Digestion and alimentary canal

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Standard Grade Biology
Topic 3 Animal Survival
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Animal Survival is divided into
A- The need for food B- Reproduction C- Water and
waste D- Responding to the environment
Colour key
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Learning Objectives (aims)
1. Explain why food is required by animals
2. Know the chemical elements and simple
structures of carbohydrates, proteins and fats
3. Define digestion and explain why it happens
(absorption and solubility)
4. Know about teeth types in a herbivore,
carnivore and an omnivore
5. Identify the main parts of the mammalian
alimentary canal and know the sites of production
of the digestive juices
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6. State that different enzymes are responsible
for the breakdown of carbohydrates, proteins and
fats and give specific examples
7. Explain the mechanism of peristalsis
8. Explain how the contractions of the stomach
help in the chemical breakdown of food
9. Explain how the structure of the small
intestine is related to what it does
10. Explain how the structures of a villus are
related to the absorption and transport of food
11. Describe how the large intestine absorbs and
eliminates water
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Why do we need food?

• For a source of energy
• For a source of raw materials for growth /
  repair

Where do we get it from?

• From plants which make their own food by
  photosynthesis (producers)
• By eating other plants and animals (food
  chains / webs)

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What do we need from food?
Food Group containing Elements Made from basic units of Function
Carbohydrates Simple sugars (eg glucose)
Proteins
Fatty acids glycerol Store energy, insulate body, in cell membranes
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Food Group containing Elements Made from basic units of Function
Carbohydrates Carbon, oxygen hydrogen Simple sugars (eg glucose) Provide energy
Proteins Carbon, oxygen, hydrogen, nitrogen Amino acids Growth and repair
Fats Carbon, oxygen hydrogen Fatty acids glycerol Store energy, insulate body, in cell membranes
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Food types (groups)
Carbohydrates
Proteins
Long chains made from more than 20 different
amino acids
Fats
Glycerol molecule joined to 3 fatty acids
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What is in different foods?
Watch and do the activities in the
presentation Digestion and Balanced Diets
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Food Research
Healthy living websites http//www.eatwell.gov.uk
and http//www.lifebytes.gov.uk

• Get information on
• What is 5-a-day?
• What should you be eating lots of and little
  of?
• How do different food groups/minerals/vitamins
  help your body?
• Any other interesting things youve found out?

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How do we get these things from food?
Through the process of digestion
What is it? The breakdown of large insoluble food
molecules into small, soluble food molecules.
Why? So that they can be absorbed into the blood
stream (through the lining of the small
intestine) for our bodies to use.
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The gut as a production line
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Digestion falls into two main types
1. Mechanical breakdown by teeth which is
followed by
2. Chemical breakdown by enzymes
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Mammalian diets
How could you investigate which foods a certain
animal eats?
Observation (plusses, minuses?)
Collecting, dissecting faeces (plusses, minuses?)
Look at their teeth (plusses, minuses?)
Teeth
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1. Teeth stuff (mechanical)
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Herbivores- sheep skull
Male deer
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Carnivores- note carnassial teeth (specialised
molar)
Tooth from Dire Wolf, N.USA, fossil from last Ice
Age (est 10,000 years old)
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Omnivores- humans
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Looking After Your Teeth
Find out what you should do to look after your
teeth. You could try http//www.lifebytes.gov.uk
Find out about nutrition for teenagers,
especially for healthy teeth and bones

• Note the addresses of any websites you use.
• You can use written resources (eg. library,
  Home Economics, PSE leaflets, science books).
• Take short notes

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2. Chemical breakdown of food
Ingestion Digestion Absorption Egestion
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The digestive system
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Salivary glands
mouth
gullet
tongue
windpipe
liver
stomach
Gall bladder Bile duct
pancreas
small intestine
colon
Large intestine
rectum
appendix
anus
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Peristalsis
Explain the mechanism of peristalsis
Peristalsis is a wave-like motion as muscles
alternately contract and relax, pushing the food
along the tube.
Watch the Feeding Video
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The Journey So Far

• The food has been made physically smaller in
  the mouth by chewing and mixed with saliva.

