© boardworks ltd 2003 key stage 4 digestion. © boardworks ltd 2003 a slide contains teacher’s...

© Boardworks Ltd 2003

Key Stage 4

Digestion


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The 7 food groups represent large chemicals. These chemicals are often chains of smaller, more useful

chemicals, joined together.

One example is Carbohydrates.

Carbohydrates are made of long chains of identical small sugar molecules.

CarbohydrateSugar molecule


The small sugar molecules are very useful. The body can use them to make…

So the body has to break these large food molecules up into smaller pieces.

ENERGY

However!


It is not enough to cut these foods up into pieces using a knife. This would not release the sugars.

i.e. cutting a loaf of bread (carbohydrate) into slices does not produce sugar.

This is because we can’t release sugars from carbohydrates by physically breaking them up.

Problem One


The chain of sugars is held together by…

Chemical bonds.

Chemical bonds require a chemical technique if they are to be broken.


This is a real problem. The food needs to be soluble so that it can dissolve in the blood and thus,

be transported around the body.

The smaller the food, the more likely they will dissolve.

So the digestive system has to cope with both these problems.

The food we start with is often large in size. Being large, the food tends to be unable to dissolve. We say it is large and insoluble.

Problem 2


Remember….

The digestive system, being an organ system, is made of a group of organs all working together.

i.e.

Each organ has a particular function but together they get the job done.

The only visible parts of the digestive system are the entry and exit points

AnusMouth


Food looks very different when it leaves, compared to when it enters!

Therefore the body must be doing something to the food during its journey.

It is digested.

This means it is broken down. However, breaking something up happens in 2 ways.

As we know all food has a physical shape and is made of chemicals. These chemicals are held

together by chemical bonds.


It must be broken down using physical and chemical methods.

This allows it to pass through the small diameter of

the digestive system.

This allows useful chemicals to be released and dissolve in the blood.

To be broken down physically, the

shape of the food must be changed.

To be broken down chemically, the bonds must

be broken.

physical chemical


Our digestive system uses both these methods of digestion.

Chemical Digestion Physical Digestion

As we move through the digestive system, we will see one or both of these methods in action at any one

time.

So, in summary so far…


Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules.

Let’s take a close look at how this happens…

Open wide!


All food enters our digestive system through the mouth and waste material leaves through the anus.

If we stretch the digestive system out, we can see that it is really one long tube with an opening at

each end. However, it is a 9m tube!

Anus

Mouth


But how does a 9m tube fit into a space, which is less than a metre long?

It is extremely folded !

In addition, the tube passes through organs on its route from the mouth to the anus.


The Digestive system


As food moves through the system, it passes through these organs. Each organ has a slightly different effect on the food.

Let’s start in the mouth.


The mouth is where digestion begins. It is therefore where we first meet chemical and physical methods of digestion.

We will consider physical digestion first.

If you look in the mirror and smile, you immediately notice your teeth.

You will also realise that your teeth are different shapes.

You have 4 basic types of teeth.


Each is designed to do a different job.

IncisorCanine

Premolar Molar

Canine

2nd Premolar

Latent Incisor

1st Molar

3rd Molar

2nd Molar

1st Premolar

Central Incisor


The shape and size of each tooth is related to the function they have in digesting (breaking down) food.

If we look at the teeth of other living organisms they too have these 4 types of teeth. However, the size and

shape maybe different.

This is because other organisms

may have a different diet.


Canine

Sharp pointed teeth, which are used to bite and tear food.

Incisors

Small rectangular shaped teeth, which are found between the canines. They are used for cutting food.

Premolars

Found behind the canines and are used to grind soft food.

Molars

Found behind the premolars and are used to grind hard food.


Together, these teeth deal with most foods that we put into our mouths.

Although they break the food up, they do not effect the chemical bonds. Therefore, they are physically

digesting the food.

Once the teeth have digested the food, it may be small enough to be swallowed. However, some food can be sharp and it would be uncomfortable to swallow. The

food also needs chemically breaking down.

Therefore, the mouth produces a substance that solves both of these problems at the same time.


These glands (a special type of tissue) produce saliva, a sticky liquid.

As mentioned, the saliva has two jobs.

Being a liquid, it softens the food and allows the digested food to be rolled into a ball just before it is swallowed.

It also contains a chemical known as an enzyme.


Enzymes are chemicals, which act to speed up chemical reactions. They are produced from glandular tissue,

which is found all over the body.

In order to understand how an enzyme works, you have to think of it as having a particular shape.

