Unit 1 - Chapter 5 Sources of Energy
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Carbohydrates can be:
• Monosaccharides • Disaccharides • Polysaccharides
An example of a monosaccharide is
glucose
An example of a disaccharide is
sucrose
An example of a polysaccharide is
Glycogen
Blood sugars which the carbohydrate
monosaccharide
Blood sugars provide an immediate source of
energy for respiration
If blood glucose levels fall they are topped up by the conversion of
muscle glycogen then liver glycogen to glucose
In prolonged periods of exercise fatty acids from the break down of fat reserves become
the major energy source as the carbohydrates are depleted
Amino acids cannot be stored in the
body
Many amino acids which are not needed (surplus) are
broken down or deaminated
When amino acids are broken down they give a
substrate for respiration and toxic urea
Toxic urea is eliminated by the
kidney
Protein from the muscles can be used as an energy source under extreme circumstances such as
starvation
Lipids make an efficient energy store as fat contains
twice as much energy per gram compared to carbohydrate or protein
The insulating properties of lipids are used to retain heat in an electrical
insulation film around nerve cells
Steroid hormones are fat soluble and so are absorbed and transported in
lipids
Steroid hormones are lipids such as
testosterone
Fat pads beneath the skin protect the
tissues beneath the skin
Fat pads are found in
feet and hands
Benedicts reagent turns a brick red in the presence of
reducing sugar
4 examples of reducing sugar are
• Glucose • Fructose • Maltose • Lactose
When sucrose fails to give a positive result with Benedicts reagent add a few drops of
Hydrochloric Acid
Barfoed’s Test turns a brick red immediately in the presence of a
reducing monosaccharide sugar
An example of a reducing monosaccharide sugar is
glucose and fructose