Digestive System.

Question 1

Food taken into the body goes through 4 different stages during its passage through the alimentary canal: Name them.

Answer 1

• Ingestion.
• Digestion.
  - Mechanical digestion.
  - Chemical digestion.
• Absorption.
• Assimilation.
• Egestion.

Question 2

Define ingestion.

Answer 2

The taking of substances, e.g. food and drink, into the body through the mouth.

Question 3

Define mechanical or physical digestion.

Answer 3

The breakdown of food into smaller pieces without chemical change to the food molecules.

Question 4

Define chemical digestion.

Answer 4

The breakdown of large, insoluble molecules into small, soluble molecules that can be absorbed.

Question 5

Define absorption.

Answer 5

The movement of small food molecules and ions through the wall of the intestine into the blood.

Question 6

Define assimilation.

Answer 6

The uptakes and use of nutrients by cells

Question 7

Define egestion.

Answer 7

The removal of undigested food from the body as faeces.

Question 8

Define digestion.

Answer 8

The breakdown of food.

Question 9

What is the role of physical digestion?

Answer 9

Physical digestion increase the surface area of food for the action of enzymes in chemical digestion.

Question 10

What are three ways in which mechanical digestion is mainly carried out?

Answer 10

It is mainly carried out by the chewing action of the teeth, the churning action of the stomach, and the emulsification of fats by bile in the duodenum.

Question 11

The differing shapes and sizes of teeth enable them to perform slightly different functions:

Answer 11

Incisors - chisel-shaped and sharp for biting and cutting.

Canines - pointed for tearing and ripping.

Premolars - Bicuspid, two roots, flat surfaces with ridges at the edges for chewing and grinding up food.

Molars - Tricuspid, three roots, flat surfaces with ridges at the edges for chewing and grinding up food.

Question 12

Teeth are held firmly in the bone of the jaw and the gums. What is the use of teeth?

Answer 12

They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly.

Question 13

Bile (physical digestion) is secreted into the small intestine where it has two effects:

Answer 13

It is alkaline to neutralize the hydrochloric acid which comes from the stomach providing the alkaline conditions needed in the small intestine.

It emulsifies fat turning large droplets of fat into lots of smaller droplets, thus providing a larger surface area over which the lipase enzymes can work.

Question 14

Where is amylase secreted?

Answer 14

Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas).

Question 15

What is the function of the following enzymes:

• Amylase.
• Proteases.
• Lipase.

Answer 15

• Amylase breaks down starch to simple reducing sugars (glucose).
• Proteases break down protein into amino acids in the stomach and small intestine.
• Lipase breaks down fats and oils (lipids) into fatty acids and glycerol.

Question 16

Where is protease (trypsin) produced and secreted?

Answer 16

Trypsin is produced in the pancreas and secreted into the duodenum

Question 17

Where is lipase produced and secreted?

Answer 17

Lipase enzymes are produced in the pancreas and secreted into the duodenum.

Question 18

The stomach produces several fluids which together are known as gastric juice and one of the fluids produced is hydrochloric acid.

Describe the functions of hydrochloric acid in gastric juice.

Answer 18

The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for enzymes to work at their fastest rates.

Question 19

How does a low pH in the stomach kill bacteria in food?

Answer 19

The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life.

Question 20

Describe the digestion of starch in the digestive system.

Answer 20

Amylase breaks down starch to maltose → maltase breaks down maltose to glucose on the membranes of the epithelium lining the small intestine.

Question 21

Describe the digestion of protein by proteases in the digestive system.

Answer 21

Pepsin breaks down protein in the acidic conditions of the stomach → trypsin breaks down protein in the alkaline conditions of the small intestine.

Question 22

Explain the use of bile.

Answer 22

Bile is an alkaline mixture that consists of bile salts that emulsify fats, increasing the surface area for lipase action, and neutralize the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action.

NOTE - Bile does not contain any enzymes, it contains bile salts.

Question 23

Where is water absorbed?

