The most common chemical elements in living things are carbon, hydrogen, oxygen, and nitrogen. Other important elements include sulfur, calcium, phosphorus, iron, and sodium, each playing roles like being part of proteins or bones. Water has a polarity that allows it to form hydrogen bonds between molecules, giving it properties useful for living things like being a solvent, coolant, and transport medium for metabolic reactions.

1. 3.1 Chemical Elements & Water
Topic 3 The Chemistry of Life

2. Chemical Elements & Water
3.1.1 State that the most frequently occurring chemical elements
in living things are carbon, hydrogen, oxygen and nitrogen.
3.1.2 State that a variety of other elements are needed by living
organisms, including sulfur, calcium, phosphorus, iron and
sodium.
3.1.3 State one role for each of the elements mentioned in 3.1.2.
(Refer to the roles in plants, animals and prokaryotes).

3. Chemical Elements & Water
3.1.4 Draw and label a diagram showing the structure of water
molecules to show their polarity and hydrogen bond formation.
3.1.5 Outline the thermal, cohesive and solvent properties of water.
3.1.6 Explain the relationship between the properties of water and
its uses in living organisms as a coolant, medium for metabolic
reactions and transport medium.

4. Elements, Atoms and Ions
Everything around us is made up of matter.
The basic building block of matter is the atom.
All matter is made up of atoms. Atoms are made up of:
• Protons, neutrons, electrons
Elements are composed of one type of atom.
The elements can be placed in order forming:
– The Periodic Table of the Elements
There are about 112 elements
– About 90 of those occur naturally, the rest are produced in laboratories
When an atoms loses or gains electrons it becomes an ion (a charged atom)
– eg:Sodium atom Na and a Sodium ion Na+
– eg: Chlorine atom Cl and a Chlorine ion Cl-

5. The Atom
electrons
neutrons
protons
Electrons
orbit the
nucleus

6. Elements, Molecules and Compounds
Elements are made of one type of atom
– eg: carbon, oxygen, iron
Molecules are 2 or more atoms chemically bonded together:
– They can be different or the same atom
Compounds are two or more different elements chemically
bonded together.

7. Elements and Living Things
All living things are similar in a number of ways.
Living organisms contain many different elements.
Some elements are needed in very small amounts while other
are needed in large quantities
The three most common chemical elements occurring in living
organisms are:
– Carbon (C) usually forms 4 covalent bonds with other elements
– Hydrogen (H) forms 1 covalent bond with other elements
– Oxygen (O) usually forms 2 covalent bonds with other elements

8. Elements and Living Things
Other elements are required by living organisms
Some of these include:
– Nitrogen -needed for proteins
– Phosphorus –part of phosphate groups in ATP and DNA molecules
– Calcium - needed to make strong bones and teeth
– Iron - needed to make haemoglobin (red blood cells)
– Sodium - needed for transmitting nervous impulses and maintaining
electrical potentials across membranes
– Sulfur needed for proteins
– Potassium - needed for transmitting nervous impulses

9. Organic and Inorganic Compounds
Organic Compounds are defined as compounds containing
carbon that are found in living organisms
All other elements are defined as Inorganic Compounds.
There are however a few inorganic compounds that contain
carbon:
– Eg: carbon dioxide and carbonates
Three type of organic compounds are found in large amounts in
living organisms:
– Carbohydrates
– Lipids
– Proteins

10. Water
Water is vitally important to all living organisms.
Water is made up of 2 Hydrogen atoms and I Oxygen
atom chemically bonded together (H2O).
Because of the shape of the molecule, water molecules have a
slightly negative side and a slightly positive side
As a result water is a polar molecule.
This means that water molecules attract each
other and form hydrogen bonds between
themselves.

11. The Properties of Water
Water is a very versatile substance.
It has many properties that make it significant to living organisms.
These include:
– Transparency
• Light can pass through water.
– Cohesion
• Water molecules stick together (H bonding due to its polar nature), surface tension
– Solvent properties
• Many substances dissolve in water (substances can be carried in water)
– Thermal properties
• Water has a relatively high specific, Melting Point and Boiling Point
• Water can store heat
• Water can be used as a coolant

12. IBO guide:
3.1.1 State that the most frequently occurring chemical elements in
living things are carbon, hydrogen, oxygen and nitrogen.
3.1.2 State that a variety of other elements are needed by living
organisms, including sulfur, calcium, phosphorus, iron and sodium.
3.1.3 State one role for each of the elements mentioned in 3.1.2.
(Refer to the roles in plants, animals and prokaryotes).

13. IBO guide:
3.1.4 Draw and label a diagram showing the structure of water
molecules to show their polarity and hydrogen bond formation.
3.1.5 Outline the thermal, cohesive and solvent properties of water.
Aim 7: Data logging could be carried out to compare the thermal
properties of water with those of other liquids.
TOK: Claims about the “memory of water” have been categorized
as pseudoscientific. By what criteria can a claim be judged to be
pseudoscientific?

14. IBO guide:
3.1.6 Explain the relationship between the properties of water
and its uses in living organisms as a coolant, medium for
metabolic reactions and transport medium.