unit 1 diet

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Biology Form 4 Page 3 Ms. R. Buttigieg

1.2 Composition and properties of carbohydrates, lipids and proteins

(GCSE Biology Chapter 2 pgs 11-13; Food test experiments pg. 95)

In this section we will be looking at the importance of these food types as:

Energy sources Food stores

Structural materials.

We shall also be investigating the materials making them up.

A. Carbohydrates

These are organic substances that contain 3 elements: Carbon, Hydrogen and Oxygen.

Hydrogen and oxygen are usually in the ratio of 2:1.

Food sources include bread, cereals, sugar.

These can be divided into 3 main groups:

1. Monosaccharides - carbohydrates made from a single sugar molecule.

a. e.g. glucose, fructose, galactose.

b. These are often made of ring structures

c. They are soluble in water

d. They are important as an energy source

e. They serve as building blocks for larger molecules

(disaccharides and polysaccharides)

2. Disaccharides carbohydrates made when two monosaccharides combine together.

a. e.g. glucose and glucose combine to form maltose

fructose and glucose combine to form

sucrose

b. When the 2 monosaccharides combine awater molecule (2 hydrogen and 1 oxygen)

is lost we call this a condensation

reaction.

c. The bond linking them together is called a

glycosidic bond.

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3. Polysaccharides - carbohydrates made from many monosaccharides linked together

(even with 10, 000).

Three important polysaccharides are: starch, cellulose, glycogen

i. Starch is a major food store in plants.

ii. Glycogen is a major food store in animals.

iii. Cellulose is the main component of cell walls and is very strong.

These are made from lots of glucose molecules joined together.

B. Lipids

Like carbohydrates, lipids are compounds that contain the elements carbon,hydrogen and oxygen. The only difference is that lipids contain much less oxygen

in their molecules.

The most common lipids arefats and oils.

The difference between them is that fats are solid at room temperature, while oils are liquids.

Both fats and oils are insoluble in water.

Lipids are made from 3 molecules of fatty acids and 1 molecule of glycerol.

These lipids are known as triglycerides as they consist of 3 fatty acids combined with glycerol.

The fatty acids, combine with glycerol in a condensation reaction where water is lost.

There are many different fats and oils depending on the fatty acid that combines with glycerol.

Examples of fatty acids are: Palmitic acid, oleic acid, stearic acid.

We need fat:

1. as a store ofenergy2. to make cell membranes3. for warmth (insulation)4. as some body organs are surrounded by fat for protection

Too much fat can be

harmful. Cholesterol

is a fatty deposit that

can narrow arteries

and contribute to heart

disease.

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C. Proteins

These are complex organic substance made up of: carbon, hydrogen, oxygen, nitrogen and often sulphurand phosphorus.

Our body cells are mostly made of protein.

Proteins are made from many amino acids joined together.

Amino acids are joined together bypeptide bonds.

Found in meat, eggs, fish, beans, and nuts.

An amino acid contains an acidic group (COOH) and an amino group (NH2)

R* is a different element or group for each amino acid. It is what makes amino acids different

from each other.

Amino acids join together by condensation reactions (water is removed) to form long

polypeptide chains.

Amino acid + Amino aciddipeptide

Amino acid + Amino acid + Amino acidtripeptide

Amino acid + Amino acid + Amino acid + Amino acid + Amino acid + polypeptide

There are 20 different amino acids and these are combined together in different ways to

form different proteins each having a different shape.

If the shape is changed this can result in a different protein. When temperatures rise above 50oC,

proteins lose their shape and so their properties. We say that they have become denatured and

their peptide bonds are broken. Even if the protein is cooled again the shape cannot be regained.

C

R*

H

H

H

N C

O

OHAmino group Acid group

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We need proteins:

1. for growth and to build new cells which replace old ones.

2. as they form part of cell membranes and of some organelles of the cells (e.g. ribosomes)

3. for forming hormones and enzymes (these will be discussed later on)

D. FibreD. FibreD. FibreD. Fibre

Fibre (also called roughage) comes from plants. Fibre is not actually digested; it just keeps food moving smoothly through

your system.

