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IB BIOLOGY:
Option D - Human Physiology
These notes are designed to help you with paper 3, the extra option
paper!
These notes include the following topics:
- Human Nutrition
- Digestion
- Function of the Liver
- The Heart
- Hormones and Metabolism
,©️StudyWithKiki on Etsy
Topic 1: Human Nutrition
Outline why nutrients cannot be synthesised by the body, and why they have
to be included in the diet
● A nutrient is a chemical substance found in foods that is used in the
human body.
● There are six classes of nutrients – carbohydrates, proteins, lipids,
vitamins, minerals and water.
● Essential nutrients are those that cannot be synthesised by the body
and must be ingested as part of the diet.
● Non-essential nutrients can be made by the body or have a replacement
nutrient which serves the same dietary purpose. Carbohydrates are not
considered essential nutrients as human diets can obtain energy from
other sources without ill effect.
Describe how malnutrition may be caused by a deficiency, imbalance or
excess of nutrients in the diet
● Malnutrition is a health condition caused by a deficiency, imbalance or
excess of nutrients in the diet.
● It can be caused by an improper dietary intake of nutrients – e.g.
overnutrition (too much) or undernutrition (not enough). It can be
caused by the inadequate utilisation of nutrients by the body – e.g. due
to illness or disease.
● The symptoms of malnutrition will vary according to the specific nutrient
and the type of imbalance involved. Common signs of malnutrition
included stunted growth and wasting (undernutrition), as well as obesity
(over nutrition).
Determine the energy content of food by
combustion
● The energy content of food can be
estimated by burning a sample of known
mass and measuring the energy released
via calorimetry.
● Combustion of the food source causes the
stored energy to be released as heat,
which raises the temperature of water.
The amount of energy required to raise 1 g
,©️StudyWithKiki on Etsy
of water by 1ºC is4.18 J – this is the specific heat capacity of water.
● The equation for calculating the energy content of a food source via
calorimetry is as follows:
○ Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature
increase (ºC)
● The biggest source of error in calorimetry is usually caused by the
unwanted loss of heat to the surrounding environment.
● The food sources should be burnt at a constant distance from the water
to ensure reliability of results.
● The initial temperature and volume of water should also be kept
constant (1 g of water = 1 cm3 or 1 ml).
Comparing Energy Content
● The three types of nutrients that are
commonly used as energy sources are
carbohydrates, lipids (fats) and
proteins.
○ Carbohydrates are
preferentially used as an
energy source because they
are easier to digest and
transport
○ Lipids can store more energy
per gram but are harder to
digest and transport (hence
are used for long-term
storage)
○ Protein metabolism produces nitrogenous waste products which
must be removed from cells
● The relative energy content of carbohydrates, proteins and fats are as
follows:
- Carbohydrates – 1,760 kJ per 100 grams
- Proteins – 1,720 kJ per 100 grams
- Fats – 4,000 kJ per 100 grams
, ©️StudyWithKiki on Etsy
Amino Acids and Lipids
Explain why some amino acids are essential and how a lack of essential
amino acids affects the production of proteins
● Amino acids are the monomeric building blocks from which proteins are
constructed.
● There are 20 different amino acids which are universal to all living
organisms.
● Amino acids can be either essential, non-essential or conditionally
non-essential according to dietary requirements.
● Essential amino acids cannot be produced by the body and must be
present in the diet.
● Non-essential amino acids can be produced by the body and are
therefore not required as part of the diet.
● Conditionally non-essential amino acids can be produced by the body,
but at rates lower than certain conditional requirements (e.g. during
pregnancy or infancy) – they are essential at certain times only.
● A shortage of one or more essential amino acids in the diet will prevent
the production of specific proteins. This is known as protein deficiency
malnutrition and the health effects will vary depending on the amino
acid shortage.
Outline the cause and treatment of phenylketonuria (PKU)
● Phenylketonuria (PKU) is a
genetic condition that results
in the impaired metabolism of
the amino acid phenylalanine.
● It is a recessive disease
caused by a mutation to the
gene encoding the enzyme
phenylalanine hydroxylase.
● Normally excess
phenylalanine within the body
into tyrosine.
● In people with PKU, the excess
phenylalanine is instead converted into phenylpyruvate (also known as
phenylketone).
○ This results in a toxic build up of phenylketone in the blood and
urine (hence phenylketonuria).