Answer 23

Water is absorbed in both the small intestine and the colon, but most absorption of water also happens in the small intestine.

Question 24

Where does absorption take place?

Answer 24

Absorption takes place in the second section of the small intestine, the ileum.

Question 25

How is the ileum adapted for absorption?

Answer 25

The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi.
These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently.

Question 26

What does microvillus do?

Answer 26

Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients.

Question 27

The wall of the villus is only __ cell thick. What does this mean?

Answer 27

The wall of the villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport.

Question 28

What is the role of the lacteal in the villi?

Answer 28

Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph.

Question 29

The wall of the villus is well supplied with a network of blood capillaries that do what?

Answer 29

Well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood.

Question 30

How many incisors, canines, premolars, molars, and wisdom teeth does an adult human have?

Answer 30

8 incisors.
4 canines.
8 premolars.
12 molars.
4 wisdom teeth.
(32 teeth altogether, excluding wisdom teeth).

Question 31

What are the two functions of the oesophagus?

Answer 31

• A tube that connects the mouth to the stomach where the food bolus goes after being swallowed.
• Wave-like contractions will take place to push the food bolus down without relying on gravity.

Question 32

What are the two functions of the stomach?

Answer 32

• Food is mechanically digested by churning actions while protease enzymes start to chemically digest proteins.
• Hydrochloric acid is present to kill bacteria in food and provide the optimum pH for protease enzymes to work.

NOTE - The stomach is a muscular bag that usually holds about 1 liter of food.

Question 33

What is the function of the duodenum (small intestine)?

Answer 33

The first section of the small intestine is called the duodenum and is where the food coming out of the stomach finishes being digested by enzymes produced here and also secreted from the pancreas.

Question 34

What are the two functions of the ileum (small intestine)?

Answer 34

• Where digested food is absorbed into the blood and lymph.

- The ileum is long and lined with villi to increase the surface area over which absorption can take place.

Question 35

What are the functions of the large intestine?

Answer 35

Water is absorbed from the remaining material in the colon to produce faeces.
Faeces are stored in the rectum and removed through the anus in a process called egestion.

Question 36

What is the function of the liver?

Answer 36

Produces bile to emulsify fats.

Question 37

What is the function of the gall bladder?

Answer 37

Stores bile before releasing it into the duodenum.

Question 38

What is the function of the salivary glands?

Answer 38

Produce saliva containing the enzyme salivary amylase, water and mucus.

NOTE - Saliva is slightly alkaline (pH8) which provides ideal conditions for amylase to work.

Question 39

What is the function of the mouth?

Answer 39

The mouth is where mechanical digestion takes place:

• Teeth chew food to break it into smaller pieces and increase its surface area to volume ratio.
• The food is shaped into a bolus by the tongue and lubricated in saliva so it can be swallowed easily.

Question 40

How does physical digestion take place in the stomach?

Answer 40

The stomach muscles churn the food to mix it with gastric juices and form a creamy liquid called chyme.

Question 41

Chemical digestion in the stomach: The stomach lining contains digestive glands.
These glands produce three important gastric juices:

Answer 41

• Protease/pepsin (protein → amino acids/peptides).
• Hydrochloric acid.
• Mucus - for lubrication and to protect the stomach lining from digestion.

Question 42

Does the digestion of carbohydrates continue in the stomach? Explain your answer.

Answer 42

The pH in the stomach is too acidic for the action of amylase so the digestion of carbohydrates comes to a halt whilst the food is in the stomach.

Question 43

What is the effect of the surface of the ileum being highly folded?

Answer 43

This increases the internal surface area for absorption.

Question 44

Chemical digestion in the duodenum: The digestion of these food molecules is completed in the small intestine, using digestive juices which contain:

Answer 44

• Enzymes secreted by the membrane on the epithelial lining of the intestine wall e.g. maltase.
• Enzymes from the pancreas. The enzymes from the pancreas carry out three tasks:
  Amylase
  Protease/trypsin.
  Lipase (fats and oils → fatty acid and glycerol).