We will use the shape below to represent on particular enzyme.

What is an enzyme?


Somewhere on the surface of the enzyme is

an important region known as the active site.

Enzyme

In order for an enzyme to be able to speed up a reaction, it must attach to the chemicals that are

reacting. It does so using its active site.


The red area on these two reacting chemicals represents the area where the active site of the enzyme will attach. The enzyme will attach to both at

the same time.

+

Enzymes are very specific

Enzymes can only speed up certain reactions. If the shape of the reacting chemicals does not match the shape of the active

site, the enzyme will not be able to work.


Therefore, enzymes are specific to certain reactions.

As well as being specific to certain reactions, enzymes are very particular about the environment that they work in.

To understand this, think of how you do homework.

You probably have a certain place to work, or you work at a certain time, you may like listening to music whilst you work or

else you can only work if it is completely silent.

Well, different enzymes work best in different conditions. If the condition is wrong, their active site can change shape. One

particular enzyme works best in acidic conditions (pH less than 7). If the pH rises and the conditions become alkaline, the

enzyme changes shape and stops working. It can no longer fit with the reacting particles of the chemical reaction.


Which enzymes are made by the digestive system?

The bulk of the food that enters the digestive system is from the three main food groups:

Proteins Carbohydrates Fats

pH 10


Therefore, it is not surprising that the digestive system has glands that produce enzymes that digest these

three types of food. Remember that the shape of the chemicals within the different food groups will be

different. Therefore the shape of the enzymes that digest these chemicals will also be different.

This means that an enzyme that digests fats will not be able to digest proteins.

Let us look at the chemical structure of Fats, proteins and carbohydrates to see why they require different

enzymes for their digestion.


CarbohydratesAs we mentioned previously, carbohydrates are chains of

identical sugar molecules. The enzyme that digests carbohydrates must be able to break the chemical bonds

between the individual sugar molecules.

Sites of enzyme attack

The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as Glucose.

An enzyme that digests carbohydrates is known as a

Carbohydrase.

Sugar


The digestion of carbohydrates can be represented by the following equation.

SugarsCarbohydrates

Carbohydrase


Proteins

As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are

different.

Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid.


The enzymes that digest proteins must be able to break the chemical bonds between the different

amino acids.An enzyme that digests protein is known as a

Protease.

Amino Acids

Site of enzyme attack

Imagine a bead necklace made up of over 20 different kinds of bead.


The digestion of proteins can be represented by the following equation.

ProteaseProtein Amino Acids


Fats

Fats are made up of a molecule of glycerol phosphate attached to three fatty acid molecules.

The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and

the fatty acids.Fats are also known as Lipids.

Its structure can be represented using the following diagram.

Fatty Acids

Glycerol PhosphateSite of

enzyme attack


The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates

and the fatty acids.

Fats are also known as Lipids.

An Enzyme that digests fat (lipid) is known as a

Lipase

The digestion of fats can be represented by the following equation.

LipaseFat Fatty Acids +Glycerol Phosphate


Of these three enzymes, the only one that is released within the mouth is Carbohydrase. This is partly because

the conditions within the mouth are suitable for Carbohydrase action. It works best within an alkaline

(pH > 7) environment.

Let’s represent the three food groups using colours.

CarbohydratesFatsProteins


The digestive action of the mouth can be summarised in the following diagram.

Physical Digestion

Chemical Digestion

Sugars

Chemically and physically

digested

The food could now pass down either the Trachea (windpipe) or the Gullet/Oesophagus.

Physically digested


Swallowing and Peristalsis


The semi-digested food has been formed into a ball by the tongue and is now swallowed. The ball firstly moves to the pharynx, the region at the back of the mouth where there is a junction between two pipes.

It needs to pass down through the Gullet. To ensure that it does not fall into the trachea and thus block our breathing, a small flap moves to cover the tube.

Swallowing Notes


The flap is known as the Epiglottis. If ever food accidentally got into the trachea, we would choke and try

to cough it back out.

How do we swallow?

Once the ball of food has passed through the top of the gullet, it is forced downwards by muscle contraction.

Swallowing Notes


The swallowing process finishes with a muscle known as a sphincter relaxing and the food passes into the stomach.The sphincter muscle found at the entry and exits points of the stomach acts rather like a

drawstring on a bag.

It allows the stomach to shut off both entry and exit points and hold food inside it.


