Nutrition

iGCSE Biology

Learning Outcome 1

• Explain in simple terms why food is required by animals.

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.

Nutrients

Learning Outcomes

• list the chemical elements that make up:– carbohydrates– fats– Proteins

• Describe the synthesis of large molecules from smaller basic units

• list the principal sources of, and describe the importance of carbohydrates, fats, proteins,.

Quick Revision

• A balanced diet must contain all the essential nutrients in the correct amounts and proportions.

• The nutrients needed are– Carbohydrate– Fat– Protein– Vitamins– Minerals– Fibre– Water.

Main Nutrients

Nutrient Elements present

Use in body

Good food sources

Carbohydrate Carbon, hydrogen, oxygen

Source of energy

Rice, potato, bread

Fats and oils Carbon, hydrogen, oxygen

Source of energyInsulation

Butter, milk, cheese, egg yolk

Protein Carbon, hydrogen, oxygen, nitrogen

Growth and tissue repair

Meat, fish, eggs, soya, milk

What you really need to remember!!

• Carbohydrates, fats and proteins are all made up of the elements carbon, hydrogen and oxygen

• Proteins always contain nitrogen and sometimes sulphur

• One way to remember this is– Carb O Hydrate

Carbohydrates

• Large carbohydrates molecules such as starch and glycogen are made up of long chains of smaller units, e.g. monosaccharides (glucose), which are held together by chemical bonds

Fats

• Fats are made up of three fatty acids and a glycerol

Proteins

• Proteins are made up of long chains of amino acids

Food Tests

• What is the test for starch?• What is the test for glucose?• What is the test for protein?• What is the test for fats?

• What does a positive result look like?

Learning Outcomes

• list the principal sources of, and describe the importance of:– vitamins (C and D only)– mineral salts (calcium and iron only) – fibre (roughage)– water

• describe the deficiency symptoms for:– vitamins (C and D only)– mineral salts (calcium and iron only)

Vitamin C

• Function– Maintain healthy skin and gums

• Good Food Source– Citrus fruits, black currants, cabbage,

tomato, guava, mango• Effect of deficiency

– Scurvy• Bleeding under skin• Bleeding gums

Vitamin D

• Function– Needed to maintain hard bones– Helps absorb calcium from small

intestine• Good Food Source

– Milk, cheese, egg yolk, fish liver oil– Made in skin when exposed to sunlight

• Effect of deficiency– rickets

Calcium

• Function– Healthy teeth and bones– Normal blood clotting

• Good Food Source– Milk, cheese, fish

• Effect of deficiency– Rickets– Slow blood clotting

Iron

• Function– Formation of haemoglobin in red blood cells

• Good Food Source– Red meat, liver, kidney, eggs, green

vegetables (spinach), chocolate

• Effect of deficiency– Anaemia

• Constant tiredness• Lack of energy

Fibre

• Function– This is cellulose which we can not digest– It adds bulk to the undigested food in the

intestines, maintaining peristalsis

• Good Food Source– Vegetables, fruit, wholemeal bread

• Effect of deficiency– Constipation– Long term deficiency may lead to bowel

cancer

Water

• Function– Formation of blood, cytoplasm– Solvent for transport of nutrients and

removal of waste– Enzymes only work in solution

• Good Food Source– Drinks, fruits, vegetables

• Effect of deficiency– dehydration

Pupil activity

• Design a mind map to summarise the information you have been taught so far on Nutrients.

fibre

water minerals

vitamins

Main Nutrients

Nutrients

Learning Outcomes

• describe the use of microorganisms in the food industry, with reference to yoghurt, bread and single cell protein

• describe the uses, benefits and health hazards associated with food additives, including colourings

Micro-organisms in the food industry

• Micro-organisms are heterotrophic – they take in ready made foods molecules from their environment.

• Examples of Microbes useful in food production– Acetobacter – vinegar production– Lactobacillus - yoghurt and cheese

production– “ripening” bacteria in cheese production– Fusarium and mycoprotein

Use of micro-organism

process Use of microorganism

Baking

Yeast is mixed with flour, sugar and water to make dough. The yeast respire the sugar and produce pockets of carbon dioxide that makes the dough rise.When the bread is baked the yeast is killed.

