Elements and Atoms
Purpose / Big Picture
● Living things are made of atoms from a limited set of elements.
● Life does not simply mirror the environment’s element supply—organisms select and
concentrate certain elements inside cells.
1) Elements
● Definition: An element is a substance made of only one kind of atom and cannot be
decomposed into simpler substances.
● How many exist:
○ ~90 elements occur naturally on Earth.
○ Only about 25 are used to build living things (mainly).
Elements in Earth vs. living things (key comparison)
● Lithosphere (Earth’s crust) most common atoms:
○ Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium, etc.
● Human body most common atoms:
○ Hydrogen, Oxygen, Carbon, Nitrogen (plus smaller amounts of calcium,
phosphorus, etc.)
● Main takeaway:
○ Living things use only a fraction of available elements, and their proportions
differ greatly from the environment.
○ Example: H, C, N are <1% of atoms in Earth’s crust but about 74% of atoms in
living matter.
Concentration of rare elements (examples)
● Some marine animals concentrate elements like vanadium and iodine up to 1000×
seawater levels.
● Some algae can concentrate uranium → idea of “mining” uranium from seawater
through biological uptake.
2) Atoms
● Definition: An atom is the smallest part of an element that can combine with other
elements.
Purpose / Big Picture
● Living things are made of atoms from a limited set of elements.
● Life does not simply mirror the environment’s element supply—organisms select and
concentrate certain elements inside cells.
1) Elements
● Definition: An element is a substance made of only one kind of atom and cannot be
decomposed into simpler substances.
● How many exist:
○ ~90 elements occur naturally on Earth.
○ Only about 25 are used to build living things (mainly).
Elements in Earth vs. living things (key comparison)
● Lithosphere (Earth’s crust) most common atoms:
○ Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium, etc.
● Human body most common atoms:
○ Hydrogen, Oxygen, Carbon, Nitrogen (plus smaller amounts of calcium,
phosphorus, etc.)
● Main takeaway:
○ Living things use only a fraction of available elements, and their proportions
differ greatly from the environment.
○ Example: H, C, N are <1% of atoms in Earth’s crust but about 74% of atoms in
living matter.
Concentration of rare elements (examples)
● Some marine animals concentrate elements like vanadium and iodine up to 1000×
seawater levels.
● Some algae can concentrate uranium → idea of “mining” uranium from seawater
through biological uptake.
2) Atoms
● Definition: An atom is the smallest part of an element that can combine with other
elements.