The stomach is basically a muscular bag, filled with Hydrochloric Acid (HCl).

food enters from the gullet

glandular tissue makes:Hydrochloric Acid, Mucus and Protease enzyme

cross section of stomach

digested food leaves

muscle tissue

liquids mix with the food

The Stomach


The food is then subjected to a coordinated attack.

…attacks any microbes (bacteria) that may have

been swallowed accidentally when the

food was eaten.

Firstly the

the hydrochloric acid

When the food enters the stomach. The sphincter contracts behind it.


…to work in. These enzymes begin digesting the proteins in the swallowed food.

These proteins are broken down to release the amino acids.

ProteaseProtein

Secondly, the hydrochloric acid provides the perfect conditions for

Protease Enzyme


Protease enzymes work best under acidic conditions (pH < 7)

Thirdly, the muscular tissue of the stomach has the ability to contract and relax and in doing so, physically grinds the food inside it.

The mucus is produced to protect the lining of the stomach from the acid. If the mucus were not present, the hydrochloric acid could actually digest the tissue that had made it.

Amino Acids


Muscle and Glandular tissue

Layer of Mucus

Wall of stomach is protected

Presence of HCl

The hydrochloric acid, mucus, food and enzyme solution is given the name, Gastric Juice.


A summary of the digestive action of the stomach can be represented in the diagram below.

Fat

Protein

Carbohydrate

Sugar

Physical Digestion

Chemical Digestion

Muscular tissue of stomach

Protease enzyme and Hydrochloric

Acid

Sugars

Amino Acids

CarbohydratesProteins

Fats


It is clear that the large insoluble foods are slowly being digested to produce the small soluble foods.

Carbohydrates Amino Acids Proteins

It is also clear that the Fat has yet to be chemically digested.

This happens in the next section of the digestive system.


The name of this organ is deceiving. Although it is called small, it can stretch up to 6 metres in length. In order to fit into the body, it is heavily folded.

When the gastric juices leave the stomach, they

pass into the small intestine.

small intestine

The Small Intestine


Luckily two substances are produced to stop this happening. The

first is mucus and we have seen how this

works. The second is Bile.

Problem!

The gastric juices are acidic! There could be a danger of the lining of the small intestine being digested.

Bile is made in the Liver. It is a yellow/green liquid that is naturally alkaline (pH > 7).


pH >7 NeutralisationpH <7+

…the result is neutralisation of the acid.

This is essential for the lipase (the enzyme that

digests fat) to function properly.

This means that when Bile and the Gastric Juices meet,


Part of the Small Intestine


Let’s consider the process of fat digestion.

This section of the digestive system exemplifies the true idea of an organ system as a group of organs

working together for a common function.

The influential organs in the digestion of fat are the:Liver

Gall bladder, Pancreas

Small intestine.

Each organ plays its part in turning Fat into fatty acids and glycerol phosphates


Fat within the gastric juice

Liver produces Bile

It is released from the Gall bladder and passes down

through the bile duct

The Bile and the fat meet within the small intestine. The Bile emulsifies the fat. This basically means the

fat is physically broken into smaller pieces.

Emulsification

Notice that the fat has not been chemically digested, only physically. The result is a greater surface area over which the

enzyme, lipase, can attack the fat.


The pancreas and the small intestine

now release enzymes. Both

organs produce all three enzymes, Carbohydrase,

protease and lipase.

If we just consider fat, the lipase begins to break its

chemical bonds.

pancreassmall intestine


Fat

Lipase

Fatty Acids

Glycerol Phosphate


Bile emulsifies the fat. Muscular action of the small intestine

Lipase enzymeProtease enzyme

Carbohydrase enzyme

Sugar

Amino Acids Fatty AcidsGlycerol

Phosphate

Chemical Digestion Physical Digestion

SugarFat

Carbohydrates Amino Acids Protein

In summary the digestive action of the small intestine and associated organs can be represented in the following diagram.


We have now digested all the large insoluble foods into small soluble foods.

The three processes of chemical digestion can be

summarised as follows.

Large insoluble food

Enzyme

Small soluble food.

Carbohydrates carbohydrase Sugars

Proteins protease Amino acids

Fats lipase Glycerol phosphates and fatty acids.


Enzymes come into contact with food.

There is a further advantage for the small intestine in being a narrow tube.

With the enzymes being produced in the lining of the tube, it is essential that the food be forced to mix with them to

ensure that there is efficient digestion before the food passes through the organ.

If the tube is tight, the food is forced against the sides of the tube and thus, mixes directly with the enzymes.


