1. Which enzyme does saliva contain?

2. Which enzyme works best in acidic condition?

3. What is digestion?4. Where does digestion begin?5. Where does digestion end?6. The small intestine is divided

into two parts. They are called _____ and ______.

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Dige

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Salivary Glands

Tongue Teeth

Oesophagus Liver Gall Bladder

Pancreas Small Intestine Large Intestine Rectum

Stomach

Anus

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The beginning – in the Mouth Digestion begins in the mouth

where food is broken down by the teeth. This is an example of physical breakdown.

The small parts of food are mixed with saliva and swallowed.

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Saliva contains enzymes that start to chemically breakdown some of the carbohydrates (starch) in the food.

The enzymes in the saliva are called amylase.

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Enzymes in Action

EnzymesEnzymes are catalysts that speed up chemical reactions in living organisms.Enzymes are specific (e.g. protease can only break down proteins)Enzymes are affected by pH (e.g. protease works much faster in an acidic condition)Enzymes are affected by temperature (body temperature of 37oC is optimal)

Enzyme Function End Product

Optimal pH

Produced by:

Amylase(e.g. salivary amylase)

Breaks down carbo-

-hydratesGlucose

pH 7(Neutral)

Salivary glands,

Pancreas

Protease(e.g. stomach pepsin)

Breaks down proteins

Amino acids

pH 1 ~ 6(Acidic) Stomach

Lipase(pancreatic lipase)

Breaks down lipids

Glycerol &Fatty acids

pH 7 ~ 8(Neutral /

Slightly Basic)

Pancreas

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Through the Oesophagus!

After being chewed and mixed with saliva, the food then passes the epiglottis, a flap of skin and cartilage that prevents food from entering the trachea (air tube).

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Peristalsis The food is then

moved down the oesophagus with the help of wave like contractions, a process called peristalsis.

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What happens next?

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In the StomachThe stomach stores and physically break down food by churning.

The stomach also produces hydrochloric acid (pH 2) and protease enzyme for chemical breakdown of proteins.

The walls of stomach is unaffected by the acid because they are protected by the mucus produced by the stomach wall cells.

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Stomach Acid (HCl Acid) = pH 2

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BacTerial War

Write the answers on your book1. Describe two things happening to

the food in the stomach2. Give the name of the enzyme

present in the stomach3. Describe why stomach acid is

needed4. Describe why stomach acid

normally does not affect the stomach walls.

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Next stop - Duodenum The contents of the stomach are

then moved to the first part of small intestine – Duodenum.

Here, the chyme is mixed with bile and pancreatic juice.

duodenum (first part of small intestine)

ileum (second part of small intestine)

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Liver

Pancreas

Duodenum

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Mmmmmm… Bile! Bile is a greeny-yellow substance

made by the liver but stored the gall bladder which emulsifies fats to allow absorption .

It also neutralizes the chyme before entering the duodenum

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The pancreas produces the pancreatic juice which contains: Pancreatic amylase Pancreatic protease Pancreatic lipaseThe juice completes all the chemical break down of food particles.

Mmmmmm… Pancreatic Juice!!

Lipase ♥ Bile (page 32)Bile breaks up large fat globules into many tiny droplets. This greatly increases the surface area of the fat, enabling the lipases included in the pancreatic juice to digest the fat much faster.Bile also neutralises the acidity of the ‘chyme’ from the stomach.

Write the answers on your book1. Bile is produced in ______ and

stored in ___________.2. Describe the two functions of bile.3. What are the contents of

pancreatic juice?4. Fully describe what happens to the

food in the duodenum

Aim: to investigate how nutrients are absorbed into the blood

1) Tie one end of the dialysis bag tightly with string

2) Fill the “sausage” with the solution of glucose and starch

3) Tie the other end of the dialysis bag tightly with string

4) Place in a beaker of water

5) Add a few drops of iodine until the beaker goes a light orange colour

Method:

glucose

starch

water

+

Absorption in ileum – Dialysis Tubing Experiment

very thin dialysis bag

Sausage Questions

1. What happened to the sausage and water?

2. What do you think happened to the starch molecules inside the sausage?

3. What do you think happened to the glucose molecules inside the sausage?

duodenum (first part of small intestine)

ileum (second part of small intestine)

Here is a question to think about…

Why do we have to “digest” food that we eat?

Here is another question to think about…

What happens to the food after being digested?

duodenum (first part of small intestine)

ileum (second part of small intestine)

Malnutrition

So what happens to the food after being digested?We must digest (break down) food into very tiny particles, so they can be absorbed into the blood stream.The blood then carries the nutrients everywhere so they can be used by the cells of the body! (energy, growth and repair)

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Most of the nutrients are absorbed in the ileum (the second part of the small intestine)

Then water is absorbed in the large intestine.

Absorption!!!

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Dige

stiv

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Salivary Glands

Tongue Teeth

Oesophagus Liver Gall Bladder

Pancreas Small Intestine Large Intestine Rectum

Stomach

Anus

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Digestion is now over… what now? - ileum After digestion is completed,

the broken down nutrients are absorbed into the blood stream

The absorption first takes place in the second part of the small intestine – ileum.

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Villi

The walls of the small intestine are not smooth. They are covered in villi

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You must be able to describe how villi in the small intestine are adapted for maximum absorption of nutrients!!!

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Large surface area Large blood supply Thin surface to move across Blood has low concentration

of nutrient which increases the rate of diffusion

How it is maximised….

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Q: Discuss the importance of the villi and how the structure of the villus aids the absorption of food in the ileum

How to answer:1. Define terms (e.g. ileum, villi)2. Describe the structural features of

villi (e.g. very think skin)3. Describe how each feature aids the

absorption of food (e.g. micro villi = increase in surface area = greater absorption)

Absorption in the ileum (page 35)

Ileum is the second part of small intestine where absorption of nutrients from digested food occurs. The finger-like projections called villi maximise the absorption process by increasing the surface area where nutrients can enter the blood stream. Villi have very thin surface so nutrients can easily be absorbed and they are well supplied with blood to allow many nutrients to be absorbed into the blood stream.

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Finally - Large Intestine After the long trip

through the small intestine, the remains enter the large intestine.

Here remains are fermented by the action of gut bacteria, excess water is absorbed and faeces is stored until released.

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Digestion Quiz – Ready?