2.  All cells are made of the same elements.
◦ There are about 100 elements; 25 of them are
necessary for life.
◦ The smallest unit of an element is the atom.
◦ Atoms bond together in
chemical reactions to
form molecules.

3.  All large molecules in living things contain carbon. Carbon
atoms can form long chains, leading to a huge number of
possible compounds. There are four types of large molecules.
◦ Carbohydrates- are sugar starch, and cellulose. They provide the cell
with energy.
◦ Lipids- are fats, oils, and waxes that cannot mix with water. Lipids
often provide cells with energy.
◦ Proteins- are made of smaller molecules- amino acids. Proteins
control chemical reactions, support growth and repair of tissue, allow
movement, fight infections, and deliver oxygen.
◦ Nucleic acids- hold the instructions for maintenance, growth, and
reproduction of the cell. The two types are DNA and RNA.

4.  A water molecule, which
consists of two hydrogen
atoms and one oxygen
atom, is a polar molecule.
Because its two sides
have slightly different
charges, water is an
excellent solvent.
 Cell membranes are
composed of special
lipids that have one end
that repels water. Cell
membranes have double
layers of lipids. Both sides
of a membrane have
water-repellent ends
facing out.

5.  All cells need energy!
◦ Molecules store chemical energy in the bonds between their atoms.
Glucose is the energy source for most cells.
 Some cells capture light energy.
◦ Plants capture light energy from the sun through photosynthesis. This
process takes place in plant cells that have chloroplasts.
◦ Plants take water from the soil and carbon dioxide from the air. In
chloroplasts a pigment called chlorophyll absorbs light.
◦ The cell uses the energy to break water into hydrogen and oxygen. The
freed hydrogen and the carbon dioxide from the air are combined to
make glucose.
◦ Most oxygen from water is released into the air

6.  All cells, plant and
animal, break down glucose
for energy. In cellular
respiration, the
mitochondria in cells
converts small glucose
molecules into
energy, carbon dioxide, and
water. This process is the
other half of the energy
cycle.
 Photosynthesis and cellular
respiration are the two
processes in the energy
cycle.

7.  Materials move by diffusion.
◦ Diffusion- occurs when molecules spread out until
they are evenly mixed.
 Molecules move from a higher concentration to a lower
one.
 Small molecules diffuse through membranes during
passive transport.
 The diffusion of water through a membrane is called
osmosis.

8.  Cells use chemical energy for active transport. This type
of transport is needed for two purposes.
◦ 1. Cells need to move materials from lesser
concentrations to greater. Our kidneys use active
transport to remove excess salt from our bodies.
◦ Cells need to move large molecules.
◦ Molecules move into the cell through endocytosis and
out of it through exocytosis.
◦ In both cases, the cell membrane encloses the molecule
in a pocket, pinches off the pocket and removes it.

9. Chapter 3-
Cell Division!

10.  All materials needed by the cell must move across
the cell membrane. If the ratio of volume to surface
area is too large and the cell doesn’t change
shape, there will not be enough membrane area to
transport materials into and out of the cell.
 Cells therefore undergo the following:
◦ 1. staying small
◦ 2. dividing
◦ 3. changing shape