Now that the large insoluble molecules have been digested down into the small soluble molecules, the

body must separate them from the waste food that has not been digested.

No food is 100% useful and so there will always be

some waste that needs excreting.

In order to understand how the body carry’s out this selection procedure, we need to take a closer look at

the lining of the small intestine.

However, if we consider what it has to do, we will understand why this idea cannot be correct.

At first glance, it appears to have a flat surface.


The small intestine is the site of absorption of useful molecules of digested food.

These molecules must pass across the lining of the small intestine and enter the blood stream.

Their destinations are the cells of the body.

EnergyThe cells constantly need these chemicals

and therefore the absorption process

must be very efficient to keep up with

demand. Therefore…..


If the absorption process had to occur across a normal lining, it would not be able to satisfy the demand of the

body for these soluble food molecules.

i.e. not enough molecules would pass across the lining in the desired time.

The only way to improve this situation would be to create a larger surface area over which absorption could occur.

That is exactly what is present in the small intestine

What looks like a normal lining, is in fact a highly folded

lining, which creates an enormous surface area in a small space.


The result of this folding means that the surface area of the lining of the

small intestine is enormous!

This increases the number of places where small soluble food molecules can pass across and move into the

blood.


Where is the blood?

The blood is found in minute small vessels known as capillaries. The capillaries are found protruding into the villi.

The blood approaches the villus, picks up the absorbed food molecules and then leaves.


Remember that the small intestine lining is made up of thousands of villi.

Here is a summary of the process of absorption.

A

S

B

R

O

T

P

N

O

I

Sugars

Amino Acids

Fatty Acids and Glycerol Phosphates

BLOOD

Any indigestible food will leave the small intestine without having been absorbed


Let us now move on to the next organ in the system, the large intestine (colon).

As the food enters this organ, all that is left is waste material and water. The body will want to leave the waste material within the

digestive system but the water is valuable.


This water will need to be retained by the body in order to prevent dehydration.

Remember that all the liquids you drink provide the largest source of water for the body. All this fluid passes through

the digestive system.

Again, this is the job of the blood.The blood reabsorbs the excess water that is mixed with

the waste food.

Again, if something is going to be absorbed, it must have somewhere to go.


Again, this is the job of the blood.The blood reabsorbs the excess water that is mixed with

the waste food.

LARGE

INTESTINE

BLOOD


Once the excess water has been reabsorbed, the waste material then passes into a storage organ called the

rectum. This waste material mainly consists of indigestible food. It makes up the bulk of the faeces

(solid excrement) that will be excreted.

It is stored here until the body is ready to excrete. In order for this to happen, another sphincter muscle

must relax. This opens the anus and the faeces can pass out of the system.

rectum


We have now finished our journey through the digestive system. We have seen the chemical and physical digestion of large insoluble into small soluble food. It is important to remember that the digestive system relies heavily on the presence of two important types of body tissue.

This is responsible for the production of the digestive

enzymes.

Through constant contraction and relaxation, the food is kept

moving through the system, from the mouth to the anus.

1. Glandular Tissue

2. Muscular Tissue


DigestionActivity oneActivity one

Chew it all overChew it all overCopy and complete the following statements which summarise the topic

of digestion. In each case, choose which of the two words is correct.

Digestion is the process of breaking LARGE / SMALLLARGE / SMALL molecules of food into LARGE / SMALLLARGE / SMALL molecules of food.

The LARGE / SMALLLARGE / SMALL molecules we start with are INSOLUBLE / SOLUBLEINSOLUBLE / SOLUBLE which means they CAN / CAN’TCAN / CAN’T dissolve in water.

The LARGE / SMALLLARGE / SMALL molecules produced by digestion are INSOLUBLE / SOLUBLEINSOLUBLE / SOLUBLE which means they CAN / CAN’TCAN / CAN’T dissolve in water. These molecules need to be SMALL / SMALL / LARGELARGE and INSOLUBLE / SOLUBLEINSOLUBLE / SOLUBLE so that they can pass through the lining of the LARGE / SMALLLARGE / SMALL intestine and into the WATER / BLOOD.WATER / BLOOD.


“Digestion involves ___________ types of process. These are firstly ____________ digestion and secondly _________ digestion. Chemical digestion is __________ out by ___________ which are chemical produced from ___________ tissue. Specific enzymes break down __________ types of food. For example ____________ enzyme breaks down ___________ . Mechanical digestion involves teeth and the tongue but mostly ____________ contraction e.g. the squeezing of the muscular lining of the __________.”

