Food &

Diet

Food is needed for:1. Energy and warmth2. Growth3. Repairing and replacing tissues4. Keeping the body healthy and fight disease

The amount of energy needed by a person depends upon:-

1) age 2) sex 3) temperature4) job

A balanced diet is composed of the right amounts of:-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or

roughage

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

The food guide pyramid

Malnutrition condition that results from taking an

unbalanced diet in which certain nutrients are:

lacking in excess (too high an intake) or in the wrong proportions

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

Uses of water in organisms:-1. as part of cytoplasm (most cells contain 75%

water)2. as a solvent in which chemical reaction occur3. to activate enzymes4. for photosynthesis in plants5. for growth and support in plants6. to transport substances round the body (blood

has a lot of water)7. brings about cooling on evaporating

Animals get water from:- 1. Drinking2. Eating3. Chemical reactions e.g.

respiration

O2

food

ATP

H2O

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

CARBOHYDRATES contain the elements:

Carbon Hydrogen Oxygen

have more oxygen than fats Glucose:

is the simplest carbohydrate (C6 H12 O6)

Easy to remember elements:

Food ElementsCarbohydrates C, H, OLipids C, H, OProteins C, H, O, N [sometimes

S and P]

Food rich in carbohydrates

Uses of carbohydrates:- a) provide energy (17kJ/g)

Sugar in energy drink equivalent to six pastries.

Question: MAY, 2004Give biological explanations for each of the following statements:

The diet of athletes is usually high in carbohydrates. (5)Athletes need a lot of energy. Carbohydrates are the body’s main energy source. Carbohydrates like starch in bread are digested into glucose. Glucose is used in respiration to release energy. If athletes take in monosaccharides, i.e. sugars e.g. glucose, they are provided with energy very quickly.

Uses of carbohydrates:-

Cell wall

c) to build cell walls in plants

b) to store energy e.g. starch in potatoes or roots

Storage organs

Uses of carbohydrates:- d) fibre is important to prevent constipation

Food sources of fibre: whole wheat, bran, fresh or dried fruit & vegetables. Constipated!!

In what form are excess carbohydrates stored?

1) in plants:

2) in animals:

Name two places in animals where glycogen is stored.

starch

glycogen

Liver & muscles

Three types of carbohydrates

1. Monosaccharidese.g. glucose, fructose

2. Disaccharidese.g. maltose, lactose, sucrose

3. Polysaccharidese.g. starch, glycogen, cellulose

Sweet &

Soluble

Monosaccharides

Disaccharides

PolysaccharidesNot sweet

& Insoluble

Name the monosaccharide which forms starch, glycogen and cellulose.

Glycogen Cellulose Starch

Glucose

How do starch, glycogen and cellulose differ?

Glycogen Cellulose Starch

The way glucose units are linked together

Question: MAY, 2008 (IIB)Where in a plant would you expect to find:

i) Cellulose (1)ii) Starch (1)

i) Cellulose – found in cell walls of plant cellii) Starch – found stored in roots /

storage organs

Why is the tired athlete choosing sugar rather than starch?

Sugars, especially monosaccharides can

be used for respiration right away.

Starch needs to be digested first.

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

LIPIDS a name for fats and oils contain the elements:- C, H, O

lard

Food rich in lipids:-

Nuts

Egg yolk

uses of lipida) provide energy (39 kJ/g)b) store energy

uses of lipidc) insulation in mammalsd) protection of delicate

organs from bumps

Fat around kidney.

Fat lines body wall of a rabbit.

Question: MAY, 2008 (IIB)Explain why one kilogram of starch crops releases less energy when burnt, compared to one kilogram of oil crops. (2)

Starch is a carbohydrate whilst oil is a lipid. Carbohydrates have a lower energy content than lipids.

building blocks of a lipid molecule: Glycerol Fatty acids

A molecule of fat

excess lipids are stored:- 1) in the ADIPOSE TISSUE under the skin2) around organs

Fat around heart.

What does this pyramid show about

intake of lipids?

Few lipids must be taken.

What happens to a person’s weight when:

Weight remains constant

What happens to a person’s weight when:

Weight increases

Obese person

What happens to a person’s weight when:

Weight decreases

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

PROTEINS contain the elements:-

C, H, O, N (sometimes S and P)

food rich in proteins:- Meat Fish Egg white Cheese

Uses of proteins:-1. for growth2. for cell repair and replacement3. to make enzymes4. to make antibodies

What are the building blocks of proteins called?

