Chap.14: Human Digestive System

Question 1

Define enzymes

Answer 1

They are biological catalysts made up of protein that alter the rate of chemical reactions without being chemically changed at the end of the reaction

Question 2

Characteristics of enzymes

Answer 2

Enzymes are specific and acts only on one type of substance

Question 3

What are the different food tests?

Answer 3

1. Iodine test
2. Biuret test
3. Benedict’s test

Question 4

Describe the iodine test on foods

Answer 4

If starch is present, after adding a few drops of iodine, it will change to a blue-black colour

Question 5

Describe the Benedict’s test

Answer 5

Add 2cmcube of Benedict’s solution to 2cmcube of food solution in a test tube
Shake well
Let it rest in a beaker of boiling water bath

If turns green, very little/no reducing sugar
If turns yellow/orange, moderate amounts of reducing sugars
If turns orange-red, brick-red precipitate, large amounts of reducing sugars

Question 6

Describe the biuret test

Answer 6

Add sodium hydroxide and copper(II)sulfate in small amounts
If solution turns violet, proteins are present

Question 7

What happens is the mouth during eating?

Answer 7

• It is the point of entry for food
• Physical digestion with teeth
• Only starch is digested here by salivary amylase
• Forms maltose

Question 8

What happens in the gullet?

Answer 8

• Longitudinal muscles on the outside
• Circular muscles on the inside
• Movement of food by peristalsis from mouth to stomach

Question 9

What are the characteristics of the stomach?

Answer 9

• It is muscular walls that are thick and well developed
• Peristalsis in the stomach churns and breaks up food
• Stomach is distensible, capable of swelling or strectching

Question 10

What does the stomach contain and what happens in it?

Answer 10

• Gastric juice made up of hyrochloric acid and proteases
• Stomach has mucas lining to protect itself from HCL
• HCL is to kill potentially harmful bacteria in food
• pH value of gastric juice is 2.0, which activates proteases to break down proteins to polypeptides

Question 11

What happens in the small intestine?

Answer 11

• It is the main site of digestion, where carbohydrates, fats and proteins are fully digested and absorbed

Question 12

What happens to the carbohydrates in the small intestine?

Answer 12

• Remaining undigested starch are broken down to maltose (partially digested carbo) by carbohydrases (pancreaticamylase)
• Further digested to glucose (simple sugars) by another carbohydrase in small intestine (maltase)

Starch (Amylase) ———-Maltose (Maltase)———Glucose

Question 13

What is the process of protein digestion on the small intestine?

Answer 13

• Remaining undigested proteins are broken down to polypeptides (partially digested proteins) by proteases (pepsin)
• Further digested to amino acids by another protease

Protein (Pepsin aka Protease)———poplypeptides (Proteases)———amino acids

Question 14

What is the process of fat digestion in the small intestine?

Answer 14

• Only occurs in the small intestine
• Fats are digested to fatty acids and glycerol by lipases

Question 15

In summary, where does proteins, carbohydrates and fats get digested?

Answer 15

Carbohydrates- Mouth, small intestine
Protein- Stomach, small intestine
Fats- Small intestine

Question 16

How does the function of absorbtion work in the small intestine?

Answer 16

1. Nutrient absorbtion: Glucose (simple sugar), amino acids, fatty acids and glycerol are absorbed into the bloodstream with the help of villi
2. Water absorbtion: Most water are absorbed in the small intestine with dissovled nutrients

Question 17

Function of the large intestine?

Answer 17

To absorb excess water from the remaining undigested food matter

Question 18

Function of the rectum

Answer 18

To temporarily store undigested and undigested food matter (faeces)

Question 19

Function of the anus?

Answer 19

To control the expulsion of faeces (bowel movement)

Question 20

Structure and function of the liver?

Answer 20

Structure: Largest gland of the body
Functions:
* Secretes bile (alkaline) which aids digestion of fat by emulsification
* No enzymes present

Question 21

What is the structure and function of the gall bladder?

Answer 21

Structure:
* Greenish-yellow bag attached to the liver
* Gall bladder contracts and forces bile to flow into duodenum via bile duct

Function:
* Temporary storage for bile

Question 22

What are the end products of digestion?

Answer 22

1. Soluble molecules of digested food are now small enough ot be absorbed by the bloodstream
2. Simple sugars are used during repiration to release energy
3. Amino acids are used for tissue repair and growth
4. Fatty acids and glycerol are used to make fats (eg. insulation) in the body