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CELL MEMBRANE AND
TONICITY
Chapter 8
Warm up I week 8
• Depth of Knowledge Level 1
• The science of naming and classifying organisms
is
• A. taxonomy.
• B. taxidermy.
• C. phylogeny.
• D. morphology.
Warm up 2 week 8
• A horse and a donkey may interbreed with each other and
produce offspring, but the offspring are sterile. This occurs
because the horse and the donkey belong to a different
• A. species.
• B. genus.
• C. class.
• D. kingdom.
Warm up 3 wk 8
• At what point in time
did the most recent
common ancestor
between the monkeys
and the hominoids
exist?
• 8 million years ago
• 14 million years ago
• 35 million years ago
• 56 million years ago
Cell Membrane Functions
• Controls the flow of nutrients in & out of cell
• Maintains homeostasis
• Selectively Permeable: allows some substances to
cross more easily than others
Cell Membrane Structure
• Composed of:
• Phospholipid Bilayer: double
layer
• Head: Hydrophilic (“water-loving”)
• Tails: Hydrophobic (“water-
fearing”)
• Proteins: act as channels or
pumps to move substances in &
out
• Carbohydrates: act as ID tags
for other cells
Diffusion
• Diffusion: the movement of
molecules from an area of higher
concentration to an area of lesser
concentration
• Eventually evens out (“Equilibrium”)
• Does NOT require any energy
• Concentration Gradient: the
difference in concentrations inside
and outside a cell
Osmosis
• Osmosis: the diffusion of
water across a membrane
• Does NOT require energy (is
passive)
• Whether water moves into or
out of the cell depends on
solute concentrations
• Solutes = salt, sugars, proteins,
etc.
Isotonic Solutions
• Isotonic: solute
concentrations are equal
on both sides of cell
membrane
• Water will osmose IN & OUT
of cell equally
• Most cells exist in isotonic
solutions
Hypertonic Solutions
• Hypertonic: more solute
outside cell than inside
• i.e.: a weak/dilute solution
inside cell
• Water will move OUT of cell
• May cause animal cells to
shrivel up & die
• Causes plants to wilt
Hypotonic Solutions
• Hypotonic: less solute
outside cell than inside
• i.e.: a strong solution inside
cell
• Water will move INTO cell
• May cause animal cells to
swell & burst
• Cell walls keep plant cells
from bursting
Tonicity
Wk 7 Warm up
• Which of the following correctly describes the motion of
particles in a gas?
A.
B.
C.
D.
They do not move at all.
They move rapidly around in random patterns.
They vibrate in a set pattern.
They flow easily, but slowly around each other.
Wk 7 Warm up
• What is the molecular arrangement like in wood and why?
A. The molecules are close together because of their strong
intermolecular attractions.
B. The molecules are randomly packed together because the
molecules can slip and slide over each other.
C. The molecules are close together because the kinetic energy is
dominant over the potential energy within the molecules.
D. The molecules are far apart because of their small intermolecular
attractions.
Wk 6 warm up
• Which of the following describes a state of matter that has
a random molecular arrangement and particles that are
far apart?
• A. A substance that takes the shape of its container and
is NOT easily compressed.
B. A substance that has a definite shape and is easily
compressed.
C. A substance that takes the shape of its container and
is easily compressed.
D. A substance that has a definite shape and
is NOT easily compressed.
Wk 6 Warm up
• Light waves travel through space
A. because they interact with subspace particles and transfer energy
to the Earth.
B. as photons with extremely small mass and turn to waves when
entering Earth’s atmosphere.
C. even though there is almost no material in the innerstellar
medium, but do transfer energy.
D. transferring energy and matter to the Earth from the Sun, distant
stars, and galaxies.