Amino acids

Two amino acids are linked by a:

dipeptide:2 amino acids linked together

Peptide bond

Polypeptide: many amino acids are linked

A protein: many polypeptides joined up

different amino acids occur in proteins

Two types of amino acids:

1. Essential [8 amino acids]must be eaten as they

cannot be made by the body

2. non-essentialcan be made by the

body

contain significant amounts of all the essential amino acids

Source: animals : eggs, meat, fish, cheese

deficient in one or more essential amino acid Source: plants

For example, corn is deficient in one amino acid

Individuals who eat only corn would show symptoms of protein deficiency.• This is true from any diet limited to a

single plant source, including: Rice Wheat or potatoes

are an exception:

Soya bean protein is a good source of protein,

for vegetarians and vegans or for people who cannot afford

meat. Explain.

Have you ever tasted: Soya bean milk Tofu

Tofu is made by coagulating soya milk and then pressing the resulting

curds into soft white blocks.

• is referred to as:

Artificial meat is manufactured from : soya beans bacteria and fungi

Artificial meat is flavoured and textured to taste like

chicken or ham.

How can protein deficiency from a vegetarian diet be avoided?

By eating a combination of plant

foods that complement each other to supply all essential amino acids.

– For example, beans supply the lysine that is missing in corn, and corn provides the methionine which is deficient in beans.

Excess proteins: cannot be stored in the body are broken down in the liver by a process

called DEAMINATION the waste product produced is called UREA

liver

Components of a balanced diet :-1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

MINERAL SALTS contain certain elements that help cells to

function properly

CALCIUM is needed for:-

a) hard bones and teeth b) muscles to contractc) to clot blood

is found in: milk cheese fish

Rickets: deformed bones

deficiency of calcium

IRON is needed to build the red pigment in blood

called haemoglobin

IRON is found in:

red meat like liver & kidneys

green vegetables: spinach, broccoli

Normal amount of red blood cells

Anaemic amount of red blood cells

A lack of iron results in: ANAEMIA

Question: MAY, 2004Give biological explanations for each of the following statements:

a) A dietician suggested to an anaemic person to include liver in the diet. (5)Person lacks iron. Red meat like liver is rich in iron. Iron is needed to form haemoglobin in red blood cells.

b) Nutritionists often recommend a low intake of fried foods. (5)

Fats provide a lot of energy. May lead to obesity.

Fried foods are rich in cholesterol that may block arteries = higher risk for a heart attack.

MAGNESIUM forms the centre of the chlorophyll molecule

in green plants

No magnesium: yellow leaves

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

VITAMINS needed in small quantities for the normal

chemical activities of the body

cannot be used as: a source of energy

OR to build cell structures

A disease develops if a vitamin is missing. How can the person be cured?

By taking the missing vitamin.

vitamins can be :- a) Water soluble – vitamins B and Cb) Fat soluble – vitamins A, D, E, K

Water-soluble vitamins are lost from the vegetables when they are boiled but

not when steamed.

Why is it better to steam vegetables

rather than boil them?

Vitamin Food source Deficiency disease

A Milk, liver Night blindness

C Citrus fruit, potatoes

Scurvy

D Milk, liver Rickets

Carrots are a rich source of vitamin A

Vitamin A prevents night blindness.

QUESTION: MAY 2010 Explain why the student used this picture when mentioning night blindness. (2)Night blindness is caused by a lack of Vitamin A in the diet. 1 markCarrots are a good source of Vitamin A that can help to prevent night blindness. 1 mark

Found in Citrus fruit

Deficiency of Vitamin C:

Which vitamin prevents colds?

Vitamin D is made by the action of sunlight on the

skin.

Deficiency of Vitamin D:

Normal Rickets

NOTE: Lack of calcium Lack of vitamin D

Reason:

Vitamin D helps the body to absorb calcium from the foods we eat. The more calcium the body can absorb, the stronger the bones will become

Question: Sep, 2004What special provisions should be made in the diet of young children and pregnant mothers? Explain why each provision you mention is important. (6, 4)Young children:1. High protein content food – e.g. meat for growth2. Drink a lot of milk – supplies proteins, calcium,

Vitamin A & D.3. Include carbohydrate-rich foods – for energy

Pregnant women:1. Folic acid (a vitamin B) – in citrus

fruit, legumes: to form the nervous system of the embryo

2. Food rich in iron – e.g. liver, green vegetables: to have enough blood in placenta to nourish embryo

3. Calcium-rich food – e.g. dairy products to supply embryo with calcium to form its skeleton

Question: Sep, 2004

Give a biological explanation for each of the following statements.a) Daily inclusion of too much Vitamin C in the

diet is a waste. (2)Vitamin C cannot be stored in the body as it is water-soluble. Lost in urine.