• Saliva softens and lubricates food. It also
  contains an enzyme (carbohydrase) which starts
  chemically breaking down carbohydrates.

• The food moves down the oesophagus by
  peristalsis and reaches the stomach, passing
  through a ring of muscle on its way in.

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Stomach
Explain how the contractions of the stomach help
in the chemical breakdown of food

• The stomach is a muscular bag which contracts
  in both directions, churning the food.

• Churning helps to physically break it down and
  also mixes it with gastric juices released by the
  stomach lining.

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What is happening inside?

• Gastric juices contain protease enzymes
  (including pepsin) and hydrochloric acid.

• Enzymes are substances which break down (or
  combine) specific chemicals.

• Pepsin breaks down proteins.
• It works best in acidic conditions.

• Churning and enzyme action continue the
  breakdown of the food that has been eaten.

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No major nutrients are absorbed in the stomach.
Aspirin and alcohol (small, fat soluble
substances) can pass into bloodstream.
The Next Steps in the Journey

• Food squirts through the lower ring of muscle
  into the small intestine.

• This happens each time the stomach relaxes
  between contractions.

• Nutrients have to be small and soluble so they
  can pass through the wall of the small intestine
  and enter the bloodstream of your body.

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Further breakdown of food is helped by the
Liver- produces bile which neutralises stomach
acid and enzymes which break down fat (lipases).
Bile is stored in the Gall Bladder and when
released passes through the bile duct into the
small intestine.
Pancreas- produces enzymes which break down all 3
food groups. These pancreatic juices break down
the food in the small intestine.
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The Small Intestine
Main role is absorption of food nutrients.
Explain how the structure of the small intestine
is related to its function
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Small Intestine - Structure
Key Points

• Good blood supply to carry nutrients around
  body

• Large surface area for digestion and
  absorption as it is folded into villi

• Villi have finger-like projections
  (microvilli) on them with a thin lining for
  absorption

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More on breakdown of food
Food contains many large, insoluble molecules.
You have made them a bit smaller mechanically by

• teeth
• churning by the stomach

BUT they are still to big and insoluble to pass
into the bloodstream
SO chemicals called enzymes can break them down
into small molecules.
Enzymes are specific and different types break
down each food group
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What are these enzymes?
The main enzymes in your digestive system are
Enzyme Break down Products
Carbohydrase Carbohydrates Maltose, Glucose
Protease Proteins Amino acids
Lipase Fats and oils Fatty acids Glycerol
The main organs producing enzymes in mammals are
salivary glands, stomach, pancreas, liver, small
intestine
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Where are they found?
Enzymes are produced in the digestive juices.

• Carbohydrate (starch) is broken down into
  glucose in the mouth and small intestine

Example of a carbohydrase- salivary amylase in
salivary glands in the mouth

• Proteins are broken down into amino acids in
  the stomach and small intestine

Example of a protease- pepsin in stomach

• Fats are broken down into fatty acids and
  glycerol in the small intestine

Example of a lipase- pancreatic lipase in pancreas
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More about the Small Intestine
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Small Intestine - digestion
Explain how the structures of a villus, including
the lacteal and blood capillaries, are related to
the absorption and transport of food - collect
handout -

• Wall of villus is only one cell thick

• Villus contains a dense network of capillaries

• Capillaries absorb the products of protein
  digestion (amino acids) and carbohydrate
  digestion (glucose) and carry it round the whole
  body

• Central lacteal absorbs the products of fat
  digestion (fatty acids and glycerol) and drains
  into lymphatic system, carrying it round the
  whole body

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Large Intestine
Describe the role of the large intestine in water
absorption and elimination

• Any food which hasnt already been absorbed
  reaches here (indigestible material)

• The main function of the large intestine is to
  absorb water and salts

• The remaining food is temporarily stored in
  the rectum then released through the anus-
  excretion.

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