Download The Cell Membrane

Bellringer

Review your organelle note chart. Will be
taking a self quiz over the cell
organelles.
Learning Targets
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Describe the structure and functions of cellular membranes
including proteins and lipids.
Explain the differences and similarities between active and
passive transport and how each of these relates to solute
concentration.
• Diffusion
• Osmosis
• Facilitated Diffusion
• Endocytosis
• Exocytosis
• Phagocytosis
Cell Membranes and
Transport
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Homeostasis
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Homeostasis is the balance cells must
maintain with their surrounding
environment.
Cells maintain homeostasis by
controlling what enters and exits the
cell.
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The Cell Membrane
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Made of a bilayer of phospholipids
Phospholipids have a hydrophobic tail (water
fearing) and hydrophilic head (water loving).
Proteins are embedded in the membrane to
help move materials in-and-out of the cell.
Proteins

Proteins serve 4 roles in the plasma
membrane:
Channel Protein: Receptor Protein: Marker Protein:
Enzymes:
The membrane is called a
fluid-mosaic – why?

Figure 7-12 The Structure of the
Cell Membrane
Section 7-3
The Cell Membrane
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer

The Cell Membrane

Cell membranes are SELECTIVELY
PERMEABLE – what does this mean?
The cell membrane has some
control over what can cross it, so
that only certain molecules either
enter or leave the cell.
Ex. The strainer lets water
pass through, yet keeps the
pasta in. It is selectively
permeable.

Passive Transport
• Movement of molecules across the cell
membrane that DOES NOT USE
ENERGY.
• Materials move from an area of HIGH
CONCENTRATION to an area of LOW
CONCENTRATION.

Diffusion

Diffusion – Movement of molecules
through the cell membrane
• A type of PASSIVE TRANSPORT because
it DOES NOT USE ENERGY.
Diffusion Checkpoint

What direction will the molecules move?

Diffusion Checkpoint Pt. 2

When is equilibrium reached?

EQUILIBRIUM is reached when
concentrations are equal on both sides
of the cell membrane.

Osmosis

Osmosis – diffusion of WATER
molecules through the cell
membrane (passive transport)
•
•

Water always diffuses from an area of LOW SOLUTE
CONCENTRATION to an area of HIGH SOLUTE
CONCENTRATION.
OR  High Water Concentration to Low Water
Concentration
Solute is…..??
Osmosis

Osmosis –

Driven by Solute Concentration
Hypotonic solution –
solute concentration
is lower on the
outside of the cell
than inside the cell.
• Water moves INTO
the cell

Hypo= low, below
normal

Osmosis

– Driven by Solute Concentration
Hypertonic solution –
solute concentration
is higher on the
outside of the cell
than inside the cell.
• Water moves out of
the cell

Hyper= excessive

Osmosis

– Driven by Solute Concentration
Isotonic solution –
solute concentration
is equal on both
sides of the cell
membrane.
• Water diffuses inand-out equally

Iso= equal or the
same

Osmosis and Plant Cells

Plant cells require a hypotonic
environment so water moves into the cell
and the cell swells
• Swelling of the cell builds up turgor pressure

Osmosis and Plant Cells
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Plant cells in hypertonic environments
lose water and the cell shrivels up.
• Shriveling of the cell is called plasmolysis.
Osmosis Checkpoint
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What would happen to animal cells in
hypotonic and hypertonic environments?
Osmosis

For example, marine fish:
Work on Diffusion/ Osmosis
Review Worksheet
Recall – Osmosis – WHAT WILL
HAPPEN TO THE CELL???
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Facilitated Diffusion

Facilitated diffusion - moves molecules
in-and-out of the cell using a carrier
protein (passive transport)

Why would molecules need help from a
carrier protein?
• Too big
• Charged
• Can not dissolve in the phospholipid bilayer.
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Active Transport

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Active transport - movement of molecules
across the cell membrane that requires
energy.
Can move materials from an area of LOW
CONCENTRATION to an area of HIGH
CONCENTRATION. (Opposite of diffusion)
Active Transport

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Why does your body need to use active
transport?
Na+/K+ pumps for neuron function
SWEET Video
Animation of Sodium/Potassium Pumps
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Endocytosis
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Large molecules can be engulfed by
cells in a process called
ENDOCYTOSIS. (Active transport)
Pinocytosis - process of engulfing a
liquid. (“Cell drinking,”)
Phagocytosis - process of engulfing a
solid. (“Cell eating,”)
Endocytosis
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Exocytosis – release material
from the cell