Unit 14: Human Digestive System

Question 1

Why do we need food?
* Living things require nutrients to:
3pt (3 subpt)

Answer 1

• provide energy to do work
• maintain a healthy body
• grow new cells and tissues
• repair damaged tissues
• Important nutrients: carbohydrates, proteins and fats
• If one part of the digestive system is not functioning, all the other parts would be affected & food cannot be completely digested!

Question 2

Digestion
2pt

Answer 2

• Digestion is the breaking down of large insoluble food molecules into smaller soluble molecules that can be absorbed by the body.
• There are 2 types of digestion processes: Physical and Chemical

Question 3

Physical digestion
definition 2pt + importance 1pt

Answer 3

Physical
* It is a mechanical/physical breakdown of large pieces of food into smaller pieces
* No new products are being formed

To increase the surface area for enzymes to work on

• Examples of physical digestion:
• Chewing action of food in the mouth
• Peristalsis in the oesophagus
• Churning action in the stomach
• Emulsification in the small intestine

Question 4

Chemical digestion
definition 2pt + importance 1pt

Answer 4

• It is a process whereby large and complex substances are broken down into smaller and simpler substances by the action of enzymes
• New products are formed To allow food substances to enter the bloodstream through the intestinal wall via diffusion (or absorption??)

Question 5

What are Enzymes?
5pt

Answer 5

• Enzymes are complex proteins that speed up the rate of chemical reactions
• Digestive enzymes in particular speed up the process of digestion by breaking up large food molecules into smaller food molecules
• Enzymes are highly specific. Each enzyme can only work on one type of food substance!
• Enzymes are not used up after the digestion. They remain chemically unchanged.

There are 4 types of enzymes: amylase, maltase, lipase and protease!

Question 6

Food tests & Digestive Enzymes
4pt
Types of food
Chemical test reagent
Observation

Answer 6

Starch
Iodine test
Brown colour of iodine solution turns blue-black

Proteins
Biuret test (made up of sodium hydroxide and copper(II) sulfate)
Blue solution of Biuret reagent turns violet

Fat
Emulsification test (containing ethanol and water)
Milky solution is observed after shaken

Glucose
Benedict’s Test
Brick-red precipitation is observed (High amount of reducing sugar present)

Question 7

Food Type
Carbohydrates (e.g. bread, potatoes, fruits, vegetables, rice, starch)

Enzyme
Final Product
Place of Ingestion

Answer 7

Initial Product
Enzyme
Final Product
Place of Ingestion

Carbohydrates
Amylase
(Carbohydrase)
Maltose
Mouth
Oesophagus (continued from mouth; no new enzymes mixed)

Maltose
Small Intestine
Maltase
(Carbohydrase)
Glucose
Small Intestine

• Amylase breaks down food into maltose, Maltase breaks down maltose into glucose
• The ratio will always remain the same!
• Carbohydrase = both Amylase and Maltase enzymes

Question 8

Food Type
Proteins
(e.g. fish, meat, eggs, dairy products, vegetables)

Enzyme
Final Product
Place of Ingestion

Answer 8

Initial Product
Enzyme
Final Product
Place of Ingestion
Initial Product

Proteins
Protease
Amino Acids
Stomach
Small Intestine

Question 9

Food Type
Fats
(e.g. oil, fast or processed food, cakes, sweets & desserts)

Enzyme
Final Product
Place of Ingestion

Answer 9

Initial Product
Enzyme
Final Product
Place of Ingestion

Fats
Lipase
Glycerol and fatty acids
Small Intestine

Ratio of Glycerol to Fatty acids will always be 1:3 !!!

Question 10

The Digestive System
how many processes & definition? (4pt)

Answer 10

1. Ingestion
   - The intake of food in the mouth
2. Digestion
   - The physical as well as chemical break down of large insoluble food molecules to smaller soluble food molecules
   - Begins in the mouth, continues in oesophagus (but no new enzymes added), stomach and ends in small intestine
3. Absorption
   - The entry of soluble food molecules into the blood and then cells
   - Occurs in the small and large intestine
4. Egestion
   - The removal of undigested food from the body stored in the rectum temporarily then through the anus

Question 11

What is ingestion?

Answer 11

• The intake of food in the mouth

Question 12

What is digestion?