Give a biological explanation for each of the following statements.a) Small doses of Vitamin D (5-10mg per day)

are recommended for housebound people spending a lot of time indoors. (2)Vitamin D cannot be made by the action of sunlight on the skin. To have enough

Vitamin D, supplements are needed.

Question: MAY, 2004Give biological explanations for each of the following statements:

a) School canteens are encouraged to sell unsweetened cereals rather than sweets. (5)Sweets are carbohydrates that provide energy. Too much sweets may lead to obesity. Obesity leads to higher risk of diseases.Sweets increase chance for tooth decay.

b) Young children are encouraged to eat dairy products regularly. (5)

Milk is rich in: calcium – needed to form

strong bones and teeth. proteins – needed for

growth. Vitamins – for healthy growth; e.g. vitamin A to

prevent night blindness and vitamin D to help in the absorption of calcium and to prevent rickets.

Components of a balanced diet :-

1. Water2. Carbohydrates3. Lipids4. Proteins5. Mineral salts6. Vitamins7. Dietary fibre or roughage

DIETARY FIBRE or ROUGHAGE sources of fibre:-

vegetables fresh fruit bran cereals wholemeal bread

Cellulose : is the main source of dietary fibre

Explain why although humans cannot digest dietary fibre, it is still important.

Functions of roughage:-1. adds bulk to the contents of the intestine

and keeps food moving along the gut

Gut

Functions of roughage:-2. prevents constipation as fibre retains water

so that the faeces are soft3. prevents cancer of the colon (part of the

intestine)

faeces

Food Test Colour change

Starch

+ iodine solution Yellow to blue black

Iodine solution

Starch

Look at this picture. Is starch present in potato? Yes.

Food Test Colour change

Protein(Biuret test)

+ sodium hydroxide solution + 1-2 drops of copper sulfate solution

Blue to purple

Egg white [protein]

1. Sodium hydroxide solution2. Copper

sulfate solution

A positive test for protein was obtained for………………albumin

Food Test Colour change

Oil+ ethanol + shake + water + shake

A white emulsion forms

Food Test Colour change

Oil rub food onto a dry piece of filter paper

A greasy spot forms

Food Test Colour change

Glucose + Benedict’s solution or Fehling’s solution + heat

Blue to brick red

or orange

Food Test Colour change

Glucose + Benedict’s solution or Fehling’s solution + heat

Blue to brick red

or orange

Food Test Colour change

Starch

+ iodine solution Yellow to blue black

Protein(Biuret test)

+ sodium hydroxide solution + 1-2 drops of copper sulfate solution

Blue to purple

Oil

1) + ethanol + shake + water + shake

2) rub food onto a dry piece of

filter paper

A white emulsion forms

A greasy spot

forms

Glucose + Benedict’s solution or Fehling’s solution + heat

Blue to brick red

or orange

When the food to be tested is a solid:

1. Crush the food with some water using a pestle and a mortar.

2. Filter.3. Add the reagents to the filtrate.

pestle

mortar

How do you find how much energy is present in

a peanut?

Burn a peanut Record rise in

temperature of a known volume of water.

Why is it better to have a larger volume of water?

To absorb more heat.

Q = mc

4.2 kJ kg-1 C-1 1000: to work mass in kg

Heat energy = mass x specific heat capacity x temperature rise

Energy in peanut = mass of water x 4.2 x temperature rise in C

1000

Question: MAY, 2011 [IIB]A group of biology students would like to

compare the energy stored in two types of nuts: a peanut and an almond.

Describe an experiment to show how this is carried out. In your report include:i) The apparatus required; (You can present

this in the form of a diagram.) (2)

ii) The method; (3)Known quantity of the nut (kept constant for both nuts) ignited and held under test tube with known amount of water (kept constant for both nuts). The temperature of water before lighting the nut and after burning will be recorded.

iii) The measurements that need to be taken; Initial temperature and final temperature Mass of peanut/almond Volume of water (2)

iv) The factors that need to be kept constant throughout the experiment; (2)Same mass of nut and same quantity of water.

v) ONE possible source of error. (1) Heat loss to surroundings Heat reaching water not evenly spread

out Burning of nut is not complete

Burning food in a bomb calorimeter.

How is the energy content of food found out?

Bomb CalorimeterThe apparatus which is used to find the energy content of food.

Better than previous setup:1. No heat loss to air.2. Even heat spread.

The End