Fibre provides something for your gut muscles to push against, so preventsconstipation.

Cereals and vegetables contain a lot of fibre.

Summary

Food substance Elements present Use in body Deficiencydisease

Found in

Carbohydrate

Basic units aremonosaccharidesconsisting of a 6

carbon ring, that jointo formdisaccharides orpolysaccharides.

Carbon (C),Hydrogen (H)Oxygen (O)

There are always

twice as manyhydrogen atoms asoxygen e.g. C6H12O6

Supply of energy

(Glycogen is a storeof energy, sugarsare a ready supply)

1g yield 17 kJ ofenergy

Often linked to lackof enough food ofany typei.e. starvation

Cane sugar,sucrose, fruitand honey(glucose)

Potatoes, rice,

cereals (starch) Liver (glycogen)

Protein

Basic units aminoacids joinedtogether by peptidebonds

Carbon (C),Hydrogen (H)Oxygen (O)Nitrogen (N)

Often also

Sulphur (S)Phosphorus (P)

Growth and repair ofcells and tissues,Making enzymes

1g yield 17 kJ of

energy

Kwashiorkor:

swollen abdomen,loss of hair

Meat, fish, soya,milk, cheese, peasand beans, eggs

Lipids (Fats & Oils)

basic units are fattyacidsjoined toglycerol

Carbon (C),Hydrogen (H)Oxygen (O)

Store of energy,For insulation

1g yield 39 kJ of

energy

Lack of certain fattyacids causes variousdiseases

Dairy products, milk,fish, nuts, oils, fattymeat

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Food Tests

Food Substances used for test Details of test Sign of a positiveresult

Starch

Iodine solution

Drop iodine solution

into the solution to be

tested

Solution turns blue

black

Glucose

Benedicts solution Add Benedicts solution

too the solution and

boil in water bath for

2 minutes

Solution turns orange

red

Fat

Ethanol Ethanol is shaken with

the substance to be

tested and then a few

drops of the ethanol

are dropped in the

water

A milky white emulsion

forms in the water

Protein

Sodium hydroxide,

copper sulphate

(Biuret test)

Add several drops of

dilute sodium

hydroxide solution

followed by several

drops of copper

sulphate solution

Solution turns purple.

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Junior Lyceum Annual 2000

1 Complete the following table about food tests:

Reducing

Sugar

Starch Protein Lipid/Fat

What are thetesting

reagent/s?

What is the

colour of a

positive

result?

(8 marks)Junior Lyceum Annual 2003

2. A student claims that nuts are rich in oil and protein. Describe two separate simple

tests by which the student can show that nuts are rich in these two nutrients. (3, 4)

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

3. Answer the following on a separate paper (or on the back of this page):

1. Why are carbohydrates important?2. Name the two main carbohydrates.3. What is the chemical test forstarch?4. What is the chemical test forglucose?5. Why is fat needed in our bodies?6. How would you test for fat?7. Why is protein important to our cells?8. What is the chemical test for protein?9. Why is fibre important in our diet?10.Name a food that contains fibre.

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1.3 Vitamins (see GSCE Biology pg. 13, 88,89)

We only need these in small amounts, but they are important for good health. These can be

found in fruit, vegetables and cereals. Deficiency diseases occur if vitamins are lacking.

Sources and functions of vitamins A, C and D in a human diet.

Vitamin Source (Found in) Function Deficiency symptoms

A

Retinol

Butter, milk, cheese,

liver, margarine, eggs

Important for the formation of

a substance important in night

vision. Helps resist disease.

Poor night vision that may lead to

complete night blindness.

C

Ascorbic

acid

Oranges, lemons,

grapefruit, carrots,

potatoes, fresh green

vegetables, tomatoes

Keeps the skin strong and

supple. Helps resistance to

infections.

Without it the skin cracks and the

gums bleed a condition called

scurvy. Wounds fail to heal.

D

Calciferol

Butter, milk, cheese,

egg-yolk, liver, fish

liver oil.

Important in bone and tooth

formation. Also helps the

bones harden in children

Without it the bones stay soft ( a

disease called rickets). In adults

causes osteomalacia which may

result in fractures.