Answer 12

• The physical as well as chemical break down of large insoluble food molecules to smaller soluble food molecules
• Begins in the mouth, continues in oesophagus (but no new enzymes added), stomach and ends in small intestine

Question 13

What is absorption?

Answer 13

• The entry of soluble food molecules into the blood and then cells
• Occurs in the small and large intestine

Question 14

What is Egestion?

Answer 14

• The removal of undigested food from the body stored in the rectum temporarily then through the anus

Question 15

What is peristalsis

Answer 15

• The whole alimentary canal is made up of muscles
• Peristalsis is a series of wave-like muscle contractions and relaxation that helps to squeeze food along the alimentary canal.

Question 16

1. Mouth
   3pt, 1 1 2

Answer 16

• Ingestion:
• The intake of food through the mouth is called ingestion
• Physical digestion:
• Chewing by the teeth cuts and grinds food into smaller pieces.
  o This increases the surface area of the food which makes digestion by enzymes faster
• Chemical digestion:
• digested in the mouth
• Starch molecules are broken down by enzyme salivary amylase (a type of carbohydrase) into maltose molecules

Question 17

2. Oesophagus (gullet)
   2pt 1 1

Answer 17

• Physical digestion:
• Peristalsis helps move the food down from the mouth to the stomach within about 10 seconds
• Chemical digestion:
• No enzymes are secreted here. But the digestion of starch by salivary amylase continues here as the food moves down the oesophagus!

Question 18

3. Stomach
   2pt 3 2sspt 2 3sspt

Answer 18

3. Stomach
   * Physical digestion:
   - The churning action (peristalsis) by the muscular walls of the stomach causes food to break up further into smaller pieces. It also helps food mix with gastric juice.
   - Gastric juice contains water, hydrochloric acid and proteases.
   - Functions of hydrochloric acid (also function of stomach):
4. kills bacteria in the food
5. provides an acidic environment for proteases to work effectively
   * Chemical digestion:
   - Complex proteins are broken down into simpler proteins (*polypeptides) by enzyme proteases in the gastric juice

• Our stomach contains hydrochloric acid, which is highly acidic and is capable of dissolving an iron nail.
• The stomach is adapted to withstand the corrosive effect of the acid as:
  1. Stomach cells secrete a thick layer of mucus.
• Mucus acts as a barrier between the acid and the stomach walls
  2. Hydrochloric acid is only produced when the stomach contains food. When the stomach is empty, hydrochloric acid is not secreted.
  3. In any case, the stomach lining is replaced every three days by the constant production of new cells in the inner lining.

Question 19

4. Small Intestine
   3pt 3 4 4

Answer 19

4. Small Intestine
   * 2 main processes: emulsification and absorption
   * Physical digestion:
   - Peristalsis continues to occur here to move food along the alimentary canal
   - Bile carries out the process of emulsification, whereby large fat globules are broken down into smaller fat droplets.
   o This increases the surface area of fats so that they can be digested by lipases faster.
   - Bile is not an enzyme. It only physically breaks down fat. Emulsification is a form of physical digestion.

• Chemical digestion:
• Remaining starch molecules are broken down by amylase (a type of carbohydrase) into maltose
• Maltose molecules are broken down by maltase (a type of carbohydrase) into glucose molecules
• Simple proteins are broken down by protease into amino acids
• Fats are broken down by lipase into glycerol and fatty acids
• Absorption:
• Absorption of food is the movement of food molecules through the walls of the small intestine into the bloodstream.
• Food stays in the small intestine for about 5 hours.
• The end products of complete digestion of food are glucose molecules, amino acids and Glycerol and fatty acids.
• These digested small and soluble food molecules diffuse through the walls of the small intestine and into the blood vessels that surround it. Blood carries these food molecules to the body cells for life processes (e.g. respiration).

Question 20

• Adaptations of the Small Intestine for Increased Absorption (4pt)

Answer 20

The small intestine is very long (~6 m)
This increases the time for more complete absorption of food

The small intestine has numerous folds in the inner walls, consisting of structures such as villi and microvilli
This increases the surface area to volume ratio for faster absorption of food substances

The small intestine is supplied with many blood capillaries
The blood capillaries help to transport away absorbed nutrients quickly, maintaining a steep concentration gradient for continued absorption to occur (by diffusion)

The villi epithelium is very thin, only one cell layer thick
This allows for easier absorption by diffusion of food molecules across the thin villi epithelium into the bloodstream

Question 21

5. Small Intestine and its associated organs (2pt, 3sp)

Answer 21

• food in the small intestine is mixed with:
  1. Bile produced by the liver and secreted from the gall bladder
  2. Pancreatic juice from the pancreas
  3. Intestinal juice that it produces itself (small intestine)
• The gall bladder, liver and pancreas are not part of the alimentary canal as food does not pass through them!