BrewingYeast respires sugar to form ethanol and carbon dioxide. The ethanol makes the drink alcoholic and the carbon dioxide gives the drink its fizz. The process is called fermentation.

Yoghurt making

Bacteria are used to ferment milk at 46oC. As a result lactic acid is produced which makes the milk lumpy (coagulate). The temperature is then reduced to 5oC to prevent further bacterial action. The whole process is carried out in sterile conditions

Single-cell

protein

This is a protein produced by microorgansism such as bacteria. Fungi or unicellular algae in a fermentation vessel. While the product contains 72% protein it does not taste very nice and is expensive to produce. An alternative is quorn – this is a mycoprotein made from a filamentous FUNGUS, which has 12.2% protein, low fat content and 6% fibre.

Food Additives

• Food Additives are substances with no nutritional value

• They are added to improve the– Appearance– Flavour– Texture– Storage properties of food

antioxidants

• Stop food reacting with oxygen, which may spoil the taste of the food or change it’s colour

Colourings

• Improve the appearance of food• Some colourings can be hazardous

– Sunset yellow • Hyperactivity• Allergic reactions and asthma

Flavourings

• Enhance the taste of the food– MSG – monosodium glutamate in

processed food– Sugar– Artificial sweetners e.g. aspartame

Preservatives

• Give processed foods a longer shelf life by preventing the growth of micro-organisms

• Disadvantages of preservatives– Sulphur dioxide - destroys vitamin B1

– Sodium nitrite - carcinogen

Progress Question

• Learn the groups of food preservatives listed below.

• Antioxidants• Colourings• Flavourings• Preservatives

• For each group state:– Its function in processed food– One advantage of its use– One disadvantage of its use

• Use page 46 and 47 in your textbooks to help you

Learning Outcomes

• describe tests for:– starch (iodine solution)– reducing sugars (Benedict's solution)– protein (biuret test)– fats (ethanol)

• Applying knowledge on food tests to identify unknown liquids

Activity

• Use your knowledge of food tests from last week to identify the food groups found in solutions A, B C and D.

Learning Outcomes

• understand the concept of a balanced diet

• describe:– a balanced diet related to age, sex

and activity of an individual– the effects of malnutrition in relation

to starvation, coronary heart disease, constipation and obesity

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 balanced diet?

Give three examples and explain the effects on health.

Dietary requirements

• Adequate diet– Provides sufficient energy for the

performance of metabolic work

• Balance diet– Provides all the dietary requirements

in the correct proportions• 1/7 fat• 1/7 protein• 5/7 carbohydrate

Dietary requirements

• Energy is provided by fat and carbohydrate intake

• Dietary requirements depend on– Age

• Energy demand increases until we stop growing

– Sex• Males use up more energy than females

– Activity• Physical work will use up more energy than office

work.

An Unbalanced dietMalnutrition

• An unbalanced diet could lead to– Obesity

• Risks include coronary heart disease and diabetes

– Too much animal fat can lead to high cholesterol

• Risks include coronary heart disease and angina

– Lack of protein in diet can lead to kwashiorkor

– Lack of fibre can lead to constipation and bowel cancer

– Vitamin and mineral deficiencies

Pupil Activity

• Calculating BMI

• Follow the instructions on the sheet to calculate your own BMI

• Answer the questions

Learning Outcomes

• Describe the effects of alcohol and the dangers of its misuse

Effects of alcohol

• Alcohol is a drug – It affects the nervous system– Depressant– Affects judgement and reaction time

Effects of Alcohol

• In small amounts– Feeling of relaxation

• In larger amounts– Affects balance– Dizziness– Slurred speech– Problems with vision– unconsciousness

Alcohol

• Long term effects– Addiction – alcoholism– Cirrhosis of the liver– Stomach ulcers– Cancers of the digestive system – Heart disease

• Drinking during pregnancy– Can affects the fetus– Increasing risk of miscarriage– Decreasing the average birth weight

Pupil Activity - BINGE

• Read through the information provided• Should pubs stop cutting prices

– Write a paragraph on what you think– Write a paragraph from the point of view

from one of the six characters.

