Transcript KS4 Digestion - Part One

KS4 Biology
Digestion - Part One
1 of 44
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
Energy from food:
The 7 food groups represent
large chemicals.
fats
proteins
minerals
vitamins
water
fibre
carbohydrates
These chemicals are often chains of smaller, more useful
chemicals, joined together.
Energy molecules in food
One example is carbohydrates.
Carbohydrates are made of long chains of identical
small sugar molecules.
sugar molecule
carbohydrate
Small sugar molecules
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
How can we release energy from food?
Problem One - releasing smaller sugars
Physical means like slicing and cleaving food does not
break down the long chain molecules and release the
sugars.
This is because we can’t release sugars from carbohydrates
by physically breaking them up.
Chemical breakdown
The chain of sugars is held together by…
chemical bonds
Chemical bonds require a chemical technique if they
are to be broken.
Problem with food size
Problem 2
- 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.
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.
Soluble product
Digestion
Blood vessel
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
The digestive system:
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.
External digestive system
The only visible parts of the digestive system are the
entry and exit points.
Mouth
Anus
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.
What happens to the food in our bodies?
What happens to the food in our body?
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.
Chemical and physical digestion
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.
physical
The shape of the food must be
physically changed so that it can
fit through the small diameter of
the digestive system.
chemical
This allows useful chemicals
to be released and dissolve
in the blood. To be broken
down chemically, the bonds
must be broken.
In we go!
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
The digestive tract
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.
mouth
Stretched out it is a 9m tube!
anus
Our guts
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.
Digestive system diagram
Physical digestion
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.
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
Teeth:
Each is designed to do a different job.
premolar
molar
canine
central
incisor
incisor
latent
incisor
canine
1st premolar
2nd premolar
1st molar
2nd molar
3rd molar
Diagram of a tooth
Tooth size and shape
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.
Mammalian tooth types
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.
Action in the mouth
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.
Saliva
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.
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
Enzyme properties:
What is 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.
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.
Active site
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.
Specificity of enzymes
+
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.
The environment matters
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.
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< 7
pH 10
Food groups and enzymes
The bulk of the food that enters the digestive system is
from the three main food groups:
proteins
carbohydrates
fats
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.
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
Digestive enzymes:
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
sugar
The product of the chemical breakdown of carbohydrates
is sugar. The sugar is known as glucose.
Enzymes that digests carbohydrates are known as
carbohydrases.
Enzyme driven reaction
The digestion of carbohydrates can be represented
by the following equation.
Carbohydrates
carbohydrase
carbohydrase
Sugars
Proteins and amino acids
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.
sites of enzyme attack
amino acids
Imagine a bead necklace made up of over 20
different kinds of bead.
Enzymes for digesting proteins
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.
protease
Protein
Amino Acids
sites of
enzyme
attack
Fat in our food
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.
fatty
acids
site of
enzyme
attack
glycerol
phosphate
Enzymes for digesting fat
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.
Fat digestion can be represented by the following equation:
lipase
Fat
Fatty Acids + Glycerol Phosphate
Carbohydrase in saliva
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.
The carbohydrase in saliva in combination with other
digestive carbohydrases added later from the pancreas
and the small intestine complete carbohydrate digestion.
Digestive action of the mouth - summary
Carbohydrates
Fats
Proteins
physical
digestion
chemical
digestion
The food could now
pass down either the
trachea (windpipe) or
the gullet/oesophagus.
chemically and
physically digested
physically
digested
sugars
Contents
Digestion – Part One
Energy from food
The digestive system
Teeth
Enzyme properties
Digestive enzymes
Summary
Multiple-choice quiz