Paper 1: Topic 2 Organisation - Digestive system & enzymes (LV)

Question 1

Define the term enzyme

Answer 1

A biological catalyst that speeds up the rate of a chemical reaction without being altered or used up itself in the reaction

Question 2

State what type of molecule enzymes are

Answer 2

Proteins

A large molecule made from many amino acids joined together

Hint: remember all proteins are made by ribosomes

Question 3

State 4 factors that affect the activity of enzymes

Answer 3

pH

temperature

concentration of enzyme

concentration of substrate

Question 4

Define the term substrate

Answer 4

A chemical that is used in the reaction and is converted to the product

Question 5

Define the term product

Answer 5

The chemical that is made at the end of a chemical reaction

Question 6

State the two different types of chemical reaction

Answer 6

Catabolic

Anabolic

Question 7

Define the terms

a) catabolic reaction
b) anabolic reaction

Answer 7

a) catabolic:

A chemical reaction that breaks down the substrate(s) into smaller product(s)

b) anabolic:

A chemical reaction that builds up smaller substrates into a larger molecule (the product)

Question 8

Define the term metabolism

Answer 8

The sum total of all the chemical reactions that take place inside a cell

Question 9

Describe the structure of an enzyme

Answer 9

An enzyme has a dip on its surface (called the active site)

The active site has a complementary shape to its specific substrate

Question 10

Explain why enzymes are specific

Answer 10

Each enzyme has an active site that is uniq​ue to specific substrates for one chemical reaction

The active site is only complementary to one substrate

Hence each enzyme can only catalyse one specific reaction

Question 11

Describe the relationship between the active site and the substrate

Answer 11

They are complementary to each other

Hint: do NOT say they are the same as each other

Question 12

Name the model that describes how enzymes work

Answer 12

Lock and key theory

IMPORTANT:

When annotating a diagram remember to add descriptions onto your diagram e.g.

• the active site is complementary to the substrate
• the substrate is specific to the enzyme’s active site

Question 13

Explain the lock and key theory model

Answer 13

The active site on an enzyme acts as a lock

The complementary substrate acts as a key that fits into the active site (lock)

This forms the enzyme-substrate complex

The chemical reaction then takes place

The substrate is converted to the product

The product is released

The enzyme remains unaltered and can carry out further identical reactions

Question 14

Define the term enzyme-substrate complex

Answer 14

An enzyme that has it specific substrate bound to its active site

Question 15

Explain the effect of low temperatures on enzyme activity

Answer 15

• At low temperatures both the substrate and enzyme have very little kinetic energy
• There are very few collisions between the substrate and the active site
• Very few enzyme-substrate complexes form
• Hence very little product is made in any given period of time
• The enzyme is described as inactive
• The rate of reaction is very low

Question 16

Explain the effect of high temperatures on enzyme activity

Answer 16

• At high temperatures both the substrate and enzyme have a high amount of kinetic energy
• There are many collisions between the substrate and the active site
• However the high temperature changes the shape of the enzyme
• This alters the shape of the active site
• The substrate is no longer complementary to the active site
• NO enzyme-substrate complexes form
• NO product is made in any given period of time
• The enzyme is described as denatured
• The rate of reaction is zero

Question 17

Why is it incorrect to say an enzyme is dead?

Answer 17

All enzymes are just proteins

They are not living and so can’t be killed

They are just specialised chemical molecules

Question 18

Describe the effect the optimum temperatures on enzyme activity

Answer 18

• At the optimum temperatures both the substrate and enzyme have very high kinetic energy
• There are many collisions between the substrate and the active site
• High numbers of enzyme-substrate complexes form
• Hence a lot of product is made in any given period of time
• The enzyme is described as working at its maximum rate
• The rate of reaction is at its maximum

Question 19

What is the typical optimum temperature for human enzymes?

Answer 19

37^oC

Question 20

Describe how an enzyme is denatured and the effect this has

Answer 20

How an enzyme is denatured:

• At high temperatures the bonds holding the enzyme in its specific shape break
• This changes the shape of the enzyme including the shape of the active site

The effect of denatureing an enzyme:

• The active site is no longer complementary to its substrate
• So no reaction can take place and no product is made

Question 21

Name an human enzyme that works at an optimal pH of 1-2 (acidic)

Answer 21

Pepsin

Remember this enzyme is found in the stomach and must be able to work efficiently in acidic conditions due to the hydrochloric acid in the stomach

Question 22

State 2 human enzymes that work at an optimal pH of 7 (neutral)

Answer 22

Amylase

Catalase

Lipase

Carbohydrases

Proteases (except trypsin)

Question 23

How do you calculate the rate of reaction?

Answer 23

Amount of product formed divided by the time

Question 24

In an experiment how can you control the temperature to ensure you are carrying out a fair test?

Answer 24

Use a thermostatically controlled water bath

Hint: don’t just say water bath

Question 25

In an experiment how can you control the pH to ensure you are carrying out a fair test?