IB BIOLOGY:
Option D - Human Physiology
These notes are designed to help you with paper 3, the extra option
paper!
These notes include the following topics:
- Human Nutrition
- Digestion
- Function of the Liver
- The Heart
- Hormones and Metabolism
,©️StudyWithKiki on Etsy
Topic 1: Human Nutrition
Outline why nutrients cannot be synthesised by the body, and why they have
to be included in the diet
● A nutrient is a chemical substance found in foods that is used in the
human body.
● There are six classes of nutrients – carbohydrates, proteins, lipids,
vitamins, minerals and water.
● Essential nutrients are those that cannot be synthesised by the body
and must be ingested as part of the diet.
● Non-essential nutrients can be made by the body or have a replacement
nutrient which serves the same dietary purpose. Carbohydrates are not
considered essential nutrients as human diets can obtain energy from
other sources without ill effect.
Describe how malnutrition may be caused by a deficiency, imbalance or
excess of nutrients in the diet
● Malnutrition is a health condition caused by a deficiency, imbalance or
excess of nutrients in the diet.
● It can be caused by an improper dietary intake of nutrients – e.g.
overnutrition (too much) or undernutrition (not enough). It can be
caused by the inadequate utilisation of nutrients by the body – e.g. due
to illness or disease.
● The symptoms of malnutrition will vary according to the specific nutrient
and the type of imbalance involved. Common signs of malnutrition
included stunted growth and wasting (undernutrition), as well as obesity
(over nutrition).
Determine the energy content of food by
combustion
● The energy content of food can be
estimated by burning a sample of known
mass and measuring the energy released
via calorimetry.
● Combustion of the food source causes the
stored energy to be released as heat,
which raises the temperature of water.
The amount of energy required to raise 1 g
,©️StudyWithKiki on Etsy
of water by 1ºC is4.18 J – this is the specific heat capacity of water.
● The equation for calculating the energy content of a food source via
calorimetry is as follows:
○ Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature
increase (ºC)
● The biggest source of error in calorimetry is usually caused by the
unwanted loss of heat to the surrounding environment.
● The food sources should be burnt at a constant distance from the water
to ensure reliability of results.
● The initial temperature and volume of water should also be kept
constant (1 g of water = 1 cm3 or 1 ml).
Comparing Energy Content
● The three types of nutrients that are
commonly used as energy sources are
carbohydrates, lipids (fats) and
proteins.
○ Carbohydrates are
preferentially used as an
energy source because they
are easier to digest and
transport
○ Lipids can store more energy
per gram but are harder to
digest and transport (hence
are used for long-term
storage)
○ Protein metabolism produces nitrogenous waste products which
must be removed from cells
● The relative energy content of carbohydrates, proteins and fats are as
follows:
- Carbohydrates – 1,760 kJ per 100 grams
- Proteins – 1,720 kJ per 100 grams
- Fats – 4,000 kJ per 100 grams
, ©️StudyWithKiki on Etsy
Amino Acids and Lipids
Explain why some amino acids are essential and how a lack of essential
amino acids affects the production of proteins
● Amino acids are the monomeric building blocks from which proteins are
constructed.
● There are 20 different amino acids which are universal to all living
organisms.
● Amino acids can be either essential, non-essential or conditionally
non-essential according to dietary requirements.
● Essential amino acids cannot be produced by the body and must be
present in the diet.
● Non-essential amino acids can be produced by the body and are
therefore not required as part of the diet.
● Conditionally non-essential amino acids can be produced by the body,
but at rates lower than certain conditional requirements (e.g. during
pregnancy or infancy) – they are essential at certain times only.
● A shortage of one or more essential amino acids in the diet will prevent
the production of specific proteins. This is known as protein deficiency
malnutrition and the health effects will vary depending on the amino
acid shortage.
Outline the cause and treatment of phenylketonuria (PKU)
● Phenylketonuria (PKU) is a
genetic condition that results
in the impaired metabolism of
the amino acid phenylalanine.
● It is a recessive disease
caused by a mutation to the
gene encoding the enzyme
phenylalanine hydroxylase.
● Normally excess
phenylalanine within the body
into tyrosine.
● In people with PKU, the excess
phenylalanine is instead converted into phenylpyruvate (also known as
phenylketone).
○ This results in a toxic build up of phenylketone in the blood and
urine (hence phenylketonuria).
