Digestive System

Question 1

Two purposes of the digestive system

Answer 1

• break down complex food substances
• provides very large surface area for maximum food adsorption

Question 2

Function of the mouth in digestion

Answer 2

• mechanically breaks down food

Question 3

Salivary glands

Answer 3

• produce amylase enzyme in the saliva

Question 4

Gullet (oesophagus)

Answer 4

• food travels down

Question 5

Stomach function

Answer 5

• pummels the food with its muscular walls
• produces the protease enzyme, pepsin
• produces hydrochloric acid for two reasons:
To kill bacteria
To give the right pH for the protease enzyme to work (pH 2 - acidic)

Question 6

Pancreas function

Answer 6

• produces protease, amylase and lipase enzyme
• releases these into the small intestine

Question 7

Small intestine function

Answer 7

• produces protease, amylase and lipase enzymes to complete digestion
• this is where the digested food is absorbed out of the digestive system into the blood

Question 8

Liver function

Answer 8

• where bile is produced
• main metabolic organ of the body
• detoxifies poisons, e.g. ethanol
• urea production
• breaks down red blood cells and storing the iron
• passage of breakdown product to blood for excreation via kidney
• removal of lactic acid, re conversion to glucose and glycogen

Question 9

Gall bladder function

Answer 9

• where bile is stored before it’s released into the small intestine

Question 10

Large intestine function

Answer 10

Where excess water is absorbed from the food

Question 11

Rectum function

Answer 11

Where faeces are stored before they are excreted from the anus

Question 12

What is the function of digestive enzymes?

Answer 12

• starch, proteins and fats are BIG molecules - too big to pass through walls of digestive system
• digestive break these BIG molecules into smaller ones like sugars (glucose and maltose) amino acids, glycerol and fatty acids
• smaller, soluble molecules can pass easily through walls of the digestive system, allowing them to be absorbed into the bloodstream

Question 13

Amylase converts carbohydrates into simple sugars

Answer 13

• amylase breaks down starch
• into maltose (and other sugars, e.g. dextrins)
• made in salivary glands, the small intestine and the pancreas

Question 14

Proteases convert proteins into amino acids

Answer 14

• proteases are made in three places - stomach (called pepsin here), pancreas and the small intestine

Question 15

Lipases convert lipids into glycerol and fatty acids

Answer 15

• lipids = fats and oils
• made in pancreas and small intestine

Question 16

Food tests for sugars

Answer 16

Benedict’s Test
• Prepare a food sample and transfer to test tube.
• Prepare a water bath set to 75•C
• Add some Benedict’s solution to the test tube (10 drops) with pipette
• place test tube in water bath using a test tube holder and leave for 5 mins - make sure tube is pointing away from you
• if sample turns brick red, positive

Question 17

Food test for starch

Answer 17

• make a food sample and transfer to test tube
• add a few drops of iodine solution and gently shake
• positive test - blue/black

Question 18

Food test for proteins

Answer 18

• prepare sample of food and transfer to a test tube
• add some biuret solution (2cmcubed) and mix contents of tube by gently shaking
• turns purple if positive

Question 19

Food test for lipids

Answer 19

• prepare a sample and transfer to test tube
• use pipette and add 3 drops of Sudan III stain solution to test tube and gently shake
• positive - mixture separates into two layers - top layer will be bright red

Question 20

Enzymes

Answer 20

• biological catalysts
• control rate of reactions
• large protein molecules
• each enzyme acts with a particular substrate
• shape is vital for enzymes to function

Question 21

Lock and key theory

Answer 21

• substrate fits into the specific active site of an enzyme
• substrate splits into products which leave the active site

Question 22

Types of metabolic reactions sped up by enzymes

Answer 22

• building large molecules from smaller ones - starch, glycogen or cellulose from glucose, lipids from fatty acids, proteins from amino acids
• changing one molecule to another, e.g. glucose to fructose
• breaking down large molecules to small ones during digestion - e.g. carbohydrates, proteins, lipids

Enzymes make sure each specific reaction doesn’t interfere with another

Question 23

Factors effecting enzyme action

Answer 23

• temperature - higher rate increases at first, but once optimum temp is surpassed the enzymes will become denatured (37degrees)
• pH - if too high/low, pH interferes with bonds holding enzymes together - changes shape of active sight and denatures the enzyme (optimum is usually 7 - but for pepsin (for proteins) in the stomach, it is pH 2

Question 24

Best conditions for enzymes

Answer 24

• acidic in stomach (protease)
• produce hydrochloric acid to maintain low pH
• enzymes made in pancreas and small intestine - alkaline

Question 25

Role of the liver

Answer 25

• main metabolic organ of the body
• detoxifies poisons
• urea production
• breaking down red blood cells and storing the iron
• passage of breakdown product blood for excretion via kidney
• removal of lactic acid