Energy in food

Question 1

How is energy released from food?

Answer 1

Energy is released from food by respiration, which is an oxidation process, similar in some ways to combustion. If food is combusted, it releases energy, mainly as heat.

Question 2

How can we work out the energy value of any particular type of food?

Answer 2

We can work out the energy value of any particular type of food by assuming that respiration releases the same energy in total as combustion does.

Question 3

How is the energy value found?

Answer 3

The energy value is found using a food calorimeter or bomb calorimeter.

Question 4

How is combustion carried out?

Answer 4

A weighed sample of food is completely burned in an atmosphere of oxygen. The heat released by this combustion is transfered to a known volume of water, which rises in temperature as a result.

Question 5

How can the energy value of food be calculated?

Answer 5

energy value of food in calories per gram= (temperature rise /°C * volume of water/cm3) / (mass of food sample / g)

energy value in kilojoules per gram = energy value in calories per gram * 4,2 / 1000

Question 6

What are the three main energy providfing organic molecules?

Answer 6

The three main energy providing organic molecules found in food are fats, carbohydrates, and proteins.

Question 7

Energy value of fats

Answer 7

39kJ per g

Question 8

Energy value of proteins

Answer 8

20kJ per g

Question 9

Energy value of carbohydrates

Answer 9

17kJ per g

Question 10

Why do carbohydrates provide most of our energy?

Answer 10

Carbohydrates provide most of our energy, not because there is most energy available per gram in carbohydrates, but because we eat more grams of carbohydrates than of proteins or fats.

Question 11

What is the SI unit of energy?

Answer 11

joule (J)

Question 12

Which units is the amount of energy contained in food measured in?

Answer 12

The amount of energy contained in food is measured in either joules (J) or calories (cal)

Question 13

1kJ

Answer 13

1kJ= 1000 J

Question 14

1 kcal

Answer 14

1 kcal=1000 cal

Question 15

What is a calorie?

Answer 15

A calorie is the amount of energy needed to raise the temperature of 1 cm3 of water by 1 C.

Question 16

Calories to joules

Answer 16

1 calorie= 4,2 joules

Question 17

What is metabolism

Answer 17

The total of all the chemical reactions in the body is called metabolism.

Question 18

What drives metabolism?

Answer 18

It is driven by the enrgy from respiration, so the amount of energy needed depends on how many metabolic reactions a person is carrying out.

Question 19

What are the three factors that the amount of metabolism depends upon?

Answer 19

BMR, activity or exercise, dynamic action of food.

Question 20

BMR

Answer 20

The processes required to simply stay alive include breathing. excretion, thinking, and maintaining a constant temperature.

The energy consumed by these processes in one day is called basal metabolic rate.

The BMR is different for males and females, and gets less as a person gets older.

Question 21

Activity or exercise

Answer 21

The amount of activity or exercise requires muscular work and extra temperature regulation.

Question 22

Dynamic action of food

Answer 22

Eating food means extra work for the digestive system and the liver. The energy demand simply caused by eating is called the dynamic action of food.

Question 23

energy requirement per day formula

Answer 23

energy requirement per day = BMR + activity + dynamic action of food.

Question 24

What kind of energy does food contain?

Answer 24

Food contains a lot of stored chemical energy; when you eat, your body breaks down these foods into smaller components and absorbs them for fuel.