The Need for Food

Animal Survival

Standard Grade Biology

Learning Outcome 1

• Explain in simple terms why food is

required by animals.

Learning Outcome 2

• State the chemical elements present

in carbohydrates, fats and proteins

• Describe the simple structure of

carbohydrates, proteins and fats in

terms of simple sugars, amino acids,

fatty acids and glycerol.

You are what you eat!!

• In this lesson you will

– Look at what is a balanced diet

– Carry out food tests on

• Starch

• Glucose

• Protein

• Fat

– Discuss what happens if you don’t eat

a balanced diet

Balanced Diet

What is a balanced diet?

• Your diet must include five groups of food substances – Carbohydrates, fats, proteins, minerals

and vitamins

• It must also include water and fibre.

• A balanced diet is a diet that provides enough of these substances in the correct proportions to keep you healthy.

Carbohydrates

• Carbohydrates give us

energy.

• Chemical elements – C, H

and O.

• Starch is made from simple

sugars.

Testing for glucose

1. Pour some glucose solution into a

test tube

2. Add a few drops of benedict's

solution

3. Heat in a water bath

Testing For Starch

• Put a few drops of starch solution on a spotting tile.

• Add a few drops of iodine.

Proteins

• Proteins are needed for growth and repair.

• Proteins are made from amino acids

• Chemical elements – C, H, O, N (and S)

Testing for Proteins

1. Put 2 ml of protein

solution in a test tube

2. Add 2ml of Biurets

reagent

Fats

• Fats are an energy store,

protecting vital organs and

providing insulation.

• Fats contain C, H and O

• Fats are made from a

glycerol molecule and three

fatty acids.

Testing for fat (the emulsion

test)

• Add a few drops of cooking oil into

a test tube

• Add 2cm3 ethanol and shake

• Add 2cm3 water and shake again.

What happens if you don’t

eat a balanced diet.

What is this cartoon

trying to demonstrate?

Can you think of any

examples of health

problems that arise

from not eating a

balances diet?

Give three examples and

explain the effects on

health.

Learning Outcomes 3

• State that digestion is the breakdown of large particles of food into smaller particles to allow absorption into the blood stream through the small intestine wall.

• Explain that digestion involves the breakdown of insoluble food substances into soluble food substances

What happens to the food

we eat?

The gut as a production line

Learning Outcome 4

• identify in a diagram / model the main

parts of the mammalian alimentary canal

and associated organs (mouth, salivary

glands, oesophagus, stomach, pancreas,

liver, gall bladder, small intestine, large

intestine, appendix, rectum and anus)

• state the sites of production of the main

digestive juices in mammals (salivary

glands, stomach, pancreas, liver, small

intestine)

Digestion

• Digestion is the breakdown of large, insoluble food molecules into small, soluble food molecules so that they can be absorbed into the blood stream.

Pupil Activity

• Label the diagram of the digestive

system.

– Use the textbook supplied to help if

needed

– Design a table to link the structure and

function of different parts of the

digestive system.

Salivary glands

stomach

trachea

tongue

mouth

anus

rectum

colon

pancreas

Large

intestine

appendix

Small

intestine ileum

Duodenum

Gall bladder

liver

oesophagus

Mammalian teeth

The Need for food Animal Survival

SG Biology

Learning Outcomes (5)

• To know the different structure and

functions of each type of tooth

• To understand the adaptations of a

herbivore, omnivore and a carnivore

to feeding.

Feeding in mammals

• Mammals have teeth which may be used to bite pieces of food and to chew it into smaller pieces before swallowing.

• The shapes of teeth are suited to their function. – Incisors and canines are used for biting

– Premolars and molars are used for chewing and crushing food.

Patterns of Teeth

Human Jaw

teeth

• There are different types of teeth, each specially shaped to perform a particular job. – Incisor - A broad flat sharp tooth found at the

front of the mouth. Designed for biting and cutting food.

– Canine - A sharp pointed tooth for piercing flesh and tearing.

– Pre-molar & molar - A broad flat tooth with many cusps. Its rough surface is used for crushing, grinding and chewing food

Carnivore adaptations

• Look at the dog skull, and the

diagrams of a dogs skull.

• With the aid of a diagram – make

notes explaining how the dogs teeth

and jaws are adapted for a

carnivorous diet.

Herbivore adaptations

• Look at the sheep’s skull, and the

diagrams of a sheep skull.

• With the aid of a diagram – make

notes explaining how the sheep's

teeth and jaws are adapted for a

herbivorous diet.

Learning Outcome 6

• Explain the mechanism of peristalsis

• Explain how the contractions of the

stomach help in the chemical

breakdown of food.

Digestion of Food

• The digestion of food can either be mechanical or chemical.

• Mechanical digestion includes – Chewing

– Action of muscles in oesophagus, stomach and small intestine

• In chemical digestion enzymes catalyse the breakdown of larger food molecules into smaller food molecules.

Digestion in the mouth and

oesophagus

• Chewed food is mixed with saliva in the

mouth

• Saliva contains

– Amylase is an enzyme which starts to digest

starch into sugars (maltose)

– Mucus helps soften the food making it easier

to swallow

• The bolus travels down the oesophagus

with the aid of peristalsis

Peristalsis in the gullet

Learning Outcome 7

• State that different enzymes are

responsible for the breakdown of

carbohydrates, proteins and fats.