Answer 25

Use **buffer** solutions to keep the pH of the experiment constant Buffers work by keeping the pH constant

Question 26

State the 3 main groups of enzymes that are involved in digestion

Answer 26

Lipases Carbohydrases Proteases

Question 27

Describe the action of a protease enzyme

Answer 27

Proteases break proteins down into amino acids

Question 28

Describe the action of a lipase enzyme

Answer 28

Lipases break lipids down into 3 fatty acids and 1 glycerol ***Hint:*** remember to state the number of each type of product made

Question 29

Describe the action of a carbohydrase enzyme

Answer 29

Carbohydrases break complex carbohydrase down into simpler sugars e.g. glucose

Question 30

Give an example of a carbohydrase. State its substrate and product

Answer 30

Carbohydrase = amylase Substrate = starch Product = maltose

Question 31

State 3 places in the human body where amylase is produced

Answer 31

Mouth (salivary amylase) Pancreas Small intestine

Question 32

State 3 places in the human body where proteases are produced

Answer 32

Pancreas Stomach Small intestine

Question 33

State 2 places in the human body where lipase is produced

Answer 33

Pancreas Small intestine

Question 34

Which 2 organs in the human body produce carbohydrases, lipases and proteases

Answer 34

Pancreas Small intestine

Question 35

Describe what happens to the fatty acids and glycerol that are produced after digestion

Answer 35

* The fatty acids and glcyerol are absorbed into the blood stream * This absorption occurs in the small intestine * They are absorbed into the lacteals * They are then **used by cells to make _new_ lipids** * The new lipids are **used to make _new_ cell membranes** for the production of new cells or **stored for energy**

Question 36

Describe what happens to the amino acids that are produced after digestion

Answer 36

* The amino acids are absorbed into the blood stream * This absorption occurs in the small intestine * They are absorbed into the blood plasma * They are then **used by cells to make _new_ proteins** * The proteins are then used to make new cells for tissue growth and organ growth

Question 37

Describe what happens to the simple sugars that are produced after digestion

Answer 37

The simple sugars are absorbed into the blood stream This absorption occurs in the small intestine They are absorbed into the plasma They are then **used by cells to make _new_ carbohydrates** The new carbohydrates are used in respiration to produce ATP

Question 38

What is the function/role of bile?

Answer 38

Bile emulsifies lipids It breaks large lipids into smaller droplets of lipid This increases the surface area for the lipase enzymes Hence the rate of reaction increases

Question 39

How does the emulsification of lipids affect the activity of lipases?

Answer 39

Emulsifying the fats into smaller droplets increases the surface area This increases the activity of lipase

Question 40

Explain why the pH falls (becomes more acidic) in during a reaction catalysed by lipase

Answer 40

Lipase breaks down lipids into 3 fatty acids and glycerol As more lipids are broken down more fatty acids are produced The greater the accumulation of fatty acids the more the pH decreases (becomes more acidic)

Question 41

State where bile is stored

Answer 41

Gall bladder

Question 42

Explain why it is important bile is released into the small intestine to allow digestion to occur

Answer 42

* The contents of the stomach are acidic (from the hydrochloric acid) * The acidic contents pass into the small intestine * The enzymes in the small intestine have an alkaline optimal pH * The bile neutralises the acid to create the optimal pH for the enzymes of the small intestine

Question 43

State where bile is produced

Answer 43

Liver

Question 44

What test would you use to detect the presence of reducing sugars?

Answer 44

Benedict’s test

Question 45

Describe the results of a positive Benedict’s test

Answer 45

The solution would change from blue to green to yellow to orange to brick red

Question 46

What colour is a negative Benedict’s test?

Answer 46

Blue

Question 47

Describe how to carry out a Benedict’s test

Answer 47

1. Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered) 2. Add 5 cm³ of the food sample to a test tube 3. Add 10 drops of Benedict’s solution 4. Heat the food sample in a water bath at 75^oC for 5 minutes

Question 48

State 3 safety precautions you should take when carrying out a Benedict’s test

Answer 48

1. Wear safety goggles 2. Make sure the test tube is pointing away from you in the water bath 3. Do not ingest the Benedict’s solution – it is harmful

Question 49

What test would you use to detect the presence of starch?

Answer 49

Iodine solution

Question 50

Describe the results of a positive starch test

Answer 50

A blue-black solution

Question 51

What colour is a negative starch test?

Answer 51

A yellow-brown solution

Question 52

Describe how to carry out a starch test

Answer 52

1. Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered) 2. Place the food sample in the well of a spotting tile 3. Add a few drops of iodine solution onto the food sample with a pipette 4. Observe the colour change

Question 53

State 2 safety precautions you should take when carrying out a starch test

Answer 53

Wear safety goggles Do not ingest the iodine solution – it is harmful

Question 54

What test would you use to detect the presence of lipids?

Answer 54

Sudan III stain solution

Question 55

Describe the results of a positive Sudan III test

Answer 55

2 layers will form The top layer will be bright red

Question 56

Describe the results of a negative Sudan III test

Answer 56

No separate red layer will form

Question 57

Describe how to carry out a Sudan III test

Answer 57

1. Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first. It does NOT need to be filtered) 2. Place the food sample in a test tube 3. Add 3 drops of Sudan III stain solution onto the food sample with a pipette 4. Gently shake the test tube 5. Observe the colour change

Question 58

What test would you use to detect the presence of proteins?

Answer 58

Biuret reagent

Question 59

Describe the results of a positive Biuret test

Answer 59

Purple solution

Question 60

Describe the results of a negative Biuret test

Answer 60

Blue solution

Question 61

Describe how to carry out a Biuret test

Answer 61

1. Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered) 2. Add 5 cm³ of the food sample to a test tube 3. Add 5 cm³ of Biuret solution 4. Gently shake the test tube 5. Observe the colour change

Question 62

Give 2 properties that amino acids, glycerol, simple sugars and fatty acids have that enable them to be absorbed into the plasma

Answer 62

Small and soluble

Question 63

Explain the purpose of digestion

Answer 63

To use enzymes to break down large insoluble molecules into small and soluble molecules that can be absorbed into the bloodstream