Fill in the gaps in the text below.

Activity twoActivity two

chemical

mechanical two

stomachmuscle

carbohydrase

specific

carbohydrates glandularenzymes carried

chemicalmechanicaltwo

stomach

muscle

carbohydrasespecificcarbohydrates

glandularenzymes

carried


Help! Use the words below to create 3 equations to show what happens when we digest:

1. Carbohydrates1. Carbohydrates 2. Fats2. Fats 3. Protein.3. Protein.

Carbohydrates Fats Amino acids

Double Sugar Lipase Glucose Protein

Single Sugar 3 Fatty Acids Protease

Glycerol Phosphate Maltose Carbohydrase

Activity threeActivity three


True or False?True or False?

Work your way along the route, answering each statement with simply ‘true’ or ‘false’. There are 15 questions.

Saliva contain enzymes?

All food is digested by the body

Blood transports the nutrients to the needy parts of the body

Digestion turns large insoluble molecules into small soluble

molecules

Nutrients are absorbed by blood in the pharynx

Blood flows along the digestive system picking

up nutrients

The food we eat can pass through the digestive system in 1hr

Activity fourActivity four


The small intestine is shorter than the large

intestine

The presence of villi increases the surface

area of the small intestine

Lipase enzyme works best in acidic

conditions

Starch and sugar are examples of

carbohydrates

Water is mainly reabsorbed in the small intestine.

Food is broken down by chemical process only?

Solid food must be turned to liquid before it can be absorbed

The small and large intestine basically perform the same function,

just at different speeds


Questions

• What type of acid is found in the stomach? (12)• The ___________ (10) links the stomach to the

pharynx.• The __________ (7) juices are found within the

stomach.• What happens to the water in the large intestine?

(10)• Where does the process of digestion actually begin?

(5)• This organ stores waste material before it is

discharged from the body? (6)• The _________ (6) moves the food around in the

mouth, preparing it for its journey.

**

**

Down the Hatch!Activity five


• ___________ (5) transports the dissolved nutrients around the body.

• The first section of the digestive system is known as the l________. (5)

• The chemicals that help to break down food are collectively called __________. (7)

• We eat or ________ food. (6)• This is the name for the soft fleshy part of the throat

that stops food going down the trachea. E___________. (10)

• At the rear of the mouth, this region receives the bolus of food from the tongue. (7)

• The main part of the small intestine is known as the D____________. (8)

**

**

**

**


• These provide the mechanical breakdown of food in the mouth? (5)

• This organ can be SMALL or LARGE? (9)• The collective name for the useful chemicals that are

absorbed across the lining of the small intestine? (9)• The product of the previous question? (5)• The name for the muscular bag that contains acid?

(7)• Food is __________ (7) down in the digestive

system using both chemical and mechanical methods.

**

**

**

Now for the bonus 5 pointsNow for the bonus 5 points


You will notice that 9 of the questions have a small green asterisk beside them.

Take the first letter of each of the answers to these questions. Put these letters in the box below.

Now rearrangerearrange them to find the mystery word!

Activity sixActivity six


Word SearchH V C N D G B L O O D Z V U M R E Y L U R W B J X B A U C P Y T D P D M N U T R I E N T O N H V N S I R T G D I O S M B O D T A O H G G O M S K S K U C E K E U R F K O L C H U Y I E L S L E N Z Y M E S O H G M T L N O A T Y U I N G E S T L F H I C P B H Z O M Q X J W F T O Z O V H E Y R R S M T E S F B I R B G A S T R I C D I A G Q W G S I A G C F B Q L H P D M C X I N Q C U O L I N T E S T I N E H X J O S R E A B S O R B E D J T Y P X L O S T R P G C N J U L O N Z J P P P B T O N G U E N H V M I A Q K R


Multiple choice questions


1. Which type of tissue helps to move food along the digestive system?

A liver tissue

C glandular tissue

B muscle tissue

D brain tissue


2. Which type of tissue makes digestive enzymes?

A liver tissue

B muscle tissue

C glandular tissue

D brain tissue


3. Which of the following are examples of carbohydrates?

A amino acids, glycerol

B starch, fatty acids

C sugar, amino acids

D starch, sugar


4. What is/are the breakdown product/s of starch?

A fatty acids

B amino acids

C glycerol

D sugars


5. What is/are the breakdown product/s of proteins?

A fatty acids

B amino acids

C glycerol

D sugars


6. What is/are the breakdown product/s of fat?

A fatty acids and glycerol

B amino acids

C glycerol

D sugars


7. Which of the following are examples of large, insoluble molecules?

A protein, amino acids, starch, glycerol

B starch, fats, proteins

C fatty acids, glycerol, glucose, amino acids

D fats, amino acids, starch, glycerol


8. Which of the following are examples of small soluble molecules?

A protein, amino acids, starch, glycerol

B starch, fats, proteins

C fatty acids, glycerol, glucose, amino acids



9. Which of the following are examples of molecules that can be absorbed across the lining of the small intestine and into the blood?

