boardworks ks4 digestion part one

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Digestion - Part One

KS4 Biology


Contents

Digestion – Part One

Energy from food

The digestive system

Enzyme properties

Digestive enzymes

Teeth

Summary


fats

proteins

minerals

vitamins carbohydrates

water fibre

The 7 food groups represent large chemicals.

These chemicals are often chains of smaller, more useful chemicals, joined together.

Energy from food:


One example is carbohydrates.

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

Energy molecules in food

carbohydrate

sugar molecule


The small sugar molecules are very useful.

The body has to break these large food molecules up into single or small chain sugar molecules. These are used to make…

ENERGY

Small sugar molecules


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

Problem One

Physical means like slicing and cleaving food does not break down the long chain molecules and release the sugars.

How can we release energy from food?

- releasing smaller sugars


The chain of sugars is held together by…

Chemical breakdown

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

chemical bonds


- The food we start with is often large in size. Problem 2

Problem with food size

Being large, the food tends to be unable to dissolve.

We say it is large and insoluble.


Food solubility

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.

Blood vessel

Digestion

Soluble product


Contents


Energy from food


Enzyme properties

Digestive enzymes

Teeth

Summary


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

Each organ has a particular function and only by working together will they get the job done.

The digestive system:


The sound of a rumbling stomach and the fact that food looks very different when it leaves, compared to when it enters mean that the body must be doing something to the food during its journey.

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

AnusMouth

External digestive system

What happens to the food in our bodies?


It is digested.

This means it is broken down.

This digestion 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.

What happens to the food in our body?


Our digestive system uses both:

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.

The shape of the food must be physically changed so that it can fit through the small diameter of the digestive system.

This allows useful chemicals to be released and dissolve in the blood. To be broken down chemically, the bonds must be broken.

physical chemical

Chemical and physical digestion


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…

In we go!

Open wide


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

The digestive system is really one long tube with an opening at each end.

Stretched out it is a 9m tube!

anus

mouth

The digestive tract


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

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

It is extremely folded!

Our guts


Digestive system diagram


The mouth is where digestion begins. Here we find both 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 type is designed for a different role.

Physical digestion


Contents


Energy from food


Enzyme properties

Digestive enzymes

Teeth

Summary


Each is designed to do a different job.

premolar molar

canine

2nd premolar

latent incisor

1st molar

3rd molar

2nd molar

1st premolar

central incisor

Teeth:

incisorcanine


Diagram of a tooth


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

If we look at the teeth of other animals many of them too have these 4 types of teeth.

However, the number of each type, their size and their shape differ between species.

This is because other organisms have different diets.

Tooth size and shape


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.

Molars

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

Premolars

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

Mammalian tooth types


Together, these teeth can break up most foods that we put into our mouths. The mechanical act of chewing food is part of physical digestion.

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.

Action in the mouth


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.

Saliva


Contents


Energy from food


Enzyme properties

Digestive enzymes

Teeth

Summary


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.

What is an enzyme?

Enzyme properties:

Somewhere on the surface of the enzyme is an important region known as the active site.


What’s so special about enzymes?

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

enzyme

In order for an enzyme to be able to speed up or catalyse a reaction, it must attach to the chemicals that are reacting. It does so using its active site.

Active site


The red areas on these two reacting chemicals represents the areas 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.

Specificity of enzymes


Therefore, enzymes are specific to certain reactions.

Enzymes are also 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.

The environment matters


Enzymes and pH

Different enzymes work best in different conditions.

If the condition is wrong, their active site can change shape. Say 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.

pH 10pH< 7


Therefore, it is not surprising that the digestive system has enzyme-producing glands that relate to 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.

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

proteins carbohydrates fats

Food groups and enzymes


Contents


Energy from food


Enzyme properties

Digestive enzymes

Teeth

Summary


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.

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

Enzymes that digests carbohydrates are known as carbohydrases.

Digestive enzymes:

sugar

sites of enzyme attack


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

SugarsCarbohydratescarbohydrase

Enzyme driven reaction

carbohydrase


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.

Proteins and amino acids

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

amino acids sites of enzyme attack


Enzymes for digesting proteins

sites of enzyme

attack

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

Enzymes that digest protein are known as proteases.

amino acids

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

proteaseProtein Amino Acids


Fat in our food

site 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.

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

fatty acids

glycerol phosphate


Fat digestion can be represented by the following equation:

lipaseFat Fatty Acids + Glycerol Phosphate

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.

Enzymes that digest fat (lipid) are known as lipases.

Enzymes for digesting fat


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.

Carbohydrase in saliva

It works best within an alkaline (pH > 7) environment.

The carbohydrase in saliva in combination with other digestive carbohydrases added later from the pancreas and the small intestine complete carbohydrate digestion.


The food could now pass down either the trachea (windpipe) or the gullet/oesophagus.

sugars

chemically and physically digested

physically digested

physical digestion

chemical digestion

CarbohydratesFatsProteins

Digestive action of the mouth - summary


Contents


Energy from food


Enzyme properties

Digestive enzymes

Teeth

Summary


Multiple-choice quiz

boardworks ks4 digestion part one

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