International Baccalaureate
Biology Option D
Human Physiology
Introduction
Welcome to the International Baccalaureate Revision Guide for Option D.
Sections D1 to D4 form the common core and sections D5 and D6 are the Additional Higher
Level sections.
The format is the same as the Core Guides with key points, simple diagrams and large
numbers of Grey Box Questions and Self-test quizzes.
Pale blue boxes contain information that helps with understanding by providing additional
information. However you do not need to learn this.
Other coloured boxes, such as these green and yellow ones,
contain information that you do need to know.
The Option is tested, along with experimental skills and techniques linked to the Core
material, in Paper 3.
I would greatly value any feedback on this Revision guide so that later editions can continue
to help students throughout the world. Please feel free to email me at Oxford Study Courses
– osc@osc-ib.com.
Ashby Merson-Davies
Contents
Core
D1 Human Nutrition
D2 Digestion
D3 Functions of the Liver
D4 The Heart
2
10
19
24
Additional Higher Level
D5 Hormones and Metabolism
D6 Transport of Respiratory Gases
35
40
Appendix
Glossary
Answers to Self-test quizzes
Answers to Grey box questions
52
52
52
Monitoring Dietary Intake
A healthy lifestyle includes a balanced diet and exercise. The nutritional content of food can be found
in tables such as the sample below.
Food
100g
Apples
Carrots
Milk
chocolate
Butter
Vitamins
B1, µg
B2, µg
0.04
0.02
0.06
0.05
Energy
kJ
197
98
Protein
g
0.3
0.7
Fat
g
0.0
0
Carbohydrate
g
12.0
5.4
Calcium
mg
4
48
Iron
mg
0.3
0.6
A, µg
5
2000
D, µg
0
0
2411
8.7
37.6
54.5
246
1.7
6.6
0
0.03
0.35
0
3006
0.5
81
0
15
0.2
995
1.25
0
0
0
C, µg
5
6
Table of the nutritional content of some foods.
Using a table like this is not only tedious but inaccurate as the values are affected by how the food is
prepared, for example the energy content for roast chicken will be very different from fried chicken.
Very detailed information can be obtained from software such as https://www.supertracker.usda.gov/
Food Tracker allows you to fill
in what you have eaten during
the day and plots this against
the recommended daily intake.
You can pair this up with the
Physical Activity Tracker.
This shows the result of
putting in some data into
Food Tracker.
Note though that it does not
give you any information
about minerals and
vitamins. These are
included in the data table at
the top of the page.
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IB Biology Option D 2016 © Ashby Merson-Davies
D2 Digestion
Secretion of Digestive Juices

Key points
 As food passes along the gut secretion of the digestive juices at each region must be coordinated with arrival of the food at that region.
 Thus juices are only secreted when required which:
 Saves resources – most digestive juices are enzymes which are synthesised from amino
acids.
 Saves energy – protein synthesis requires ATP.
 Control of secretion is carried out by both nervous and hormonal mechanisms.
 Digestive juices are secreted into the lumen of the gut by exocrine glands.
Exocrine Glands

Key features
 Exocrine glands secrete onto the surface of the body, e.g. tear glands, as well as the lumen of the
gut.
 Secretory cells of the gland are in groups called acini.
 A single group, an acinus, opens into a duct.
 Digestive juices are released by exocytosis.
 The secretory cells have a number of features that can be seen in an electron micrograph:
 Many mitochondria to provide energy for protein synthesis.
 Large amount of rER for synthesis of digestive enzyme.
 Nucleoli in the nucleus to synthesise ribosomes for rER.
 Several Golgi apparatuses for processing protein from rER.
 Large numbers of vesicles for storing the enzyme prior to secretion.
A single acinus
secretory cells
secretory vesicles
duct
A group of three acini with their ducts connecting
together, as seen under the light microscope.
nucleus
mitochondrion
rough endoplasmic reticulum
secretory vesicles
2.1 A single acinus cell
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IB Biology Option D 2016 © Ashby Merson-Davies