Experiment to estimate the amount of vitamin C

DCPIP is a liquid that loses its colour when it comes into contact with vitamin C.

Pour 1cm3 of DCPIP solution into a test tube.

Take a 1cm3 syringe of vitamin C and see how many drops it takes to decolorize the DCPIP.

Compare the amounts of vitamin C in different fruit juices.

Natural fats in the skin change to a form of calciferol in sunlight.

DID YOU KOW THAT: Vegetarians do not eat meat but there are

different kinds of vegetarians.

Some dont eat meat but eat fish; others eat no meat or fish but eat dairy

products.

Vegans eat no animal products at all, but it is important they replace the

protein, vitamins and minerals (like iron and calcium) with other forms

like cereals, seeds, beans and nuts.

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1.4 Mineral salt requirements (see GSCE Biology pg. 43-44, 87,88)

Also referred to as: mineral, salts or mineral salts.

Functions of nitrogen and magnesium in plants.

Plants obtain their minerals by absorbing them with the help of their roots from the soil. They

pass into the xylem, which then transports them through the plant cells.

Mineral Use in plant Deficiency symptoms

Nitrogen For growth as it is important to buildamino acids and proteins.

Poor growth and yellow leaves

Magnesium Used to make chlorophyll. Yellow leaves

Note: Nitrogen is obtained in the form of nitrates from the roots.

Sources and functions of calcium, phosphorus and iron in a human diet.

Mineral Source (Found in) Function Deficiency symptoms

Iron Red meat (liver & kidney),eggs, groundnuts, bread,

spinach and gree n

vegetables.

Needed for the hemoglobin thatis found in blood and is

important in carrying oxygen

round the body.

Anemia not enoughred blood cells.

Insufficient hemoglobin

is made and theoxygen carrying

capacity of blood isreduced.

Phosphorus Present in nearly all food.Mostly found in: cheese, meat

and fish

Needed in bones and in DNA Usually present sodeficiencies dont occur

Calcium Milk, cheese, hard tap water 1. Deposited in bones andteeth to make them hard.

2. Helps in blood clotting.

3. Helps in transmission ofnerve impulses.

Weak bones, ricketsand excess bleeding.

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Work to do:Work to do:Work to do:Work to do:

1. Choose 2 vitamins and 2 minerals and state a) the food in which they can be found, b) their uses in thebody and c) their deficiency diseases. (12 marks)

2. Junior Lyceum 2002.

Explain why each of the following is needed in the human diet. Name one good source for each.

a. Calcium: ___________________________________________________________________

_____________________________________________________________(1)

Source: _____________________________________________________________________(1)

b. Iron: _______________________________________________________________________

_____________________________________________________________(1)

Source: _____________________________________________________________________(1)c. Vitamin C: __________________________________________________________________

_____________________________________________________________(1)

Source: _____________________________________________________________________(1)

(total 6 marks)

3. Junior Lyceum 2003.

The table below shows four different snacks and four statements relevant to different food

groups.

MEAL STATEMENT

A ) scrambled eggs on toast a) stops scurvy

B) glass of milk b) helps towards healthy bones and teeth

C) spaghetti c) body builders and iron providers

D) glass of orange juice d) good energy food

a) Pair up each of the meals above with the most appropriate statement.

A ________ B ________ C _________ D ________ (4)

b) People who do a lot of physical exercise often believe that they need a large amount ofprotein.

(i) Explain why this belief may be wrong.

___________________________________________________________________________(2)

(ii ) Suggest a more appropriate nutrient and give a good source of the nutrient suggested.

Nutrient _______________________ Source _______________________ (2)

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1.5 Enzymes (see GSCE Biology pg. 14-18)

Enzymes are PROTEIS that are capable of making reactions happen at a faster rate so are

also CATALYSTS.

There are 2 main types of enzymes Breaker enzymes (catabolic) & Builder enzymes (anabolic)

Breaker enzymes called catabolic enzymes help break large molecules into smaller ones.An example where these enzymes are important is in digestion where large food molecules are

broken down into small ones that can be used.

In the digestive system 3 of the main substances that need digesting are starch, proteins and fats.

