Transcript What do you know about light?

Cells and Their
Environment
The Cell Membrane
• The Cell Membrane is composed of
two layers of phospholipids (fat).
Phospholipids
• Each phospholipid has one end that
is “water loving” containing a
phosphate group. The other end is
a fatty tail (lipid), and is “water
fearing”.
Phosphate group
(water loving)
Fatty tail
(water fearing)
• A cell membrane is formed by a
double layer of phospholipid
molecules in which protein
molecules are embedded.
Protein Molecules
• Protein molecules are embedded in the
cell membrane, the fatty ends of the
phospholipid hold them in place.
• Proteins serve as an attachment site for
molecules that are entering the cell.
• When an appropriate molecule comes
along it attaches itself to the protein,
which pulls it into the cell.
Channels
• Cell membranes have several
channels through which calcium,
sodium, and other atoms can enter
or exit the cell.
Cell Membrane Function
• The cell membrane encloses the
inside of the cell and acts as a
protective barrier against molecules
outside of the cell.
• Cells allow some materials to enter
or leave but not others.
Permeable/Impermeable
• Cells are permeable to some
materials and impermeable to
others.
• Permeable means permitting passage
and impermeable means to not
permit passage.
• The cell membrane is semipermeable (or selectively permeable);
that is it allows only specific
substances in and out of the cell.
Movement Across the
Membrane
• There are various ways that
substances enter and leave cells.
– Passive Transport
– Active Transport
Passive Transport
• Passive Transport involves the movement
of molecules across the cell membrane
without the use of energy.
• Water, lipids, and lipid-soluble particles
pass through the membrane in this way.
• Diffusion and Osmosis are examples of
passive transport.
• Passive Transport:
• http://www.brainpop.com/science/c
ellularlifeandgenetics/passivetransp
ort/preview.weml
Diffusion
• Diffusion is the movement of molecules from an
area of high concentration to an area of low
concentration.
• Molecules are constantly moving. When the
molecules collide with each other they bounce
off of each other.
• This movement causes the molecules to
gradually spread outward and become evenly
distributed. This condition is called dynamic
equilibrium.
• Diffusion:
• http://www.brainpop.com/science/m
atterandchemistry/diffusion/previe
w.weml
Diffusion and Cells
• Diffusion is one of the ways substances
move into and out of the cell.
• If a substance that a cell uses, such as
oxygen, is in low concentration inside the
cell, the molecules of the substance will
diffuse across the membrane until the
concentration is the same inside and
outside.
Concentration gradient
• When a molecule moves from an
area of high concentration to an
area of lower concentration, it is
moving down a concentration
gradient.
Diffusion
Text Book Questions
• Complete questions 1 – 5 on page 29
of the text book.
Osmosis