• Remember whether or not you are for the scheme or against it you must give reasons.

Learning outcomes

• discuss:– the problems of world food supplies– the problems which contribute to

famine

Famine

• A severe shortage of food can lead to famine.

• Malnutrition– Suffer from deficiency disease– weakened immune system

• Results in– Adults too ill to work– Children become ill, adults care for them– People die and society lacks experience and

knowledge

Problems that lead to famine

• unequal distribution of food– Some areas produce more food

• environment is more suitable• More advanced agriculture

– Food surpluses can not always be moved to areas where food is limited

• Drought– Water is essential for plant growth and for

healthy animals– Low rainfall reduces crop yield.

Problems that lead to famine

• Flooding– Unpredictable flooding can reduce crop

yield– Plants are damaged– Fertile soil can be washed away

• increasing population– Need for food increases– More buildings reduces land available– More domestic animals reduces land

available for food production

Prep - Questions on Energy

• For Wednesday– Question 1

• For Friday– Questions 2, 3 and 4

Digestion

Learning Outcomes

• identify the gross structure of the alimentary canal and associated organs (mouth, oesophagus, stomach, small intestine: duodenum and ileum, large intestine: colon and rectum, anus, pancreas, liver)

• define ingestion, digestion, absorption, assimilation and egestion

What happens to the food we eat?

The gut as a production line

What happens to the food we eat?

• Ingestion– Intake of food into the mouth

• Digestion– Breaking down large, insoluble food

molecules into smaller soluble ones using enzymes

• Absorption– Digested food molecules pass across

the wall of the small intestine into the blood or the lymph

• Assimilation– Uptake of food molecules by cells

• Egestion– Passing out of undigested food, in the

form of faeces, from the anus

• Deamination– Removal of nitrogen containing

part of an amino acid as urea.

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

rectumcolon

pancreas

Large intestine

appendix

Small intestine

ileumDuodenum

Gall bladder

liver

oesophagus

Learning Outcomes

• define ingestion, digestion, absorption, assimilation and egestion

• describe the functions of the alimentary canal's various parts in relation to ingestion, digestion, absorption, assimilation and egestion of food

Learning Outcomes

• identify the types of human teeth and describe their functions

• state the causes of dental decay and describe the proper care of teeth

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.

Feeding in mammals

• Mechanical digestion– teeth are used to bite pieces of food

and to chew it into smaller pieces

• 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.

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

Structure of a tooth

• Colour in your diagram of the tooth,

• Colour in the positions of the different types of teeth in the human jaw

Structure of a tooth

crown

root

enamel

dentinegumPulp cavity

cement

Causes of dental decay

• Bacteria and food deposits form plaque• Bacteria feed on sugars and produce

acid• Acid dissolves the enamel forming a

hole• Dentine dissolves more rapidly• If hole reaches pulp cavity can lead to

bacterial infection, toothache and abscess

Proper care of teeth

• Avoid sugary foods• Use dental floss or a tooth pick• Use a fluoride toothpaste• Visit dentist regularly

Fluoride

• Growing children absorb fluoride from their diet

• It becomes part of enamel of developing teeth

• Enamel becomes more resistant to tooth decay

Adding fluoride to public water supplies

• Advantages– Tooth decay in

children decreases

– No need to buy fluoridated toothpaste

• Disadvantages– Form of mass

medication– Fluoride can cause

mottling (white patches) of teeth

– Only benefits growing children

– Unnecessary if proper care of teeth is taken

– Side effects (bone cancer?)

Learning Outcome

• describe the processes of chewing and peristalsis

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

Digestion of Starch

• Take 10ml of 1% starch solution– Test for starch– Test for sugars

Action of amylase on starch

• Put a drop of iodine solution into all the wells on a white spotting tile

• Add 10ml 1% starch solution and 10ml 1% amylase solution to a test tube.

• Every minute, test the contents of the test tube for starch.