Question 22

Function of gall bladder?

Answer 22

stores bile and releases bile into small intestine only when food is present

Question 23

Function of pancreas?

Answer 23

produces pancreatic juice which contains enzymes that can help with digestion in the small intestine

Question 23

Function of liver?

Answer 23

produces bile

Question 24

6. Large Intestine
   3pt 1 3 2

Answer 24

• No digestion occurs here
• Only food that cannot be digested reaches the large intestine
• Absorption:
• As food passes through the large intestine, a lot of water is absorbed back to the body into the bloodstream
• Here, only water and mineral salts are absorbed!
• Fibres are not absorbed by the large intestine (undigested fibres)
• Egestion:
• Food stays in the large intestine for up to 24 hours (or longer if person has constipation)
• The indigestible material (faeces) is stored in the rectum temporarily and expelled through the anus by a process known as egestion.

Question 25

End products of Digestion
4pt, 3 1 1 1

Answer 25

• What are the end products of digestion used for?
• Provide energy for daily activities
• Promote growth of new cells and tissues
• Repair damaged tissues in times of injury or illness
• Keep us in good health
• Glucose (from amylase then maltase enzyme)
• Cells in our body use glucose during respiration to provide energy
• Amino acids (from protease enzyme)
• Amino acids combine to form proteins, which are used for growth of new cells and repair of damaged tissues
• Glycerol and fatty acids (from lipase enzyme)
• Glycerol and fatty acids combine again to form fats which are stored in the body. Fats are used to provide energy and keep our bodies warm

Question 26

Issues affecting the digestive system
3pt, 2 1 1

Answer 26

• Gastric pain
• Antacids are used to reduce excess stomach acid. They work by neutralising the acid, preventing inflammation, relieving pain and discomfort and allow the mucus layer and stomach lining to mend
• Mg(OH)2(s) + 2HCl(aq) → MgCl2(aq) + 2H2O(l) (neutralisation)
• Constipation
• Can be caused by not eating enough fibre, such as fruit, vegetables and cereals
• Food poisoning
• Caused by the presence of harmful bacteria in the contaminated food or drinks

Question 27

Starch (for Amylase)

Iodine Test
positive and negative test observation and conclusion?

Answer 27

1. Add 1 drop of iodine solution on white tile
2. Followed by 1 drop of the test solution and mix well.
3. Observe any colour change.

Positive
Mixture turned from orange to blue-black.

Positive
Starch is present.

Negative
Mixture remained orange.

Negative
Starch is absent.

Question 28

Reducing sugar (for Maltose)

Benedict’s Test

positive and negative test observation and conclusion?

Answer 28

As colour of rainbow goes from red to blue, the amount of reducing sugar decreases to 0 at blue!

Positive
Brick red precipitate was obtained from the blue mixture. (solid)

Orange precipitate was obtained from the blue mixture.

Yellow precipitate was obtained from the blue mixture.

Green precipitate was obtained from the blue mixture.

Negative
Mixture remained blue.

Positive
A large amount of reducing sugar is present.

A moderate amount of reducing sugar is present.

A low amount of reducing sugar is present.

A trace amount of reducing sugar is present.

Negative
Reducing sugar is absent.

Question 29

1. Mouth
   * Ingestion:
   1pt

Answer 29

• Ingestion:
• The intake of food through the mouth is called ingestion

Question 30

1. Mouth
   * Physical digestion:
   1pt and purpose

Answer 30

• Physical digestion:
• Chewing by the teeth cuts and grinds food into smaller pieces.
  o This increases the surface area of the food which makes digestion by enzymes faster

Question 31

1. Mouth
   * Chemical digestion:
   2pt

Answer 31

• Chemical digestion:
• digested in the mouth
• Starch molecules are broken down by enzyme salivary amylase (a type of carbohydrase) into maltose molecules

Question 32

2. Oesophagus (gullet)
   * Physical digestion:
   1pt

Answer 32

• Peristalsis helps move the food down from the mouth to the stomach within about 10 seconds

Question 32

2. Oesophagus (gullet)
   1pt

Answer 32

• No enzymes are secreted here. But the digestion of starch by salivary amylase continues here as the food moves down the oesophagus!

