production, site of action

Answer 20

Protein
Amino acids
Stomach—stomach
Pancreas and small—small intestine

Question 21

Lipases

Substrate, products, site of production, site of action

Answer 21

Lipids
1 glycerol and 3 fatty acids
Pancreas and small intestine—small intestine

Question 22

Protease enzyme has a optimum pH of 2
How is optimum pH maintained in stomach

Answer 22

HCl acid

Question 23

Bile key functions

Answer 23

Neutralisation—so the enzymes working on the food after coming from the stomach wouldn’t denature as they would not be at the optimum pH

Emulsification—breaks lipids into smaller droplets which increases the surface area so more lipase enzymes able to bind to and digest lipids—>faster digestion