Digestion &
Respiration
Cell Respiration can be
divided into two parts
»
Aerobic Respiration
˃ Aer- = prefix, means air
˃ Requires oxygen to generate ATP
˃ One glucose molecule produces 36-38 ATP
»
Anaerobic Respiration
˃ An- = prefix, means not or without
˃ Does not require oxygen
˃ Generates very little ATP
˃ Examples:
What is energy?
» Energy is the power used to do work or to produce heat or light.
Energy cannot be created or destroyed, but can be changed from one form to another.
» It is measured in kilojoules (kJ) or calories (kcal, cal)
1kJ = 1000J 1MJ = 1000kJ
Energy from food
» When we consume food and drink, energy provided by carbohydrates,
proteins, and fats (and alcohols) are metabolized and used by our bodies.
» Carbohydrates, proteins, fats and alcohols are broken down into smaller
compounds which are then oxidized in the cells of the body (cellular respiration).
» Carbon dioxide is removed when food is oxidized. The heart and lungs
work together to get oxygen-rich blood to all the organs, tissues, and
cells. The circulatory system moves all these substances to and from cells where they are need or produced, responding to changing physical
Metabolism
»
Your metabolism is a set of chemical reactions
that breaks down matter to acquire energy.
»
There are two categories:
˃ Catabolism: breaks down organic matter to acquire energy in cellular
respiration
Energy providing nutrients
» Energy in the diet is provided by the carbohydrates, proteins,
and fats.
» 1 gram of carbohydrate provides 66.88 kcal.
» 1 gram of protein provides 71.06 kcal.
Energy in the diet - alcohol
» Alcohol also provides the body with energy.
» However, it is not considered a nutrient, because it is not
essential for survival.
» 1 gram of alcohol provides 121.22 kcal.
» People who regularly consume excessive amounts of alcoholic
drinks derive much of their energy intake from alcohol.
» They may also suffer from nutritional deficiencies and alcohol
Energy expenditure
Different people need different amounts of energy, depending on a variety of factors, including their:
» basal metabolic rate (BMR)
» level of physical activity
» age
» gender
Energy in the diet
» The energy provided by a food or drink depends on the amount
of carbohydrates, proteins, alcohols and fats it contains.
» Carbohydrates provide less energy than proteins, fats and
alcohols.
» Look closely at the following examples of foods high in
Which nutrient contributes the
most energy?
Per 3.53
oz. Energy Carbohydrate Fat Protein
White bread 3891.58 kcal 3083.168 kcal 247.038 kcal 561.374 kcal
Butter 12,794.98
kcal 0 kcal 12,759.45 kcal 35.53 kcal
Canned tuna 1762.706
kcal 0 kcal 92.796 kcal 1669.91 kcal
Energy intakes
Experts have estimated the average requirements for energy for different types of people.
These figures are known as Estimated Average Requirements (EAR) for energy.
Experts also recommended that:
» about 50% of our energy intake should come from carbohydrates
» no more than 35% of our energy intake should come from fats
Energy intakes
» The average energy intake for an adult age 31-50 that walk
1.5-3 miles a day at 3 mph (in addition to regular daily
physical activity) should consume on average of 2400 calories/ day.
» Requirements vary from person to person depending on a
Adolescents’ Energy Balance
»
In order to develop and grow normally,
adolescents need more food energy than just
for metabolic & physical activities.
Basal metabolic rate
» The basal metabolic rate (BMR) is the rate at which a person
uses energy to maintain the basic functions of the body, for example breathing.
» BMR is measured when a person is at complete rest, and
varies between person to person (depending on physical activity, body composition, and energy used).
» Men usually have a higher BMR than women because they
tend to have a larger muscle mass.
» The BMR accounts for approximately 60% of an individual’s
Being active everyday
» It is recommended that children and young
people participate in at least 60 minutes of moderate intensity everyday where breathing rate and heart rate increase.
» The increase in heart rate increases the amount
of oxygen available for the body to use to process food into energy.
» Activities that increase muscle strength and
flexibility as well as bone strength, should also be included at least once a week.
» Regular activity will help maintain energy
Energy balance
» To maintain body weight it is necessary to balance the energy
derived from food with that expended in activity.
» Energy balance is achieved when energy in = energy out.
» It is important to maintain a healthy weight and is a delicate
balance between healthy diets and physical activities.
» 60% should be used by the BMR; 30% should be used by daily
physical activities; 10% should be used to digest and oxidize food
» Food components can be used three ways:
˃ Fuel metabolic and physical activities ˃ Used in growing body tissues
Positive energy balance
» When the diet provides more energy than is needed, it
is stored as fat and the person puts on weight over time.
» People who are in positive energy balance over an
Overweight and obese
» Excess energy is stored in adipose tissue (fat tissue) and can
build up if energy intake continues to be too high, or activity levels remain too low.
» Being overweight or obese is associated with an increased risk
Negative energy balance
» A person is said to be in negative energy balance when there
is insufficient energy from the diet to meet energy demands of the body.
» Energy is derived from energy stores and the person loses
weight.
» People who achieve a negative energy balance over an
Underweight
» When too little energy is consumed over a period of time, the
body derives energy from fat stores leading to weight loss.
» When too much fat is lost, the person becomes underweight.
» Being underweight is associated with health problems, such as
Monitoring energy balance
» For adults, change in weight is a good guide to energy balance.
» The Body Mass Index (BMI) is a good indicator of whether a
person is underweight, overweight or a healthy weight.
» The BMI range should only be used for people aged 18 years of
age and over.
» We are all encouraged to maintain a healthy weight by