Question 33

3. Stomach
   * Physical digestion:
   3pt 2subpt
   1pt physical digestion 2pts function of hcl

Answer 33

• The churning action (peristalsis) by the muscular walls of the stomach causes food to break up further into smaller pieces. It also helps food mix with gastric juice.
• Gastric juice contains water, hydrochloric acid and proteases.
• Functions of hydrochloric acid (also function of stomach):
  1. kills bacteria in the food
  2. provides an acidic environment for proteases to work effectively

Question 34

3. Stomach
   * Chemical digestion:
   2pt 3subpt

Answer 34

• Complex proteins are broken down into simpler proteins (*polypeptides) by enzyme proteases in the gastric juice
• Our stomach contains hydrochloric acid, which is highly acidic and is capable of dissolving an iron nail.
• The stomach is adapted to withstand the corrosive effect of the acid as:
  1. Stomach cells secrete a thick layer of mucus.
• Mucus acts as a barrier between the acid and the stomach walls
  2. Hydrochloric acid is only produced when the stomach contains food. When the stomach is empty, hydrochloric acid is not secreted.
  3. In any case, the stomach lining is replaced every three days by the constant production of new cells in the inner lining.

Question 35

4. Small Intestine
   what are the 2 main processes in the small intestine?

Answer 35

emulsification
absorption

Question 36

4. Small Intestine
   * Physical digestion:
   3pt

Answer 36

• Physical digestion:
• Peristalsis continues to occur here to move food along the alimentary canal
• Bile carries out the process of emulsification, whereby large fat globules are broken down into smaller fat droplets.
  o This increases the surface area of fats so that they can be digested by lipases faster.
• Bile is not an enzyme. It only physically breaks down fat. Emulsification is a form of physical digestion.

Question 37

4. Small Intestine
   Chemical Digestion
   4pt

Answer 37

• Chemical digestion:
• Remaining starch molecules are broken down by amylase (a type of carbohydrase) into maltose
• Maltose molecules are broken down by maltase (a type of carbohydrase) into glucose molecules
• Simple proteins are broken down by protease into amino acids
• Fats are broken down by lipase into glycerol and fatty acids

Question 38

4. Small Intestine
   Absorption
   4pt

Answer 38

• Absorption of food is the movement of food molecules through the walls of the small intestine into the bloodstream.
• Food stays in the small intestine for about 5 hours.
• The end products of complete digestion of food are glucose molecules, amino acids and Glycerol and fatty acids.
• These digested small and soluble food molecules diffuse through the walls of the small intestine and into the blood vessels that surround it. Blood carries these food molecules to the body cells for life processes (e.g. respiration).

Question 39

4. Small Intestine
   Adaptation
   The small intestine is very long (~6 m)
   Function?

Answer 39

This increases the time for more complete absorption of food

Question 40

4. Small Intestine
   Adaptation
   The small intestine has numerous folds in the inner walls, consisting of structures such as villi and microvilli
   Function?

Answer 40

This increases the surface area to volume ratio for faster absorption of food substances

Question 41

4. Small Intestine
   Adaptation
   The small intestine is supplied with many blood capillaries
   Function?

Answer 41

The blood capillaries help to transport away absorbed nutrients quickly, maintaining a steep concentration gradient for continued absorption to occur (by diffusion)

Question 42

4. Small Intestine
   Adaptation
   The villi epithelium is very thin, only one cell layer thick
   Function?

Answer 42

This allows for easier absorption by diffusion of food molecules across the thin villi epithelium into the bloodstream

Question 43

6. Large Intestine
   does digestion occur here?

Answer 43

• No digestion occurs here
• Only food that cannot be digested reaches the large intestine

Question 44

6. Large Intestine
   Absorption 2pt

Answer 44

• As food passes through the large intestine, a lot of water is absorbed back to the body into the bloodstream
• Here, only water and mineral salts are absorbed!
• Fibres are not absorbed by the large intestine (undigested fibres)

Question 45

6. Large Intestine
   Egestion 2pt

Answer 45

• Food stays in the large intestine for up to 24 hours (or longer if person has constipation)
• The indigestible material (faeces) is stored in the rectum temporarily and expelled through the anus by a process known as egestion.