They are each broken down with the help of a different enzyme

Food Broken into Enzyme Produced in

Starch Maltose (a sugar) Amylase Mouth, pancreasProtein Amino acids Protease Stomach, pancreas

Fat Fatty acids and

glycerol

Lipase Pancreas

Answer these:

1. Name the enzyme that digests proteins2. Explain why lipase does not digest starch.3. List the 5 properties of enzymes

Enzymes work on substances called the substrates. Theplace on the enzyme where the reaction takes place is called

the active site. Each enzyme is specific for one substrate.

Enzymes have 5 important properties:

1. They are all proteins2. Each enzyme controls one particular reaction

3.

They can be re-used4. They are affected by temperature

5. They are affected by pH

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Builder enzymes called anabolic enzymes help small molecules to join together and form

bigger ones. These are important in helping to build important molecules in our cells.

An example where builder enzymes are used is in the formation of new proteins from amino

acids that are joined together by peptide bonds.

Enzymes and temperature

In many reactions, increasing the temperature results in an increase

in the reaction rate, while decreasing them results in a slower rate.

The same can be said for enzyme-controlled reactions. However,

this is only true up to 50oC for above this temperature, enzymes get

denatured (lose their shape so cannot combine with the

substrates) and cannot continue to carry out their function.

What is the optimum temperature indicated by the graph? _______

Enzymes and pH

Most enzymes have a particular pH at which they workbest. For example protease enzymes in the stomach work

best at pH 2. Amylase (the enzyme in saliva) cannot

work at this pH. The pH at which an enzyme works best

is called the optimum pH.

If an enzyme is placed in an extreme pH it can also getdenatured.

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Intracellular and extracellular enzymes

Intra means inside; extra means outside

Intracellular enzymes are those that work inside cells in reactions that take place there; likerespiration. Extracellular enzymes are those that are secreted from cells to work outside them,

like what happens with fungi that digest food extracellularly by secreting enzymes e.g. on bread.

Another example are the enzymes secreted into the digestive system by organs like the pancreas

to break down food particles.

Economic uses of enzymes (see GSCE Biology pg. 18, 330)

Enzymes are cheap to use in industry as: They dont need high temperatures to work so less fuel needed

Can be re-used so are only needed in small amounts.

They are specific for particular substances so can be controlled more.

Examples of enzyme uses are in:

Brewing (making beer)

Baking

Cheese making Biological washing powders

In brewing and baking enzymes present in living yeast change sugar to alcohol and carbon dioxide.

In cheese making an enzyme called rennin is extracted from calves stomachs (now produced artificially

by genetic engineering calledchymosin). It helps in clotting milk in the first stages of cheese making.

Complete the following: (9 marks)

a) Enzymes __________________ up the rate of chemical __________________.

b) Enzymes are __________________ because they only work on one substrate.

c) The substrate fits into the __________________ site on the surface of the

__________________.

d) With an increase in __________________, the rate of reaction __________________ but

eventually a temperature is reached which __________________ the enzyme.

e) Enzymes can be re-used, so only __________________ amounts are needed.

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1.6 A balanced diet in humans (see GSCE Biology pg. 89-91)

This is a diet containing the right balance of the different foods that meet the needs of

individuals. These needs are dependent on the lifestyle, activity and developmental stage

of an individual.

Basically it must contain:

Carbohydrates

Lipids

Proteins

Minerals

Vitamins

Fibre

Water

In the right quantities.

Foods like bread, cereal and potatoes they would be very important providing energy, andthat would give us the energy for growth, the energy to run round to do normal activities,

or the energy to go out and play.

Fruit and vegetables would give us lots of important vitamins and minerals which weneed and some of these can help protect us against heart disease and cancer.

As for milk and diary foods go they would be very important from the point of view ofproviding enough calcium.

Calcium is needed for bone development and growth. Meat and foods like chicken andfish and eggs, they are important for protein and also for some minerals and especially

iron.

Protein would be very important again for growth and the development of muscles andtissue which makes our body grow and iron is also important for healthy blood.

http://www.bbc.co.uk/northernireland/schools/4_11/uptoyou/healthy/t_cf01.shtml

unit 1 diet

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