and exercise :
body mass and what are our energy requirements? (and a note on inherited
Doc Brown's GCSE level Biology exam study revision notes: There are various sections to work through, after 1 they can be read and studied in any order.
Sub-index of biology notes on health, diet and exercise
body mass and what are our energy requirements?
Metabolism is the scientific term used for all the
chemical reactions that go on inside an organism's body. Metabolic reactions
synthesise molecules of all shapes and size for specific uses in an
organism. Metabolic reactions break down larger molecules down into smaller
ones (e.g. in digestion). Metabolic reactions supply the energy needs for
the chemistry of every cell from respiration in the mitochondria.
is your metabolism? What is metabolic rate? What energy do you
need and why?
The rate at which all the chemical
reactions in the cells of the body are carried out (the metabolic rate)
varies with the amount of activity you do and the proportion of muscle to
fat in your body.
A person loses mass when the energy
content of the food taken in is less than the amount of energy expended by
You need energy to fuel the chemical
reactions in your body to keep you alive and these reactions are called your
Different people have small differences
in their resting metabolic rates because e.g. muscle needs more energy than
fatty tissue, so more muscular people tend to have a higher metabolic rate
because of the higher ratio of muscle to fat.
Bigger people tend to have a higher
metabolic rate because more energy is needed to maintain a greater mass of
On average men tend to have a greater
metabolic rate because they tend to have a greater proportion of muscle.
If your job involves heavy manual labour, not surprisingly,
you energy intake needs to be higher.
Different people have different energy requirements
depending on you body mass ('weight').
For every kg of body mass, it is reckoned that you need 5.4
kJ of energy per hour, as the basic energy requirement (BER) that you
need to maintain all your bodily functions.
This can be calculated: BER (kJ/day) = 5.4 x 24 hours x body
All the cells of your body need chemical energy, therefore
the bigger you are and the more physically active you are, the more energy
you need e.g. very physical work or movement e.g. running or physically
demanding hard labour.
Average daily energy requirements: men 12180 kJ (2900 kcal)
and women 9240 kJ (2200 kcal)
Remember this varies widely because of your weight or age,
how you spend the day - an office worker sitting at a desk will need far
less energy than somebody doing a hard physical job working on a building
For example, a 70 kg person may use 450 kJ of energy walking
for 30 minutes, but use 1800 kJ running for 30 minutes.
Note on energy units
Calories are 'old' units of energy, but still in common use.
1 calorie = 4.2 joules of energy (1 kcal = 4.2 kJ, k
indicating a factor of 1000)
If a person needs 2000 kcal/day, that is equal to 8400
inherited factors also affect our health
Metabolic rate may be affected by
Your DNA profile ==> gene expression ==>
inherited characteristics, can have some bearing on your metabolic rate eg
an underactive thyroid gland which can lower metabolic rate, increase
fatigue and ultimately cause obesity. Any energy not used will be stored as
People can inherit factors that affects
the blood cholesterol level.
Cholesterol is an essential fatty
substance for good health and its in every cell in the body but if it is too
high it causes fatty deposits on the inner surfaces of blood vessels causing
higher blood pressure and heart disease.
who exercise regularly are usually healthier than people who take little
Summary of learning objectives and key words or phrases about our 'basic energy
Know what is meant by your 'basic energy requirement' (BER).
Know how BER is defined BER and be able to calculate it, given
Be able to relate BER to the body's metabolism, body mass in
terms of our energy requirements.
Know that inherited factors may influence a person's
metabolic rate and therefore their basic energy requirement.
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