• Give an example of an amylase, a

protease and a lipase. State their

substrates and products.

Digestion of Starch

• Take 2ml of 1% starch solution

– Test for starch

– Test for sugars

• Take 2 ml 1% starch solution, add

2ml 2% amylase solution

– Leave for 20 minutes

– Test for starch

– Test for sugar

Action of amylase on starch

• Put two drops of iodine solution into

all the wells on a white spotting tile

• Add 2ml 1% starch solution and 2ml

2% amylase solution to a test tube.

• Every minute, test the contents of

the test tube for starch.

• Write a conclusion on your results

Protein Digestion

• Protein digestion occurs in the stomach and small intestine.

• Protease enzymes are produced by the gastric pits in the stomach lining or by the pancreas.

• In the stomach, hydrochloric acid is also produced which provides the optimum pH for trypsin to work (as well as killing bacteria in food)

Protein Digestion

• Add 2ml of protein solution to three test tubes.

• Number the test tubes 1, 2 and 3 1. Add 1ml HCl

2. Add 1ml Water

3. Add 1ml HCl

• Do not add the trypsin until last 1. Add 0.5 ml water

2. Add 0.5 ml trypsin

3. Add 0.5ml trypsin

Protein digestion

• Leave for 10 minutes

• Test each of the test tubes for the

presence of protein using Biurets

reagent.

• Explain your results.

Fat Digestion

• Milk does not dissolve in water, in the

digestive system, bile produce by the liver

(stored in the gall bladder) emulsifies fats

to give a larger surface area for enzymes

to work on.

• You are going to use phenolphthalein to

investigate the effect of bile on the

digestion of fat.

Fat Digestion

• Take 4 test tubes and number them

1, 2, 3 and 4.

• set up the test tubes as shown in the

table below.

Test tube 1 2 3 4

Milk 3 ml 3ml 3ml 3ml

Bile 0 0.5ml 1 ml 1ml

Water 1ml 0.5ml 0 0

Fat Digestion

• Add 5 drops of phenolphthalein to each test tube

• Add sodium carbonate to each test tube until the solution goes pink.

• Add 0.5ml of lipase to test tubes 1, 2 and 3.

• Add 0.5 ml water to test tubes 4.

• Observe your results. Try to explain what you are observing.

Chemical Digestion

• Enzymes – Are proteins – Are produced by cells – Change chemical substances into new

products

– Are “specific” to one substance – Work best at their “optimum

temperature” (around 30 – 40o) – Work best at an optimum pH

Digestive enzymes

• There are different types of digestive enzyme – Proteases break down proteins into amino acids

– Lipases break down fats into fatty acids and glycerol

– Amylase breaks down starch (carbohydrase enzyme) into maltose (sugar) • Maltose is then broken down by maltase to form

glucose

Chemical Digestion

• There are also other substances in the digestive system which help with the breakdown of food.

• Hydrochloric acid – Secreted by stomach – Kills the bacteria in food

– Enzymes in stomach work best at a low pH e.g. pepsin

Chemical Digestion

• Hydrogen carbonate ions – Secreted by pancreas

– Neutralises acid, enabling enzymes in small intestine to work

• Bile – Produced by liver, stored in gall bladder,

secreted into small intestine

– Emulsifies fats (Larger surface area for enzymes to work on)

Learning Outcome 8

• State that only small soluble molecules can pass through the wall of the small intestine.

• Explain how the structure of the small intestine is related to its function.

• Explain how the structure of a villus, including the lacteal and the blood capillaries, are related to the absorption and transport of food.

• Describe the role of the large intestine in water absorption and elimination.

Digestion in the small

intestine

• 3 important liquids are added to the

food

– Pancreatic juice (carbohydrases,

proteases and lipases)

– Bile (neutralises acid and emulsifies fat)

– Intestinal juice (carbohydrases,

proteases and lipases)

What happens next?

Absorption in the ileum

• The small intestine is well designed

for absorption, it has

– Thin lining

– A good blood supply

– A very large surface area (about 9m2)

Absorption in the Villi

The Model Gut

A model of absorption

“the model gut”

Making a model gut

• Wash a 12cm length of visking tubing (A) in

warm water.

• Tie a knot in one end

• Fill the tubing with 10cm3 of starch and

glucose solution(B).

• Wash the outside of the tubing.

• Put it into a boiling tube containing DI water

(C) (holding it in place with a rubber band.

• After 20 minutes, test the surrounding water

for starch and glucose.

C

B

A

Comparing the model gut

with the villi

• Draw conclusions from the

experiment, explaining what the

results were, and how the model gut

represents the real situation

• E.g. what does the water represent,

what does the Visking tubing

represent, etc.

Large intestine and the

elimination of waste.

• A watery mix of enzymes and

undigested food (mainly fibre)

moves into the colon.

• Water is absorbed back into the

blood stream.

• Faeces are compacted in the

rectum and egested through the

anus.

The end What do

they think

they are

looking at?

Learning Outcome 9

• To revise the learning outcomes

taught in this sub topic.

What happens to the food

we eat?

The gut as a production line