• After 15 minutes – test the solution for the presence of sugars

• Write a conclusion on your results

Learning Outcomes

• The significance of producing small, soluble molecules

• describe:– digestion in the alimentary canal– the functions of a typical amylase,

protease and lipase, listing the substrate and end-products

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.

Digestion in Alimentary Canal

• Physical Digestion– Increases the surface area of food

• Chewing in the mouth• Churning food in stomach and small

intestine• Bile emulsifies fats – turns them into

smaller droplets with a larger surface area

• Chemical Digestion– Breakdown of large insoluble

molecules into smaller soluble ones– Enzymes act as biological catalysts –

they speed up the process– They work efficiently at body

temperature (37OC) and at a suitable pH

Digestion in Alimentary Canal

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 into maltose

(sugar) • Maltose is then broken down by maltase to form

glucose

Summary – digestive enzymes

Enzyme

Site of action

substrate

End products

Amylase

Mouth,duodenum

StarchMaltoseGlucose

Protease

Stomach, duodenum

Protein Amino acids

lipaseduodenum fat

Fatty acidsglycerol

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)

Prep

• Surface area and digestion– Read the information– Answer questions 1- 3– Answer question Ho2

• A snake swallowed a mouse whole. Explain why it took several days to digest it.

Learning Outcomes

• define the term catalyst• define enzymes as proteins that

function as biological catalysts• describe the effect of changes in

temperature and pH on enzyme activity

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 – 40oC)• Work best at an optimum pH

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

Protein Digestion

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

• Number the test tubes 1, 2 and 31. Add 1ml HCl2. Add 1ml Water3. Add 1ml HCl

• Do not add the trypsin until last1. Add 0.5ml water2. Add 0.5ml trypsin3. 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.

Learning Outcomes

• define enzymes as proteins that function as biological catalysts

• describe the effect of changes in temperature and pH on enzyme activity

Effect of temperature on enzymes

• The optimum temperature for enzyme controlled reactions is around 37oC– Above optimum

• Slows reaction down• Enzyme becomes denatured – enzyme loses it

shape, deforming the active site so that the substrate no longer fits.

– Below optimum• Slower reaction – lack of energy in molecules

Graph – effect of temperature on the rate of enzyme activity

Effect of pH on enzymes

• pH of a solution is how acid or alkaline it is• Most enzymes have optimum pH 7• Exceptions

– Pepsin pH2.0 stomach– Salivary amylase pH 6.8 mouth– Catalase pH 7.6 plants– Pancreatic amylase pH 9.0 duodenum

Effect of pH on enzymes

• An extreme pH can denature enzymes – permanently altering the active site

Graph - Effect of pH on enzyme activity

Pupil Activity

• Question sheet on enzymes

Learning Outcomes

• identify the small intestine as the region for the absorption of digested food

• describe the significance of villi in increasing the internal surface area

• describe the structure of a villus, including the role of capillaries and lacteals

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)

Villi

• Increase the surface area for absorption• Each villus contains

– Blood capillaries that absorb glucose and amino acids

– Lacteals which absorb fatty acids and glycerol

• Absorption is by– Diffusion – thin lining only 1 cell thick– Active transport – cells contain mitochondria

to provide energy

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

C

B

A

Model Gut Results

• In the next lesson– Take a sample of the water in the

boiling tube• Test the water for glucose• Test the water for starch

Conclusions of the experiment

• 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.

• indicate the role of the hepatic portal vein in the transport of absorbed food to the liver

Learning Outcomes

Hepatic portal vein

• Transports absorbed food from the small intestine to the liver

• After a meal, high concentrations of glucose and amino acids are in the blood– The liver reduces the levels back to

normal

The liver

• Excess glucose arriving in the liver is converted to glycogen for storage

• Excess amino acids can not be stored in the body– The liver removes these from the

blood and breaks them down to form an energy source and urea.

Fat

• Fatty acids and glycerol are absorbed into the lacteals

• Body cells take up the re-formed fat molecules– Used in respiration as a source of

energy– Stored

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.

Pupil Activity - Diagrams

• Use your notes and your textbooks to help you label the diagrams.

• Complete for prep.

• There are key words and phrases in the boxes beside the diagrams to help you.

The endWhat do they think they are looking at?