Transcript Cell Membrane

Name the organelle that performs each
function:
1.
a.
b.
c.
d.
2.
3.
Creates ATP from other compounds
Tags and packages other molecules
Conducts photosynthesis
Contains DNA and controls the cell
A cell is eukaryotic, and has a cell wall and
chloroplasts. What kind of cell is it?
A cell is eukaryotic, but has no cell wall or
chloroplasts. Does it have mitochondria?
How do cell boundaries work?
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The cell membrane provides some protection
and support for the cell.
It also regulates the materials that enter and
leave the cell. This is due to its composition:
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The cell membrane is a lipid bilayer, meaning that it is
made of two layers of lipids (fats). The individual
phospholipids form a strong but flexible barrier.
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Both proteins and
carbohydrates are
embedded in the cell
membrane.
Some of those proteins
form pores, channels,
pumps and carrier
proteins, which serve to
import and export
materials.
The carbohydrates are
used to function as an I.D.,
which enables cell-to-cell
interaction.
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Cell walls are used to
provide further
support and
protection.
Most cells have them.
Animal cells are the
most common cells
that don’t have one.
Cell walls are often
made of fibers, such
as cellulose and chitin.
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As stated earlier, passive transport is the
movement of molecules WITHOUT spending
energy.
Diffusion is the simplest type of passive
transport to understand. In any solution,
particles will spread out from a high
concentration to a low concentration.
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Experiment: At home, place a sugar cube in a glass
of water, and leave it alone. Over time, the sugar
dissolves, and diffuses equally in the water.
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Diffusion is important for equally distributing
molecules without spending energy.
Sometimes, membranes can interrupt diffusion,
however.
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If the membrane allows diffusion a substance X, it is
permeable to X.
If it doesn’t, it is impermeable to X.
Most barriers – including the cell membrane –
are selectively permeable, meaning that they
allow only some substances to diffuse.
1.
2.
3.
4.
The cell membrane functions as a lipid bilayer,
meaning it is made of _____________________.
Diffusion is the spread of particles over time.
Does it use energy?
Diffusion occurs when particles move from
_____ concentration to _____ concentration.
The cell membrane allows some substances to
pass, but not others. It is ___________________.
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Because the cell membrane is only permeable
to some compounds, they CANNOT move
from high to low concentrations.
The cell membrane is a good example of a
semipermeable membrane. It only allows some
materials to pass, but blocks many other
compounds as well.
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However, the cell membrane IS permeable to
water. This leads to a fascinating phenomena:
If a cell is dunked in extremely salty water,
then the salt CANNOT enter the cell.
However…
The water inside the cell CAN LEAVE the cell.
This results in both the inside and outside of
the cell having the same levels of salt.
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As another example, we place another cell in a
beaker of pure water. In this case, the salt inside
the cell cannot leave the cell to make the inside
and outside have the same concentration.
However, the water outside the cell CAN rush
in, which does make both environments have
the same concentration of salt.
This diffusion of water across a semipermeable
membrane is called osmosis.
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Note the image to the
left. The left side is very
salty, and the right side
is not.
The salt CANNOT pass
through the membrane.
The water can, though.
This results in both
sides having the same
salt content (though
different volumes).
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To determine whether
water will enter or
leave the cell, we
compare the
concentration of the
cell to the
concentration of the
solution.
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If the cell is less
concentrated, the
solution is
hypertonic.
If the cell is more
concentrated, the
solution is hypotonic.
If they have the same
concentration, the
solution is isotonic.
Osmosis is the diffusion of what compound?
The purpose of osmosis is to make the
concentration of solute the same inside and
outside the cell. Why does water diffuse, and
not the actual solute?
What will happen to a cell placed in:
1.
2.
3.
a.
b.
c.
A hypertonic solution?
An isotonic solution?
A hypotonic solution?
Use the picture to the right
to answer the Q’s.
1.
Is the solution
hypertonic, hypotonic
or isotonic?
2.
Which direction will
water flow into the
cell?
3.
What happens to the
cell?
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Facilitated diffusion is a variant of passive
transport. In this case, some materials diffuse in
and out of the cell through the assistance of
various proteins.
Protein channels are gated pores in the cell
membrane. They allow ions (charged particles)
to pass.
Carrier proteins are used to transport large
molecules in and out of the cell. They are
specific to one type of molecule.