Section 3, Chapter 1
Cells and Heredity
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An element is any substance that cannot be
broken down into simpler substances.
Ex: Oxygen
The smallest unit of an element is an atom.
The elements found in living things include
carbon, hydrogen, oxygen, nitrogen,
phosphorus, and sulfur.
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When two or more elements combine
chemically, they form a compound.
Ex: Carbon Dioxide
The smallest unit of many compounds is
called a molecule.
Most elements in living things occur in the
form of compounds.
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Some important groups of organic
compounds found in living things are
carbohydrates, lipids, proteins, and nucleic
acids.
Most compounds that contain carbon are
called organic compounds.
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A carbohydrate is an energy-rich organic
compound made of the elements carbon,
hydrogen and oxygen.
Sugars and starches are examples of
carbohydrates.
Carbs are important components of some cell
parts. Ex: the cellulous found in the cell walls
of plants is a type of carbohydrate.
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Lipids are energy-rich organic compounds
made of carbon, hydrogen, and oxygen.
They contain even more energy than
carbohydrates.
Cells store energy in lipids for later use.
EX: during winter, a dormant bear lives on
energy stored in fat within its cells.
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Proteins are large organic molecules made of
carbon, hydrogen, oxygen, nitrogen and in
some cases, sulfur. A bird’s feather, a
spider’s web, and your fingernails are mainly
made of proteins.
Protein molecules are made up of smaller
molecules called amino acids. Although there
are only 20 common amino acids, cells can
combine them in different ways to form
thousands of different proteins.
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Much of the structure of cells is made up of
proteins.
The proteins known as enzymes perform an
important function in the chemical reaction
that takes place in the cells.
An enzyme is a type of protein that speeds up
a chemical reaction in a living thing.
EX: enzymes in your saliva speed up the
digestion of food by breaking down starches
into sugars in your mouth.
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Nucleic acids are very long organic molecules
made of carbon, oxygen, hydrogen, nitrogen
and phosphorus.
There are two kinds of nucleic acids:
Deoxyribonucleic Acid (DNA) and Ribonucleic
Acid (RNA)
DNA – is the genetic material that carries
information about an organism and is passed
from parent to offspring.
RNA – plays an important role in the
production of proteins.
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Most chemical reactions within cells could not
take place without water.
Water also helps cells keep their size and
shape.
Because water changes temperature slowly, it
helps keep the temperature of cells from
changing rapidly.