A balanced diet

Question 1

The food that we eat is called our diet. No matter what you like to eat

Answer 1

your dis must include the following five groups of food substances if your body is to work properly and stay healthy - carbohydrates

Question 3

Carbohydrates

Question 4

Carbohydrates only make up about 1% of the mass of the human body

Answer 4

but they have a very important role. They are the body’s main ‘fuel’ for supplying cells with energy. Cells release this energy by oxidising a sugar called glucose

Question 5

Glucose is found naturally in many sweet-tasting foods

Answer 5

such as fruits and vegetables. Other foods contain different sugars

Question 6

We can get all the sugar we need from natural foods such as fruits and vegetables

Answer 6

and from the digestion of starch. Many processed foods contain large amounts of added sugar. For example

Question 7

In fact

Answer 7

we get most of the carbohydrate in our diet not from sugars

Question 8

Starch is only found in plant tissues

Answer 8

but animal cells sometimes contain a very similar carbohydrate called glycogen. This is also a polymer of glucose

Question 9

As you will see

Answer 9

large carbohydrates such as starch and glycogen have to be broken down into simple sugars during digestion

Question 10

Another carbohydrate that is a polymer of glucose is cellulose

Answer 10

the material that makes up plant cell walls. Humans are not able to digest cellulose

Question 13

Lipids

Question 14

Lipids contain the same three elements as carbohydrates - carbon

Answer 14

hydrogen and oxygen - but the proportion of oxygen in a lipid is much lower than in a carbohydrate. For example

Question 15

The chemical ‘building blocks’ of lipids are two types of molecule called glycerol and fatty acids. Glycerol is an oily liquid. It is also known as glycerine

Answer 15

and is used in many types of cosmetics. In lipids

Question 16

These substances have been linked to heart disease

Question 18

Proteins

Question 19

Proteins make up about 18% of the mass of the body. This is the second largest percentage after water. All cells contain protein

Answer 19

so we need it for growth and repair of tissues. Many compounds in the body are made from protein

Question 20

Most foods contain some protein

Answer 20

but certain foods such as meat

Question 21

However

Answer 21

we don’t need much protein in our diet to stay healthy. Doctors recommend a maximum daily intake of about 70g. In more economically developed countries

Question 22

Like starch

Answer 22

proteins are also polymers

Question 25

Minerals

Question 26

All the foods you have read about so far are made from just five chemical elements: carbon

Answer 26

hydrogen

Question 27

Some are present in large amounts in the body

Answer 27

for example calcium

Question 28

Table 4.1 shows just a few of these minerals and the reasons they are needed.If a person doesn't get enough of a mineral from their diet

Answer 28

they will show the symptoms of a 'mineral deficiency disease'. For example

Question 29

Similarly

Answer 29

16-year-olds need about 12 mg of iron in their daily food intake.

Question 30

If they don't get this amount

Answer 30

they can't make enough haemoglobin for their red blood cells . This causes a condition called anaemia.

Question 31

People who are anaemic become tired and lack energy

Answer 31

because their blood doesn't carry enough oxygen.

Question 32

During the early part of the twentieth century

Answer 32

experiments were carried out that identified another class of food substances. When young laboratory rats were fed a diet of pure carbohydrate

Question 33

Vitamin A is needed to make a light-sensitive chemical in the retina of the eye.. A lack of this vitamin causes night blindness

Answer 33

where the person finds it difficult to see in dim light. Vitamin C is needed to make fibres of a material called connective tissue. This acts as a 'glue'

Question 34

Lack of vitamin C causes scurvy

Answer 34

where the mouth and gums become damaged and bleed.

Question 35

Vitamin B is not a single substance

Answer 35

but a collection of many different substances called the vitamin B group. It includes vitamins B1 (thiamine)

Question 36

The main vitamins

Answer 36

their role in the body and some foods which are good sources of each

Question 37

Notice that the amounts of vitamins that we need are very small

Answer 37

but we cannot stay healthy without them.