A fatty acids, glycerol, glucose, amino acids

B starch, fats, carbohydrates, proteins

C protein, amino acids, starch, glycerol



10. Water is absorbed across the wall of this structure.

A liver

B large intestine

C oesophagus

D pancreas


11. What is digestion?

A The breakdown of large molecules into small molecules.

B The building up of large molecules from small molecules.

C The absorption of large molecules across the lining of the small intestine.

D The removal of waste products from food.


12. What is absorption?

A The movement of large molecules from the small intestine into the circulatory system.

B The movement of small molecules from the large intestine into the circulation.

C The movement of small molecules from the circulation into the small intestine.

D The movement of small molecules from the small intestine into the circulation.


13. A carbohydrase is an enzyme that speeds up the breakdown of

A vitamins.

B fats.

C carbohydrates.

D proteins.


14. A lipase is an enzyme that speeds up the breakdown of

A vitamins.

B fats.

C carbohydrates.

D proteins.


15. A protease is an enzyme that speeds up the breakdown of

A vitamins.

B fats.

C carbohydrates.

D proteins.


16. Where are carbohydrases produced?

A stomach, pancreas and small intestine

B salivary glands, pancreas and small intestine

C pancreas and small intestine

D salivary glands and small intestine


17. Where are lipases made?






18. Where are proteases made?






19. Which of the following conditions best suits the action of the protease enzymes in the stomach?

A alkaline

B neutral

C acidic

D doesn’t matter


20. What is the name of the acid that is found in the stomach?

A citric acid

B sulphuric acid

C nitric acid

D hydrochloric acid


21. Which of these is a function of the acid found in the stomach?

A speed up the reproduction of bacteria

B neutralise the food entering the stomach

C kill bacteria

D make the food entering the stomach more alkaline


22. What is the name of the alkaline fluid that is produced by the liver and stored within the gall bladder? This liquid will then be released into the small intestine.

A urea

B bile

C lipase

D hydrochloric acid


23. What does the bile do to the acidity of the food arriving from the stomach?

A breaks it down

B nothing

C neutralises it

D makes it alkaline


24. Bile also causes the emulsification of fats. What does this mean?

A This is the break-up of a large fat droplet into many smaller fat droplets.

B This is the change in colour of food when it comes into contact with bile.

C This is the joining together of fat droplets to make a chain.

D This is the breakdown of fats into fatty acids and glycerol.


25. Why is the emulsification of fats useful?

A It reduces the surface are of the fats so lipases work more effectively.

B It increases the surface area of fats so that lipases work less effectively.

C It increases the surface are of fats so that lipases work more effectively.

D It reduces the surface area of fats so that lipases work less effectively.


26. Enzymes in the digestive system “speed up” the digestion of food. The scientific word for “speeding up” such chemical reactions is

A acceleration

B catalysis

C absorption

D neutralisation


27. The scientific name for the material that leaves the digestive system via the anus is…

A urine.

B fibre.

C faeces.

D solids.


28. Which of the following foods are examples of carbohydrates?

A meat, pulses, cereals and eggs

B milk, butter, margarine, eggs

C cereals, fruits and vegetables

D meat, fruits and milk


29. Which of the following foods would be useful if you wanted to make cell membranes?

A fish, eggs and pulses

B cheese, butter and margarine

C vegetables, cereals and cheese

D eggs, cereals and fruits


30. If a piece of food was passing through your digestive system, which of these is the correct order of organs that it would pass through?

A mouth, gullet, pancreas, small intestine, large intestine, anus

B mouth, gullet, stomach, large intestine, small intestine, anus

C mouth, gullet, stomach, pancreas, large intestine, anus, rectum

D mouth, gullet, stomach, small intestine, large intestine, rectum, anus

© boardworks ltd 2003 key stage 4 digestion. © boardworks ltd 2003 a slide contains teacher’s...

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